Removal of Co(II) and Cr(III) from aqueous solution by graphene nanosheet/δ-MnO2: Batch and column studies

Abstract

In this work, graphene nanosheet/δ-MnO2 (GN-MnO2) was synthesized via a microwave-assisted method. The adsorption behavior of cobalt (Co(II)) and chromium (Cr(III)) ions onto GN-MnO2 adsorbent was investigated through batch and column experiment under various conditions. GN-MnO2 was characterized using Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption/desorption (BET) and Boehm's titration method. Under static conditions, the effect of parameters like pH level, initial metal ion concentration, temperature, contact time and adsorbent dosage was studied. The optimum batch adsorption capacity of 403.4mg/g and 491.98mg/g were obtained at a temperature of 303K and pH of 6 and 4 for Co(II) and Cr(III), respectively. Additionally, adsorption kinetics, isotherm, and thermodynamic were created. Regarding the column mode operation, the influence of both flow rate and bed height was examined and the data obtained for the total removal for both heavy metals were well described by Thomas and Bed depth service time (BDST) models. The column regeneration experiment was carried out for six cycles of desorption. The graphene nanosheet/δ-MnO2 was proven to be a highly effective adsorbent and could easily be used for separation purpose.