Promoting superoxide generation in Bi2WO6 by less electronegative substitution for enhanced photocatalytic performance: an example of Te doping

Because of their interesting properties and relatively high stability, Bi2WO6 photocatalysts have been widely investigated. Several strategies have been proven effective in improving their performance. Here, we investigate the enhancement of Bi2WO6 photocatalytic activity via Te substitution by means of experiments and first-principles calculations. A maximum of 5 at% can be successfully doped into the Bi2WO6 lattice with no impurity by a facile hydrothermal method. Replacing W6+ with Te6+ does not affect the crystal structure but evidently changes the samples' morphologies and electronic structure. The plate-like structure of Bi2WO6 is altered to a thinner nanosheet, which eases the carrier diffusion and increases the surface active sites. The extra Te 5s state increases the density of states at the bottom of the conduction band and consequently increases the carrier mobility. As a result, carrier recombination is significantly reduced upon Te doping. Moreover, the lower electronegativity of the Te dopant shifts the band edge potential towards more negative values which additionally enables the generation of superoxide radicals. As a result, an optimum doping content of 2.5 at% Te gives rise to 48 times higher Rhodamine B photodegradation compared to pure Bi2WO6. The obtained results provide insights into the effects of doping, specifically the effects of the dopants' electronegativity, on the photocatalytic activity which could be a very effective strategy to improve other related oxide-based photocatalysts.