In-situ design of efficient hydroxylated SiO2/g-C3N4 composite photocatalyst: Synergistic effect of compounding and surface hydroxylation

Visible-light responded graphitic carbon nitride (g-C3N4, CN) is one kind of promising photocatalytic semiconductors since its simple synthesis and element composition. Nevertheless, extensive application is limited due to the serious lamellar aggregation and high recombination rate of photo-generated carriers. Herein, the dispersed SiO2/g-C3N4 composite photocatalyst (Si-CN) was prepared with SiO2 as the dispersion components, and the surface hydroxylation modification of Si-CN was subsequently carried out (Si-CN-HO). It is aimed at increasing the specific surface area and improving the separation efficiency of photo-generated carriers of CN through the synergistic effect of SiO2 compounding and the trapping of photogenerated holes by the grafted hydroxyl groups, thereby enhancing the photocatalytic activity. The effect of SiO2 nanoparticles and surface hydroxylation modification on the photocatalytic performance enhancement of CN was investigated using rhodamine B as the target pollutant. Results show that the degradation rate of rhodamine B under solar light irradiation by Si-CN-HO is 8.9, 20.9 and 5.6 times higher than that of Si-CN, bulk CN and hydroxylated CN (CN-HO), respectively. Furthermore, compared with the bulk CN, the surface hydroxylation of Si-CN promotes the combination between SiO2 and CN as well as the dispersion of CN. Besides, the mechanism results suggest that more electrons could react with oxygen to form the superoxide radicals with strong oxidation. The increased specific surface area and improved light utilization capacity of Si-CN-HO also contribute to the enhanced photocatalytic activity.