In-situ synthesis of single-atom CoN clusters-decorated TiO2 for highly efficient charge separation and CO2 photoreduction

Solar-driven CO2 reduction reaction (CO2RR) to produce chemical fuels is an attractive way to alleviate the greenhouse effect and energy crisis. Herein, a novel single-atom CoNx clusters-decorated TiO2 (CoNx/TiO2) is synthesized in situ by calcining a composite derived from immersing a metal organic framework (Mil-125) into cobalt tetra(4-pyridyl)porphyrin (CoPy4) solution. The resultant CoNx/TiO2 delivers an excellent CO2RR activity with CO/CH4 yields of 24.4/119.9 μmol g−1 h−1, corresponding an overall photoactivity of 1007.6 μmol g−1 h−1, 10.6 time higher than that of TiO2 alone. It is found that CoPy4 molecules can enter Mil-125′s micropores, which helps to pyrolyze CoPy4 into highly dispersed single-atom-contained CoNx clusters and to form strong interaction with the primary nanoparticles of TiO2 quasi-nanocube-like aggregated particles derived from Mil-125. These factors of CoNx/TiO2 enable efficient photogenerated charge separation, strong chemical adsorption to reactants and high atom utilization, thus providing a new strategy for constructing TiO2-based photocatalysts with highly dispersed single-atom catalytic sites for CO2 photoreduction.