Selective electrostatic sorption of water-soluble anionic molecules over electrospun cationic polymer fibers

Abstract

The development of cationic-decorated polymeric electrospun fibers is a promising approach for removing soluble anionic contaminants in wastewater treatment applications. Ionomers exhibit excellent performance in binding and capturing ionic contaminants, but preventing their dissolution in aqueous environments necessitates cross-linking the ionomeric chains. However, cross-linked ionomeric networks do not lend themselves well to various polymer-processing techniques, which restricts their utilization as membranes and fibers for water treatment. Herein, we report the successful formulation of dispersed cross-linked ionomer into linear polymer solution to construct a spinning matrix for fiber electrospinning. The generation of water-permeable electrospun fibers decorated with a cationic network demonstrated high adsorption capacities and a selective affinity towards anionic pollutants, including methyl orange, phenol red, eosin yellow, and Congo red. The electrostatic interactions between the cationic fibers and the anionic contaminants resulted in removal efficiencies up to 99%, with adsorption capacities reaching 500 mg g⁻¹, in contrast to cationic pollutants (≤5%). Moreover, comparative studies revealed that the fibers incorporating the cationic cross-linked polymer outperformed a control fiber membrane utilizing the linear polymer polycaprolactone, confirming the critical role of the cationic surface charges in achieving the recorded uptake. Interestingly, the adsorption isotherms highlighted the influence of the contaminant size and structure on the adsorption mechanism, where small molecules demonstrated adsorption isotherms best fitted by the Langmuir model, while bulky, long-chain contaminants, such as Congo red, followed the Freundlich model. Additionally, the nanofibers demonstrated outstanding regeneration and reusability, maintaining removal efficiencies of 99% for MO and 78% for PR after ten adsorption–desorption cycles. The data collectively highlight the potential of this approach for practical applications in sustainable water treatment.