Enhanced reduction and oxidation capability over the CeO2/g-C3N4hybrid through surface carboxylation: performance and mechanismElectronic supplementary information (ESI) available. See DOI: 10.1039/d0cy00395f

The CeO2/g-C3N4hybrid is a kind of efficient photocatalyst with both photoinduced oxidation and reduction capability, which is of great concern in solar energy application. Herein, we reported a facile method for the synthesis of the CeO2/g-C3N4hybrid with enhanced CO2reduction and ciprofloxacin degradation performance using surface carboxylated g-C3N4(C-g-C3N4) as the substrate. The characterization results demonstrated the abundant oxygen-containing groups of C-g-C3N4in the CeO2/C-g-C3N4hybrid can effectively improve the dispersion of CeO2nanoparticles and enhance the interfacial bonding with the C-g-C3N4substrate. Density functional theory (DFT) calculations showed that a built-in electric field was formed in the CeO2/C-g-C3N4heterojunction, which can greatly improve the charge separation and transfer efficiency. Consequently, the yield of CO and the ciprofloxacin degradation efficiency have been remarkably improved. The maximum CO yield through CO2photoreduction over 3%CeO2/C-g-C3N4was 9.083, 3.922, and 2.868 times higher than that of pure CeO2, C-g-C3N4and 3%CeO2/g-C3N4bulk, respectively. The 3%CeO2/C-g-C3N4heterojunction also showed excellent photoinduced oxidation activity for ciprofloxacin degradation with a 73% degradation efficiency in 2 h, which was 1.89 and 2.76 times higher than that of pure CeO2and C-g-C3N4, respectively. Furthermore, a good photostability for a five cycle test of CO2reduction was observed over the 3%CeO2/C-g-C3N4hybrid. The possible photocatalytic mechanism was investigated by theoretical calculations and capture experiments to further understand the charge transfer behavior over the CeO2/C-g-C3N4heterojunction for CO2reduction and pollutant degradation.