Visible light activation of persulfate by magnetic hydrochar for bacterial inactivation: Efficiency, recyclability and mechanisms.

The development of "green" water disinfection technology utilizing solar energy is highly desired but remains challenging. In this study, sulfate radical (•SO)-mediated bacterial inactivation was first attempted by using FeO-based magnetic hydrochar (MHC) as a recyclable catalyst for persulfate (PS) activation under visible light (VL) irradiation. Complete treatment of 8.0 log E. coli cells was reached within 40 min in VL/PS/MHC system, compared with that of only 2.0 log-reduction was obtained in the PS/MHC system under the same conditions. The system was applicable in wide range of pH (3.0-9.0), and increasing dissolved O could further promote the efficiency. A three-route mechanism was proposed, in which the PS activation by ≡Fe(II) of FeO and photo-generated electron captured by PS were the major processes. The bacterial cell lesion process was found to be triggered directly via •SO, which caused the damage of outer membrane, followed by up-regulation of intracellular ROSs and destroy of chromosomal DNA, finally leading to irreversible cell death. Moreover, the VL/PS/MHC system is also effective to inactivate versatile pathogenic bacteria including P. aeruginosa and S. aureus. As a proof-of-concept, our study provides meaningful information to advance the areas of "green" water disinfection technology which can be realized by recyclable photocatalytic systems using solar energy.