A green l-cysteine modified cellulose nanocrystals biosorbent for adsorption of mercury ions from aqueous solutions

Using a green biosorbent to remove toxic mercury ions from aqueous solutions is a significant undertaking. In the present study, a novel biosorbent, l-cysteine modified cellulose nanocrystals (Lcys-CNCs), was prepared by functionalizing high surface area cellulose nanocrystals with l-cysteine through periodate oxidation and reductive amination reaction. Lcys-CNCs were characterized by FT-IR, ¹³C CP-MAS NMR, elemental analysis, XPS, zeta potential and SEM. As cellulose nanocrystals are the natural nanomaterial, and l-cysteine contains strong mercury chelating groups, Lcys-CNCs show excellent adsorption capacity for mercury ions. The experimental conditions such as pH, contact time, and initial mercury ion concentration are discussed. The pseudo-second order model can describe the removal kinetics of Hg(ii) more accurately than the pseudo-first order model. The adsorption isotherm study of Hg(ii) followed the Langmuir model of monolayer adsorption. The maximum uptake capacity of Lcys-CNCs was determined to be 923 mg g^-1. Lcys-CNCs can remove mercury ions with 93% removal efficiency within 5 min from a 71 mg L^-1 solution. For Cd(ii), Pb(ii), Cu(ii) and Zn(ii) ions, Lcsy-CNCs can selectively adsorb Hg(ii) ions and the removal efficiency is 87.4% for Hg(ii). This study suggests Lcsy-CNCs are a green and highly efficient biosorbent for adsorption of mercury ions from aqueous solutions.