Photocatalysis activation of peroxydisulfate over oxygen vacancies-rich mixed metal oxide derived from red mud-based layered double hydroxide for ciprofloxacin degradation

In this work, a low-cost and oxygen vacancies (OVs) enriched mixed metal oxide (M−RM/MMO) derived from red mud-based layered double hydroxide (M−RM/LDH) was applied as an efficient peroxydisulfate (PDS) activator to realize the degradation of ciprofloxacin (CIP) under visible light (VL) irradiation. The optimal composite of M−RM/MMO-700 exhibited good performance, and approximately 87.4% of CIP (10 mg/L) could be degraded at 60 min via the photocatalysis activation of PDS (1.0 mM) over M−RM/MMO-700 (0.2 g/L). The result indicated the abundant OVs in M−RM/MMO-700 could improve light absorption and promote electron-hole separation, both of which were favorable for the activation of PDS, resulting in promoting the generation of active species in M−RM/MMO-700/PDS/VL system. Quenching experiments and EPR technology indicated that O2−, 1O2 and h+ were the main active species for the degradation of CIP. The M−RM/MMO catalyst possessed excellent reusability, stability and magnetic behavior in use. The degradation pathways of CIP were deduced based on DFT calculation and LC-MS analysis. Based on the quantitative structure–activity relationship (QSAR), the ecotoxicity of the degradation intermediates was analyzed in detail. This work provided a new insight for future designing of red mud-based LDHs-derived MMO heterogeneous catalyst with abundant OVs to efficiently treat antibiotics wastewater via the photocatalysis activation of PDS.