Ag₃PO₄/CuBi₂O₄ heterojunction with enhanced visible-light photocatalytic performance

A simple single-step hydrothermal method was used to synthesize Ag₃PO₄ (APO)/CuBi₂O₄ (CBO) composites. C.I. Reactive Red 2 (RR2) was the target pollutant, which was degraded under visible-light to evaluate the photocatalytic performance of the composites. Various APO/CBO molar ratios were used to evaluate the effect of this ratio on the performance. All prepared photocatalysts were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible (UV–Vis) spectroscopy, Brunauer–Emmett–Teller analysis and X-ray photoelectron spectroscopy. Scavenger experiments were conducted to determine the photocatalytic mechanism. APO/CBO composites exhibited higher surface areas than both pristine APO (0.13 m²/g) and CBO (0.11 m²/g) and they all responded to visible light. The photodegradation of RR2 satisfied pseudo-first-order reaction kinetics. As the proportion of APO in the APO/CBO composites increased, the photocatalytic activity firstly increased to a maximal value and then declined. The optimal APO/CBO molar ratio was two (AC2). The rate constant obtained with AC2 (0.200 ± 0.009 min⁻¹) was 6.1 times that of APO alone. The degradation efficiency of RR2 decreased from 91 to 73% after three cycles, revealing that AC2 exhibited general reusability; additionally, the photocatalytic stability and reusability of AC2 exceeded those of APO. The scavenger experimental results suggested that hydroxyl radicals had an important role in RR2 photodegradation in the AC2 system. The improved photodegradation efficiency of AC2 was attributed to its larger surface area and greater absorption of visible-light than those of APO and CBO, as well as the formation of heterojunctions at the interfaces of APO and CBO nanoparticles.