CuO nanoparticles doping recovered the photocatalytic antialgal activity of graphitic carbon nitride

In this work, graphitic carbon nitride (g-C3N4) and CuO nanoparticles doped g-C3N4 (Cu-g-C3N4) was synthesized, and the mechanisms of humic acid (HA) impact on the photocatalytic antialgal activities of g-C3N4 and Cu-g-C3N4 to harmful algae were investigated. The 72 h median effective concentrations of g-C3N4 and Cu-g-C3N4 to two algae (Microcystis aeruginosa, Chlorella vulgaris) were (56.4, 89.6 mg/L) and (12.5, 20.6 mg/L), respectively. Cu-g-C3N4 exhibited higher photocatalytic antialgal activity than g-C3N4 because that: I) Cu-g-C3N4 was easier to aggregate with algal cells due to its lower surface potential and higher hydrophobicity than g-C3N4; II) Cu-g-C3N4 generated more O2−, OH*, and h+ due to its higher full-wavelength light utilization efficiency and higher electron-hole pairs separation efficiency than g-C3N4. HA (10 mg/L) inhibited the photocatalytic antialgal activity of g-C3N4, however, HA had no effect on that of Cu-g-C3N4. The mechanisms were that: I) doped CuO nanoparticles occupied the adsorption sites of HA on g-C3N4, which alleviated the inhibition of HA on the g-C3N4-algae heteroaggregation; II) HA adsorbed on CuO nanoparticles enhanced the oxygen reduction rate of Cu-g-C3N4. This work provides new insight into the inhibition mechanisms of NOM on g-C3N4 photocatalytic antialgal activity and addresses the optimization of g-C3N4 for environmental application.