Immobilizing magnetic glutaraldehyde cross-linked chitosan on graphene oxide and nitrogen-doped graphene oxide as well-dispersible adsorbents for chromate removal from aqueous solutions.

Glutaraldehyde cross-linked chitosan with an Fe3O4 core was prepared and immobilized on the graphene oxide and nitrogen-doped graphene oxide surfaces to achieve magnetic nanocomposites as excellent adsorbents for removal of chromate. The prepared magnetic nanocomposite adsorbents were characterized. Then, the applicability of these nanocomposites for adsorptive removal of chromate was investigated and the adsorption conditions were optimized. In this regard, to determine the relationship between effective parameters on chromate adsorption, the response surface methodology was applied. The statistical parameters of the resulting models were checked and confirmed that the predicted adsorption efficiencies were in good agreement with the experimental values. For removing of 50 ppm chromate, the pH of 2 and 3, the adsorbent dose of 4 and 2.7 mg mL-1 and contact time of 60 and 45 min were defined as optimum for MCC@GO and MCC@NGO, respectively. We found that kinetic data followed a pseudo second-order kinetic model. The evaluation of adsorption equilibrium isotherms models was conducted and it was found out the latter two fit well, reflecting the monolayer adsorption of the chromate molecules on the nanocomposites. Finally, the adsorption tests on real aqueous samples indicated the capability of these nanocomposites in removing over 90% of chromate ions.