Kinetic, equilibrium, and thermodynamic investigations of malachite green adsorption using KOH-activated groundnut shell–derived adsorbent

Approximately 80% of people worldwide, mostly in developing countries, lacks access to potable water due to the surge of water pollution. Industrial dyes are among the pollutants in water that are non-biodegradable and pose health risks. Hence, these dyes must be eliminated from industrial effluents before discharge into aquatic environments. The study investigated the removal of a model dye (malachite green, MG) from aqueous solutions using batch adsorption experiments. The effects of pH, temperature, time, and initial MG concentrations on the removal of MG using potassium hydroxide-activated powdered groundnut shells were investigated. The adsorbent was characterized using Fourier transforms infrared spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, thermogravimetric analysis and X-ray diffraction spectroscopy. The optimum pH and equilibrium time for the removal process are 7 and 40 min, respectively. Avrami fractional model best described the kinetic data while the equilibrium data were accurately described by the Dubinin–Radushkevich model. Moreover, the adsorbent excellently adsorbed MG from aqueous solutions with adsorption capacity (Q_max) of 150.1 mg g^–1 as predicted by Dubinin–Radushkevich model at 50 °C. The adsorption process was feasible, endothermic and spontaneous. Physisorption process dominated the adsorption of MG onto the adsorbent. The produced eco-friendly KOH-activated groundnut shell could serve as a promising adsorbent for the remediation of industrial dyes from contaminated wastewater.