Preparação e caracterização óptica de filmes finos de sílica/orgânico dopados com molibdênio
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2018-12-06
Autores
Scarpa, Elaine Ziviani [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Filmes fotocrômicos dopados com heteropoliânions de molibdênio apresentam interessantes propriedades ópticas e fotocatalíticas com aplicações em inúmeras áreas desde materiais para optoeletrônica até células de combustível e energia. Neste trabalho materiais híbridos de sílica/orgânico dopados com o ácido fosfomolíbdico, H3PMo12O40, (HPMo) foram preparados na forma de filmes finos para estudo das propriedades ópticas e fotossensibilidade por exposição dos filmes finos a radiação ultravioleta. A matriz de sílica/orgânico no estado coloidal foi sintetizada através do processo sol-gel a partir da hidrolise ácida dos alcóxidos de silício 3-glicidoxipropiltrimetoxisilano (GPTS) e tetraetilortosilicato (TEOS). A matriz de sílica/Orgânico foi dopada com HPMo dissolvido em acetonitrila (ACN) e tetrahidrofurano (THF) e um segundo conjunto de amostras dopada com HPMo:THF e HPMo:ACN com a adição de Cloreto de Cobre (CuCl). Filmes finos fotossensíveis foram preparados por deposição das matrizes coloidais de sílica/orgânico dopadas com HPMo:ACN e HPMo:THF (HA e HT) e dopadas com HPMo:ACN:CuCl e HPMo:THF:CuCl (HAC e HTC). Pela técnica de absorção óptica e/ou transmitância na região do UV/VIS foi possível estudar os processos fotossensíveis nestas amostras, como o surgimento de bandas de absorção na região UV-VIS após exposição das amostras a luz UV (fotoescurecimento por redução do Mo+6→ Mo+5) e a velocidade do processo (constantes de tempo) e sua reversibilidade (clareamento, Mo+5→ Mo+6). Os conjuntos de amostras HA, HT, e HAC, HTC apresentaram intenso fotocromismo reversível, sendo que as amostras com adição de CuCl (HAC, HTC) apresentaram maior velocidade para o processo de clareamento comparado as amostras sem cobre. Medidas de transmitância in situ em 780 nm durante a exposição das amostras ao UV e após cessada a exposição ao UV com a amostra submetida a diferentes temperaturas durante o processo possibilitaram determinar as constantes de tempo do processo de clareamento que é ativado termicamente. A partir das constantes de tempo de clareamento para diferentes temperaturas determinamos a energia de ativação das diferentes composições de amostras. As amostras HA e HAC apresentaram energia de ativação de 24,9 KJ/mol e 20,7 KJ/mol, respectivamente, e as amostras HT e HTC apresentaram energia de ativação de 28,0 KJ/mol e 13,9 KJ/mol, respectivamente. Nos casos dos dois solventes utilizados com o molibdênio, as amostras com adição de cobre apresentaram menor energia de ativação do processo de clareamento.
Photochromic films doped with molybdenum heteropolyanion present interesting optical and photocatalytic properties with applications in several areas such as optoelectronics, fuel cells and energy. In this work thin films of Silica/organic hybrid materials doped with phosphomolybdic acid H 3 PMo 12 O 40 , (HPMo) were prepared for the study of the photosensitivity with exposition to UV light. Colloidal Silica/organic hybrid matrix was synthesized by sol-gel process via acid hydrolysis of 3- glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS) silicon alkoxides. The colloidal Silica/organic matrix was doped with HPMo dissolved into acetonitrile (ACN) and tetrahydrofuran (THF) and also HPMo in ACN and HPMo in THF with addition of copper chloride (CuCl). Photosensitive thin films were deposited by dip- coating from Silica/organic colloidal matrix doped with HPMo:ACN and HPMo:THF (HA e HT) and also HPMo:ACN:CuCl e HPMo:THF:CuCl (HAC e HTC). The photosensitivity of the samples was studied by UV-VIS optical absorption spectroscopy allowing indentifying the rising of absorption bands aroud 780 nm after UV irradiation of the films (photodarkening related to Mo +6 → Mo +5 ) and also the reversibility of the process without UV (bleaching due to Mo +5 → Mo +6 ). Samples HA, HT, e HAC, HTC showed strong reversible photodarkening and the samples doped with copper (HAC, HTC) showed a faster bleaching process compared with samples without copper. Optical transmittance at 780 nm was measured in-situ during samples UV irradiation and also after UV irradiation at different samples temperature allowing determining the time constants of the bleaching process and also the activation energy for the different samples compositions. Film samples HA and HAC presented activation energy of 24,9 KJ/mol and 20,7 KJ/mol, respectively, and the film samples HT and HTC presented activation energy of 28,0 KJ/mol and 13,9 KJ/mol, respectively. In both cases of the two solvents used with molybdenum, the film samples with copper showed lower activation energy for the bleaching process.
Photochromic films doped with molybdenum heteropolyanion present interesting optical and photocatalytic properties with applications in several areas such as optoelectronics, fuel cells and energy. In this work thin films of Silica/organic hybrid materials doped with phosphomolybdic acid H 3 PMo 12 O 40 , (HPMo) were prepared for the study of the photosensitivity with exposition to UV light. Colloidal Silica/organic hybrid matrix was synthesized by sol-gel process via acid hydrolysis of 3- glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS) silicon alkoxides. The colloidal Silica/organic matrix was doped with HPMo dissolved into acetonitrile (ACN) and tetrahydrofuran (THF) and also HPMo in ACN and HPMo in THF with addition of copper chloride (CuCl). Photosensitive thin films were deposited by dip- coating from Silica/organic colloidal matrix doped with HPMo:ACN and HPMo:THF (HA e HT) and also HPMo:ACN:CuCl e HPMo:THF:CuCl (HAC e HTC). The photosensitivity of the samples was studied by UV-VIS optical absorption spectroscopy allowing indentifying the rising of absorption bands aroud 780 nm after UV irradiation of the films (photodarkening related to Mo +6 → Mo +5 ) and also the reversibility of the process without UV (bleaching due to Mo +5 → Mo +6 ). Samples HA, HT, e HAC, HTC showed strong reversible photodarkening and the samples doped with copper (HAC, HTC) showed a faster bleaching process compared with samples without copper. Optical transmittance at 780 nm was measured in-situ during samples UV irradiation and also after UV irradiation at different samples temperature allowing determining the time constants of the bleaching process and also the activation energy for the different samples compositions. Film samples HA and HAC presented activation energy of 24,9 KJ/mol and 20,7 KJ/mol, respectively, and the film samples HT and HTC presented activation energy of 28,0 KJ/mol and 13,9 KJ/mol, respectively. In both cases of the two solvents used with molybdenum, the film samples with copper showed lower activation energy for the bleaching process.
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Palavras-chave
Sol-gel, Sílica/orgânico, Filmes fotossensíveis, Fotocromismo, Molibdênio, Silica/organic, Photosensitive films, Photochromism, Molybdenum