Hydrothermal synthesis of Ti3+-self-doped TiO2 photocatalysts using wool fibers as a biotemplate

Abstract

A biotemplate method was used for the synthesis of self-doped TiO2 photocatalysts via the impregnation of sheep wool fibers with a solution containing titanium hydroxocomplexes under mild hydrothermal conditions (115 °C, 170 kPa), followed by the removal of the wool template during calcination in air at 600 °C. An intermediate wool-TiO2 composite, formed as a product of hydrothermal impregnation of a wool biotemplate, was comprehensively studied using IR spectroscopy, XRD, SEM, TG analysis, and DSC with mass spectrometric analysis of evaporation products to evaluate the mechanism of TiO2 crystallization. The phase composition, morphology, texture, and optical properties of the synthesized TiO2 photocatalysts were studied using XRD, SEM, nitrogen adsorption/desorption, and UV–Vis diffuse reflectance spectroscopy. High-temperature treatment after hydrothermal impregnation led to the formation of anatase and rutile TiO2 nanocrystallites with a characteristic size of 15–20 nm. The as-prepared TiO2 photocatalysts had an optical band gap of ∼3.0 eV due to the high content of the rutile phase but also absorbed visible light due to impurity atoms and defects. The samples exhibited very high photocatalytic activity in the degradation of Rhodamine B dye, which was used as a probe molecule, under both UV and visible light. Based on the XPS and EPR results, the enhanced photocatalytic activity of the prepared photocatalysts was attributed to the self-doping effect due to the many defects (Ti3+ sites and oxygen vacancies) formed during TiO2 crystallization, probably via the reduction of Ti4+ to Ti3+ in disproportionation reactions of disulfide bonds involving titanium hydroxocomplexes.