Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation

As an emerging carbon nanomaterial, carbon dots (CDs) have superior prospects for applications in the area of photocatalysis due to their unique optical and electronic properties. In this study, a novel CDs modified g-C3N4/SnO2 photocatalyst (CDs/g-C3N4/ SnO2) was successfully synthesized by the thermal polymerization. Under visible light irradiation, the resulting CDs/g-C3N4/SnO2 photocatalyst exhibited excellent photocatalytic activity for the degradation of indomethacin (IDM). It was demonstrated that a 0.5 % loading content of CDs led to the highest IDM degradation rate, which was 5.62 times higher than that of pristine g-C3N4. This improved photocatalytic activity might have been attributed to the unique up-conversion photoluminescence (PL) properties and efficient charge separation capacities of the CDs. Moreover, the combination of g-C3N4 with SnO2 improved the separation of photoinduced carriers and augmented the specific surface area. Reactive species (RSs) scavenging experiments and electron spin resonance (ESR) revealed that superoxide radical anions (O2·−) and photogenerated holes (h+) played critical roles during the photocatalytic process. The results of the detection of H2O2 and ESR confirmed that CDs/g-C3N4/ SnO2 was a Z-scheme heterojunction photocatalyst. Further, HRAM LC–MS/MS was employed to identify the byproducts of IDM, and the major IDM degradation pathways of the CDs/g-C3N4/SnO2 photocatalyst were proposed. This study provides new ideas for the design of novel CDs modified photocatalysts for environmental remediation.