Fast photocatalytic inactivation of Microcystis aeruginosa by metal-organic frameworks under visible light.

In this work, Metal-organic Frameworks (MOFs) were applied to inactivate algae under visible light with low doses. Five MOFs with different compositions (Zn and Fe; carboxylates or imidazolates) were successfully synthesized and characterized by XRD, SEM and UV-vis. The effects of MOFs on Microcystis aeruginosa were evaluated with regard to morphology characteristics, physiological activity, cell integrity and pigment degradation. The results indicated that Ag/AgCl@ZIF-8 outperformed MOF-235, ZIF-8, BiWO/MIL-100(Fe) and BiOBr/MOF-5 in the degradation of chlorophyll a at the dose of 10 mg L. After 6 h of irradiation, 93.1% of Microcystis aeruginosa died and was unable to regrow and reproduce, which was demonstrated by changes in cell morphology, damage of cell membrane integrity and antioxidant enzyme system. Besides, the intracellular organic matter (IOM) and extracellular organic matter (EOM) were proven to be efficiently removed by MOF-assisted photocatalytic inactivation. Superoxide radical (O·) was demonstrated to be the major reactive oxygen species. A probable mechanism was proposed that the electrons in the valence band of Ag/AgCl@ZIF-8 transfer into the conduction band under irradiation to produce O· which inactivated the algae cells. Furthermore, Ag/AgCl@ZIF-8 can effectively remove Microcystis aeruginosa under sunlight and is of great application prospects for algae removal in real water bodies.