(464b) Graphene-Mediated Removal of Microcystin-LR for Treatment of Harmful Algal Blooms

Harmful algal blooms are an increased global issue as they are severely impacting water quality due to their ability to directly alter the ecosystem and their threat to public health and safety. These cyanobacteria release cyanotoxins, such as microcystin (MC), which contaminant water sources and pose as hazards to humans and animals. Currently there is a need for environmentally compatible and economically viable media to address large scale application for HAB impacted waters. Our lab has previously shown that chitosan/graphene (CSG) composites are effective in the removal of cyanobacteria (anabaena, synechocystis, and microcystis aeruginosa) density and toxin levels. This study evaluated the interactions between graphene nanoplatelets with two common cyanotoxins, microcystin-LR and saxitoxin. Isotherm adsorption studies show that graphene nanoplatelets effectively adsorb microcystin-LR and saxitoxin via a Freundlich isotherm model, indicating multi-layered adsorption of the toxins. As compared to granular activated carbon (GAC), an industrial standard in carbon adsorptive materials, graphene drastically outperforms it in terms of adsorption capacity and kinetics, or time to reach adsorption equilibrium. We have directly proven that pi-pi interactions between the sp² carbons in graphene and the aromatic ring of microcystin are the driving forces for microcystin adsorption onto graphene nanoplatelets. This pi-pi removal mechanism of microcystin via the graphene materials offers a promising sustainable and selective media suitable for deployable treatment of HAB impacted waters.