Enhanced Visible-Light Photocatalytic Activity of BiOI/BiOCl Heterojunctions: Key Role of Crystal Facet Combination

TLDR

In general, photocatalyst activity correlates positively with light harvesting, charge separation, and charge injection. The study proposes a design framework for heterojunction photocatalysts that fine‑tunes interface structures to optimize charge injection and enhance activity. Two BiOI/BiOCl heterojunction models—BiOI(001)/BiOCl(001) and BiOI(001)/BiOCl(010)—were fabricated by combining nanostructure construction with crystal facet engineering. BiOI(001)/BiOCl(010) showed markedly higher visible‑light photocatalytic activity than BiOI(001)/BiOCl(001), due to a higher charge‑injection efficiency from a shorter electron diffusion distance and internal electric fields, underscoring the importance of crystal facet combination.

Abstract

Two comparable models of BiOI/BiOCl heterojuctions with different interface structures (crystal surface orientation and crystal surface combination), denoted as BiOI(001)/BiOCl(001) and BiOI(001)/BiOCl(010), have been prepared via integrating heterojuncton nanostructure construction with crystal facet engineering. BiOI(001)/BiOCl(010) had a greater degree of lattice mismatch and displayed higher visible-light photocatalytic activity than BiOI(001)/BiOCl(001). In general, the activity of a photocatalyst (ηPC) has a positive correlation with light harvesting (ηLH), charge separation (ηCS), and charge injection (ηCI). On the basis of the experimental results, we considered that the higher ηCI value of BiOI(001)/BiOCl(010) was the main reason for its better visible-light photocatalytic performance. In combination with theoretical calculations, we found that the higher ηCI value of BiOI(001)/BiOCl(010) was the result of a shorter photogenerated electron diffusion distance, assisted by the self-induced internal electric fields of the BiOCl slabs. This indicated that the crystal facet combination is the key to enhancing the photocatalytic activity of BiOI/BiOCl. Our work offers an archetype for the further design of heterojunction photocatalysts with a fine tuning of the interface structures in order to reach optimized charge injection and enhanced photocatalytic activity.