Flame preparation of visible-light-responsive BiVO 4 oxygen evolution photocatalysts with subsequent activation via aqueous route

Visible-light-active BiVO ₄ photocatalyst prepared by a onestep flame spray pyrolysis demonstrates the structural evolution from amorphous to crystalline scheelite-tetragonal and further to scheelitemonoclinic (the photocatalytic active phase). Up to 95% scheelitemonoclinic content, the rest being scheelite-tetragonal, can be achieved in situ by exposing the collection filter to higher flame temperature. Reasonable activity in terms of photocatalytic O ₂ evolution was obtained with the increase in crystallinity and scheelite-monoclinic content. Although analogous postcalcination of BiVO ₄ improves crystallization and phase transformation, it inevitably induces vacancy defects that are detrimental to the photocatalytic activity. Hence a facile aqueous acid treatment on the flame-made BiVO ₄ is introduced, which in the presence of small addition of Bi and V promotes full transformation to scheelite-monoclinic and reduces charge trapping defects. As a result, the photocatalytic O ₂ evolution activity was increased by a remarkable 5 folds compared to the best performing untreated flame-made BiVO ₄. © 2011 American Chemical Society.