Effects of SnO2 coupling on the structure and photocatalytic performance of TiO2/sepiolite composites

The use of titanium dioxide in the degradation of water pollutants encounters several challenges, including particle agglomeration leading to a reduction in its specific surface area and a high rate of photogenerated electron-hole recombination, resulting in a lower quantum efficiency. Therefore, in this work, we first employed sepiolite to load titanium dioxide, mitigating particle agglomeration. Building upon this, tin dioxide was coupled with it to enhance the photogenerated charge separation. The SnO2/TiO2/sepiolite photocatalytic composites were synthesized using the sol–gel method at 450 ℃. The resulting composites underwent thorough characterization encompassing phase composition, morphology, chemical valence states, specific surface area, optical properties, and photocatalytic activity. The outcomes demonstrate an augmentation in the specific surface area of TiO2/Sep composites following the sepiolite (Sep) loading. Among these, the TiO2/Sep composite (with a Sep: TiO2 mass ratio of 10 %) exhibited the most favorable photocatalytic performance, displaying a first-order reaction rate constant of 0.010 min−1, surpassing that of pure TiO2 by a factor of 2.0. The introduction of SnO2 expedited the migration of photogenerated charge across interfaces, curbing the recombination of photogenerated pairs, thus enhancing quantum efficiency. In light of the presence of sepiolite, the addition of SnO2 further amplified the photocatalytic performance. Optimal results were achieved when the molar ratio of SnO2:TiO2 was set at 1:4, leading to the highest photocatalytic efficiency observed in the SnO2/TiO2/Sep composite. This composite exhibited a first-order reaction rate constant of 0.027 min−1, marking a notable 2.7-fold increase compared to the TiO2/Sep counterpart. The investigation of band potentials, charge transfer pathways, and the photocatalytic mechanism within SnO2/TiO2/Sep composite materials was conducted through a comprehensive analysis involving electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) valence band spectroscopy, electron paramagnetic resonance spectra (EPR) and active radical experiments.