Preparation And Performance Study Of Graphene Oxide Modified Nanofiltration Membrane

Nanofiltration（NF）membranes water treatment technology,as an important part of membrane water treatment technology,which has shown excellent effects in various wastewater treatment fields.However,NF membranes generally have some disadvantages such as low flux,poor anti-fouling property and short service life,which limits the large-scale application in industry.Therefore,research and fabrication of membranes with high flux,high rejection rate,low operating costs,long service life has been the focus of the development of NF membranes technology.Inorganic nanoparticles have advantages of large specific surface area,good mechanical properties,and stable physical and chemical properties.The performance of NF membrane would be improved obviously if inorganic nanoparticles were coupled into the functional layer of NF membranes.At present,it has become the research hotspot to improve the comprehensive performance of the NF membrane by doping nanoparticles in interfacial polymerization process which can improve the water flux of the NF membrane.And it would not affect or slightly affect the NF membrane rejection rate.In this study,composite NF membranes were prepared by graphene oxide（GO）modification and GO and multi-walled carbon nanotubes（MWCNTs）modification.GO has two-dimensional lamellar structure,and there are a large number of reactive hydroxyl groups,carboxyl groups around GO molecules.GO presents the advantages of large specific surface area,good hydrophilicity and stable chemical properties.GO modified polyamide NF membranes were fabricated by blending GO and piperazine（PIP）in the aqueous phase and then reacted with trimesoyl chloride（TMC）.The preparation conditions were optimized and the optimal preparation conditions of the NF membrane were that PIP concentration was 0.3 wt%,TMC concentration was 0.15 wt%,GO concentration was 0.03 wt%,aqueous phase immersion time was 10 min,the reaction time of interfacial polymerization was 50 s,the heat treatment temperature and time were 60℃and 10 min,respectively.The flux and the rejection rate of the GO modified NF membrane prepared under optimal were41.6 L/m²·h and 94.6%for Na₂SO₄,respectively.And the molecular weight cut off of（MWCO）of the NF membrane was approximately 370 Da.What’s more,the rejection rate of the NF to four inorganic salts under neutral conditions decreased in the order of Na₂SO₄>MgSO₄>MgCl₂>NaCl,which presented typical rejection characteristics of negatively charged NF membrane.In order to improve the permeation flux of NF membrane in further and make full use of the excellent characteristics of two-dimensional structure of GO,GO/MWCNTs were used to modify NF membranes.It is expected to improve the permeation of NF membrane by improving the spacing of GO molecules layers.GO/MWCNTs modified NF membrane was prepared through blending GO,MWCNTs and PIP in the aqueous phase and then reacted with TMC.The fabrication conditions of binary modified NF membrane were optimized.And the optimal fabrication conditions of GO/MWCNTs modified membrane were that PIP concentration was 0.3 wt%,TMC concentration was 0.15 wt%,GO concentration was0.03 wt%,the MWCNTs concentration was 0.015 wt%,sodium dodecyl benzene sulfonate（SDBS）concentration was 0.03 wt%,the heat treatment temperature and time were 60℃and 10 min,respectively.The flux and the rejection rate for Na₂SO₄of GO/MWCNTs modified NF membrane was 55.6 L/m²·h and 94.0%,respectively.And the MWCO of the membrane was approximately 382 Da.In addition,the rejection rate of the NF membranes to four inorganic salts under neutral conditions decreased in the order of Na₂SO₄>MgSO₄>MgCl₂>NaCl,which also presented the typical rejection characteristics of negatively charged NF membrane.The results showed that the permeate flux of GO modified NF membrane was obviously improved by adding MWCNTs,and the rejection rate did not changed significantly.