An in-situ approach to cyanobacterial harmful algal blooms degradation of microcystin-LR cyanotoxins using TiO₂photocatalysts coated on nylon mesh supports

Dispersed and immobilized photocatalytic titanium dioxide (TiO2) nanoparticles were investigated for the removal of microcystin-LR (MC-LR) cyanotoxin in water. Dispersed TiO2 concentrations (0.25 g/L, 0.025 g/L, 0.0025 g/L, and 0 g/L) were compared to TiO2 coated on nylon net supports and uncoated nylon nets to determine MC-LR degradation performance. Adsorption of MC-LR onto dispersed TiO2 was tested for 1 h prior to ultraviolet (UV) light exposure, and the maximum adsorption observed was 1%. With UV exposure, 0.25 g/L dispersed TiO2 degraded MC-LR by 99% over a 2-hour time period, while 0 g/L, 0.0025 g/L, and 0.025 g/L TiO2 did not cause significant MC-LR removal. TiO2 nets spray coated 2x, 5x, and 8x with Nafion-TiO2 composite were tested for stability, where the 2x and 8x spray coated nets lacked attachment and stability compared to the 5x coated net. MC-LR adsorption testing on uncoated and 5x coated TiO2 nets resulted in 0% and 13% adsorption, respectively. The 5x coated TiO2 net removed MC-LR by 96%, 64%, and 10% for UV, indirect UV, and no UV exposure over 2 h. MC-LR removal by dispersed 0.25 g/L TiO2 and 5x coated TiO2 nets fit pseudo first-order kinetics, where the rate constants were k = 0.0375 min-1 and k = 0.0264 min-1 for dispersed TiO2 and 5x coated TiO2 nets, respectively. Overall, the study indicated TiO2 photocatalysts coated on nylon supports are comparable to dispersed TiO2 and provide an immobilization approach for in-situ MC-LR removal by TiO2 nanoparticles.