Study On LBL Self-assembly Preparation And Performance Of GO-Ceramics Composite Nanofiltration Membrane

The advanced film material is the key to the continuous development of membrane technology.Graphene oxide?GO?,due to its unique two-dimensional flake structure with net work of carbon atoms,has the characteristics to prepare ultra-thin separation film.At present,the preparation method of GO has been studied quite well,however,researches on its washing process are insufficient.The washing and removing impurities method of GO in a efficient way with low energy consumption and low cost will greatly promote its application.There are many reports about the use of GO to prepare multi-layer film,but it is not commonly reported that the combination of GO and Al₂O₃ ceramic film to make nanofiltration membrane with high retention performance of inorganic salts.In this paper,the GO sample was prepared by Hummers method with optimizing the washing process.According to the theory of using layer-by-layer?LBL?self-assembly technique to make multilayer film and the feature that the carboxyl hydrolysis makes GO sheets negatively charged;GO and Polyethylene mine?PEI?are composed into polyelectrolyte pairs,which are driven by electrostatic action to make multilayer film.At last,after multilayer film being cross-linked with Epichlorohydrin?ECH?,GO-ceramics composite nanofiltration membrane is produced.It is a new type of positively charged organic-inorganic composite nanofiltration membrane.The conclusions of the study are as follows:?1?In this paper,vacuum filtration and cross-flow filtration are combined to solve the problem that GO is difficult to be washed and its impurities are difficult to be removed.the washing process is easy to recover the waste acid of the reaction solutions and it is also easy to wash and enrich GO rapidly when dealing with GO reaction solutions.?2?GO-ceramics composite nanofiltration membrane is a new type of positively charged composite nanofiltration membrane.The order of interception to inorganic salts is MgCl₂>MgSO₄>NaCl>Na₂SO₄,and the rejection rates of anions and cations are Mg²⁺>Na⁺,Cl^->SO₄^2-.With the operating pressure of 0.6MPa,the interceptions of 2 g·L-1 MgCl₂ to 1-4 layers of composite nanofiltration membrane are 90.16%,93.71%,97.54%and 92.93%respectively.And the filtrate fluxes are 21.92 L·m-2·h-1,6.68 L·-m-2·h-1,5.78 L·m-2·h-1,4.71 L·m-2·h-1 respectively.The studies on the performance of the composite nanofiltration membrane have found that it has excellent stability under the conditions of different concentrations?pressures and continuous operation time.?3?Composite nanofiltration membrane is composed of ceramic porous support,Al₂O₃ ceramic base film and GO/PEI/ECH composite film.Due to the unevenness force of GO,the morphology of the outer surface of GO/PEI/ECH composite film presents wrinkle texture;and the morphology of the inside surface of GO/PEI/ECH composite film is showed a sheet-like morphology,indicating that GO sheets of the inner surface of the film is in a force equilibrium state.?4?The composite nanofiltration membrane has the rejective effect to MgCl₂,MgSO₄,NaCl and Na₂SO₄,because that the dense PEI film has the electrostatic interaction to the inorganic salt ions and PEI space network structure and GO layer structure have the sieve effect to the inorganic salt ions.And GO inter-layer channels are the rapid transport channel of water molecules.