Preparation Of PDMS/SiO₂/PVDF Superhydrophobic Composite Membrane For Desalination By Membrane Distillation

As a very promising membrane separation technology with hydrophobic membrane as the medium,membrane distillation has become a research hotspot in the field of water treatment.The separation membrane selected for membrane distillation needs to have good anti-wetting properties and stability to achieve long-term operation of membrane distillation.This article aims to explore a method for preparing superhydrophobic membranes for membrane distillation and at the same time use hydrophilic nanoparticles to explore the influence of the rough surface layer composed of hydrophilic particles on the anti-wetting properties of the superhydrophobic composite membrane.Then this method was applied to superhydrophobic modification of macro-porous hydrophobic membranes,which is rarely used in membrane distillation,to explore the possibilities and limitations of this type of membranes in membrane distillation applications.Firstly,a hydrophilic silica solution was prepared under normal temperature and alkaline conditions by the sol-gel method,and the solution was coated on the surface of the hydrophobic polyvinylidene fluoride(PVDF)membrane to prepare the SiO₂/PVDF composite membrane.The experiment explored the effects of SiO₂ particle size,SiO₂ solution coating time and standing treatment time on the properties of the composite membrane.The results showed that a composite film with higher surface roughness was obtained,and the contact angle reached 25.8°.Then,the polydimethylsiloxane(PDMS)solution was prepared using the existing experimental program in the research group,and coated on the surface of the SiO₂/PVDF composite membrane to prepare the PDMS/SiO₂/PVDF superhydrophobic composite membrane.While improving the stability of nanoparticles,it provides a hydrophobic coating with low surface energy for the composite membrane.The experiment explored the influence of PDMS solution coating time and PDMS mass fraction on the performance of the composite membrane.The contact angle of the composite membrane is 162.3°.During the 60-hour direct contact membrane distillation,which with 3.5wt%sodium chloride solution,the flux is stable at 24.5kg/(m²·h)and the rejection rate is above 99.8%.Finally,the macro-porous polytetrafluoroethylene(PTFE)hydrophobic membrane is modified using the superhydrophobic membrane modification method that obtained from the above investigation,and explore the membrane distillation performance of the composite membrane Macro-porous PTFE hydrophobic composite membrane achieves superhydrophobicity.The thin hydrophobic layer is the reason why this type of membranes is difficult to cope with long-term membrane distillation.By increasing the thickness of the hydrophobic layer of the composite membrane,the membrane distillation performance is stable.