Embedded carbon dot mediator in a Ce-MoO3−x heterojunction for improved visible-light-driven N2 fixation: performance and interfacial activation mechanism

Abstract

The photocatalytic N₂ reduction process using solar energy as an environmentally friendly method has attracted significant attention. Herein, the simultaneous tuning of the energy band structures for CeO₂ and MoO_3−x to generate an all-solid-state heterostructure for improved nitrogen photofixation performance is reported, and a carbon dot charge-transport mediator is introduced in the photocatalytic system. Within the heterojunction, the electronic interaction between the layers creates electron-deficient Mo-sites and electron-sufficient Ce-sites with enhanced N₂ chemisorption ability, and the carbon dot mediator can promote electron transfer to further reduce the energy barrier for N₂ activation. The as-prepared sample displays a high ammonia synthesis rate of above 897 µmol g_cat⁻¹ h⁻¹, two times higher than that achieved using the CeO₂/MoO_3−x sample without the carbon dot mediator. The variation trend in the AQE value is generally in accordance with the absorption spectrum, and an AQE of nearly 1.2% at 420 nm is obtained. This sample also has higher photocatalytic selectivity for ammonia. The N₂ reduction pathway under light irradiation follows the associative alternating process through the density functional theory (DFT) calculations. The increased photocatalytic performance is also ascribed to higher visible-light utilization, stronger nitrogen adsorption and faster charge separation efficiency.