In-situ co-doping of sputter-deposited TiO2:WN films for the development of photoanodes intended for visible-light electro-photocatalytic degradation of emerging pollutants

We report on the magnetron sputtering deposition of in-situ codoped TiO₂:WN films intended for electro-photocatalytic (EPC) applications under solar irradiation. By varying the RF-magnetron sputtering deposition parameters, we were able to tune the in-situ incorporation of both N and W dopants in the TiO₂ films over a wide concentration range (i.e., 0–9 at. % for N and 0–3 at. % for W). X-ray photoelectron spectroscopy analysis revealed that both dopants are mostly of a substitutional nature. The analysis of the UV-Vis transmission spectra of the films confirmed that the optical bandgap of both TiO₂:N and TiO₂:WN films can be significantly narrowed (from 3.2 eV for undoped-TiO₂ down to ∼2.3 eV for the doped ones) by tuning their dopant concentrations. We were thus able to pinpoint an optimal window for both dopants (N and W) where the TiO₂:WN films exhibit the narrowest bandgap. Moreover, the optimal codoping conditions greatly reduce the recombination defect state density compared to the monodoped TiO₂:N films. These electronically passivated TiO₂:WN films are shown to be highly effective for the EPC degradation of atrazine (pesticide pollutant) under sunlight irradiation (93% atrazine degraded after only 30 min of EPC treatment). Indeed, the optimally codoped TiO₂:WN photoanodes were found to be more efficient than both the undoped-TiO₂ and equally photosensitized TiO₂:N photoanodes (by ∼70% and ∼25%, respectively) under AM1.5 irradiation.