Organic pollutant degradation for micro-molecule product emission over SiO2 layers-coated g-C3N4 photocatalysts

Abstract

In this study, a SiO₂ layer-coated g-C₃N₄ catalyst was prepared by a sol–gel method to overcome the poor adsorption ability and high recombination rate of charge carriers of pristine g-C₃N₄. SEM and TEM images indicated that SiO₂ nanoparticles were coated on the surface of g-C₃N₄ nanoparticles with a layered structure and the layers were tightly contacted with g-C₃N₄. XRD patterns, FTIR spectra, UV-vis spectra and XPS spectra revealed that the structure of g-C₃N₄ was not destroyed and its photoelectric catalytic properties were not suppressed by the coating of SiO₂ layers. Adsorption experiments revealed that the SiO₂ layers improved the adsorption performance of g-C₃N₄ and their ratios were adjusted. The molecular weights of the final products of the degradation of RhB and antibiotics were at the micro-molecule level while the amount of g-C₃N₄ reached 1.2% of the mass fraction, which were more suitable for pollutant degradation compared with those of g-C₃N₄ due to its poor adsorption ability. The reason for this was likely that the SiO₂ layers were not only beneficial for the adsorption of pollutants and intermediate products but also for prolonging the life time of the separated electrons and holes. Finally, active trapping experiments confirmed that both the holes and superoxide radicals were the main factors in the degradation of RhB and antibiotics, with the superoxides being the most active species.