Graphitic carbon nitride loaded with FeOOH quantum dots for synergistic photocatalysis-Fenton inactivation of pathogenic marine bacteria: Mechanisms and coupling coefficients

Sustainable and environmental benign technologies for inactivation of pathogenic marine bacteria in ballast water remains a challenge. Herein, graphitic carbon nitride (g-C₃N₄) loaded with FeOOH quantum dots (QDs) were fabricated and a synergistic photocatalysis-Fenton system was established, which inactivated Vibrio alginolyticus (7 log) in ballast water within 30 min under visible light irradiation. The bacterial inactivation rate constant in the coupling system was 26.5 and 6.6 times higher than traditional photocatalysis and Fenton system, respectively, exhibiting 88.8 % of synergistic coupling coefficient. The bactericidal efficiency remained consistent across varying pH levels, allowing direct application of this method in alkaline marine conditions. Free radicals including OH and O₂⁻ were proved to be the predominant contributors in the coupling system. The loading of FeOOH QDs could upshift conduction band potential of g-C₃N₄, thus photogenerated electrons were more easily trapped by O₂ to enhance the separation of charge carriers. The photogenerated electrons also accelerated the faster circulation of Fe(III)/Fe(II), which further inhibited electron-hole recombination. Furthermore, bacterial inactivation mechanisms were elucidated by examining total protein changes, intracellular ROSs level and enzyme activities. This work offers innovative approaches for marine bacterial inactivation and ballast water disinfection, which can also find applications in other environmental-related fields.