Exciton-Free, Nonsensitized Degradation of 2-Naphthol by Facet-Dependent BiOCI under Visible Light: Novel Evidence of Surface-State Photocatalysis

Photoreactivity for photodegradation of 2-NAP on BiOCl nanosheets with dominant exposed (010) and (001) facets is studied under visible light via an exciton-free and nonsensitized mechanism. This phenomenon cannot be explained by semiconductor theory or self-sensitized (as those involve dyes) mechanisms. The photocatalytic activities are mainly owing to the formation of the surface state, which is confirmed to be the surface complex Bi-O-C10H7. This surface complex is characterized with ultraviolet visible diffuse reflectance spectra, Fourier transformed infrared spectroscopy, Raman scattering, X-ray photoelectron spectroscopy, and photoelectrochemical measurement. The optical absorptivity of BiOCl is shifted from the ultraviolet light toward the visible light via a charge-transfer-complex pathway. Charge transfer after the excitation of visible light induces efficient visible photocatalytic activities. The results show that single-crystalline BiOCl nanosheets exposing (010) facets exhibit higher photoactivity due to more surface complex and more terminal bismuth atoms on the surface of BiOCl (010). Our current work is expected to offer new insight into photocatalytic theory for better understandings to photocatalytic reactions and for rational design and synthesis of photocatalyst with high activity.