This work deals on the preparation of silicon oxycarbide (SiOC) and silicon boron oxycarbide (SiBOC) ceramics from pyrolysis involving alkoxysilanes with different organic groups. Boron content, organic substituent and annealing time were evaluated on crystallization and composition of resulting ceramics. B-free precursors composed of methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES) and vinyltrimethoxysilane (VTMS) were obtained by the sol-gel method, whilst B-containing precursors were prepared by adding to each alkoxysilane a proper amount of boric acid resulting in B/Si atomic ratios of 0.1 and 0.5. Precursors were pyrolyzed at 1500 ºC for 1 and 3 h to produce respective SiOC and SiBOC ceramics. X-ray diffraction (XRD) patterns revealed enhanced SiC phase crystallization for PTES-derived ceramics, followed by those containing vinyl and methyl groups, which was also confirmed by X-ray photoelectron spectroscopy (XPS) from percentages of SiºC and Si?O bonds. Csp2 and Csp3 amounts varied among ceramics, indicating direct influence of organic substituent on conductive carbon phase development. Boron addition induced the growth of SiC crystallites, having more evident effect in matrices with higher proportions of amorphous fraction and lower residual carbon amounts. Organic group nature, boron content and annealing time played an important role for production and evolution of SiC and C phases into ceramics.

No presente trabalho foram confeccionados de maneira simples e eficiente fotoeletrodos baseados em ZnO produzidos a partir de síntese de combustão, diretamente na superfície de óxido de índio dopado com estanho (ITO), na presença de diferentes combustíveis: ácido cítrico, glicina e ureia, submetidos a tratamento térmico em 500 e 600 ºC. Os filmes foram caracterizados por análise termogravimétrica, difratometria de raios X, Raman, refletância difusa, microscopia eletrônica de varredura e medidas eletroquímicas, na presença e ausência de luz. O poder redutor de cada combustível investigado, bem como baixas temperaturas de tratamento térmico foram determinantes para a área superficial disponível dos materiais de ZnO formados. A completa conversão a óxido de zinco a baixas temperaturas de calcinação, bem como o tamanho das partículas foram determinantes para a eficiência fotoeletrocatalítica. O fotoeletrodo obtido ao utilizar a glicina como combustível da síntese e tratado a 500 ºC, por 2 h, apresentou melhor resposta em relação a fotocorrente (103 µA cm-2 mg-1) e aos parâmetros cinéticos (22,9 × 10-3 min-1 cm-2 mg-1) para a fotoeletrocatálise do corante azul de metileno, sob irradiação UV.

In this work photoelectrodes based on ZnO produced from combustion synthesis were prepared in a simple and efficient way, directly on the surface of indium tin oxide (ITO), in the presence of different fuels: citric acid, glycine and urea, and undergoing heat treatment at 500 and 600 ºC. The films were characterized by thermogravimetric analysis, X-ray diffraction, Raman, diffuse reflectance spectroscopy, scanning electron microscopy and electrochemical measurements in the presence and absence of light. The reducing power of each fuel was investigated, as well as low temperature heat treatment was crucial to the available surface area of the formed ZnO materials. The complete conversion to zinc oxide at low calcination temperatures, as well as the particle size were crucial for the photoeletrocatalytic efficiency, since the photoelectrode fuel obtained with glycine and treated at 500 ºC showed better response of the photocurrent (103 µA cm-2 mg-1) and the kinetic parameters (22.9 × 10-3 min-1 cm-2 mg-1) for the photoelectrocatalysis of methylene blue dye under UV irradiation.