Study of ZnO1-xSx synthesis by non-alcoxide sol-gel method employed in the photocatalytic degradation of a persistent organic pollutant in water

Abstract

Non-Alcoxide Sol-Gel method was used as synthesis route to obtain the ZnO1-xSx compounds at calcination temperatures of 250 ° C, 300 ° C and 400 ° C, doped with Sulfur at mole fractions of x = 0.05, 0.50, 0.80. The samples obtained were characterized structural and optically by both X-ray diffraction (XRD) and diffuse reflectance spectrophotometry. The XRD analysis showed the formation of the Wurtzite type structure proper of ZnO up to Sulfur mole fraction of x = 0.50. It was observed that this phase disappears at a mole fraction of x = 0.80 and converts to Cubic Zinc blende type structure proper of Zinc Sulfide. Furthermore, was observed that increasing calcination temperature higher crystallinity was achieved for all set of samples. The Rietveld refinement method was used to obtain lattice parameters for Wurtzite structure as well as cell volume and the ratio c/a. These parameters show slight incremental changes in relation to S doped ZnO crystalline structure. On the other hand, it was determined optically, that increasing the dopant concentration to a mole fraction x = 0.50, a maximum reduction of the band gap from 3,29 eV to 2,70 eV was reached, while increasing the calcination temperature shows a general tendency to band gap reduction. Photocatalytic activity of Sulfur doped and pure ZnO powders were tested for degradation of p, p’-DDT under visible light, measuring the p, p’-DDT time-dependent concentration by gas chromatography-μECD coupling. The results revealed that the sulfur modified ZnO material showed an improved photocatalytic activity towards p, p’-DDT under visible light illumination respect to pure ZnO.