Maximizing the utilization of photo-generated electrons and holes of g-C3N4 photocatalyst for harmful algae inactivation

• Sulfuric acid exfoliated C 3 N 4 (S-CN) exhibited excellent algal removal activity. • Positive charge, smaller size, ultrathin structure contributed to the high activity. • Addition of H 2 O 2 can further improve the efficiency of algal removal. • The released and leaked organic matters from algal cells can also be removed. Effective contact between photocatalysts and algal cells is important for algae inactivation because of the efficient transfer/utilization of photo-generated charges. Herein, sulfuric acid exfoliated C 3 N 4 (S-CN) is found to be efficient for algae inactivation under visible light irradiation (92% removal rate within 3.5 h). The high performance can be ascribed to the positive surface charge (S-CN can be rapidly adsorbed on the surface of algal cells) and small sized/ultrathin structure (high separation/transfer efficiency of charges). Furthermore, the efficiency can be improved significantly by H 2 O 2 addition (94.3% removal rate within 1.5 h). The addition of H 2 O 2 not only reduce the recombination of photo-induced carriers but also generate more ·OH. Decreased photosynthetic activity, membrane damage and cell rupture occur in the inactivation process. In addition, the organic matters release and leak from algal cells are also partly removed. The present work has great significance in the application of photocatalytic technology for algal remediation.