Biomimetic Polycaprolacton Membranes As Highly Efficient Oil-Water Separator And Their Properties

Large discharges of oily sewage in industry and oil spill accidents have caused catastrophic destruction to the ecological environment and human health.Various technologies for oil-water separation,such as gravity-driven,air floatation,adsorption,and membrane separation approaches,have been developed.Among these,adsorption and membrane separation have received considerable interest because of their simple,low-cost operation and high efficiency.At the same time,in combination with effective separation methods,the development of novel adsorbents with superhydrophobicity,outstanding adsorption performance and reusability was also a key issue to achieve oil-water separation.In the current research,the preparation of superhydrophobic membranes was mostly based on polymers with high hydrophobicity,such as poly?vinylidene fluoride??PVDF?,polyurethane?PU?,polystyrene?PS?.However,polymers such as PVDF and PS are non-degradable and cause secondary pollution.The environmentally friendly polymer material polycaprolactone?PCL?has been widely used due to its nontoxicity,biodegradability,robust mechanical properties and facile processing.However,due to its limited hydrophobicity,PCL is rarely used as a hydrophobic material.In recent years,the preparation of oil-water separation membranes by simulating superhydrophobic surfaces in nature has attracted the attention of researchers.In this study,environmentally friendly PCL was selected as the substrate with small amount of low surface energy additives for oil oil-water separation.PCL superhydrophobic membranes with hierarchical structures were prepared by electrospinning/electrospraying method.The preparation of superhydrophobic membrane with hierarchical structure and its oil-water separation performance were studied.The research work mainly included two parts:?1?A superhydrophobic,superoleophilic and eco-friendly polycaprolactone composite?PCL_C?membrane with a hierarchical microsphere structure was developed by alternated electrospinning/electrospraying technology.The PCL_C membrane was subtly designed with two parts to imitate the lotus leaf structure:low surface energy silica?SiO₂?nanoparticles on the surface of PCL smooth microspheres?PCL_M?imitate the hydrophobic bio-wax of the lotus leaf surface,and PCL porous microspheres(PCL_M-porous)imitate the surface micro-and nano-protrusions of the lotus leaf.The average size of the potholes on the PCL_M-porous surface was only about 300 nm,which was superior to the micron-sized protrusions obtained by the preparation of bionic lotus leaf structures in related work reported in the current literature.The water contact angle?WCA?of PCL_C could reach162.0±1.5°.Compared with membranes based on PCL_M-porous?WCA=148.9±1.2°?and 4%SiO₂ nanoparticles on PCL_M?WCA=158.6±2.3°?,the PCL_C membrane not only showed higher superhydrophobicity but also ultra-high oil-water separation efficiency,oil flux and stability.Most importantly,the PCL_C membrane exhibited excellent oil adsorption performance for four different oils with different densities?n-hexane,corn oil,sunflower oil and motor oil?,and the separation efficiency remained ultrahigh?>99.93%?even after10 cycles.?2?In order to further simplify the preparation process of the oil-water seperator,the superhydrophobic PCL based composite membrane with microsphere-fiber interlinked hierarchical structure by one-step electrospinning technology.12%PCL solution with chloroform?CF?and 1,2-propanediol as solvents was used as eletrospun precursor solution.The unique porous microsphere-fiber interlinked hierarchical structure greatly improved the hydrophobicity of the membrane,thus providing sufficient support for oil adsorption and oil-water separation.A small amount of addition of low surface energy methyl silicone oil?MSO?or 1H,1H,2H,2H-Perfluorodecyltrimethoxysilane?PFDTS?in the PCL membrane were expected to improve the hydrophobicity of PCL membranes.When the PFDTS content was 2.5%,the PCL_P-2.5 membrane exhibited superhydrophobicity,low pore size and excellent adsorption performance,which could be used to separte immiscible oil-water mixture and water-in-oil emulsions,and exhibited excellent separation efficiency,reusability and anti-corrosive.