Graphene-analogue h-BN coupled Bi-rich Bi4O5Br2 layered microspheres for enhanced visible-light photocatalytic activity and mechanism insight

Abstract

The novel boron nitride coupled Bi-rich Bi4O5Br2 layered microspheres (h-BN/Bi4O5Br2-LMs) were successfully synthesized via a facile ionic liquid-in-water (IL/W) microemulsion-mediated route. The physical, chemical and optical properties of these heterojunction photocatalysts were thoroughly characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and UV–vis diffuse reflection spectroscopy (DRS). Their photocatalytic activities were primarily evaluated by degradation of 4-tert-butylphenol (PTBP), which found 1.0wt% h-BN/Bi4O5Br2-LMs to be the best one. The photocurrent experiments showed that the photocurrent density of 1.0wt% h-BN/Bi4O5Br2-LMs was four times higher than that of pure Bi4O5Br2-LMs due to enhanced charge transfer ability of the former. It revealed that the addition of h-BN was in favor of suppressing the photoinduced electron-hole pair recombination of Bi4O5Br2-LMs, so as to improve the photocatalytic activity of the composite. O2− and h+ were proved to be the main reactive species in the photocatalytic process by scavenger experiments and electron paramagnetic resonance (EPR) spectra. In addition, the photocatalytic mechanism of h-BN/Bi4O5Br2-LMs was further elaborated in this work. The probable degradation products were identified by GC–MS. The proposed conjugated addition and oxidation reactions were described to be the main pathways by combining the frontier electron density calculation and GC–MS results.