Xiaochen Fan

Antifouling, High-Flux Nanofiltration Membranes Enabled by Dual Functional Polydopamine

A facile method for fabricating antifouling and high-flux nanofiltration (NF) membranes was developed based on bioinspired polydopamine (PDA). Polyethersulfone (PES) ultrafiltration membrane as the support was first deposited a thin PDA layer and then chemically modified by a new kind of fluorinated polyamine via Michael addition reaction between fluorinated polyamine and quinone groups of PDA. PDA coating significantly reduced the pore sizes of the PES support membrane and endowed the NF membrane with high separation performance (flux about 46.1 L/(m(2) h) under 0.1 MPa, molecular weight cutoff of about 780 Da). The grafted fluorinated polyamine on the PDA layer could form low free energy microdomains to impede the accumulation/coalescence of foulants and lower the adhesion force between foulants and the membrane, rendering the membrane surface with prominent fouling-release property. When foulant solutions (including bovine serum albumin, oil and humic acid) were filtered, the resultant NF membrane exhibited excellent antifouling properties (the minimal value of total flux decline ratio was ∼8.9%, and the flux recovery ratio reached 98.6%). It is also found that the structural stability of the NF membrane could be significantly enhanced due to the covalent bond and other intermolecular interactions between the PDA layer and the PES support.

Engineering amphiphilic nanofiltration membrane surfaces with a multi-defense mechanism for improved antifouling performances

Antifouling nanofiltration (NF) membrane surfaces capable of combating membrane fouling caused by different foulants are highly desirable for their broad applications. In this study, amphiphilic NF membranes with both hydrophilic domains and low surface energy domains were prepared to optimally integrate the fouling-resistant defense mechanism and fouling-release defense mechanism for enhanced antifouling performance. The construction of amphiphilic surfaces involved two-step surface modification of the hydrophilic polyamide NF membrane: (1) the introduction of primary amine groups as active sites by grafting triethylenetetramine (TETA) onto the carboxyl groups of the polyamide membrane; (2) the subsequent grafting of 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFBM) through the Michael addition reaction. The amphiphilic membranes had better antifouling properties compared with the hydrophilic polyamide membrane during the filtration of bovine serum albumin (BSA) protein solution, humic acid solution and oil/water emulsion, which exhibited lower flux decline during utilization and higher flux recovery after water cleaning. Hopefully, this study is applicable to prepare a broad spectrum of antifouling NF membranes.

Constructing a zwitterionic ultrafiltration membrane surface via multisite anchorage for superior long-term antifouling properties

Zwitterions bearing balanced charge groups have attracted increasing attention to fabricate antifouling membranes due to their highly hydrated structure. The simple and efficient method of covalent connection to enhance the stability of the zwitterions on membrane surfaces is still challenging. Herein, s branched polyethyleneimine (PEI) was employed to synthesize the zwitterion by a quaternary amination reaction with sodium chloroacetate. A novel zwitterionic surface with neutral surface charge was constructed by grafting the PEI-based zwitterion (Z-PEI) onto the hydrolyzed PAN (H-PAN) membrane surface. Covalent bonds were formed between the Z-PEI and H-PAN membrane while the electrostatic attraction would promote this reaction. The zwitterionic membranes exhibited superior antifouling ability (flux recovery ratio of about 99.8% and total flux decline of about 31.4%) due to the formation of a tight hydration layer by zwitterions on the membrane surface. Furthermore, the flux recovery ratio was not changed obviously during the long term experiment and could be maintained at as high as 96.3 and 98.4% after immersion in acid and alkali solution, respectively. These results demonstrated that the long term and chemical stability of zwitterionic functional surfaces were significantly enhanced via multisite covalent anchorage.