Composite Anion Exchange Membranes Based on Quaternary Ammonium-Functionalized Polystyrene and Cerium(IV) Phosphate with Improved Monovalent-Ion Selectivity and Antifouling Properties

The possibility of targeted change of the properties of ion exchange membranes by incorporation of various nanoparticles into the membranes is attracting the attention of many research groups. Here we studied for the first time the influence of cerium phosphate nanoparticles on the physicochemical and transport properties of commercial anion exchange membranes based on quaternary ammonium-functionalized polystyrenes, such as heterogeneous Ralex^® AM and pseudo-homogeneous Neosepta^® AMX. The incorporation of cerium phosphate on one side of the membrane was performed by precipitation from absorbed cerium ammonium nitrate (CAN) anionic complex with ammonium dihydrogen phosphate or phosphoric acid. The structures of the obtained hybrid membranes and separately synthesized cerium phosphate were investigated using FTIR, P31 MAS NMR, EDX mapping, and scanning electron microscopy. The modification increased the membrane selectivity to monovalent ions in the ED desalination of an equimolar mixture of NaCl and Na₂SO₄. The highest selectivities of Ralex^® AM and Neosepta^® AMX-based hybrid membranes were 4.9 and 7.7, respectively. In addition, the modification of Neosepta^® membranes also increased the resistance to a typical anionic surfactant, sodium dodecylbenzenesulfonate.