The critical challenge in the photocatalytic treatment of low-concentration nitrogen oxides (NOx) 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 (radical dotOH). As the dominant reactive species, radical dotOH 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 NOx contaminants under visible-light-driven conditions.
