Electrochemical performance and enhanced nitrate removal of homogeneous polysulfone-based anion exchange membrane applied in membrane capacitive deionization cell

This paper aims to investigate different strategies toward the enhancement of nitrate removal in a membrane capacitive deionization cell using different membrane functionalizing agents such as trimethylamine, triethylamine, and N,N,N',N'-tetramethyl-1,6-hexanediamine as well as a double-layer, novel homogeneous polysulfone-based anion exchange membrane. The prepared membranes exhibited nitrate versus chloride transport number ratio in the range of 0.96-1.52. The salt adsorption capacity for the NaNO3 feed was about 1.4-fold compared to that of using NaCl in case of triethylamine functionalized membrane under individual feeding solutions of 30 mL NaCl or NaNO3 during 30 min, and adsorption/desorption voltages of 1.6/0.0 V process conditions. At the same time, this parameter was about 1.2-fold weaker for the cell with a double-layer membrane. Based on the experiments, it can be inferred that the affinity toward nitrate could be promoted as the chain length of the alkyl group increases (i.e., increasing hydrophobicity of the groups). However, due to decrement in water uptake, the overall electrochemical performance of the membranes tended to weaken as the affinity toward nitrate increased. Results showed that the prepared membranes are suitable substitutions to conventional polystyrene-based ones utilized in membrane capacitive deionization cells.