Linear alkylbenzenes (LAB) are key intermediates in the synthesis of linear alkylbenzene sulfonate surfactants that are used in the manufacture of detergents. Production of LAB with traditional Lewis acids as catalysts, such as hydrofluoric acid, results in the formation of large amounts of toxic wastes and corrosion of industrial equipment. Phosphotungstic acid (PTA) has gained much attention in recent years as a solid catalyst for various alkylation reactions. This research work aims to develop a novel material based on PTA-containing silica gel, which can effectively catalyze LAB synthesis. Sol-gel synthesis of silica gel in the presence of PTA and tetraethyl orthosilicate as precursors produced a mesoporous aterial containing covalently embedded PTA clusters. Obtained superacidic catalyst demonstrated high catalytic activity in liquid-phase alkylation of benzene by various alkenes. Covalent embedding of catalytically active HPA clusters prevents their leaching from the catalyst surface, which enabled its excellent catalytic properties.

An adsorbent for Cs removal from contaminated water based on phosphotungstic acid (PTA) embedded in SiO 2 network was synthesized and granulated with γ-Al 2 O 3 . PTA/SiO 2 had a high adsorption capacity towards Cs while the binder provided excellent mechanical characteristics of the material. It was shown that small particles of PTA/SiO 2 with the sizes of 0.1–1 µm occupied space between larger particles of the binder (up to 5 µm). Chemical interaction between PTA and γ-Al 2 O 3 during the adsorbent preparation also took place. The obtained porous material with the specific surface area of 286.9 m 2 /g contained 4.73% of PTA. Presence of Keggin units in the structure was confirmed by solid state NMR spectroscopy. Study of the adsorbent in Cs + adsorption from solutions demonstrated its high adsorption capacity. The concentrations of Cs + in the solutions after the column tests decreased by 3.3–5.2 times. The presence of Na + and K + as competing ions did not affect the adsorption. The material was tested in clean-up of radioactive water from the shelter of Chernobyl nuclear power plant (Ukraine). A significant decrease of 137 Cs radioactivity was detected in all samples of radioactive water, especially in acidic solutions. Thus the adsorbent can be used for water treatment after incidents resulting in release of radioactive isotopes 134 Cs and 137 Cs.

Linear alkylbenzenes (LAB) are semi-products in the manufacture of linear alkylbenzene sulfonate surfactants that are active ingredients of various detergents. The use of traditional soluble acids (e.g. hydrofluoric acid or aluminum chloride) as catalysts for production of LAB results in the formation of large amounts of acidic toxic wastes. In this work, an efficient heterogeneous catalyst containing immobilized phosphotungstic acid (PTA) was synthesized and tested in the alkylation of benzene by higher alkenes. Sol–gel synthesis of silica gel from tetraethyl orthosilicate and PTA, as precursors, produced a mesoporous material containing covalently embedded PTA clusters. Obtained superacidic catalyst demonstrated high catalytic activity in liquid-phase alkylation of benzene by higher alkenes. Conversion of alkenes to corresponding phenylalkanes on this catalyst was significantly higher than on pure PTA. Covalent embedding of catalytically active HPA clusters prevented their leaching from the catalyst surface, which enabled its excellent catalytic properties.

Superacidic mesoporous materials containing covalently embedded PTA were synthesized by sol-gel method. Tetraethyl orthosilicate (TEOS) and phosphotungstic acid (PTA) were used as precursors in the synthesis, ionic and nonionic surfactants were used as pore-forming agents, the reaction proceeded in acidic media. TEM images revealed mesoporous structure with embedded PTA clusters. FT-IR spectra of obtained materials contained characteristic bands of PTA at 957 cm-1. Synthesized catalysts had high BET surface area and high concentration of acidic sites. Alkylation of 1,3,5-trimethylbenzene by 1-decene demonstrated high catalytic activity. The catalyst obtained with Pluronic P123 as a template was the most effective and resulted in highest conversion of 1-decene into alkylated products. Covalent embedding of PTA clusters in addition to thermal and chemical stability of synthesized catalysts enabled their recyclability. Catalysts remained active during subsequent cycles of alkylation.

Long-chain alkylbenzenes are industrially synthesized precursors to commercial surfactants such as laundry detergent. The currently used catalysts in the processes of their synthesis are corrosive and harmful to the environment. These problems can be avoided utilizing heterogeneous highly acidic catalysts. Solid catalysts do not corrode equipment and are relatively simple to remove from the post-reaction mixture. Phosphotungstic acid (PTA) supported on silica gel could be a possible catalyst due to its high acidity with an estimated pKa ≈ -13. The catalyst PTA-SiO2 was prepared via the sol-gel method to covalently embed it in a silica support. The catalyst was granulated with γ-alumina for use in a fixed bed flow reactor during the alkylation of benzene with long chain alkenes. The isomerization of 1-octene, 1-decene, and 1-octadecene as well as the conversion of 1-decene in the alkylation of benzene were studied under varying conditions. During these reactions, the catalyst demonstrated good catalytic activity at temperatures above 200 °C with an optimal temperature of 250 °C. Of all three alkenes, 1-octadecene showed the highest conversion into respective isomers. The alkylation of benzene with 1-decene experiments showed decreasing of flow rate and increasing the ratio of benzene to 1-decene lead to higher conversions of 1-decene. Characterization of the catalyst after the reaction showed little changes in porosity and particle size. No leaching of PTA was observed. However, carbon deposits were found on the catalyst that requires regeneration before next use in catalysis.

Mesoporous silica gel containing embedded phosphotungstic acid (PTA) was synthesized by sol-gel co-condensation of tetraethoxysilane with PTA in acidic media. The obtained material had high BET surface area and pore volume. A characteristic band of the Keggin structure of PTA was present in its FT-IR spectrum while its XRD patterns were absent. This proved the embedding of PTA on a sub-molecular level. The material demonstrated high adsorption capacity of Cs. Unexpectedly, porosity of the adsorbent increased after substitution of most protons by cesium cations. Cation exchange also favored agglomeration of the material particles. Kinetic studies showed that the adsorption data correlates strongly with the pseudo-second order model. The adsorbent had two types of adsorption sites: heteropolyacid anions and silanol groups. However, adsorption on silanol groups was very sensitive to the temperature. At the increased temperature, the nature of adsorption fit the Langmuir model extremely well. The obtained results can be used in the development of an effective adsorbent for clean-up of water contaminated by radioactive cesium-137.

Esta dissertação mostra um estudo preliminar da preparação de precursores catalíticos a base de níquel (II) e de sua conversão em catalisadores de xerogéis contendo níquel (NS), bem como o estudo da sua atividade catalítica na reação de deslocamento gás-água. Esta reação foi escolhida como reação modelo para avaliar a atividade catalítica, em especial frente a adição do ácido fosfotungstico (HPW) como promotor catalítico e de organosilanos como agentes promotores da dispersão do Ni. Foram preparados catalisadores NS e NS-x (x = 0,5; 1; 2; 3; 5 e 10% em massa de HPW) via processo sol-gel. A caracterização estrutural foi realizada utilizando-se as técnicas de Energia Dispersiva de Raios X, Difratometria de Raios X, Redução a Temperatura Programada, Fisissorção de Nitrogênio, Espectroscopia de Absorção de Raios X e Espectroscopia de Absorção na Região do Infravermelho. Os testes catalíticos foram realizados no Laboratório de Catálise Heterogênea do IQSC/USP numa temperatura de 250-425 °C, em uma lin ha de reação acoplada a um cromatógrafo a gás para análises in situ dos produtos reacionais gasosos. Os resultados obtidos da primeira parte mostraram que a adição do HPW até 2% em massa de precursor catalítico leva a uma melhora gradual na atividade catalítica de 10 a 31 % medido pela taxa de conversão do CO. Contudo acima de 2% ocorre uma queda de atividade catalítica resultando num comportamento global da conversão de CO do tipo gaussiano com o máximo em 2%. Para explicar este comportamento um modelo qualitativo é proposto baseado na formação de fosfotungstato de níquel amorfo acima de 2%. Na segunda parte do trabalho, a concentração de HPW foi fixada em 2% e a temperatura de reação em 425 °C e foram adicionados organosilanos nitrogenados (amino e nitrila) para avaliar a sua capacidade de funcionar como agentes de dispersão do cátion metálico no precursor híbrido (Ormosil) e do metal no catalisador. O catalisador proveniente do precursor contendo grupo amina possui maior atividade catalítica que aquele contendo nitrila, porém ambos possuem menor atividade que o xerogel catalítico obtido de precursores sem grupos nitrogenados. Contudo, os catalisadores preparados a partir de Ormosils mostravam-se estáveis ao longo do tempo da reação estudada quando comparados com os xerogeis NS-x. / This dissertation describes the preparation of Ni (II)-based catalyst precursor material and its subsequent conversion to Ni-based xerogels catalyst as well as the catalytic activity of the resultant catalyst in water-gas shift reaction. The water-gas shift reaction was selected as a model reaction for the evaluation of catalytic activity of the prepared catalysts. The effect of addition of phosphotungstic acid (HPW) as an activity promoting agent and organosilane as dispersing agents of Ni was also studied. For this purpose, Ni-based catalyst (NS-x) containing various amounts (x) of HPW (x= 0, 0.5, 1, 2, 3, 5, 10 wt. %) were prepared using the sol-gel process. These catalysts were characterized by x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), temperature-programmed reduction (TPR), nitrogen adsorption measurements (BET method) and Fourier transform infrared spectroscopy (FTIR). The catalytic tests were performed at a temperature of 250-425 °C in a reactor coupled with gas chromatograph (GC) for direct in situ analysis of the reaction products. The results obtained showed that addition of HPW up to 2 wt % leads to an increase in the efficiency of the catalyst from 10% to 31%, as measured by the rate of conversion of CO. However, further increase in the amount of HPW above 2 wt. % leads to a decrease in activity of the catalyst. A qualitative model based on the formation of amorphous Ni-phosphotungstate salt is proposed to explain this behaviour of the catalyst. In a second part of this study, the amount of HPW (2 wt. %) and temperature (425 °C) were fixed and nitrogenate d silanes with amine and nitrile functional groups were added to the catalyst to evaluate the role of these ormosils as dispersing agents for metallic cations in the hybrid precursor material as well as metallic nickel in the final catalyst. The catalyst derived from precursor containing ormosils with ammine functional groups (3-Aminopropyltriethoxysilane) showed better catalytic activity than those containing nitrile functional groups (4-(Triethoxysilyl)butyronitrile). However, the catalytic activity of the catalysts obtained using ormosils bearing nitrogenated silanes was lower than xerogels catalyst prepared without addition of these silanes. Although, the catalysts prepared using the ormosils bearing nitrogenated silanes showed higher stability than NS-x catalyst.

O objetivo desta Tese é preparar e caracterizar nanopartículas de TiO2 e SiO2@ TiO2 e obter filmes finos baseados nesses materiais nanoestruturados usando a metodologia de preparação de filmes conhecida como layer-by-layer (LbL). Primeiramente, TiO2 amorfo sintetizado a partir de sulfato de titanila (TiOSO4) foi cristalizado por método de tratamento hidrotérmico brando (HTT). O efeito da temperatura e tempo de tratamento hidrotérmico na cristalinidade, tamanho de partícula e fotoatividade de TiO2 foi estudado. A análise de MET, DRX e área de superfície confirmou que o HTT a temperatura tão baixa quanto 105°C pode ser utilizada para obter as nanopartículas de anatase com boa cristalinidade (~95%), pequeno tamanho de cristalito (<10 nm), alta área de superfície (>200 m2.g-1) e excelente seletividade da fase. Em uma segunda etapa do projeto, o nanocatalisador de TiO2 foi depositado, via rota sol-gel, na superfície de NPs de sílica Stöber (diâmetro 200 nm), formando um sistema core@shell (SiO2@ TiO2). O objetivo desse processo foi de se obter melhor estabilidade térmica (1000°C), boa dispersão e menor aglomeração do nanocatalisador (TiO2). As análises de microscopia eletrônica (MEV e MET) confirmaram a formação de uma camada porosa (espessura 10-30 nm) de TiO2 formadas por cristalitos com cerca de 5 nm. Um estudo das propriedades ópticas das amostras SiO2@ TiO2 mostrou que o deslocamento no onset de absorção é função do espalhamento Rayleigh. Finalmente, desenvolveu-se um novo e versátil procedimento LbL para a preparação de filmes multicamadas, porosos e uniformes de TiO2 empregando fosfato de celulose (CP) como polieletrólito eficiente e não convencional. A formação dos filmes (CP/ TiO2 e CP/ TiO2/HPW) foi monitorada por espectroscopia UV/Vis e a interação entre os componentes dos filmes (CP, TiO2 e HPW) foi estudada pelas técnicas MET, XPS e FTIR. Estes filmes LbL apresentaram boa fotoatividade para degradação de ácido esteárico, cristal violeta e azul de metileno sobre irradiação UV. Os filmes CP/HPW formados em celulose bacteriana apresentaram boa resposta fotocrômica, que é aumentada pela presença do TiO2 devido a uma transferência eletrônica interfacial do TiO2 para o HPW. A interface entre nanopartículas de titânia e nanopartículas de ácido fosfotungstico foi pela primeira vez caracterizada por Microscopia Eletrônica de Transmissão como sendo não-cristalina. Este método simples e ambientalmente amigável pode ser utilizado para formar recobrimentos em uma grande variedade de superfícies com filmes fotoativos de TiO2 e TiO2/HPW. / The aim of the present investigation was to prepare and characterize TiO2 and core@shell (SiO2@TiO2) nanoparticles (CSNs) and form layer-by-layer (LbL) films with these nanoparticles (NPs) on various substrates. Firstly, amorphous TiO2 were prepared from oxotitanium (IV) sulfate (TiOSO4) and crystallized by low-temperature hydrothermal treatment (HTT). The effect of hydrothermal temperature and treatment time on crystallinity, particle size and photoactivity of TiO2 was studied. The TEM, XRD and BET surface area analysis confirmed that HTT at temperature as low as 105°C can be used to obtain phase-pure anatase nanoparticles with good crystallinity (~95%), small crystallite size (<10 nm), high surface area (>200 m2.g-1) and excellent phase selectivity. Secondly, TiO2 nanocatalyst was directly deposited, via sol-gel route, on the surface of Stöber silica NPs of around 200 nm in a core@shell (SiO2@ TiO2) configuration to obtain better thermal stability, good dispersion and less agglomeration of the nanocatalyst. SEM and TEM observation confirmed the formation of a porous anatase shell of crystalline TiO2 consisting of around 5-8 nm small crystallites, in accordance with XRD results. The shell thickness was varied between 10-30 nm by varying the quantity of precursor titanium (IV) isopropoxide (TiP). Compared to the uncoated silica, the BET surface area also increased by 147-365% depending on the amount of TiP added during synthesis step. The effect of shell morphology and TiO2 loading on surface area and photoactivity has been studied and compared among different CSNs. Finally, a new and versatile LbL procedure for the preparation of porous and highly dispersed multilayer films of TiO2 and phosphotungstic acid (HPW) on different substrates was developed using Cellulose Phosphate (CP) as an efficient and non-conventional binder. The films formation was monitored by UV/Vis spectroscopy and the interaction between the films components (CP, TiO2 and HPW) was studied by HRTEM, XPS and FTIR techniques. These CP/ TiO2 and CP/ TiO2/HPW LbL films showed good photoactivity against stearic acid (SA), crystal violet (CV) and methylene blue (MB) under UV irradiation. The CP/HPW films formed on bacterial cellulose showed good photochromic response, which is enhanced in presence of TiO2 due to an interfacial electron transfer from TiO2 to HPW. This simple and environmentally safe method can be used to form coatings on a variety of surfaces with photoactive TiO2 and TiO2/HPW films.

Silica gels containing incorporated heteropolyacids (HPAs) were synthesized in acidic media by co-condensation of tetraethoxysilane (TEOS) with phosphotungstic or phosphomolybdic acids using sol-gel technique. Effect of the synthesis conditions on their structure and morphology was studied. Yields of modified materials were some lower as compared to non-modified silica gels. All materials were mesoporous but contained micropores in their structures. Presence of bands of Keggin’s structures in FT-IR spectra along with absence of XRD patterns of crystalline HPAs confirmed their fine incorporation into silica network. Particle sizes of modified materials were 800-1100 nm excepting for W-containing sample obtained with trimethylstearylammonium chloride. This unusual effect was attributed to stabilization of primary silica nanoparticles by interaction between surfactant and HPA. High ratio HPA/TEOS resulted in partial loss of porosity. Obtained results might be used for optimization of synthesis of effective catalysts and adsorbents containing HPAs in mesoporous structure.

Mesoporous silica gel containing embedded phosphotungstic acid (PTA) was synthesized by sol-gel co-condensation of tetraethyl orthosilicate with PTA in acidic media. The obtained material had high Brunauer-Emmett-Teller Theory (BET) surface area and pore volume. A characteristic band of the Keggin structure of PTA was present in its FT-IR spectrum while its X-ray diffraction patterns were absent. This proved the embedding of PTA on a sub-molecular level and not as a second phase. Acidic sites were determined by neutralization with base in aprotic solvent, followed by titration of the remaining base with an acid. The material demonstrated high adsorption capacity of Cs. Kinetic studies showed that the adsorption data correlates strongly with the pseudo-second order model. At higher temperatures, the nature of adsorption fit the Langmuir model extremely well. The obtained results can be used in the development of an effective adsorbent for clean-up of water contaminated by radioactive 137Cs.