Rapid adsorption of malachite green onto a low-cost adsorbent prepared from Pupalia lappacea stalk

Abstract

Water pollution caused by synthetic dyes, such as malachite green (MG), poses significant environmental and health risks, necessitating efficient removal strategies. In this study, we evaluated the potential of raw Pupalia lappacea (RPL), an agricultural waste-derived adsorbent, for MG removal from aqueous solutions. The adsorption process was studied under varying conditions of pH, contact time, adsorbent dosage, initial dye concentration, and temperature. Characterization of RPL was done with the aid of scanning electron microscope, Fourier transform infrared spectroscopy and pH-point-of-zero charge. Isotherm, kinetics and thermodynamics analyses were carried out on the experimental data. Optimal adsorption occurred at pH 5, with equilibrium achieved within 120 minutes. Kinetic analysis showed the process followed the pseudo-second-order model. Equilibrium data fitted best with the Freundlich isotherm. Thermodynamic studies revealed an exothermic process (ΔH = -1332.86 J/mol) that was spontaneous at lower temperatures (ΔG = -5.39 kJ/mol at 303 K). These findings establish RPL as an efficient and sustainable adsorbent for MG removal from wastewater.