Anti-fouling Structure Control Of Polyvinylidene Fluoride Superhydrophobic Membrane And Its Membrane Distillation Performance

Membrane distillation(MD)is a new type of efficient and environmentally friendly membrane separation process.It has the advantages of simple structure and easy operation,and can treat some high salt and high heat wastewater under low temperature and low pressure conditions.In particular,it can utilize waste heat,solar energy,etc.as a heat source.Therefore,it has important applications in seawater desalination and wastewater treatment.The problem of membrane durability caused by membrane fouling and membrane wetting is a bottleneck that hinders the development of MD technology.In this study,starting from the physical structure and material chemistry of the membrane surface,polyvinylidene fluoride(PVDF)and carbon nanotubes(CNT)were selected as the membrane substrate,and various methods for preparing superhydrophobic membranes based on nanocasting and in-situ lamination were proposed,aiming to improve the separation perfonnance of the membrane in the MD process.The main research contents and results are as follows:Firstly,a preparation method of superhydrophobic membrane based on nanocasting technology was proposed,using PVDF as membrane substrate,starting from the construction of physical micro-nano structure on the surface of the membrane.Two kinds of PVDF membranes with different surface textures were prepared by using stainless steel mesh(SSM)or its negative structure polydimethylsiloxane(PDMS)as gel a fabrication template.The resulting film was systematically characterized in terms of film surface morphology,wetting properties,MD properties,and antifouling properties.The results show that the membrane based on PDMS template has the same woven surface texture as SSM,and its surface static contact angle and sliding angle are?1530 and>90°,respectively,exhibiting hydrophobic but highly adherent wetting characteristics.In contrast,membranes made based on SSM templates have a wavy surface texture with surface static contact angles and rolling angles of?164° and?6.8°,respectively,exhibiting superhydrophobic properties.In addition,both membranes have higher water flux and enhanced antifouling properties,and their salt rejection is>99.8%.Secondly,from the chemistry of membrane materials,the non-polar CNTs were selected as the basic materials.A super-aligned CNT hydrophobic film was prepared by the cross-stacking method.The basic properties and MD properties of super-aligned CNT films with different braid layers were systematically studied.The results show that the cross-layer number affects the structure and performance of the super-aligned CNT film.Compared with the commercial film,the CNT film has higher flux stability and the rejection is higher than 99.8%,showing good anti-fouling ability.Finally,combining the first two parts,based on the combined application of nanocasting and in-situ lamination,a superhydrophobic PVDF membrane with a surface non-polar coating was prepared.The membrane was systematically characterized in terms of basic properties,MD properties,and anti-fouling properties.In the results,compared with the pristine membrane(uncoated CNT),the loading of CNTs is beneficial to maintain a stable rejection(>99.9%),and improve the anti-fouling ability of the membrane.The above superhydrophobic membranes have good anti-fouling and anti-wetting properties,and have good application potential,and provide some new ideas for the development and application of such membrane materials for MD.