Novel N-Black In2O3−x/InVO4 heterojunction for efficient photocatalytic fixation: synergistic effect of exposed (321) facet and oxygen vacancy

Abstract

Utilizing semiconductors to catalyze the conversion of N₂ to NH₃ has brought great promise in alleviating the issue of energy shortage. However, the wide band gap and high recombination rate of photogenerated (e⁻/h⁺) charge restrict their photocatalytic efficiency. Herein, a novel catalyst, N-Black In₂O_3−x/InVO₄ was developed by coupling InVO₄ nanosheets into defect-rich N-Black In₂O_3−x nanorods to construct multiple heterojunctions using the NH₂-MIL-68(In) metal–organic-framework as a template. The N-Black In₂O_3−x/InVO₄ multiple heterojunctions with oxygen vacancies could expand the light absorption range, act as electron trap centers, promote the separation of photogenerated carriers, and significantly improve the adsorption as well as activation of N₂. Density functional theory (DFT) calculations revealed that the exposed (321) planes of the N-Black In₂O_3−x possess a higher surface energy than the (222) planes, which indicates that the exposed (321) planes can adsorb more N₂ molecules and transform them into NH₃ molecules. Consequently, owing to the efficient separation of photogenerated carriers, the nitrogen fixation rate of the N-Black In₂O_3−x/InVO₄ heterostructure was as high as 2.07 mmol g⁻¹ h⁻¹ without any organic scavengers and precious-metal cocatalysts, which was 20.7, 2.4, 2.1, and 1.8 times that of NH₂-MIL-68(In), N-In₂O₃, InVO₄, and N-Black In₂O_3−x, respectively.