Preparation Of Superhydrophobic Composite Membrane And Research On Anti-Fouling In Membrane Distillation

As a new type of membrane separation technology,membrane distillation（MD）has the advantages of high separation efficiency,small footprint,and operation at low temperature and normal pressure.However,the problems,such as membrane fouling and low membrane flux during operation restrict the rapid development of industrialization.Therefore,improving the anti-fouling ability and flux of the membrane,which was by developing anti-fouling membranes with low cost and simple preparation process,analyzing the mechanism of membrane fouling,optimizing membrane distillation operating conditions,is beneficial to promote the industrial development of membrane distillation technology.In this research,nano-SiO₂ and low surface energy reagents 1H,1H,2H,2H-perfluorooctyltrichlorosilane[C₈H₄Cl₃F₁₃Si,PFTS]were used as modified materials to develop a super-hydrophobic composite membrane,which was used in the direct contact membrane distillation process（DCMD）.The experiment compared the effects of spray deposition,dynamic filtration,and the surface grafting methods on the superhydrophobic modification of the membrane surface.The performance of the superhydrophobic composite membrane was further tested by the perspectives of pore size,thermal stability,and mechanical properties.The superhydrophobic mechanism of the membrane was analyzed through the characterization results of atomic force microscopy（AFM）,attenuated total reflection-Fourier transform infrared spectroscopy（ATR-FTIR）and the Cassie-Baxter theoretical model.Through direct contact membrane distillation experiments,the anti-pollution ability of the modified superhydrophobic composite membrane against single inorganic salt,mixed inorganic salt and mixed pollutants of inorganic and organic pollutants was investigated.The surface parameters of pollutants and membrane and the reason why the superhydrophobic membrane was resistant to pollution were analyzed by XDLVO theory.The response surface（RSM）method was used to optimize the DCMD process,and the best operating parameters were determined,which provided a theoretical and practical basis for the industrial application of membrane distillation technology in the future.The research results showed that the superhydrophobic composite membrane prepared by the surface grafting method had good hydrophobicity and thermal stability.The grafted fluorinated nano-SiO₂ was evenly distributed on the membrane surface,which had no significant effect on the average pore size of the membrane,but made the pore size distribution narrower.The fluorinated nano-SiO₂ and PTFS grafted on the surface of the membrane reduced the surface energy of the membrane and increased the surface roughness,which was the main reason for the superhydrophobic properties of the modified superhydrophobic composite membrane.The calculation results of the Cassie-Baxter model showed that only 13.9%of the droplets were in contact with the surface of the superhydrophobic membrane,and the superhydrophobic composite membrane with a water contact angle（WCA）of 155°showed good superhydrophobicity.The self-cleaning function and surface modification of the super-hydrophobic composite membrane changed the force between it and pollutants so that showed better anti-pollution ability and can maintain a stable membrane flux and effluent quality in the DCMD experiment.Response surface（RSM）experiments showed that the model fitted by the response surface method fitted well with the experimental values.R² was 0.9985 and P value was less than 0.0001,which can effectively simulate the experimental process.The temperature difference between the two sides of the membrane and the flow velocity had a significant interaction effect on the membrane flux.The greater the temperature difference between the two sides,the greater the flow velocity and the higher the membrane flux.