Biosorption of lead ions (Pb2+) from water samples using dried Lemna minor biomass: experimental and density functional theory studies

Lemna minor biomass, a novel source of biosorbent, was found to exhibit high adsorption potential over a wide range of concentrations of Pb2+. The biosorbent was characterized by Fourier transform infrared (FTIR) spectrophotometry, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA). Biosorption experiments were carried out under the optimized parameters such as solution pH, biosorbent amount, equilibrium time, and temperature. During the sorption, it has been observed that the above 85% removal of Pb2+ ions was achieved at acidic pH (4.5–5.1). Moreover, the maximum sorption was achieved using the 150 mg L−1 biosorbent. Equilibrium experiments were validated by the Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. From the results, it has been noticed that the experimental data was best fitted to the Langmuir model (R2, 0.986 and 969.18 mmol g−1). Standard enthalpy (∆H°), free energy (∆G°), and entropy (∆S°) changes were calculated. Results showed that biosorption of Pb2+ was spontaneous and endothermic. The biosorption mechanism was analyzed through pseudo-first-order and pseudo- second-order kinetic models. The results demonstrated that the biosorption of Pb2+ followed the pseudo-second-order kinetic model. Adsorbate-adsorbent interactions were scrutinized by density functional theory (DFT).