Solar-driven semi-conductor photocatalytic water treatment (TiO₂, g-C₃N₄, and TiO₂+g-C₃N₄) of cyanotoxins: proof-of-concept study with microcystin-LR

Cyanobacteria and their toxins are a threat to drinking water safety as increasingly cyanobacterial blooms (mass occurrences) occur in lakes and reservoirs all over the world. Photocatalytic removal of cyanotoxins by solar light active catalysts is a promising way to purify water at relatively low cost compared to modifying existing infrastructure. We have established a facile and low-cost method to obtain TiO₂ and g-C₃N₄ coated floating photocatalysts using recycled glass beads. g-C₃N₄ coated and TiO₂+g-C₃N₄ co-coated beads were able to completely remove microcystin-LR in artificial fresh water under both natural and simulated solar light irradiation without agitation in less than 2 h. TiO₂ coated beads achieved complete removal within 8 h of irradiation. TiO₂+g-C₃N₄ beads were more effective than g-C₃N₄ beads as demonstrated by the increase reaction rate with reaction constants, 0.0485 min⁻¹ compared to 0.0264 min⁻¹ respectively, with TiO₂ alone found to be considerably slower 0.0072 min⁻¹. g-C₃N₄ based photocatalysts showed a similar degradation pathway to TiO₂ based photocatalysts by attacking the C6–C7 double bond on the Adda side chain.