Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH₄-reduced N_(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C₃N₄ photooxidation for NO removal. In this paper, flake graphite-phase g-C₃N₄ is prepared by thermal polycondensation. Then g–C₃N₄–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N_(ligancy-3)) was prepared by NaBH₄ reduction at room temperature. The introduction of N vacancies in g-C₃N₄ narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C₃N₄–x shows a superior NO removal performance, especially g–C₃N₄–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO₂, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)₂ produced from NO adsorption on the surface of g–C₃N₄–1.5 is an important intermediate. Additionally, NO₂⁻ is observed as an intermediate and a primary product, and NO₃⁻ is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N_(ligancy-3) vacancy introduces impurity energy levels in g-C₃N₄ and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C₃N₄–N_(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C₃N₄ to remediate environmental pollution. Copyright © 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.