A MOF@MOF S-scheme Heterojunction with Lewis Acid-Base Sites Synergistically Boosts Cocatalyst-Free CO Cycloaddition.

The photocatalytic cycloaddition reaction between CO and epoxide is one of the most promising green routes for CO utilization, for which high performance photocatalysts are intensely desired. Herein, we have constructed an S-scheme heterojunction of MIL-125@ZIF-67 modified by amino groups, which achieves a cyclic carbonate yield of as high as 99 % without employing any co-catalyst, outperforming the previously reported photocatalysts. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in-situ electron paramagnetic resonance (EPR) spectroscopy reveal the important role of photogenerated electron migration from Lewis acid (Co) sites to the O atom of epoxide in triggering its ring-opening (the rate-determining step of CO cycloaddition reaction) under the assistance of photogenerated hole. Synergistically and concurrently, the Lewis base (amino groups) sites activate CO to CO*, facilitating the following CO cycloaddition. Such a synergistic effect provides a most favorable approach to design efficient heterogeneous photocatalysts with dual/multiple-active sites for CO cycloaddition reaction.