Computational DFT study of magnetite/graphene oxide nanoadsorbent: Interfacial chemical behavior and remediation performance of heavy metal hydrates from aqueous system.

Abstract

Herein, magnetite/graphene oxide hybrid (MGO) was facilely synthesized and analyzed by various techniques such as X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, Brunauer, Emmett, and Teller surface area analyzer, and Raman spectroscopy. A computational density functional theory (DFT) has been applied for the first time to determine the removal mechanism of zinc (Zn2+ ), nickel (Ni2+ ), and chromium (Cr6+ ) hydrates onto the prepared MGO. The adsorption binding energy and geometries of the metal hydrates with oxygen functional group (i.e., hydroxyl, epoxide, carboxylic, carbonyl groups, and magnetite on the MGO surface) were estimated. The complexes configurations comprised via sitting the metal ion perpendicular and above the MGO surface. The zinc hydrate portended to bind more strongly than Ni2+ and Cr6+ . Zinc hydrate is favorable to coordinate with hydroxyl and carboxylic group than the other functional groups. The pseudo-second-order kinetic and Langmuir isotherm models are well convenient for kinetics and isotherm sorption process, respectively. The results determined that the sorption of heavy metals by nanostructure MGO was observed in the following order: zinc>nickel>chromium as revealed by the DFT computations. The maximum adsorption capacity of Zn2+ , Ni2+ , and Cr6+ was 333, 250, and 200mg/g, respectively. Thermodynamic constants depicted that the sorption process is naturally instantaneous and exothermic. The calculated predicted results are fitted with the experimental results. PRACTITIONER POINTS: Combination of MGO with DFT calculations in the sorption of Zn, Ni, and Cr hydrates. MGO applied on the removal of Zn+2 , Ni+2 , and Cr+6 with high sorption capacity. DFT calculations revealed that Zn hydrate is more favorably adsorbed than others. DFT calculations proved that ZnOH is favorable to coordinate with OH and COOH groups. DFT calculation offers guidance on the mechanism of coordination of heavy metals.