Micro-structure Impact And Performance Improvement Of Ultrafiltration Membrane Via Graphene Oxide/water Coagulation Bath

As a polymer organic material,polyvinylidene fluoride(PVDF)has become the mainstream membrane material in the manufacture of membranes.However,PVDF membranes also face many problems,such as their naturally hydrophobic,which limit their anti-pollution ability.At the same time,the mainstream PVDF membranes are basically finger-like-pore structures so that their retention,mechanical properties and service life are not fully qualified for more stringent water treatment needs.Therefore,effective modification of PVDF membrane is an important means and fundamental way to solve the above problems.Graphene oxide(GO)is a popular multifunctional material in chemical industry today.In this experiment,GO plays a huge role in membrane modification.because of its high hydrophilicity and high viscosity of solution.In order to improve the microstructure of the membrane,PVDF/GO modified ultrafiltration membrane was prepared by phase inversion method and GO solution as the coagulation bath.The hydrophilicity,flux,rejection,porosity,pore size,mechanical strength and anti-pollution performance were characterized.It can be seen that the GO solution as the coagulation bath not only effectively improved the hydrophilicity of the membrane,but also improved the BSA retention rate,mechanical strength and anti-pollution ability of the membrane,thereby effectively improving the performance of the membrane.Finally,the best performance membranes were tested for BOD,COD and color performance of the sewage removal,in order to highlight the performance improvement of the sponge-like PVDF membrane modified by the GO coagulation bath.The cross-section and surface of the membrane were characterized by scanning electron microscopy(SEM)and atomic force microscopy(AFM).It is clear from the SEM of the membrane that the modified membrane has transformed from the original finger-like pore structure into a dense sponge-like pore structure.At the same time,the surface of the modified membrane became smoother and more uniform.The effect of GO coagulation bath form of PVDF membrane formation was analyzed by FTIR.It was found that many hydrophilic oxygen-containing functional groups were formed on the surface of the membrane.The membrane was analyzed by XRD and it was found that the membrane lattice did not change.Therefore,the method of modifying the PVDF membrane by the GO coagulation bath only changed physically,not chemically.The ternary phase diagram of the casting solution system was determined by cloud point titration method.The thermodynamic influence of the casting solution in the membrane formation process was analyzed,and the influencing factors of the phase conversion rate were further explained.The results showed that the phase transformation rate determined the morphology of the membrane microstructure.After transient phase separation,the membrane was generally a finger-like pore structure;after delayed phase separation,the membrane was generally a sponge-like pore structure.The viscosity of the non-solvent affects the phase inversion rate.The higher the viscosity,the more difficult it is to phase separate.As a result,the rate of phase inversion will be slower and eventually the membrane will gradually change from finger pores to sponge pores.