Tuning separation behavior of tailor-made thin film poly(piperazine-amide) composite membranes for pesticides and salts from water

The present study describes some appealing results concerning the TFC membrane performances prepared by varying the solvents of piperizine (viz. water, acetonitrile and water-acetonitrile). The membrane selectivity of bivalent over mono-valent anions reduces from water > acetonitrile-water > acetonitrile (i.e. Memb-I > Memb-II > Memb-III). The partition co-efficient values support the trend. The retention order of salts is Na2SO4 > MgSO4 > MgCl2 > CaCl2 > NaCl. pH dependence separation study shows different behaviors for NaCl, Na2SO4 and MgSO4. Memb-I and II show minimum NaCl separation at pH 7 whereas in acidic and alkaline medium it is increasing trend, but Memb-III shows differences in alkaline pH. On the contrary Memb-I and II show improvement in retention with pH for Na2SO4 and MgSO4, whereas Memb-III shows the fall in retention at alkaline pH. The separation performance of diuron and isoproturon follows order Risoproturon(90.95%) > Rdiuron(79.34%) for Memb-II at pH 7. The separation performances follow the trend Memb-II > Memb-I > Memb-III. It reflects that acetonitrile-water mixture for piperizine optimizes maximum permeability as well as a charge of the membrane. The higher retention of isoproturon at alkaline pH is explained by higher molecular size and low polarity compared to diuron. The low separation trend of diuron at higher pH may be explained by relatively more polarity and low molecular size.