A chitosan-separation-layer nanofiltration membrane prepared through homogeneous hybrid and copper ion enhancement

Abstract A novel method of homogeneous hybrid and copper ion (Cu(II)) enhancement was employed to prepare chitosan separation layer over polyacrylonitrile support. Firstly, chitosan nanoparticles (CSPs) and free chitosan molecules in the suspension prepared through adding sodium polyphosphate (SPP) into chitosan solution were simultaneously electrostatically attracted onto the surface of alkali-treated polyacrylonitrile (mPAN) support to obtain chitosan separation layer (CSPM) that was homogeneously hybrided by CSPs. Then, CSPM/mPAN membrane obtained was immersed into CuSO4 solution for chelation cross-linking to obtain CSPM-Cu(II)/mPAN membrane. Results showed the ratio of chitosan to SPP and Cu(II) chelation had markedly affected on the membrane performance. When the ratio of chitosan to SPP was 3.4, CSPM3.4-Cu(II)/mPAN membrane had a Na2SO4 rejection of 93.3% with a pure water flux of 74.8 L/(m2·h), simultaneously increasing by 30.3% rejection and 24.0% flux compared with CSPM3.4/mPAN membrane due to improvement of hydrophilicity and cross-linking degree resulted from Cu(II) enhancement. CSPM3.4-Cu(II)/mPAN membrane showed 3.6 fold flux and almost the same rejection compared with chitosan nanofiltration membrane by interfacial cross-linking reported. Meanwhile, CSPM3.4-Cu(II)/mPAN membrane exhibited 100% anti-bacteria to Escherichia coli, 96.1% flux recovery rate and separation stability. This work provides a new way for nanofiltration membrane preparation and performance improvement.