ADSORPTION OF CD(II) IONS USING IMMOBILIZED OAT STRAW MODIFIED WITH A DEEP EUTECTIC SOLVENT: KINETIC AND STRUCTURAL INSIGHTS

The present study provides a potential use of waste biomass, oat straw (ST), as an efficient adsorbent in the removal of heavy metals from aqueous solutions. ST was modified with the selected deep eutectic solvent (DES) to enhance its adsorption capacity and obtain a structure-altered material (DST). Additional functionalization was done by immobilizing the modified biomass (DST) in alginate beads (IDST) to improve handling and applicability in realistic water treatment systems. The adsorption studies were performed in a batch system to investigate the removal of Cd(II) ions from water by native, modified, and immobilized oat straw. It could be seen that the adsorption capacity increased significantly after DES modification and immobilization. The maximum adsorption capacities were 20.4, 49.41, and 89.87 mg/g for ST, DST, and IDST, respectively. The kinetic investigation demonstrated that the adsorption behavior agreed with a pseudo-second-order model, indicating that the adsorption of Cd(II) ions on adsorbents was driven by chemisorption. Consistent with the enhanced adsorption efficiency scanning electron microscopy SEM presented the direct evidence of morphology changes caused by DES treatment. These results suggest that the DES-modified biomass can be sustainably and effectively used for the removal of heavy metal ions, and therefore could afford environmentally benign and cost-effective purification strategies on aqueous solutions