Size Effect of Cu Nanoparticles in Cu/g-C3N4 Composites on Properties for Highly Efficient Photocatalytic Reduction of CO2 to Methanol

The main goal of this work is to develop cheap photocatalysts for the efficient photocatalytic reduction of CO2 to methanol with water. A series of composites of Cu/g-C3N4 were prepared via a solvothermal method. Copper nanoparticle (Cu NP) size in Cu/g-C3N4 can be easily controlled by adjusting the synthesis temperature. The Cu/g-C3N4 material with the proper size of Cu NP (CuCN-100) had the best photocatalytic property (675 μmol·g-1·h-1) in reducing the amount of CO2 to methanol at room temperature under normal pressure. The particle size of Cu NPs is the key factor to improve the catalytic activity and stability because of the improved transfer and separation of photogenerated charges with the small Cu NPs. Although the sample with large Cu NPs (CuCN-200) initially gave a better activity than that of CuCN-100 due to the formation of double heterojunction, its activity was thoroughly lost after two runs resulting from the continuous photocorrosion. This work provides a valuable insight for preparing efficient semiconductor-metal photocatalysts.