Adsorption Behavior of Methyl Violet 2B Using Duckweed: Equilibrium and Kinetics Studies

This study focuses on the adsorption behavior of using Lemna minor (Duckweed) as a potential low-cost biosorbent for the removal of methyl violet 2B (MV). The effects of parameters such as contact time (30–240 min), settling time (30–240 min), pH of dye solution from pH 2 to 12 were studied. Optimum contact time and settling time for the maximum removal of MV were 2 and 1 h, respectively. Maximum MV removal was observed at its ambient pH. Elemental analysis and functional group characterization of the biosorbent were carried out using X-ray fluorescence and Fourier-transformed infrared spectroscopy, respectively. Surface morphology of Duckweed, before and after adsorption of MV, was characterized using scanning electron microscope, and ionic strengths and pre-treatment of biosorbent were also investigated. Six different isotherm models, namely Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Redlich–Peterson and Sips isotherms, were performed on the equilibrium adsorption isotherm of MV. Experimental data for adsorption of MV correlate well with both the Langmuir and Sips isotherm models. The maximum biosorption capacity ( q max ) at 298 K was 332.5 mg g −1 (Langmuir) and 307.3 mg g −1 (Sips) for MV, which is far superior to most biosorbents reported. Kinetics study followed the pseudo-second order.