Enhanced visible-light photocatalysis of clofibric acid using graphitic carbon nitride modified by cerium oxide nanoparticles

Recently, the emerging pharmaceutical micropollutants have become an environmental concern. Herein, we report an efficient elimination of clofibric acid (CA) using visible light-driven g-C3N4/CeO2 prepared by hydrothermal method. Among the catalysts with different compound ratios, g-C3N4/CeO2-3 (1.2 g g-C3N4 with 3 mmol Ce(NO3)3∙6H2O) exhibited the best photocatalytic performance. The effect of catalyst dosage was investigated and the optimal value was determined as 0.5 g L–1. The effect of initial pH (pH0) showed CA elimination decreased with increasing pH0. The underlying mechanism for CA oxidation was proposed based on synthetical analysis of photoluminescence emission spectra, transient photocurrent responses, electron paramagnetic resonance, chemical quenching experiments and band edge potential of g-C3N4 and CeO2. Photogenerated hole was primarily responsible for CA elimination while singlet oxygen played an auxiliary role. The products of CA oxidation were detected using liquid chromatography mass spectrometry (LC-MS) method and a possible pathway was put forward. Various organics were used as target contaminants to assess photocatalytic performance of g-C3N4/CeO2 heterojunction under acidic and alkaline pH conditions. The analysis of relationship between the oxidation peak potential (EOP) and the reaction rate constant indicated that photocatalysis using as prepared g-C3N4/CeO2-3 heterojunction is apt to oxidize contaminants with electron withdrawing group under acid condition.