A greener approach to synthesize visible light responsive nanoporous S-doped TiO2 with enhanced photocatalytic activity

A visible light responsive nanoporous sulfur doped TiO2 nanophotocatalyst was prepared by a greener approach using ultrasonic irradiation. The synthesized product was characterized by physicochemical techniques such as X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The elemental composition, morphology and surface area were determined by Energy Dispersive X-ray Spectroscopy (EDXS), Scanning Electron Microscopy (SEM), and High Resolution Transmission Electron Microscopy (HRTEM), Brunauer-Emmett-Teller (BET) surface area analysis, respectively. The results confirmed the formation of a nanoporous S-doped TiO2 photocatalyst having the anatase phase and exhibiting a particle size of about 8-24 nm. The influence of sulfur doping on the phase transition, band gap and crystalline size of the TiO2 was investigated by varying the molar ratio of titanium and sulfur. Sulfur doping leads to the lowering of the band gap of TiO2 from 3.25 eV to 2.47 eV and also delays the phase transition of TiO2 from the anatase to rutile form. The response of the synthesized catalysts towards the photo-induced degradation of an organic pollutant was investigated in different regions (490 nm, 565 nm and 660 nm) of the solar spectrum using 2-chlorophenol as a model compound. Maximum photocatalytic degradation efficiency was found with S-550 at pH 6 under visible light of 660 nm. The synthesized S-doped TiO2 photocatalyst showed profound improvement in photocatalytic activity under solar light as compared to TiO2 Degussa and TiO2 Merck.