| With the rapid development of global economy and industrialization degree unceasing enhancement,as a result,industries such as petrochemicals,printing and dyeing,textile,metal smelting,and food processing have been produced a significant amount of oily wastewater that has a complex composition,with components such as insoluble oils,water-soluble pollutants,and oil-soluble organic pollutants.Untreated oily wastewater has caused serious pollution and irreparable damage to the water environment and ecosystem,thereby posing significant threats to the health of humans and the environment.The effective treatment of oily wastewater has become a key problem to be solved urgently in the field of environmental protection.At present,oil/water separation medias generally have problems such as poor structure stability,low separation efficiency,poor repeatability and practicability,and easy to cause secondary pollution,which can not meet the treatment standards and discharge indexes of oil-bearing wastewater in related industries.In view of the above problems,to find a kind of environmental protection material with high efficiency,high structural strength,easy recycling and no secondary pollution has become the research focus in the field of oil/water separation.Hard quartz sand filter material is a natural environmental protection material,cheap and easy to obtain,has good mechanical wear resistance and chemical stability,avoiding the defects of traditional matrix materials（such as sponge,activated carbon,cotton fabric,filter paper,etc.）.In this paper,two kinds of stimuli-responsive special wettability quartz sand filter materials were fabricated by grafting nanoparticles and modified coating onto the surface of hard quartz sand filter material by a simple dip-coating synthesis route,and their oil/water separation performance was studied.（1）PEI/ZnO-SA/CS-coated quartz sand filter media（PEI/ZnO-SA/CS@QS）was fabricated by introducing ZnO nanoparticles,hydrophobic alkyl long chain,and amino group-rich hydrophilic groups into the surface of quartz sand filter media.The preparation mechanism of PEI/ZnO-SA/CS coating was studied in detail.The components of PEI/ZnO-SA/CS coating were grafted onto the surface of quartz sand coated with ZnO nanoparticles by condensation reaction,hydrogen bond,van der Waals force and other forces,and stable stimuli-responsive coating was formed on the surface of granular quartz sand.Elastomeric poly（styrene-block-isoprene-block-styrene,SIS）was used as the experimental adhesive to enhance the adhesion between hard quartz sand and ZnO nanoparticles,and a large number of ZnO nanoparticles were grafted onto the surface of quartz sand by physical bonding,resulting in a rough micro/nano structure.The synthesis scheme of coating can be optimized by combining the condensation of coating components and schiff base reaction.SEM,EDS,XPS,FT-IR,XRD and TGA were used to characterize the surface morphology,functional group elements and chemical composition of PEI/ZnO-SA/CS@QS filter media before and after the modification process and wettability response.The formation mechanism of p H and ammonia response reversible wettability conversion of PEI/ZnO-SA/CS@QS and the graft of surface coating were systematically investigated.PEI/ZnO-SA/CS@QS can convert the superhydrophobicity/superoleophilicity surface to superhydrophilicity/underwater superoleophobicity surface within 10 seconds,and realize the controllable separation and demulsification of oil/water mixture,oil-in-water and water-in-oil emulsions by switching the surface wettability.In addition,PEI/ZnO-SA/CS@QS has rich amino and hydroxyl groups on the surface,which has high separation efficiency and adsorption capacity for industrial methylene blue and Congo red dyes.PEI/ZnO-SA/CS@QS filter media has excellent oil/water separation and dye adsorption performance,which provides a new reference direction for the development of rigid filter material.It has high development potential and application value in oil-bearing wastewater treatment and industrial dye adsorption.（2）Solvent-responsive superoleophobic/superhydrophilic quartz sand（SSQS）was manufactured by introducing ZnO nanoparticles,short-chain fluorinated compounds,and hydrophilic-induced units into the surface of quartz sand.The structure mechanism of superoleophobic and superhydrophilic surface of SSQS filter material was studied,and a mathematical model was established to fit the surface free energy and its components.SEM,EDS,XPS,FT-IR,XRD and TGA were used to characterize the microstructure and chemical composition of SSQS surface,and the formation mechanism of superoleophobic and superhydrophilic surface in air was systematically explored.SSQS has good solvent response wettability and can reversible switch between superoleophobicity/superhydrophilicity and superoleophilicity/underoil superhydrophobicity,can realize the controllable separation of oil/water mixture,its unique superoleophobicity/superhydrophilicity wetting surface has great advantages in oil/water separation and oil treatment.The excellent solvent response wettability transformation characteristics of SSQS filter material surface can realize demulsification and separation of oil/water emulsion on demand.The separation efficiency of oil/water emulsion is above 98.38%,and the oil/water separation flux is higher than 797.25 L m-2h-1.In the experiment,"┴"oil/water separation device was used to separate oil phase and water phase synchronously in the stratified oil/water mixtures.The oil/water separation efficiency was as high as 99.33%and the oil/water separation flux was high.SSQS filter media provides a new research direction for the reversible wettability conversion of hard filter media,and has broad application prospects and development potential in the field of controllable oil/water separation. |
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