Graphene Oxide Nanocomposite Hydrogel Beads for Removal of Selenium in Contaminated Water

Selenium in water is becoming of increasing risk to human exposure because only recently serious health effects have been associated with their presence in water resources. The present study investigated the development and optimization of the composition of graphene oxide polymeric nanocomposite hydrogel beads by using response surface methodology. The use of polymers such as chitosan and polyethylenimine, which are rich in amine and alcoholic functional groups, provided enhanced removal of anionic selenium species from the water. Experimentally validated polymeric beads were used to perform batch adsorptions of selenium under different conditions such as pH, bead dosage, and diverse selenium concentrations to investigate their potential use, adsorption kinetics, and selenium removal mechanisms. Acidic conditions were found to best remove negatively charged selenium ions from aqueous solutions via −OH, −COOH, and amine functional groups present in the beads. The adsorption kinetic mechanism was better described by the pseudo-second-order adsorption kinetics, indicating that the beads remove selenium via chemisorption mechanisms. The isotherm studies showed an adsorption capacity of 1.62 mg/g based on the Langmuir isotherms at 25 °C. Regeneration studies showed loss of available adsorption sites after the first desorption treatment with different concentrations of NaOH and HCl. The mathematically optimized nanocomposite was further used to treat selenium spiked in real environmental water samples, which confirmed that the best removal of selenium occurs in acidic conditions.