Boosted photocatalytic NO conversion with inhibited NO2 generation over Nb2O5/g-C3N4 S-scheme heterojunction: nanostructured engineering and mechanism insight

Abstract

The critical challenge in the photocatalytic treatment of low-concentration nitrogen oxides (NO_x) is to achieve deep oxidation of NO while suppressing the formation of toxic intermediate NO₂. Herein, a Nb₂O₅/g-C₃N₄ S-scheme heterojunction is designed to address this challenge through tailored charge dynamics. Experimental results and theoretical calculations synergistically validate the S-scheme heterojunction featuring an interfacial electric field (IEF)-driven directional charge separation mechanism. This configuration synergistically enhances charge separation efficiency while maintaining robust redox potentials, thereby effectively activating hydroxyl radicals (OH). As the dominant reactive species, OH facilitates deep oxidation of NO while effectively inhibiting toxic NO₂ by-product formation. At an initial NO concentration of 800 ppb, the Nb₂O₅/g-C₃N₄ S-scheme heterojunction achieved an excellent removal rate of 68.3 % with suppressed NO₂ byproduct generation (24.6 ppb) under visible light irradiation (λ ≥ 420 nm) within 20 min. Furthermore, the reaction intermediates were monitored by in-situ diffused reflection Fourier transform infrared spectroscopy (DRIFTS), identifying nitrate as the terminal oxidation product. This work advances the rational design of S-scheme photocatalysts and offers a viable strategy for environmental remediation of NO_x contaminants under visible-light-driven conditions.