| With the development of economy,oil/water separation has become a worldwide challenge due to large volumes of industrial oily wastewater and frequent oil spill accidents,which constitutes an enormous threat to ocean,soil and human life.Although there are a lot of oil-water separation techniques,such as centrifugation,chemical oxidation,coagulation and flocculation,air flotation,etc.,but these methods are restricted by high energy input,complex separation steps,generation of secondary pollutants,and low separation efficiency in treating oil-in-water emulsions.Therefore,it is very necessary to find a fast and simple method for separation of oily wastewater.Membrane separation technology has been acknowledged as an advanced method that is environmentally friendly,economical,highly efficient,possesses a small footprint,and is easy to scale up compared to other techniques.Chitosan(CS),as a nontoxic,naturally biodegradable and biocompatible polysaccharide,has become an attractive polymer with high hydroxyl and amino functional groups present on the surface with hydrophilicity.Moreover,the amines of chitosan are protonated under acidic conditions to confer chitosan positive charges and membrane-forming properties.Titanium dioxide(TiO2)nanoparticles with a superhydrophilic surface,high safety and stability,wide availability,low cost,and self-cleaning surface,have been regarded as the optimal candidate material for effective oil/water separation.In this paper,we expect to develop a superhydrophilic and underwater superoleophobic membrane by the filtration technique under a vacuum filtration device based on chitosan and TiO2 on a cellulose acetate membrane for the separation of oil-in-water emulsions.We used a variety of characterization methods,including scanning electron microscope(SEM)to observe the changes of membrane surface before and after the oil/water separation,atomic force microscope(AFM)to detect the membrane surface roughness,X-ray photoelectron spectroscopy(XPS)and attenuated total reflection Fourier transform infrared spectroscopy(ATR-FTIR)to analyze the composition of membrane surface chemical,etc.,to comprehensively analyze the mechanism of oil/water separation.The conclusions are as follows:(1)The titanium dioxide nanoparticles on the membrane surface could be clearly seen by SEM images,and the ATR-FTIR and XPS results indicated that the chitosan and TiO2 were successfully loaded onto the surface of the cellulose acetate membrane.(2)When the mass ratio of CS and TiO2 was 3:4,the modified membrane has the best wettability and flux,and has the characteristics of superhydrophilic and underwater superhydrophobic.The modified membrane demonstrated an excellent flux up to 6002.5 L m-2 h-1 for hexadecane-in-water emulsion and the oil rejection ratio was 99.77%.(3)A small amount of water was used to rinse the membrane after the separation of oily wastewater for the CST(3:4)membrane,and the number of cycles for oil-in-water emulsion separation could be reached 10 times.The oil adhesion experiment showed that the modified membrane surface has a superior anti-oil-fouling property.(4)With the addition of TiO2 nanoparticles,surface roughness is reduced,but the improvement of membrane surface wettability is obvious.Therefore,the superhydrophilic TiO2 nanoparticles played a key role in membrane surface hydrophilicity in this study.(5)As clearly presented by SEM images,there were no obvious change for the surface morphology of the CST(3:4)membrane in those corrosive solutions before and after the oil/water separation and it maintained superhydrophilicity and underwater superoleophobicity.These results demonstrated that the CST(3:4)membrane was stable and possessed advantages for industrial applications. |
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