Influence of the modification method on the immobilization ratio of crown ethers on the chitosan resin

In the presented study, a chitosan resin was modified by hydroxydibenzo-14-crown-4 ether, which is a highly selective complexing agent, often used in lithium extraction processes. Three immobilization methods of the analyzed ether were investigated: surface modification of dry chitosan beds, modification of fresh, wet resin, and pre-polymerization modification in solution. The immobilization efficiency was evaluated by analyzing organic residues in post-modification and storage solutions, while structural and morphological changes were assessed using SEM imaging. The pre-polymerization method resulted in the highest immobilization efficiency (over 90%), likely due to the incorporation of the crown ether into the resin matrix. The second highest immobilization ratio was observed for a fresh resin modification, obtaining over 30% immobilization of crown ether on the surface of chitosan beds. One of the possible explanations for these results is that the hydration state significantly affects reagent diffusion and surface coverage. SEM analysis revealed that each method induced distinct microstructural transformations, with pre-polymerization modification, giving the most porous and irregular surface morphology. These results demonstrate that the modification technique critically influences both the functional and structural properties of the chitosan resin, which may impact its future applications in different kinds of metal recovery processes.