Enhanced Visible-Light-Driven Photocatalytic Bacterial Inactivation by Ultrathin Carbon-Coated Magnetic Cobalt Ferrite Nanoparticles

Ultrathin hydrothermal carbonation carbon (HTCC)-coated cobalt ferrite (CoFe2O4) composites with HTCC coating thicknesses between 0.62 and 4.38 nm were fabricated as novel, efficient, and magnetically recyclable photocatalysts via a facile, green approach. The CoFe2O4/HTCC composites showed high magnetization and low coercivity, which favored magnetic separation for reuse. The results show that the close coating of HTCC on CoFe2O4 nanoparticles enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. The composites exhibited superior photocatalytic inactivation toward Escherichia coli K-12 under visible-light irradiation, with the complete inactivation of 7 log10 cfu·mL–1 of bacterial cells within 60 min. The destruction of bacterial cell membranes was monitored by field-effect scanning electron microscopy analysis and fluorescence microscopic images. The bacterial inactivation mechanism was investigated in a scavenger study, and •O2, H2O2, and h+ were identified as the major reactive species for bacterial inactivation. Multiple cycle runs revealed that these composites had excellent stability and reusability. In addition, the composites showed good photocatalytic bacterial inactivation performance in authentic water matrices such as surface water samples and secondarily treated sewage effluents. The results of this work indicate that CoFe2O4/HTCC composites have great potential in large-scale photocatalytic disinfection operations.