High entropy spinel oxide nanoparticles for visible light-assisted photocatalytic degradation of binary mixture of antibiotic pollutants in different water matrixes

Abstract

This study comprehensively investigates for the first time the photocatalytic potential of a magnetic high entropy oxide (HEO), i.e., (FeCoNiCuZn)_aO_b, and unravels the fundamental mechanisms governing its exceptional performance over conventional semiconductor photocatalysts in degrading two common antibiotic pollutants, viz., sulfamethoxazole (SMX) and ofloxacin (OFX), in their aqueous phase. Synthesized via a facile, robust, and straightforward approach, the (FeCoNiCuZn)_aO_b nanoparticles (NPs) exhibit a remarkable photocatalytic degradation efficiency of 97% and 95% for SMX and OFX, respectively, upon exposure to visible light for 90 min. This outstanding activity can be primarily attributed to the coexistence of a vast number of distinct multielement active sites and numerous surface oxygen defects, intense and broadband absorption in the visible spectral region, and enhanced charge separation and transfer, as verified through optical, electrochemical, and photophysical analyses. Additionally, investigation into the contribution of active oxygen species reveals the predominant role of superoxide anions in the degradation and mineralization of antibiotics. In order to showcase the versatility of (FeCoNiCuZn)_aO_b NPs in water and wastewater treatment, the simultaneous dissociation of SMX and OFX is directly tested in six different real water matrixes, with the mean degradation efficiency decreasing in the sequence: groundwater (89%) > tap water (81%) > surface water (78%) > municipal wastewater (71%) > hospital wastewater (66%) > pharmaceutical wastewater (55%). Further, the HEO NPs can be readily separated from the reaction mixture via magnetic decantation, and reused multiple times without significant loss in stability or activity. These findings highlight the enormous potential of (FeCoNiCuZn)_aO_b NPs as next-generation photocatalysts for the removal of antibiotic residues from urban water systems.