Montmorillonite-reduced graphene oxide composite aerogel (M−rGO): A green adsorbent for the dynamic removal of cadmium and methylene blue from wastewater

Abstract

In this study, a type of montmorillonite-reduced graphene oxide aerogel (M−rGO) was successfully prepared by the sol–gel method and used for the effective removal of heavy metals (cadmium, Cd) and cationic dyes (methylene blue, MB) in wastewater. The chemical composition and micromorphology of the resulting M−rGO were characterized utilizing scanning electron microscopy and energy dispersive spectrometry, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, and X-ray diffraction. Furthermore, the effects of the initial concentration, adsorption time, and temperature on the static adsorption process were systematically studied. Equally important, the effects of the concentration, pH, ionic strength (IS), and pumping flow rate of contaminated solution on the dynamic removal of Cd and MB by M−rGO were investigated by a fixed-bed column experiment. The kinetics, isothermals, and thermodynamic adsorption experiment results showed that the Langmuir and pseudosecond-order models best suited the adsorption process in which physical adsorption and chemical adsorption act together. Functional groups containing O and C were involved in the adsorption of Cd and MB, and the hydrogen bonds, π-π, n-π interaction, and hydrophobic interaction between M−rGO and MB made important contributions to adsorption. The lower initial concentration, higher pH value, and slower pumping flow rate of the contaminated solution can effectively increase the dynamic adsorption capacity of Cd and MB on M−rGO. Contrary to that of Cd, the adsorption capacity of MB on M−rGO increased with IS. Both static adsorption and dynamic column experiments confirmed that the presence of Cd promoted the adsorption of MB, and MB inhibited the adsorption of Cd by M−rGO. In addition, the Cd/MB combined pollution wastewater experiment and the regeneration study showed that M−rGO could be a cost-effective and promising sorbent for Cd and MB wastewater treatment due to its high efficiency and excellent reusability.