In this work, the effect of applying layers of polyethyleneimines with different molecular weights (1300 and 25 000 Da), polystyrene sulfonic acid or sodium polyacrylate on the surface of the heterogeneous membrane MK-40 on the selectivity to singly charged ions was investigated. It is shown that the modification leads to an increase in the selectivity coefficients P(Na+/Ca2+) and P(Li+/Mg2+), and in membranes based on polyethyleneimine with a molecular weight of 1300 Da this effect is more pronounced. For a couple of Na+/Ca2+, the highest selectivity value (3.95) was obtained using a membrane with two layers of polyethyleneimine with a molecular weight of 1300 Da and polystyrene sulfonic acid.
Yurova et al. (Sun,) studied this question.