Na+-doping induced synergistic oxygen vacancies and compressive strain for enhanced photocatalytic formaldehyde mineralization.

The efficiency of photocatalytic formaldehyde (HCHO) mineralization is often limited by insufficient adsorption and activation of O2 and HCHO on conventional semiconductor surfaces. In this work, we demonstrate a 'kill two birds with one stone' strategy-Na+ doping in ZnWO4-which simultaneously introduces oxygen vacancies and compressive lattice strain. This synergistic defect and strain engineering injects electrons into the W 5d orbitals, creating electron-rich W sites and shifting the d-band center upward. The resulting electronic structure enhances the adsorption and activation of both O2 and HCHO, with adsorption energies reaching -2.08 eV and - 1.02 eV, respectively, significantly reducing the energy barrier of the rate-limiting formate oxidation step from -0.26 eV to -1.45 eV. Consequently, Na-ZnWO4 achieves markedly improved reactive oxygen species generation, an 80.2% HCHO removal efficiency, and a high CO2 yield under simulated solar light, greatly outperforming pristine ZnWO4. This work demonstrates a co-regulation strategy for defects and strain via cation doping as an effective route toward high-performance photocatalytic materials.