Engineering a pyrene MOF composite photocatalyst toward the formation of carbon dioxide radical anions through regulating the charge transfer from type II to Z scheme via a chemical bond-modulated strategy

The CO2 radical anion ((center dot)CO2-) is a powerful single electron reductant and an important intermediate in CO2 involved reactions. Herein, we report an approach to engineer a pyrene MOF composite photocatalyst toward the formation of (center dot)CO2- through regulating the charge transfer from type II to Z scheme via a chemical bond-modulated strategy. Through a post-synthetic modification, cysteamine (Cys) was rationally anchored onto the unsaturated Cd clusters of a pyrene-based MOF (namely WYU-11) via chemical bonds, giving rise to a modified MOF of WYU-11-Cys. This modification induced the growth of CdS nanoparticles (NPs) on the surfaces of WYU-11-Cys via the chemical bonds between CdS and Cys, resulting in the formation of a MOF composite of CdS@WYU-11-Cys. The introduction of Cys could regulate the charge transfer between CdS and WYU-11, leading to the conversion from type II to Z scheme with a high redox potential of -1.93 V vs. a normal hydrogen electrode. CdS@WYU-11-Cys could reduce CO2 to (center dot)CO2-, which was confirmed by an electron paramagnetic resonance (EPR) experiment, and promote the photocatalytic cyclization of CO2 and propargylic amines. This work provides useful inspirations for the rational design of Z-scheme MOF composites for CO2 conversion.