摘要
Excess carbon dioxide emission accompanied by gross fossil fuel consumption has worsened the global warming crisis in recent decades. Photo-induced conversion of CO2 into hydrocarbons is a potential solution to mitigate both energy and environmental problems. However, conventional photocatalysts suffer low efficiency in CO2 conversion with often C1 and/or C2 products. In this work, pyrolyzed cobalt type zeolitic imidazolate framework (ZIF-67), namely ZIF-derived carbon (ZDC) with residual Co nanoparticles and the corresponding ZDC/TiO2 composite (ZDC/T), were adopted as gas-phase CO2 reduction photocatalysts. The ZDC photocatalyst is inclined to form C2 compound (acetaldehyde), while the ZDC/T composite has high selectivity in C3 product (acetone). High pyrolysis temperature would degrade the photocatalytic performance in neat ZDC due to enhanced cobalt aggregation and nitrogen loss after breaking ZIF-67 Co-N coordination. Alternatively, the pyrolyzed ZDC/T revealed superior photocatalytic CO2 reduction performance because the Co-N bonds were found to decrease without changing Co nanoparticle size and dissociation of nitrogen notably. In conclusion, we synthesized novel photocatalysts for multi-carbon (C2-C3) products with high selectivity, and provided a plausible mechanism to illustrate the formation process of multi-carbon products during photoreduction of CO2.