Deep eutectic solvent-assisted optimisation of carboxymethyl cellulose: A sustainable methodology for pollutant elimination.

Abstract

For the first time, deep eutectic solvents (DES) featuring choline chloride: urea (ChCl:U) and choline chloride: glycerol (ChCl:G), were utilised to modify carboxymethyl cellulose (CMC) into a stable bead via a simple and environmentally friendly procedure. The influence of metal ions in various Cu2+, Fe3+, and Al3+-mediated beads on adsorbent stability and adsorption performance was examined. Therefore, batch adsorption experiments were conducted to remove malachite green (MG) from aqueous solution under various conditions, including pH, initial MG concentration, agitation time, adsorbent dosage, ionic strength, and temperature. Essential characterisations assessing functional group incorporation, thermal stability, internal pore diameter, crystalline phases, and surface morphology of the adsorbents were performed. Additionally, solubility and stability tests, as well as desorption and reusability tests, showcase the adsorbent's sustainability potential. Linear and non-linear isotherm models (Langmuir, Freundlich, D-R and Temkin), kinetics models (pseudo-first-order, pseudo-second-order, Elovich, intraparticle, and Boyd), and Van't Hoff plot of thermodynamic studies were tested on adsorption data. Adsorption of MG onto all the 6 adsorbents can best be explained by the Langmuir isotherm, Elovich and pseudo-second-order kinetics, as the Van't Hoff plot revealed an exothermic process. The maximum adsorption capacities for CMC-DES A to F were recorded as 23.8660 mg/g, 20.8732 mg/g, 22.5616 mg/g, 19.6976 mg/g, 22.9132 mg/g, and 17.2864 mg/g under optimal conditions, respectively. Furthermore, the adsorbents show potential for removing MG from real water samples, including lake water and seawater. The results revealed that all six adsorbents provide a practical solution for removing MG from aqueous solution.