LbL assembly of sulfonated cyclohexanone–formaldehyde condensation polymer and poly(ethyleneimine) towards rejection of both cationic ions and dyes

The use of new polymeric building block is one of the important routes to extend the layer-by-layer (LbL) assembly technique to fabricate novel nanofiltration (NF) membrane. In this work, the low cost sulfonated cyclohexanone–formaldehyde (SCF) condensation polymer is used as anionic building blocks to prepare a novel positively charged nanofiltration membrane by LbL self-assembly technique. The LbL assembly process was investigated by XRD, FTIR, SEM and AFM measurements. The separation performance of cationic ions and dyes was evaluated by pressure-driven nanofiltration tests. It is found that the multilayer surfaces exhibited periodic variations in positive charges. And the prepared membrane showed an effective rejection of both cationic ions and dyes. The multilayer membrane of 4.5 bilayers exhibited rejections of 92.8% and 90.6% to Ni2+ and Ca2+, along with flux of 40.8 and 44.9L/(m2·h·MPa) and pure water flux of 49.3L/(m2·h·MPa), respectively. Simultaneously, this membrane also showed rejection of 93.7% and 90.8% to RdB and EbT, along with flux of 24.3 and 20.5L/(m2·h·MPa), respectively. Moreover, the long-term performance stability of the membrane was improved through cross-linking the multilayer membrane.