Preparation And Performance Of Carbon Nanotubes/graphene Conductive Nanofiltration Membrane

Nanofiltration(NF)membrane has been widely used in domestic sewage advanced treatment,industrial wastewater compliance and reuse treatment.However,the problems of high energy consumption and membrane fouling in the application of nanofiltration membranes severely restrict its further application.The conductive separation membrane with retention and conductivity properties could display great water flux under an external electric field,selectivity retention and anti-fouling characteristics,etc.,which is considered to be a suitable path to solve the high energy consumption and membrane pollution of nanofiltration membrane.However,there are problems such as limited conductivity and non-uniform structure,and low conductivity stability for conductive organic membranes via blending method.Therefore,it is necessary to develop a conductive separation membrane with high conductivity and high stability.Thus,in this study,polyether sulfone(PES)was used as the base membrane,and carbon nanotubes(MWCNTs-COOH)and graphene(Gr)were preferably used as conductive modification materials.The conductive layer of functional nanofiltration membrane was modified by using a blended phase inversion method.The results show that under the conditions of the optimal ultrasonic frequency of 40 k Hz and the optimal ultrasonic time of 90 min,a conductive nanofiltration membrane with good conductivity stability can be obtained by doping 5 wt% MWCNTs-COOH and 0.5 wt% Gr and the highest conductivity is 0.1 S/cm.An improved blended phase inversion method was used to prepare the modified conductive membrane and its filtration performance was optimized.The results show that the pure water permeability of the modified conductive membrane prepared by the membrane base layer / conductive layer thickness ratio of 150: 100 is 116.2 Lm-2h-1 under 0.1 MPa.The retention rate of the dye Congo red is 81.3% without electricity.Furthermore,the modified conductive membrane improved hydrophilicity,reduced roughness,had a stable electrochemical property,and could operate stably under acidic and neutral conditions.The separation and anti-fouling characteristics of modified conductive membranes against characteristic pollutants under an external electric field were studied.The results show that,the retention rates of modified conductive membranes for the characteristic pollutants of printing and dyeing wastewate were great under t an external electric field,the rejection of Congo Red(CR)and methylene blue(MB),are 99.7% and 93.1%,respectively,Cu(?)and Ni(?)retention rates were 98.1% and 95.7%,respectively.The results of antifouling experiments showed that the flux recovery rate(FRR)of PES-based membrane and modified conductive membrane under electric field to protein organic matter(BSA)was 46.8% and 75.8%,respectively.The FRR for Humic acid(HA)was 78.8% and 97.7%,respectively and the FRR for polysaccharide organic sodium alginate(SA)was 72.9% and 96.6%,respectively.The degree of anti-fouling properties of modified conductive membranes on BSA,HA,and SA was HA> SA> BSA in descending order under the electric field,indicating that conductive nanofiltration membranes can alleviate membrane fouling stably under an external electric field.