Adsorptive removal of anionic dyes by graphene impregnated with MnO2 from aqueous solution

Abstract

Graphene nanosheet-manganese dioxide (GN-MnO2) composite was synthesized by a microwave-assisted method. The physico-chemical properties of modified graphene (GN) were characterized by different techniques, such as scanning electron microscopes (SEM), Fourier-transform infrared spectrometers (FTIR), X-ray diffraction (XRD) and Raman spectroscopy. The effects of contact time, pH, concentration, temperature, and the dose of adsorbent on the adsorption attributes of Congo red (CR) and Acid green 25 (AG25) on GN-MnO2 composite was studied. The experimental facts of the isotherm were found to be more fitted with the Langmuir isotherm rather than the Freundlich one, while the pseudo-second-order kinetic model/curve was found to be fitted with experimental data, giving an indication that the experiment was controlled by chemical processes. The maximum adsorption capacities is derived from the Langmuir model equation at 303 K were 270.06 and 324.26 mg/g for CR and AG25, respectively. The thermodynamic study revealed that the adsorption of CR and AG25 dyes onto the GN-MnO2 was pretty much spontaneous in nature and showed that the GN-MnO2 was a decent adsorbent for the elimination of CR and AG25 ions in aqueous conditions. The column studies were conducted in varying flowrates (4−12 mL/min), and bed heights (0.5–1.5 cm), with a concentration of 100 mg/L, while at pH of 3 and 4 for CR and AG25, respectively. The adsorption capability increased with the increasing influent level and column depth while it was reduced by upturn in flow-rate. The results obtained were fitted well with the Bed Depth Service Time BDST and Thomas models.