Enhanced reduction and oxidation capability over the CeO2/g-C3N4 hybrid through surface carboxylation: performance and mechanism

Abstract

The CeO₂/g-C₃N₄ hybrid 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-C₃N₄ hybrid with enhanced CO₂ reduction 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-C₃N₄ in the CeO₂/C-g-C₃N₄ hybrid can effectively improve the dispersion of CeO₂ nanoparticles and enhance the interfacial bonding with the C-g-C₃N₄ substrate. Density functional theory (DFT) calculations showed that a built-in electric field was formed in the CeO₂/C-g-C₃N₄ heterojunction, 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 CO₂ photoreduction over 3%CeO₂/C-g-C₃N₄ was 9.083, 3.922, and 2.868 times higher than that of pure CeO₂, C-g-C₃N₄ and 3%CeO₂/g-C₃N₄ bulk, respectively. The 3%CeO₂/C-g-C₃N₄ heterojunction 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 CeO₂ and C-g-C₃N₄, respectively. Furthermore, a good photostability for a five cycle test of CO₂ reduction was observed over the 3%CeO₂/C-g-C₃N₄ hybrid. The possible photocatalytic mechanism was investigated by theoretical calculations and capture experiments to further understand the charge transfer behavior over the CeO₂/C-g-C₃N₄ heterojunction for CO₂ reduction and pollutant degradation.