Comparative study for removal of cationic dye from aqueous solutions by manganese oxide and manganese oxide composite

Abstract

Manganese oxide-poly vinyl chloride (MnO2-PVC) composite has been synthesized for the removal of methylene blue from aqueous solution. Manganese oxide (MnO2) was first prepared by mixing manganese chloride tetra hydrated with tetramethylammonium hydroxide and hydrogen peroxide followed by functionalization with polyvinyl chloride (PVC). The successful synthesis of the composite was confirmed by Fourier transform infrared, X-ray diffraction and energy-dispersive X-ray analysis. The point of zero charge and the surface area of MnO2 nanosheets were increased from 4.10 and 214 m2/g to 5.01 and 226 m2g, respectively, after functionalization with PVC. The adsorption experiments under different experimental conditions, such as pH, concentration, time, dosage and temperature, were conducted to study the removal of methylene blue (MB) from aqueous solution by MnO2 and MnO2-PVC composite. The adsorption capacity of MnO2-PVC was 16 times greater than pristine MnO2, which is attributed to its high surface area, stability, polarizability and porosity. The Langmuir isotherm model was a good choice to probe into the mechanism of adsorption. Moreover, the adsorption process followed the pseudo-second-order kinetics, and the intra-particle diffusion was accompanied by the film diffusion for controlling the rate of adsorption. The thermodynamic parameters such as free energy, enthalpy and entropy indicated that the adsorption process was found to be exothermic and more spontaneous at 298 K. These results demonstrate that MnO2-PVC is an efficient, environment-friendly and versatile adsorbent for dyes removal from wastewater.