Heterostructured ZnAl–LDH/Bi4O5Br2 photocatalyst with enhanced surface molecular adsorption for efficient bisphenol A removal

Abstract

A novel dual-function ZnAl–LDH/Bi₄O₅Br₂ nanocomposite photocatalyst was synthesized using a self-assembly process and optimized by response surface methodology for the advanced treatment of wastewater micropollutants. A series of characterizations revealed that ZnAl–LDH/Bi₄O₅Br₂ exhibits suitable heterojunction structure and excellent optoelectronic properties. As a result, ZnAl–LDH/Bi₄O₅Br₂ achieved the near-complete removal of bisphenol A (BPA) after 120 min through a synergistic process of adsorption and visible-light photocatalysis. The corresponding reaction rate constant for photocatalytic degradation approached 0.14 min⁻¹, which is significantly higher than those by Bi₄O₅Br₂ and ZnAl–LDH. Regarding the enhanced BPA removal over ZnAl–LDH/Bi₄O₅Br₂, the adsorption behavior occurred via hydrogen bonding and π-π stacking interactions, while the photocatalytic degradation involved the efficient photoexcitation and separation of charge carriers for the formation of reactive oxygen species (ROS) under the heterojunction effect. Electron spin resonance (ESR) and radical quenching experiments indicated that ROS including ·OH, ·O₂⁻, and ¹O₂, mainly contribute to BPA degradation. The predominant ROS formation mechanism was the interfacial reactions of the nanocomposite with H₂O molecules, as verified by the density of states, charge density differences, and adsorption energy calculations. Furthermore, the intermediate products of BPA degradation were identified, the degradation pathways were proposed, and the related ecotoxicity consequences were evaluated. This study confirmed that ZnAl–LDH/Bi₄O₅Br₂ has superior synergistic adsorptive and photocatalytic performance, offering guidance in the further construction and application of functional nanocomposites for wastewater treatment.