Research On Modification Of Superhydrophobic Membrane And Its Application In Membrane Distillation Treatment Of High-salinity Wastewate

Due to the rapid growth of global population and economic development,the shortage of freshwater resources has become one of the major challenges facing the world today.In order to solve the shortage of freshwater resources,seawater desalination and wastewater treatment have emerged.High salinity wastewater is difficult to be effectively treated because of its high salinity,which has become a difficult problem in wastewater treatment.Membrane distillation technology has good development prospects in the treatment of high-salt wastewater due to its advantages of high separation efficiency,simple operation,and theoretically zero emission.However,the use of membrane distillation to treat high-salt wastewater will inevitably face membrane fouling and membrane wetting problems,which limits the engineering application of membrane distillation.Therefore,it is very important to develop a superhydrophobic membrane with anti-fouling and anti-wetting properties in the long-term treatment of high-salt wastewater by membrane distillation.In this experiment,the hydrophobic polyvinylidene fluoride（PVDF）basement membrane was modified by vacuum assisted and wet modification.Firstly,carbon black nanoparticles were uniformly dispersed on the surface of PVDF membrane,and then FDTS with low surface energy was adsorbed on the hydrophobic PVDF membrane to prepare hydrophobic FDTS-BC@PVDF membrane with water contact angle of 144°.The PVDF membrane was characterized by various techniques,including scanning electron microscopy,energy dispersive spectroscopy,X-ray photoelectron spectroscopy,laser scanning confocal microscopy,a liquid-liquid porometer and contact angle measurements.The average pore size（0.41μm）and surface energy（2.03 m N/m）of the prepared FDTS-BC@PVDF membrane were significantly lower than those of the original PVDF membrane and BC@PVDF membrane.FDTS-BC@PVDF membrane showed significantly improved anti-wetting and anti-fouling properties when dealing with salt water below 3.5 wt%Na Cl solution concentration or salt solution containing different organic pollutants.At the same time,membrane distillation for actual landfill leachate with high salinity and high concentration also has strong anti-pollution performance and long-term stability.However,FDTS-BC@PVDF membrane showed poor antifouling and anti-wetting properties when dealing with high salt solution or oily solution with a concentration higher than 5.5 wt%Na Cl.It shows that the performance of FDTS-BC@PVDF membrane in membrane distillation treatment of high salt and high organic wastewater needs to be improved.Based on the above research,on the basis of commercial PTFE microporous membrane,a superhydrophobic F-Si O₂@PTFE membrane with a water contact angle of 158°was prepared by surface silanization and fluorination.Compared with the original commercial PTFE membrane,the average pore size of the prepared PTFE membrane was slightly reduced to 0.37μm.Therefore,the permeation pressure increases to 0.38 MPa.The developed superhydrophobic PTFE membrane had a very low surface energy of 1 m J/m²,only one third of that of the unmodified commercial membrane.Compared with the original commercial PTFE membrane,the superhydrophobic F-Si O₂@PTFE membrane exhibits significantly enhanced anti-wetting and anti-fouling properties when dealing with various high salinity or solutions containing different organic pollutants.The application of F-Si O₂@PTFE membrane to the actual landfill leachate with high salinity and high organic matter by membrane distillation also showed excellent anti-pollution,anti-wetting and long-term stability.The fabricated PTFE membrane with simultaneously antiwetting and antifouling properties opens a new avenue for treating challenging waste liquids via MD.This study also provides an important strategy to develop superhydrophobic simultaneously antiwetting and antifouling membranes for stable long-term MD applications.