The Preparation Of Polycaprolactone/SiO₂ Aerogel Composite Membranes With Controllable Structure And Their Mechanism Study On Oil-Water Separation

The large amount of oily wastewater discharge and the frequent occurrence of oil spill accidents had posed a great threat to the global ecological environment and public health.There are many threatment methods for oily wastewater,including gravity,centrifugation and membrane separation,etc.Among these methods,membrane separation had the advantages of simple operation,no hazardous by-products,low cost and high separation efficiency,which had been widely used in the field of oil-water separation.The preparation of superhydrophobic oil-water separation membrane material with high performance was crucial.The commonly used hydrophobic materials are polyvinylidene（PVDF）,fluorinated modified polymer,polyurethane（PU）,polystyrene（PS）,etc.However,these materials are non-degradable and could cause secondary contamination during post-treatment.With the strengthening of environmental protection,eco-friendly polymer materials recevied more and more attention by researchers.At present,the eco-friendly hydrophobic polymers are mainly polylactic acid（PLA）,polycarbonate（PC）and polycaprolactone（PCL）.PCL had outstanding advantages in hydrophobicity,flexibility and processing.In this work,PCL was selected as the matrix material,PCL/SiO₂ aerogel superhydrophobic composite membranes with controllable structure was obtained via electrospinning/electrospraying technique.Oil-water separation performance and mechanism of PCL superhydrophobic membrane were studied in details.The researchs had two parts:（1）The superhydrophobic PCL/SiO₂ aerogel composite membrane with hierarchical structure were prepared by electrospinning and electrospray technology.The highest water contact angle（WCA）of 166.8±1.5°was obtained when SiO₂ aerogel content was 0.5%（PCL/SiO₂-a0.5）in PCL composite membrane.SiO₂ aerogel lowered PCL composite membrane surface energy.The triply curvature structure composed of microspheres,nanospheres and nanofibres produced on PCL/SiO₂-a0.5 membrane endowed the excellent roughness of the surface.And the inner hierarchical structure of the PCL/SiO₂-a0.5 composite membrane composed by micro-nano spheres,nano-fibers and micro-fibers increased the porosity of the separation membrane,which would provide more adsorption space.The PCL/SiO₂-a0.5 composite membrane could be used as a separator with ultra-high separation efficiency and flux for surfactant-stabilized water-in-oil emulsions.Meanwhile,the PCL/SiO₂-a0.5 composite membrane had outstanding chemical resistance,self-cleaning ability and good reusability.This research provided a very simple method to design the eco-friendly high-efficiency separator through the construction of the alternated micro-nano hierarchical structure.（2）The rice leaves exhibited ultrahigh hydrophobicity and super self-cleaning ability because of the parallel vein structure and the one-dimensional ordered micropapillae dispersing along the vein surface.In this work,inspired by the directional hierarchical structure of rice leaves,PCL_C composite nanofibers with parallel arrangement were fabricated by electrospinning PCL and carbon black nanoparticles.Meanwhile,SiO₂ aerogel with porous network structure could adsorb the conductive solvent DMF.Thereby SiO₂ aerogel could be electrosprayed along the axial direction of conductive fiber.PCL_C fibers with one-dimensional order arrangement simulated rice leaf veins,and uniformly dispersed SiO₂aerogel along the fiber imitated micropapillae on the of rice leaves.The water contact angle（WCA）and sliding angle（SA）of PCL_C/SiO₂-4 fibrous membrane were 169.0±0.2°and 1.9±0.1°,which exhibited superhydrophobicity and self-cleaning performance of membrane.The permeation flux of PCL_C/SiO₂-4 membrane for the separation of oil-water mixture was as high as 19,000±1,000 L m^-2 h^-1 with the efficiency of 99.93±0.01%.After 20 cycles of separation,the separation efficiency and permeation flux were higher than 99.9%and 18,000 L m^-2 h^-1.The bionic fibrous membrane in acidic,alkaline salt solution and organic solvent after 24 h,the WCAs of membrane exceeded 152°.After 10 abrasion tests,WCA of PCL_C/SiO₂-4 membrane was still higher than 150°.These results showed that the fibrous membrane had excellent chemical corrosion resistance and cycling stability.