Elucidating the Photocatalytic Behavior of TiO2-SnS2 Composites Based on Their Energy Band Structure

TiO2-SnS2 composite semiconducting photocatalysts with different building component ratios were prepared by hydrothermal synthesis (TiO2-SnS2-HT) and by immobilization of commercial TiO2 and SnS2 particles (TiO2-SnS2-COMM). The band gap values, which determine the catalysts' photoactivity, were examined by diffuse reflectance spectroscopy and Kubelka-Munk transformations. The catalysts' surface properties: specific surface area, charge and adsorption capacitance at the solid-solution interface were characterized using BET analysis, potentiometric titration and electrochemical impedance spectroscopy, respectively. The electronic band structure of TiO2-SnS2 photocatalyst, as the key property for the solar-driven photocatalysis, was deduced from the thermodynamic data and the semiconducting parameters (type of semiconductivity, concentration of the charge carriers, flat band potential) obtained by Mott-Schottky analysis. The photoactivity of both composites was studied in photocatalytic treatment of diclofenac (DCF) under simulated solar irradiation and was compared to the benchmark photocatalyst (TiO2 P25) activity. The influence of process parameters, such as pH, H2O2, and composite formulation on the effectiveness of DCF removal and conversion was investigated and discussed by employing response surface modeling (RSM) approach. The photocatalytic efficiency of both composite materials was discussed on the basis of the hetereojunction formation that facilitated the photoelectron transfer, promoting more efficient photocatalytic degradation of DCF.