Role of Charge Accumulation in MoS2/Graphitic Carbon Nitride Nanostructures for Photocatalytic N2 Fixation

Abstract

Constructing a heterojunction is an effective way to overcome the handicaps of single-component photocatalysts for the photocatalytic N₂ reduction reaction (PNRR). However, the fundamental photophysical processes between two semiconductors with different nanostructures are still unclear. Drawing upon a combination of experimental observations and theoretical calculations, a series of binary nanohybrid photocatalysts of MoS₂ (nanodot, monolayer, and few nanolayers) and carbon nitride are systematically evaluated as potential N₂ reduction reaction photocatalysts. Owing to the atomically well-defined interfacial interaction between MoS₂ and graphitic carbon nitride (GCN), charge accumulates in MoS₂. Meanwhile, the electron density of MoS₂ increases with the reduction of nanosize, thereby facilitating N₂ adsorption on the Mo-edge and boosting the potential-determining step of the desorption of the NH₃ molecule. Simultaneously, the MoS₂ nanodot anchored on GCN manifests a compelling photothermal effect upon solar light irradiation and raises the temperature of the compound in situ, leading to efficient charge transfer and thereby enhancing the photocatalytic performance. Encouragingly, the final product reaches a high ammonia synthesis rate of 2.71 mmol h^–1 g^–1 at ambient conditions and an apparent quantum of 0.62% at 430 nm. Establishing the relationship between the nano-, electronic structure and PNRR performance of MoS₂/GCN heterojunction materials provides valuable insights for their potential application in PNRR technology.