Preparation And Application Of Ionic Liquid/ Graphene Oxide/PVDF Microfiltration Membrane

Water pollution is a serious environmental problem in the whole world,and traditional methods of treating wastewater have been limited as they have many shortcomings.Membranes separation technology has been widely used in wastewater separation processes due to their low cost,high treatment effect and simple operation.In a process that membrane technology treats water one or several components in raw material liquid pass through a membrane quickly,and other components are remained in raw material solution.Mass transfer driving force can be pressure difference,concentration difference,or potential difference.Herein,we have chosen poly(vinylidene fluoride)(PVDF)as the basic material to fabricate membranes to separate wastewater.However,PVDF has hydrophobic nature which can lead to the membrane fouling in separation process.And thence many research have been focused on the improvement in hydrophobicity of PVDF membrane.In this paper,the hydrophilic material,graphene oxide(GO),is selected for improving the hydrophilicity of PVDF membrane.First,modified Hummers method was used to synthesize GO containing polar hydrophilic groups such as-OH,-COOH,C-O-C.Then GO synthesized was added into PVDF casting solution.At the same time,in order to improve the dispersion of GO in the casting solution further and enhance the separation performance of PVDF membranes,a hydrophilic ionic liquid(1-butyl-3-methylimidazolium tetrafluoroborate)was introduced.The IL/GO/PVDF microfiltration membrane was prepared.In this study,PVP and LiCl were used as porogen,DMAc was used as solvent,and GO with different concentrations were added to prepare GO/PVDF microfiltration membrane.The effects of GO concentration on membrane properties were investigated.The results showed that the introduction of GO into PVDF membrane can all enhance the pure water flux by increasing the average pore diameter,porosity,and hydrophilicity of the microfiltration membrane whatever the LiCl or PVP were used as porogen.During the period of yeast separation experiment,it was found that the permeation flux and flux recovery ratio of GO/PVDF membrane increased significantly.The pore structure distribution of the membranes with LiCl was more uniform than that of membranes with PVP.The mutual solubility of PVP and PVDF is poor,so the viscosity of the casting solution is high.Therefore,the dispersion is non-uniform and phase separation time is prolonged during the membrane formation process.Furthermore,the pore structure is unevenly distributed.To improve the dispersion of GO in PVDF membranes,GO was functionalized by the addition of IL and formed mixture of IL-GO.When the IL concentration was kept at 2wt% and GO concentrations were varied from 0 to 0.3wt%,the membranes tended to form a typical asymmetric finger-like porous structure,and the porosity,average pore diameter and hydrophilic of the membrane can be increased;The removal of yeast and the flux recovery ratio of membranes were improved,indicating that the antifouling property of the membrane was enhanced.But when GO concentration was 0.5 wt%,the removal of yeast and flux recovery ratio were both reduced.Excessive GO can lead to the uniform in GO and result in the reduction in hydrophilicity and antifouling.When the GO concentration was kept at 0.5wt% and IL concentrations were varied from 0 to 3wt%,the membranes tended to form a sponge-like porous structure,and both the porosity and the average pore diameter of microfiltration membranes were reduced.The removal of yeast and the flux recovery ratio of membranes were improved,but too much IL can lead to excessive sponge-like porous and result in the reduction of the water flux.However,membranes can kept the high antifouling property because the GO was constant.