First-principles studies on facet-dependent photocatalytic properties of bismuth oxyhalides (BiOXs)

The photocatalytic properties were compared for the {001}, {110} and {010} facets of bismuth oxyhalides (BiOXs) through density functional theory (DFT) computations. X-terminated bulk-like {001} facets with clear boundary of [Bi2O2] and halogen slabs result in high thermodynamic stability and efficient separation of photo-induced e(-)-h(+) pairs. Moreover, surface O vacancies, which act as e(-)-h(+) recombination centers, are energetically unfavorable within {001} facets. BiX-terminated {110} and other facets with surface O vacancies introduce deep defect levels to the band gap, which are detrimental to the separation of e(-)-h(+) pairs. These findings can better understand the origin of facet-dependent photocatalytic activities in BiOXs, and provide guidance for the design of high-efficiency photocatalysts.