The Study Of Preparation And Oil-Water Separation Performance Of The Underwater Superoleophobic Cellulose Composite Membranes

Large amounts of oily wastewater produced in industrial production and catering has caused severe hazards to the ecology system and physical fitness,so it is necessary to find a process which is more efficient and less costly than the traditional separation method.In recent years,superwetting materials have been widely studied and applied to oily wastewater treatment.Among them,superhydrophilic/underwater superhydrophobic membrane materials have stood out because of outstanding separation performance.However,the poor anti-fouling performance,mechanical stability and chemical resistance of most of the membranes greatly limit their wide application.In this paper,a series of superhydrophilic/underwater superhydrophobic cellulose composite membrane materials with preeminent anti-fouling performance were prepared by using biodegradable and renewable cellulose as raw materials.The surface micromorphology,chemical composition and wettability of the membranes were comprehensively analyzed.And the separation performance for different emulsions and the stability of the membranes were mainly investigated.The main contents of this paper include:（1）Superhydrophilic/underwater superoleophobic polyacrylonitrile（PAN）-cellulose acetate（CA）nanofiber membrane mixed with Si O₂ particles（PAN/CA-Si O₂composite membrane）was constructed through electrospinning strategy.The design of simple double-layer anti-fouling structure can effectively avoid the problem that single layer hydrophilic layer is easy to be polluted by oil.By comparing the separation performance of single PAN membrane and PAN/CA-Si O₂ composite membrane,it is found that the separation efficiency and flux of PAN/CA-Si O₂ composite membrane for various oil-in-water emulsions are increased to 99.3%and 1011.2 L m^-2 h^-1,respectively,which proves that PAN/CA-Si O₂ composite membrane displays better oil-water separation and anti-fouling performance.The composite membrane has outstanding recycling performance,and this reusable oil-water separation membrane effectively reduces the production cost.In addition,the contact angle of the PAN/CA-Si O₂ composite membrane is still greater than 150°after sand impact experiment,showing excellent mechanical stability.（2）Superhydrophilic/underwater superoleophobic silver chloride（AgCl）-cellulose acetate（CA）modified PVDF membrane（AgCl/CA composite membrane）was prepared by phase inversion and alternate dipping methods.The influence of different dipping times on the wettability was studied,and it was found that the AgCl-4/CA composite membrane made by alternating dipping 4 times had underwater oil contact angle of 160°,and the separation efficiency of the oil-in-water emulsion was greater than 99.2%,and the flux was higher than 1408 L m^-2 h^-1.Most importantly,the oil contact angle of AgCl-4/CA composite membrane was still higher than 150°after 100 times of sandpaper wear and 50 min of ultrasonic treatment,demonstrating protruding mechanical stability of the cellulose composite membrane.In addition,the composite membrane still maintains high separation performance under corrosive environment（1 M HCl,1 M Na OH and 3.5%Na Cl）,showing excellent acid,alkali and salt resistance.（3）Superhydrophilic/underwater superoleophobic PDA@ZIF-8-carboxymethyl cellulose（CMC）coated PTFE membrane（PDA@ZIF-8/CMC composite membrane）was prepared by vacuum filtration method.The composite membrane demonstrated superior separation efficiency（greater than 99.2%）and flux(more than 1306.5 L m^-2 h^-1)for high-viscosity oil-in-water emulsions.After many times of cyclic separation tests,it could still achieve effective separation.In addition,the underwater oil contact angle of PDA@ZIF-8/CMC composite membrane is still higher than 150°for various oils in corrosive environments,and the successful separation of oil-in-water emulsion can still be achieved after soaking in different corrosive environments.Furthermore,PDA@ZIF-8/CMC composite membrane has satisfactory mechanical stability,and can maintain outstanding underwater superoleophobicity after long distance friction tests and multiple bending tests.