Adsorption efficiency of glycyrrhiza glabra root toward heavy metal ions: Experimental and molecular dynamics simulation study on removing copper ions from wastewater

Abstract

• Glycyrrhiza glabra root is effective for removing copper ions from wastewater. • Adsorption is confirmed by (EDS) and (FTIR) analyses. • Effect of biosorbent and solution characteristics are studied. • Adsorption is exothermic, reduces entropy and is described by Freundlich isotherm. • Simulations show hydroxyl functional groups have the dominant role in adsorption. Heavy metal ions in wastewater are a major source of water and soil pollution. In this study, glycyrrhiza glabra root is introduced as a novel biosorbent for removing copper ions from wastewater. The adsorption parameters (biosorbent dosage, biosorbent size, contact time, initial copper ion concentration, ionic strength and pH), as well as the adsorption isotherms and thermodynamics, are studied. Molecular dynamics is also applied to simulate the adsorption using LAMMPS. Maximum adsorption occurs at the early stage (5 min) the biosorbent comes into contact with the solution containing copper ions. Results also indicate that the maximum adsorption capacity is 181.6 mg/g for the solution with the initial concentration of 400 mg/L. Energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared analysis (FTIR) confirm the adsorption. Adsorption isotherms are best described by the Freundlich model, and the adsorption is found to be exothermic and entropy-decreasing. Molecular dynamics simulations of the non-bonding interactions between the biosorbent oxygens and the copper ions show that the oxygen atoms of hydroxyl functional groups (R - O - H) are most influential in the adsorption. The results of the study could suggest the cultivation of glycyrrhiza glabra as a cheap and environmentally friendly biosorbent for wastewater treatment.