ZnO Photocatalyst Revisited: Effective Photocatalytic Degradation of Emerging Contaminants Using S-Doped ZnO Nanoparticles under Visible Light Radiation

Zinc oxide (ZnO) nanoparticles were synthesized by the hydrothermal method and incorporated with diverse amounts of the nonmetal element sulfur (0.5, 0.8, 1.1, 1.3, 2.1, 2.5, 3.2, 6.8, 7.8, 11.9, 12.3, and 17.4 wt %). The physicochemical properties of all nanoparticles were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and N-2 adsorption/desorption isotherms, as well as Fourier transform infrared, diffuse reflectance, ultraviolet-visible absorption, and photoluminescence (PL) emission spectra. Pure ZnO and 12 S-containing ZnO nanoparticles were examined as photocatalysts for the degradation of the rhodamine B (RhB) contaminant. Among the S-containing samples, 0.10 g of the sample doped with 0.5 wt % S could degrade 100% of RhB (5 ppm) at pH = 5 in 90 min. It was also found that the 0.8 and 1.1 wt % S-doped ZnO samples could degrade 99 and 97% of RhB in 150 min, respectively. The photocatalytic property of the 0.5 wt % S-doped ZnO was improved by adding a small quantity of ammonium persulfate (0.005 g), so that it could degrade 100% of RhB in 60 min but 10 ppm RhB in 210 min. Moreover, the pure ZnO and the optimal 0.5 wt % S-doped ZnO photocatalysts displayed 2 and 53% degradation of the phenol pollutant in 180 min at pH = 5, respectively. The reusability of the 0.5 wt % S-doped ZnO optimal photocatalyst was tested under optimized conditions (catalyst dosage = 0.10 g, pH = 5, and RhB concentration = 5 ppm) for the RhB degradation exhibiting the degradation efficiency was slightly decreased from 100 to 92% after five successive reactions. Thus, such a photocatalyst could be used as a promising material for application in industrial wastewater treatment processes.