Zwitterions functionalized multi-walled carbon nanotubes/polyamide hybrid nanofiltration membranes for monovalent/divalent salts separation

N-aminoethyl piperazine propane sulfonate (AEPPS) modified multi-walled carbon nanotubes (MWCNTs) (AEPPS-PD@MWCNTs) were prepared by co-deposition of dopamine and AEPPS on MWCNTs surfaces. AEPPS-PD@MWCNTs were mixed with piperazine aqueous solution and polymerized with 1,3,5-benzenetricarboxylic chloride (TMC, dissolved in hexane solution) to prepare negatively charged NF membranes, which were characterized by Fourier Transform Infrared Spectroscopy, X-ray Photoelectron Spectroscopy, Transmission Electron Microscopy and Atomic Force Microscopy. It was found that compatibility between AEPPS-PD@MWCNTs and polyamide matrix was enhanced as a result of the multiple interactions between AEPPS-PD@MWCNTs and TMC monomers. At optimized conditions, pure water permeability of hybrid membrane was 127.3 L m −2  h −1  MPa −1 , 1.8 times as high as pristine PIP/TMC membrane without compromising Na 2 SO 4 rejection. Meanwhile, NaCl rejection of hybrid membrane was 19.0%, much lower than pristine PIP/TMC membrane. Hybrid membrane exhibited applications in separation of monovalent/divalent salts and monovalent salts/neutral organics coupled with good stability and better anti-fouling property which was sought for applications in the field of desalination, food and biological separation processes.