Preparation Of Advanced Surface With Extreme Wetting Behaviors And Application In The Oil-water Separation Based On SiO₂ Areogel

Oil and water play an important role in our lives and social development process. Due to the mismanagement and stagnant technological development, oil spill accident often occurs in the oil mining, transport, storage and applications. The pollution of oil and water often leads to serious waste of resources and damage the environment. Thus, the separation of oil and water mixture is one of urgent challenges, which needs to be solved.Traditional oil-water separation methods include gravity separation, skimming, centrifugation and flotation, etc., that have a good effect. While the separation process will spend a long time, and the operation is complex, which cannot be continuous separation and the separated is incomplete. Because of its unique surface wetting properties, Superhydrophobic（superoleophilic） surface has the ability to separate oil and water mixture, which is an innovative and effective oil-water separation methods. Through Sol-Gel method, SiO₂ aerogel has been prepared using MTMS as a precursor, which has good hydrophobicity, large surface area, high porosity and good stability. Thus, based on SiO₂ aerogel, superhydrophobic（superoleophilic） surface has been prepared using two different substrates, and then designing a simple separation instrument to separate the layered oil-water mixture and emulsified oil-water mixture respectively. The main contents and results are as follows:（1）Janus fabric preparation and its application in the layered oil-water mixture separation.Through Sol-Gel method and atmospheric drying technology, SiO₂ aerogel particles have been prepared by using MTMS as a precursor, acetic acid and ammonia as the catalyst. By spray-drying method, the dispersed particles of SiO₂ aerogel has been sprayed onto the surface of knitted cotton fabrics, preparing Janus fabric with one side hydrophilic and the other side superhydrophobic. By controlling the content of the spray-coated SiO₂ aerogel particles, the wettability of the fabric’s surface can be regulated. When the proportion of SiO₂ aerogel particles to the fabric is between 1.73% and 2.49%, the Janus fabrics with unidirectional wet performance was prepared and the droplet of water can transfer from superhydrophobic side to hydrophilic side. When the proportion of SiO₂ aerogel particles to the fabric is above 2.49%, the static water contact angle of the Janus fabric’s superhydrophobic surface was 154 °, meanwhile the Janus fabric’s hydrophilic surface exhibited excellent hydrophilicity. In hydrophobic surface of the stable Janus fabric, water droplets remained superhydrophobic condition in 60 min. By using the designed oil-water separator device, “heavy oil”（up water and down oil layered mixture） and “light oil”（up oil down water layered mixture） has been effectively separated, respectively.（2） Preparation of the superhydrophobic nanofibrous membrane and its application in the oil-water emulsion separation.Through electrospinning technology, PVDF micro-nano fibrous membrane was prepared by using polyvinylidene fluoride（PVDF） as raw materials, then by spray-coating SiO₂ aerogel, the modified PVDF nanofibrous membrane was prepared with the static water contact angle of 156°. Meanwhile the PVDF nanofibrous membrane has good mechanical properties with the breaking strength of 12 MPa, the elongation at break of 119.2%, and the hydrostatic pressure height of more than 30 cm. The pore size of the superhydrophobic PVDF electrospun fibrous membrane which was 20μm thick in average,mainly ranged between 2-15 nm and 15-80 nm, and a 45 nm peak centered at 30-60 nm formed. Thus, the fibrous membrane showed good separation effect in separating oil-water emulsion with emulsion particle size of 1-20μm.