title: Nanofiltration Membranes with Narrow Pore Size Distribution via Contra-Diffusion-Induced Mussel-Inspired Chemistry.
abstract: Nanofiltration membranes (NFMs) are widely used in saline water desalination, wastewater treatment, and chemical product purification. However, conventional NFMs suffer from broad pore size distribution, which limits their applications for fine separation, especially in complete separation of molecules with slight differences in molecular size. Herein, defect-free composite NFMs with narrow pore size distribution are fabricated using a contra-diffusion method, with dopamine/polyethylenimine solution on the skin side and ammonium persulfate solution on the other side of the ultrafiltration substrate. Persulfate ions can diffuse through the ultrafiltration substrate into the other side and in situ trigger dopamine to form a codeposited coating with polyethylenimine. The codeposition is hindered on those sites completely covered by the polydopamine/polyethylenimine coating, although it is promoted at the defects or highly permeable regions because it is induced by the diffused persulfate ions. Such a "self-completion" process results in NFMs with highly uniform structures and narrow pore size distribution, as determined by their rejection of neutral solutes. These near electrically neutral NFMs show a high rejection of divalent ions with a low rejection of monovalent ions (MgCl2rejection = 96%, NaCl rejection = 23%), majorly based on a steric hindrance effect. The as-prepared NFMs can be applied in molecular separation such as isolating cellulose hydrogenation products.
authors.affiliation: MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.|Key Laboratory of Adsorption and Separation Materials & Technologies of Zhejiang Province, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Du
authors.affiliation: MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.|Key Laboratory of Adsorption and Separation Materials & Technologies of Zhejiang Province, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.
authors.forename: Wen-Ze
authors.initials: WZ
authors.lastname: Qiu
authors.affiliation: MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.|Key Laboratory of Adsorption and Separation Materials & Technologies of Zhejiang Province, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Lv
authors.affiliation: Department of Chemistry, Zhejiang University , Hangzhou 310027, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Wu
authors.affiliation: MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.|Key Laboratory of Adsorption and Separation Materials & Technologies of Zhejiang Province, Department of Polymer Science and Engineering, Zhejiang University , Hangzhou 310027, China.
authors.forename: Zhi-Kang
authors.initials: ZK
authors.lastname: Xu
keywords: contra-diffusion; mussel-inspired chemistry; nanofiltration membrane; polydopamine; pore size distribution