Development of a novel PAN nanofibrous composite membrane for water desalination using hyperbranched PEI by interfacial polymerization

Abstract

A novel nanofiltration membrane prepared with hyperbranched polyethyleneimine (PEI) and trimesoyl chloride (TMC) by interfacial polymerization onto polyacrylonitrile (PAN) nanofibrous support was investigated. The morphology of PAN nanofibrous mid-layer was one of the major factor to determine the performance of the NFC membrane by affecting the formation of top active layer. We concluded that the nanofibrous membrane with smaller diameter is better for successful interfacial polymerization in terms of ion rejection. In addition, the conditions of interfacial polymerization, such as concentration of each monomer and reaction time, were also gave a lot of influence to the performance of the NFC membrane. First, the concentration of PEI in aqueous solution should be higher than 10wt%. Also, the concentration of TMC was prepared as low as possible to fabricate less crosslinked structures which would increase the donnan exclusion effect by remaining a lot of amine groups in each PEI molecules unreacted. In this experiment, the concentration of TMC in organic solution was 0.1wt%. Unlike typical interfacial polymerization reaction, we needed around 10 min reaction time to obtain high ion rejection (over 90% for divalent ions).The rejection order of different salts in this membrane was $MgCl_2>MgSO_4>NaCl>Na_2 SO_4$, which showed typical rejection order of positively charged membranes with donnan exclusion effects. At 100psi, the performance of a HPEI-NFC membrane was around 35LMH, over 90% ion rejection for divalent ions ($MgSO_4$), and over 75% rejection for monovalent ions (NaCl).