Synthesis and characterization of S-doped Degussa P25 with application in decolorization of Orange II dye as a model substrate

Abstract The commercially available and relatively cheap TiO 2 , Degussa P25, was modified and doped with sulfur (using thiourea as a source of sulfur) by simple and effective hydrolysis method at room temperature followed by calcination in the presence of air. S-doped P25 photocatalyst with different TU:P25 mass ratios of 0:1, 0.25:1, 1:1, 3:1 and 5:1 have been prepared and investigated. The photocatalytic activity of the prepared S-doped P25 was examined by photo-decolorization of azo dye Orange II under natural solar light irradiation. X-ray diffraction (XRD), UV–vis spectroscopy, X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the catalyst. The results showed that the S-doped P25 catalyst at mass ratio of (1:1) and calcinated at 550 °C for 4 h exhibited the highest photocatalytic activity under solar light irradiation; the undoped-P25 photocatalytic activity increased about 23% by doping with sulfur. The XPS and UV–vis spectra results suggest that the crystal lattices of S-doped P25 powder are locally distorted by incorporating S 6+ species into TiO 2 and substitutes for some of the lattice titanium (Ti 4+ ). The XRD results showed that doped sulfur can retard the grain growth of TiO 2 to some extend. Increasing the TU:P25 ratio up to (1:1) reduced the crystalline size and increased the anatase content. Higher ratios (3:1 and 5:1) have negative effect on the photocatalytic activity of the catalysts. The calcinations temperature for S-doped P25 (1:1) have been also investigated and it was found that calcination at 550 °C is the optimum one. The commendable visible photoactivities of S-doped P25 are predominantly attributed to an improvement in anatase crystallinity, low band gap and low particle size. We suggest that Degussa P25 could be used as a Ti precursor for further improving its activity under natural solar light.