Multi-stepwise electron transfer via MOF-based nanocomposites for photocatalytic ammonia synthesis†
Photocatalytic ammonia (NH3) synthesis can realize the reaction of nitrogen (N2) and water using solar energy as the sole driving force under mild conditions. However, the inferior electron transfer capability in the catalyst remains a critical challenge. Herein, we proposed a multi-stepwise electron transfer strategy to improve the electron transfer efficiency in photocatalysis. Benefitting from the excellent bio-inspired adhesion of polydopamine (PDA), the rationally designed UiO-66/PDA/graphic carbon nitride nanosheet (UiO-66/PDA/CNNS) composite was prepared. An innovative CNNS–PDA–ligand–metal four-step electron transfer pathway was constructed in UiO-66/PDA/CNNS, which enhanced the lifetime of photo-generated electrons and boost their transfer efficiency. The grand canonical Monte Carlo (GCMC) methods and density functional theory (DFT) calculations demonstrate that UiO-66/PDA/CNNS exhibits superior N2 adsorption capability, excellent activation capacity for inert NN triple bonds and reduced potential activation energy barrier. As a result, the NH3 evolution rate of the optimal UiO-66/PDA/CNNS composite can reach 147.8 μmol h−1 g−1 under a full spectrum. Moreover, five types of metal–organic framework (MOF)-based composites, including UiO-66/PDA/CdS, UiO-66/PDA/TiO2, MIL-53/PDA/CNNS, MIL-53/PDA/CdS and MIL-53/PDA/TiO2, were synthesized by similar method, further confirming the universality of this strategy. This work may offer some enlightenment for designing MOF-based composite photocatalysts with intensified electron transfer process.