Zwitterions Construction Via Michael Addition On The Surface Of Reverse Osmosis Membrane

Membrane fouling problem is one of the development bottlenecks of reverse osmosis membrane technology. In this work, based on the anti-fouling mechanism of zwitterions, zwitterions were constructed mildly and efficiently on the surface of polyamide (PA) reverse osmosis membrane via Michael addition reaction between positively charged candidates (PCC) and negatively charged candidates (NCC), and therefore zwitterionic reverse osmosis membranes with excellent anti-fouling property were fabricated successfully. At first, hyperbranched polyethylenimine (PEI) and acrylic acid (AA) were used as PCC and NCC, respectively, to construct zwitterionic PEI-AA. Then zwitterionic PEI-AA160/PA membrane was fabricated and the key factor of this zwitterion construction method was investigated. The anti-fouling property of PEI-AA160/PA membrane was studied through the static and dynamic protein adsorption tests. The microstructure, surface property, separation performance of PEI-AA160/PA membrane were characterized to study the influence of zwitterion on the structure and property of membrane. Afterwards, the physicochemical stabilities of PEI-AA160/PA membrane to NaOH, HC1 and active chlorine aqueous solutions were investigated. At last, the designability of zwitterions construction via Michael addition was investigated through screening different kinds of PCC and NCC. Different kinds of zwitterions and zwitterionic membranes were obtained. The structural features of PCC and NCC were summarized. Conclusions in this work including:(1) Fabrication of zwitterionic PEI-AA/PA membrane via Michael addition: zwitterionic PEI-AA was constructed successfully mildly in aqueous solution under 35 ℃. Zwitterionic PEI-AA160/PA membrane with optimal anti-fouling property was obtained, and charge balance between positively charged group and negatively charged group was the key factor of the zwitterion construction.(2) Anti-fouling study of zwitterionic PEI-AA160/PA membrane:PEI-AA160/PA membrane exhibited excellent anti-fouling property in all solutions with pH values of 5,7,9, and the protein adsorption amount on PEI-AA160/PA membrane surface was only about 5% with respect to that on the surface of traditional PA membrane. PEI- AA160/PA membrane showed strong resistance to different kinds of proteins with either positive or negative charged. This membrane also owned good flux recovery.(3) Investigation of structure and separation performance of PEI-AA160/PA membrane:the construction of zwitterionic PEI-AA increased the surface hydrophilicity of PA membrane without increasing the thickness of selective layer and membrane surface roughness. As a result, the water flux of membrane increased by 20%, and membrane rejection to NaCl was also increased slightly.(4) Stability study of zwitterion on PEI-AA160/PA membrane surface:zwitterion on PEI-AA160/PAmembrane surface showed good stabilities in acid and alkaline solutions, however owned poor stability in solution containing active chloride because of the decomposition of aromatic polyamide.(5) Design and fabrication of different zwitterionic PCC-NCC/PA membranes:six kinds of zwitterions and zwitterionic PCC-NCC/PA membranes were designed and fabricated successfully via screening different kinds of PCC and NCC. All zwitterionic membranes owns excellent anti-fouling property. Influence factors including molecular size, molecular structure, kinds of charged groups, showed strong designability.(6) Structural analysis of PCC and NCC:PCC, used to construct zwitterions on the surface of PA membrane via Michael addition, should contain group A which can react with-COOH group on PA membrane surface, group B which can react with Michael acceptor, and alkaline group C. And NCC can own olefine acid structure, olefine ester structure with acid group, and maleimide structure with acid group.In this work, different kinds of zwitterions were designed efficiently and zwitterionic PCC-NCC/PA membranes were fabricated mildly. The key influence factor of zwitterion construction and structural features of PCC and NCC were obtained, providing ideas and theoretical basis to future design and fabrication of zwitterions and zwitterionic membranes.