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.