The effects of extracellular polymeric substances on magnetic iron oxide nanoparticles stability and the removal of microcystin-LR in aqueous environments

The behaviors of nanoparticles rely on the aqueous condition such as natural organic matter (NOM). Therefore the presence of NOM would influence the interaction of nanoparticles with other substances possibly. Here, microcystin-LR (MC-LR) adsorption on iron oxide nanoparticles (IONPs) was studied in an aqueous solution with different types of NOM, including extracellular polymeric substances (EPS) from cyanobacteria and alginic acid sodium salt (AASS) from brown algae. Results revealed that EPS played an important role in stabilizing IONPs and in the toxin adsorption efficiency. The stability of IONPs was heavily depended on the concentration and type of NOM, which can affect the surface charge of IONPs significantly in solution. The enhanced stability of IONPs was due to the electrostatic interactions. Adsorption kinetics and isotherm studies confirmed that NOM can affect the IONPs' adsorption efficiency, and pseudo-second-order kinetics better explained this process. The removal efficiency for MC-LR decreased in the presence of NOM (Control > EPS-M1 > AASS > EPS-M9), indicating that NOM and MC-LR compete for limited adsorption sites. The presence of NOM in a eutrophic environment stabilized the IONPs while inhibiting the MC-LR removal efficiency. This investigation emphasized the negative effect of cyanobacterial EPS on the removal of microcystins when using magnetic separation technology. And this results could also be used to model the transportation of iron minerals carrying toxic substances in aqueous environment.