Enhanced photocatalytic activity of sulfur doped TiO2 for the decomposition of phenol: A new insight into the bulk and surface modification

Abstract

Sulfur ion (S6+) was doped into the anatase TiO2 prepared by sol–gel method (SG-TiO2) using sulfur powder as a sulfur source (S-TiO2) and its photoreactivity was probed for the degradation of phenol under UV/solar light illumination. The S-TiO2 and SG-TiO2 were characterized by PXRD, UV–vis DRS, FTIR, SEM, XPS, BET and PL techniques. It was observed that S6+ ion was incorporated into the TiO2 crystal lattice at Ti4+ lattice site and the sulfur on the surface gets modified to SO42− due to the heat treatment under atmospheric conditions. The high photocatalytic activity of S-TiO2 compared to SG-TiO2 is attributed to the surface modification of sulfur as sulfate which plays a crucial role in trapping electrons. S-TiO2 shows significant increase in the surface area, reduced crystallite size, increased surface acidity, visible light absorption and prolonged lifetime of the photogenerated charge carriers. Hole scavengers like potassium iodide and tertiary butanol suggested the surface degradation mechanism rather than the bulk degradation pathway. Addition of oxidizing agents to the degradation reaction did not show any enhancement in the degradation rates since the presence of SO42− on the TiO2 surface itself acts as the efficient electron trapping centers. Both trapping and detrapping of the electron takes place more efficiently at SO42− centers. The enhanced activity of S-TiO2 is attributed to the synergistic effect between S6+ dopant with surface modified SO42−.