Removal efficiency of methylene blue from aqueous medium using biochar derived from Phragmites karka, a highly invasive wetland weed

Abstract

The potential of biochar derived from pyrolysis of Phragmites karka—an invasive wetland plant biomass—for the adsorption of methylene blue (MB) dye from the aqueous medium was studied. The physico-chemical properties of the resultant char were studied using SEM-EDS, FTIR, TGA, ICP-MS, and Brunauer–Emmett–Teller (BET). Batch adsorption experiments were carried out to investigate the effect of different operational parameters on MB adsorption. Experimental data were analyzed by adsorption isotherm and kinetic models. Study results revealed that dye adsorption increased with biochar dosage, contact time, initial dye concentration, and solution pH. Contrary to the monovalent NaCl salt system, the presence and increase of the FeCl trivalent salt system increased the adsorption process. The process of adsorption followed the pseudo-second-order kinetic model. The equilibrium data was found well fitted by the Langmuir model, with a maximum dye adsorption capacity of 438.2 mg g−1. Interactions including surface precipitation, physical and electrostatic attraction, cation exchange, intermolecular hydrogen boding and n-π interactions are proposed to be the combined adsorption mechanisms behind the MB adsorption. The reusability of the spent adsorbent was comparatively high even after several adsorption–desorption cycles. The better dye adsorption capacity could be attributed to the innate properties of biochar as revealed through the characterization study. The study result indicated that the preparation of biochar from P. karka plant biomass and its further utilization as an effective adsorbent is a viable strategy towards wastewater treatment and wetland weed management.