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 N2 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.

Mesoporous sulfur-doped graphitic carbon nitride (MCNS) materials were successfully synthesized using thiourea as a low-cost precursor and SiO gel solution as a template through a simple thermal condensation method. The effects of three synthesis key factors, namely, the reaction temperature, the reaction time, and the weight ratio of SiO/thiourea, and also their interactions on the removal rate of methyl orange (MO) were investigated using response surface methodology, and the samples were subjected to several characterization techniques. Results showed that the optimized physicochemical properties could be achieved for the MCNS samples by controlling the synthesis key factors, and it was found that the reaction temperature and the reaction time had significant influences on the MO photocatalytic removal. Among bulk graphitic carbon nitride (g-CN), CN (undoped g-CN), CNS (sulfur-doped g-CN without template), and TiO (Degussa P25) samples, the optimized MCNS-4 illustrated the highest photocatalytic activity toward the removal of MO under visible light irradiation. The enhanced performance originated from the synergistic effects of high surface area, mesoporous texture, sulfur doping, and high visible light absorption, which were helpful for the separation and transportation of the photogenerated electron-hole pairs. Furthermore, MCNS-4 revealed high reusability and stability without any significant decrease in its efficiency. Our findings not only confirm the importance of simultaneous sulfur doping and mesoporous structure to synthesize highly active photocatalysts but also might provide a new insight into textural engineering of carbon nitride materials only by the optimization of the synthesis key variables, considering their interactions without relying on extra metal oxides.

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In this work, an Fe-supported cagelike mesoporous silica type SBA-16 catalyst (Fe/SBA-16) was successfully synthesized using iron nitrate as the precursor through a simple impregnation method. Results of X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy, and elemental mapping analysis showed that the mesoporous structure of the support was retained during catalyst preparation and that iron nanoparticles were dispersed on the SBA-16 surface. Moreover, ultraviolet–visible and X-ray photoelectron spectroscopic studies revealed that the iron­(III) oxidation state was dominant in the Fe-supported cagelike mesoporous silica. It was found that the Fe/SBA-16 was an appropriate catalyst for the benzene hydroxylation to phenol using H2O2 as the oxidant. The effects on the catalytic performance of operating parameters such as the amount of H2O2, reaction temperature, reaction time, and catalyst dosage were investigated. Under the optimized conditions, 11.7% phenol yield and 96.4% selectivity to phenol were obtained; in addition, the catalyst could be recycled at least three times.

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