New carbon xerogel-TiO2 composites with high performance as visible-light photocatalysts for dye mineralization

•Carbon xerogels-TiO2 composites were prepared by sol-gel synthesis.•TiO2 nanoparticles are highly and homegeneously dispersed on the carbon matrix.•Carbonization induces the formation of oxygen vacancies.•The synergetic behaviour provokes band gap tuning and photocatalytic activity under visible light.•Dye is totally mineralized avoiding toxicity in water.

A series of carbon xerogels-TiO2 samples was prepared by sol-gel synthesis, modifying the synthesis procedure to have carbon-TiO2 composite or TiO2-coated materials. Textural, morphological and chemical properties were extensively characterized and correlated with the photocatalytic activity. In the case of composites, a homogeneous and highly mesoporous structure is formed, where the intimate contact between both phases allows a high and homogeneous dispersion of TiO2 nanoparticles. During carbonization, the formation of oxygen vacancies is favoured, but the transition anatase to rutile is avoided by the carbon matrix. In the case of coated samples, microporous materials structured as microspheres were obtained, TiO2 present a greater crystal size and some transformation to rutile. The synergetic role of carbon phase and the formation of oxygen vacancies in the TiO2-phase contribute to narrow the composite band gap in such a manner that all samples are active under visible radiation reaching the total mineralization of the pollutant and the elimination of the toxicity.

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