Channel-Doping-Stabilized Hexagonal WO3 for Synergistic Photothermal Ammonia Removal via a Photo-iSCR Pathway

Ammonia (NH3) emissions pose significant risks to both the environment and human health, yet the efficient removal of low-concentration NH3 under mild conditions remains a considerable challenge. Herein, we report a Na-doped WO3 photocatalyst synthesized via a hydrothermal route, where Na incorporation stabilizes the metastable hexagonal WO3 phase through a channel-doping mechanism, consistent with previous studies on alkali-metal-modified hexagonal WO3. The stabilized hexagonal Na/WO3 exhibits a high specific surface area (65.68 m2·g–1) and enhanced NH3 adsorption affinity (DFT adsorption energy of −1.37 eV). Under full-spectrum irradiation, the optimized Na/WO3-1 catalyst achieves an NH3 removal efficiency of 80.4% within 120 min, significantly outperforming its monoclinic counterparts. This superior performance is attributed to the synergistic coupling of efficient charge separation and photothermal conversion, which elevates the catalyst surface temperature to 71.3 °C and facilitates NH3 oxidation kinetics. In situ DRIFTS analyses reveal that NH3 oxidation proceeds via a photoinduced internal selective catalytic reduction (photo-iSCR) pathway, which differs fundamentally from the conventional thermally driven iSCR mechanism. This work establishes a structure–activity relationship between channel-doping-induced phase stabilization and photothermal catalytic performance, providing a rational strategy for designing efficient WO3-based catalysts for low-temperature NH3 purification.