Study On Polyphenols Modification And Properties Of Organic Filter Membrane Based On Inkjet Printing

Membrane separation technology,with its advantages of low energy consumption,high separation efficiency,environmental protection and long-term reuse,has shown a good application prospect in various waste water treatment,and is considered as one of the most powerful and optimal research directions for wastewater separation.However,membrane fouling will increase energy consumption and shorten the life cycle of membrane,which has long restricted the engineering application of membrane filtration.By modifying the traditional membrane,the hydrophilicity of the membrane can be improved,the degree of membrane pollution can be reduced,and the flux and antifouling performance of the traditional organic membrane can be improved.Membrane modification technology has far-reaching significance for the application of membrane separation in the engineering field.Polyphenols exist in many natural systems.They are the general term for substances with benzene rings and the combination of hydroxyl groups.Polyphenols have been used in the surface coating technology of different materials and the preparation of composite nanoparticles due to their excellent biological adhesion,cohesion characteristics and the presence of catechol or catechol groups and the hydrophilic properties of hydroxyl groups.The main advantages of ink-jet printing technology are wide range of applicable ink materials,no need to contact with the substrate,easy to modify the design to highlight personalized,less ink consumption cost saving and environmentally friendly.In recent years,inkjet printing technology has developed into a new surface coating method,which is widely used in electrical equipment,sensors,solar cells and thin composite membranes.This study proposed that traditional organic membranes represented by PVDF and PP were surface modified by introducing polyphenols（such as DA,CA,TA）using inkjet printing technology to improve their flux and antifouling performance.This provides a feasible solution for membrane fouling in engineering application of membrane separation technology.The main research contents are as follows:（1）Through the ink-jet printing technology,DA was polymerized on the PP membrane surface to form a polydopamine coating by the oxidative induction of SP.The changes of hydrophilicity before and after membrane modification were compared by measuring the water contact angle of membrane surface.The change of membrane surface morphology was observed by SEM.The element composition of the membrane was measured by XPS.The qualitative change of chemical functional groups on membrane surface was investigated by ATR-FTIR.The water flux and antifouling properties of the modified membrane were tested by filtration experiment and stability experiment.The results show that printing SP layer can significantly improve the aggregation rate of DA.With the increasing of the number of SP layers,the water contact angle of PP membrane decreased from 120.7°to67.3°,and the hydrophilicity was significantly improved.The water contact angle of the modified membrane decreased rapidly and stabilized within 2h.Studies have shown that the hydrophilicity of PP membrane can be greatly improved by the polydopamine coating prepared by inkjet printing,and the hydrophilicity of PP membrane can be regulated by adjusting the ratio of DA/SP and reaction time.Under optimized conditions,the water flux of the modified membrane increased from 717.9 L·m^-2·h^-1 to 1323.5 L·m^-2·h^-1,and the flux recovery rate of the yeast suspension was 85.6%.In addition,the modified coating prepared by printing has good long-term stability in aqueous solutions with a wide pH range（pH 2.0-9.0）.Compared with the PDA modification method of O₂ oxidation,the method of this study improved the degree of polydopamine oxidation through SP,the reaction rate was faster,and the modified membrane obtained was better.（2）The hydrophilic PVDF modified membrane was directly prepared by using SP induced polyphenols（CA and TA）by ink-jet printing technology.XPS showed that polyphenols were successfully loaded on the membrane surface.The water contact angle of the modified membrane reflects the hydrophilic modification of polyphenols.The SEM image of the modified membrane shows that the pore size of the membrane has changed,which further proves that the modified substance exists on the membrane surface.The results show that under the experimental conditions of this study,CA and TA have similar properties to DA and can improve the hydrophilicity of PVDF membrane.The results show that the modification effect can be controlled by adjusting the ratio and reaction time of polyphenol/SP.Improved the hydrophilicity of the modified layer with polyphenols（PVDF membrane water contact angle is 83.3°,CA modified membrane fell to 72.0°,TA modified membrane fell to 64.0°）,the pure water flux of the membrane have significantly improved（the pure water flux of the modified layer with CA is 2.3 times of the pristine membrane,the water flux of the modified layer with TA is 3.9 times of the pristine membrane）,oil water separation effect were better than the pristine PVDF membrane,modified membrane flux of several kinds of oil-water emulsion were improved obviously.At the same time,the modified membrane has good stability under acidic conditions（pH 2.0-7.0）.（3）Through the inkjet printing technology,by adjusting the pH,the Fe（Ⅲ）and d-PDA complexing deposition on PVDF membrane surface.The modification scheme proposed in this study makes use of the characteristics of ink-jet printing technology,which can greatly improve the utilization rate of PDA and provide a new idea for saving modification cost.XPS detected signals of N,O and Fe,indicating that PDA coating was successfully fixed;ATR-FTIR detected the presence of PDA characteristic peaks,which indicated the existence of PDA on the membrane surface,and proved that the complexation deposition of PDA was successful.The SEM image of the modified membrane shows that the pore size of the membrane has changed,which further proves that the modified substance exists on the membrane surface.Studies have shown that ink-jet printing technology can utilize dissolved polydopamine to hydrophilic modify PVDF membrane,and further improve the utilization rate of dopamine.By adjusting the times of printing and reaction time,the modification effect can be controlled.The water contact angle of the modified membrane is 66.6°,hydrophilicity is significantly improved,and the pure water flux is 635.2 L·m^-2·h^-1·bar^-1,which is 286%higher than the pristine membrane.The modified coating has good stability in the weak acid environment.