Thèses : « Carbonic snow »

1

Cardoso, William da Silva. « Oxido misto de SiO2/SnO2,SiO2/SnO2/Fosfato : propriedades e aplicações ». [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249698.

Texte intégral

Résumé :

Orientador: Yoshitaka Gushikem
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-08-04T23:27:35Z (GMT). No. of bitstreams: 1 Cardoso_WilliamdaSilva_D.pdf: 740346 bytes, checksum: bbae1435b7392cf211b02cc55af7333d (MD5) Previous issue date: 2005
Doutorado
Quimica Inorganica
Doutor em Ciências

Styles APA, Harvard, Vancouver, ISO, etc.

2

Hanks, Karari O. « Water insoluble particulate organic and elemental carbon concentrations and ionic concentrations from snowpits obtained at Summit, Greenland ». Thesis, Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180212/unrestricted/hanks%5Fkarari%5Fo%5F200312%5Fms.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

3

Svensson, Jonas. « Horizontal Meter Scale Variability of Elemental Carbon in Surface Snow ». Thesis, Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-59712.

Texte intégral

Résumé :

Soot deposited in snow and ice lowers the albedo of the surface and affects the radiative balance. Soot’s climatic forcing has received increased attention during the last decade, however, measurements of soot concentrations in Arctic snow are rare. This thesis investigates the horizontal variability of elemental carbon (EC), a proxy of soot, on a meter scale in surface snow from a site with limited regional pollution in Arctic Finland and a site with significant regional pollution near Stockholm, Sweden. A variability of EC in the sampled grid-nets was observed at both of the sites; however, the site with less pollution affecting it presented greater variation in comparison to the polluted site. In side-by-side ratios between neighboring samples, a ratio of as much as ~16 is observed, presenting the potential variation at the less polluted site. An important process that is partly responsible for the variation at this site is wind. The EC concentrations increased over time at both of the sites, which supports the hypothesis that EC remains at the snow surface even as snow melt occurs in the spring.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Hadley, Odelle L. « Black carbon transport and deposition to the California mountain snow pack ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3307698.

Texte intégral

Résumé :

Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed July 18, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Robertson, Noel Arthur. « Model-based and satellite estimates of snow hydrology and carbon fluxes at high latitudes ». Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555106.

Texte intégral

Résumé :

This thesis is a study of how satellite data can be used to improve our understanding of the snow hydrology of boreal regions and its effects on their hydrological and carbon balance. The key parameter is the snow water equivalent (SWE). The thesis addresses two themes; (1) snow parameter retrieval from satellite data, and (2) the dependence on SWE of the hydrological and carbon balance of boreal regions. Using radiative transfer models, linked to a climate-driven snow model, it was found that the brightness temperature is most sensitive to the snow grain size, with SWE the second most significant parameter. Comparison of model predictions with SSMII satellite data showed a significant difference in spatial patterns in central Siberia. The most likely reasons are thought to be either an inaccurate estimate of snow grain size, or errors in the land cover description. For SWE or snow depth retrieval from passive microwave data to be successful, the evolution of the grain size needs to be better quantified. The combination of dynamic algorithm in early winter and static algorithm in middle to late winter produces the best overall results, particularly in Eurasia. The final part of the thesis uses a Dynamic Vegetation Model, SDGVM, to model the hydrological and carbon balance of the major boreal catchments, using a simple climate-driven model of SWE. It was found that there. was broad agreement in the annual water balance between the SDGVM and measured data of river discharge. There is a significant difference in seasonal timing due to the absence of some hydrological processes in SDGVM. Analysis of 21 SI century climate scenarios for the Ob basin indicates a slight reduction in annual runoff, but a significant increase in Net Biome Productivity.

Styles APA, Harvard, Vancouver, ISO, etc.

6

Winchell, Taylor S., David M. Barnard, Russell K. Monson, Sean P. Burns et Noah P. Molotch. « Earlier snowmelt reduces atmospheric carbon uptake in midlatitude subalpine forests ». AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/621684.

Texte intégral

Résumé :

Previous work demonstrates conflicting evidence regarding the influence of snowmelt timing on forest net ecosystem exchange (NEE). Based on 15years of eddy covariance measurements in Colorado, years with earlier snowmelt exhibited less net carbon uptake during the snow ablation period, which is a period of high potential for productivity. Earlier snowmelt aligned with colder periods of the seasonal air temperature cycle relative to later snowmelt. We found that the colder ablation-period air temperatures during these early snowmelt years lead to reduced rates of daily NEE. Hence, earlier snowmelt associated with climate warming, counterintuitively, leads to colder atmospheric temperatures during the snow ablation period and concomitantly reduced rates of net carbon uptake. Using a multilinear-regression (R-2=0.79, P<0.001) relating snow ablation period mean air temperature and peak snow water equivalent (SWE) to ablation-period NEE, we predict that earlier snowmelt and decreased SWE may cause a 45% reduction in midcentury ablation-period net carbon uptake.

Styles APA, Harvard, Vancouver, ISO, etc.

7

Mellander, Per-Erik. « Spring water stress in Scots pine : interaction of snow and soil temperature / ». Uppsala : Dept. of Environmental Assessment, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/s287.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

8

Gervillie, Charlotte. « Composite carbone/SnO2 fluoré comme matériau d’électrode négative pour les accumulateurs lithium-ion ». Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLM021.

Texte intégral

Résumé :

Ce travail de thèse se propose de réfléchir à des solutions permettant de stabiliser les performances électrochimiques des électrodes négatives à base de SnO2 pour les accumulateurs lithium-ion. Tout d’abord, l’influence de la nanostructuration du SnO2 et des défauts inhérents sur les performances électrochimiques est étudiée. Puis, des composites carbone/SnO2 sont élaborés afin de contenir l’expansion volumique et l’influence de la dimensionnalité de la matrice carbonée (1D, 2D, 3D) sur les performances électrochimiques est démontrée. Finalement, la surface du matériau est fluorée en utilisant soit la fluoration moléculaire par F2(g) soit la fluoration radicalaire par décomposition thermique du XeF2(s). La stabilité de l’interface entre le matériau et l’électrolyte est alors améliorée et d’excel-lentes propriétés électrochimiques sont obtenues
This thesis work proposes solutions to stabilize the electrochemical performances of SnO2-based negative electrodes for lithium-ion batteries. First of all, the influence of SnO2 nanostructuration and inherent defects on electrochemical performances are studied. Then, carbon/SnO2 composites are synthesized to contain the volume expansion and the influence of the dimensionality of the carbonaceous matrix (1D, 2D, 3D) on the electrochemical performances is demonstrated. Finally, the surface of the material is fluorinated using either molecular fluorination by F2(g) or radical fluorination by thermal decomposition of XeF2(s). The stability of the interface between the material and the electrolyte is then improved and excellent electrochemical properties are obtained

Styles APA, Harvard, Vancouver, ISO, etc.

9

Guidi, Lionel. « Particle flux transformation in the mesopelagic water column : process analysis and global balance ». Diss., Texas A&M University, 2008. http://hdl.handle.net/1969.1/85946.

Texte intégral

Résumé :

Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km).

Styles APA, Harvard, Vancouver, ISO, etc.

10

Aldridge, James K. W. « Heterogeneous CuMn2O4, Pt, Pd and SnO2 catalysts for ambient temperature oxidation of carbon monoxide ». Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/33320/.

Texte intégral

Résumé :

Ambient temperature oxidation of carbon monoxide is a vital reaction for life support in enclosed atmospheres such as submarines and spacecraft. This reaction is usually achieved through the use of two classes of catalyst. Firstly, mixed copper and manganese oxides designated ‘Hopcalite’ or CuMn2O4. Secondly, high surface area noble metal catalysts deposited on durable metal oxide supports. Both of these classes of catalyst are investigated in this thesis, with the aim of producing novel, reproducible, robust and active ambient temperature carbon monoxide oxidation catalysts. In this thesis, CuMn2O4 is sequentially doped and/or impregnated with low weightings (1-10%) of the transition metals V and Ce, noble metals Pd and Pt and metalloid Si in an attempt to improve activity and moisture resistance. It was observed that doped V, Ce, Pd and Si are catalytic poisons toward CuMn2O4. This is likely due to their interference in the Cu ↔ Mn redox mechanism. XRD investigations infer doped Pd is a structural promoter toward CuMn2O4, increasing surface area and decreasing catalyst crystalinity. Impregnation of noble metals Pt and Pd onto CuMn2O4 surface causes deactivation of the noble metals, most likely due to the oxidation of Pt and Pd by Mn. No novel catalyst tested in this thesis displayed increased resistance to moisture deactivation. Noble metals Pt and Pd were impregnated upon 3 mm diameter Al2O3 spheres and tested for ambient temperature CO oxidation activity. The positive synergy between the two metals is measured, and the most efficient Pt:Pd ratio is discovered to be ~ 1:4. A novel, atom efficient method, for synthesising Pt/Pd/SnO2/Al2O3 catalysts using tin oxalate was conceived of and investigated. Compared to existing reference catalysts, oxalate derived catalysts preformed favourably and can be described as equivalently active.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Ma, Ning, Guo-Yue Niu, Youlong Xia, Xitian Cai, Yinsheng Zhang, Yaoming Ma et Yuanhao Fang. « A Systematic Evaluation of Noah-MP in Simulating Land-Atmosphere Energy, Water, and Carbon Exchanges Over the Continental United States ». AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/626444.

Texte intégral

Résumé :

Accurate simulation of energy, water, and carbon fluxes exchanging between the land surface and the atmosphere is beneficial for improving terrestrial ecohydrological and climate predictions. We systematically assessed the Noah land surface model (LSM) with mutiparameterization options (Noah-MP) in simulating these fluxes and associated variations in terrestrial water storage (TWS) and snow cover fraction (SCF) against various reference products over 18 United States Geological Survey two-digital hydrological unit code regions of the continental United States (CONUS). In general, Noah-MP captures better the observed seasonal and interregional variability of net radiation, SCF, and runoff than other variables. With a dynamic vegetation model, it overestimates gross primary productivity by 40% and evapotranspiration (ET) by 22% over the whole CONUS domain; however, with a prescribed climatology of leaf area index, it greatly improves ET simulation with relative bias dropping to 4%. It accurately simulates regional TWS dynamics in most regions except those with large lakes or severely affected by irrigation and/or impoundments. Incorporating the lake water storage variations into the modeled TWS variations largely reduces the TWS simulation bias more obviously over the Great Lakes with model efficiency increasing from 0.18 to 0.76. Noah-MP simulates runoff well in most regions except an obvious overestimation (underestimation) in the Rio Grande and Lower Colorado (New England). Compared with North American Land Data Assimilation System Phase 2 (NLDAS-2) LSMs, Noah-MP shows a better ability to simulate runoff and a comparable skill in simulating R-n but a worse skill in simulating ET over most regions. This study suggests that future model developments should focus on improving the representations of vegetation dynamics, lake water storage dynamics, and human activities including irrigation and impoundments.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Santos, Alexandre Manuel Gonçalves Araújo dos. « Sensores de gás para domótica ». Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/17103.

Texte intégral

Résumé :

Mestrado em Engenharia de Materiais
O presente trabalho propôs-se comparar sensores semicondutores de gases baseados em diferentes morfologias do óxido de SnO2 para a deteção de monóxido de carbono, recorrendo aos métodos de síntese hidrotermal e deposição eletroforética. Este estudo visa entender a importância da morfologia na resposta elétrica e sensibilidade de um sensor semicondutor. Por alteração do precursor de Sn obtiveram-se partículas de SnO2 de diferentes morfologias (nanopartículas e nanobastonetes). Para além da morfologia estas nanoestruturas comportam-se diferentemente em termos de grau de cristalinidade, de distribuição, de tamanho de partícula e de estabilidade coloidal. Estas diferença a nível de suspensão afetam marcadamente a deposição eletroforética e a qualidade dos filmes obtidos. A deposição dos filmes é facilitada para as nanopartículas. Sensores de SnO2 que combinam síntese hidrotermal das nanopartículas com deposição eletroforética do óxido sensor apresentam valores de sensibilidade de 11 e 3 para concentrações de 2000 e 5000 ppm respetivamente.
The main goal of this work is the comparison of semiconductor gas sensors based on different morphologies of SnO2 for the carbon monoxide detection, using techniques such hydrothermal synthesis and electrophorectic deposition. This work compromises to study the importance of morphology in the electric response and sensibility of a semiconductor sensor. By changing the precursor Sn, SnO2 particles were obtained with differents morphologies (nanoparticles and nanorods). This different structures present different cristalinity, particle size distribution and colloidal stability. For each suspension, the results of electrophorectic deposition and the quality of the obtained films were very distinct. Nanoparticles Deposition is easier when compared to nanorods. SnO2 sensors that combine hydrothermal synthesis and electrophorectic deposition presente values of sensibility of 11 and 3 to 2000 and 5000 ppm of carbon monoxide concentration.

Styles APA, Harvard, Vancouver, ISO, etc.

13

Haouas, Ammar. « Cinetique d'oxydation du monoxyde de carbone sur des catalyseurs cuo sno ::(2) : etude physicochimique et simulation informatique ». Paris 6, 1988. http://www.theses.fr/1988PA066654.

Texte intégral

Résumé :

Etude cinetique de la reaction de co avec l'oxygene moleculaire en regime dynamique permanent. Etude formelle de la cinetique des reactions de type langmuir avec exploitation au moyen d'un logiciel. Determination experimentale des energies d'activation, des ordres partiels et mecanisme reactionnel

Styles APA, Harvard, Vancouver, ISO, etc.

14

Haouas, Ammar. « Cinétique d'oxydation du monoxyde de carbone sur des catalyseurs CuO SnO étude physico-chimique et simulation informatique / ». Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37614289p.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

15

Flintrop, Clara [Verfasser], Morten [Akademischer Betreuer] Iversen, Helle [Gutachter] Ploug et Wolfgang [Gutachter] Bach. « From microstructures to macroscale carbon export : influences of marine snow composition on settling velocity and microbial colonization / Clara Flintrop ; Gutachter : Helle Ploug, Wolfgang Bach ; Betreuer : Morten Iversen ». Bremen : Staats- und Universitätsbibliothek Bremen, 2019. http://d-nb.info/1199003735/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

16

Syk, Madeleine, et Joakim Vollmer. « Characterizing particulate carbon using dielectric property measurements ». Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-346536.

Texte intégral

Résumé :

Interest in effects of carbonaceous particles in the atmosphere has recently taken an upswing due to knowledge of how these particles affect our environment. Carbonaceous aerosols are characterized by their dark color, giving them the ability to absorb both incoming and outgoing radiation of all wavelengths in the atmosphere. If these particles are deposited on snow or ice they blacken the surface, with an increased rate of melting as a consequence. These particles play a significant role in climate change and it is important to characterize the particles in order to determine their environmental impact and their origin. In this thesis, two non-destructive dielectric measurement approaches for characterizing carbonaceous particles at microwave frequencies were explored: measurements with an impedance analyzer and measurements using a cavity resonator. Measurements were carried out on quartz filters containing concentrations of carbon normally found in snow in northern Scandinavia. To validate the carbon concentration on the filters a field trip to northern Sweden was conducted. Snow samples were collected and analyzed in regards of carbon content, confirming that the amount of carbon on the filters were accurate. The impedance analyzer showed great uncertainty and the results were not precise enough to determine the credibility of the approach. Measurements with the cavity resonator showed some promising results due to its extreme sensitivity but require adjustments to distinguish different particle types from each other. Thus, it is expected that the use of a cavity resonator operating at microwave frequencies will become an applicable method for characterizing carbonaceous particles in the future.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Ayoub, Jamil Mahmoud Said. « Preparação de eletrocatalisadores PtSb2O5.SnO2 suportados em carbono e ATO pelo método da redução por álcool para oxidação eletroquímica do etanol ». Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-15042013-092732/.

Texte intégral

Résumé :

Os eletrocatalisadores PtSn / C-ATO com Pt e Sn com diferentes relações atômicas (90:10, 70:30 e 50:50) foram preparados em uma única etapa pelo processo de redução por álcool usando H2PtCl6.6H2O e SnCl2.2H2O como fontes de metais e etileno glicol como solvente e agente redutor e de uma mistura física de carbono Vulcan XC72 (85% em peso) e ATO(Sb2O5.SnO2) (15% em peso) como o suporte (C-ATO). Os materiais obtidos foram caracterizados por difração de raios X (DRX) e microscopia eletrônica de transmissão (MET). A atividade catalítica para oxidação eletroquímica do etanol em meio ácido foi investigada por voltametria cíclica e cronoamperometria em células unitárias de combustível de etanol direto (DEFC). As análises de DRX revelou que Pt (FCC), SnO2, carbono e fases ATO coexistem nos materiais obtidos. Os estudos eletroquímicos mostraram que os eletrocatalisadores PtSn / C-ATO são mais ativos para oxidação eletroquímica do etanol em comparação ao eletrocatalisador de PtSn / C . As experiências a 100 ° C em células a combustível unitárias (DEFC) mostrou que a densidade de potencia da célula usando PtSn / C-ATO (90:10) foi de aproximadamente 100% mais elevado do que o obtido utilizando PtSn / C (50:50). Os experimentos de infra vermelho FTIR in-situ indicaram que a adição de ATO no suporte para eletrocatalisadores PtSn / C favorece a formação do ácido acético como produto, enquanto para PtSn / C o acetaldeído foi o principal produto formado.
PtSn/C-ATO electrocatalysts with different Pt:Sn atomic ratios (90:10, 70:30 and 50:50) were prepared in a single step by an alcohol-reduction process using H2PtCl6.6H2O and SnCl2.2H2O as metal sources and ethylene glycol as solvent and reducing agent and a physical mixture of carbon Vulcan XC72 (85 wt%) and Sb2O5.SnO2 (15 wt%) as support (C-ATO). The obtained materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The catalytic activity for ethanol electro-oxidation in acid medium was investigated by cyclic voltammetry and chroamperometry and in single direct ethanol fuel cell (DEFC). XRD analyses showed that Pt(FCC), SnO2, carbon and ATO phases coexist in the obtained materials. The electrochemical studies showed that PtSn/C-ATO electrocatalysts were more active for ethanol electro-oxidation than PtSn/C electrocatalyst. The experiments at 100oC on a single DEFC showed that the power density of the cell using PtSn/C-ATO (90:10) was nearly 100% higher than the one obtained using PtSn/C (50:50). FTIR measurements showed that the addition of ATO to PtSn/C favors the formation of acetic acid as a product while for PtSn/C acetaldehyde was the principal product formed.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Castro, José Carlos de. « Desempenho de eletrocatalisadores PtSnRh suportados em carbono-Sb2O5.SnO2 para a oxidação eletroquímica do etanol, preparados pelo método de redução por álcool ». Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-28082013-090145/.

Texte intégral

Résumé :

Os eletrocatalisadores PtSnRh suportados em carbono-Sb2O5.SnO2, com 20% de massa de metal, foram preparados pelo método de redução por álcool, utilizando H2PtCl6.6H2O (Aldrich), RhCl3.xH2O (Aldrich) e SnCl2.2H2O (Aldrich), como fontes de metais; Sb2O5.SnO2 (ATO) e carbono Vulcan XC72, como suporte; e etileno glicol como agente redutor. Os eletrocatalisadores obtidos foram caracterizados fisicamente por difração de raios-X (DRX) e microscopia eletrônica de transmissão (MET). Por meio dos difratogramas observou-se que os eletrocatalisadores PtSnRh/C-ATO possuem estrutura CFC para a Pt e ligas de Pt, além de vários picos associados ao SnO2 e ATO. Os tamanhos médios dos cristalitos ficaram entre 2 e 4 nm. Por meio das micrografias verificou-se uma boa distribuição das nanopartículas sobre o suporte. Os tamanhos médios das partículas ficaram entre 2 e 3 nm, com boa concordância para os tamanhos médios dos cristalitos. Os desempenhos dos eletrocatalisadores foram analisados por meio de técnicas eletroquímicas e em condições reais de operação utilizando uma célula a combustível unitária alimentada diretamente por etanol. Na cronoamperometria, a temperatura de 50ºC, os eletrocatalisadores com proporção de 85%C+15%ATO para o suporte, apresentaram a melhor atividade, e as proporções atômicas que obtiveram os melhores resultados foram PtSnRh(70:25:05) e (90:05:05). Nos experimentos em célula, o eletrocatalisador PtSnRh(70:25:05)/85C+15ATO apresentou o melhor desempenho.
PtSnRh electrocatalysts supported on carbon-Sb2O5.SnO2, with metal loading of 20 wt%, were prepared by an alcohol-reduction process, using H2PtCl6.6H2O (Aldrich), RhCl3.xH2O (Aldrich) and SnCl2.2H2O (Aldrich), as source of metals; Sb2O5.SnO2 (ATO) and carbon Vulcan XC72, as support; and ethylene glycol as reducing agent. The electrocatalysts obtained were characterized physically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diffractograms showed which PtSnRh/C-ATO electrocatalysts had FCC structure of Pt and Pt alloys, besides several peaks associated with SnO2 and ATO. The average sizes of crystallites were between 2 and 4 nm. TEM micrographs showed a good distribution of the nanoparticles on the support. The average sizes of particles were between 2 and 3 nm, with good agreement for the average size of the crystallites. The performances of the electrocatalysts were analyzed by electrochemical techniques and in real conditions of operation using single direct ethanol fuel cell. In the chronoamperometry at 50ºC, the electrocatalysts with carbon (85 wt%) and ATO (15 wt%) support, showed the best activity, and the atomic proportions which achieved the best results were PtSnRh(70:25:05) e (90:05:05). PtSnRh(70:25:05)/85C+15ATO electrocatalysts showed the best performance in a direct ethanol fuel cell.

Styles APA, Harvard, Vancouver, ISO, etc.

19

CASTRO, JOSE C. de. « Desempenho de eletrocatalisadores PtSnRh suportados em carbono-Sb2O5.SnO2 para a oxidação eletroquímica do etanol, preparados pelo método de redução por álcool ». reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10526.

Texte intégral

Résumé :

Made available in DSpace on 2014-10-09T12:41:30Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T13:59:48Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Styles APA, Harvard, Vancouver, ISO, etc.

20

Bach, Delpeuch Antoine. « Etude du mécanisme de la réaction d'oxydation de l'éthanol sur électrocatalyseurs à base de Pt, Rh, SnO2 sur support carboné en milieu acide ». Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI089/document.

Texte intégral

Résumé :

L'étude du mécanisme de la réaction d'oxydation de l'éthanol (EOR) a été réalisée sur des électrocatalyseurs bi- et tri-métalliques à base de Pt, Rh et SnO2 sur support carboné à l'aide de méthodes électrochimiques couplées (DEMS, in situ FTIR). Deux importantes problématiques de l'EOR ont été abordées: la déshydrogénation de la molécule d'éthanol et la cassure de sa liaison C-C.L'investigation de certains paramètres expérimentaux, comme l'épaisseur de la couche d'électrocatalyseur, a permis de démontrer q'une couche active épaisse conduit à une meilleure électrooxydation plus complète de l'éthanol en CO2, mais également que l'empoisonnement de l'électrocatalyseur par de très forts adsorbats advient dans l'épaisseur de couche active.Les performances de chaque électrocatalyseur ont été comparées entre elles et ont mis en évidence une meilleure sélectivité de l'EOR sur Pt-Rh-SnO2/C, ainsi que l'engendrement de courants plus élevés à bas potentiel à température ambiante. La tendance est amplifiée à température plus élevée (T = 60 °C)
The study of the ethanol oxidation reaction (EOR) mechanism was performed on carbon supported bi- and tri-metallic Pt-, Rh-, SnO2-based electrocatalysts via electrochemical coupled techniques (DEMS, in situ FTIR). Two of the most important issues related to the EOR have been broached: the dehydrogenation of the ethanol molecule and its C-C bond breaking.The investigation of some experimental parameters, such as the thickness of the electrocatalyst layer, enabled demonstrating the better complete ethanol electrooxidation into CO2 for large electrocatalysts layers, combined to the enhanced poisoning effect inside the catalyst layer by very strong adsorbates.The performances of each electrocatalyst were compared and evidenced an improved selectivity of the EOR on Pt-Rh-SnO2/C, as well as the generation of higher currents at low potential at room temperature. The tendency was amplified at elevated temperatures (T = 60 °C)

Styles APA, Harvard, Vancouver, ISO, etc.

21

PEREIRA, JULIAN M. de S. « Estudo da preparação do catalisador Au-SnO2/TiO2 para uso na reação de oxidação preferencial do monóxido de carbono em misturas ricas em hidrogênio ». reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28624.

Texte intégral

Résumé :

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2018-03-02T17:57:58Z No. of bitstreams: 0
Made available in DSpace on 2018-03-02T17:57:58Z (GMT). No. of bitstreams: 0
Neste trabalho foi estudada a viabilidade de preparação do catalisador Au-SnO2/TiO2 pelo método da redução por álcool, o qual apresentou excelentes resultados na preparação de eletrocatalisadores PtSnO2/C aplicados em células a combustíveis. Inicialmente a preparação dos catalisadores Au-SnO2/TiO2 foi efetuada sem modificações em relação a metodologia de preparação dos catalisadores PtSnO2/C por meio da qual foi possível obter nanopartículas de Pt e SnO2 da ordem de 2-4 nm bem dispersas no suporte de carbono. Os resultados iniciais não se mostraram adequados obtendo-se para o catalisador Au/TiO2 nanopartículas de Au da ordem 100-200 nm, enquanto que para os catalisadores Au-SnO2/TiO2 com diferentes % em massa de SnO2, apesar da fase SnO2 apresentar-se bem dispersas sobre o suporte, as nanopartículas de Au apresentaram tamanhos da ordem de 10 nm, sendo desejável nanopartículas menores que 10 nm para a reação preferencial do monóxido de carbono em misturas ricas em hidrogênio (reação CO-PROX). Os catalisadores Au/TiO2, Au/SnO2 e AuSnO2/TiO2 com diferentes % em massa de SnO2 obtidos dessa maneira apresentaram baixa atividade e seletividade na reação CO-PROX. Dessa forma, modificações foram efetuadas na metodologia de preparação por meio de diferentes rotas visando à diminuição e uma melhor dispersão das nanopartículas de Au na preparação do catalisador Au/TiO2. Por meio do uso de citrato de sódio como agente estabilizante e por modificações na forma de adição do precursor de Au foi possível diminuir o tamanho das nanopartículas de Au e melhorar sensivelmente a atividade e a seletividade do catalisador Au/TiO2 na reação CO-PROX. Os catalisadores Au-SnO2/TiO2 foram também preparados por esta nova rota obtendo-se também para estes materiais um menor tamanho de partícula de Au e uma melhor dispersão sobre o suporte TiO2. A atividade catalítica e a seletividade dos catalisadores AuSnO2/TiO2 obtidos por esta nova rota também apresentaram uma melhora significativa na atividade e seletividade na reação CO-PROX.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Styles APA, Harvard, Vancouver, ISO, etc.

22

Pereira, Julian Maciel de Souza. « Estudo da preparação do catalisador Au-SnO2/TiO2 para uso na reação de oxidação preferencial do monóxido de carbono em misturas ricas em hidrogênio ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-29012018-082110/.

Texte intégral

Résumé :

Neste trabalho foi estudada a viabilidade de preparação do catalisador Au-SnO2/TiO2 pelo método da redução por álcool, o qual apresentou excelentes resultados na preparação de eletrocatalisadores PtSnO2/C aplicados em células a combustíveis. Inicialmente a preparação dos catalisadores Au-SnO2/TiO2 foi efetuada sem modificações em relação a metodologia de preparação dos catalisadores PtSnO2/C por meio da qual foi possível obter nanopartículas de Pt e SnO2 da ordem de 2-4 nm bem dispersas no suporte de carbono. Os resultados iniciais não se mostraram adequados obtendo-se para o catalisador Au/TiO2 nanopartículas de Au da ordem 100-200 nm, enquanto que para os catalisadores Au-SnO2/TiO2 com diferentes % em massa de SnO2, apesar da fase SnO2 apresentar-se bem dispersas sobre o suporte, as nanopartículas de Au apresentaram tamanhos da ordem de 10 nm, sendo desejável nanopartículas menores que 10 nm para a reação preferencial do monóxido de carbono em misturas ricas em hidrogênio (reação CO-PROX). Os catalisadores Au/TiO2, Au/SnO2 e AuSnO2/TiO2 com diferentes % em massa de SnO2 obtidos dessa maneira apresentaram baixa atividade e seletividade na reação CO-PROX. Dessa forma, modificações foram efetuadas na metodologia de preparação por meio de diferentes rotas visando à diminuição e uma melhor dispersão das nanopartículas de Au na preparação do catalisador Au/TiO2. Por meio do uso de citrato de sódio como agente estabilizante e por modificações na forma de adição do precursor de Au foi possível diminuir o tamanho das nanopartículas de Au e melhorar sensivelmente a atividade e a seletividade do catalisador Au/TiO2 na reação CO-PROX. Os catalisadores Au-SnO2/TiO2 foram também preparados por esta nova rota obtendo-se também para estes materiais um menor tamanho de partícula de Au e uma melhor dispersão sobre o suporte TiO2. A atividade catalítica e a seletividade dos catalisadores AuSnO2/TiO2 obtidos por esta nova rota também apresentaram uma melhora significativa na atividade e seletividade na reação CO-PROX.
In this work the feasibility of preparation of the Au-SnO2/TiO2 catalyst by the alcohol reduction method was studied, which presented excellent results in the preparation of PtSnO2/C electrocatalysts applied in fuel cells. Initially the preparation of the Au-SnO2/TiO2 catalysts was carried out without modifications in relation to the methodology of preparation of the catalysts PtSnO2/C through which it was possible to obtain nanoparticles of Pt and SnO2 of the order of 2-4 nm well dispersed in the carbon support. The initial results were not shown to be adequate for the Au/TiO2 catalyst. Au nanoparticles of the order 100-200 nm, while for the Au-SnO2/TiO2 catalysts with different mass% of SnO2, if well dispersed on the support, Au nanoparticles presented sizes of the order of 10 nm, with nanoparticles smaller than 10 nm being desirable for the preferential reaction of carbon monoxide in hydrogen-rich mixtures (CO-PROX reaction). The Au/TiO2, Au/SnO2 and AuSnO2/TiO2 catalysts with different wt% of SnO2 obtained in this way showed low activity and selectivity for CO-PROX reaction. Thus, modifications were carried out in the preparation methodology by means of different routes aiming at the decrease and a better dispersion of the Au nanoparticles in the preparation of the Au/TiO2 catalyst. By using sodium citrate as a stabilizing agent and by modifications in the addition form of the Au precursor it was possible to decrease the size of the Au nanoparticles and to improve significantly the activity and selectivity of the Au/TiO2 catalyst for CO-PROX reaction. The Au-SnO2/TiO2 catalysts were also prepared by this new route obtaining also for these materials a smaller Au particle size and a better dispersion on the TiO2 support. The catalytic activity and selectivity of the Au-SnO2/TiO2 catalysts obtained by this new route also showed a significant improvement in the activity and selectivity for CO-PROX reaction.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Ngqongwa, Lundi Vincent. « Electrochemical characterization of nanostructured SnO2 and TiO2 for potential application as dielectric materials in sulfonated-polyaniline based supercapacitors ». Thesis, University of the Western Cape, 2010. http://hdl.handle.net/11394/2575.

Texte intégral

Résumé :

Magister Scientiae - MSc
In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).
South Africa

Styles APA, Harvard, Vancouver, ISO, etc.

24

Venkrbec, Lukáš. « Chemorezistivní senzor plynů ». Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-318163.

Texte intégral

Résumé :

This thesis deals with the detection of gases. Based on the research, the theoretical part is devoted to the principles and construction of chemical gas sensors, especially the chemoresistive gas sensors, mainly with the active layer consisting of metal oxides and carbon nanotubes. In the second half of the theoretical part the carbon nanostructures, their properties and the methodology of preparation are reviewed. The experimental part deals with the type of support structure, preparation of the active layer and the method of its deposition and he principle of detection. In the results and discussion, the thesis focuses on the detailed processing of the results and the evaluation of the response ammonia, the impact of the modifications and procedures. In the end, the results obtained are compared, both with each other and with the relevant literature.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Petrucco, Toffolo Edoardo. « Climate change and pine processionary moth role of the host plant ». Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3425070.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

26

Tuzet, François. « Dépôt, devenir et impact radiatif des impuretés dans le manteau neigeux : analyse des processus, simulations numériques et implications ». Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30316.

Texte intégral

Résumé :

L'une des propriétés les plus fascinantes de la neige est sa blancheur, capable de transformer complètement un paysage en quelques heures. Cette couleur vient de la capacité unique de la neige à réfléchir le rayonnement solaire dans les longueurs d'onde visibles, c'est-à-dire son fort albédo. Cette particularité de la neige est d'une importance cruciale pour le bilan énergétique de surface et par conséquent pour un large éventail de questions sociales, écologiques et climatiques. La blancheur de la neige peut, cependant, être altérée par la présence d'impuretés absorbantes. Dans les Alpes européennes, deux types d'impuretés absorbantes impactent significativement l'évolution saisonnière du manteau neigeux : le carbone suie et les poussières minérales du Sahara. Cette thèse vise à mieux comprendre et modéliser le dépôt, l'évolution et l'impact de ces impuretés absorbantes sur les manteaux neigeux saisonniers des Alpes françaises. À cette fin, trois problématiques principales sont abordées : * Quels types d'impuretés absorbantes sont présents dans un manteau neigeux saisonnier alpin et en quelle quantité? Avec quelle incertitude peut-on estimer leurs concentrations à partir de mesures? * Quels impacts radiatifs ont les dépôts d'impuretés absorbantes sur l'évolution du manteau neigeux et comment varient t-ils d'une année à l'autre? * Peut-on modéliser cet impact en se servant des modèles de manteau neigeux et des modèles atmosphériques de chimie-aérosols? Tout d'abord, une représentation explicite du dépôt et de l'évolution des impuretés absorbantes a été implémentée dans le modèle détaillé de manteau neigeux SURFEX/ISBA-Crocus. Ces nouveaux développements permettent de modéliser l'assombrissement de la surface de la neige par les impuretés absorbantes (impact direct) ainsi que leurs interactions avec le métamorphisme de la neige (impacts indirects). Les simulations de l'enneigement au Col de Porte, forcées par des flux de dépôt d'impuretés absorbantes provenant du modèle atmosphérique de chimie-aérosols ALADIN-Climate, mettent en évidence un raccourcissement de la saison de neige allant jusqu'à 9 jours en raison du carbone suie et des poussières minérales sahariennes. Ensuite, une campagne de terrain de deux ans a été menée au site d'étude du Col du Lautaret. Pendant deux saisons d'hiver, la concentration en impuretés absorbantes ainsi que les propriétés physiques et optiques du manteau neigeux ont été mesurées chaque semaine. Ce jeu de données unique est d'abord utilisé pour ouvrir la voie à une nouvelle méthode visant à estimer le profil vertical de concentration en impuretés absorbantes dans la neige à partir de mesures de profils d'irradiance spectrale. L'évaluation de cette méthode par rapport aux mesures chimiques met en évidence la difficulté d'établir un lien entre la chimie de la neige et ses propriétés optiques. Une seconde étude compare ensuite les mesures d'albédos spectraux, les mesures chimiques d'impuretés absorbantes et des simulations du manteau neigeux.[...]
One of the most fascinating properties of snow is its whiteness, and its ability to fully transform a landscape in a couple of hours. This color is due to the unique ability of snow to reflect solar radiation in the visible wavelengths, i.e. its high albedo. This particularity of snow is of crucial importance for the surface energy budget and consequently for a wide range of social, ecological and climatic issues. However, the whiteness of the snow cover can be altered by the presence of Light Absorbing Particles (LAPs) on and close below its surface. In the European Alps, two types of LAPs are suspected to have a significant impact on the evolution of seasonal snow: Black Carbon (BC) and Saharan mineral dust. This thesis aims at a better understanding and modelling of the deposition, evolution and impact of LAPs on the seasonal snowpack in the French Alps. To this aim, three main questions are addressed: * What types of LAPs are present in a seasonal alpine snowpack and in what quantity? How well can we estimate their concentration in snow based on measurements? * What is the impact of LAPs on snowpack evolution and how does this impact vary in time? * Are we able to model this impact using state-of-the-art atmospheric chemical transport models and detailed snowpack models? First, an explicit representation of LAPs was implemented in the detailed snowpack model SURFEX/ISBA-Crocus. These new developments enable to account for darkening of the snow surface by LAPs (direct impact) as well as their interactions with snow metamorphism (indirect impacts). Snowpack simulations at Col de Porte (1326 m a.s.l.) using LAP deposition fluxes from an atmospheric model highlight a shortening of the snow season by up to 9 days due to BC and dust. Second, a two-year field campaign was conducted at Col du Lautaret study site (2058 m a.s.l, French Alps). During two winter seasons, concentrations of LAPs as well as physical and optical properties of the snowpack were measured weekly from the onset to the total melt-out of the snowpack. This unique dataset was first used to pave the way for a novel method to estimate vertical profiles of LAP concentration in snow from spectral irradiance profile measurements. This method was evaluated against chemical measurements pointing out difficulties to relate snow chemistry to its radiative properties. A second study was then dedicated to the comparison of spectral albedo measurements, chemical measurements of LAPs near the surface and snowpack simulations. This latter study corroborates the issue previously mentioned and points out a gap in the current understanding of chemical measurements of BC in snow. The impact of LAPs at Col du Lautaret over the two years was evaluated using the ensemble modeling framework of SURFEX/ISBA-Crocus. We estimated that the shortening of the snow season due to LAPs was around 10±5 and 11±1 days for both seasons respectively. The studies of the impact of LAP carried out at a single location during this thesis pave the way for a larger scale study of the impacts of LAP deposition across the Alps over longer periods

Styles APA, Harvard, Vancouver, ISO, etc.

27

Rodriguez, Alvaro A. « Corrosion inhibition mechanism of a surfactant admixture on carbon steel alloy ASTM A36 [UNS K02600] coated with a high performance UV-cured coating ». University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460564870.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

28

RIGONI, FEDERICA. « EXPLORING DETECTION LIMITS AND RESPONSE TIME SCALES OF CHEMIRESISTOR GAS SENSORS BASED ON CARBON NANOTUBE AND HYBRID LAYERS ». Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/262413.

Texte intégral

Résumé :

Crucial features in gas sensors for environmental monitoring are the gas sensitivity in the low ppb range and the ability to discriminate variations of a certain polluting gas from other interfering gases. Monitoring of ammonia gas concentrations is mandatory to reduce the hazard for human health and vegetation determined by the widespread use of ammonia derivatives as agricultural nitrogen fertilizers, industrial production and traffic. In particular, ammonia, besides being a toxic molecule is one of the main precursors of secondary fine particulate matter (PM10, PM2.5). Ammonia could hence be used as a local marker of secondary fine particulate formation, allowing indirect control of particulate emission sources. In spite of this urgency, the detection of NH3 concentrations in urban areas with chemiresistor gas sensors (CGSs) has been so far widely overlooked, since the average levels are usually low, i.e. in the 20-30 ppb range, while the CGSs are generally tested by exposure to ammonia in the ppm range. Carbon nanotubes (CNTs), discovered more than 20 years ago, are well known and studied systems for many applications, among which (of course) gas sensing. With respect to commercial electrochemical sensors (mostly based on metal oxide materials), CNTs show a higher physical and chemical stability, better transport of charge to the electrodes and a wide range of possible hybrid architectures and operational features, among which the operation at room temperature, that make them unique materials for gas detection. The main goal of this thesis is to increase the sensitivity to [NH3] and to lower the detection limit (DL), exploring sample preparation strategies of low-cost single walled carbon nanotubes (SWCNT)-based gas sensors operating at room temperature, considering also the response to other interfering gases. Furthermore, effects of metal oxide nanoparticles functionalization and gas response of hybrid layers have been also investigated.

Styles APA, Harvard, Vancouver, ISO, etc.

29

Conner, Lafe G. « Environmental and Adaptive Buffers that Mediate the Response of Subalpine Ecosystems to Environmental Change ». BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5913.

Texte intégral

Résumé :

This document reports the results of 4 studies of subalpine ecosystem ecology, describing ways that spatial heterogeneity in soils and plant communities mediate ecosystem responses to environmental change. Ecosystem responses to environmental change are also mediated by regional climate patterns and interannual variability in weather. In the first chapter we report the results of an experiment to test for the mediating effects of associational resistance in a forest community that experienced wide-spread beetle kill. We found that Engelmann spruce were more likely to survive a beetle outbreak when growing in low densities (host dilution) and not through other types of associational resistance that relate to higher tree-species richness or greater phylogenetic diversity of the forest community. In the second chapter we report the effects of early snowmelt on soil moisture in subalpine meadow and aspen communities. We found that soil organic matter, soil texture, and forest cover mediated the effects of early snowmelt and were more important drivers of growing-season soil moisture than was snow-free date. In the third chapter we report the effect of early snowmelt on growth and seed production of early-season and midsummer herbaceous species. We found that the primary effect that snowmelt timing had on plant growth was through its effect on species distribution. Changes in the timing of snowmelt had limited effect on the growth, flowering, and seed count of species after they were established. In the final chapter, we report the effect of early snowmelt on soil respiration, microbial biomass, dissolved organic carbon and soil organic carbon. We found that early snowmelt resulted in warmer soil temperatures compared to neighboring snow-cover plots, and that microbial biomass and soil respiration showed no signs of a snowmelt legacy effect during the growing season. Soil organic carbon in rapid and slow-turnover pools was affected more by plant community than by snowmelt timing, and the primary drivers of soil respiration during the snow-free period were first soil organic matter and second soil temperature. Taken together, this dissertation reports our findings that subalpine ecosystems are resilient to environmental change in part because organisms in these systems are adapted to environmental conditions that are highly variable between sites, seasons, and years.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Demir-kivrak, Hilal. « Synthesis And Characterization Of Ethanol Electro-oxidation Catalysis ». Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12613887/index.pdf.

Texte intégral

Résumé :

ABSTRACT SYNTHESIS AND CHARACTERIZATION OF ETHANOL ELECTRO-OXIDATION CATALYSIS Demir-Kivrak, Hilal Ph.D., Department of Chemical Engineering Supervisor : Prof. Dr. Deniz Ü
ner Co-supervisor : Dr. Sadig Kuliyev October 2010, 196 pages In this study, the role of defects, the role of Sn in relation to defects, and the role of oxide phase of tin in ethanol electro-oxidation reaction were investigated. Firstly, adsorption calorimetry measurements were conducted on monometallic (1%Pt, 2%Pt, and 5%Pt) and bi-metallic (5% Pt-Sn) &gamma
-Al2O3 supported Pt catalysts. It was observed that while saturation coverage values decreased, intermediate heats remained same for Pt-Sn catalysts by the increasing amount of tin. The effect of particle size was investigated on Pt/C (pH=5), Pt/C (pH=11) catalysts at different scan rates. At high scan rates (quite above diffusion limitations), current per site activities were nearly the same for 20% Pt/C (E-Tek), Pt/C (pH=11), and Pt/C (pH=5) catalysts, which explained as electro-oxidation reaction takes place at the defects sites. Furthermore, the effect of support on ethanol electro-oxidation was investigated on CNT supported Pt catalyst. Results indicate that only the metal v dispersions improved ethanol electro-oxidation reaction and support did not have any effect on ethanol electro-oxidation reaction. Results on the 20% Pt-Sn/C (15:1 to 1:1 Pt: Sn atomic ratios) and 20% Pt-SnO2/C (6:1 and 1:1) catalysts indicated that ethanol electro-oxidation activity increased by increasing tin amount. For 20% Pt-Sn/C catalysts, Pt-Sn (6:1)/C indicated best activity. On the other hand, 20% Pt-SnO2 (6:1)/C catalyst was better than Pt-Sn (6:1)/C in terms of ethanol electro-oxidation activity due to the fact that there was low contact between Pt and tin oxide particles.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Sergent, Nicolas. « Dioxyde d'étain : Synthèse, Caractérisation et Etude des Interactions avec Différents Gaz Polluants - Application à la Catalyse DeNOx ». Phd thesis, Université Jean Monnet - Saint-Etienne, 2003. http://tel.archives-ouvertes.fr/tel-00002302.

Texte intégral

Résumé :

Deux dioxydes d'étain de surface spécifique élevée après calcination sous flux de O2 à 600°C ont été synthétisés : SnO2-HNO3 (24 m2 g-1) et SnO2-N2H4 (101 m2 g-1). Le solide SnO2-N2H4 se caractérise par un plus grand nombre d'espèces hydroxyles de surface que SnO2-HNO3. Le traitement thermique sous O2 entraîne la formation de lacunes d'oxygène principalement mono-ionisées, menant à des dioxydes d'étain sous stœchiométriques. Un refroidissement jusqu'à 25°C sous O2 conduit à une surface exempte de lacunes d'oxygène. Un traitement spécifique comme l'évacuation sous vide dynamique à des températures supérieures à 300-400°C, est nécessaire pour arracher des atomes d'oxygène de surface. L'adsorption de CO à la température de l'azote liquide sur le solide SnO2-N2H4 a révélé l'existence de deux sites cationiques Sn4+, possédant des acidités de Lewis différentes. En ce qui concerne les groupements OH, on a pu distinguer : i) des OH inaccessibles aux molécules de CO, ii) des OH de surface très faiblement acides et iii) des OH de surface présentant une acidité de Brönsted faible. Une étude des interactions entre le solide SnO2-N2H4 calciné à 600°C et différents gaz polluants a ensuite été menée par spectroscopie IRTF en transmission. Le dioxyde de carbone interagit avec la surface de SnO2 pour donner des espèces CO2 adsorbées sur des sites cationiques ainsi que des espèces carbonates et hydrogénocarbonates. L'absence de participation d'électrons libres aux réactions de surface envisagées, explique que les capteurs à base de SnO2 ne présentent aucune sensibilité vis-à-vis de CO2. Le monoxyde de carbone provoque la réduction partielle de la surface de SnO2 par réaction de CO avec les atomes d'oxygène de surface pour former des espèces carbonates et CO2. Cette réduction s'accompagne d'une libération d'électrons et de la formation de lacunes d'oxygène de surface, entraînant des variations importantes de la transmission qui traduisent la grande sensibilité de SnO2 vis-à-vis de CO. En ce qui concerne NO2, nous avons pu constater la présence d'espèces NO+, nitrites et surtout nitrates adsorbées. Les réactions de surface dans lesquelles ces espèces interviennent ont permis d'interpréter les variations de conductivité de SnO2 en présence de NO2. L'adsorption de NO sur SnO2-N2H4 a montré la formation d'espèces à la fois donneurs (espèces nitrites et nitrates) et capteurs (espèces nitrosyles) d'électrons. La présence de ces espèces explique, en partie, les variations complexes de conductivité avec la température. Enfin, en ce qui concerne la réduction catalytique sélective (RCS) des NOX par le propène en présence d'un excès d'oxygène, le dioxyde d'étain s'est révélé actif à haute température (> 350°C) et sélectif en N2. Cependant, les sites actifs sont bloqués par des espèces polymères oxygénés du propène (coke). Dans le cas du solide SnO2-N2H4, la présence d'eau permet d'inhiber la formation du coke, entraînant une légère amélioration de l'activité catalytique, tandis que pour un SnO2 commercial, l'eau a un effet inhibiteur sur la RCS des NOX. Une plus grande acidité de surface pour le solide SnO2-N2H4 pourrait expliquer ce comportement.

Styles APA, Harvard, Vancouver, ISO, etc.

32

cappelli, alessio. « Innovations and improvements in flours production chains : a focus on machinery and plants ». Doctoral thesis, 2021. http://hdl.handle.net/2158/1226547.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

33

Yi-JnnShen et 沈逸俊. « Investigation on Flashing Atomization and Snow Formation of Carbon Dioxide Spray ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/39620555388396246416.

Texte intégral

Résumé :

博士
國立成功大學
航空太空工程學系
102
This research investigates the mechanism of CO2 snow formation and the application of CO2 snow jet. The CO2 snow particles are produced by the process of flash-atomization. The particles are agglomerated to clusters in the formation chamber. The cryogenic CO2 snow can be used in cryosurgery. First, the influences of superheat on flashing spray characteristics and on the snow formation of liquid CO2 are investigated. Results show that liquid, two-phase flow or even three-phase flow can be found upon the release of liquid CO2 from high pressure to atmospheric pressure. This is due to complicated phase transition processes that involve hydrodynamic instabilities and thermal non-equilibrium conditions. Results also show that the spray pattern transfers from jet spray to cone spray, and then to a bowl spray configuration with the increase of superheat. The drastic changes in spray angle and mass flow rate indicate onset conditions from external-flashing to internal-flashing atomization mode. This is due to bursts of bubbles inside the nozzle chamber that result in the choking of the two-phase flow. Under internal-flashing atomization mode, a critical spray angle resulting from two competing phenomena is also found. Moreover, a few microns of CO2 snow size are measured in this research, which is consistent with records from literature on this topic. As superheat increases, the standard deviation of particle size distribution decreases, reaches its lowest value and remains constant as the spray turns to the internal-flashing mode. This is due to gradual changes in the double layer shattering configuration of the spray caused by transition from heterogeneous to homogeneous nucleation in the upstream flow. The influences of ambient pressure and length-to-diameter ratio (L/D) of the orifice on CO2 flash-spray patterns are also investigated. Results show that flash-evaporation is one of major factors on expansion of CO2 flash-spray angle. The spray angle reduces with ambient pressure. This is due to the decrease of flow expansion and flash-evaporation of CO2 flash-spray. The interaction between length-to-diameter ratio of the orifice and liquid superheat on the transition of flash-mode is observed. Secondly, the agglomeration mechanisms of CO2 primary particles inside a tube type formation chamber are experimentally investigated. The results show that a complicated particle motion in the upper portion of the formation chamber is responsible for the formation of large snow particles. The high speed and complicated motion of the snow particles inside the tube provide both the opportunities and time for the collision of particles, which implies that only particle deposition and re-entrainment cannot completely describe the phenomenon of particle agglomeration. The results also show the mechanisms of particle agglomeration inside the formation chamber, which include primary particle agglomerate in jet vortexes, agglomerated particles flowing upward into the recirculation region, particle clusters growing in the recirculation flow, and finally particles being released with the jet flow. A minimum tube length (30mmin this case) is needed to ensure the complete formation of the agglomeration mechanisms with recirculation flow, and thus the formation of considerable amounts of agglomerated particles. The results of this study thus improve current understanding of the agglomeration process and mechanisms of CO2 snow formation inside the formation chamber. Finally, the effects of injection pressure, formation chamber and bypass flow on spray performances and cryogenic characteristics of CO2 snow on cryosurgery guided by endoscopic are experimentally investigated. Results show that CO2 snow has a superior freezing capability in the application of cryosurgery. The length of formation chamber is an effective design parameter to control spray performances and cryogenic characteristics. Increase in the length of formation chamber can increase snow size and conversion ratio, as well as the cooling rate and impact area of the tissue. Thus, it is suitable for the application on wider range nidus. Moreover, the bypass flow can efficiently modulate the cooling effect of the main flow with CO2 snow particles, and it can not only be a control parameter, but also extend the operation time of cryosurgery. The experimental results also show that decrease the cylinder pressure, decrease the length of formation chamber, and increase the diameter of bypass apertures can slow down the flying velocity of CO2 snow which are effective methods to control the jet velocity and prevent the risk of penetration.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Chun-HanLien et 連君翰. « Designing formation chamber of Carbon Dioxide Snow for Endoscopic Cryotherapy Application ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/03915753945390362001.

Texte intégral

Résumé :

碩士
國立成功大學
航空太空工程學系碩博士班
101
This research investigates the characteristics of cryotherapy treatment on living organism by using carbon dioxide snow. Tissue elevation was performed before cryotherapy treatment to separate the cancer cells from the healthy tissue. Pressurized Liquid carbon dioxide was first injected into a formation chamber at room pressure. The pressure drop of carbon dioxide within the formation chamber results in a phase change and CO2 snow jet was injected on the tissue for cryotherapy treatment. CO2 snow is a gas-solid mixture with temperature low down to -78℃. It can be used to destroy the cancer cells by cryotherapy treatment. The working channels of endoscope were used for the supply of the liquid carbon dioxide as well as for air extracting and hemostasis. The outside diameter of the formation chamber of carbon dioxide was reduced for the patient’s comfort during the treatment. Design parameters investigated in this research are length and slit open angle of the formation chamber and the position of the side wall opening on the formation chamber. The evolution of temperatures of the upper and lower surfaces of biological tissue was recorded during the cryotherapy treatment. Results show that the temperature of the upper surface of the tissue is -68℃±2.0℃ as the length of formation chamber is 11 mm. The temperature of the upper surface is -78℃ as the slit open angle of the formation chamber is 15 degree. The temperature of the upper surface does not change as the position of the side wall opening is 10 mm and 13 mm. In the other hand, the temperature of the upper surface increase to -38℃ as the position of the side wall opening is 15 mm. We further applied cryotherapy technique on the freezing processes of porcine colon tissues. Results show that the temperature of upper surface decreases as the spray angle of carbon dioxide snow is increased. Freezing rate is up to 200℃/min and upper surface temperature is -50℃ as the spray angle of carbon dioxide snow is between 30⁰ and 40⁰in the test with porcine colon tissue . The freezing rate is up to 200℃/min and the freezing depth is 5 mm and 10 mm when the temperature difference and spray angle of carbon dioxide snow are 5℃ and 40⁰, respectively. In the treatment of freeze-thaw-freeze processes, the temperature difference of the lower surface of small loin tissue is 2℃ between first cycle and second cycle under spray angle of carbon dioxide 10⁰、20⁰and 30⁰. The temperature diference of the lower surface of the small loin tissue is 6.5℃ between the first and second cycle if the spray angle of carbon dioxide is further increased to 40⁰. It indicates that the lower surface temperature of small loin tissue would be further decreased during the freezing and thawing cycles.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Sheng-ChungYang et 楊勝仲. « Study of the Carbon Dioxide Snow Jet on Precision Cleaning and Cryogenics Applications ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/15157017703192870022.

Texte intégral

Résumé :

博士
國立成功大學
工程科學系碩博士班
101
Carbon dioxide (CO2) snow, the solid formed by rapid evaporation of liquid CO2, is generally applied in numerous fields such as refrigeration, cooling, medical treatment, cleaning, and others due to the characteristics of natural, odorless and tasteless, chemically stable, environmentally friendly, and harmless coolant with a high cooling performance. Generally, the precision cleaning and cryogenics are the major two considered functions to make use of a CO2 snow jet. In this study, researches on precision cleaning and cryogenics engineering applications by the CO2 snow jet are carried out and discussed. First, I demonstrated the optimization of a pulsed CO2 snow jet system for the removal of particles on the surface of complementary metal oxide semiconductor (CMOS) image sensors by using the Taguchi method. The parameters of the CO2 snow cleaning system, which can have an influence on the residue rate of particles, were optimized, resulting in optimal values of 15 degree incident angle, 40 mm cleaning distance, 0.30 mm orifice size, and a 50 millisecond time-base with above 95% confidence. A novel pulsed CO2 snow jet, triggered by ordered pulsing signals, was introduced to the experiments for solving the cryogenic effect on the surface. The pulsed CO2 snow jet gained a total of 10.6°C difference in average temperature on the substrate surface. So, I achieve not only less (even none at all) hot air consumption but also less CO2 consumption. Due to the optimization, the average residual particle rate can be controlled, and all particles larger than 2 µm will be removed. In the G2 glass substrates cleaning tests, the substrate was cleaned by a new proposed spread CO2 snow jet nozzle with 100 mm width. The particle removal rate of the spread denser CO2 snow jet is up to 99.08%. Secondly, a novel, environmentally friendly, inexpensive, and non-destructive method for removing SU-8 after being an electroplating mold in microfluidic fabrication is demonstrated in this study. A controllable thermal delaminating method, assisted by an efficient high speed aerosol jet consisting of two major steps, delamination followed by removal by lifting, is presented. Results show that the predictable delaminations were observed in the thermal process tests. The morphology of the thermal buckling-driven delamination was edge initiated and straight sided. The effects of the CO2 snow jet at a distance of 10 mm from the nozzle exit as well as the lift force Fdp, drag force Fd, and impact force Fi were determined. Based on the analysis of the lift, drag, and impact forces, the lifting force dominates the effects of the CO2 snow jet and is tens of times larger than the others. Experiments and analyses showed that the best distance for the CO2 snow jet to the nozzle exit was 6-10 mm. Using the proposed method, the SU-8 photoresist with aspect ratio 1:1 was the delaminated and removed. Finally, I developed and evaluated a highly efficient method for protecting magnesium melts by cooling and shielding the magnesium melt with CO2 snow using a newly modified technique to achieve denser CO2 snow than competing methods. Experiments, using a replicate CO2 snow nozzle in Bach’s study, were conducted for protection of the AZ91D alloy and pure magnesium in a 3-kg furnace to identify the protectiveness. The issue of CO2 consumption was immediately apparent at the beginning of the phase-two tests using two Bach’s nozzles. Hence, the modified denser CO2 snow nozzle was designed and optimized to generate more dry ice. The optimized trigger mode to improve the efficiency of the dry ice manipulation was also proposed. Finally, a specialized pilot run of the protective system with the proposed denser CO2 snow technique for a 200-kg melting furnace was developed and tested. This system had an excellent performance with a low CO2 consumption of 1.2 kg/h for the AM60 magnesium alloy and demonstrated a quite low running cost of 0.55 USD/h compared with a non-denser CO2 snow system. The proposed modified snow nozzle presents three major advantages: an improved cooling efficiency by almost 10 times, a longer lifetime for the solenoid valve, and a reduced need for furnace maintenance as a result of the sulfur-free operation.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Chih-YuanHu et 胡志源. « Cryogenic Mechanism of Carbon Dioxide Snow for Tissue and Its Application in Endoscopic Cryotherapy ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/28871136106488857003.

Texte intégral

Résumé :

碩士
國立成功大學
航空太空工程學系碩博士班
100
This study investigates the freezing mechanism and the performance of carbon dioxide snow jet on organism tissue by an endoscopic needle-free cryogenic system. This system includes four units such as the pressure supply unit, the controller, the needle-free micro injector, and the cryogenic unit. CO2 snow is used as the refrigerant. The testing material is porcine colon of six-months-old pigs. The freezing rate, the freezing temperature, the freezing field of tissue surface are investigated by various formation chamber designs, include various formation chamber lengths, sidewall holes areas, and locations of sidewall holes. The first step of the experiments is using organic fiber solution as working fluid to make tissue elevation by the needle-free injection system for marking the location of tumors or lesions. At the second step, CO2 snow spray is used to freeze the elevated portion and determine the surface temperature, the freezing rate, and the freezing area by IR thermal-images and thermocouples. According to the results, the tissue surface temperature is lower when a shorter formation chamber and smaller sidewall holes are applied, and the surface temperature can reach below -60 ℃. The freezing area increases when formation chamber lengths and sidewall holes decrease. Considering the size of tumors, surgeons can choose a right formation chamber design making the best performance in clinical treatments. This study combines the cryotherapy system with an industrial endoscope to simulate the performance of an endoscopic cryotherapy system, and the results demonstrate there are no problems on observation and operation during experiments.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Wu, Chuo-ying, et 吳卓穎. « A study on the cleaning effect of carbon dioxide snows ». Thesis, 2008. http://ndltd.ncl.edu.tw/handle/30611071915349541214.

Texte intégral

Résumé :

碩士
國立成功大學
工程科學系碩博士班
96
CO2 emission is one of the main reasons causing green house effect which impacts the global climate and requires special attention. In order to reduce the quantities of CO2 emission, industrial circles make much research on new applications of CO2 to reduce environment at impact and harmful effects. CO2 cleaning technology is one of them. This study uses different nozzle types (different channel structure、material and tube length) to make CO2 flows to compare the CO2 cleaning performance. The snow sizes from different nozzles and their effects on the cleaning performance are explored. The experimental results show that the multi-orifice flat plate type nozzle has short distance between nozzles and produces turbulence more easily than the single-orifice flat plate type nozzle. Thus, the jet has large cleaning area、higher speed、small snow size and tight distribution. The effective cleaning distance can be prolonged to 45cm. Using low conductivity single-orifice tube type nozzle of acrilan material leads to nozzle blockage periodically which enlarges CO2 snow particles. On the other hand, single-orifice tube type nozzle of stainless steel material has no blockage and smaller CO2 snow particles are generated more uniformly and result in less efficient cleaning. From the cleaning performance of nozzles of different tube length, the one with a longer tube perform better.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Morris, Jennifer Nicole. « Quantification of Impurities in Prairie Snowpacks and Evaluation and Assessment of Measuring Snow Parameters from MODIS Images ». Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-08-10155.

Texte intégral

Résumé :

Extensive research on soot in snow and snow grain size has been carried out in the Polar Regions. However, North American prairie snowpacks lack observations of soot in snow on snow albedo which adds uncertainty to the overall global effect that black carbon on snow has on climate. Measurements in freshly fallen prairie snowpacks in Northwestern Iowa and Central Texas were collected from February 25 to March 3, 2007 and April 6, 2007, respectively. Multi-day monitoring locations and a frozen lake were study sites at which snow samples were collected to measure soot in snow concentrations. Ancillary measurements were collected at a subset of the sample sites that included: temperature, density, depth, and grain size. At some locations snow reflectance and snow radiance was collected with an Analytical Spectral Device visible/near infra-red spectroradiometer (350 ? 1500 nm). Snow impurity, consisting of light-absorbing particulate matter, was measured by filtering meltwater through a nucleopore 0.4 micrometer filter. Filters were examined using a photometer to measure mass impurity concentration. Soot observations indicate prairie snowpack concentrations ranging from 1 ng C gm^-1 to 115 ng C gm^-1 with an average of 34.9 ng C gm^-1. These measurements are within range of previously published values and can lower snow albedo. As expected, spectral albedo was found to decrease with increasing impurities. Additionally, as grain size increased impurity concentration increased. Differences in soot concentration were observed between the two Iowa snowfall events. The Texas event had higher soot concentrations than both Iowa snowfalls. Validation of an ADEOS-II snow product algorithm that compares simulated radiances to measured sensor radiances for retrieval of snow grain size and mass fraction of soot in snow was attempted using satellite images acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS). The algorithm was unable to uniquely identify a particular snow grain size and soot concentration that would lead to a converging radiance solution in the two spectral bands measured and compared by the algorithm. The in situ data at the validation site fell within published ranges for freshly fallen snow for both snow grain size and soot concentration; however; the closest algorithm retrievals were considerably higher than in situ measurements for both grain size and impurity concentrations.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Yu-HaoLi et 李御豪. « Investigation on Reflux Apparatus on Sidewall of Formation Chamber Applied to Snow Formation of Carbon Dioxide Spray ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/zah6mz.

Texte intégral

Résumé :

碩士
國立成功大學
航空太空工程學系
104
Carbon dioxide (CO2) snow jets are widely used in medical and industrial applications, such as cryogenic therapy, food processing, pharmaceutical granulation, particle removal and surface cleaning. In semiconductor fabrication, CO2 snow cleaning has unique organic and particle removal abilities with eco-friendly that are better than those of traditional surface cleaning methods. A model for the agglomeration of CO2 snow particles is derived by our research team this year, and it provide clear evidence of the agglomeration of CO2 snow inside a tube that has never been published in the literature and indeed providing highly opportunity to advance performance of CO2 cleaning. To prolonging the research results of agglomeration mechanism of primary CO2 snow, this research aim at the controlling-technologies of snow particles, include the onset mechanism, onset length of agglomeration of snow particle and designed chambers. By using the additive manufacturing method by 3D printer, complicated design with opened-air chamber configuration and curved surface can easily be realized. This paper experimentally investigates the agglomeration mechanism of CO2 primary particles inside a tube and lateral jet forming a second recirculation. Results show that a complicated particle motion in the upper portion of the tube is responsible for the formation of large snow. By the change of the condition of the flow recirculation area, the snow particles can be controlled and thus ensure the formation of considerable agglomerated particles. Results also show that the onset condition of agglomeration is influenced by the flow condition, as well as the lateral jet.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Chien-ILin et 林倩儀. « Synthesis and Properties of Sn/SnO2 Coated Multi-Walled Carbon Nanotubes ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/31648452088346762385.

Texte intégral

Résumé :

碩士
國立成功大學
材料科學及工程學系碩博士班
101
This study tried to functionalize the surface of pristine multiwall carbon nanotubes(P-MWCNTs) with various methods. Thus treated MWCNTs were mixed with Sn ion containing solution to reduce Sn ion and to produce Sn/MWCNTs composite. One of the processes attempted was to oxidize the surface of P-MWCNTs with nitric acid treatment so as to provide appropriate surface for the following Sn deposit. The oxidized MWCNTs were then dispersed in SnCl2 solution to form SnO2 coated MWCNTs. The SnO2 coated CNTs were further reduced and reflowed under reducing atmosphere to form Sn/MWCNTs. The other process for producing Sn/MWCNTs was incorporated with the functionalization of MWCNTs with DBA, C7H8N2O2, as capping agent. The MWCNTs functionalized with DBA were then dispersed in SnCl2 solution followed by titrating with the reducing agent, NaBH4 solution. The size and theshape of particles coated on the wall could be manipulated by DBA. The SEM and TEM images showed that the surface of DBA/MWCNTs was uniformly coated with Tin particles and is termed Sn-DBA/MWCNTs. For the interest of thermal management in electronic packages the Sn-DBA/MWCNTs powders were pressed and then sintered for thermal conductivity evaluation. It was found that the thermal conductivity of sintered Sn-DBA/MWCNTs is better than the as pressed Sn-DBA/MWCNTs.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Sorensen, Patrick. « Effects of winter snowpack on microbial activity, community composition, and plant-microbe interactions in mixed-hardwood temperate forests ». Thesis, 2016. https://hdl.handle.net/2144/19576.

Texte intégral

Résumé :

Mean winter air temperatures have risen by 2.5˚C over the last 50 years in the northeastern U.S., reducing mean annual winter snowpack depth by 26 cm and the duration of winter snow cover by four days per decade. Because snow cover insulates soil from below-freezing air temperatures, continued declines in snowpack depth are projected to be accompanied by colder winter soil temperatures and more frequent soil freeze-thaw events. Soil bacteria and fungi will play a significant role in the forest ecosystem response to snowpack loss because they are the primary agents that carry out soil organic matter decomposition and soil nutrient cycling. Additionally, the effect of winter snowpack decline on soil bacterial and fungal communities may act indirectly via winter climate change effects on plant roots. The objectives of my dissertation research were to first determine the effect that reductions in winter snow cover has on microbial exoenzyme activity, microbial respiration, net nitrogen (N) mineralization, and net nitrification rates in two mixed-hardwood forests (Harvard Forest, MA and Hubbard Brook Experimental Forest, NH). Additionally, I sought to determine the relative role that abiotic factors (i.e., winter snow cover or soil frost) versus biotic factors (i.e., altered root-microbe interactions) contribute to overall changes in soil biogeochemical processes as winter snow cover declines. I found that winter snow depth and duration are related positively to microbial exoenzyme activity and microbial respiration following snowmelt in spring, but this relationship is transient and attenuates into the growing season. By contrast, soil freeze-thaw events during winter result in persistent declines in microbial oxidative enzyme activity that are not compensated for by warming soils during the growing season. Together, these results suggest that loss of winter snow cover will result in lower rates of nutrient cycling in northeastern U.S. hardwood forests. Tree roots interact with winter snow depth to affect net mineralization and nitrification rates, as well as bacterial and fungal community composition. Thus, winter climate change portends a reorganization of root-microbe interactions with important consequences for soil biogeochemical cycling in mixed hardwood forests of the northeastern U.S.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Laurenceau, EC. « Ecosystem controls on carbon export efficiency from the naturally iron-fertilised phytoplankton bloom over the Kerguelen Plateau ». Thesis, 2015. https://eprints.utas.edu.au/23226/1/Laurenceau_whole_thesis.pdf.

Texte intégral

Résumé :

In the ocean, the perpetual 'snowfall' of biogenic marine particles exports organic carbon from the well-lit surface layer to the deep sediments, promoting its sequestration. The efficiency of this 'biological carbon pump' (BCP), presents strong spatio-temporal variations that are not yet fully explained. Changes in surface plankton communities and trophic interactions appear important because they lead to modifications of sinking particle characteristics (e.g. composition, structure, sinking velocity). These controls are explored here via the characterization of sinking particles originating from varying planktonic community structures and evaluation of their ability to export carbon. During the second KErguelen Ocean and Plateau compared Study (KEOPS2) conducted in Oct.-Nov. 2011, six sites were sampled over and downstream of the Kerguelen Plateau (Southern Ocean), where a mosaic of phytoplankton blooms of changing communities forms in response to natural iron fertilisation. Sinking particles were collected with free-drifting sediment traps at four mesopelagic depths to examine their form and composition, including optical characterization using polyacrylamide gel filled traps. Concurrently, aggregates were formed in roller tanks from surface water phytoplankton assemblages, to explore the intricate influences of particle size, structure and composition on the sinking velocity. At each site, carbon export efficiencies were calculated as the ratio of carbon flux to net primary productivity (e-ratio). High productivity was associated with the lowest carbon export efficiency (e-ratio ~0.02) while maximum export efficiency (e-ratio ~0.2) was found at low-productivity sites. Two explanations were identified. Firstly, at high-biomass sites, strong zooplankton grazing generated large fecal pellets sustaining high carbon fluxes at 100-200 m (180 mg C m⁻² d⁻¹). This export pathway represented a 'dead end' due to rapid attenuation of the fecal pellet flux at 200-400 m, releasing most of the carbon (48±21 % carbon flux decrease). Secondly, based on the roller tank results, the morphology of dominant diatom species appeared to be an important control on aggregate sinking velocities, possibly via species-specific coagulation efficiency affecting particle structure and density. At high-biomass sites, dominant small spine-forming species formed loose slow-sinking aggregates (~10 m d⁻¹), whereas chain-forming diatoms without spines, at low-productivity sites, produced compact fast-sinking aggregates (~250 m d⁻¹). The similarity of aggregate morphology and structure from roller tank and gel traps (2-D fractal number = 1.8 and 1.9 respectively), increased confidence in applying these results to in situ conditions. A generic 3-D physical-biogeochemical (BGC) model was modified to investigate conceptually the influence of planktonic community variations on carbon export efficiency through their control on detritus composition and sinking velocity. This was achieved by introducing in the model a variable detritus sinking velocity based on phytoplankton and zooplankton detrital fractions (using experimental results). Changes from a constant (100 m d⁻¹) to a variable sinking velocity induced a significant increase of the annual integrated carbon flux at 100 m (45±23 %) highlighting the importance of sinking velocity parameterisation in BGC models. Simulations indicate that export efficiency could depend upon subtle trophic interactions between phyto- and zooplankton communities influencing the relative rates of productivity and associated carbon flux and determining the conditions of biomass retention or export. The insights and tools developed here improve our understanding of how a climate-mediated shift of surface plankton communities can alter the efficiency of the BCP.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Luus, Kristina. « Improving estimates of net ecosystem CO2 exchange between the Arctic land surface and the atmosphere ». Thesis, 2013. http://hdl.handle.net/10012/7591.

Texte intégral

Résumé :

Feedbacks between the climate system and the high-latitude carbon cycle will substantially influence the intensity of future climate change. It is therefore crucial that the net ecosystem exchange of CO2 (NEE) between the high-latitude land surface and the atmosphere is accurately quantified, where NEE refers to the difference between ecosystem respiration (R) and photosynthesis (gross ecosystem exchange, GEE): NEE=-GEE+R in umol/m^2/s. NEE can only be directly measured over areas of 1 km^2 through eddy covariance, and modeling approaches such as the Vegetation Photosynthesis Respiration Model (VPRM) are required to upscale NEE. VPRM is a remote sensing based model that calculates R as a linear function of air temperature (Ta) when air temperature is above a given threshold (Tlow), and sets respiration to a constant value when Ta50%, and as a linear function of air temperature when SCA<50%, thereby reflecting the influence of snow on decoupling soil/air temperatures. Representing the effect of SCA on NEE therefore reduced uncertainty in VPRM estimates of NEE. In order to represent spatial variability in high-latitude estimates of NEE due to vegetation type, Arctic-specific vegetation classes were created for PolarVPRM by combining and aggregating two existing vegetation classifications: the Synergetic Land Cover Product and the Circumpolar Arctic Vegetation Map. Levene's test indicated that the PolarVPRM vegetation classes divided the pan-Arctic region into heterogeneous distributions in terms of net primary productivity, and passive microwave derived estimates of snow and growing season influences on NEE. A non-parametric statistical approach of Alternating Conditional Expectations found significant, non-linear associations to exist between passive microwave derived estimates of snow and growing season drivers of NEE. Furthermore, the shape of these associations varied according to the vegetation class over which they were examined. Further support was therefore provided to the idea that uncertainty in model estimates of NEE could be reduced by calculating snow and growing season NEE separately within each vegetation class. PolarVPRM estimates of NEE in 2001-2012 were generated at a three hourly and 1/6 x 1/4 degree resolution across polar North America (55-170 W, 55-83 N). Model calibration was conducted over three sites: Daring Lake, Ivotuk, and Atqasuk, Alaska, USA. Model validation was then conducted by comparing PolarVPRM estimates of year-round daily average NEE to non-gap-filled eddy covariance observations of daily average NEE acquired over the three calibration sites, as well as six other Arctic sites. PolarVPRM performed well over all sites, with an average mean absolute error (MAE) of 0.20 umol/m^2/s, and had diminished error rates when the influence of SCA on respiration was explicitly represented. Error analysis indicated that peak growing season GEE was underestimated at Barrow because GEE at this site showed a stronger response to the amount of incoming shortwave radiation than at the calibration site, suggesting that PolarVPRM may underestimate GEE over wetland and barren vegetated regions. Despite these uncertainties, PolarVPRM was found to generate more accurate estimates of monthly and three-hourly NEE relative to eddy covariance observations than two established models, FLUXNET Model-Tree Ensemble (MTE) and CarbonTracker. Relative to eddy covariance observations and PolarVPRM estimates, MTE tended to overestimate snow season respiration, and CarbonTracker tended to overestimate the amount of midday photosynthesis. Analysis of PolarVPRM output across North America (north of 55 N) found an increase in net annual carbon efflux over over time (2001-2012). Specifically, increased rates of respiration are estimated when soil and air temperatures are warmer. Although increases in growing season vegetation indices and air temperature enable greater photosynthetic uptake by Arctic vegetation, forests and shrublands uptake less CO2 in the middle of the growing season when air temperatures rise above the physiological optima for photosynthesis. As a result, PolarVPRM estimated a decline in net photosynthetic uptake over time. Overall, PolarVPRM output indicates that North American regions north of 55 N are losing strength as a carbon sink in response to rising air temperatures.

Styles APA, Harvard, Vancouver, ISO, etc.

44

CERASA, MARINA. « Studio di adsorbenti innovativi finalizzati alla determinazione di microinquinanti organici in matrici ambientali. Study of innovative adsorbents aimed at investigating organic micropollutants in environmental matrices ». Doctoral thesis, 2021. http://hdl.handle.net/11573/1545225.

Texte intégral

Résumé :

The following PhD study is aim to understand how the Activated Carbon Fiber adsorbent ca be used in analytical chemistry world for the study of Persistent Organic Pollutants. After a deep bibliography research, comes to light the importance of choosing an ACF typology depending on its raw material, industrial process and chemical physical properties. This was the starting point for establish the suitability of ACF-F-2000 as the best adsorbent for this purpose after physical chemical characterization and extraction tests. For a study of POPs in the atmosphere, due to their persistence, is mandatory to consider their distribution in both the gaseous phase and the depositions, dry and wet (rain and snow). For this reason, the study took into consideration both the air and water matrix, the latter as rain and snow. Thanks to its versatility, the ACF is well suited to be used in several currently existing sampling methods. The work presents the validation tests of ACF-F-2000 through isotopically labelled standards for the sampling in air of PeCB, HCB according to the criteria of the EPA TO4A reference standard method. The material was also validated as a passive adsorbent in water for PCDD / Fs and PCBs according to EPA standard methods 1613B and 1668B. The work led to the definition of a sampling method for snow and the extraction of POPs from melted snow. This extraction method, which uses ACF-F-2000 as the adsorbent, has been validated for PCDD/Fs, PCB, PeCB, HCB, α-BHC, γ-BHC, p,p'-DDE, o,p-DDT, according to EPA 1668B, 1613B, TO-4A, 1699. Both the sampling and extraction systems were applied in the field on real samples carried out in the Svalbard Islands, in the Arctic region. The ACF-F-2000 was finally used for the simultaneous and parallel sampling of ambient air and snow of PCDD / F, PCB, α-BHC, γ-BHC, p, p'-DDE, o, p-DDT, HCB and PeCB, sampling at Terminillo Mount, Italy. The real samples allowed to perform analyses by GC-Orbitrap for the determination of the above analytes and for the study of the scavenged effect. Furthermore, it allowed to start a research on non-target compounds to understand to which classes of environmental interest to extend the use of ACF-F-2000 in the future.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Lin, Yung-Cheng, et 林雍政. « Preparation of Pt/SnO2-amorphous tin phosphate/carbon black composites as binary catalysts for fuel cells ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/08079160652997120633.

Texte intégral

Résumé :

碩士
國立中興大學
材料科學與工程學系所
104
Direct methanol fuel cells (DMFC) are electrochemical conversion device that can produce electricity at high fuel efficiencies, and Pt the excellent and major catalyst in them, is too expensive to be developed for applications widely. Before large-scale consumer use, three technological problems should be solved. 1. The activity of electrodes should be improved to increase efficiency, and then the amount (i.e. cost) of platinum catalyst in electrodes. 2. Poisoning effects of CO on Pt catalyst should be removed. 3. The conductivity of catalyst should be enhanced to reduce the energy waste in system. According to the previous study in our lab, Nano-sized platinum (Pt) particles were successfully reduced on iron phosphate (FeP) precipitated carbon black (CB) to form Pt/FeP/CB catalysts. In methanol oxidation reaction, these catalysts revealed the excellent electrochemical mass activity without obvious CO poisoning effects to become bi-functional catalysts. In this study, we attempted to reduce Pt on tin phosphate (SnP) precipitation CB to form Pt/SnP/CB bi-functional catalysts. Firstly, the surface of carbon black (CB) was modified by H2O2. Subsequently, the precursors SnP, including SnCl2, and NH4H2OPO4, were added in CB solution to form SnP/CB supports. Finally, H2PtCl6, CTABr, and then alcohol were added in to reduce Pt on SnP/CB catalysts. To investigate the effect of SnP on catalysts, Pt was reduced on supports with 20, 33, and 50wt% SnP in SnP/CB, respectively to derive catalysts A, B, and C. Through the characterization of Zeta potential, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), and inductively coupled plasma-mass spectrometry (ICP-MS), the final composition of catalyst is Pt/SnO2-SnP/CB, where the ratio of SnO2 to SnP for catalysts A is the highest and catalyst C the lowest. The electric resistance has been reduced from 335 for Pt/SnHPO4 to 90.5, 98.2, 120.1 Ω for catalysts A, B, and C, respectively. The particle size of platinum was 5.45, 5.29, and 4.26 nm by XRD analyses and 5.10, 4.94, and 3.9 nm observed by TEM. The electrochemical surface area (ECSA) was 426, 658, 765 (cm2/mg) while it increased to 476, 700, and 785 (cm2/mg) and the more obvious hydrogen desorption peak of Pt (110) facet was found after one more time CB added in and assigned to catalysts, A/CB, B/CB, and C/CB. In methanol oxidation reaction (MOR), catalyst C/CB illustrates the highest mass activity 63.8 (A/gPt) at 0.4 V and the lowest on-set potential 0.220 V (vs. Ag/AgCl). No forward current peaks was observed, indicating the deletion of CO poison effect on Pt. TEM observations indicate that SnP is the nucleation site of Pt. Therefore, it is concluded that the catalyst with higher content of SnP, such as catalyst C is helpful for increasing the nucleation sites of nano-sized Pt, leading to the better electrochemical performance. In contrast, catalyst A with lower content of SnP reveals the greater sizes of Pt due to the less nucleation sites, although it presents the greater conductivity owing to more SnO2, finally resulting in worse electrochemical performance.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Chang, Pei Yi, et 張珮怡. « Fabrication of SnOx (x = 0-2) and ordered mesoporous carbon composites for Li ion battery application ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/85479337999483856518.

Texte intégral

Résumé :

博士
國立清華大學
生醫工程與環境科學系
104
Nowadays, the society of highly dependent with electrical technologies is facing with seriously environmental pollution, over-consumption of limited fossil fuel, climate changed by greenhouse gas effect. For sustainable life in the future most be based on the development of low carbon footprint and high efficient energy storage. Since 1990s, Li ion batteries (LIBs) have been considered as high potential energy conversion due to the merits of chemical stability, higher capacity, longer lasting recharging, optimal operating potential and portable weight. For commercialization, graphitized carbon is commonly used as anode material, but there is a knotty problem of very low theoretical and experimental capacity for useless applying to high speed calculation and/or electric vehicles. In the past decade, Sn-based materials have been chosen as active materials for anode of LIBs because of its high theoretical capacity, abundant, easily synthesizing and low price. On the other hand, fabricating with the ordered mesoporous carbon spheres (OMCS) seems useful to buffer the huge volume change of Li-Sn formation due to their high surface area, hierarchical porous structures and good conductivity, resulting to stabilizing the microstructures and increase the cycle life. Herein, it was focused on the fabrication of various tin-based materials involved Sn, SnO and SnO2 composited with OMCS and further to estimate the electrochemical performances for Li storage in this study. At first, a series of OMCS has been successfully synthesized with various diameters of 50, 90 and 130 nm via an environmentally benign, most effective and conventional hydrothermal method. The physical and chemical properties of OMCS have been evaluated by performing scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption analysis, small-angle scattering system (SAXS), X-ray diffraction (XRD), Raman spectroscopy and electrochemical performances of coin type cell for Li storage. The results show that the OMCS with largest size has wide distribution of diameters and exhibit high specific capacity of 560 mA h g-1 at 0.1 C and 240 mA h g-1 at 5 C attributed by i) coexistence of mesopores and macropores for facilitating Li+ diffusion and ii) highest micropore surface area for increase of Li storage. Various SnOx (x = 0-2) nanoparticles with various Sn/C ratio from 5 to 35 wt% composited OMCS have been successfully fabricated by the simple and green process of microwave assisted hydrothermal method. The present work followed the same physiochemical and electrochemical analysis. The SnO2/OMCS composite with highest Sn/C ratio (35 wt%), highly ordered mesoporous structure, smaller particles size of SnO2 (3-6 nm) and nanoscale composite (approximately 120 nm) exhibited high reversible capacity of 1122-293 mA h g-1 under the current densities of 35-3500 mA g-1 for 75 discharge-charge cycles. Also, the first coulombic efficient was significantly increased from 40% to 60% resulting to decrease the irreversible capacity in 1st cycle. Furthermore, it shows 400 mA h g-1 under ultra-high current density of 3500 mA g-1 for as longer as 400 cycles. Before and after cycles, the results from TEM images exhibited the uniform nanocomposites with Sn particles sizes of 5-10 nm and maintenance of spherical carbon with ordered mesopores. As excellent LIBs performance of SnO2/OMCS nanocomposites was contributed by rapid charge transfer, stable SEI layers and minimizing polarization effects carried out from highly integrated hierarchical pores and closed packing morphology between inter SnO2 nanoparticles with optimization of Sn loading amounts.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Lin, Cheng-Wei, et 林政維. « CoO nanoparticles and SnO2/ MoS2 composite confined in tube-like mesoporous carbon as efficient nanocomposite anodes for lithium-ion batteries ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/556wth.

Texte intégral

Résumé :

碩士
國立中央大學
化學學系
106
Transition metal oxides and Transition-metal dichalcogenides as anode materials in lithium ion batteries have attracted tremendous attention because of their high theoretical capacities compared with commercial graphite. However, the large volume expansion during the charge-discharge process leads to low electrical conductivities. In first part, we design a tubular nanocomposite of CoO@CMK-9 to overcome this problem. A three-dimensional (3-D) hollow-type ordered mesoporous carbon (CMK-9) could not only provide enough space during the Li+ insertion-extraction process, but also increase the electrical conductivity. CoO is regarded as one of the most promising anode material for lithium ion batteries (LIBs), due to its high theoretical capacity (715 mAh/g), natural abundance, and low cost. CoO@CMK-9 delivers a reversible capacity of 828 mAh/g after 200 cycles at a current density of 100 mAh/g with an outstanding rate performance. The CoO@CMK-9 nanocomposite is expected to have high specific capacity and good cycling performance. In second part, we design a novel structured SnO2/MoS2@CMK-9, MoS2 is a graphene-like layered structure, Mo is sandwiched between two S layers. The atoms in the layers are bound strongly by covalent bonds, while the adjacent layers interact by weak van der Waals forces. MoS2 nanosheets can be easily restacked together during charge–discharge processes. To solve this problem, we add SnO2 nanoparticles which can avoid to restack of MoS2 nanosheets. SnO2/MoS2@CMK-9 demonstrate an excellent Li-storage performance as an anode of LIBs, deliver a high reversible charge capacity of 782 mAh/g after 50 cycles at a current density of 100 mAh/g.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Ding, L., S. He, S. Miao, M. R. Jorgensen, S. Leubner, C. Yan, Stephen G. Hickey, A. Eychmüller, J. Xu et O. G. Schmidt. « Ultrasmall SnO(2) nanocrystals : hot-bubbling synthesis, encapsulation in carbon layers and applications in high capacity Li-ion storage ». 2014. http://hdl.handle.net/10454/10440.

Texte intégral

Résumé :

Yes
Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908 mA.h.g(-1) at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs.
National Natural Science Foundation of China (21103039), Anhui Province Natural Funds for Distinguished Young Scientists, https://bradscholars.brad.ac.uk/browse?order=ASC&rpp=20&sort_by=-1&etal=-1&offset=6150&type=authorResearch Fund for the Doctoral Program of Higher Education of China (20110111120008), Beijing National Laboratory for Molecular Sciences (BNLMS), and Deutsche Forschungsgemeinschaft Grant (DFG): H1113/3-5. C.Y. acknowledges the support from the “Thousand Talents Program” and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

Styles APA, Harvard, Vancouver, ISO, etc.

49

Kao-HsienCho et 卓高賢. « Studies of the High Performance Pd–SnOx / i-diamond / p+ diamond (CAIS) Diode Carbon Monoxide Gas Sensor with Nano-tip Structure ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/77876226457438874534.

Texte intégral

Résumé :

碩士
國立成功大學
微電子工程研究所碩博士班
98
The Catalyst/ SnOx/ i-diamond/ p+-diamond p+-silicon (CAIS) diodes with a nano tip structure are prepared by a Bias-assisted Hot-wire chemical vapor deposition (BAHWCVD) system for carbon monoxide (CO) gas sensing applications. With the added DC bias, a better quality film can be deposited under a lower temperature. We use Raman, XRD, and SEM for bond structure measurement, examination of surface morphology, analyzing crystallinity, and investigation of carbon atomic concentration with significant sp3 bonding in the film, respectively. Furthermore, effects of various patterns Pd catalyst electrode and SnO2 thicknesses on the CO sensing ability are investigated, and find the device with 50nm thick SnOx and the square Pd electrode has the highest diode sensing current and thus the highest sensitivity. Experimental results show that with and without the nano tip structure, the diode sensing current can be enhanced up to 75 times. Besides, under 200℃, 3V forward bias, and 1000ppm CO / air ambient, the developed CAIS diode has a sensing current of 112 mA and sensitivity of 72.3%, which are respectively 75 times and 1.5 times to a reported CAIS diode diamond CO sensor prepared by a PECVD on Si substrate.

Styles APA, Harvard, Vancouver, ISO, etc.

50

Chen, Yu-Yu, et 陳余育. « Study of Photocatalytic Removal of Nitrogen Oxides by using Nitrogen-Doped Carbon Quantum Dots and Zinc Hydroxide Stannate/SnO2 Binary Complexes ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/7ppkv7.

Texte intégral

Résumé :

碩士
中原大學
環境工程學系
106
Source of Nitrogin Oxide mainly divided into nature and hunam factors. The formation of nitrogan oxides in nature is mainly caused by lighting, fire and microbial nitrogen fixation. Human activities are mainly emitted by combusion behavior, while the combustion process comes from stationary pollution sources (such as power plants, incinerators ,etc.) and mobile pollution sources (such as steam locomotive). Nitrogen oxides not only cause harm to the human body, but also may cause bronchitis, emphysema, and environmental hazards such as photochemical smog, acid rain, and ozone layer damage. In order to solve the problem of nitrogen oxide pollution, this study uses photocatalytic technology to degrade nitrogen oxides. However, most semiconductor photocatalysts can only be excited by ultraviolet light, and it is easy to produce photo-generated carriers that are easy to recombine. In this study, N-CQDs were prepared by simple and low-cost hydrothermal method with citric acid and urea as carbon sources, and then N-CQDs/ZnSn(OH)6/SnO2 was successfully synthesized by using solvothermal method with SnCl4∙5H2O and C4H10O6Zn as metal sources. The composite photocatalyst utilizes a simple and non-primary photocatalytic reaction to degrade nitrogan oxides, and further utilizes XRD, DRS, FTIR, ESR and other instruments for feature analysis. Using different pH of precursor solution and different additions of N-CQDs to find the best synthetic materials and experimental parameters in experiment of removal NO at 400 ppb. Then discussed the reaction principle of N-CQDs/ ZnSn(OH)6/SnO2 photocatalyst on NO degrade. The experimental results show that the pH of the ZnSn(OH)6 precursor affects whether the product contains SnO2, and in the 400 ppb NO photocatalytic degradation experiment, the presence or absence of SnO2 is observed in the visible light of ZnSn(OH)6. Under the conditions of introducing N-CQDs, 36.6% of the activity of N-CQDs/ZnSn(OH)6/SnO2 is greater than 16.8% of the activity of N-CQDs/ZnSn(OH)6; and the amount of N-CQDs added is adjusted. N-CQDs/ZnSn(OH)6/SnO2-600 has the best degradation effect under visible light, achieving a degradation rate of 35.5% and a removal of 149.13 ppb, and the production of nitrogen dioxide was almost 0 ppb.This suggests that the catalyst does not produce secondary contaminants - nitrogen dioxide. It is an environmentally friendly material. The introduction of N-CQDs enables its photocatalyst to directly degrade pollutants by visible light and is not easily deactivated during the decomposition of pollutants. Because of the synergistic action of SnO2 and ZnSn(OH)6, the catalytic activity of N-CQDs/ZnSn(OH)6/SnO2 composite is optimal under four conditions.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Carbonic snow »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres