Academic literature on the topic 'Co2+ doped nanoparticles'

Over the past years, an interest has arisen in resolving the problems of the increased carbon monoxide and carbon dioxide emissions, leading to the serious air pollution and many detrimental effects. A convenient solution would be a process that could utilize metal oxide nanoparticles such as TiO2 to control the concentration of atmospheric pollutants. The chemisorption of CO and CO2 molecules over the semiconductor titanium dioxide (TiO[Formula: see text] is such a process. In this way, density functional theory (DFT) calculations were performed to investigate CO and CO2 adsorptions on undoped and N-doped TiO2 anatase nanoparticles. The supercell approach is conducted to construct the considered nanoparticles and the adsorption of COx molecule was simulated by use of these chosen nanoparticles. By including van der Waals (vdW) interactions between COx molecule and TiO2 nanoparticle, we found that both CO and CO2 molecules can bind strongly to the N-doped nanoparticles. The adsorption on the five-fold coordinated titanium site of TiO2 nanoparticles including the bond lengths, bond angles, adsorption energies, density of states (DOSs), Mulliken population analysis and molecular orbitals has been broadly studied in this work. Based on the obtained results, it can be concluded that the adsorption on the N-doped nanoparticle is more energetically favorable than the adsorption on the pristine one, representing the higher tendency of N-doped nanoparticles for COx detention, compared to the undoped ones. Therefore, the results indicate that the N-doped TiO2 would be an ideal COx gas sensor in the environment.

The results of carbon-doped zinc oxide nanoparticles synthesized by CO2 microwave plasma at atmospheric pressure are presented. The 2.45-GHz microwave plasma torch and feeder for injecting Zn granules are used in the synthesis of zinc oxide nanoparticles. The Zn granules (13.5 g/min) were introduced into the microwave plasma by CO2 (5 l/min) swirl gas. The microwave power delivered to the CO2 microwave plasma was 1 kW. The synthesis of carbon-doped zinc oxide nanoparticles was carried out in accordance with CO2 + Zn → carbon-doped ZnO + CO. The synthesized carbon-doped zinc oxide nanoparticles have a high purity hexagonal phase. The absorption edge of carbon-doped zinc oxide nanoparticles exhibited a red shift from a high-energy wavelength to lower in the UV-visible spectrum, due to band gap narrowing. A UV-NIR spectrometer, X-ray diffraction, emission scanning electron-microscopy, energy dispersive X-ray microanalysis, Fourier transform infrared spectroscopy, and a UV-Vis-NIR spectrophotometer were used for the characterization of the as-produced products.

Co2+-doped Fe3O4magnetic nanoparticles were synthesized via the solvothermal method with reaction system of H2O and glycol in a high pressure autoclave. The products are of the inverse spinel structure confirmed by X-ray Diffraction. Fourier Transform Infrared Spectroscopy, Transmission Electron Microscope, Particles Size Analyzer and AC Gradient Magnetometer are also used to characterize the particles. The obtained Co2+-doped Fe3O4magnetic nanoparticles display well crystalline state. Those particles are globular of which the diameter is above 15 nm with homogeneous size distribution, smaller than 20 nm of the non-doped products. Co2+-doped Fe3O4magnetic nanoparticles show superparamagnetic behavior, and the saturation magnetization is 76.84 emu/g, which is higher compared with 54.42 emu/g of the non-doped. In the crystals structure of Fe3O4magnetic nanoparticles, ferric ions occupy the tetrahedral sites and one-half of octahedral sites, and the ferrous ions occupy the remaining half of the octahedral sites. The magnetic moments of cations on tetrahedral and octahedral sites are anti-parallel. Therefore, the net moment is provided by the divalent ions. In the preparation process, bivalent cobalt ions replace the partial sites of the ferrous ions and the ferric ions, and enhance the net magnetic moment. Above all, the doping of Co2+could improve properties of the Fe3O4magnetic nanoparticles, i.e., enhancing the saturation intensity, decreasing the particle size and making the size distribution homogeneous.

In this research, we synthesised nickel (Ni)-doped zinc oxide (ZnO) nanoparticles (NZ) with various atomic ratios of [Ni]/[Zn], i.e., 0.02, 0.04 and 0.06 using a simple sol–gel method. The synthesized materials were examined by different techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) attached with energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The observed XRD results confirmed that all the prepared samples exhibited a hexagonal wurtzite structure with no additional secondary phases, confirming that Ni ions were successfully incorporated into the lattices of ZnO crystals. The average size of the synthesized nanoparticles is in the range of 30–80 nm, as was confirmed from the TEM observations. The synthesized Ni-doped ZnO nanoparticles were used as functional material to fabricate efficient CO2 gas sensors. The gas detection results demonstrated an improvement in the response of the Ni-doped ZnO sensor towards CO2 gas. The data obtained at 350 ˚C working temperature reveal that this sensor has a modest reaction to CO2. With increasing Ni doping, we noticed that the baseline and the dynamic responses rises. Based on the obtained results, a plausible sensing mechanism towards CO2 gas sensor based on Ni-doped ZnO nanoparticles is also proposed and presented in this paper.

The present paper describes the synthesis and first application of Nd-doped BaCeO3 nanoparticles as catalyst for the catalytic oxidation of methane (CH4) into CO2. Nd-doped barium cerate BaCeO3 nanoparticles, with the formula BaNdxCe(1-x)O3, have been prepared using a simple sol gel method starting from acetate precursors. The as-prepared nanoparticles have been fully characterized by XRD, TEM, HRTEM and specific surface area measurement. Results confirmed the formation of highly crystallized nano-sized particles with small crystallite size. In-situ FTIR spectroscopy was used to study the catalytic conversion of methane (CH4) into CO2 in the presence of the as-prepared Nd-doped BaCeO3 nanocatalyst. The catalytic properties of such nanocatalysts have been discussed and correlated to Nd-doping rate, crystallite diameter, and specific surface area of the materials. Excellent catalytic properties have been obtained with BaNd0.05Ce0.95O3, such as, superior conversion efficiency, longer catalysis lifetime and lower activation temperature compared to un-doped BaCeO3 catalyst. Interestingly, it was found that BaNd0.05Ce0.95O3 nanocatalyst successfully converts the totality of CH4 present in a mixture of CH4-Air into CO2 at much lower temperature compared to the conventional Pd/Al2O3 catalyst.

Cobalt doping enhances visible absorption in ZnO nanoparticles as a result of d–d transitions. By co-precipitation method, Zn_1−xCo_xO nanoparticles had been synthesised and multiband photodetectors were fabricated after characteristic analysis.

Objective: The influence of Manganese (Mn2+) and Cobalt (Co2+) ions doping on the optical and magnetic properties of ZnO nanoparticles was studied. Methods: Nanoparticle samples of type ZnO, Zn0.97Mn0.03O, Zn0.96Mn0.03Co0.01O, Zn0.95Mn0.03 Co0.02O, Zn0.93Mn0.03Co0.04O, and Zn0.91Mn0.03Co0.06O were synthesized using the wet chemical coprecipitation method. Results: X-ray powder diffraction (XRD) patterns revealed that the prepared samples exhibited a single phase of hexagonal wurtzite structure without any existence of secondary phases. Transmission electron microscope (TEM) images clarified that Co doping at high concentrations has the ability to alter the morphologies of the samples from spherical shaped nanoparticles (NPS) to nanorods (NRs) shaped particles. The different vibrational modes of the prepared samples were analyzed through Fourier transform infrared (FTIR) measurements. The optical characteristics and structural defects of the samples were studied through Photoluminescence (PL) spectroscopy. PL results clarified that Mn2+ and Co2+ doping quenched the recombination of electron-hole pairs and enhanced the number of point defects relative to the undoped ZnO sample. Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer (VSM). (Mn, Co) co-doped ZnO samples exhibited a ferromagnetic behavior coupled with paramagnetic and weak diamagnetic contributions. Conclusion: Mn2+ and Co2+ doping enhanced the room temperature Ferromagnetic (RTFM) behavior of ZnO. In addition, the signature for antiferromagnetic ordering between the Co ions was revealed. Moreover, a strong correlation between the magnetic and optical behavior of the (Mn, Co) co-doped ZnO was analyzed.

[ES] Teniendo en cuenta el agotamiento de los combustibles fósiles y la creciente concentración de CO2 en la atmósfera, la hidrogenación de CO2 es una forma prometedora de convertir el CO2 en productos químicos y combustibles de carbono de alto valor añadido. Considerando la gran influencia del tamaño de partícula, la composición química, la naturaleza del soporte y las condiciones de operación sobre el comportamiento catalítico de los catalizadores, se han desarrollado una serie de catalizadores para la hidrogenación de CO2 basados en metales abundantes no nobles y polisacáridos naturales como precursores del grafeno. En la presente tesis doctoral, las especies metálicas soportadas sobre una matriz de carbono grafítico defectuosa, con diferentes tamaños de partículas, muestran diferente actividad catalítica y selectividad para la hidrogenación de CO2. Se prepararon, de forma controlada, nanopartículas de aleaciones de Co y Co-Fe soportadas en grafenos dopados con N defectuosos, con una amplia distribución de tamaño de nanopartículas, para la reacción de Sabatier, presentando una selectividad a metano superior al 90% con valores de conversión de CO2 superiores al 85%. En el caso de un solo metal, Co o Fe, y sus aleaciones en forma de "clusters" y pequeñas nanopartículas soportadas en el mismo material, la selectividad de la hidrogenación de CO2 cambia a CO, en lugar de metano, obteniéndose un valor del 98 % y alcanzando una conversión de CO2 del 56%. Conviene resaltar que, los catalizadores basados en "clusters" de aleaciones de metal con una carga de metal incluso por debajo del 0.2 % en peso, exhiben una mayor selectividad y rendimiento que los que tienen nanopartículas de aleaciones de Co-Fe más grandes que varían de 1 a 4 nm y una carga de metal más alta en una composición similar. Siguiendo la línea de investigación de hidrogenación de CO2, se desarrollaron una serie de nanopartículas de aleaciones de Co-Fe soportadas sobre grafenos dopados con N defectuosos con distribución de tamaño de nanopartículas controlada en el rango de 7-17 nm, obteniendo una selectividad hacia hidrocarburos C2+ alrededor del 45% y una conversión del CO2 cercana al 60%. Además, se realizó un estudio comparativo de la actividad catalítica de catalizadores similares basados en Co-Fe con promotores e inhibidores para la hidrogenación de CO2, observando su influencia en la conversión y selectividad de CO2. Finalmente, además de los catalizadores basados en Co-Fe, también se han preparado catalizadores basados en Cu-ZnO mediante un método de dos pasos. Estas nanopartículas de Cu-ZnO soportadas sobre grafeno defectuoso dopado con N exhiben una alta selectividad hacia la conversión de CO2 a metanol.
[CA] Tenint en compte l'esgotament dels combustibles fòssils i la creixent concentració de CO2 en l'atmosfera, la hidrogenació de CO2 és una forma prometedora de convertir el CO2 en productes químics i combustibles de carboni d'alt valor afegit. Considerant la gran influència de la grandària de partícula, la composició química, la naturalesa del suport i les condicions d'operació sobre el comportament catalític dels catalitzadors, s'han desenvolupat una sèrie de catalitzadors per a la hidrogenació de CO2 basats en metalls abundants no nobles i polisacàrids naturals com a precursors del grafé. En la present tesi doctoral, les espècies metàl·liques suportades sobre una matriu de carboni grafític defectuosa, amb diferents grandàries de partícules, mostren diferent activitat catalítica i selectivitat per a la hidrogenació de CO2. Es van preparar, de manera controlada, nanopartícules d'aliatges de Co i Co-Fe suportades en grafens dopats amb N defectuosos, amb una àmplia distribució de grandària de nanopartícules, per a la reacció de Sabatier, presentant una selectivitat a metà superior al 90% amb valors de conversió de CO2 superiors al 85%. En el cas d'un sol metall, Co o Fe, i els seus aliatges en forma de "clústers" i xicotetes nanopartícules suportades en el mateix material, la selectivitat de la hidrogenació de CO2 canvia a CO, en lloc de metà, obtenint-se un valor del 98% i aconseguint una conversió de CO2 del 56%. Convé ressaltar que, els catalitzadors basats en "clústers" d'aliatges de metall amb una càrrega de metall fins i tot per davall del 0.2% en pes, exhibeixen una major selectivitat i rendiment que els que tenen nanopartícules d'aliatges de Co-Fe més grans que varien d'1 a 4 nm i una càrrega de metall més alta en una composició similar. Seguint la línia d'investigació d'hidrogenació de CO2, es van desenvolupar una sèrie de nanopartícules d'aliatges de Co-Fe suportades sobre grafens dopats amb N defectuosos amb distribució de grandària de nanopartícules controlada en el rang de 7-17 nm, obtenint una selectivitat cap a hidrocarburs C2+ al voltant del 45% i una conversió del CO2 pròxima al 60%. A més, es va realitzar un estudi comparatiu de l'activitat catalítica de catalitzadors similars basats en Co-Fe amb promotors i inhibidors per a la hidrogenació de CO2, observant la seua influència en la conversió i selectivitat de CO2. Finalment, a més dels catalitzadors basats en Co-Fe, també s'han preparat catalitzadors basats en Cu-ZnO mitjançant un mètode de dos passos. Aquestes nanopartícules de Cu-ZnO suportades sobre grafé defectuós dopat amb N exhibeixen una alta selectivitat cap a la conversió de CO2 a metanol.
[EN] Considering the depletion of fossil fuels and the increasing atmospheric CO2 concentration, CO2 hydrogenation is a promising way to convert CO2 into value-added carbon-containing chemicals and fuels. Taking into account the significant influences of the particle size, chemical composition, nature of the support, and operation conditions on the catalytic performance of catalysts, a series of catalysts for CO2 hydrogenation have been developed based on the use of abundant non-noble metals and natural polysaccharides as graphene precursors. In the present PhD Thesis, metal species supported on defective graphitic carbon matrix with different particle sizes show different catalytic activity and selectivity for CO2 hydrogenation. Under effective control, Co and Co-Fe alloy nanoparticles wrapped on defective N-doped graphenes with a broad nanoparticle size distribution were prepared and performed for the Sabatier reaction, exhibiting a selectivity to methane over 90 % at CO2 conversion values over 85 %. In the case of single Co or Fe metal and their alloys in the form of clusters and small nanoparticles wrapped on the same support, the selectivity for CO2 hydrogenation shifts to CO, rather than methane, reaching a conversion of 56 % with 98 % CO selectivity. It is worth noting that the metal alloy clusters-based catalysts with the metal loading even below 0.2 wt.% exhibit a higher selectivity and better performance than the ones with larger Co-Fe alloy nanoparticles ranging from 1-4 nm and higher metal loading in a similar composition. Following the research line for CO2 hydrogenation, a series of Co-Fe alloy nanoparticles supported on defective N-doped graphenes with controlled nanoparticle size distribution in the range of 7-17 nm are developed, obtaining a selectivity towards C2+ hydrocarbons about 45% with a CO2 conversion close to 60%. In addition, a comparative catalytic activity of similar Co-Fe-based catalysts with promoters and poison has been studied for CO2 hydrogenation to observe their influence on CO2 conversion and selectivity. Finally, besides Co-Fe-based catalysts, Cu-ZnO-based catalysts have also been prepared by a two-step method. These Cu-ZnO nanoparticles supported on N-doped defective graphene exhibit a high selectivity for CO2 conversion to methanol.
Peng, L. (2021). Metal Nanoparticles Wrapped on Defective Nitrogen-doped Graphitic Carbons as Highly Selective Catalysts for C02 Hydrogenation [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172329
TESIS

2009/2010
Nanosized inorganic particles constitute a field of rapidly growing interest and their tailored synthesis is currently subject of intense study. These particles may show unique properties that are not shared by bulk materials and therefore find a palette of innovative applications, e.g., as diagnostic means, or in drug and even gene delivery, offering the advantage over polymer nanoparticles because they are stable, biologically inert, biocompatible and it is easy to introduce functional groups by modification of the surface hydroxyls. Among various synthetic routes the most explored are the ones carried out in bulk, especially the Stöber synthesis, however the final product are mostly polydisperse particles whose size is difficult to control. On the other hand, w/o microemulsion is providing suitable environment for the control of the particle nucleation and growth kinetics, as the nanodroplets of water are nanoreactors for the synthesis. The main advantage is that the procedure does not require extreme conditions of temperature and pressure and the particle size and shape can be controlled simply by controlling the microemulsion parameters where the most important are the water-to-surfactant molar ratio, R, and water-to-TEOS molar ratio, h. The previous studies focused on the latter synthetic route, in base-catalyzed systems, concerned mainly the evolution of silica nanoparticles and the best results were achieved by SAXS. The volume fraction versus time data gave an insight into nucleation and growth and is in agreement with first order kinetics with respect to TEOS concentration. However, we wanted to understand better the environment in which the synthesis takes place and shed light on the evolution of the soluble species, both of the constituents of the microemulsion and of those taking part to reaction. The soluble species present in the reaction mixture that leads to silica nanoparticle production through the base catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and the successive condensation were investigated in situ, under the actual synthesis conditions, by means of 1H, 13C, and 29Si NMR spectroscopy. The two former nuclei, owing to higher sensitivity and their presence both in the reacting species and in the constituents of the w/o microemulsion (cyclohexane-Igepal CA520 (5 polyoxyethylene iso-octylphenyl ether)-concentrated ammonia solution) afforded insight into the inverse microemulsion and allowed us to assess the kinetic rate of the hydrolysis step. It was verified that the microemulsion microstructure is maintained during the reaction. Special attention was paid to the reaction medium, and an extended assignment of the 1H and 13C resonances of the surfactant head group was performed. These head group signals undergo some changes due to the environmental modifications induced by transition from cyclohexane solution to w/o microemulsion and further to NH3 containing w/o microemulsion. We followed the quantitative evolution of TEOS and EtOH and assessed their preferential distribution in the various environments provided by this, on the mesoscale heterogeneous, reaction medium. Most authors agree that TEOS is localized mainly in the oil however they argue whether EtOH is preferentially in the water-pools or in oil. The clarification was achieved by means of PGSTE NMR since the diffusion coefficients are commonly exploited to characterize microemulsions, to determine the connectivity of the phase and they can be used to obtain the size of water droplets. It was revealed that NH3 exchanges among the inverse micelles diffusing through cyclohexane and confirmed that the preferred localization for ethanol, a byproduct of the reaction, is the bulk oil. Moreover, it was confirmed that TEOS is localized mainly in the oil. The characterization of the final nanoparticles was carried out by means of transmission electron microscopy (TEM) and it was revealed that the final product were monodispersed particles with radius of 20 nm. The synthesis of SiO2 nanoparticles in an acid-catalyzed system is especially interesting from nanotechnological point of view, owing to the different physical nature of silica synthesized under acidic rather than basic conditions, and from an applicative point of view since intended guest species are not always base resistant. Unfortunately, the application of an acid-catalyzed sol-gel process seems less than straightforward. An inverse microemulsion looks like an optimal reaction medium able to limit the growth of silica particles within the nanometer range. However, relatively few studies have been reported to date, and to the best of our knowledge, only one involves the entire process conducted in an inverse microemulsion with a water core that remains stable throughout the course of the reaction. The cyclohexane-Igepal inverse microemulsion, comprehensively established for the synthesis of silica nanoparticles in NH3-catalyzed sol-gel process, was alternatively studied with an acid-catalyzed sol-gel process. TEOS was used as the silica precursor, while two different aqueous phases containing either HNO3 or HCl at two different concentrations, 0.1 and 0.05 M, were examined in the presence and in the absence of NaF, a catalyst of the condensation step. The evolution of the overall reacting system, specifically hydrolysis and polycondensation of reaction intermediates, was monitored in situ by SAXS. No size variation of the inverse micelles was detected throughout the sol-gel process. Conversely, the density of the micellar core increased after a certain time interval, indicating the presence of the polycondensation product. The IR spectra of the reacting mixture were in agreement with such a hypothesis. 1H and 13C NMR measurements provided information on the soluble species, the surfactant, and TEOS. The TEOS consumption was well fitted by means of an exponential decay, suggesting that a first-order kinetics for TEOS transpires in the various systems examined, with rate constants dependent not only on the acid concentration but also on its nature (anion specific effect), on the presence of NaF, and on the amount of water in the core of the inverse micelle. The self-diffusion coefficients, determined by means of PGSTE NMR, proved that a sizable amount of the byproduct ethanol was partitioned inside the inverse micelles. Moreover, the DOSY spectrum contributed to the assignment of the signals of various oligomeric species present in the commercial mixture of Igepal CA520, since the head group, which is a short polyoxyehtylene chain, is somewhat polydisperse. The embedment of Igepal CA520 in an acid-catalyzed inverse microemulsion led to the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head group and the partition degree, between the two environments, for each individual oligomeric species, and afforded further insight into nonionic inverse microemulsions. It was possible to ascertain that the length distribution of the polyethyleneoxide chains is in good agreement with the Poisson distribution theoretically predicted for the polymerization of ethylene oxide. Characterization of the final product was carried out by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and TEM, which concurrently confirmed that the silica isolated from the inverse nonionic microemulsion is not significantly different from the product of a bulk acid-catalyzed sol-gel synthesis. TEM micrographs illustrated particles with diameters smaller than the diameter of the inverse micelles as determined by SAXS, due to a shrinkage effect, in addition to nanostructured aggregates in the range 20-100 nm. The metal doped silica systems are important for optical applications and if the metal ions are finely dispersed on silica matrix very efficient catalysators can be obtained. The synthesis of silica nanoparticles in HCl-catalyzed inverse microemulsion was carried out in the presence of both Cu2+ and Co2+ ions with the aim to get correspondingly doped nanoparticles. The systems were characterized by means of 1H and 13C NMR and the quantitative evolution of TEOS and EtOH was followed. The introduction of metals in the glass matrix strongly influences their optical visible absorption spectrum so the UV-Vis spectroscopy was applied in the study. The isolated nanoparticles were characterized by means of IR and Raman spectroscopy and their size was determined by TEM. It was demonstrated that inverse micelles can be used to produce Co2+ and Cu2+ doped SiO2 nanoparticles with diameter of about 3 and 4 nm, respectively. Spherical particles smaller than the micellar size and, in the case of Cu2+ doped system, larger, irregularly shaped aggregates with diameter up to 1 μm were observed. Lots of darker zones were observed in the TEM images of some larger particles and aggregates containing Cu and may be assigned to Cu metal particles encapsulated in silica matrix. Therefore, cobalt was successfully doped in silica nanoparticles while copper doping seemed less satisfactory.
Particelle inorganiche di grandezza nanometrica costituiscono un settore di interesse in rapida crescita e la loro sintesi è attualmente oggetto di intenso studio. Queste particelle possono presentare proprietà uniche non condivise da materiali bulk e quindi trovare una vasta gamma di applicazioni innovative, ad esempio, come mezzo diagnostico, o per drug delivery e anche gene delivery, offrendo il vantaggio rispetto nanoparticelle polimeriche di essere stabili, biologicamente inerti, biocompatibili e facilmente funzionalizzabili con gruppi funzionali modificando dei ossidrili superficiali. Tra le varie vie sintetiche più esplorate sono quelle effettuate in bulk, in particolare la sintesi di Stöber, ma il prodotto finale sono particelle per lo più polidisperse la cui dimensione è difficile da controllare. D'altra parte, la microemulsione a/o sta fornendo l'ambiente adatto per il controllo della cinetica di nucleazione e crescita delle particelle, siccome le nanogoccioline d'acqua sono i nanoreattori per la sintesi. Il vantaggio principale è che la procedura non richiede condizioni estreme di temperatura e pressione e la dimensione delle particelle e la forma possono essere controllati semplicemente attraverso il controllo dei parametri di microemulsione tra cui i più importanti sono il rapporto molare acqua-tensioattivo, R, e acqua-TEOS, h. Gli studi precedenti focalizzati su quest'ultima linea sintetica, nei sistemi base-catalizzati, riguardavano principalmente l'evoluzione delle nanoparticelle di silice ed i migliori risultati sono stati raggiunti con SAXS. I dati di frazione di volume in funzione del tempo hanno fornito informazioni sui processi di nucleazione e di crescita e sono in accordo con una cinetica di primo ordine rispetto alla concentrazione di TEOS. Tuttavia, era importante capire meglio l'ambiente in cui la sintesi accade e mettere in luce l'evoluzione della specie solubile, sia dei componenti della microemulsione che di coloro che prendono parte alla reazione. Le specie solubili presenti nella miscela di reazione che porta alla produzione di nanoparticelle di silice attraverso l’idrolisi base-catalizzata di tetraetile ortosilicato (TEOS) e la successiva condensazione sono state studiate in situ, alle condizioni effettive di sintesi, mediante spettroscopia NMR di 1H, 13C, e 29Si. I primi due nuclei, a causa di una maggiore sensibilità e la loro presenza sia nel reagente che nei componenti della microemulsione a/o (cicloesano-Igepal CA520 (5 poliossietilene iso-octilfenil etere)-soluzione di ammoniaca concentrata) hanno offerto una visione della microemulsione inversa e ci hanno permesso di valutare la velocità di idrolisi. È stato verificato che la microstruttura della microemulsione è mantenuta durante la reazione. L’attenzione è stata rivolta particolarmente verso il mezzo di reazione, ed è stata effettuata un’assegnazione estesa delle 1H e 13C risonanze della testa del tensioattivo. Questi segnali della testa subiscono variazioni a causa delle modificazioni ambientali indotte dal passaggio dalla soluzione di cicloesano a microemulsione a/o e in seguito alla microemulsione a/o contenente NH3. Abbiamo seguito l'evoluzione quantitativa del TEOS e EtOH e valutato la loro distribuzione preferenziale nei vari ambienti forniti da questo mezzo di reazione, eterogeneo sulla mesoscala. Molti autori concordano sul fatto che il TEOS è localizzato principalmente in olio. Tuttavia, si dibatte se EtOH si trova preferenzialmente nelle goccioline d'acqua o nell’olio. Il chiarimento è stato realizzato per mezzo di PGSTE NMR in quanto i coefficienti di diffusione sono comunemente sfruttati per caratterizzare le microemulsioni, per determinare la connettività delle fasi e possono essere utilizzati per ottenere le dimensioni delle goccioline d’acqua. È stato rivelato che NH3 scambia tra le micelle inverse diffondendo attraverso il cicloesano ed è stato confermato che la localizzazione preferita per l'etanolo, il sottoprodotto della reazione, è l'olio. Inoltre, è stato confermato che il TEOS è localizzato principalmente nell’olio. La caratterizzazione delle nanoparticelle finali è stata effettuata per mezzo di microscopia elettronica a trasmissione (TEM) ed è stato rivelato che il prodotto finale sono le particelle monodisperse con raggio di 20 nm. La sintesi di nanoparticelle di SiO2 in un sistema con catalisi acida è particolarmente interessante dal punto di vista nanotecnologico, a causa della diversa natura fisica di silice sintetizzata in condizioni acide, piuttosto che in quelle basiche, e da un punto di vista applicativo in quanto le specie ospite previste non sempre sono resistenti alle basi. Purtroppo, l'applicazione di un processo sol-gel catalizzato da acido è meno chiara. Una microemulsione inversa sembra un mezzo di reazione ottimale in grado di limitare la crescita delle particelle di silice alle grandezze nanometriche. Tuttavia, relativamente pochi studi sono stati riportati fino ad oggi, e al meglio delle nostre conoscenze, solo uno riguarda l'intero processo condotto in una microemulsione inversa con un nucleo d’acqua che rimane stabile durante tutto il corso della reazione. La microemulsione inversa cicloesano-Igepal, stabilita per la sintesi di nanoparticelle di silice in processo sol-gel NH3-catalizzato, in alternativa è stata studiata con il processo sol-gel catalizzato da acido. Il TEOS è stato utilizzato come precursore di silice, mentre diverse fasi acquose contenenti HNO3 o HCl a due differenti concentrazioni, 0.1 o 0.05 M, sono state esaminate in presenza ed in assenza di NaF, un catalizzatore della fase di condensazione. L'evoluzione del sistema reagente complessivo, in particolare l’idrolisi e la policondensazione dei intermedi di reazione, è stata monitorata in situ mediante SAXS. Nessuna variazione delle dimensioni delle micelle inverse è stata rilevata durante tutto il processo sol-gel. Al contrario, è aumentata la densità dell’interno micellare dopo un certo intervallo di tempo, indicando la presenza del prodotto di policondensazione. Gli spettri IR della miscela di reazione erano d'accordo con tale ipotesi. Misure NMR 1H e 13C hanno fornito le informazioni sulle specie solubili.. Il consumo di TEOS era in accordo con un decadimento esponenziale, suggerendo una cinetica di primo ordine in TEOS, con costante di velocità dipendente non solo dalla concentrazione di acido, ma anche dalla natura (effetto anione specifico), dalla presenza di NaF, e dalla quantità di acqua nel nucleo della micella inversa. I coefficienti di auto-diffusione, determinati mediante PGSTE NMR, hanno dimostrato che una quantità considerevole del sottoprodotto etanolo è presente all'interno delle micelle inverse. Inoltre, lo spettro DOSY ha contribuito alla assegnazione dei segnali delle varie specie oligomeriche presenti nella miscela commerciale di Igepal CA520, poiché la testa, che è una breve catena di poliossietilene, è un po’ polidispersa. L’inserimento di Igepal CA520 in una microemulsione inversa contenente acido ha portato alla separazione di segnali 1H dei vari componenti oligomerici. Questo risulterebbe dal partizione differenziale tra l'olio e la superficie delle micelle inverse, che dipende dal numero di ossido di etilene (EON) della testa e il grado di partizione, tra i due ambienti, per ogni singola specie oligomerica, offrendo una visione più completa sulle microemulsioni inverse non ioniche. È stato possibile accertare che la distribuzione della lunghezza delle catene poliossietileniche è in buon accordo con la distribuzione di Poisson teoricamente prevista per la polimerizzazione di ossido di etilene. La caratterizzazione del prodotto finale è stata effettuata mediante analisi termogravimetrica (TGA), calorimetria differenziale a scansione (DSC), e TEM, che contemporaneamente hanno confermato che la silice isolata dalla microemulsione inversa non ionica non è significativamente diversa dal prodotto di sintesi sol-gel da catalisi acida in bulk. Le micrografie TEM hanno illustrato, oltre ad aggregati nanostrutturati nel range 20-100 nm, le particelle con diametro inferiore al diametro delle micelle inverse ,determinato da SAXS, a causa di un effetto di contrazione. I sistemi di silice dopati con metalli sono importanti per le applicazioni ottiche, e se gli ioni metallici sono finemente dispersi in matrice di silice possono essere ottenuti catalizzatori molto efficienti. La sintesi di nanoparticelle di silice in microemulsione inversa catalizzata da HCl è stata effettuata in presenza di entrambi ioni, Cu2+ e Co2+, con l'obiettivo di ottenere le nanoparticelle conseguentemente dopate. I sistemi sono stati caratterizzati mediante 1H e 13C NMR ed è stata seguita l'evoluzione quantitativa di TEOS e EtOH. L'introduzione dei metalli nella matrice vetrosa influenza fortemente il loro spettro di assorbimento ottico visibile per cui nello studio è stata applicata la spettroscopia UV-Vis. Le nanoparticelle isolate sono state caratterizzati mediante spettroscopia IR e Raman e la loro dimensione è stata determinata mediante TEM. È stato dimostrato che le micelle inverse possono essere utilizzate per produrre le nanoparticelle di SiO2 dopate di Co2+ e Cu2+ con diametro di circa 3 e 4 nm, rispettivamente. Sono state osservate le particelle sferiche più piccole rispetto alle dimensioni micellari e, nel caso del sistema dopato di Cu2+, aggregati più grandi di forma irregolare con diametro fino a 1 micron. Nei immagini TEM di alcune particelle più grandi e aggregati contenenti Cu sono state osservate molte zone più scure che possono essere assegnate alle particelle di metallo Cu incapsulato in matrice di silice. Pertanto, il cobalto è stato dopato con successo nelle nanoparticelle di silice, mentre il doping con il rame sembrava meno soddisfacente.
XXIII Ciclo
1983

El desenvolupament de nanotermòmetres luminescents de no contacte basats en ions lantànids per ser utilitzats com a eines de diagnòstic precises, eficients i ràpides, propietats atribuïdes a la seva versatilitat, estabilitat i perfils de banda d'emissió estrets, ha portat cap a la substitució de les sondes tèrmiques de contacte convencionals. L'aplicació de nanopartícules dopades amb ions lantànids com nanosensors de temperatura, excitats amb llum ultraviolada, visible o infraroja propera, i la generació d'emissions en les regions espectrals de les finestres biològiques: I-BW (650 nm-950 nm), II-BW (1000 nm -1350 nm), III-BW (1400 nm-2000 nm) i IV-BW (centrada en 2200 nm), està creixent notablement a causa d’avantatges com la reducció de la fototoxicitat i el fotoblanqueig, un contrast d'imatge millor i una major profunditat de penetració en els teixits biològics. Entre aquestes finestres biològiques, la III-BW permet lectures tèrmiques més profundes dins de teixits biològics específics, atribuïdes a una major profunditat de penetració a causa de la reducció de l'absorbància i la dispersió en comparació amb les altres finestres biològiques. No obstant això, la termometria de luminescència en aquest règim espectral s'ha explorat poc. Aquí, hem sintetitzat i caracteritzat materials luminescents dopats amb Ho3+ i Tm3+ amb emissions ubicades a la III-BW per a la seva aplicació com a termòmetres luminescents i agents fototèrmics. Hem utilitzat partícules de KLu(WO4)2 i Y2O3 dopades amb Ho3+ i Tm3+ com a possibles agents fototèrmics automonitoritzats capaços d'alliberar calor i de determinar la temperatura simultàniament. Per a la seva síntesi, hem adaptat mètodes solvotermals (autoclau convencional i assistit per microones) i químics humits (descomposició tèrmica i maduració digestiva). Per acabar, hem aprofitat la peculiar configuració electrònica i les característiques morfològiques de les nanopartícules de Y2O3 per aplicar-les com a emissors de llum blanca i com a agents antioxidants ex vivo.
El desarrollo de nanotermómetros luminiscentes de no contacto basados en iones lantánidos para ser usados como herramientas de diagnóstico precisas, eficientes y rápidas, propiedades atribuidas a su versatilidad, estabilidad y perfiles de banda de emisión estrechos, ha llevado a la sustitución de las sondas térmicas de contacto convencionales. La aplicación de nanopartículas dopadas con lantánidos como nanosensores de temperatura, excitados con luz ultravioleta, visible o infrarroja cercana, y la generación de emisiones en las regiones espectrales de las ventanas biológicas: I-BW (650 nm-950 nm), II-BW (1000 nm -1350 nm), III-BW (1400 nm-2000 nm) y IV-BW (centrada en 2200 nm), está creciendo notablemente debido a ventajas como la reducción de la fototoxicidad y el fotoblanqueo, un mejor contraste de imagen y una mayor profundidad de penetración en tejidos biológicos. Entre estas ventanas biológicas, la III-BW permite lecturas térmicas más profundas dentro de tejidos biológicos específicos, atribuidas a una mayor profundidad de penetración debido a la reducción de la absorbancia y la dispersión en comparación con las otras ventanas biológicas. Sin embargo, la termometría de luminiscencia en este régimen espectral se ha explorado poco. Aquí, hemos sintetizado y caracterizado materiales luminiscentes dopados con Ho3+ y Tm3+ con emisiones ubicadas en la III-BW para su aplicación como termómetros luminiscentes y agentes fototérmicos. Hemos utilizado partículas de KLu(WO4)2 y Y2O3 dopadas con Ho3+ y Tm3+ como posibles agentes fototérmicos automonitorizados capaces de liberar calor y determinar la temperatura simultáneamente. Para su síntesis, hemos adaptado métodos solvotermales (autoclave convencional y asistido por microondas) y químicos húmedos (descomposición térmica y maduración digestiva). Para finalizar, hemos aprovechado la peculiar configuración electrónica y las características morfológicas de las nanopartículas de Y2O3 para aplicarlas como emisores de luz blanca y como agentes antioxidantes ex vivo.
The development of non-contact luminescent lanthanide nanothermometers as accurate, efficient and fast diagnostic tools, attributed to their versatility, stability and narrow emission band profiles, have led to the replacement of the conventional contact thermal probes. The application of lanthanide doped nanoparticles as temperature nanosensors, excited with ultraviolet, visible or near infrared light, and the generation of emissions lying in the biological windows spectral regions: I-BW (650 nm-950 nm), II-BW (1000 nm-1350 nm), III-BW (1400 nm-2000 nm) and IV-BW (centered at 2200 nm), is notably growing due to the advantages of reduced phototoxicity and photobleaching, better image contrast and deeper penetration depths into biological tissues. Among these biological windows, the III-BW allows for deeper thermal readings within specific biological tissues, attributed to a higher penetration depth due to the reduction of absorbance and scattering when compared to the other biological windows. Nevertheless, luminescence thermometry in this spectral regime is randomly explored. Here, we synthesized and characterized luminescent Ho3+ and Tm3+ doped materials with emissions located in the III-BW for their application as luminescent thermometers and photothermal agents. We explored Ho3+ and Tm3+ doped KLu(WO4)2 and Y2O3 particles as potential self-assessed photothermal agents able to release heat and determine temperature simultaneously. For their synthesis, we adapted solvothermal (microwave-assisted and conventional autoclave) and wet-chemical (thermal decomposition and digestive ripening) methods. To conclude, we took profit of the peculiar electronic configuration and morphological characteristics of the Y2O3 nanoparticles to apply them as white light emitters and as ex-vivo antioxidant agents.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The present work describes the synthesis of a new catalyst of palladium nanoparticles supported on multi-walled carbon nanotubes containing nitrogen (Pd@CNxNCPM) 1 and its use in carbon-carbon coupling reactions (Suzuki and Heck) as well as reactions catalytic hydrogenation (reduction of double C-C bonds and nitro compounds reduction). The synthetic strategy employed afforded the simple way to obtain the catalyst with reaction in a short time and efficiently. To this was employed as the palladium precursor, the salt potassium hexacloropalladate IV and hydrazine monohydrate as the reducing agent, without the need for stabilizing agents for the control of nucleation and size of nanoparticle. The catalyst system was characterized as its morphology: dispersion, size and shape of nanoparticles by scanning electron microscopy. Also the catalyst was performed Raman spectroscopy and determination of amount of palladium. After characterization the catalyst, it was tested for coupling reactions of carbon-carbon: Suzuki and Heck leading to the formation of their products with 70-> 95% for Suzuki coupling and 75-> 95% for Heck. For the synthesis in question were used 0.5 mol% of catalyst (based amount of palladium) for Suzuki and 10 mol% for Heck. It should be noted that the catalyst shown stable in the reaction conditions tested, and observed the possibility of reuse of this system for additional reaction cycles without loss of efficiency for the Suzuki coupling. Also, the catalyst was efficient and chemoselectiv for catalytic hydrogenations of unsaturated carbon-carbon bonds and nitro compounds leading to their products in good yields. Thus, the synthesized catalyst proved versatile and can be used in reactions of carbon-carbon coupling well as in catalytic reduction may also be recovered and reused, which provides an environmentally friendly at the same characteristic.
O presente trabalho apresenta a síntese de um novo catalisador de nanopartículas de paládio suportadas em nanotubos de carbono de paredes múltiplas contendo nitrogênio (Pd@CNxNCPM) 1 e sua utilização em reações de acoplamento carbono-carbono (Suzuki e Heck) bem como em reações de Hidrogenações catalíticas (reduções de duplas ligações C-C e redução de nitrocompostos). A estratégia sintética utilizada permitiu a obtenção do catalisador de maneira simples, em curto tempo reacional e de maneira eficiente e sem a presença de agentes estabilizantes externos. Para isso foi empregado como precursor de paládio o sal hexacloropaladato IV de potássio e como agente redutor, hidrazina monohidratada sem a necessidade de agentes estabilizantes para o controle da nucleação e tamanho de nanopartículas. O sistema catalítico foi caracterizado quanto sua morfologia: dispersão, tamanho e forma de nanopartículas através de microscopia eletrônica de varredura. Também foi realizada espectroscopia Raman do catalisador bem como determinação do teor de paládio. Após devidamente analisado o catalisador, o mesmo foi testado para reações de acoplamento carbono-carbono de Suzuki e Heck levando a formação dos respectivos produtos com rendimentos de 70-> 95% para os acoplamentos de Suzuki e 75-> 95% para Heck. Para as sínteses em questão foram usados 0,5 mol% de catalisador (baseados na massa de paládio) para Suzuki e 10 mol% para Heck. Cabe salientar que o catalisador se mostra estável nas condições reacionais testadas, sendo observada a possibilidade de reuso deste sistema por ciclos reacionais adicionais, sem perdas de eficiência para o acoplamento de Suzuki. Ainda, o catalisador se mostrou eficiente para hidrogenações catalíticas quimiosseletivas de ligações de carbono-carbono insaturadas e nitrocompostos levando aos respectivos produtos em bons rendimentos. Dessa forma o catalisador sintetizado se mostrou versátil, sendo possível ser utilizado em reações de acoplamento carbono-carbono bem como em reduções catalíticas, também pode ser recuperado e reutilizado, o que confere ao mesmo uma característica ambientalmente correta.

碩士
國立交通大學
分子科學研究所
98
In order to rapidly synthesize a catalyst to improve the hydrogen selectivity of ethanol steam reforming process, we employ a new microwave assisted method to prepare for the catalysts, CeO2 and La-doped CeO2 nanoparticles and nanorods. The catalytic activities for ethanol to hydrogen conversion have been studied extensively, with varying experimental conditions, including temperature、synthesis time and basic solution. We have found that the best hydrogen selectivity (113±3%) can be reached under the operational condition at 180℃、30min and 15M basic solution. Following the above-mentioned synthesis conditions, we can fabricate CexLa1-xO2 with the microwave assisted method. When x= 0.1~0.6, we have found two phase structures by XRD, the cubic crystal structure of CeO2 and the hexagonal crystal structure of La2O3 . But when we reduce the lanthanum molar ratio, Ce0.7La0.3O2, Ce0.8La0.2O2 and Ce0.9La0.1O2 appear to be single phase. In the catalytic activity study for ethanol to hydrogen conversion, the catalysts with 5% wt Ru/ Ce0.7La0.3O2 and 5% wt Ru/CeO2 nanoparticles have been investigated；the hydrogen selectivity of the former reaches 117±4% under appropriate conditions.

Engineered nanomaterials with tailored properties are highly required in a wide range of industrial fields. Consequently, the researches dedicated to the identification of new applications for existing materials and to the development of novel promising materials and cost effective, eco-friendly synthesis methods gained considerable attention in the last years. Cobalt ferrite is one of the nanomaterials with a wide application range due to its unique properties such as high electrical resistivity, negligible eddy current loss, moderate saturation magnetization, chemical and thermal stability, high Curie temperature and high mechanical hardness. Moreover, its structural, magnetic and electrical properties can be tailored by the selection of preparation route, chemical composition, dopant ions and thermal treatment. This chapter presents the recent applications of nanosized cobalt ferrites doped or co-doped with divalent transition ions such as Zn2+, Cu2+, Mn2+, Ni2+, Cd2+ obtained by various synthesis methods in ceramics, medicine, catalysis, electronics and communications.

CeO2 materials doped with the di- or tri-valent metals possess high oxide ionic conductivity at low temperature for potential electrolyte use in intermediate temperature solid oxide fuel cell (SOFC). However, multi-elements doped CeO2-based electrolyte, (La1-x-ySrxBay)0.175Ce0.825O2-δ (LSBC) in this work, with pure phase is difficultly synthesized at low calcination temperature. High sintering temperature, e.g. > 1500°C, is also needed in conventional mixed oxide method. In this work, nanoparticles less than 50nm of LSBC can be prepared by solution-evaporation method at constant temperature. Pure fluorite crystal structure can be obtained lower than 700°C. The optimal mole ratio of LSBC/citric acid in prepared solution is 1/2 to achieve homogeneous composition and pure phase of LSBC. Small grain size of about 1μm average is observed for 1300°C-microwave sintered LSBC by solution-evaporation method. The ionic conductivity of 1400°C-conventional sintered and 1300°C-microwave sintered LSBC prepared by solution-evaporation method is about 0.006 S/cm at 600°C but less than 0.004 S/cm at 600°C even for 1500°C-conventional sintered LSBC prepared by mixed oxide method.