Controlled metal loading on poly(2-acrylamido-2-methyl-propane-sulfonic acid) membranes by an ion-exchange process to improve electrodialytic separation performance for mono-/bi-valent ions

Abstract

Highly cross-linked poly(2-acrylamido-2-methyl-propane-sulfonic acid) (PMPS) based cation-exchange membranes (CEMs) were prepared and the mono-valent selectivity of the membranes was significantly improved using the pore-sieving strategy by metal (copper) loading by the ion-exchange process. The prepared membranes were characterized for their morphological, physicochemical, electrochemical, and electrodialytic properties. Metal (Cu) loading in the PMPS membrane matrix improved thermal, mechanical, oxidative and hydrolytic stabilities. The results demonstrated that fine control over membrane permselectivity is possible and can be effectively tuned. Metal modification on the CEM surface improved the blocking behaviour and restricted the transport (leakage) of bi-valent metal cations (Ni²⁺ and Zn²⁺) during electrodialytic separation of mono- and bi-valent ions. However, partial deterioration in membrane ionic conductivity showed a slight adverse effect on the electrodialytic performance of the modified membranes. Extremely low Zn²⁺ leakage for the prepared PMPS-3 membrane in comparison with other state-of-the-art CEMs was attributed to the excellent pore-size sieving effect. The metal loaded PMPS-3 membrane showed improved surface compactness, which hindered the easy accessibility of bulky counter-ions (Ni²⁺/Zn²⁺) to fixed charge and thus quite low transport (leakage) of bi-valent ions was observed.