Fabrication of oppositely charged thin-film composite polyamide membranes with tunable nanofiltration performance by using a piperazine derivative

A piperazine derivative, N-aminoethyl piperazine (AEP) was utilized as the amine monomer to react with trimesoyl chloride (TMC) and to fabricate thin-film composite nanofiltration membranes via interfacial polymerization. Interestingly, AEP-TMC membranes with the oppositely charged surface have been obtained by simply regulating the mole ratio of AEP to TMC and the oppositely charged membranes performed quite different separation capabilities toward differently charged salts and dyes. For instance, the positively charged membrane (AEP/TMC = 240) presented a salt rejection in this order: MgCl2>MgSO4>Na2SO4>NaCl while the rejection order changed to: Na2SO4>MgSO4>MgCl2> NaCl for the membrane (AEP/TMC = 15) with a negatively charged surface. Meanwhile, the membranes also showed good water permeabilities (8.18 L m−2 h−1∙bar−1 for AEP/TMC = 15 and 7.78 L m−2 h−1∙bar−1 for AEP/TMC = 240). Besides, promising stabilities of the obtained AEP-TMC membranes were also confirmed via a 30-h continuous test with salt solutions and a 27-h cycled test with dye solutions. Considering the tunable surface and nanofiltration performance, together with the quite large commercially available resource of AEP, the resultant AEP-TMC TFC membrane presents great potential in further practical applications towards different charged components.