Self-assembled embedding of ion exchange materials into nanofiber-based hydrogel framework for fluoride capture

The development of fluoride selective separation technology is essential for water purification and simultaneous ion capture. In this paper, a novel Kevlar amide nanofiber (KANF) based anion exchange membrane for fluoride capture was reported. The incorporation of positively charge groups into the KNAF's framework was enabled through a novel yet facile method, i.e., through the embedding and subsequent self-assembly of hydroxypropyltrimethyl ammonium chloride chitosan (HACC) into the KANF-based hydrogel framework. The membrane surface was further sulfonated to enhance the fluoride selectivity. Dissipative particle dynamics simulation revealed that the highly hydrophilic and positively charged HACC was homogeneously embedded into the KANF-based hydrogel framework. Membranes with varying HACC content showed up to 3.7 mmol g−1 ion exchange capacity and 17% water content. Compared to a commercial anion exchange membrane (AMX membrane), the HACC#KNAF membranes exhibited a much lower surface electrical resistance (e.g., ∼1.23 Ω cm2) and exceptional desalination/concentration efficiency with NaF solution in electrodialysis. The sulphonated membrane S-HACC#KNAF achieved a permselectivity of 2.75 and selective efficiency of 17% favoring the F- cross-membrane transport over SO42-, outperforming its commercial counterpart. The resulting membranes were significantly less prone to foulant deposition and exhibited superior stability over semi long-term tests. The design principles developed will greatly broaden the possibilities of KANF-based membranes' fabrication for achieving efficient ion separation towards sustainable ion capture.