Photocatalytic inactivation of harmful algae Microcystis aeruginosa and degradation of microcystin by g-C3N4/Cu-MOF nanocomposite under visible light

In this work, g-C3N4/Cu-MOF nanocomposites were prepared to inactivate Microcystis aeruginosa and degrade microcystin under visible light irradiation. Doping with g-C3N4 statistically enhanced the photocatalytic efficiency of Cu-MOF, and followed the order of 10 wt% g-C3N4/Cu-MOF > 20 wt% g-C3N4/Cu-MOF > 2 wt% g-C3N4/Cu-MOF. Specially, the performance of 10 wt% g-C3N4/Cu-MOF was 1.86- and 2.93-fold of Cu-MOF in photocatalytic antialgal activity and degradation of microcystin. Mechanistically, 1) heteroaggregation between algal cells and photocatalyst is a primary prerequisite for eliminating harmful algae by photocatalyst, g-C3N4/Cu-MOF nanocomposites exhibited greater ability of heteroaggregation with algal cells than Cu-MOF; 2) g-C3N4 doping increased the visible light utilization of Cu-MOF, with subsequent enhancing its free radicals generation ability; 3) the presence of g-C3N4 elevated the hydrostability of Cu-MOF, and then enhanced the sustainable free radicals production ability of Cu-MOF. The higher performance of 10 wt% g-C3N4/Cu-MOF as compared with 20 wt% g-C3N4/Cu-MOF was because that the excess g-C3N4 doping in 20 wt% g-C3N4/Cu-MOF enhanced the recombination rate of electron-hole pairs, inhibiting the generation of free radicals. O2– and ·OH were main free radicals inducing algal inactivation and microcystin degradation. Two possible photocatalytic degradation pathway of microcystin was identified. The findings provide new insight into enhancing the photocatalytic efficacy of Cu-MOF and the obtained g-C3N4/Cu-MOF nanocomposites have high potential in harmful algal blooming control.