Visible-light-driven photocatalytic removal of PPCPs using magnetically separable bismuth oxybromo-iodide solid solutions: Mechanisms, pathways, and reusability in real sewage

Abstract

In testing a series of bismuth oxybromo-iodide (BiOBrxI1−x; 0 ≤ x ≤ 1) solid solutions, BiOBr0.9I0.1, due to its superior charge-carriers separation, exhibited the best performance in the visible-light-driven photocatalytic degradation of pharmaceutical and personal care products (PPCPs). Subsequently, its superparamagnetic version, BiOBr0.9I0.1/Fe3O4@SiO2, possessing a mesoporous hierarchical morphology, was solvothermally developed, and completely degraded the two model PPCPs, ibuprofen and benzophenone-3, in 1 and 2 h, respectively. Scavenger studies revealed that the ibuprofen degradation was dominated by e−, O2−, and h+, while the benzophenone-3 degradation was dominated by e− and O2−. Hydroxylation, decarboxylation, and demethylation were found to be the major reactions involved in the degradation pathways. The aquatic toxicity of the intermediates – estimated using the ECOSAR software – was found to be lower than for the parent PPCP molecules, indicating a reduced environmental risk after photocatalytic degradation. The solution matrix study elaborated the varying extent of the interacting roles of the co-present anions, cations, and NOM. The reusability and stability of BiOBr0.9I0.1/Fe3O4@SiO2 was examined in real secondary treated sewage in a prototype photocatalytic reactor equipped with a magnetic separator. Due to the interferences and unwanted interactions caused by the co-present constituents in secondary treated sewage, a gradual loss in the photocatalytic performance of BiOBr0.9I0.1/Fe3O4@SiO2 was observed during consecutive rounds of recycling.