Efficient visible light activities of Ag modified ZnO/g-C3N4 composite for CO2 conversion

Methane and CO have superior economic value and application panorama compared with other products, and these are the ideal products of CO2 photo-reduction. However, low CO2 conversion efficiency and poor selectivity are huge obstacles to its practical application. Herein, we develop a three-component photocatalyst hetero-junction of Ag-ZnO/g-C3N4 for superior CO2 reduction. It is demonstrated that the amount-optimized nanocomposite exhibited exceptional visible-light photoactivities for CO2 conversion to CO, with ≈ 9-time (36 µmol g−1 h−1) enhancement compared to the widely accepted g-C3N4 prepared from melamine as the raw material. Similarly, the silver-modified samples exhibit a considerable increase in methane production, with 14 µmol g−1 h−1, which is significantly more than the CH4 production of 2 µmol g−1 h−1 by pure g-C3N4. Based on the photo-physical data, it is concluded that the coupled ZnO, which accepts electrons and improves reactant adsorption, and the modified Ag, which further promotes the photocatalytic reaction, are much more responsible for the high photoactivities. Moreover, it is suggested based on the photocatalytic experiments with isotopic 13CO2 that the produced •CO2 as active radicals dominated the conversion of CO2 to CO/CH4. This work provides a feasible strategy to design high-performance, low-cost, and sustainable g-C3N4-based nanocomposite photo-catalysts with a wide range of visible light activity for CO2 reduction.