Development of novel polyacrylate-based adsorbents for precise fluoride removal: role of polar skeleton and chelating...

Conventional polystyrene-based adsorbents for fluoride (F^-) often suffer from slow adsorption kinetics and low uptake capacity. To overcome these limitations, two novel Al³⁺-immobilized adsorbents were developed using a high-polar polyacrylate matrix functionalized with carboxylic or phosphonic groups, denoted as DCA and DPA, respectively, for precise F^- removal. Compared with the conventional polystyrene-based adsorbent (D860A), both DCA and DPA showed higher adsorption capacity and nearly twofold faster kinetics. Both adsorbents also demonstrated superior F^- selectivity in the presence of common coexisting substances and could be efficiently regenerated because of their polar frameworks. Among the two adsorbents, DPA exhibited stronger Al³⁺ immobilization, resulting in higher adsorption capacity and selectivity, while DCA showed faster kinetics and more efficient utilization of immobilized Al³⁺. Detailed characterization confirmed that F^- adsorption occurred through inner-sphere complexation with immobilized Al³⁺ sites. Further analysis indicated that Al³⁺ chelated with carboxylic and phosphonic groups at stoichiometric ratios of 1:2 and 1:1, respectively. The lower steric hindrance of carboxylic groups improved the accessibility of Al³⁺ sites in DCA, whereas the stronger electronegativity of phosphonic groups promoted Al³⁺ coordination in DPA. In column experiments using actual F^--containing wastewater, the treatment capacities of DCA and DPA were 1.5-2.0 times higher than that of D860A. This work offers two effective adsorbents for precise F^- removal and highlights the role of the metal-chelated microenvironment in governing their structure-activity relationship.