Adsorption of microcystin-Lr onto iron oxide nanoparticles

In this study, the adsorption of microcystin-LR onto iron oxide (maghemite) nanoparticles from water was examined. Factors influencing the sorption behavior included microcystin and maghemite concentration, pH, ionic strength, and the presence of natural organic matter. Adsorption of microcystin-LR was strongly affected by pH. The adsorption increased with decreasing pH, with a maximum adsorption around pH 3. Adsorption of microcystin-LR on maghemite was primarily attributed to electrostatic interactions, although hydrophobic interactions may also play a role. The extent of microcystin-LR adsorption onto maghemite increased with increasing ionic strength at pH 6.4, since salt ions screened the electrostatic repulsion between adsorbed microcystin molecules. Adsorption of microcystin-LR was not significantly affected by the presence of Suwannee River Fulvic acid (SRFA) below 2.5 mg/L. However, adsorption decreased at higher SRFA concentrations (2.5–25 mg/L) due to competitive adsorption between SRFA and microcystin-LR for limited sorption sites.

Molecular structure of microcystin-LR (after Sielaff et al. [47]).Figure optionsDownload as PowerPoint slideResearch highlights▶ Adsorption of microcystin-LR was strongly affected by pH, with adsorption decreasing with increasing pH primarily due to the development of repulsive electrostatic interactions. ▶ At near neutral pH, adsorption of microcystin-LR increased with increasing ionic strength due to the screening of electrostatic repulsive forces. ▶ The presence of Suwannee River Fulvic Acid (SRFA) reduced microcystin-LR adsorption due to competition for limited adsorption sites.