Visible-light-driven heterostructured g-C3N4/Bi-TiO2 floating photocatalyst with enhanced charge carrier separation for photocatalytic inactivation of Microcystis aeruginosa

The increase in occurrence and severity of cyanobacteria blooms is causing increasing concern; moreover, human and animal health is affected by the toxic effects of Microcystin-LR released into the water. In this paper, a floating photocatalyst for the photocatalytic inactivation of the harmful algae Microcystis aeruginosa (M. aeruginosa) was prepared using a simple sol-gel method, i.e., coating g-C3N4 coupled with Bi-doped TiO2 on Al2O3-modified expanded perlite (CBTA for short). The impact of different molar ratios of Bi/Ti on CBTA was considered. The results indicated that Bi doping in TiO2 inhibited photogenerated electron-hole pair recombination. With 6 h of visible light illumination, 75.9% of M. aeruginosa (initial concentration = 2.7 × 106 cells/L) and 83.7% of Microcystin-LR (initial concentration =100 µg/L) could be removed with the addition of 2 g/L CBTA-1% (i.e., Bi/Ti molar ratio = 1%). The key reactive oxygen species (ROSs) in the photocatalytic inactivation process are h+ and ⦁OH. The induction of the Bi4+/Bi3+ species by the incorporation of Bi could narrow the bandgap of TiO2, trap electrons, and enhance the stability of CBTA-1% in the solutions with coexisting environmental substances.