Introduction of α-MnO2 nanosheets to NH2 graphene to remove Cr6+ from aqueous solutions

Abstract

The planar structure of the designed α-MnO₂–NH₂–RGO hybrid was prepared and characterized and used to remove hexavalent chromium ions (Cr⁶⁺) from aqueous solutions. The characterization of the novel adsorbent was carried out using the Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and the Brunauer–Emmett–Teller (BET) theory. Cr⁶⁺ adsorption efficiency was investigated as a function of the pH of Cr⁶⁺ solution, contact time and temperature. The results showed that the adsorption capacity strongly depended on the pH and that the adsorption equilibrium data were best described by the Freundlich isothermal model. The maximum sorption capacity towards Cr⁶⁺ was 371 mg g⁻¹. The kinetic adsorption was fitted to the pseudo-second-order kinetics model and it indicated that the adsorption mechanism is physical or chemical sorption on heterogeneous materials. The thermodynamic parameters were obtained, and the results showed that the adsorption process is spontaneous and exothermic. The adsorption capacity of α-MnO₂–NH₂–RGO can remain as high as 81% after five usage cycles. As a result, these findings propose that α-MnO₂–NH₂–RGO could be used as an outstanding adsorbent for Cr⁶⁺.