Preparation And Characterization Of Polysulfone Separation Membrane

In recent decades,the separation membranes have been widely applied in water treatment?including seawater desalination,sewage treatment,purification of brackish water,preparation of ultrapure water?,energy,traditional industries,ecological environment and other fields.The development of next generation of separation membranes with higher water flux,higher rejection,and lower operating pressure is the current consensus of industrial development.It is necessary to develop new technologies for evaluating the structure of the membrane.Thus,in this paper,the nanostructure of polysulfone membrane was characterized by different techniques,such as positron annihilation techniques and electrochemical impedance spectroscopy.The correlation between the obtained parameters and the membrane performance was discussed in detail..In order to understand the relationship between pore-structure information of organic separation membrane and the membrane performance,the pore size,porosity of the organic separation membranes were characterized.A series of commercial membranes?UTC70,UTC80 and the substrate?were studied first.Scanning electron microscopy was used to observe the cross-sectional morphology of UTC70,UTC80 as well as the substrate.The positron annihilation techniques coupled with positron beam were applied to in situ examine the layer structure of these commercial membranes.The results are as follows:the separation membrane UTC70 and UTC80 exibit similar layered structure,that the surface layer is dense,while the beneath layer is porous.According to the positron annihilation lifetime results,the free volume hole in the dense layer of UTC70 is larger than that of UTC70.The membrane performance results indicated that UTC80 has a higher rejection rate and smaller water flux than UTC70.In order to develop the anti-fouling membrane,the photo catalytic ability of theTiO₂ nanoparticles wrapped by the polysulfone was explored.The experiment explored the ultraviolet light transmission through the polysulfone membranes with different thicknesses.The positron annihilation Doppler broadening spectroscopy coupled with a positron beam was used to study the depth profile of the membranes.The experimental results show that covered layer would weaken the photocatalytic ability of polysulfone/TiO₂ membrane.The electrochemical impedance spectroscopy implies that the covered membrane would generate the charges under UV irradiation,and the charges may permeate through the covered layer,which may be the reason that the photocatalytic ability of covered membrane is weaker than the uncovered one.In order to develop an efficient and convenient method for measuring the water flux of organic separation membranes,an attempt was made to find the relationship between water flux and resistance of separation membranes.A series of polysulfone membranes with different pore structures were prepared by adjusting the pore-forming agent content.Electrochemical impedance spectroscopy?EIS?,positron 3?annihilation technique,and water flux measurement were employed to probe the nanostructure of the membranes.The experimental results show that with increasing the pore-forming agent content,the resistance of the membrane increases,the pore size expands and water flux increases.In addition,combining pores is predominant with increasing PEG content from 0 to 2%,while the forming new pores and/or expanding the pore size are dominant with increasing the PEG content larger than 2%.Moreover,the water flux value is inversely proportional to the pore resistance of the present studied membranes,and this correlation is consistent with the equation deduced from the pore model of the separation membrane.Therefore,electrochemical impedance spectroscopy and positron annihilation techniques are effective methods for evaluating the nanostructure of a separation membrane.