Research On The Construction Of Asymmetric Wettability Janus Fiber Membrane And Its Oil-water Separation

Current special wettable oil-water separation membranes are functionally single and limited by oil density.Preparation of surfaces with micro/nano structures is the key to develop functional membranes for oil-water separation.Fabrication of microstructures with uniform and dense surface by an effective and easy method is of great interest.In this study,based on the bionic concept,the lotus leaf model and mussel effect were introduced into the field of oil/water separation.Janus polytetrafluoroethylene/titanium dioxide（PDA-PTFE/TiO₂）fiber membranes with asymmetric wettability were designed and prepared by carrier spinning,calcination and single-surface modification techniques.The membranes are suitable for oil-water separation of general purpose oil/water mixtures..The details of the study and the results are as follows:（1）Micro/nano-fiber membranes were designed and prepared using hydrophobic polytetrafluoroethylene as the substrate.The effects of different influencing factors on the tetrafluoroethylene/titanium dioxide（PTFE/TiO₂）membrane fibers were investigated,and the effect of PVA mass ratio on the membrane structure of Janus fibers was examined.It proved that the optimal percentage of PVA fraction was explored to be 7 wt%when spinning with centrifugal spinning machine and electrostatic spinning machine.The effects of centrifugal spinning machine speed and electrostatic spinning machine voltage as well as the effect of calcination temperature of muffle furnace on roughness and contact angle were investigated.The results showed that the superhydrophobic centrifugal spinning film could be obtained at 1600 r/min rotational speed for centrifugal spinning and 385℃ calcination temperature.If an electrostatic spinning machine is used to prepare the pristine fiber film,it is better to spin the PTFE/TiO₂ fiber film morphology at 18 k V and 385℃ calcination temperature.Under these conditions,the contact angle of the fiber membranes could all reach above 150°.（2）The effects of PDA buffer concentration and PDA loading on the wettability of the fiber membrane surface were investigated.The results showed that the centrifugal fiber membranes were superhydrophilic at p H 7.5 with 10 treatments of PDA concentration of 6 g·L^-1.The electrostatic spinning membranes were superhydrophilic at PDA concentration of 8 g·L^-1 for 8 h.The mechanical strengths of the centrifugally and electrostatically spun modified membranes were 3.02 MPa and 2.71 MPa,respectively.Their average pore sizes were 1.3μm and 1.1μm,respectively.（3）The changes in the preparation process of PVA/PTFE/TiO₂ fiber membrane were investigated,and the microscopic morphology of the fiber membrane was observed and its surface groups and elemental composition were tested by applying field emission scanning electron microscopy（FESEM）,TG-IR coupler,infrared spectrometer（FT-IR）and X-ray spectrometer（XPS）.The results showed that the O element and hydrophilic group characteristic peaks in the fiber membrane disappeared after high temperature sintering,and N element and phenolic hydroxyl characteristic peaks existed,in which the PVA component decomposed completely and PDA was encapsulated on the fiber membrane.The PDA component and TiO₂ particles had good stability with the fiber membrane as a whole.（4）The oil-water separation performance of the prepared fiber membranes was investigated.The results showed that the prepared fiber membranes could maintain stable oil-water separation performance and good recycling performance for different oil-water mixtures.The first separation rates of centrifugal spun fiber membranes were99.21%and 99.16%for water/1,2-dibromoethane and hexane/water mixtures,respectively,and the separation rates could still reach 98.34%and 98.32%after 20cycles of separation.The first separation rates of water/1,2-dibromoethane and n-hexane/water were 99.51%and 99.64%,respectively,and the separation rates were98.01%and 99.2%after 20 cycles.Also,it exhibited 99.44%separation for surfactant-stabilized emulsions.The separation rates of both Janus membranes remained above96%after 24 h immersion in strong acidic and alkaline solutions.