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Orientadores: Ulf F. Schuchardt, Heloise de Oliveira Pastore / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-05T04:44:02Z (GMT). No. of bitstreams: 1 Gallo_JeanMarcelRibeiro_M.pdf: 5237424 bytes, checksum: 618c52e79b92842d0ef0d9e910c1ebc8 (MD5) Previous issue date: 2005 / Resumo: Otimizamos a síntese da Nb-MCM-41 à temperatura ambiente, variando a base, as fontes de sílica e nióbio e a ordem de adição da fonte de nióbio. Os materiais, antes e após a calcínação, foram caracterizados por difração de raios-X e reflectância difusa na região do UV-Vis. A Nb-MCM-41 com o melhor resultado foi silanizada e caracterizada por espectroscopia de emissão atômica por plasma indutivamente acoplado (ICP-OES), análise termogravimétrica (TGA), adsorção-dessorção de nitrogênio, ressonância magnética nuclear no ângulo mágico (RMN-MAS) de Si, análise elementar de carbono, hidrogênio e nitrogênio (CHN) e espectroscopia na região do infravermelho (IV). As Nb-MCM-41 calcinada e a silanizada foram testadas na epoxidação de cis-cicloocteno com terc-butilhidroperóxido (TBHP) 69,4 % em cicloexano obtendo após 48 h, 46,6 e 62,2 % de conversão e 77 e 94 % de seletividade, respectivamente. Usando peróxido de hidrogênio 70 % em água obtivemos após 5 h, 8 % de conversão e 80% de seletividade para a amostra calcinada e 13 % de conversão e 70 % de seletividade para a silanizada. Nas reações usando peróxido de hidrogênio aquoso. este foi todo consumido nas 10 primeiras horas. mostrando que o nióbio decompõe facilmente o peróxido de hidrogênio. Montmorilonita K-10 foi trocada com polihidroxi-nióbio e caracterizada por difração de raios-X, TGA, adsorção-desorção de nitrogênio e ICP-OES. O material foi então calcinado a 300. 500 e 900°C para se obter a montmorilonita pilarizada com nióbio que foi caracterizada por difração de raios-X. Observando que mesmo quando a argila é calcinada a 900°C mantém-se a microporosidade, o que é surpreendente, pois a maioria das argilas pilarizadas com óxidos metálicos perde sua microporosidade a cerca de 600°C. A montmorilonita K10 pura, a trocada com nióbio e a pilarizada foram testadas como catalisadores ácidos nas reações de abertura do anel oxirano do oleato de metila epoxidado, usando metanol como nucleófilo, para se obter o b-hidroxiéter correspondente. A argila trocada com nióbio foi mais ativa que as demais. mostrando que a incorporação de nióbio realmente aumenta a acidez de Bronsted. As amostras calcinadas eram menos ativas quanto maior a temperatura de calcinação / Abstract: Nb-MCM-41 synthesis was optimized at room temperature varying the hydroxide, the silica and niobium sources and the order of addition of the niobium source. The materials, before and after the calcinations, were characterized by XRD and UV-Vis diffuse reflectance. The Nb-MCM-41 with best results was silylated and characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantify the niobium, thermogravimetric analysis (TGA) , adsorption-desorption of nitrogen, magic angle spinning nuclear magnetic resonance (RMN-MAS) of Si, elementary analysis of carbon, hydrogen and nitrogen (CHN) and infrared spectroscopy (FTIR). The calcined and the silylated Nb-MCM-41 were used in the epoxidation of ciclooctene with feributylhydroperoxide (TBHP) 69,4 % in ciclohexane obtaining after 48 h, 46,6 and 62,2 % of conversion and 77 and 94 % of selectivity, respectively. Using hydrogen peroxide 70 % in water it was obtained after 5 h, 8% of conversion and 80 % of selectivity for the calcinated sample and 13 % of conversion and 70 % of selectivity for the silylated. When using hydrogen peroxide all the peroxide was decomposed after 10 h, showing that niobium decompose easily hydrogen peroxide Montmorillonite K10 was ion-exchanged with polyhydroxyniobium characterized by XRD, TGA, adsorption-desorption of nitrogen and ICP. Then the material was calcined at 300, 500 e 900°C to obtain the Nb-pillared montmorillonite. These materials were characterized by XRD, and even when calcined at 900°C the microporosity is maintained, which is surprising since most of metal oxide pillared clays lose the microporosity at temperatures around 600°C. The montmorillonite K10 pure, niobium exchanged and Nb-pillared were used as acid catalysts in the oxirane ring-oppening reactions of the epoxidazed methyl oleate with methanol as nucleophile, to obtain the correspondent b-hydroxyether. The ion-exchanged clay was more active that the pure clay, proving than niobium incorporation improves Bronsted acidity. The calcined samples were less active the higher was the calcination temperature / Mestrado / Quimica Inorganica / Mestre em Química

The purpose of this thesis was to conduct preliminary research into the feasibility of using MCM-41 as a catalyst support material in the treatment of organochloride contaminated water. Specifically, the stability of MCM-41 in water and its efficiency as a Pd metal catalyst support in the degradation of trichloroethylene (TCE) was examined. MCM-41 is a mesoporous siliceous material that was developed by scientists with the Mobile Corporation in 1992. Since its development, MCM-41 has been the subject of a great deal of research into its potential application in catalytic sciences. The material possesses two especially notable characteristics. First, the diameter of its pores can be adjusted between 2 and 10 nm depending on the reagents and procedure used in its synthesis. Second, MCM-41 has an exceptionally high surface area, often in excess of 1 000 m2/g in well-formed samples. Other researchers have succeeded in grafting a variety of different catalytic materials to the surfaces and pores of MCM-41 and reported dehalogenation reactions proceeding in the presence of hydrogen. Thus, MCM-41 shows promise in treating a variety of chlorinated volatile organic compounds (cVOCs), such as chlorinated benzenes, trichloroethylene (TCE), perchloroethylene (PCE) and some polychlorinated biphenyls (PCBs). Preliminary stages of this research were devoted to synthesising a well-formed sample of MCM-41. The method of Mansour et al. (2002) was found to be a reliable and repeatable procedure, producing samples with characteristic hexagonal crystallinity and high surface areas. Crystallinity of all materials was characterized by small angle X-ray powder diffraction (XRD). Samples of MCM-41 prepared for this research exhibited a minimum of three distinct peaks in their XRD traces. These peaks are labelled 100, 110, and 200 according to a hexagonal unit cell. The 100 peak indicates that the sample is mesoporous. The 100, 110, and 200 peaks together indicate a hexagonal arrangement of the mesopores. An additional peak, labelled 210, was also observed in materials prepared for this research, reflecting a high degree of crystallinity. The position of the 100 peak was used to calculate the unit cell parameter - ???a??? - of the samples according to Bragg???s Law. The value of the unit cell parameter corresponds to the centre to centre distance of the material???s pores and thus the relative diameter of the pores themselves. The unit cell parameter of samples prepared for this research ranged from 4.6 nm to 5.3 nm with an average value of 4.8 nm. Surface areas of prepared samples were determined by BET nitrogen adsorption analysis and ranged from 1 052 to 1 571 m2/g with an average value of 1 304 m2/g. Field emission scanning electron microscope (SEM) images of a representative sample of MCM-41 revealed a particle morphology referred to as ???wormy MCM-41??? by other researchers. A sample of aluminum-substituted MCM-41 (Al-MCM-41) was also synthesized. The crystallinity of Al-MCM-41 was characterized by small angle XRD. The XRD trace of the material showed only one distinct peak centred at 2.1 degrees 2??. The 110 and 200 peaks seen in MCM-41 were replaced by a shoulder on the right hand side of the 100 peak. The shape of this trace is typical of Al-MCM-41 prepared by other researchers and is indicative of the lower structural quality of the material, i.e. a less-ordered atomic arrangement in Al-MCM-41 compared to that of regular MCM-41. The unit cell parameter of the Al-MCM-41 sample was 4.9 nm. The surface area of the sample was determined through BET nitrogen adsorption analysis and found to be 1 304 m2/g. Attempts were made to synthesize an MCM-41 sample with enlarged pores. Difficulties were encountered in the procedure, specifically with regards to maintaining high pressures during the crystallization stage. Higher temperatures used during these procedures caused failure of the O-ring used in sealing the autoclave, allowing water to be lost from the reaction gel. Samples generated in these attempts were amorphous in character and were subsequently discarded. A solubility study involving MCM-41 was undertaken to determine the stability of the material in water at ambient temperature and pressure. The experiment included several different solid/water ratios for the dissolution experiments: 1/200, 1/100, 1/75, 1/25. Results indicated that MCM-41 is metastable at ambient temperatures and more soluble than amorphous silica in water. The maximum silica concentration observed during the experiment was used to calculate a minimum Gibbs free energy of formation for MCM-41 of - 819.5 kJ/mol. The higher free energy value compared to quartz (- 856.288 kJ/mol) is indicative of the metastability of the material in water. Supersaturation with respect to amorphous silica was observed in samples prepared with relatively high concentrations of MCM-41. A subsequent decrease in dissolved silica concentration with time in these samples represented precipitation of amorphous silica, driving the concentration downward towards saturation with respect to this phase (120 ppm). The equilibrium concentration of 120 ppm recorded in these samples represented 4.8 mg out of 200, 400, 500, and 1 600 mg of initial MCM-41 dissolving into solution in the solid/liquid ratios of 1/200, 1/100, 175, and 1/25, respectively. Supersaturation with respect to amorphous silica did not occur in experiments with very low solid/water ratios. It also did not occur in higher solid/water experiments from which the SiO2 saturated supernatant was decanted and replaced with fresh deionized water after two weeks of reaction. The difference in dissolution behaviour is believed to result from deposition of a protective layer of amorphous silica from solution onto the MCM-41 surfaces, which reduces their dissolution rate. Thus, supersaturation with respect to amorphous silica is only manifested at early time and only when relatively large amounts of fresh MCM-41 are added to water. The solubility experiment was repeated using samples of Al-MCM-41 to determine the effect of Al substitution on the stability of the MCM-41. Dissolution curves for the Al-MCM-41 samples revealed behaviour that was analogous to that of the silica-based MCM-41 at similar solid/water ratios. Substitution of Al into the structure of MCM-41 appeared to have no positive or negative effects on the stability of the material in water. Solid MCM-41 material was recovered on days 28 and 79 of the solubility experiment and dried under vacuum. Solid material was also recovered from the Al-MCM-41 solubility experiment on day 79. These recovered samples were characterized by XRD and BET nitrogen adsorption analysis. An increase in background noise in the XRD plot of MCM-41 from the fresh to the 79 d sample indicated an increased proportion of an amorphous phase in the sample. The XRD plot of the 79 d sample of Al-MCM-41 also showed increased background noise corresponding to an increased proportion of an amorphous phase. The increased amorphous phase would have resulted from the continuous dissolution of the crystalline MCM-41 and reprecipitation as amorphous silica in the samples. BET surface area analysis of recovered MCM-41 compared to the freshly prepared material showed no significant change in surface area after 28 and 79 days in water. Analysis of the 79 d Al-MCM-41 indicated a 10% decrease in surface area relative to the as-prepared material. A set of SEM images were taken of the day 28 and 79 MCM-41 samples and compared to a sample of freshly prepared material. No substantial change in morphology was observed in the day 28 sample when compared to the fresh material. Some change was noted in the day 79 sample particle morphology, with worm-like structures appearing to be better developed than in the as-synthesized material. A series of palladized MCM-41 (Pd/MCM-41) samples with varying mass percent loadings of Pd was prepared to investigate the dehalogenation efficiency of Pd/MCM-41 in contact with TCE. TCE degradation was investigated in batch experiments. MCM-41 samples were prepared with calculated Pd loadings of 0.1, 1, and 5 mass %. The actual palladium content of the materials was determined using an EDAX-equipped SEM. The success of the loading technique was better at lower mass loadings of Pd, i.e. there was a greater deviation of actual Pd content from targeted or calculated contents at higher loadings of Pd. It was found that a procedure designed to yield 1% by mass Pd/MCM-41 produced an average loading of 0.95% Pd by mass. A procedure designed to produce a 5% Pd/MCM-41 sample resulted in an average loading of 2.6 mass %. These deviations were attributed to error inherent in the EDAX analysis and reduced effectiveness of the loading technique at higher Pd concentrations. All batch experiment reaction bottles were prepared with solid/liquid ratios of 1/800. The various Pd/MCM-41 samples induced rapid dehalogenation reactions, with the maximum extent of TCE degradation occurring before the first sample was taken at 7 to 12 min and within 35 min in the case of 0.1% Pd/MCM-41. The 0.1% Pd/MCM-41 sample degraded 70% of total TCE in solution with an estimated degradation half-life of 14 min. The 1% Pd/MCM-41 sample degraded 92% of total TCE in solution with an estimated half life of between 3 and 6 min. The 5% Pd/MCM-41 sample degraded only 22% of total TCE in solution; degradation half-life could not be determined. The seemingly paradoxical result of lower degradation efficiency at higher Pd loadings is proposed to result from absorption of hydrogen from solution by Pd, which is unreactive relative to the dissolved hydrogen in solution. Production of reaction intermediates and daughter products was also lower in the 1% by mass Pd/MCM-41 experiment compared to the 0.1 and 5% by mass Pd/MCM-41. Analysis of degradation products results from the experiments indicated that TCE degrades to ethane in the presence of Pd/MCM-41 with relatively low concentrations of chlorinated daughter products resulting from a random desorption process. A batch experiment using pure silica MCM-41 was also conducted to determine if there was adsorption of TCE to the support material itself. A lack of change in TCE concentration between the control sample and the MCM-41 sample during the experiment indicated no significant adsorption of TCE onto MCM-41. The conclusion of this research is that although MCM-41 is relatively unstable in water, its high TCE degradation efficiency shows promise for its application in developing water treatment technologies. However, more research needs to be conducted to fully determine the potential use of MCM-41 in water treatment and to investigate ways to improve its long-term stability in water.

Made available in DSpace on 2014-06-12T18:02:35Z (GMT). No. of bitstreams: 2 arquivo164_1.pdf: 3053526 bytes, checksum: 2e5eafdf454df7889e3e5ba1c87ceb2a (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A corrosão por ácidos naftênicos a altas temperaturas nas unidades de refino é um dos maiores problemas nas refinarias de todo o mundo, uma vez que, podem causar envenenamento de catalisadores e paradas operacionais de alto custo. Os ácidos naftênicos correspondem a uma mistura complexa de ácidos carboxílicos presentes no petróleo, responsáveis diretamente pela sua acidez e corrosividade. Tais compostos também estão presentes nas frações destiladas do petróleo, causando diversos problemas na qualidade final do produto. Dentre estas frações do petróleo pode-se destacar o querosene de aviação (QAV) que é produzido através do fracionamento por destilação à pressão atmosférica. Os óleos nacionais estão cada vez mais ácidos, estimulando a busca por novos e eficientes métodos de mitigação. Métodos propostos por estudos científicos e industriais para minimizar a corrosão provocada por ácidos naftênicos vêm apresentando custos elevados e problemas de operação. O processo de adsorção tem a vantagem da possibilidade de recuperação dos ácidos orgânicos, que são precursores de surfactantes e aditivos para lubrificantes, não havendo formação de resíduos poluentes e contribuindo com o meio ambiente. As peneiras moleculares mesoporosas (MCM-41) vêm despertando grande interesse na comunidade científica em função da perspectiva da sua aplicação em processos de adsorção e catálise. A fim de reduzir o alto custo dos processos de separação por adsorção, principalmente devido ao elevado valor de alguns adsorventes, a utilização de resíduos agroindustriais como adsorventes vem se destacando como método alternativo. O objetivo deste trabalho foi a remoção da acidez naftênica de uma mistura modelo de QAV (ácido dodecanóico em ndodecano) com uso do adsorvente Sr-MCM-41 e de adsorvente preparado a partir de resíduo agroindustrial. No presente trabalho foi sintetizada a peneira molecular mesoporosa Sr-MCM- 41, na qual a incorporação do estrôncio resultou no aumento da basicidade do material e consequentemente da sua afinidade pelos ácidos. O adsorvente Sr-MCM-41 foi caracterizado por análise termogravimétrica (TG) e termogravimétrica diferencial (DTG), difração de raios- X (DRX), medida de área superficial por adsorção de N2 (BET), espectrometria de emissão óptica com plasma indutivamente acoplado (ICP-OES) e espectroscopia na região do infravermelho com transformada de Fourier (FT-IR). Os resultados da caracterização deste material indicaram que a incorporação do estrôncio não comprometeu a estrutura mesoporosa e que os materiais sintetizados apresentaram um bom grau de organização. Foi utilizada a técnica de planejamento fatorial para otimização do processo adsortivo visando a determinação das melhores condições de operação. Em seguida foram realizados estudos de cinética e equilíbrio de adsorção com o adsorvente Sr-MCM-41, obtendo-se como capacidade máxima adsortiva 2,0 gácido.g-1 adsorvente, a partir do estudo de equilíbrio de adsorção. Os dados de equilíbrio foram ajustados a isoterma de BET tipo IV. A cinética de adsorção foi modelada considerando-se um modelo de força motriz linear. Também foi preparado o carvão ativado a partir da casca da laranja, o qual foi caracterizado através da medida de área superficial por adsorção de N2 (BET) apresentando isoterma do tipo I, característica de materiais microporosos e foram realizados testes para avaliação de sua capacidade adsortiva que foi em torno de 0,40 gácido.g-1 adsorvente. O estudo de adsorção utilizando a Sr-MCM-41 apresentou significativa eficiência, uma vez que o adsorvente apresentou uma alta capacidade adsortiva. Para o adsorvente carvão ativado preparado a partir da casca da laranja constatou-se a potencialidade de sua aplicação por ser um resíduo agroindustrial, porém, verificou-se a necessidade de um estudo mais detalhado

Made available in DSpace on 2014-12-17T15:42:29Z (GMT). No. of bitstreams: 1 MirnaFF_TESE.pdf: 7322446 bytes, checksum: 0ef1d9562cc97f24609fa13f5580a92e (MD5) Previous issue date: 2013-04-29 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Statistics of environmental protection agencies show that the soil has been contaminated with problems often resulting from leaks, spills and accidents during exploration, refining, transportation and storage oil operations and its derivatives. These, gasoline noteworthy, verified by releasing, to get in touch with the groundwater, the compounds BTEX (benzene, toluene, ethylbenzene and xylenes), substances which are central nervous system depressants and causing leukemia. Among the processes used in remediation of soil and groundwater contaminated with organic pollutants, we highlight those that use hydrogen peroxide because they are characterized by the rapid generation of chemical species of high oxidation power, especially the hydroxyl radical ( OH), superoxide (O2 -) and peridroxil (HO2 ), among other reactive species that are capable of transforming or decomposing organic chemicals. The pH has a strong effect on the chemistry of hydrogen peroxide because the formation of different radicals directly depends on the pH of the medium. In this work, the materials MCM-41 and Co-MCM-41 were synthesized and used in the reaction of BTEX removal in aqueous media using H2O2. These materials were synthesized by the hydrothermal method and the techniques used to characterize were: XRD, TG/DTG, adsorption/desorption N2, TEM and X-Ray Fluorescence. The catalytic tests were for 5 h of reaction were carried out in reactors of 20 mL, which was accompanied by the decomposition of hydrogen peroxide by molecular absorption spectrophotometry in the UV-Vis, in addition to removal of organic compounds BTEX was performed as gas chromatography with detection photoionization and flame ionization and by static headspace sampler. The characterizations proved that the materials were successfully synthesized. The catalytic tests showed satisfactory results, and the reactions containing BTEX + Co-MCM-41 + H2O2 at pH = 12.0 had the highest percentages of removal for the compounds studied / Dados estat?sticos das ag?ncias de prote??o ambiental demonstram que o solo tem sido contaminado frequentemente com problemas decorrentes de vazamentos, derrames e acidentes durante a explora??o, refino, transporte e opera??es de armazenamento do petr?leo e seus derivados. Destes, a gasolina merece destaque, verificado pela libera??o, ao entrar em contanto com a ?gua subterr?nea, dos compostos BTEX (benzeno, tolueno, etilbenzeno e xilenos), que s?o subst?ncias depressoras do sistema nervoso central e causadoras de leucemia. Dentre os processos utilizados em remedia??o de solos e ?guas contaminadas por poluentes org?nicos, destacam-se os que utilizam o per?xido de hidrog?nio por serem caracterizados pela r?pida gera??o de esp?cies qu?micas de alto poder de oxida??o, principalmente o radical hidroxil ( OH), super?xido (O2 -) e peridroxil (HO2 ), dentre outras esp?cies reativas que s?o capazes de transformar ou decompor produtos qu?micos org?nicos. O pH tem um forte efeito na qu?mica do per?xido de hidrog?nio, pois a forma??o dos diferentes radicais depende diretamente do pH do meio. Neste trabalho, os materiais MCM-41 e Co-MCM-41 foram sintetizados e utilizados na rea??o de remo??o dos BTEX em meio aquoso utilizando H2O2. Estes materiais foram sintetizados atrav?s do m?todo hidrot?rmico e as t?cnicas utilizadas na caracteriza??o foram: DRX, TG/DTG, adsor??o/dessor??o de N2, MET e Fluoresc?ncia de Raios-X. Os testes catal?ticos ocorreram durante 5 horas de rea??o e foram realizados em reatores de 20 mL, onde foi acompanhada a decomposi??o do per?xido de hidrog?nio por espectrofotometria de absor??o molecular na regi?o do UV-Vis, al?m da remo??o dos compostos org?nicos BTEX que foi realizada por cromatografia em fase gasosa com detec??o por fotoioniza??o e ioniza??o de chama e amostrador por headspace est?tico. As caracteriza??es comprovaram que os materiais foram sintetizados com sucesso. Os testes catal?ticos apresentaram resultados satisfat?rios, sendo que as rea??es contendo BTEX + Co- MCM-41 + H2O2 em pH = 12,0 apresentaram os maiores percentuais de remo??o para os compostos estudados

The purpose of this thesis was to conduct preliminary research into the feasibility of using MCM-41 as a catalyst support material in the treatment of organochloride contaminated water. Specifically, the stability of MCM-41 in water and its efficiency as a Pd metal catalyst support in the degradation of trichloroethylene (TCE) was examined. MCM-41 is a mesoporous siliceous material that was developed by scientists with the Mobile Corporation in 1992. Since its development, MCM-41 has been the subject of a great deal of research into its potential application in catalytic sciences. The material possesses two especially notable characteristics. First, the diameter of its pores can be adjusted between 2 and 10 nm depending on the reagents and procedure used in its synthesis. Second, MCM-41 has an exceptionally high surface area, often in excess of 1 000 m2/g in well-formed samples. Other researchers have succeeded in grafting a variety of different catalytic materials to the surfaces and pores of MCM-41 and reported dehalogenation reactions proceeding in the presence of hydrogen. Thus, MCM-41 shows promise in treating a variety of chlorinated volatile organic compounds (cVOCs), such as chlorinated benzenes, trichloroethylene (TCE), perchloroethylene (PCE) and some polychlorinated biphenyls (PCBs). Preliminary stages of this research were devoted to synthesising a well-formed sample of MCM-41. The method of Mansour et al. (2002) was found to be a reliable and repeatable procedure, producing samples with characteristic hexagonal crystallinity and high surface areas. Crystallinity of all materials was characterized by small angle X-ray powder diffraction (XRD). Samples of MCM-41 prepared for this research exhibited a minimum of three distinct peaks in their XRD traces. These peaks are labelled 100, 110, and 200 according to a hexagonal unit cell. The 100 peak indicates that the sample is mesoporous. The 100, 110, and 200 peaks together indicate a hexagonal arrangement of the mesopores. An additional peak, labelled 210, was also observed in materials prepared for this research, reflecting a high degree of crystallinity. The position of the 100 peak was used to calculate the unit cell parameter - “a” - of the samples according to Bragg’s Law. The value of the unit cell parameter corresponds to the centre to centre distance of the material’s pores and thus the relative diameter of the pores themselves. The unit cell parameter of samples prepared for this research ranged from 4.6 nm to 5.3 nm with an average value of 4.8 nm. Surface areas of prepared samples were determined by BET nitrogen adsorption analysis and ranged from 1 052 to 1 571 m2/g with an average value of 1 304 m2/g. Field emission scanning electron microscope (SEM) images of a representative sample of MCM-41 revealed a particle morphology referred to as ‘wormy MCM-41’ by other researchers. A sample of aluminum-substituted MCM-41 (Al-MCM-41) was also synthesized. The crystallinity of Al-MCM-41 was characterized by small angle XRD. The XRD trace of the material showed only one distinct peak centred at 2.1 degrees 2θ. The 110 and 200 peaks seen in MCM-41 were replaced by a shoulder on the right hand side of the 100 peak. The shape of this trace is typical of Al-MCM-41 prepared by other researchers and is indicative of the lower structural quality of the material, i.e. a less-ordered atomic arrangement in Al-MCM-41 compared to that of regular MCM-41. The unit cell parameter of the Al-MCM-41 sample was 4.9 nm. The surface area of the sample was determined through BET nitrogen adsorption analysis and found to be 1 304 m2/g. Attempts were made to synthesize an MCM-41 sample with enlarged pores. Difficulties were encountered in the procedure, specifically with regards to maintaining high pressures during the crystallization stage. Higher temperatures used during these procedures caused failure of the O-ring used in sealing the autoclave, allowing water to be lost from the reaction gel. Samples generated in these attempts were amorphous in character and were subsequently discarded. A solubility study involving MCM-41 was undertaken to determine the stability of the material in water at ambient temperature and pressure. The experiment included several different solid/water ratios for the dissolution experiments: 1/200, 1/100, 1/75, 1/25. Results indicated that MCM-41 is metastable at ambient temperatures and more soluble than amorphous silica in water. The maximum silica concentration observed during the experiment was used to calculate a minimum Gibbs free energy of formation for MCM-41 of - 819.5 kJ/mol. The higher free energy value compared to quartz (- 856.288 kJ/mol) is indicative of the metastability of the material in water. Supersaturation with respect to amorphous silica was observed in samples prepared with relatively high concentrations of MCM-41. A subsequent decrease in dissolved silica concentration with time in these samples represented precipitation of amorphous silica, driving the concentration downward towards saturation with respect to this phase (120 ppm). The equilibrium concentration of 120 ppm recorded in these samples represented 4.8 mg out of 200, 400, 500, and 1 600 mg of initial MCM-41 dissolving into solution in the solid/liquid ratios of 1/200, 1/100, 175, and 1/25, respectively. Supersaturation with respect to amorphous silica did not occur in experiments with very low solid/water ratios. It also did not occur in higher solid/water experiments from which the SiO2 saturated supernatant was decanted and replaced with fresh deionized water after two weeks of reaction. The difference in dissolution behaviour is believed to result from deposition of a protective layer of amorphous silica from solution onto the MCM-41 surfaces, which reduces their dissolution rate. Thus, supersaturation with respect to amorphous silica is only manifested at early time and only when relatively large amounts of fresh MCM-41 are added to water. The solubility experiment was repeated using samples of Al-MCM-41 to determine the effect of Al substitution on the stability of the MCM-41. Dissolution curves for the Al-MCM-41 samples revealed behaviour that was analogous to that of the silica-based MCM-41 at similar solid/water ratios. Substitution of Al into the structure of MCM-41 appeared to have no positive or negative effects on the stability of the material in water. Solid MCM-41 material was recovered on days 28 and 79 of the solubility experiment and dried under vacuum. Solid material was also recovered from the Al-MCM-41 solubility experiment on day 79. These recovered samples were characterized by XRD and BET nitrogen adsorption analysis. An increase in background noise in the XRD plot of MCM-41 from the fresh to the 79 d sample indicated an increased proportion of an amorphous phase in the sample. The XRD plot of the 79 d sample of Al-MCM-41 also showed increased background noise corresponding to an increased proportion of an amorphous phase. The increased amorphous phase would have resulted from the continuous dissolution of the crystalline MCM-41 and reprecipitation as amorphous silica in the samples. BET surface area analysis of recovered MCM-41 compared to the freshly prepared material showed no significant change in surface area after 28 and 79 days in water. Analysis of the 79 d Al-MCM-41 indicated a 10% decrease in surface area relative to the as-prepared material. A set of SEM images were taken of the day 28 and 79 MCM-41 samples and compared to a sample of freshly prepared material. No substantial change in morphology was observed in the day 28 sample when compared to the fresh material. Some change was noted in the day 79 sample particle morphology, with worm-like structures appearing to be better developed than in the as-synthesized material. A series of palladized MCM-41 (Pd/MCM-41) samples with varying mass percent loadings of Pd was prepared to investigate the dehalogenation efficiency of Pd/MCM-41 in contact with TCE. TCE degradation was investigated in batch experiments. MCM-41 samples were prepared with calculated Pd loadings of 0.1, 1, and 5 mass %. The actual palladium content of the materials was determined using an EDAX-equipped SEM. The success of the loading technique was better at lower mass loadings of Pd, i.e. there was a greater deviation of actual Pd content from targeted or calculated contents at higher loadings of Pd. It was found that a procedure designed to yield 1% by mass Pd/MCM-41 produced an average loading of 0.95% Pd by mass. A procedure designed to produce a 5% Pd/MCM-41 sample resulted in an average loading of 2.6 mass %. These deviations were attributed to error inherent in the EDAX analysis and reduced effectiveness of the loading technique at higher Pd concentrations. All batch experiment reaction bottles were prepared with solid/liquid ratios of 1/800. The various Pd/MCM-41 samples induced rapid dehalogenation reactions, with the maximum extent of TCE degradation occurring before the first sample was taken at 7 to 12 min and within 35 min in the case of 0.1% Pd/MCM-41. The 0.1% Pd/MCM-41 sample degraded 70% of total TCE in solution with an estimated degradation half-life of 14 min. The 1% Pd/MCM-41 sample degraded 92% of total TCE in solution with an estimated half life of between 3 and 6 min. The 5% Pd/MCM-41 sample degraded only 22% of total TCE in solution; degradation half-life could not be determined. The seemingly paradoxical result of lower degradation efficiency at higher Pd loadings is proposed to result from absorption of hydrogen from solution by Pd, which is unreactive relative to the dissolved hydrogen in solution. Production of reaction intermediates and daughter products was also lower in the 1% by mass Pd/MCM-41 experiment compared to the 0.1 and 5% by mass Pd/MCM-41. Analysis of degradation products results from the experiments indicated that TCE degrades to ethane in the presence of Pd/MCM-41 with relatively low concentrations of chlorinated daughter products resulting from a random desorption process. A batch experiment using pure silica MCM-41 was also conducted to determine if there was adsorption of TCE to the support material itself. A lack of change in TCE concentration between the control sample and the MCM-41 sample during the experiment indicated no significant adsorption of TCE onto MCM-41. The conclusion of this research is that although MCM-41 is relatively unstable in water, its high TCE degradation efficiency shows promise for its application in developing water treatment technologies. However, more research needs to be conducted to fully determine the potential use of MCM-41 in water treatment and to investigate ways to improve its long-term stability in water.

Solid state ¹H MAS NMR spectroscopy was used to investigate the temperature and hydration dependance of water and hydroxyl proton spectra of hydrated mesoporous MCM-41. The NMR spectra show a complex peak structure, with hydroxyl proton resonances seen in dry MCM-41 disappearing as water is introduced into the pores, and new peaks appearing representing water and hydrated silanol groups. Until now the assignment of these peaks was unclear and the consensus was that magnetization exchange played an important role in the coalescence of the various peaks which appear in the spectra. It was found recently that magnetization exchange is not necessary to produce the spectral featured observed [Niknam, M., M.Sc. Thesis, University of Waterloo (2010)]. In the present study a simplified model, based on chemical shift averaging by the making and breaking of hydrogen bonds as water undergoes rotational motion and translational self-diffusion on the pore surface, has been developed to explain the NMR spectral results. The model is able to reproduce the experimental ¹H MAS NMR spectra for all hydrations and temperatures studied. For the first time, definitive spectral assignments for all hydroxyl and water protons in the sample has been achieved. Spectral features arising due to temperature change have been explained by using the known result that the proton chemical shift of a hydrogen atom involved in hydrogen bonding varies linearly with temperature. Furthermore, it is reported for the first time, that with increasing hydration, water molecules begin to favour forming two hydrogen bonds to the surface. This may represent the first step in the pore filling process.

Solid state ¹H MAS NMR spectroscopy was used to investigate the temperature and hydration dependance of water and hydroxyl proton spectra of hydrated mesoporous MCM-41. The NMR spectra show a complex peak structure, with hydroxyl proton resonances seen in dry MCM-41 disappearing as water is introduced into the pores, and new peaks appearing representing water and hydrated silanol groups. Until now the assignment of these peaks was unclear and the consensus was that magnetization exchange played an important role in the coalescence of the various peaks which appear in the spectra. It was found recently that magnetization exchange is not necessary to produce the spectral featured observed [Niknam, M., M.Sc. Thesis, University of Waterloo (2010)]. In the present study a simplified model, based on chemical shift averaging by the making and breaking of hydrogen bonds as water undergoes rotational motion and translational self-diffusion on the pore surface, has been developed to explain the NMR spectral results. The model is able to reproduce the experimental ¹H MAS NMR spectra for all hydrations and temperatures studied. For the first time, definitive spectral assignments for all hydroxyl and water protons in the sample has been achieved. Spectral features arising due to temperature change have been explained by using the known result that the proton chemical shift of a hydrogen atom involved in hydrogen bonding varies linearly with temperature. Furthermore, it is reported for the first time, that with increasing hydration, water molecules begin to favour forming two hydrogen bonds to the surface. This may represent the first step in the pore filling process.

The recently discovered mesoporous molecular sieve MCM-41 was synthesized, modified, and characterized and proposed as an alternative adsorbent for VOC control. The synthesis conditions for pure-silica and aluminosilicate MCM-41 were optimized as follows: 4.5Na2O:30SiO2:5.2C16H33(CH3)3N + :2500H2O and 7.5Na2O:30SiO2:xAl2O3:7.2C16H33(CH3)3N + :3500H2O (x < 1), respectively, and at 373 K for 4 days. Our studies showed that MCM-41 is not stable in the presence of water vapor. For example, a hydrothermal treatment of MCM-41 at 723 K for 2 hour resulted in 50 % of structure collapses. Again, when a template-free MCM-41 sample was exposed to air with a relative humidity of 60 % for three months, almost total pore structure collapses were observed. Adsorption equilibrium results showed that MCM-41 has a narrow pore size distribution and exhibits extraordinary pore volume compared to the classical microporous adsorbents, such as molecular sieves and activated carbons. Despite the impressive adsorption capacities of this material, the Type IV isotherm behavior requires the VOCs, in the gas phase, to be at high partial pressure. This is not the case with most industrial VOC streams. A real VOC stream requires an adsorbent with not only a high adsorption capacity but also a high adsorption affinity at a low VOC concentration. To overcome the above mentioned two problems, both the surface chemistry and the pore-opening sizes of MCM-41 were modified. To modify the surface chemistry, one has to better understand the surface chemistry. Our pioneering study of the surface chemistry of MCM-41 using FTIR, 29 Si CP/MAS NMR, pyridine-TPD, and TGA demonstrated that three types of silanol groups, i.e. single, (SiO)3Si-OH, hydrogen-bonded, (SiO)3Si-OH---OH-Si(SiO)3 and geminal, (SiO)2Si(OH)2 are distributed over the surface of MCM-41. The number of silanol groups per unit nm 2 , aOH, varies between 2.5 and 3.0 depending on the template-removal method. To improve the hydrothermal stability and enhance the hydrophobicity, the surface chemistry of MCM-41 was modified by silylation. Though both the free and hydrogen-bonded SiOH groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol -1 , respectively, only the free SiOH groups are highly accessible to the silylating agent, chlorotrimethylsilane. The surface coverage of the modifying agent was found to has a linear relationship with the surface free silanol groups which can be controlled by different heating temperatures. Modification by silyaltion can significantly improve hydrophobicity and stability. Rehydration/dehydration experiments demonstrate that the surface-silylated MCM-41 is highly tolerable to water vapor due to the complete replacement of surface-hydrophilic silanols. A novel modification method, namely selective tailoring (ST), was developed to tailor the pore-opening sizes of MCM-41 (rather than the entire pores). The novelty is that only the pore mouths at both ends of a cylindrical pore of MCM-41 was modified by deposition of some alkoxides. By doing so, the types of adsorption isotherms of VOCs can be changed from Type IV to Type I while the pore volume can be significantly preserved. This is of course significance in VOC removal since the adsorption affinity has been drastically enhanced. Adsorption equilibria and kinetics for VOCs in the pore-opening-modified MCM-41 materials were measured, modeled and compared to that of activated carbons and hydrophobic molecular sieves. The pore-modified MCM-41 has a much higher adsorption capacity than that of the traditional microporous adsorbents such as activated carbons and molecular sieves. The adsorption equilibrium data fit the Langmuir-Uniform distribution (Unilan) models very well. Upon the equilibrium parameters being obtained and considering the pore structure of our pore-modified MCM-41 adsorbents, the kinetic data were further modeled using the literature-existed models recently developed by Do and coworkers, i.e. the constant surface diffusivity macropore, surface and micropore diffusion (CMSMD) model and the macropore and surface diffusion (MSD) model. Results demonstrated that the CMSMD model can predict our kinetic uptake curves reasonably fine. Some key kinetic parameters including pore and surface diffusivities, apparent diffusivity, activation energy for adsorption, and pore tortuosity factor can be readily obtained. The porosity of the MCM-41 materials were primarily evaluated using the traditional methods based on nitrogen adsorption/desorption data. Results indicated that the BJH method always underestimates the true pore diameter of MCM-41. An comparison plot (t-plot or as-plot) method was suggested and improved. Plotting of nitrogen adsorption data at 77 K versus the statistical film thickness reveals three distinct stages, with a characteristic of two points of inflection. The steep intermediate stage is caused by capillary condensation occurred in the highly uniform mesopores. From the slope of the section after condensation, the external surface area can be obtained. Therefore, the true surface area of the mesopores is readily calculated. The linear portion of the last section is extrapolated to the adsorption axis of the comparison plot, and this intercept is used to obtain the volume of the mesopores. From the surface area and pore volume, average mesopore diameter is calculated, and the value thus obtained is in good agreement with the pore dimension obtained from powder X-ray diffraction measurements. The principle of pore size calculation, the thickness of adsorbed nitrogen film, and the problems associated with the BJH method were discussed in detail. It has been found that at a given relative pressure, the smaller the pore radius, the thicker the adsorbed film. Thermodynamics analysis established that the stability of the adsorbed film is determined by interface curvature and the potential of interaction between adsorbate and adsorbent. A semi-empirical equation is proposed to describe the state of stable adsorbed films in cylindrical mesopores. It is also shown to be useful in calculations of pore size distributions of mesoporous solids. The desorption of four representative volatile organic compounds (VOCs), i.e. n-hexane, cyclohexane, benzene, and methanol from MCM-41 were also investigated and compared with the hydrophobic zeolite, silicalite-1, using the technique of temperature programmed desorption (TPD). The desorption energies of these organics to MCM-41 were evaluated and compared with the adsorption isosteric heats. The affinity of organics to MCM-41 and silicalite-1, which represents surface hydrophobicity/hydrophilicity were studied and discussed. Results showed that only one desorption peak can be found for all organics from MCM-41, different from that from the microporous adsorbents (activated carbons and hydrophobic molecular sieves). The activation energies for desorption of non-polar molecules are slightly higher than their latent heats of evaporation, whereas the activation energy for desorption of methanol is well above its latent heat of evaporation. These results are consistent with those derived from the adsorption isotherm measurements. The very high activation energy for the desorption of methanol is due to the hydrogen bonds between methanol molecules and silanol groups over MCM-41 surfaces. The affinity of volatile organics to MCM-41 are in the order of methanol > n-hexane > benzene > cyclohexane.

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-02-26T16:11:44Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 5.-Tesis doutorado Yesmin 2015 UFPE Bibliot.pdf: 2813580 bytes, checksum: c994d000e414c2f79bd7b8711d5f2714 (MD5) / Made available in DSpace on 2016-02-26T16:11:44Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 5.-Tesis doutorado Yesmin 2015 UFPE Bibliot.pdf: 2813580 bytes, checksum: c994d000e414c2f79bd7b8711d5f2714 (MD5) Previous issue date: 2015-06-05 / CAPES / CNPq / FACEPE / Neste trabalho, apresentamos a síntese e caracterização do material mesoporoso MCM-41 para o desenvolvimento de capacitores MOS. A motivação deste trabalho deve-se às propriedades interessantes que MCM-41 apresenta, tais como: área superficial e volume de poro grande e estrutura ordenada de poros. Inicialmente apresentamos a síntese do material mesoporoso MCM-41 pelo método Sol-Gel, e sua caracterização estrutural (DRX e IV), morfológica (MEV e TEM) e texturais (Análise de Adsorção e Dessorção de Nitrogênio), e fazemos uma comparação de resultados com o mesmo material produzido pela Sigma-Aldrich. Também foram obtidos filmes pelo método químico, que foram caracterizados por MEV e DRX e em seguida foram fabricados capacitores MOS. As medidas elétricas do capacitor MOS com dielétrico de MCM-41 foram comparadas com capacitores com dielétrico de SiO2 térmico. Os resultados mostraram uma clara diferença nas curvas de Corrente-Tensão. Conclui-se que a água confinada dentro do filme dielétrico é associada com os valores elevada de capacitância por unidade de área, estes valores permanecem altos depois do aquecimento, indicando que a resposta dielétrica é devida á água ligada ao material dielétrico, formando camadas paralelas á superfície do substrato. Capacitores de MCM-41 foram expostos a vários solventes polares e apolares, assim como á radiação gama e apresentaram distorção na resposta da capacitância e deslocamento nas curvas de corrente – tensão. Finalmente, capacitores de MCM-41 foram hidrolisados com o objetivo de aumentar a concentração dos grupos silanol na superfície do MCM-41 e como consequência alterar a capacitância do dispositivo. / In this work, we report the synthesis and characterization of MCM-41 mesoporous material for the development of devices types MOS capacitors. The motivation of this work is due to the MCM-41 interesting properties such as: surface area and pore volume large and pore ordered structure. Initially, we present a synthesis of MCM-41 mesoporous material by sol-gel method and their structural characterization (XRD and IR), morphological (SEM and TEM) and texture (Nitrogen Desorption and Adsorption Analysis) and make a comparison with the same material produced by Sigma. Also, films were obtained by chemical method, which were characterized by SEM and XRD, and then MOS capacitors were fabricated. The electrical characteristics MCM-4 MOS capacitors were compared with thermal SiO2, the results showing a clear difference in the voltage-current curves. It concludes that water confined within the dielectric film is associated with high values of capacitance per unit area these values remain high even after heating, indicating a dielectric response due to water strongly bonded to the dielectric material forming layers parallel to the substrate surface. The MCM-41 capacitors were exposed to various polar and nonpolar solvents and gamma radiation and showed good results were due to variations in the response to capacitance and the voltage-current curves showed displacement and distortion. Finally, the MCM-41 capacitors were hydrolyzed in order to be able to increase the concentration of silanol groups on the surface of MCM-41; as a consequence the material is more sensitive to moisture and therefore, the capacitance of the device response.