The Preparation Of Phytic Acid Modified Membrane By Layer Self-assembly And The Thermodynamic Analysis Of Its Anti-pollution

Membrane bioreactor is a kind of efficient process of wastewater treatment,which has been developed rapidly in recent years.It has many advantages that traditional processes do not have,such as the high quality of produced water,increased water scarcity,the increasingly strict discharge and reuse quality legislation and many more.However,due to the high membrane cost,high energy consumption and membrane pollution problems,Leading to problems in practical application.Membrane fouling,which shortens membrane life and increases operating costs,has long been regarded as a major drawback that hinder the widespread use of membrane technology for water treatment.In order to solve the problem of membrane fouling,extensive efforts have been made to produce membranes with excellent properties,including optimizing membrane pores or surface structures,modifying contaminant properties and controlling membrane preparation conditions.This study was the first report of an easy way,based on the self-assembly technique of layers,a phytic acid-modified membrane was prepared.The modified membrane with the best anti-fouling property was obtained by the test of anti-fouling property.At the same time,The XDLVO theory(Extended Derj aguin-Landau-Verwey-Overbeek)interface thermodynamic analysis provides potential solutions to optimize the LBL assembly technology and adjust the membrane’s anti-fouling ability quantitatively.The main findings are as follows:(1)Through the method of layer self-assembly(LBL),polyvinylidene fluoride(PVDF)membranes were modified by zinc nitrate and phytic acid as the polyelectrolyte solution by alternately depositing Zn2+ and phytic acid(PA)In the experiment,the five-layer modified membrane showed a flux recovery rate of 88.335%,which was higher than that of the PVDF membrane and the other layers modified membranes,the antifouling property of the membrane is improved.Since the outermost layer of the membrane was phytic acid,Phosphate groups decreased the contact angle of the membrane surface from 72.87 to 14.65.At the same time,the electronegativity of the membrane increased from-19.19 mV to-21.90 mV.The electrostatic repulsion between the membrane and the negatively charged organic pollutant is enhanced,and the synergistic effect of the hydrophilic and the negative electricity on the membrane surface is favorable for improving the antifouling property of the membrane.Characterization of the surface morphology of the membrane showed that the surface of the membrane modified with 5 layers showed obvious bulging and uniform distribution of the membrane,indicating that the polyelectrolyte was successfully assembled on the surface of the PVDF membrane.(2)Super-hydrophilic and low-contamination multi-layer coatings were prepared on polyvinylidene fluoride(PVDF)membranes by alternating Fe3+ and phytic acid(PA)layer by layer(LBL)assembly.Successful modification analysis was verified by scanning electron microscopy(SEM)and elemental verification.It is found that the PA/Fe@PVDF-OH membrane with five layers of double-layer modification has the best antifouling performance under the conditions of this study.Compared with the original PVDF-OH membrane,the surface of the coating has superhydrophilicity(water contact angle is 11.34 °)and improved negative charge.(3)Thermodynamic analysis shows that,the change in the interaction energies caused by both the modified thermodynamic properties and the morphology of the surface is the reason for the improvement of the antifouling property of the coating membranes.The easy coating strategy and the method used to evaluate the interaction energy in this study provide a potential solution to optimize the LBL assembly technique and quantitatively adjust the fouling resistance of the membrane.