Multi-stepwise electron transfer via MOF-based nanocomposites for photocatalytic ammonia synthesis

Abstract

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.