Vacancy Associates Promoting Solar-Driven Photocatalytic Activity of Ultrathin Bismuth Oxychloride Nanosheets

TLDR

Crystal facet engineering of semiconductors is a growing strategy to tune solar‑driven photocatalytic activity, yet the decisive factor among exposed facets remains unclear. We demonstrated that ultrathin BiOCl nanosheets with fully exposed {001} facets exhibit markedly enhanced solar‑photocatalytic activity because atomic‑scale thinning creates triple vacancy associates that improve adsorption, charge separation, and electron reduction, opening new avenues for quasi‑2D photocatalyst design.

Abstract

Crystal facet engineering of semiconductors is of growing interest and an important strategy for fine-tuning solar-driven photocatalytic activity. However, the primary factor in the exposed active facets that determines the photocatalytic property is still elusive. Herein, we have experimentally achieved high solar photocatalytic activity in ultrathin BiOCl nanosheets with almost fully exposed active {001} facets and provide some new and deep-seated insights into how the defects in the exposed active facets affect the solar-driven photocatalytic property. As the thickness of the nanosheets reduces to atomic scale, the predominant defects change from isolated defects V(Bi)‴ to triple vacancy associates V(Bi)‴V(O)••V(Bi)‴, which is unambiguously confirmed by the positron annihilation spectra. By virtue of the synergic advantages of enhanced adsorption capability, effective separation of electron–hole pairs and more reductive photoexcited electrons benefited from the V(Bi)‴V(O)••V(Bi)‴ vacancy associates, the ultrathin BiOCl nanosheets show significantly promoted solar-driven photocatalytic activity, even with extremely low photocatalyst loading. The finding of the existence of distinct defects (different from those in bulks) in ultrathin nanosheets undoubtedly leads to new possibilities for photocatalyst design using quasi-two-dimensional materials with high solar-driven photocatalytic activity.