Ultra-high nitrate-selective metal-polymer membranes based on cardo polybenzimidazole for electrodialysis

Abstract

Ion exchange membranes with high monovalent ion selectivity are essential for extracting valuable components from natural and waste waters. One of the approaches to their fabrication is the creation of nanostructured materials with ion-conducting channels. In this study, materials based on cardo polybenzimidazole (PBI–O-PhT) containing Zn²⁺, Cr³⁺ and Cu²⁺ ions were obtained and used for the first time for electrodialysis separation. The formation of crosslinked structure due to metal-benzimidazole coordination bonds was demonstrated. The obtained metal-polymer membranes have ionic conductivity comparable to commercial ones, reaching 0.32 mS cm⁻¹, and high values of nitrate ion transport numbers (99.2 %). It is shown that the obtained membranes achieve incredibly high values of selectivity coefficients for anion separation. The highest and most stable values were obtained for the copper-containing membrane PBI/Cu-50, which are P(NO₃/SO₄) = 729, P(Cl/SO₄) = 109 and P(NO₃/Cl) = 6.66.