Role of Acid Functionalized-Nano Porous Carbon/MnO2 Composite for Removal of Arsenic from Aqueous Medium

Contamination of water with toxic substances due to rapid urbanization has become a worldwide cause of concern. Among these substances, arsenic occupies the topmost position in the priority list of hazardous substances given by ATSDR. Hence in the present study in order to eliminate the extra step of oxidizing As(III) in the process of arsenic removal by adsorption, a composite of acid-functionalized nanoporous carbon (Af-NPC) with MnO2 nanoparticles was synthesized. Nanoporous carbon (NPC) structures synthesized from grass clippings mown at the yard were acid-functionalized and coated with manganese oxide nanoparticles at room temperature. The synthesized composite was characterized by FTIR, XRD, BET, TEM, TGA and XPS. Characterization results showed the formation of an acid-functionalized nanoporous carbon/MnO2 (Af-NPC/MnO2) composite which was amorphous in nature. Af-NPC/MnO2 was further explored for the removal of As(III) and As(V) from the aqueous medium. Effects of factors such as pH, contact time, initial concentration and interfering ions on the adsorption of arsenic by Af-NPC/MnO2 were studied in detail. The mechanism of adsorption was also studied using experimental data determined. The kinetic study indicated that removal of arsenic followed pseudo-second-order kinetics and the experimental equilibrium data fitted better in the Langmuir isotherm model with maximum monolayer adsorption capacity of 8.85 mg/g and 9.43 mg/g for As(III) and As(V), respectively. The removal rate of arsenic was found to be very fast compared to other adsorbents. The results of this study imply that Af-NPC/MnO2 is an efficient adsorbent for the removal of As(III) and As(V) from an aqueous medium.