A Novel Sunflower-like MOF@COF for Improved Photocatalytic CO2 Reduction

Metal-organic framework (MOF) and covalent organic framework (COF) hybrid materials have drawn much research attention in the field of photocatalysis due to their complementary advantages, massive specific area, customizable structure and performance, and suitable band gap. Herein, the MOF@COF hybrid platform with a novel sunflower-like strong pi-pi bond stacking was formed by introducing the preformed synthetic COF into the MOF precursor solution and modulating its morphology by vacuum thermal-assisted growth. More importantly, the synthesized MOF on the COF hybrid platform with multiple active centers exhibits excellent catalytic activity in the sacrificial agent-free photocatalytic CO2 reduction reaction under simulated sunlight. Additionally, the maximum CH4 yieldrate of the synthesized PCN-222-Cu@TpPa-1 (1:2) reached 21.27 mu mol g-1h-1, with an AQY (apparent quantum yield) about 10.46 % (in pure water system, lambda = 550 nm) and a methane selectivity of about 27.25 %. The best performance of PCN-222-Cu@TpPa-1 is approximately 4.3 times higher than that of pure PCN-222-Cu and 100 times higher than that of the reported NH2-MIL-125(Ti) NMB. The selectivity of the products CO and CH4 can be improved by adjusting the ratio of MOF and COF. Finally, the goal of providing an optimal photocatalytic platform for increased photocatalytic CO2 reduction with highly effective morphology-tunable MOF@COF was expanded upon by a potential photocatalytic reaction mechanism, which was suggested based on the analysis of experimental results.