In situ formed Bi/BiOBrxI1−x heterojunction of hierarchical microspheres for efficient visible-light photocatalytic activity

Abstract

Bi nanoparticles deposited in situ in BiOBr_xI_1−x hierarchical microspheres (Bi/BiOBr_xI_1−x heterojunction) were synthesized by a facile one-step solvothermal method. The as-prepared samples were characterized via XRD, SEM, TEM, XPS, UV-vis absorption spectroscopy and N₂ adsorption–desorption. The hierarchical microspheres were composed of numerous nanosheets aggregated together compactly to form a spherical geometry. Results indicated that Bi nanoparticles were generated on the surface of BiOBr_xI_1−x microspheres via the in situ reduction of Bi³⁺ by ethylene glycol. BiOBr_xI_1−x microspheres with deposited Bi nanoparticles were employed for the degradation of RhB under visible-light irradiation and the samples exhibited exceptionally enhanced photocatalytic activity. This immense enhancement in photocatalytic activity was attributed to the contribution of Bi nanoparticles to the efficient separation of electron–hole pairs and prolongation of the lifetime of charge carriers. The behavior of Bi nanoparticles as a cocatalyst for enhancing photocatalytic activity is similar to that of noble metals in photocatalysis. The as-prepared Bi/BiOBr_0.266I_0.734 sample exhibited highest photocatalytic activity, which exceeded those of other types of visible-light photocatalysts such as N-TiO₂, Eu³⁺-BiOI, BiOBr, BiOBr_0.2I_0.8/graphene and even Ag/AgBr/BiOBr. The Bi/BiOBr_0.266I_0.734 sample displayed high photochemical stability under repeated visible-light irradiation, which is especially important for its practical application. The active species produced from Bi/BiOBr_xI_1−x under visible light were hydroxyl radicals. Bi/BiOBr_xI_1−x could generate more hydroxyl radicals due to the Bi nanoparticles, contributing to the enhance oxidation ability. This study demonstrated the high feasibility of utilizing low-cost Bi nanoparticles as a substitute for noble metals to enhance visible-light photocatalysis.