Preparation And Performance Of Graphene-based/carbon Nanotube Composite Membranes

With the rapid development of Chinese economy,the amount of organic wastewater and dye wastewater is increasing day by day,fresh water is decreasing,so the problem of water resources can not be ignored.Membrane separation technology has many advantages such as simple operation,remarkable treatment effect,low energy consumption,low cost of equipment maintenance and easy operation and management.In this dissertation,we use graphene oxide?GO?,carbon nanotubes?CNT?as raw materials,with 100nm of polyvinylidene fluoride?PVDF?membrane as the support layer,using vacuum filtration method to prepare the GO/CNT composite membranes with three-dimensional network structure.The removal of organic humic acid?HA?and the antifouling performance of the membranes were mainly studied.GO/CNT composite membranes was reduced by HI vapor to obtained the graphene/carbon nanotube?rGO/CNT?composite conductive membranes.rGO/CNT membranes have small interlamellar spacing and strong conductivity.The effect of the applied voltage on the dye wastewater and the low concentration of NaCl were studied.The GO solution was prepared by the modified Hummers method,and the CNT dispersed solution was obtained by H₂SO₄ and HNO₄ acidification.GO and CNT mixed,ultrasonic then vacuum filtration into three-dimensional GO/CNT composite membranes.SEM,XRD characterization results showed that CNT was successfully incorporated into the GO lamellas.The effect of CNT dosage,pH value and ionic strength on the removal efficiency of HA was studied.The results showed that with the increase of CNT content,the water flux increased obviously,and the rejection rate decreased.The GO-20%CNT achieved a rejection of over 90%on HA,and its water flux was improved to 2 times higher than of GO membrane.Acidic conditions and low ionic strength are beneficial to the increase of rejection rate.The flux recovery rate of GO-20%CNT membrane is 99.68%,which is 6.18%higher than that of GO membrane,and exhibited an excellent antifouling performance.The GO/CNT membranes was reduced by HI at 90?for 1h to prepare the rGO/CNT conductive membranes,The characterization of XRD,XPS showed that HI reduced-COOH,-OH and the lamellar spacing became smaller.The effects of CNT content and voltage on the removal of different dyes were investigated.The results showed that the removal effect of rGO/CNT membranes for different dyes was RhB>MB>MO,and the rejection rate decreased with the increase of CNT dosage.When the-1.0V voltage is applied,the rejection rate of RhB with two kinds of electrical properties and MO with negatively charged were increased,while the rejection effect of the positive MB was not changed significantly.The influence of CNT content,voltage and concentration of NaCl on desalting efficiency was studied by increasing load to 60 g/cm² for rGO/CNT membranes,then discussed the reason of removal change when voltage was applied.The results showed that voltage and concentration of NaCl were positively correlated with rejection rate,and CNT content was negatively correlated with rejection rate.When the CNT content was 30%,the-1.0V voltage was applied,and the rejection rate is as high as 67.15%.Applied electric can produced electric field on the ions,then the Donnan effect was enhanced,caused the enhancement of the repulsive force for ions,so the rejection rate of salt was improved.The electrochemical test shows that the removal rate of the membranes were positively correlated with the specific capacitance and the ion diffusion rate.