Photocatalytic transformation of climbazole and 4-chlorophenol formation using a floral array of chromium-substituted magnetite nanoparticles activated with peroxymonosulfate

Climbazole (CBZ) is an emerging contaminant with adverse effects on aquatic organisms. In this study, a floral array of chromium-substituted magnetite nanoparticles was synthesized, characterized, and used in photocatalytic degradation of CBZ. The results showed that Cr incorporation did not change the spinel structure of magnetite, but resulted in the obvious decrease of its crystallinity. The Cr content greatly influenced the morphology and micro-structure of magnetite nanoparticles, which led to a significantly larger surface area, and more abundant pores and surface hydroxyl groups. Factors such as the UV light source, catalyst concentration, initial level of CBZ, solution pH, peroxymonosulfate (PMS) dosage, and Cr level in magnetite affected the transformation of CBZ. Under the optimized photocatalytic conditions, i.e., 0.2 g L^-1 Fe_2.52Cr_0.48O₄, 2.0 μmol L^-1 CBZ, 1.0 mmol L^-1 PMS, and pH = 3.08, CBZ was almost completely eliminated within 30 min, which was much faster than under photodegradation, biodegradation, or chlorination reported previously. The reactive oxygen species including OH and SO₄^- coexisted and participated in the photocatalytic reaction. The GC-MS analysis revealed the generation of 4-chlorophenol (4-CP) as a primary intermediate following CBZ transformation, based on the stoichiometric relationship between CBZ and 4-CP. The resultant 4-CP in the present study does not increase the risk to aquatic life. The results highlight an environmentally friendly strategy for effective elimination of CBZ.