Performance And Mechanism Of Ag₂O@PG Composite Photocatalyst For Efficient Inactivation Of Microcystis Aeruginosa Under Visible Light Irradiation

The outbreak of harmful algal blooms caused by eutrophication in the aqueous environment has been a major focus of attention in the field of environmental protection and remediation for many years due to its negative impacts on ecosystems and human life.The existing remediation strategies have many shortcomings and are unable to achieve efficient and ecofriendly removal of harmful algal blooms,making it imperative to develop new technologies for harmful algal bloom management.As research progress in photocatalysis,this technology has attracted much attention in the field of harmful algal inactivation due to its low cost,non-toxic and environmentally friendly characteristics and high stability.The development of a photocatalyst with high algal inactivation capacity under visible light irradiation can provide a reference for the application of photocatalytic technology to the treatment and remediation of harmful algal blooms,and is of great significance for deepening the application practice of basic photocatalytic research results.In this study,silver oxide composite phosphorus-doped carbon nitride（Ag₂O@PG）photocatalysts with unique tubular structure were prepared to investigate the removal effect and mechanism of Ag₂O@PG composite photocatalysts on Microcystis aeruginosa under visible light irradiation.The main conclusions include the following aspects.1.An Ag₂O@PG composite photocatalyst with hollow tubular structure was successfully constructed.The loading of P elements changed the energy band structure.The composition of Ag₂O enhanced the adsorption of visible light and changed the carrier migration path of the material,which improved the efficiency of photogenerated electron-hole separation.2.It was found through photocatalytic algal inactivation experiments that the photocatalytic activity of Ag₂O@PG was influenced by the composition ratio of the materials,in which the Ag₂O-PG-0.4 composite photocatalyst with a dosage of 0.2 g/L could remove 99,1%of chlorophyll a from algal solution with an initial concentration of 4.5×10⁶ cells/mL after 5-hour’s visible light irradiation.The change of dissolved organic matter and the ion concentration in the solution revealed that the algal cell morphology and cell membrane permeability were altered during photocatalytic algal inactivation.By measuring the peroxide dismutase（SOD）,glutathione（GSH）and malondialdehyde（MDA）contents in Microcystis aeruginosa cells,it was found that the intracellular SOD,GSH and MDA contents increased until the antioxidant enzyme system of Microcystis aeruginosa was finally destroyed in order to mitigate oxidative damage.3.Ag₂O@PG produced superoxide radicals（·O₂^-）,hydroxyl radicals（·OH）and photogenerated holes（h⁺）with strong oxidative properties under visible light excitation.The contribution of each radical in the photocatalytic algal inactivation process was:·O₂^->h⁺>·OH.It can be speculated that its photocatalytic algal inactivation is through the photocatalyst under the light irradiation to produce oxidative damage to the cells of Microcystis aeruginosa,destroy the cell morphology,change the cell membrane permeability,make the intracellular organic matter outflow,further make organic matter mineralized and cells apoptosis.This study provides an efficient and ecofriendly technological option for the removal of harmful cyanobacteria from water bodies and shows that carbon nitride photocatalysts can be promising for the remediation of eutrophic water bodies through morphology modulation,compounding and doping modifications.