Academic literature on the topic 'Aqueous sol-gel method'

Composite sol with spinnability was prepared from an aqueous solution using polyvinyl butyral (PVB), Al (NO3)3·9H2O (AN) and tetraethylorthosilicate (TEOS) via non-hydrolytic sol-gel method. The mullite fibers with good flexibility were also obtained. The viscosity of composite sol increased with the increasing PVB content, water-bathing temperature and aging time. FTIR spectroscopy of composite gel showed a new absorption peak due to the C=O group, which implied the presence of new reaction product. It could be explained by the reaction among PVB, AN and TEOS.

Over the last decade, the number of publications concerning the non-aqueous sol-gel synthesis of metal oxide nanostructures has rapidly increased, as this method affords an immense variety of sizes and shapes of the products. This review highlights the versatility of non-aqueous sol-gel routes, under solvothermal conditions, to metal oxide and hybrid materials. In particular, the easier control over the reaction kinetics, compared to aqueous methods, allows to better match the reactivity between metal oxide precursors. This permits to produce complex multimetal and doped oxides at low temperature, as it is discussed in detail for the case of doped group IV metal oxides

Abstract Zinc oxide nanoparticles were prepared using the sol-gel method. Zinc is one of the most important elements in living organisms and similarly zinc derived compounds have attracted much attention because of their applications in various fields like agricultural, medicinal, industrial, etc. These nanoparticles have piezoelectric, semiconducting, photocatalytic activities, and very high surface area. Also, they possess the unique property of being biodegradable and biocompatible. To synthesize the pure ZnO nanoparticles, zinc nitrate hexahydrate [Zn(NO3)2.6H20] is used as the precursor. Sol-gel can be done either in an aqueous or non-aqueous medium. But in this work, the ZnO nanoparticles are prepared in the aqueous medium (i.e in water) at room temperature. The prepared zinc oxide nanoparticles are characterized using X-ray diffraction to determine their crystallinity and scanning electron microscopy (SEM) is used to study the morphology of the sample.

In this study, an aqueous sol-gel synthesis method and subsequent dip-coating technique were applied for the preparation of yttrium iron garnet (YIG), yttrium iron perovskite (YIP), and terbium iron perovskite (TIP) bulk and thin films. The monophasic highly crystalline different iron ferrite powders have been synthesized using this simple aqueous sol-gel process displaying the suitability of the method. In the next step, the same sol-gel solution was used for the fabrication of coatings on monocrystalline silicon (100) using a dip-coating procedure. This resulted, likely due to substrate surface influence, in all coatings having mixed phases of both garnet and perovskite. Thermogravimetric (TG) analysis of the precursor gels was carried out. All the samples were investigated by X-ray powder diffraction (XRD) analysis. The coatings were also investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Mössbauer spectroscopy. Magnetic measurements were also carried out.

The article presents experimental data confirming the effect of capillary active substance (surfactants) and sedimentation stability on the final structure of the gel with stabilized silicic acid. Studies of the macrostructure of silica gel depending on the method of emulsifi ation of silicic acid sol and the effect of the resulting fractality on the strength of the mold are presented.The direction of modifying the binder for lost‑wax casting (LWC) with obtaining the specified properties of the ceramic shell is shown.The complex effect of organic polymers on the sol – gel system has been established. The conclusion is made about the possibility of using an aqueous dispersion of acrylic to form a given structure of a silica gel.

Aluminum silicate powder was prepared using two different syntheses: (1) co-precipitation and (2) two-step sol-gel method. All synthesized powders were characterized by various techniques including XRD, FE-SEM, FT-IR, BET, porosimeter, and zetasizer. The particle morphology of the synthesized aluminum silicate powder was greatly different depending on the synthesis. The synthesized aluminum silicate powder by co-precipitation had a low specific surface area (158 m2/g) and the particle appeared to have a sharp edge, as though in a glassy state. On the other hand, synthesized aluminum silicate powder by the two-step sol-gel method had a mesoporous structure and a large specific surface area (430 m2/g). The aluminum silicate powders as adsorbents were characterized for their adsorption behavior towards Pb (II) ions and methylene blue in an aqueous solution performed in a batch adsorption experiment. The maximum adsorption capacities of Pb (II) ions and methylene blue onto the two-step sol-gel method powder were over four-times and seven-times higher than that of the co-precipitation powder, respectively. These results show that the aluminum silicate powder synthesized with a two-step sol-gel method using ammonia can be a potential adsorbent for removing heavy metal ions and organic dyes from an aqueous solution.

Materials with defined porous structures have drawn considerate attention for decades. Most of these materials display similar porous structure within the entity. Sometimes materials with different surface and internal structures would be appreciated. In the present study, a microporous silica material with surface macroporous arrays was prepared by a sol-gel technique combined with a template method. The sol was prepared via hydrolysis of tetraethoxylsilane by hydrochloric acid. To this sol, monodispersed, hydrophobic polystyrene spheres were added. By ultrasonication, the spheres floated and assembled to regular arrays on the aqueous sol surface. At low temperature, the sol was gradually gelated, which froze the spheres in-situ. By washing with toluene, the polystyrene spheres were dissolved, leaving aligned arrays on the surface of the gel. The macropores can be easily controlled by selecting particles with suitable sizes. The material would find application in catalysis, sensor and adsorption.

Great interest was recently devoted to the use of inorganic particles as a reinforcing filler in tires for the automotive industry. In fact,the reinforcing of elastomers by the addition of these fillers affects the stiffness, strength, elongation at break, fracture toughness, energy dissipation (rolling resistance), friction to ice or wet grip, wear (abrasion resistance)and on the material processability. Therefore, the technology improvement of tires currently has to satisfy the requirements of sustainable development in order to reduce fuel consumption, environmental pollution and acoustic noise. Carbon black has been the only additive used for this purpose for a long time but silica is now becoming the alternative reinforcing filler; as it offers a lot of advantages, such as better rolling resistance and reduction of the heat buildup; moreover, it can be suitably employed in all cases where the black color is not required. Natural rubber-silica (NR-SiO2) composites are usually prepared by mechanical mixing. Unfortunately, silica particles have a strong tendency to interact with each other within the elastomeric matrix, favoring the inhomogeneous dispersion due to particle tendency to agglomerate and in principle to reduce the filler-rubber interaction. Significant contributions to overcome the disadvantages derived from filler-filler interaction of the silica particles; they are obtainable by enhancing the filler-rubber interaction, which causes additional cross-linking in the rubber structure. The enhancement of filler-rubber interaction is obtained by the use of coupling agents which interact with both the polymer (hydrophobic) and the silica(hydrophilic) surface groups,due to the presence of different functionalities at the ends of the molecules. An alternative approach and object of the present Ph.D thesis,is to prepare composites by in situ formation of the silica filler particles by sol-gel hydrolysis and condensation of tetraethoxysilane(TEOS. Therefore,the aim of this work is to prepare silica-natural rubber (NR-SiO2) composites, with the intention of improving the properties which normally the compound, prepared by mechanical blending possesses. Several factors like nature of the solvent, nature of the catalyst, medium pH, molar ratio between alkoxysilane and water or solvent, gelling and drying temperatures are fundamental sol-gel parameters which can modify the process of the nanocomposite preparation in order to optimize the better homogeneity of the filler distribution inside the rubber matrix. Therefore, considering the filler particle growth in situ in the polymeric matrix, it is possible to distinguish two possible preparation techniques which differ in some of the factors affecting the sol-gel process: aqueous and non-aqueous in situ sol-gel methods. In addition to these factors that influence the preparation of the composite, the amount of the filler present in the silica-rubber composite affects the final performance. In fact, the enhancement in mechanical properties can be achieved when the composite contains the optimal amount of the filler required to form a continuous filler network within the rubber matrix; filler amounts less of this percolation threshold show mostly constant and poor mechanical properties. The presence of a continuous filler network and its homogeneity depends on the filler characteristics, such as size and shape of the particles and on the in situ composite preparation method used. The formation of a convenient filler network is in turn relatable to the physical and chemical interactions among the particles and among their aggregates (filler-filler interaction) and to the chemical and physical interactions between the particles and the matrix (filler-rubber interaction). The presence of functional groups on the particle surface can significantly influence the interface between the filler particles and the rubber matrix; consequently, modifying the filler-filler and filler-rubber interaction leads to the variation of the reinforcement level of the composites. With the intention to investigate and to rationalize the effects induced by surface functionalization of the filler on the properties of rubber composites, during the aqueous sol-gel synthesis of the silica the surface was functionalized by using trialkoxysilane having different functional groups. These functionalities were selected among those which are suitable for promoting the formation of differently shaped silica particles or for modulating the filler-filler and the filler-rubber interactions. Silica particles were modified by molecules containing alkylthiol, thiocarboxylate, alkyldisulfide, alkyltetrasulfide (silica functionalized with containing S groups); vinyl, propyl, octyl chains, alkylamine, alkylcyanate and alkylisocyanate groups (silica functionalized with containing N groups). For this purpose a mixture of TEOS and TMSPM ((3-mercaptopropy)trimethoxysilane) or TESPD (bis(3-triethoxysilylpropyl)disulfide) or TESPT (bis(3-triethoxysilylpropyl) tetrasulfide) or NXT (3-octanoylthio-1propyltriethoxy) or VTEOS (vinyltriethoxysilane) or PTEOS (triethoxy(propyl)silane) or OCTEOS (triethoxy(octyl)silane) or APTEOS ((3-aminopropyl)triethoxysilane) or CPTEOS (3-cyanopropyltriethoxysilane) or ICPTEOS (3-(triethoxysilyl)propylisocyanate) were introduced in NR latex (containing 60 % dry rubber, 39.3 % of water and 0.7% of NH3) during the aqueous sol-gel process. The functionalized molecules were selected with the aim of promoting the formation of different shapes on silica particles (anisotropic or spherical), moreover of modifying the filler-filler and filler-rubber interaction through the chemical functionalities of substituents. In the aqueous in situ sol-gel method, the presence of large amounts of water helps the silica precursors to react quickly in the early stage of the synthesis in rubber matrix, allowing thus to increase the hydroxyl group numbers on particle surfaces, making them less compatible with the rubber and in this way favoring particle aggregation. Through the non aqueous in situ sol gel method, the oxygen present in silica nanoparticles is provided by a suitable reaction and not, as in the aqueous in situ sol gel method, by the water solvent. During this method, the addition of two simple solvents on the metal oxide precursor can generate water in situ that can start sol-gel hydrolysis and condensation reactions. In order to work in an environment without the presence of the water as initial reactant, the silica-rubber composite by the non-aqueous in situ sol-gel method was prepared starting from a solution of dry NR with toluene (inert solvent) and TEOS, which was added to formic acid and alcohol (ethanol of benzylalcohol). Therefore, well defined amounts of water were formed through the esterification reaction produced by formic acid and alcohol, which control the formation of metal oxide growth within the rubber matrix. Moreover, in order to understand better the morphology of the silica particle growth in NR through the in situ sol-gel method, bare silica and functionalized silica powders were prepared by using the same method without the rubber. These powders were morphologically characterized with the intention of more easily evaluating the shape, the size, the surface area, the effect of the metal oxide precursor and the modification of the silica surface. Regarding the composites, the amount of silica was determined by thermogravimetric analysis(TGA) in air. The stability and the reactivity of the functional groups and the hydrolysis rate of the alkoxy groups of the trialkoxysilanes in the early stage of the sol-gel reaction were evaluated by ATR-FTIR. The homogeneity of the particle dispersion, the dimension and shape of silica aggregates were investigated by SEM and TEM, to draw appropriate relations between the filler morphology and the reinforcement of the elastomeric network. The efficacy of the filler network in reinforcing the rubber matrix was assessed by swelling measurements. The Electron Spin Resonance(ESR) behavior of nitroxide radical, introduced as spin probe in order to check the rigidity of the rubber chains, was also investigated. The static and dynamic-mechanical properties of the nanocomposites, both uncured and vulcanized, were investigated and discussed referring to the network morphology, allowing to suggest a connection between the silica precursors used and the functional properties and the amount of the filler. The vulcanization kinetics was also studied, as well as the homogeneity of the dispersion of the filler and the rubber networks. Hardness, abrasion resistance, tensile analysis and compression set results of vulcanized composites were discussed taking into account the structural, morphological and mechanical characteristics determined before. Silica-natural rubber composites for tire applications with a controlled composition and morphology was obtained by in situ sol-gel method and compared with conventional mechanical blending prepared by using silica Rhodia and dried NR. Regarding the in situ sol-gel method of nanocomposite preparation, two different synthetic approaches were carried out by starting from the same silica precursor: aqueous and non aqueous methods. Deep investigation on the relationship between composition, size and morphology of the silica particles, dispersion network degree and dynamic mechanical behavior of uncured composites allowed to rationalize the final performance of the cured composites. In fact, the efficacy of silica filler to improve the mechanical properties of the tires for the automotive industry is related both to the interaction among the silica particles and aggregates (filler-filler interaction) and to their capability to interact with the rubber matrix (filler-rubber interaction). Therefore, the characteristics of the silica such as shape, size, surface area, nature of the surface (OH group, functional molecules and amount), degree of aggregation lead to modify the nature of the interface with the rubber and also the homogenous distribution of the filler network. The obtained results for aqueous in situ sol-gel silica-natural rubber preparation led to the following conclusions: - The aqueous sol-gel method is a promising procedure to prepare nanocomposites from silica precursor TEOS mixed to trialkoxisilanes having different functional groups when the filler precursor doesn’t react quickly through hydrolysis and condensation reactions in water environment and allow to control the filler-filler and filler-rubber interactions. - The functional groups from different substituted silicon alkoxide precursors promote during the sol-gel process the formation of different silica particle shapes and modify the filler-filler and filler-rubber interaction.In particular,the precursor functionalities induced the formation of anisotropic shaped silica particles, unlike the spherical ones derived from TEOS. - Different precursors give rise to particle networks with different degrees of continuity, depending on physical and chemical properties of particles they originate. Spherical or slightly anisotropic particles with homogeneous size show the best self assembling behavior and form continuous networks. When particles contain surface groups able to interact with each other (e.g. hydroxyl, amino and thiol groups), the formation of chemical bonds makes the filler-filler interaction stronger along the network. - The network continuity within the composite is the main prerequisite to obtain strong rubber reinforcement. Not homogeneous distribution of the filler and irregular segregation of particles induce large voids in the network, lowering the dynamic-mechanical properties. However, it appears that a strong chemical interaction among particles can balance the absence of a fully continuous network, preserving high storage modulus. This is the case of the network in NR-TMSPM, where the thiol functionality assists the bonding interaction. On the contrary, the large voids observed in the network of NR-OCTEOS are not compensated by bonding interactions among particles, which are absent or very weak due to the presence of the surface alkyl groups. - The different filler-rubber interaction due to substituents able to chemically interact with the polymer, promotes the homogeneous distribution of the filler particles even if its contribution to the reinforcement properties is less effective than that to the filler-filler interaction. Thus filler-filler interaction governs the dynamic-mechanical properties of silica rubber composites either through the shape induced physical interactions responsible for the network formation, or by the chemical interaction among particle surface groups. - To sum up when a choice among different functionalized silica is required, the suggestion is to look for well assembled and continuous filler networks, eventually assisted by chemical interaction among particles. The second condition seems very important, in fact in the case of NXT network, the homogeneous particle distribution is not sufficient to guarantee strength; instead the dynamic-mechanic behavior of NR-NXT is enhanced after thermal treatment which allows the sulphur-rubber interaction. - Regarding the properties of the vulcanized composites, it is evident that the preparation of the silica in situ improve the rigidity, the hardness, the tensile strength and reduce the dissipation of the energy, which means an improvement in rolling resistance. The obtained results for non-aqueous in situ sol-gel silica-natural rubber preparation led the following conclusions: -The non-aqueous in situ sol-gel synthesis is a procedure to prepare nanocomposites allowing the in situ growth of small particles in rubber matrix in the absence of large amount of water. In addition, due to the slow hydrolysis and condensation reaction rate of the precursors it possible to control at molecular level the growth of the metal oxide particles and therefore the filler-filler interaction and the dispersion in rubber matrix. - Non-aqueous in situ sol-gel silica-natural rubber nanocomposites were prepared by in situ esterification reaction between formic acid and ethylalcohol or benzylalcohol which produce controlled amount of water for the hydrolysis and condensation reaction. Therefore inside the dried NR it is possible to growth high amount of silica particles well distributed in a network were the particles are less aggregated and show lower filler-filler interaction in comparison with the composite prepared by conventional blending route. - Silica-natural rubber composites were obtained containing large amount of well dispersed silica (75 phr or 43% wt) without using coupling agents. -The nature of the alcohol involved in the esterification reaction influences the shape and the size of the silica prepared in swollen natural rubber. Silica particles produced in ethanol environment are bigger than those produced in presence of benzylalcohol, and create an effective reinforcement of the rubber when their amount is higher than 60 phr (37% wt). In spite of the different particle dimensions, silica produced from the two different routes are equally highly dispersed in the rubber matrix, due to the lower hydrophilicity of the surface, and a large amount of filler is required to form an efficient silica network able to reinforce the composite. -This behavior, peculiar of silica particles prepared by non aqueous in situ method, confirm that even if a homogeneous distribution of the particles in the matrix is required to obtain an efficient and strong reinforcement of the rubber, highly separated particles with low filler-filler interaction hinder an efficient filler network. On the other side the non aqueous synthesis allows to load a large amount of silica in the rubber, which could not be loaded with the traditional blending method without using a compatibilizer or disperdent agent.

Ce travail concerne la synthèse et la caractérisation structurale de nanocristaux de faible taille (~1-3 nm) d’oxydes métalliques simples, à savoir le dioxyde de titane (TiO2), le dioxyde d’étain (SnO2) et le monoxyde de zinc (ZnO). Les synthèses ont été réalisées au moyen de méthodes sol-gel non-aqueuses voire strictement non-hydrolytiques sous contrôle cinétique. La caractérisation structurale s’est principalement appuyée sur la diffraction des rayons X, la microscopie électronique en transmission et la méthode des fonctions de distribution de paires atomiques, obtenues grâce à la diffusion totale des rayons X, couplées à des méthodes de modélisation à l’échelle atomique. Dans le cas de TiO2, des nanoparticules d’anatase bien cristallisées de 4 nm à 8 nm ont été synthétisées. Le ratio molaire de donneur d’oxygène par rapport au titane s’est avéré être un paramètre influençant fortement la taille des particules. Nous avons également mis en évidence la formation d’une phase intermédiaire caractérisée par des nanoparticules faiblement cristallisées de très faible taille dont la structure pourrait s’apparenter à une structure brookite désordonnée. Pour SnO2, des nanocristaux présentant une structure rutile ont été obtenus avec des tailles comprises entre 2 nm et 4 nm. Dans le cas de l’utilisation d’un éther, nous avons mis en évidence la formation concomitante d’une phase organique polymérisée et de nanoparticules primaires dont la structure intermédiaire présente de fortes similitudes avec la structure rutile. L’utilisation de solvants possédant une fonction benzyle en présence de tétrachlorure d’étain a conduit à la formation d’eau dans le système. Dans le cas de ZnO, nous avons montré que l’utilisation d’une base organique pour initier la formation du réseau oxyde dans une solution méthanolique d’acétate de zinc en présence d’un agent complexant du zinc permettait d’obtenir des nanoparticules de l’ordre de 1 nm. Même pour les faibles valeurs de taille, les nanoparticules présentent une structure très proche de la wurtzite avec un désordre croissant au niveau du réseau cationique
The aim of this work was to synthesize small size (~1-3 nm) metal oxide nanocrystals namely titanium dioxide (TiO2), tin dioxide (SnO2) and zinc oxide (ZnO), and to study their structure. Syntheses were conducted via non-aqueous or even strictly non-hydrolytic sol-gel methods under kinetic control. The structural characterization was mainly carried out by X-Ray diffraction methods, transmission electronic microscopy and the study of pair distribution functions, obtained by X Ray total scattering, coupled with atomic scale modelling methods. In the case of TiO2, anatase nanocrystals were obtained with sizes ranging between 4 nm and 8 nm. The molar ratio of the oxygen donor with respect to titanium was shown to be an important parameter to control the nanoparticle size. In peculiar conditions we have been able to isolate an intermediate phase characterized by very small sized and poorly crystallized nanoparticles which the structure can be assimilated to a disordered brookite structure. Concerning SnO2, rutile-type nanocrystals were synthesized with sizes ranging between 2 nm and 4 nm. The use of an ether as oxygen donor led to the simultaneous formation of an organic polymeric phase and of primary nanoparticles characterized by an intermediate structure close but still different from the rutile-type structure. Moreover, the use of benzyl-type solvents in the presence of tin tetrachloride led to the formation of water in the system. Lastly, for ZnO, we have shown that using an organic base to induce the formation of the metal oxide network in a methanolic solution of zinc acetate in the presence of a strong complexing agent of the zinc allowed us to obtain wurtzite nanocrystals of ultrasmall sizes around 1 nm. Even for the smallest sizes, the nanoparticles exhibit a structure very close to that of wurtzite with an increasing disorder of the cationic network

Ce travail est consacré à l'élaboration par voie humide (pontage, solvothermale et colloïdale) de photocatalyseur TiO2 supporté sur trois types de minéraux argileux d'origine marocaine: la stévensite, la beidellite et la palygorskite, à leurs caractérisations et finalement à l'évaluation de leurs activités photocatalytiques vis-à-vis de l'élimination en milieu aqueux du colorant anionique l'Orange G (OG) très utilisé en industrie textile. La stévensite et la beidellite sont toutes les deux des smectites de types magnésien trioctaédrique et aluminifère dioctaédrique respectivement. En revanche, la palygorskite est un minéral fibreux riche en Al doté d'un caractère dioctaédrique très marqué. Les matériaux photocatalyseurs supportés développés par le pontage de la stévensite ou de la beidellite ne révèlent pas de formation de piliers interlamellaires de TiO2, mais plutôt l'obtention dans les deux cas de matrice de TiO2 amorphe dans laquelle sont éparpillées quelques rares particules indemnes de phyllosilicates. De même, ceux à base de stévensite élaborés par la méthode solvothermale révèlent des particules du phyllosilicate désintégrées au sein d'une matrice de TiO2 toutefois cristallisée sous forme d'anatase. Néanmoins, la fonctionnalisation selon la voie colloïdale a permis d'immobiliser avec succès des nanoparticules d'anatase (10 nm) sur aussi bien des feuillets plus ou moins exfoliés de stévensite ou de beidellite que sur des fibres de palygorskite. L'anatase attachée aux particules de ces minéraux argileux demeure extraordinairement stable jusqu'à 900 °C alors que celle formée en absence de ces phyllosilicates se convertit complètement en rutile vers 650 °C. Cette stabilité remarquable de l'anatase supportée est due à l'empêchement de la croissance, par coalescence à haute température, de la taille de ses particules au-delà de la taille critique (30 nm) requise pour sa conversion en rutile relativement moins photoactive. Les essais de photocatalyse révèlent que l'activité catalytique des différents matériaux élaborés croit selon la méthode de fonctionnalisation: pontage - méthode solvothermale - voie colloïdale et aussi selon la nature du minéral argileux : stévensite - beidellite - palygorskite. En outre, les matériaux photocatalyseurs supportés, à base de beidellite ou de palygorskite, développés par la voie colloïdale, manifestent une activité deux fois supérieure à celle de la poudre commerciale TiO2 Degussa P25. Leurs particules floculent aisément, ce qui facilite leur élimination du milieu aqueux sans recourir à la microfilitration requise dans le cas de la Degussa P25
This work was devoted to the elaboration by wet route (pillaring, solvothermal and colloidal) of TiO2 supported photocatalysts on three kinds of clay minerals (stevensite, beidellite and palygorskite) from Morocco, to their characterizations and finally to the evaluation of their photocatalytic activities towards the removal from aqueous media of anionic Orange G dye, widely used in textile industry. Stevensite and beidellite were magnesian trioctahedral and aluminiferous dioctahedral smectites respectively. Nevertheless, palygorskite was a fibrous Al-rich clay mineral with a predominant dioctahedral character. The photocatalyst materials elaborated by the pillaring of stevensite or beidellite did not reveal the formation of TiO2 interlayer pillars, but the observation of an amorphous matrix of Ti-rich phase within which were distributed some rare unaltered particles of phyllosilicates. Those based on stevensite elaborated according to solvothermal method also showed dissolved phyllosilicates particles, but within crystalline TiO2 anatase matrix. Nevertheless, the functionalized materials developed according to colloidal route exhibited successful immobilization of anatase nanoparticles (10 nm) onto as well as more or less exfoliated layers of stevensite or beidellite than on palygorskite fibers. Anatase remained remarkably stable up to 900 °C when attached to particles of clay minerals in comparison with that developed in their absence which underwent a complete transformation into rutile at around 650°C. This remarkable stability at high temperature of anatase supported on clay minerals particles was due to the hindrance of particles growth by sintering whose the sizes remained below the nucleus critical sizes (30 nm) required for its transition into less photoactive rutile. The photocatalysis tests revealed that the catalytic activity of different elaborated materials increased according to the synthesis route: pillaring process - solvothermal method - colloidal route and according to the nature of clay mineral: stevensite - beidellite - palygorskite. In addition, the supported photocatalysts based on beidellite or palygorskite prepared by colloidal route were found to be twice more active than the commercial TiO2 powder Degussa P25. Furthermore, their particles easily floculated so that they are readily removable from treated solutions without resorting to expensive microfiltration required upon the use of Degussa P25

碩士
國立雲林科技大學
光學電子工程研究所
99
In this study, we fabricated 1D ZnO NRs by low-temperature aqueous solution method. First, we used zinc acetate、ethanol、monoethanolamine to prepare sol-gel solution, and than spin coating the sol-gel solution on glass substrates to complete ZnO seed layers by different times：6、9、12、15、18. Second, we used zinc nitrate and HMTA to prepare aqueous solutions, the concentration were 0.1M、0.05M、0.025M、0.0125M to growth 1D ZnO NRs in 90℃ at 90mins. Finally, the process of ZnO seed layer and 1D ZnO NRs on the UV light separately, to discuss the properties of fabrication with non-UV and with UV. We used FE-SEM to see the morphology of ZnO. It can be found 1D ZnO NRs is wurtzite structure. And with the aqueous solution concentration increase, the ZnO nano- column diameter and length and density will increase too. The 1D ZnO NRs analysis by XRD can show the Wurzite structure and have the most strong diffraction peaks (002). The 1D ZnO NRs analysis by PL, we can find the structure of ZnO with UV light had better crystal than non-UV fabrication. Finally, we use 1D ZnO NRs as UV sensor、humidity sensor、and gas sensor，1D ZnO NRs with UV fabrication have the best performance.

碩士
國立雲林科技大學
環境與安全工程系碩士班
99
Granular N-doped photocatalysts using glass bead as a carrier and using a microwave/sol-gel method adding urea as N source were prepared. Degradation of aqueous bisphenol A (BPA) using these granular photocatalysts with a column reactor under artificial light (365 and 410 nm) and sunlight was investigated. The UV-Visible spectra analysis was indicated that the N-doped photocatalysts shifted absorption band to the visible light, resulting in the narrower band gap to enhance radicals on the surface of photocatalysts. The result of FTIR was shown that N-doped photocatalyst was found function of nitrogen. In addition, the XPS result of N-doped photocatalyst was found O-Ti-N and Ti-O-N. Moreover, when aqueous BPA though this column system reacting 61 minutes under 410 nm irradiation, comparison with N-doped photocatalyst (N/Ti = 8 mol%), commercial non-N photocatalyst, and prepared non-N photocatalyst, the effects of degradation BPA were 66, 58, and 50%, respectively. Under sunlight irradiation and other conditions as the same, the effects of degradation BPA were 91, 84, and 64%, respectively. This result indicated that N-doped photocatalyst was suitable using under visible light achieving energy-saving. In five runs of repetitious experiments, the photodegradation efficiency of N-doped photocatalyst (N/Ti = 8 mol%) was better than commercial non-N photocatalyst, showing good ability of reusing.

Trabalho de Projeto do Mestrado Integrado em Engenharia Biomédica apresentado à Faculdade de Ciências e Tecnologia
Silica synthesis for biological applications presents an array of challenges, namely the incorporation of drugs or other biological compounds due to the high temperatures and pressures at which the synthesis occurs. biomimetism is a technique that imitates natural systems, models, or reactions. In silica synthesis, this technique draws inspirations from various organisms such as the diatoms.By using biomimetic catalysts, silica can be synthesized at low temperatures and pressures. With that being, the purpose of this work was synthetizing silica in an aqueous media, using TEOS as a precursor and, hexamethylenediamine, spermine, spermidine, norspermidine, taurine and both branched and linear poly(ethyleneimines) as biomimetic catalysts. Post-synthesis, the various silica samples were treated and subjected to physical, chemical and morphologic characterization. The obtained silica particles’ properties were analyzed according to the catalysts’ chemical proprieties and reaction media pH results.All catalysts were able to synthetize silica. The samples synthetized by polyamines or poly(ethyleneimines) presented a reduction on mass yield after 24h of synthesis. Which can be driven by the fast condensation and silica depolymerization, given the high pH at which the synthesis occurred. The silica sample yielded by hexamethylenediamine presented the bigger mass yield out of the polyamines, as well as the smallest particle diameter (313,32±99,96 nm), even though it had the lowest surface area (3,205 m2/g) and biggest pore diameter (19,40 nm nm). Silicas obtained by taurine and branched poly(ethyleneimine) presented the biggest surface area (3,37 nm and 4,81 nm) and smallest pore diameter (399,088 m2/g e 274,121 m2/g), according to the N2 adsorption. The catalysts which demonstrated the highest silica mass yield were the branched poly(ethyleneimine) and taurine.As such, the use of polyamines as biomimetic catalysts induces the formation of spherical mesoporous silica particles at low temperature and pressures. Other catalysts were not able to obtain spherical particles but rather mesoporous monoliths of amorphous silica. Therefore, this approach demonstrated its applicability in biomedical science.
A síntese de sílica para aplicações biológicas apresenta vários desafios, nomeadamente a incorporação de fármacos ou outros compostos de interesse devido às altas temperaturas e pressões a que ocorre a síntese. O biomimetismo é uma técnica que consiste na imitação de modelos, sistemas ou reações que ocorrem na Natureza. Para a síntese de sílica, esta técnica inspira-se em organismos como as diatomáceas Recorrendo a catalisadores biomiméticos é possível sintetizar sílica a temperaturas e pressões baixas. Como tal, o objetivo deste trabalho é a síntese de sílica em meio aquoso, utilizando o TEOS como precursor e, a hexametilenodiamina, a espermina, a espermidina, a norespermidina, a taurina, poli(etilenoimina) linear e poli(etilenoimina) ramificada como catalisadores biomiméticos. Após a síntese, as várias amostras de sílica obtidas foram tratadas e sujeitas a caracterização química, física e morfológica. As propriedades das partículas de sílica obtidas foram analisadas de acordo com as propriedades químicas dos catalisadores e diferenças de pH do meio de reação.Todos os catalisadores foram capazes de sintetizar sílica a temperaturas e pressões baixas. As amostras que utilizaram poliaminas ou poli(etilenoiminas) verificaram uma redução da massa sintetizada a partir das 24h, devendo-se à rápida condensação e posterior despolimerização da sílica, característica de síntese a valores altos de pH. A amostra de sílica obtida com hexometilenodiamina como catalisador revelou o maior rendimento mássico, dentro das poliaminas, assim como menor diâmetro de partículas de sílica (313,32±99,96 nm). No entanto apresenta a menor área de superfície (3,205 m2/g) e maior diâmetro médio de poros (19,40 nm). As sílicas obtidas usando a taurina e a poli(etilenoimina) ramificada como catalisadores apresentam a maior área de superfície (399,088 m2/g e 274,121 m2/g) e menor diâmetro de poros (3,37 nm e 4,81 nm) segundo a análise de adsorção de azoto. Os catalisadores que demonstraram maior rendimento mássico foram também a taurina e a poli(etilenoimina) ramificada.Como tal, o uso de poliaminas como catalisadores biomiméticos induz a formação de partículas esféricas de sílica mesoporosa a temperaturas e pressões ambiente. Nos outros catalisadores não foi possível a obtenção de partículas esféricas, mas de monólitos com mesoporosidade. Pelo que, esta abordagem demonstrou capacidade de ser vantajosa em aplicações biomédicas.

Controlling water pollution are huge challenges throughout the world especially concerning pharmaceutical pollutants. Common practices at industrial wastewater treatment facilities need to be upgraded with advanced wastewater treatment techniques. TiO2 based photocatalytic processes have shown great potential for removal of these aqueous pharmaceutical pollutants. Reverse micelle based modified sol-gel method is utilized for the synthesis of TiO2 nanomaterial. Generated reverse micelle nanodomains have controlled size and particle size distribution (PSD) of synthesized TiO2 nanomaterial, as revealed by SEM and DLS analysis. Thermal behaviour of synthesized sample is characterized by TGA analysis. TiO2 photocatalyst is also characterized through XRD, BET surface area, and UV-Vis spectroscopy. TiO2 photocatalyst is used for degradation of three model pharmaceutical pollutants viz. Levofloxacin hemihydrate (LFX), Metronidazole (MNZ) and Ketorolac tromethamine (KRL) under a UV light source. Reverse micelle mediated modified sol-gel method synthesized TiO2 nanomaterial has shown excellent photocatalytical performance, where degradation efficiency of LFX, KRL and MNZ were found to be 99.6%, 98% and 91.4% respectively within a little as 60 minutes.

Controlling water pollution are huge challenges throughout the world especially concerning pharmaceutical pollutants. Common practices at industrial wastewater treatment facilities need to be upgraded with advanced wastewater treatment techniques. TiO2 based photocatalytic processes have shown great potential for removal of these aqueous pharmaceutical pollutants. Reverse micelle based modified sol-gel method is utilized for the synthesis of TiO2 nanomaterial. Generated reverse micelle nanodomains have controlled size and particle size distribution (PSD) of synthesized TiO2 nanomaterial, as revealed by SEM and DLS analysis. Thermal behaviour of synthesized sample is characterized by TGA analysis. TiO2 photocatalyst is also characterized through XRD, BET surface area, and UV-Vis spectroscopy. TiO2 photocatalyst is used for degradation of three model pharmaceutical pollutants viz. Levofloxacin hemihydrate (LFX), Metronidazole (MNZ) and Ketorolac tromethamine (KRL) under a UV light source. Reverse micelle mediated modified sol-gel method synthesized TiO2 nanomaterial has shown excellent photocatalytical performance, where degradation efficiency of LFX, KRL and MNZ were found to be 99.6%, 98% and 91.4% respectively within a little as 60 minutes.

In recent years the spectroscopic investigations of the probe molecules in heteroclusters have become widely applied method for studying the dynamic size effects in clusters.1 Herewith we consider the process of gelation of agueous gelatin solution, which can be analysed in terms of growing clusters of gelatin molecules connected by intermolecular hydrogen bonds2. The sol- gel transition is investigated by detection of the fluorescence yield of probe dye molecules conjugated to the gelatin coils. We prove experimentally and theoretically that the time evolution of the dye fluorescence spectrum reflects the kinetics of helix formation in this process.

Manganese-oxide material prepared by simple sol-gel method was used as an adsorbent of Hg(II) in aqueous solution. X-ray diffraction pattern and Raman spectroscopy were conducted to prove the cryptomelane crystal. The Hg(II) adsorption behavior of the synthesized material well obeyed kinetic models of pseudo-second-order and Elovich equations indicating a chemisorption from the collected kinetic parameters. 500 mgHg2+/gcryptomelane of equilibrium uptake capacity from pseudo-second-order and 7.87x103 mgHg2+/gcryptomelane/day of initial adsorption rate from the Elovich model were obtained for adsorption of Hg2+ cation over cryptomelane adsorbent. Desorption constant of 0.018 gcryptomelane/mgHg is a significant small value, in comparison to initial adsorption rate, proposing a possible chemisorption for remediation of Hg(II) on cryptomelane structure.

The ultimate goal of cold start of hydrogen-powered polymer electrolyte fuel cell vehicles is to minimize the significant system thaw energy requirement and to achieve the short time period desired for freeze start (e.g. less than 30 seconds) in a subfreezing environment. As part of an effort to improve cold start capability for fuel cell vehicles, this work presents a new thaw-at-start strategy using electrical characteristics of vanadium oxide thin films as self-heating source at sub-zero temperature. Vanadium-based thin film coated on the surface of flat bipolar plates (e.g. carbon-based graphite and metallic bipolar plates) have been synthesized by a dip-coating method via aqueous sol-gel chemistry. Subsequently, the detailed in-/ex-situ analyses of the thin films have been carried out using diverse diagnostic techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition, crystallinity, and microstructure. In addition, electrical switching characteristics of the thin films on bipolar plates was cautiously observed over a temperature range from −20°C to 80°C by means of 4-point probes installed in a thermo -hygrostat. By doing so, it has been possible to correctly infer the relationship between a tendency of the thermally-induced electrical switching hysteresis and bipolar plate materials. Also, comprehensive theoretical study on the basis of the experimental results have been performed to estimate the heat dissipation rate by Joule heating from the solid thin films on bipolar plates for the rapid cold-start operation of fuel cell vehicles.

Spray drying is a physical process of granulating fine powders that is used widely in the chemical, pharmaceutical, ceramic, and food industries. It is generally used to produce flowable fine powders for mechanized processing. Occasionally it is used to fabricate sintered bodies like cemented carbides, and has been used to produce sintered fuel and actinide microspheres [1]. As a physical process, it can be adapted to many powder types and mixtures and thus, has appeal for dispersion nuclear fuels, and waste forms of various compositions. It also permits easy recycling of unused powders, and generates minimal chemical waste streams that can arise in chemical sol/gel processing. On the other hand, the containment of the radioactive powders, present safety challenges that need to be addressed [2]. Detailed formal procedures and methods for characterizing and processing UO2/ThO2 mixtures have been established and approved by the Purdue Radiological Control Committee for (1) ball-milling, (2) viscosity and rheology measurements on slurries, (3) sintering, (4) co-precipitation, (5) particle size analysis using laser scattering, (6) surface area analysis using the BET technique, (7) X-ray diffraction, (8) stoichiometry measurement, (9) zeta potential measurements and (10) ceramographic preparation. The spray drying procedures represented a particular challenge since they deal with the handling of loose powders. Studies were carried out to formulate suitable stable, dense and homogeneous aqueous slurries of urania and thoria powders for the production of urania-thoria microspheres by the spray drying method. The studies included (a) particle size distribution after ball-milling, (b) viscosity, (c) zeta potential, (d) slurry flowability, stability and cleanability, (e) microsphere green strength, and f) effects of organic dispersants on the above properties. After formulating the slurry, U,ThO2 microspheres were produced using a commercial, laboratory-scale spray dryer modified for handling these radioactive materials. The microspheres thus obtained were dried at 473 K for 4 hours, presintered at 1173 K for 2 hours and sintered at 1923 K for 10 hours.