One-Dimensional/Two-Dimensional Core–Shell-Structured Bi₂O₄/BiO_2–<i>x</i> Heterojunction for Highly Efficient Broad Spectrum Light-Driven Photocatalysis: Faster Interfacial Charge Transfer and Enhanced Molecular Oxygen Activation Mechanism

Abstract

Deliberate tuning of nanoparticles encapsulated with nanosheet shells can bring about fascinating photocatalytic properties because of the fast charge-transfer characteristics of a nanosized core-shell structure. Herein, a novel core-shell-structured Bi₂O₄/BiO_{2- x} composite was fabricated through a one-step hydrothermal method. The core-shell Bi₂O₄/BiO_{2- x} composite presented distinct optical absorption property, including UV, visible, and near-infrared (NIR) light regions. Compared to Bi₂O₄ and BiO_{2- x}, the Bi₂O₄/BiO_{2- x} composite revealed improved broad spectrum light-responsive molecular oxygen activation into ^•O₂^-, especially achieving ^•O₂^- generation under NIR light irradiation. The achievement that enhanced broad spectrum light-activated molecular oxygen activation could be ascribed to the faster electron transfer confirmed by the electron spin resonance (ESR) spectra, photoluminescence (PL) spectra, photoelectrochemical test, and quantitative analysis of ^•O₂^-. The strong interface effect of the Bi₂O₄/BiO_{2- x} composite was confirmed by X-ray photoelectron spectroscopy analysis. Density functional theory calculated results suggested that the Bi₂O₄/BiO_{2- x} composite revealed increased density of states near the Fermi level, suggesting that it possessed higher carrier mobility as compared to Bi₂O₄ and BiO_{2- x}, contributing to the faster separation of photoinduced carriers and the generation of ^•O₂^-. Benefiting to the heterojunction, the Bi₂O₄/BiO_{2- x} composite showed improved photocatalytic activity and anti-photocorrosion activity during rhodamine B (RhB) and ciprofloxacin (CIP) degradation with the irradiation of UV, visible, and NIR lights. Besides, the possible photocatalytic mechanism and transformation pathway of RhB and CIP degradation by the Bi₂O₄/BiO_{2- x} composite were proposed by the analyses of the liquid chromatography-mass spectrometry. This study furnishes a new strategy for fabricating high-efficient and broad spectrum light-driven heterojunction photocatalysts for environment purification.