Porous self-floating 3D Ag2O/g-C3N4 hydrogel and photocatalytic inactivation of Microcystis aeruginosa under visible light

The practical application of photocatalytic technology in the natural water body is limited by the low reuse capability and potential secondary pollution risk of powder catalysts. Consequently, it is highly desirable to develop the stable floating photocatalytic composites for efficient alleviating harmful algal blooms. In this study, the self-floating Ag2O/g-C3N4/hydrogel composites with a porous three-dimension (3D) network nanostructure via the cross-linking of chitosan and polyvinyl alcohol have been synthesized. The effects of doping load, initial algal density and dissolved organic matter on Microcystis aeruginosa (M. aeruginosa) removal were investigated by Ag2O/g-C3N4/hydrogel under visible light irradiation. Among the synthesized photocatalysts, the 20-Ag2O/g-C3N4/hydrogel showed the highest adsorption, good reusability performance and excellent photocatalytic activity within 4 h for the removal of M. aeruginosa. Algal cell membrane and phycobiliprotein were severely damaged during the photocatalytic process. The inactivation mechanisms are attributed to the water-adsorbing swelling of the hydrogel and the generated reactive oxygen species (mainly ·O2− and ·OH) by Ag2O/g-C3N4. Moreover, the antioxidant system of the algae cells was also collapsed under the effects of reactive oxygen species. The superoxide dismutase (SOD) and catalase (CAT) content of algal cells decreased rapidly after photocatalytic reaction by Ag2O/g-C3N4/hydrogel, while the malondialdehyde (MDA) activity was higher than that of the control group. The self-floating Ag2O/g-C3N4/hydrogel photocatalyst would have real practical applications for harmful algae in the fields of natural water body.