Arsenic Adsorption on Nanoscale Zerovalent Iron Immobilized on Reduced Graphene Oxide (nZVI/rGO): Experimental and Theoretical Approaches

Abstract

Arsenic (As) contamination of water and foodstuff has motivated the development of methods to sense, quantify, and/or remediate As contamination in such samples. Nanoscale zero-valent iron (nZVI) particles have recently emerged as a suitable material for adsorbing As. In order to enhance its performance, these nanoparticles were assembled into reduced graphene oxide (rGO) sheets via a direct iron reduction to yield nZVI/rGO materials. Transmission electron microscopy images showed that nZVI particles of 7 nm mean particle size were well dispersed over the rGO sheets. Zeta potential was measured in a pH range from 2 to 12 and showed a point of zero charge at pHpzc 6.5. As adsorption onto nZVI/rGO materials, using 15 ppm As solutions of pH ranging from 3.6 to 7.9, showed that adsorption is better in acidic pH, reaching approximately 80% of As adsorption in 10 min. Density functional theory calculations were carried out to evaluate the As adsorption over nZVI/rGO by using simplified models of magnetite nanoparticles supported on graphene. As bonds to surface oxygen atoms and adsorption are greatly favorable near lattice defects, with adsorption energies between -6.61 and -6.44 eV. After adsorption, As transfers electron density to the surface, resulting in a positive charge of +3.