Hierarchical BiOCO wrapped with modified graphene oxide for adsorption-enhanced photocatalytic inactivation of antibiotic resistant bacteria and resistance genes.

There is growing pressure for wastewater treatment plants to mitigate the discharge of antibiotic resistant bacteria (ARB) and extracellular resistance genes (eARGs), which requires technological innovation. Here, hierarchical BiOCO microspheres were wrapped with nitrogen-doped, reduced graphene oxide (NRGO) for enhanced inactivation of multidrug-resistant E. coli NDM-1 and degradation of the plasmid-encoded ARG (bla) in secondary effluent. The NRGO shell enhanced reactive oxygen species (ROS) generation (•OH and HO) by about three-fold, which was ascribed to broadened light absorption region (red-shifted up to 459 nm) and decreased electron-transfer time (from 55.3 to 19.8 ns). Wrapping enhanced E. coli adsorption near photocatalytic sites to minimize ROS scavenging by background constituents, which contributed to the NRGO-wrapped microspheres significantly outperforming commercial TiO photocatalyst. ROS scavenger tests indicated that wrapping also changed the primary inactivation pathway, with photogenerated electron holes and surface-attached hydroxyl radicals becoming the predominant oxidizing species with wrapped microspheres, versus free ROS (e.g., •OH, HO and •O) for bare microspheres. Formation of resistance plasmid-composited microsphere complexes, primary due to the π-π stacking and hydrogen bonding between the shell and nucleotides, also minimized ROS scavenging and kept free plasmid concentrations below 10 copies/mL. As proof-of-concept, this work offers promising insight into the utilization of NRGO-wrapped microspheres for mitigating antibiotic resistance propagation in the environment.