Дисертації з теми "Oxidation reduction"
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1
Monsen, Bodil Elisabeth. "Iron ore concentrates : oxidation and reduction." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 1992. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5747.
2
Hong, William Sungil. "Oxidation-reduction kinetics of porous titanium dioxide /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487331541711442.
3
Zweni, Pumza P. "Dendrimer-transition metal catalyzed oxidation and reduction reactions." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/10529.
Анотація:
This project was launched with the aim of developing dendrimer catalysts for oxidation and reduction reactions. Poly(amidoamine) (PAMAM) and poly(propyleneimine) (PPI) dendrimers were of interest because of their well-established synthesis. Chapter 1 describes the fundamentals of dendrimers and provides a brief insight of their application in catalysis. In particular, examples of dendritic catalysts that have been previously employed as oxidation and reduction catalysts are presented. Chapter 2 presents the synthesis and characterization of silica-supported PAMAM dendrimers, their phosphomethylation with Ph2 PCH2OH, and their complexation to palladium complexes. Chapter 3 reports the application of the silica-supported PAMAM-Pd complexes to the oxidation of alkenes to methyl ketones under Wacker-type conditions as well as the use of tBuOOH as the oxidant in these reactions. Chapter 4 discusses the use of the above-mentioned complexes to catalyze the selective hydrogenation of dienes to monoolefins in the presence of H2 under mild reaction conditions. Chapter 5 presents our efforts in modifying PPI dendrimers with the salen moiety to give ligands that are coordinated to the metals Ti and V. Attempts at using the former complexes to promote the epoxidation of alkenes and the latter complexes to catalyze the epoxidation of olefinic alcohols are discussed.
4
Bowsher, C. G. "Nitrite reduction and carbohydrate oxidation in root plastids." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234223.
5
Minuzzi, Felipe Crivellaro. "Reduction techniques applied to the oxidation of ethanol." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/182056.
Анотація:
A simulação numérica de escoamentos reativos, como a combustão, tem um caráter altamente não-linear devido a presença de diversas reações químicas que acontecem entre as espécies que descrevem o processo de oxidação do combustível. Além disso, tais processos ocorrem a nível molecular, tornando o sistema de equações governantes rígido, o que implica na necessidade de esquemas numéricos de alta ordem bem como malhas finas e passo de tempo pequeno, aumentando consideravelmente o custo computacional. Neste sentido, o uso de mecanismos de oxidação detalhados na simulação numérica é proibitivo, e técnicas de redução química são necessárias de modo a desenvolver modelos reduzidos com menos variáveis e rigidez moderado, mantendo a precisão e abrangência do modelo detalhado. O objetivo do presente trabalho é obter uma comparação dos resultados obtidos para duas técnicas de redução química diferentes, Directed Relation Graph - DRG, baseada no desenvolvimento de mecanismos esqueletos, e a Reaction Diffusion Manifolds - REDIM, baseada na separação das escalas de tempo. Como validação dos modelos propostos, simulações numéricas 1D de chamas pré-misturadas e não pré-misturadas, bem como de reatores homogêneos, são desenvolvidas. Além disso, uma estratégia que une as duas técnicas de redução é apresentada, com o objetivo de ser aplicada em mecanismos cinéticos grandes.Numerical simulation of reactive flows, such as combustion, has a highly non-linear character due to the presence of several chemical reactions that occur among the chemical species that describe the process of fuel’s oxidation. Besides, such processes occur at a molecular level, making the system of governing equations stiff, which implies in the need of high order numerical schemes as well as fine meshes and small time step, enhancing considerably the computational cost. In this sense, the use of detailed oxidation mechanisms in the numerical simulation is prohibitive, and chemical reduction techniques are needed in order to develop reduced models with less variables and moderate stiffness, while maintaining the accuracy and comprehensiveness of the detailed model. The objective of the present works if to obtain a comparison between two chemical reduction techniques, the Directed Relation Graph - DRG, based on the skeletal mechanisms generation, and the Reaction Diffusion Manifolds - REDIM, based on the separation of time scales. As validation of the proposed models, one-dimensional numerical simulations of premixed and non-premixed flames, as well as homogeneous reactors, are carry out. Besides, a coupled methodology between DRG and REDIM is presented, that will provide a useful tool for simulation of fuels with very large detailed kinetic mechanisms.
6
Ayub, Ibrar. "Oxidation and reduction properties of iron-containing oxides." Thesis, n.p, 2001. http://ethos.bl.uk/.
7
Sim, Andrew Gregory Chemical Sciences & Engineering Faculty of Engineering UNSW. "Reduction-oxidation cycling of metal oxides for hydrogen production." Awarded By:University of New South Wales. Chemical Sciences & Engineering, 2010. http://handle.unsw.edu.au/1959.4/44763.
Анотація:
A process for the production of clean hydrogen from methane based upon the sequential reduction and oxidation of metal oxides has been studied. The original process, based on iron oxide, suffers from significant disadvantages including deactivation by sintering and coke deposition. Improvement of the iron based system and identification and development of alternative metal oxides for hydrogen production has formed the basis of this study. The literature review outlines current methods for hydrogen production, followed by a review of the Steam-Iron Process as an improved and simpler method for clean hydrogen production. Thermodynamic assessment shows Fe3O4/FeO/Fe, WO3/WO2/W and SnO2/SnO/Sn to be the most prospective systems for the Steam-Metal Process. Experimental testing showed that Fe and W based systems were suitable for hydrogen production, but Sn based systems were unsuitable due to poor reducibility using methane. Attention was then focused on the addition of CeO2/ZrO2 promoters to Fe and W based systems in order to improve reactivity and prevent catalyst deactivation. CeO2/ZrO2 promoted Fe2O3 showed improved redox reactivity and increased stability, with formation of FeO. This aided in mitigation of sintering and introduced the possibility of prevention of coking, as catalysed by methane decomposition over fully reduced Fe metal. Although WO3 was found to be a suitable oxide, complete reduction to tungsten metal resulted in the formation of tungsten carbide and contamination of hydrogen produced. The formation of 31mol% [CeO2/ZrO2] / 69 mol% WO3 showed stabilised reduction using methane, allowing for redox cycling of the WO3-WO2 couple and preventing complete reduction to W metal. The use of the doped metal oxide showed the best performance of all the metal oxides tested, with clean hydrogen production over multiple redox cycles and high metal oxide stability. Further kinetic studies of both the reduction and oxidation reactions show reduction is chemical reaction controlled process (WO3/WO2.9 → WO2) with an apparent activation energy of 142 ?? 3 kJ/mol. Oxidation is also fitted to a chemically controlled process, with a reaction rate expression derived as: rH2 = [0.064 + (F x 0.00038)].e^(-108750/8.314xT).[PH2O]^(0.75) The apparent activation energy for oxidation was calculated as 109 ?? 1 kJ/mol.
8
Aldea, Ioana Raluca. "Oxidation and reduction processes, investigation of new catalytic systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0018/NQ48082.pdf.
9
Shan, Jingning. "Polymer-supported catalysts for oxygen reduction and methanol oxidation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0017/MQ55541.pdf.
10
Yu, Kyunghee. "Test of copper red glazes in reduction and oxidation." Virtual Press, 1987. http://liblink.bsu.edu/uhtbin/catkey/495302.
Анотація:
The problem is to test how the copper red color will turn out depending on the recipes of the glazes and the firing methods. Sixteen different copper red glazes are tested for the reduction and the oxidation firing. Through the repeated firings some glazes are recommended for its consistency and color. It is also learned that the unpredictability is the biggest problem in the reduction firing. Unlike the reduction firing, the result from the oxidation firing is quite consistent, but none of the glazes has the successful local reduction in the oxidation firing.
11
Padmanabhan, Anita Rema. "Novel Simultaneous Reduction/Oxidation Process for Destroying Organic Solvents." Digital WPI, 2008. https://digitalcommons.wpi.edu/etd-theses/465.
Анотація:
Trichloroethylene (TCE) is one of the most common groundwater pollutants in the United States and is a suspected carcinogen. The United States Environmental Protection Agency (EPA) estimated that between 9% and 34% of the drinking water sources in the United States may contain TCE, and have set a maximum contaminant level of 5 ìg/L for drinking water. Traditional treatment technologies such as granular activated carbon and air stripping have only had marginal success at removing TCE from contaminated sites. Chemical oxidation processes have provided a promising alternative to traditional treatment methods. The objective of this research was to examine the conditions under which zero valent iron (Fe0) activates persulfate anions to produce sulfate free radicals, a powerful oxidant used for destroying organic contaminants in water. With batch experiments, it was found that persulfate activated by zero valent iron removed TCE more effectively than persulfate oxidation activated by ferrous iron. This laboratory study also investigated the influence of pH (from 2 to 10) on TCE removal. TCE was prepared in purified water and a fixed persulfate/TCE molar ratio was employed in all tests. The results indicated that this reaction occurred over a wide range of pH values. The production and destruction of daughter products cis 1,2 dichloroethylene and vinyl chloride were observed. The effect of persulfate dose on this reaction was also studied. Results showed that a molar ratio of 10/1/1 (persulfate/ZVI/TCE) yielded over 95 percent TCE destruction. Increasing the persulfate dose resulted in greater TCE destruction as well as destruction of the daughter products. Kinetic experiments at a molar ratio of 10/1/1 (persulfate/ZVI/TCE) show that approximately 90 percent of the TCE was destroyed in less than 15 minutes.
12
Radhakrishnan, Praveen Kumar. "Stratified Arrays of Needle-Type Oxidation Reduction Potential Sensors." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250709803.
13
Radabaugh, Timothy. "Oxidation and reduction of inorganic arsenic in mammalian systems." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280379.
Анотація:
Arsenic is a toxic metalloid and is ubiquitous in our environment. In ancient cultures it was valued as a poison and today is becoming an increasing public health problem. Chronic arsenic exposure has a broad range of toxic effects including cancer. Currently millions of people are exposed to higher levels of arsenic in their food and drinking water than is considered safe by the World Health Organization. Although arsenic metabolism is not completely understood, it is known that inorganic arsenate is reduced to arsenite which can then be methylated and excreted in the urine. It is also known that some arsenic is retained in the body, presumably by binding to cellular proteins. To better understand how arsenic is metabolized, our approach was to identify and characterize proteins that are involved in arsenic metabolism. Using biochemical approaches we demonstrated that arsenate reductase activity from human liver was purine nucleoside phosphorylase (PNP). We were able to demonstrate that calf spleen PNP has arsenate reductase activity in vitro in the presence of inosine and dihydrolipoic acid, and that the reaction exhibits Michaelis-Menten kinetics. This identifies an enzymatic route for arsenate reduction. We also demonstrate that ferritin, an iron storage protein containing phosphate, can bind arsenic both in vitro and in vivo. In addition, we demonstrate that ferritin can oxidize arsenite to arsenate, and then interact with arsenate as it does with phosphate. We also establish that arsenate can inhibit ferritin's ability to store iron in vitro. Our results combined with data reported by others, suggest that DNA damage and enzyme inactivation associated with arsenic challenge may occur via reactive oxygen species generated by arsenic-iron redox reactions in ferritin, and that iron may augment arsenic toxicity. The interaction between ferritin and arsenate has two important implications. First, it suggests that iron exposure may be an important parameter to examine in epidemiological studies of arsenic sensitivity. Second, it suggests that iron chelation therapy might be beneficial in conjunction with arsenic chelation therapy for patients suffering from acute arsenic poisoning.
14
Hayes, Elizabeth Jane. "Macrocyclic complexes as redox-active receptors /." St. Lucia, Qld, 2001. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16372.pdf.
15
Bakke, Bruce W. "Reduction of sulfur release through indigester oxidation in kraft pulping." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11691.
16
Vuki, Maika. "A study of the electrochemical oxidation and reduction of polyaniline." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239637.
17
Crosby, Sarah H. "Cyclometallated complexes of platinum : C-H activation, oxidation and reduction." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/55449/.
Анотація:
Within this thesis, research related to the synthesis of Pt(II) and Pt(IV) cyclometallated complexes involving both aryl and alkyl C-H activation is discussed. The introduction reviews literature relevant to C-H activation, cyclometallation and reductive elimination, both historic and current. Four pyridine based pro-ligands, all with a 4-fluorophenyl substituent and a varying alkyl substituent, were synthesised in order to study both aryl and alkyl C-H activation. Initial reactions with K2PtCl4 led to the cyclometallation of the phenyl ring via a reversible aryl C-H activation, which then resulted in a variety of Pt(II) complexes by the addition of different co-ligands. Oxidation of these Pt(II) species gave Pt(IV) complexes, which subsequently underwent isomerisation to give the thermodynamic product. For the DMSO derivatives this was shown to occur via five coordinate complexes stabilised by agostic interactions with the alkyl chain and resulted in the first crystallographically characterised oxygen bound DMSO Pt(IV) complexes. Pt(II) and Pt(IV) sp2 cyclometallated complexes, each with an sp3 agostic interaction, were isolated and characterised when using the more sterically demanding tbutyl derivative of the pro-ligand. Subsequent alkyl C-H activation of the tbutyl group was observed via an intra-molecular transcyclometallation reaction to give complexes with an sp3 cyclometallation. From these species a series of complexes with a C(sp2)^N^C(sp3) tridentate ligand were also synthesised. It was also noted that a reversible rollover reaction of the Pt(II) agostic complex occurred in DMSO solvent by exchanging the C(sp2)^N cyclometallation for a C(sp2)^C(sp2) cyclometallation via decyclometallation, rotation about the central C-C bond and subsequent C-H activation. Reductive elimination of a chloride ligand with both sp2 and sp3 cyclometallated carbons occurred to give functionalised phenyl rings and tbutyl groups, respectively. Steric interactions were shown to play a major role in these reactions.
18
Tong, Giang. "Oxidation of mercury during selective catalytic reduction of nitric oxide." Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2009p/tong.pdf.
Анотація:
Thesis (Ph. D.)--University of Alabama at Birmingham, 2009.Additional advisors: Heng Ban, Chih-Hsiung Cheng, Thomas K. Gale, Melinda M. Lalor. Description based on contents viewed June 3, 2009; title from PDF t.p. Includes bibliographical references (p. 113-123).
19
Campion, Michael J. (Michael John). "Understanding the oxidation and reduction process in transparent conducting oxides." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121604.
Анотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 133-141).
Transparent conductors play important roles in many optoelectronic devices such as LEDs, thin film solar cells, and smart windows through their ability to efficiently transport both photons and electrons. Simultaneous requirements of a wide band gap, high free carrier concentration, and high electron mobility limits the selection of available transparent conductor materials. Further improvements in the optical and electrical properties, along with improvements in processing tolerance, are highly desirable for this material class. One key limitation of current transparent conducting oxides is their response to oxidation, which can cause severe decreases to the conductivity of the material through ionic compensation. Materials with slow oxygen kinetics or resistance to the formation of compensating ionic defects could lead to more flexible operating and processing conditions for applications requiring transparent conductors.
The properties of transparent conducting oxides, Al-doped ZnO and La-doped BaSnO₃, were examined through a variety of methods with a focus on the impact of processing on the free carrier concentration, electron transport, and optical properties. Al-doped ZnO was examined as a well-known alternative to indium tin oxide (ITO) that has been shown to be limited by relatively narrow processing conditions and large variances in reported properties. BaSnO₃ is a comparatively new material in the field of transparent conductors, attractive mainly due to its exceptionally high electron mobility for an oxide. Little is currently known about the nature of defects and processing on the optical and electrical properties of this material, but this information will be important to understand before implementing this material in practical devices.
For these materials, I examined the roles of oxygen stoichiometry and point defect formation in impacting properties and stability under both processing conditions and harsh operating conditions and explored the limitations and opportunities provided by these transparent conducting oxide systems. Al-doped ZnO thin films were produced by pulsed laser deposition under a variety of oxygen conditions demonstrating the strong dependence of free electron concentration and mobility on the oxidation state of the material. The free carrier absorption in the infrared photon range was measured and modeled and found to agree well with theory assuming ionized impurity scattering as the limiting electron scattering mechanism. These effects were understood through the framework of the formation of compensating zinc vacancies under oxidizing conditions, leading to decreases in the free electron concentration.
Atom probe tomography was applied to Al-doped ZnO thin films deposited on Si substrates, demonstrating an effective accumulation of Al near the ZnO/Si interface, but with no detected precipitation or agglomeration in the x-y plane of the film, even for heavily doped films. This was surprising due to the high concentration of Al-dopant in the material, exceeding the thermodynamic solubility limit of bulk ZnO. An accumulation of Al-dopant was observed at the ZnO/Si interface under multiple conditions, with the oxygen atmosphere during deposition and nature of the Si substrate affecting the degree of accumulation. Because transparent conductors are typically used to transfer charge through interfaces, understanding the nature and implications of this observed accumulation effect could be essential to understanding device performance.
La-doped and undoped BaSnO₃ thin films and bulk samples were tested for their electrical conductivity in-situ under various temperatures and oxygen partial pressures. In the undoped case, a p-type to n-type transition was observed at lower temperatures with decreasing oxygen partial pressure, with the behavior correlated to the formation and annihilation of oxygen and cation vacancies. Under donor-doping, a measurable, but weak n-type dependence of conductivity was demonstrated, pointing to a surprisingly weak role played by cation vacancy charge compensation over the measured temperature ranges. Compared to other similar oxide systems, compensation by cation vacancies would normally be expected to be strong under oxidizing conditions.
This is a key advantage for La-doped BaSnO₃ as a high temperature oxygen stable material compared to other competing materials that are more susceptible to conductivity degradation due to ionic compensation of the donor dopant under oxidizing conditions. This was directly demonstrated in the testing of the conductivity response of La-doped BaSnO₃ thin films that maintained high conductivity under a large range of oxygen and temperature conditions. Oxygen diffusion in the material was estimated from conductivity relaxation and further explored with oxygen tracer diffusion studies. These studies revealed an activation energy of 2 eV for the oxygen diffusion process, as well as a depth dependent diffusivity leading to depressed oxygen diffusivities near the surface. Study of epitaxial and polycrystalline thin films of La-doped BaSnO₃ revealed a difference in the rate of oxidation response of the conductivity.
Epitaxial thin films exhibited a weak power law dependence on temperature while polycrystalline thin films under oxidizing conditions exhibited an activation energy of 0.36 eV. This effect was attributed to the formation of narrow space charge regions at the grain boundaries under oxidizing conditions. Simultaneous measurements of the infrared transmission and electrical conductivity of thin films were performed as a means of correlating infrared transmission with conductivity at high temperatures under various controlled atmospheres. These two measurements were found to be strongly correlated and were demonstrated to be connected to the formation and annihilation of free carriers in the thin films. A novel measurement technique was explored in which the conductance response was measured across a substrate during pulsed laser deposition of Al-doped ZnO.
The measured conductance profile as a function of time was correlated to the expected growth regimes typical of an island growth mode, and the thickness dependence of resistivity was directly observed. Additional information about the growth conditions was obtained through conductance relaxation after single pulses, performed under different growth chamber atmospheres.
by Michael J. Campion.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
20
ANNAMALAI, ABINAYA. "Electrochemical Energy Conversion Catalysts for Water Oxidation and CO2 Reduction." Doctoral thesis, Università degli studi di Genova, 2022. http://hdl.handle.net/11567/1086344.
Анотація:
Numerous efforts have been made for the development of renewable energies to replace fossil fuels and thus reduce greenhouse gas emissions. Renewable energy has the advantage of having a limitless supply over time and is clean. This thesis reports on novel transition metal-based electrocatalysts for acidic water splitting and CO2 reduction, which are two significant technologies to produce chemical fuels (i.e. H2 and C-based compounds) from renewable electricity. The target is to develop and investigate cost-effective, stable, and efficient electrocatalysts for acidic water splitting and CO2 reduction, replacing noble metals and achieving performances above the current state of the art.
In the first part, the preparation and oxygen evolution properties of the oxygen plasma-treated and acid-activated carbon paper are investigated. This part also presents the Ru incorporated Carbon paper, as an efficient, stable, and self-standing catalyst for OER in acid. This catalyst shows an overpotential of 230 mV vs. RHE at 1 mA cm−2, comparable to the other carbon-based materials. It shows a small Tafel slope of 74 mV dec-1 and 20 hours of stability at 10 mA cm−2.
In the second part, the template-assisted wet synthesis and electrochemical OER studies of yolk-shell Co3O4/Co1−xRuxO2 hollow microspheres (MSs) are discussed. It demonstrates a lower overpotential of 240 mV at 10 mA cm-2 and a small Tafel slope of 70 mV dec−1. Also, the MSs exhibit high mass activity of 600 A g−1 and show high stability for 24 hours Chronopotentiometry tests at constant current densities of 10 and 20 mA cm−2 in 0.5 M H2SO4.
Finally, nanostructured CdSe/Cu3P/CdSe heterostructures (in the form of nanocoral and sandwiches), obtained through colloidal synthesis, were used as efficient electrocatalysts for CO2 reduction. The nanocoral and Sandwich structured catalyst demonstrated higher CO2-to- HCOO– conversion giving a FEHCOO– of about 60% and 40% at –1.4 V vs RHE, respectively in 0.5 M KCl.
21
Davies, Arthur John. "The development and teaching of redox concepts /." Title page, table of contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09EDM/09edmd255.pdf.
22
Miedzinska, K. M. E. (Katarzyna Malgorzata Ewa) Carleton University Dissertation Chemistry. "A study of the redox mechanism of exchanged zeolites." Ottawa, 1985.
23
Venables, Dean Stuart. "Reduction of tungsten oxides with carbon and hydrogen." Thesis, Rhodes University, 1996. http://hdl.handle.net/10962/d1005004.
Анотація:
The reductions of WO₃ with hydrogen, with CO, and with carbon, as well as the reduction of WO₃/graphite mixtures with hydrogen, were studied using thermogravimetry, evolved gas analysis, X-ray powder diffraction, and scanning electron microscopy. The intermediate phases W₂₀O₅₈, W₁₈O₄₉ and WO₂, were observed in the reductions. The final product of the reductions with hydrogen and carbon was tungsten, and we was formed in the reduction with CO. The reaction paths in the overall processes were determined. The reactant/product gas ratio had a considerable influence on which reactions took place. The morphology of the sample was characterised at different stages of the reduction. The shape of the WO₃ particles was retained during the reduction. Particle growth was observed in the reduction with hydrogen and was attributed to the formation of WO₂(OH)₂(g). The kinetics of the reductions were investigated , and the reaction mechanisms determined. The reduction of WO₃ with CO was studied from 650 to 900°C, and occurred at a phase boundary with an activation energy of 40 kJ mol⁻¹ . The reduction of WO₂, was studied under the same conditions. The reaction also occurred at a phase boundary and had an activation energy of 62 kJ mol⁻¹. The reduction of WO₃ with carbon was studied from 935 to 1100°C and took place via CO and CO₂. Two stages were observed in the reduction . The first stage, which corresponded approximately to the formation of WO₂ had an activation energy of 66 kJ mol⁻¹ and was limited by diffusion through the porous reacting particles. The second stage was first order and had an activation energy of 40 kJ mol⁻¹. The reduction of WO₃ and WO₃ graphite mixtures with hydrogen were studied from 575 to 975 °C. The reactions were controlled by mass-transfer under the conditions investigated. The addition of carbon increased the rate of the reduction process , but did not affect the phases formed in the system. CO₂ was evolved mainly at the start, and CO mainly at the end of the process.
24
Barber, Drew. "Selenium In Thioredoxin Reductase: Resistance To Oxidative Inactivation, Oxidation States, And Reversibility Of Chemical Reactions." ScholarWorks @ UVM, 2018. https://scholarworks.uvm.edu/graddis/943.
Анотація:
Selenium is a required trace element which was originally discovered by the Swedish chemist Jons Jacob Berzelius in 1817. It was initially believed to be a toxin as it was identified as being the cause of hoof maladies and excessive hair loss in horses that feed upon plants with high selenium content. It wasn’t until 1957 that the potential contributions of selenium to physiology were first demonstrated. Selenium is now known to play a critical role in the maintenance of human health. Interestingly, unlike other trace metals/semi-metals, selenium is directly incorporated into proteins in the form of the amino acid selenocysteine (Sec) in a very complicated and energetically costly fashion. Though rare, being found in only 25 human proteins, Sec proteins are involved in numerous vital biological processes including maintenance of redox homeostasis and anti-oxidant defense. Even though Sec is essential, the reason that Sec replaces its structural analog cysteine (Cys) in only 25 proteins is not widely agreed upon. A previous model suggests that the replacement of Cys with Sec provides enzymes with a type of catalytic advantage. The presence of Cys-containing orthologs of mammalian Sec-enzymes in other eukaryotes argues against this model. A newer model to explain the use of Sec is that the gain of function imparted to an enzyme by replacing Cys with Sec is the ability of Sec to impart chemical reversibility.
Building on previous results from our lab demonstrating the ability of Sec to confer proteins with the ability to resist over oxidation we have elucidated the mechanism by which Sec containing thioredoxin reductase (TrxR) resists over oxidation. The ability of Sec-TrxR to resist oxidative inactivation is due to the greater electrophilicity of Sec relative to Cys. This allows for quicker resolution and prevents over oxidation. Based on these findings we also investigate the utility of the alkylating agent dimedone to probe the oxidation state of Sec. Interestingly, it was discovered that dimedone will react with seleneninic acid with the resulting adduct being labile. Additonally it was discovered that dimedone will also react with seleninic acid, resulting in the formation of a dimedone dimer. These results call into question the usefulness of dimedone in deteremining the oxidation state of Sec. Finally, we provide evidence that Sec-TrxR enzymes are able to catalyze single electron reductions. This is most likely due to the formation of a stable Sec radical intermediate. As a whole this project provides support for the theory that Sec was selected for due to its ability to convey chemical reversiablity to proteins.
25
Hsu, Songman. "Oxidation and reduction studies of polyphenylene suldide and its model compounds." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/30006.
26
Carr, Reuben. "Deracemisation of chiral amines via a cyclic oxidation and reduction sequence." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/13323.
Анотація:
This investigation examined the deracemisation of chiral amines via a cyclic oxidation and reduction sequence. The deracemisation relies on the combination of monoamine oxidase enzyme to perform an enantioselective oxidation of a single enantiomer of a racemic amine substrate to the imine. The imine is subsequently reduced back to the amine. Cycles of oxidation and reduction are required to produce high yields and enantiomeric excess. Directed evolution was used to screen for monoamine oxidase variants that showed superior activity towards novel secondary amine substrates. The specificity and enantioselectivity of the identified variants was examined. The optimised monoamine oxidases variant was used in the preparative deracemisation of secondary amine substrates in either whole cell or purified protein immobilised on resin. Various reducing agents were examined to identify those that showed the fastest rate of imine reduction under deracemisation conditions in order to minimise imine hydrolysis.
27
Kim, Minkyu. "Multiscale Modeling of Oxidation and Reduction Chemistry on Transition Metal Oxides." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531307161494595.
28
Crevier, Thomas J. "Oxidation and reduction of small molecules by tungsten and osmium compounds /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11581.
29
Alhazza, Abdulsalam A. "Reprocessing of tungsten alloy swarf by oxidation-reduction, pressing and sintering." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/35298.
Анотація:
Tungsten and the tungsten alloy group materials have a wide range of uses extending from everyday ones, e.g. the coil of an incandescent lamp or the contact tip of an electrical switch or an automobile horn, to components of nuclear fusion reactors or ion drive motors in space probes. The reason for this range of uses lies in the many outstanding properties of tungsten, in particular its high melting point, low vapor pressure, high atomic number, good electrical and thermal conductivity. In the Tungsten–Oxygen system (W–O) there are not only the stoichiometric oxides WO3, WO2.9, WO2.7, WO2, but also non-stoichiometric structures that represent the ordered or partially ordered defect structures of the oxygen-rich oxide in which the central W atom is octahedrally surrounded by six oxygen atoms. In WO3 neighbouring octahedra are in contact only at the corners. With increased oxygen deficiency (reduction, conversion to lower oxides) common edges and surfaces are progressively formed. The aim of this work was to produce a homogeneous powder for recycling from heavy metal swarf.
30
Anderlund, Mikael. "Redox balancing in recombinant strains of Saccharomyces cerevisiae." Lund : University of Lund, 1998. http://books.google.com/books?id=uc5qAAAAMAAJ.
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Lau, Ngai Ting. "Catalytic reduction of sulfur dioxide and nitric oxide /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?CENG%202006%20LAU.
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Lee, Lester Y. C. "Transmembrane electron transfer in artificial bilayers /." Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,86.
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Kaighobadi, Joni N. "Transition state studies on protocatechuate 3,4-dioxygenase." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/27285.
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Duff, Jack Lawrence. "Single electron transfer in nucleophilic reactions of substituted norbornanes." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/27444.
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Sun, Xiao-Jing. "The extent and importance of single electron transfers in organic reactions." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/27981.
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Sanii, Laurie Shireen. "The effect of terminal base identity on radical cation injection into the DNA duplex." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/29377.
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Holder, Grant Newton. "Redox reactivity of mononuclear and binuclear rhenium complexes." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/30392.
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Beard, Collen Alana. "Rubredoxin cobalt substitution and crystallization attempts." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/29863.
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Haffenden, Luke John William. "Investigation into the role of redox reactions in Maillard model systems : generation of aroma, colour and other non-volatiles." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111850.
Анотація:
The role of redox reactions in the formation of aroma volatiles, colour and other non-volatiles in the Maillard Reaction was investigated. The electrochemical properties of individual reactants and Maillard model mixtures were monitored via ORP (oxidation-reduction potential) and oxygen electrodes. All models exhibited unique electrochemical activities represented by their corresponding ORP profiles. Investigation into the redox potentials of several model systems demonstrated that the increased negative value of a redox potential is not necessarily correlated with its browning potential. An optimal redox potential range, where browning is favoured, was found to represent a balance between carbonyl and hydroxyl moieties in the structure. Adjustment of this redox potential by introducing reducing or oxidizing species can shift this balance resulting in modifications in browning capacities. However, it was concluded that there is a clear relationship between browning ability and reducing capacity of the model systems. Furthermore, a novel oxidative pyrolysis technique was developed to study the role of oxidative environment on the product distribution during pyrolysis and to investigate the mechanism of formation of non-volatiles through 13C and 15N-label incorporation. Application of this technique to glucoselglycine model system have indicated that most non-volatile Maillard reaction products can arise from glucose oxidation intermediates such as glucosone, gluconic acid and deoxyglucosones. To study the specific role of redox reactions in the formation of non-volatiles, a post-pyrolytic derivatization technique was developed and optimized. Several non-volatile end products were identified and mechanistically confirmed to involve oxidation and reduction reactions for their formation, such as lactones, hydroxylated benzenes and hydroxylated pyrazine. The latter was identified and confirmed to be generated via the dimerization of glycine and subsequent oxidation. In addition, the formation of different volatiles such as pyrazole, imidazole and oxazole was mechanistically confirmed to depend on redox reactions.
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劉強 and Keung Lau. "Kinetics and mechanisms of redox reactions of some macrocyclic tertiary anine complexes of ruthenium." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1988. http://hub.hku.hk/bib/B31231226.
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Qi, Hongyi, and 齐红艺. "Molecular characterization of Chinese medicines for the regulation of the intracellular redox signaling." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46921801.
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Massam, A. D. "Studies towards the synthesis of lepidine and hydroxyterphenyllin." Thesis, University of East Anglia, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297473.
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PETSOM, AMORN. "SYNTHETIC AND MECHANISTIC STUDIES ON THE ELECTROOXIDATION OF ORGANIC THIOETHERS." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184178.
Анотація:
This research has been directed at the study of neighboring group participation in electrooxidation of thioethers. Controlled potential oxidation of substituted 1,3-dithiane in wet acetonitrile provides substituted 1,2-dithiolane 1-oxide in good yield. Thioethers appended with neighboring alcohols and carboxylate are catalytically oxidized in a redox cycle by bromide ion. The formation of the alkoxysulfonium salt intermediates in such reactions is confirmed by product study. On the other hand, the acyloxysulfonium salt intermediates in the electrooxidation of endo -6-methylthio-bicyclo [2.2.1] heptane-2- endo -carboxylic acid (1) are unstable at room temperature. Control experiments using ¹⁸O labeled compounds prove unequivocally the existent of the acyloxysulfonium salt intermediates. Diastereospecific oxidation of 1 and its methyl ester with DABCO.2Br₂ complex and m-CPBA is sterically controlled. In both cases, similar product ratios are observed which is explained by the participation of the carboxylic acid group in the case of DABCO.2Br₂ oxidation but not in the case of m-CPBA oxidation. The structure of one of the diastereomer of the endo acid sulfoxide is unequivocally proved by x-ray crystallographic analysis.
44
Liu, Pei. "Development of redox proteomics methods and the identification of redox-sensitive proteins in arabidopsis." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/184.
Анотація:
Cellular redox homeostasis mediates a wide range of physiological and developmental processes. Various stresses trigger over-production of reactive oxygen/nitrogen species which leads to oxidative modifications of redox-sensitive proteins. Identification and characterization of redox-sensitive proteins are important steps toward understanding molecular mechanisms of stress responses. In the study, a high-throughput quantitative proteomic approach termed OxiTRAQ was developed for identifying proteins whose thiols undergo reversible oxidative modifications in Arabidopsis cells subjected to oxidative stress. In this approach, a biotinylated thiol-reactive reagent is used for differential labeling of reduced and oxidized thiols, and the biotin-tagged peptides are affinity-purified and labeled with iTRAQ reagents for quantitation. This approach allows identification of the specific redox-regulated cysteine residues in proteins and offers an effective tool for elucidation of redox proteomes. With this approach, we identified 195 cysteine-containing peptides from 179 proteins whose thiols underwent oxidative modifications in Arabidopsis cells following the treatment with hydrogen peroxide. A majority of those redox-sensitive proteins, including several transcription factors, were not identified by previous redox proteomics studies. Besides, this method was also used to identify proteins that underwent oxidative modifications in Arabidopsis cells subjected to 15 minute treatment of salicylate (a key signaling molecule in the plant defense pathway) or flg22 (a peptide from bacterial flagellin that induces pathogen associated molecular patterns-triggered immunity). In total, 127 peptides from 111 distinct proteins were identified as salicylate- and/or flg22-responsive redox-sensitive proteins. Among the identified redox sensitive proteins are many regulatory proteins including those involved in chromatin remodeling, transcription, nucleocytoplasmic shutting, and posttranslational regulation. Furthermore, in vivo 15N metabolic labeling method combined with a cysteine-containing peptide enrichment technique was applied to identify proteins that undergo oxidative modifications in plants in response to pathogen attack. The identification of redox-sensitive proteins provides a foundation from which further study can be conducted toward understanding the biological significance of redox signaling in plant stress response.
45
Peters-Libeu, Clare Ann. "Structural and electrostatic contributions to differences in oxidation-reduction potentials of two mutants of the copper protein, pseudoazurin /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/5683.
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Lau, Keung. "Kinetics and mechanisms of redox reactions of some macrocyclic tertiary anine complexes of ruthenium /." [Hong Kong] : University of Hong Kong, 1988. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12358770.
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Pham, Long Vo. "Oxidation and reduction reactions of the water-oxidizing complex in photosystem II." Doctoral thesis, Umeå universitet, Kemiska institutionen, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-111862.
Анотація:
The oxygen that we breathe and food that we eat are products of the natural photosynthesis. Molecular oxygen is crucial for life on Earth owing to its role in the glycolysis and citric acid pathways that yield in aerobic organisms the energy-rich ATP molecules. Photosynthetic water oxidation, which produces molecular oxygen from water and sunlight, is performed by higher plants, algae and cyanobacteria. Within the molecular structure of a plant cell, photosynthesis is performed by a specific intracellular organelle – the chloroplast. Chloroplasts contain a membrane system, the thylakoid membrane, which comprises lipids, quinones and a very high content of protein complexes. The unique photosynthetic oxidation of water into molecular oxygen, protons and electrons is performed by the Mn4CaO5 cluster in photosystem II (PSII) complex. Understanding the mechanism of water oxidation by Mn4CaO5 cluster is one of the great challenges in science nowadays. When the mechanism of this process is fully understood, artificial photosynthetic systems can be designed that have high efficiencies of solar energy conversion by imitating the fundamental principle of natural system. These systems can be used in future for generation of fuels from sunlight. In this thesis, the efficiency of water-splitting process in natural photosynthetic preparations was studied by measuring the flash-induced oxygen evolution pattern (FIOP). The overall aim is to achieve a deeper understanding of oxygen evolving mechanism of the Mn4O5Ca cluster via developing a complete kinetic and energetic model of the light-induced redox reactions within PSII complex. On the way to reach this goal, the hydrogen peroxide that is electrochemically generated on surface of Pt-cathode was discovered. The chemical effect of electrochemically produced H2O2 that can interfere in the oxygen evolution pathway or change the observed FIOP data was demonstrated. Therefore, in order to record the clean FIOP data that are further characterized by global fitting program (GFP), H2O2 has to be abolished by catalase addition and by purging the flow buffer of the Joliot-type electrode with nitrogen gas. After FIOPs free of H2O2-induced effects were achieved, these clean data were then applied to a global fitting approach (GFP) in order to (i) result a comprehensive figure of all S-state decays whose kinetic rates were simultaneously analyzed in a high reliability and consistency, (ii) the dependence of miss parameter on S-state transitions and the oxidation state of tyrosine D (YD) can be tested, (iii) how dependent of all S-state re-combinations (to S1 state) on the various pH/pD values can be also determined in case of using Cyanidioschyzon merolae (C. merolae) thylakoids. Our data support previous suggestions that the S0 → S1 and S1 → S2 transitions involve low or no misses, while high misses occur in the S2 → S3 transition or the S3 → S0 transition. Moreover, the appearance of very slow S2 decay was clearly observed by using the GFP analysis, while there are no evidences of very slow S3 decay were recorded under all circumstances. The unknown electron donor for the very slow S2 decay which can be one of the substances of PSII-protective branch (i.e. cytochrome b559, carotenoid or ChlZ) will be determined in further researches.
48
Martin, D. J. "Investigation into high efficiency visible light photocatalysts for water reduction and oxidation." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1453161/.
Анотація:
Solar water splitting using an inorganic semiconductor photocatalyst is viewed as one of the most exciting and environmentally friendly ways of producing clean renewable fuels such as hydrogen from abundant resources. Currently, there are many diverse semiconductors that have been developed, the majority for half reactions in the presence of sacrificial reagents. However, for industrial facilitation, there exists an essential, non-debatable trifecta of being robust, cheap and efficient for overall water splitting. To date, no system has combined all three, with most examples missing at least one of the necessary trio. Therefore one of the current challenges of the field is to develop low cost, highly efficient and stable photocatalysts for industrial scale-up use. In order to achieve that aim, researchers must focus on novel semiconductors to improve efficiencies and also understand the fundamental mechanisms. The primary focus of this thesis then, is to investigate some of the newest photocatalysts for water photooxidation, reduction, and overall water splitting. In doing so, the thesis aids to shed light on the mechanisms behind what makes certain photocatalysts either efficient or inefficient. Firstly, test station was set up to analyse gaseous products such as hydrogen and oxygen produced from photocatalytic water splitting, by using a custom made high purity borosilicate reactor in conjunction with a gas chromatography unit. Gaseous products could be measured with very small sampling error (<1%), which improved the throughput of experiments. The photooxidation of water using a novel faceted form of Ag3PO4 was investigated. A novel synthetic method was created that made it possible to control the exposing facets of silver phosphate in the absence of surfactants to yield tetrahedral crystals composed entirely of {111} facets. It was found that due to high surface energy of {111}, and low hole (h+) mass in the 111 direction, Ag3PO4 tetrahedral crystals could outperform all other low index facets for the oxidation of water under visible light. The quantum yield was found to be nearly unity at 400 nm, and over 80% at 500 nm. With the exception of Ag3PO4 tetrahedral crystals, no photocatalyst has exhibited quantum efficiencies reaching 100% under visible irradiation. Therefore, the strategy of morphology control of a photocatalyst, led by DFT calculations of surface energy and charge carrier mobility, in order to boost photooxidation yield has been demonstrated to be very successful, and could be applied to improve other semiconductors in future research. Hydrogen production from water was further studied using the only known robust organic photocatalyst, graphitic carbon nitride (g-C3N4). It was discovered that using a novel preparation method, urea derived g-C3N4 can achieve a quantum yield of 26% at 400 nm for hydrogen production from water; an order of magnitude greater than previously reported in the literature (3.75%). The stark difference in activity is due to the polymerisation status, and consequently the surface protonation status as evidenced by XPS. As the surface protonation decreases, and polymerisation increases, the performance of graphitic carbon nitride for hydrogen production increases. The rate of hydrogen production with respect to BET specific surface area was also found to be non-correlating; a juxtaposition of conventional photocatalysts whose activity is enhanced with larger surface areas - believed to be because of an increase in surface active sites. Finally, overall water splitting was probed using Z-scheme systems comprising of a redox mediator, hydrogen evolution photocatalyst, and oxygen evolution photocatalyst. Ag3PO4 was found not be not suitable for current Z-scheme systems, as it is unstable in the pH ranges required, and also reacts with both of the best known electron mediators used in Z-schemes, as evidenced by XRD, TEM, and EDX studies. However, it has been demonstrated that urea derived g-C3N4 can participate in a Z-scheme system, when combined with either WO3 or BiVO4 – the first example of its kind, resulting in a stable system for an overall water splitting operated under both visible light irradiation and full arc irradiation. Further studies shows water splitting rates are influenced by a combination of pH, concentration of redox mediator, and mass ratio between photocatalysts. The solar-to-hydrogen conversion of the most efficient system was experimentally verified to be ca. 0.1%. It is postulated that the surface properties of urea derived graphitic carbon nitride are related to the adsorption of redox ions, however, further work is required to confirm these assumptions.
49
Walpita, Janitha Kumara. "Iminium Based Electrocaralysts for Water Oxidation and Organic Photohydrides for Proton Reduction." Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1431967855.
50
Hicks, Robert Paul. "Probing Electrocatalytic and Photocatalytic Processes with Structure-Specific Spectroscopies:." Thesis, Boston College, 2019. http://hdl.handle.net/2345/bc-ir:108657.
Анотація:
Thesis advisor: Matthias M. WaegeleStudying the adsorption and reaction kinetics of surface-bound chemical species, on different metal catalysts or electrodes, is of paramount importance in the development of inhomogeneous catalytic methodology. Our study of the oxidation of CO on platinum was accomplished by designing a thin layer flow cell in an external reflection configuration. A charge-injection circuit was successfully implemented which decreased the time required to charge the double layer in the electrochemical cell. We were able to obtain a signal via Stark shift spectrum, of the adsorbed CO, using the thin layer cell configuration. Additionally, electrochemical impedance spectroscopy was used as a diagnostic tool to assess the effect of electrode geometry, on the voltage response, in the thin layer cell. The coupling of visible light-driven photoexciation with transition metal catalytic plat- forms is emerging as a synthetic strategy to achieve unique reactivity that has previously been inaccessible. One such example is the iridium/nickel-dipyridyl system discovered recently. Characterizing the interactions between the iridium and nickel catalysts, under reaction conditions, is important to develop a better understanding of the system. In order to apply infrared spectroscopic measurement techniques, in-situ, we made modifications to the synthetic scheme by changing the solvent and by utilizing different iridium catalysts for the synthesis of the desired methyl 4-(benzoyloxy)benzoate product. Using our trans- mission infrared setup we effectively demonstrated in-situ product detection of the aryl- ester coupled product. Additionally, after constructing a transient infrared pump-probe setup, we collected preliminary results of the triplet state lifetime of the iridium dye. The surface morphology of copper has been shown to affect the electrochemical reduction of CO2. Using surface-enhanced Raman spectroscopies, the reversible formation of nanoscale metal clusters on a copper electrode was revealed at sufficiently cathodic potentials where we observed the appearance of a new band at 2080 cm-1 corresponding to C≡O adsorbed to undercoordinated copper defect sites. The formation of new undercoordinated sites additionally resulted in the surface enhancement of the Raman scattering which amplified the intensity of the other spectral bands
Thesis (MS) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry