Fe S bridged CdS/MIL-68(Fe) heterojunction for biomimetic photocatalytic N2 fixation

Inspired by biological nitrogen fixation (BNF) via nitrogenase, researchers develop novel metal-organic frameworks (MOFs)-based photocatalytic nitrogen fixation (PNF) systems to address the challenge of activating N 2 . However, the inherent low mobility of charge carriers in MOFs results in insufficient migration of photogenerated electrons to active sites for N 2 reduction. In this work, a series of CdS/MIL-68(Fe) heterojunctions (x%CdS/MF) were successfully developed by in-situ growth of various mass fractions of ultrafine CdS nanoparticles (about 5.0 nm) for biomimetic photocatalytic N 2 fixation. A tightly combined interface between MIL-68(Fe) and CdS via a Fe–S bond induces interfacial electric field, promoting the charge mobility. CdS functions as an electron donor (the role of the Fe protein in nitrogenase) to transfer additional electrons to the active sites (the role of the FeMo-cofactor in nitrogenase), i.e. the coordinatively unsaturated Fe sites in MIL-68(Fe). Consequently, CdS/MIL-68(Fe) heterojunctions effectively mimic the behavior of the two fundamental components in nitrogenase. 10 %CdS/MF exhibits the highest NH 4 + production rate (51.6 µmol·h –1 ·g –1 ), which is 15.6 and 5.1 times higher than those of unmodified MIL-68(Fe) and pristine CdS, respectively. This work sheds new light on the rational design of MOF-based photocatalysts for biomimetic N 2 fixation. CdS/MIL-68(Fe) type II heterojunctions are developed for boosting biomimetic photocatalytic N 2 fixation by the promotion of electron transfer and N 2 activation. • A series of CdS/MIL-68(Fe) heterojunctions are developed for biomimetic photocatalytic N 2 fixation. • A tightly combined heterojunction interface via a Fe‒S bond induces interfacial electric field. • The coordinatively unsaturated Fe sites in MIL-68(Fe) act as active sites to facilitate the N2 activation. • The promotion of electron transfer and N 2 activation significantly enhances the photocatalytic N 2 fixation performance.