Preparation Of Superhydrophilic/underwater Superoleophobic Cellulose Based Composite Membrane And Study On Oil/water Separation Performance

More and more oil leakage,chemical product leakage and oily wastewater discharge lead to serious ecological and environmental problems.How to efficiently separate oil and water has become a global urgent problem.So far,methods including gravity separation,coalescence,centrifugation,biological treatment and flotation have been used for oil/water separation.These methods have high cost,need to consume too much energy and complex instruments,and often have secondary pollution,which seriously limits their practical application.Membrane separation technology is considered as an excellent method to treat oily wastewater because of its advantages of simple operation,low cost,no phase change and no secondary pollution.In recent years,inspired by fish scales and mussels,the superhydrophilic/under superoleophobic materials used and prepared in the treatment of oily wastewater are considered to have the advantage of effectively avoiding oil pollution on the membrane surface.However,most of the super superhydrophilic/under superoleophobic materials designed by researchers have the disadvantages of high cost,complex preparation,easy pollution and unsustainable regeneration.Cellulose is taken from nature and is rich in resources.It is a renewable resource in nature.Moreover,cellulose has the advantages of biodegradability and easy chemical modification,so it is an ideal membrane separation material.In this paper,cellulose was used as the substrate of the membrane,and the cross-linking properties of sodium alginate and dopamine were used to grow on the surface of the membrane.The inorganic materials Ca CO₃ and Ba SO₄ were introduced into the membrane surface by the alternate impregnation method to construct the micro nanostructure.The superhydrophilic/under superoleophobic cellulose based composite membrane with low cost and easy preparation was prepared for the separation of oil/water mixture.Dopamine and Ba SO₄ enhanced the acid,alkali and salt resistance of the membrane.The super superhydrophilic/under superoleophobic cellulose based composite membrane which can separate emulsion is prepared by combining cellulose and chitosan in the waste cigarette butt through a green phase transformation method.The micro morphology,chemical composition and surface wettability of the composite membrane were analyzed in detail,and the oil/water separation performance and stability were systematically studied.The main research contents are as follows:1.Preparation of FP@SA/Ca CO₃membrane and its oil water separation performanceCellulose based oil/water separation membranes were prepared by using a very simple alternating soaking process.First,sodium alginate（SA）was coated on the surface of cellulose membrane（filter paper）,and then Ca CO₃ particles were assembled on the surface of the membrane by alternating soaking process to obtain FP@SA/Ca CO₃membrane.The effects of alternate immersion times on membrane surface morphology,wettability,separation efficiency and flux were studied.After many times of experiments,the selected FP@SA/Ca CO₃ has the best separation performance.The underwater oil contact angle（OCA）of the membrane is 151.1°,indicating that FP@SA/Ca CO₃ has good underwater superhydrophobicity.Moreover,for different oil/water mixtures,The separation efficiency of the FP@SA/Ca CO₃membrane is up to 99.2%,the flux is over 400 L m^-2 h^-1,and the oil adhesion is low.In addition,even if it is reused 20 times,FP@SA/Ca CO₃ membrane still showed high flux and separation efficiency,indicating that FP@SA/Ca CO₃ has good reusability.2.Preparation of PF@PDA/Ba SO₄membrane and its oil/water separation performanceFirstly,polydopamine（PDA）was coated on paper fiber（PF@PDA）through Cu SO₄/H₂O₂ catalysis to speed up the reaction.Then,Ba SO₄ nanosheets were deposited on the surface of the PF@PDA membrane by alternating soaking process to obtain a superhydrophilic/underwater superoleophobic PF@PDA/Ba SO₄membrane for oil/water separation.The influence of the number of alternating immersion times on its microscopic morphology,wettability and separation performance was studied.The underwater oil contact angle（OCA）of the selected PF@PDA/Ba SO₄ membrane after many experiments is 156°,indicating that PF@PDA/Ba SO₄ has good underwater superoleophobicity.PF@PDA/Ba SO₄ shows good separation efficiency（over 99%）and high flux(over 550 L m^-2 h^-1)for various oil/water mixtures.Importantly,the membrane exhibits excellent resistance to acid,alkali and salt,and maintains high separation performance even in acid,alkali and salt solution environments.In addition,the PF@PDA/Ba SO membrane has been used repeatedly for 20 times and still maintains high separation performance,and the surface has excellent antifouling performance and excellent reusability.3.Preparation of CA/CS membrane and its oil/water emulsion separation performanceIn this paper,discarded cigarette butts were used as raw materials,combined with chitosan,and a superhydrophilic/underwater superoleophobic CA/CS membrane was formed through a phase inversion method.The performance of CA/CS membrane is controlled by adjusting the ratio of cellulose acetate and chitosan.The prepared CA/CS composite membrane has superhydrophilicity/underwater superoleophobicity.After many experiments,it has been proved that CA/CS-3 has the best separation performance.For the oil-in-water emulsion,the filtrate of the CA/CS membrane can hardly see the oil droplets through electron microscope.CA/CS membrane has a higher emulsion permeation flux(more than 340 L m^-2 h^-1)and a higher separation efficiency（more than 97.1%）.In addition,the membrane can have good reusability within 10 cycles.