Fu Liu,Bi-rong Ma,Dong Zhou,Li-Jing Zhu,Yin-Yi Fu,Li-xin Xue
A novel positively charged loose nanofiltration (NF) membrane was fabricated feasibly by UV-induced photografting polymerization of diallyl dimethyl ammonium chloride (DADMAC) on Polysulfone ultrafiltration membrane. A possible reaction mechanism was proposed that a linear chain structure and/or pyrrole like five-membered nitrogen heterocycles structure on the side chain were grafted to form the active barrier layer. NF membrane demonstrated a looser average pore size of 8.6 nm and positive charges surface. Owing to the nanoscale ultrathin nanoscale barrier layer and the combination of Donnan exclusion and steric hindrance , NF membrane exhibited good hydrophilicity , a high pure flux of 60 L/m 2 h (0.5 MPa), a good salt rejection to Mg 2+ (90.8%), Al 3+ (94.0%), Ca 2+ (91.5%), and a high dye rejection to methylene blue (99.4%) and congo red (100.0%) respectively. The salts rejection of NF membrane to different salts followed the order of AlCl 3 > CaCl 2 > MgCl 2 > NaCl > LiCl > MgSO 4 > Na 2 SO 4. NF membrane showed certain fouling resistance to seawater and BSA solution. The grafting polymerization kinetics were comprehensively investigated including irradiation time, monomer concentration and irradiation intensity. X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurement were employed to investigate membrane chemistry, morphologies, and hydrophilicity.
A novel polymer of intrinsic microporosity , acyl chloride-functionalized polymer of intrinsic microporosity (PIM-COCl), was obtained by hydrolysis under alkaline conditions and acylation in thionyl chloride of PIM-1. PIM-COCl is soluble in common organic solvents , and it is used for the first time for organic solvent nanofiltration (OSN). The acyl chloride groups in PIM-COCl can be further cross-linked with an amine-functionalized polyacrylonitrile (APAN) ultrafiltration membrane to form an interconnected layer, which shrinks pore size and provides better structural stability and selectivity. The PIM-COCl composite membranes exhibit high rejection and alcohol flux during OSN. Compared with the reported PIM OSN membranes , [email protected] exhibits higher rejection for crystal violet (408 g mol −1 , over 94%) in ethanol and several times higher alcohol flux. The membrane shows outstanding stability in ethanol for 14 days. PIM provides a microporous structure, while the interconnected layer maintains this structure in organic solvents via hydrogen bonding , electrostatic interactions and covalent cross-linking. Other PIMs can readily undergo acyl chloride functionalization, which provides them with high reactivity towards amine groups to form stable interconnected layers. This work offers new strategies for the design and preparation of high performance OSN membranes .
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