Li, Jian, et al. Journal of membrane science 486 (2015): 89-96.
Ion exchange membrane is indispensable in electrodialysis. However, the presence of multivalent ions, such as Ca2+, Mg2+, or CO32-, SO42-, may lead to harmful membrane scaling risks. Monovalent cation selective membrane can solve this problem. Polyquaternium-7 (PQ-7) was used to modify the cation exchange membrane. The membrane modified with PQ-7 was shown to be potentially effective.
Preparation of Monovalent Cation Selective Membrane
1. Before the experiment, the cation exchange membrane was rinsed with deionized water in an ultrasonic bath for 15 min to remove excess sodium chloride.
2. The membrane surface was dried with a paper towel and soaked in toluene for 24 h to fully exchange water. After that, the membrane was stored in fresh toluene using a 250 mL three-necked flask.
3. Thionyl chloride was titrated into a 30 °C solution under reflux conditions. The temperature was increased in steps of 10 °C per hour until 80 °C was reached, and then maintained for 24 h.
4. Then, the membrane was washed several times with fresh toluene. The chlorosulfonated membrane reacts with the degraded PQ-7 in a sodium carbonate solution to form a thin film on the membrane surface. Sodium hydroxide is used as a deacidification agent because amines have the ability to react with nucleophilicity; the deacidification agent should be alkaline and have low nucleophilicity to absorb the acid produced by the reaction.
Zhan, Zi-Ming, et al. Industrial & Engineering Chemistry Research 60.39 (2021): 14297-14306.
Polyamide nanofiltration (NF) membranes with enhanced desalination and antifouling properties were prepared by grafting polyquaternium-7 (PQ-7) using dimethyldiallylammonium chloride and acrylamide as monomers. Compared with the control polyamide NF membrane, the PQ-7 grafted membrane exhibited higher hydrophilicity, rougher membrane surface, and stronger positive charge. The surface grafting process has no significant effect on the film thickness. After modification, the water flux of the resulting membrane was increased from 47.8 liters to 79.6 liters m-2 h-1 at 5 bar, and the permeability was significantly improved. At the same time, the rejection of divalent ions is improved to superior levels due to the introduction of positively charged quaternary ammonium groups from PQ-7. In addition, antifouling evaluation showed that the modified polyamide nanofiltration membrane had excellent flux recovery capability and antifouling properties for both sodium alginate solution and bovine serum albumin.
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