Preparation And Performance Study Of A Novel Nanofiltration Membrane Modified By Levodopa-modified Graphene Oxide

Membrane separation technology combines the function of separation,purification and concentration and the feature of high efficiency,energy saving,environmental friendly,simple process and controllable which endow it to be widely used in electronic,bionic,biology,food industry,medicine,environmental protection,metallurgy,energy,petrochemical industry,water treatment,and etc.As one of the essential components,nanofiltration?NF?membrane has molecular weight cut-off of 100–1000Da which is between ultrafiltration membrane and reverse osmosis membrane.Graphene oxide?GO?of faveolate plane is constituted by sp2 and sp3 hybrid monolayer carbon atoms which has carboxyl and hydroxyl at the edge and epoxide and carbonyl in the plane.Negatively charged GO and unbalanced force of sp3 hybrid carbon atoms result in much ruleless wrinkles and defects in GO which promotes its multiple channels and large flux in NF performance.Most methods of preparing GO membrane would exclude solvent in GO dispersion by external pressure or electrostatic attraction during which no organic solvent and chemical reaction are involved.So the process possesses the advantages of low cost and easy operation which meet the principles of green chemistry.Membrane integrality must be ensured to be used in practical industrial cross flow filtration but GO is likely to break up if transmembrane pressure shorts or fierce turbulence occurs in aqueous atmosphere due to its super hydrophilia.To solve this problem,adjacent GO nanosheets must be integrated together through a sort of force linking both the substrate?if needed?and outermost layer tightly.Upon the discussion above,first,graphite oxide was prepared by modified Hummers method.Second,in gentle weak alkaline condition offered by Tris-HCl buffer solution,amino group in levodopa?LDA?would set off chemical reactions with carboxyl and hydroxyl in GO sheets which was able to crosslink GO sheets together and thus ensured the stability of GO membrane.Last,LDA modified GO membranes were fabricated through vacuum filtration process driven by pressure.We found GO membranes were wrinkled,lamellar and negatively charged through a series of characterization methods,such as TEM?FTIR?XRD?XPS?Zeta.All the performance tests were conducted in a fierce turbulence cross flow filtration device under the pressure of 1 bar and all dyes were in the concentration of 0.1 g/L.GO membranes without LDA owned a rejection of 60%for X-3B whose relative molecular mass was615 Da and a flux of 21.66 L.m^-2.h^-1.bar^-11 while LDA crosslinked GO membranes can reach a value higher than 97%and flux between 1.52 L.m^-2.h^-1.bar^-1 and 3.47L.m^-2.h^-1.bar^-1.LDA crosslinked GO membranes can block 93%higher dyes of relative molecular mass bigger than 300 Da and show better rejection for positively charged dyes.Performance tests were performed more than 26h.Flux decay rate of 8.9%and stable rejection higher than 90%showed our prepared membranes can keep good performance for a long time and have considerable potential to be used in industry.