Preparation Of Superhydrophilic Underwater Superoleophobic Organic-inorganic Composite Membrane And Study On The Oil-water Separation Performance

With the frequent occurrence of oil spill accidents on the sea and the massive discharge of industrial oily sewage,the environmental problems caused by oil pollution have become increasingly serious.The traditional oil-water separation method has the disadvantages of long time consumption,high energy consumption,and complex equipment requirements.It is of great significance to explore and develop an effective oil-water separation method.In recent years,special wettability separation membrane materials have attracted wide attention,and can selectively separate oil-water mixtures according to differences in the wettability of oil and water.The process is simple,efficient,low in energy consumption,and continuous.In particular,the superhydrophilic-underwater superlyophobic membrane developed according to the concept of imitation fish scale has become a research hotspot in the field of oil-water separation due to the oil-repelling during the separation process,thereby maintaining the self-cleanliness.The organic-inorganic compound modification method is one of the effective ways to construct the micro-nano rough structure and hydrophilic modification on the surface and achieve super-lyophobic underwater.Biomass-based hydrogels have the advantages of environmental protection,easy surface modification,hydrophilicity,etc.Compared with the traditional polymer modification methods,they also have the advantage of fast modification speed and are an ideal choice for membrane surface modification.In this paper,four superhydrophilic-underwater and superoleophobic membranes were prepared by using different methods based on a variety of metal meshes and biomass-based hydrogels as modifiers.The microstructure,surface composition,and crystallinity of the as-prepared membrane were characterized by a series of technical methods,and oil-water separation performance was systematically tested.The main research work is as follows:（1）Using Ni mesh as the substrate,Ni（OH）₂ micro-nanostructures were grown in-situ on the surface by hydrothermal method,followed by coordinated cross-linking of carboxymethyl cellulose sodium（CMC）with Fe³⁺in Ni（OH）₂@Ni surface.Fe（Ⅲ）-CMC biomass-based hydrogel was self-assembled on the surface of Ni（OH）₂@Ni membrane and modified with hydrophilicity to prepare Fe（Ⅲ）-CMC@Ni（OH）₂@Ni composite membrane.Underwater oleophobicity attributed to the joint action of surface-growing petal-like Ni（OH）₂ rough structures and coated biomass hydrogels.The underwater contact angle of the Fe（Ⅲ）-CMC@Ni（OH）₂@Ni composite membrane is up to 160°（using dichloroethane as an example）.The oil-water separation performance test results show that membrane can selectively separate a variety of oil-water mixtures,the oil-water separation efficiency is greater than 99.0%,and the membrane flux is 220000 L m^-2 h^-1.The membrane has high invasive pressure（1.30kPa）,acid and alkali resistance,suitable for high salt environment,and good reusability.（2）The superhydrophilic-underwater superoleophobic Fe（Ⅲ）-CMC@CuO@Cu composite membrane was prepared using a copper mesh as a substrate via calcination and surface assembly methods.The effects of calcination temperature and time on the morphology and size of CuO on the surface of copper mesh were investigated,as well as the effects on the wettability and oil-water separation performance of the product.Nano-sized acicular CuO and Fe（Ⅲ）-CMC hydrogels on the surface of Cu mesh are the key to construct underwater superoleophobic.For many kinds of light oil or heavy oil,OCA of membrane is more than 150°,and the adhesion force of underwater oil is low.Fe（Ⅲ）-CMC@Cu O@Cu composite membrane exhibit excellent oil-water separation performance（separation efficiency>99%）,high membrane flux(160000 L m^-2 h^-1)and self-cleaning properties.Due to the presence of needle-like structure CuO,the high intrusion pressure reaches 2.29 kPa.Furthermore,the membrane has low adhesion to underwater oils,good self-cleaning ability,acid and alkali resistance,salt resistance,and excellent repetitive cycle performance.（3）Using Ni mesh as the substrate,dilute hydrochloric acid（HCl）and potassium ferrocyanide（K₄Fe（CN）₆·3H₂O）as raw materials,a rough structure-like Prussian blue（LPB）was constructed by combining the simultaneous acid etching method and the in-situ growth method,and then surface layer self-assembled Fe（Ⅲ）-CMC biomass hydrogel to prepare a superhydrophilic-underwater superoleophobic Fe（Ⅲ）-CMC@LPB@Ni composite membrane.The characterization results show that the cubic LPB exhibits a step-like ordered structure and the hydrogel layer is evenly coated.Fe（Ⅲ）CMC@LPB@Ni composite membrane has superhydrophilicity and underwater superoleophobicity.The maximum OCA is 156°and the sliding angle is less than 5°.The oil-water separation efficiency of membrane for various oil-water mixtures is>99.0%,with high membrane flux(180000 L m^-2 h^-1)and high intrusion pressure（1.24 kPa）.Moreover,the membrane has low adhesion to underwater oils,good self-cleaning ability,acid and alkali resistance,salt resistance,and excellent repetitive cycle performance.（4）In view of the fact that K₄Fe（CN）₆·3H₂O and Fe³⁺produce Prussian blue,and that sodium alginate（SA）can be chelated with to form iron-alginate（Fe（Ⅲ）-ALG）hydrogel（Fe（Ⅲ）-ALG）.In this section,Fe（Ⅲ）-ALG-PB@Fe composite membrane was prepared in one step by using K₄Fe（CN）₆·3H₂O and SA as raw materials and simultaneously reacting and assembling Fe³⁺on the surface of Fe mesh.The characterization results show that the surface of membrane is loaded with a coarse structure of Fe（Ⅲ）-ALG-PB hybrid particle,the size of which is about 50 nm;The water contact angle is close to 0°,for diesel,corn oil,cyclohexane,the contact angles of gasoline,dichloroethane and chloroform are all above 150°and the sliding angle is less than 5°,showing superhydrophilic-underwater oleophobic properties.It was found that the presence of ferric alginate gel limits the size increase of Prussian blue during simultaneous growth assembly.