Magnetic composite photocatalyst NiFe₂O₄/ZnIn₂S₄/biochar for efficient removal of antibiotics in water under visible light: Performance, mechanism and pathway

The widespread presence of antibiotics in aquatic environments, resulting from excessive use and accumulation, has raised significant concerns. A NiFe₂O₄/ZnIn₂S₄/Biochar (NFO/ZIS/BC) magnetic nanocomposite was successfully synthesized, demonstrating significantly enhanced electron-hole separation properties. Comprehensive investigations were conducted to evaluate the impact of various parameters, including catalyst mass, pH, and the presence of co-existing ions on the composite's performance. The nanoparticles of NiFe₂O₄ (NFO) and ZnIn₂S₄ (ZIS) were found to improve the surface stability and sulfamethoxazole removal capabilities of porous biochar, while also demonstrating high total organic carbon removal efficiencies. •O₂⁻ and h⁺ were identified as the predominant reactive oxygen species (ROS) in NFO/ZIS/BC-4 during the degradation process. The degradation outcomes of sulfamethoxazole under natural sunlight and water conditions were consistent with laboratory findings, affirming the robust applicative potential of NFO/ZIS/BC. Density functional theory (DFT) calculations were performed to elucidate the photocatalytic mechanism and identify potential intermediate products. Additionally, the types of heterojunctions present in the system were characterized and discussed. After multiple iterations, NFO/ZIS/BC-4 maintained effective photodegradation capabilities through five cycles. This study presents an effective method for the treatment of antibiotics in aquatic environments, offering significant potential for environmental applications. [Display omitted] •NiFe₂O₄ and ZnIn₂S₄ can improve the surface stability.•NFO/ZIS/BC-4 can completely degrade SMX within 60 min.•Total organic carbon was removed efficiently using NiFe₂O₄ and ZnIn₂S₄.••O₂⁻ and h⁺ were identified as the predominant reactive oxygen species in NFO/ZIS/BC-4.