Rigid polyelectrolyte multilayer membrane with ultrahigh permeance and excellent dye/salt separation performance

Two kinds of polyelectrolyte assembled membranes have been prepared using a rigid sulfonated polysulfone (SPSU) and a flexible poly(sodium 4-styrenesulfonate) (PSS) as anionic polyelectrolytes, respectively, with a polyethyleneimine (PEI) as a common cationic polyelectrolyte. The effects of molecular backbone’s rigidity and flexibility on the characteristics and performances of SPSU/PEI and PSS/PEI membranes have been investigated in detail. The SPSU/PEI membrane with two bilayers (SPSU/PEI-2.0) has a thinner and looser separation layer due to expanded molecular conformation and bulky benzene rings of the SPSU. In addition, the SPSU/PEI-2.0 membrane exhibits an ultrahigh pure water permeance up to 70.0 L m −2 h −1 bar −1 . The optimized separation performance for Congo red (CR)/NaCl and CR/Na 2 SO 4 displays the same high CR rejection of 99.6 %, low NaCl rejection of 1.2 % and Na 2 SO 4 rejection of 7.9 %. The SPSU/PEI-2.0 membrane also shows excellent acid-resistance stability, thermal stability and long-term operation stability. This research presents that choosing polyelectrolytes with appropriate molecular structures can be attractive when designing polyelectrolyte multilayer membrane to separate dye and salt.