Preparation Of Highly Hydrophobic 3D Porous Materials And Their Synchronous Oil Adsorption-water Filtration To Emulsion

Oil-in-water emulsion,as the most difficult oily wastewater to treat,causes serious harm to ecological environment.Although commonly used treatment technologies such as chemical flocculation and membrane separation have good demulsification effect,it is difficult to achieve synchronous recovery of oil resources.3D porous materials with special wettability have the advantages of good oil-water selectivity,large adsorption capacity,easy recovery of oil resources and low cost,thus have been widely used in the treatment of oil floating on water.However,for O/W emulsion,it is still a challenge for overcoming the obstacles of continuous water phase,improving the contact efficiency between skeleton and oil droplets.The migration and evolution mechanism of oil droplets on the skeleton needs to be clarified urgently.In this study,a highly hydrophobic and positively charged 3D porous material was innovatively synthesized by DA-PEI co-deposition method,and its synthesis mechanism was explored.A synchronous "oil absorption-water filtration" device was designed to improve the contact efficiency between materials and emulsified oil droplets,further realizing the continuous and efficient oil-water separation of O/W emulsion.On this basis,the evolution of emulsion droplets spreading on the surface and removing in pores of the material was explored.The phase separation process and mechanism of emulsion in 3D porous materials were revealed as well.3D porous materials with different wettability and charge were prepared by adjusting the co-deposition process of DA-PEI on the melamine sponge,and the key factors affecting the surface wettability and electricity of the materials were identified.The molecular simulation technique was introduced to reveal the directional regulation mechanism of PDA-PEI copolymerization system on the surface properties of materials.It was found that when DA:PEI=1:1 and reaction time set as 8h,the highly hydrophobic(WCA=141.9°±1.6°)and positive charged 3D porous materials(MS@DP-R5T8)was successfully fabricated.Compared with stirring speed,reaction temperature and oxygen concentration,DA/PEI mass ratio and reaction time are the key factors affecting the surface properties of materials.The surface hydrophobicity increased firstly and then decreased with the enhanced PEI mass ratio and prolonged reaction time,while the surface positive charge increased monotonically with the increase of PEI mass,which is different from the results of DA-PEI modification to superhydrophilic membrane materials in previous studies.Therefore,structural characteristics analysis,chemical composition identification and molecular simulation techniques are used to reveal the internal mechanism of the unique surface properties of MS@DP-R5T8.Results showed that the effective load of PDA-PEI copolymer improved the surface roughness and introduced a large number of hydrophobic carbon chain groups,which provided the structural and chemical basis for the formation of high hydrophobic surface.PDA and PEI were more likely to be copolymerized by schiff base reaction during our modification process.The binding mode of the PDA-PEI copolymer and melamine sponge substrate brought out hydrophobic and positive functional groups on the final product,resulting in the corresponding unique surface properties.This study provides a new way to synthesize hydrophobic three-dimensional porous materials in DA-PEI co-deposition system,and enrichis the research results of da-PEI co-deposition system on interface wettability regulation.The adsorption and reuse properties of MS@DP-R5T8 for various organic phase were evaluated.A treatment mode of synchronous oil absorption-water filtration was constructed to analyze the treatment efficiency of O/W emulsion containing different particle sizes,charged droplets and surfactant concentration,and to explore the influence of wettability of materials and pore size on the treatment effect.The thermal kinetics of the adsorption process was analyzed.It was found that the sponge could adsorb 67.21g/g to 178.57g/g oil with different viscosity and density.The synchronous "oil absorption-water filtration" treatment treatment mode avoids the problems of small scale and difficult long-term operation existing in the immersion or filtration methods,and realizes the continuous treatment of O/W emulsion.For O/W emulsion with droplet size more than 5 μm,as the material volume was reduced to 33%,the initial transimittance of filtrate reached 99.21%,the critical transmittance is 35.36%,the saturated capacity is 576 m L,and the cumulative oil absorption is 26.94 g/g.The hydrophobicity of MS@DP-R5T8 mainly affects the critical transmittance of water,and the pore size mainly affects the saturated oil absorption.In the process of oil absorption,the material framework plays two roles of oil droplet adsorption and polymerization respectively,which accords with Langmuir model in thermodynamics and pseudo-first-order kinetic reaction in kinetics.This study provides a new idea for hydrophobic three-dimensional porous materials to continuously capture emulsified oil droplets in water,and realizes synchronous water phase purification and oil resource recovery.The distribution state of oil/water phase in MS@DP-R5T8 was observed in situ,and the behavior evolution of droplet in sponge were investigated.The driving mechanics of oil droplets in sponge were revealed.Through the observation of fluorescence microscope and freeze scanning electron microscopy,it is intuitively clear that there are three distribution states of oil droplets in the framework,node and mesh of hydrophobic porous sponge during oil absorption and water filtration of O/W emulsion by :(1)adsorption on the framework;(2)aggregation at nodes and spread out towards the skeleton;(3)forming continuous smooth oil film between adjacent pores.The enhancement of hydrophobicity improves the radial discharge and diffusion capacity of oil droplets.Through self-designed microscale high-speed droplet motion behavior observation platform,discovered the roles of droplets spreading and penetration on on the surface of 3D porous materials with different wettability,the enhanced hydrophobicity of the material improves the radial drainage and diffusion capacity of oil droplets.And the function formula of droplet height and contact line length with time is constructed by using contact Angle value.The force of oil droplets in the process of migration and enrichment in the material skeleton was calculated.It was found that the high hydrophobicity of the skeleton is favorable for the oil droplets adsorbed on it to move rapidly to the framework node driven by Laplace force.The decrease of the pore size of sponge is beneficial to improve the capillary force of oil droplets.This study revealed the interaction process and demulsification mechanism between droplets and sponges,and deepened the theory of oil absorption and water filtration of threedimensional porous materials.In conclusion,the hydrophobic and positively charged surfaces was innovatively formed by DA-PEI coating on sponge substrates,the application mode of "oil absorption and water filtration" was developed to continuously treat various O/W emulsions,improving the contact effecicency between materials and emulsion droplets.The study enriched the application value of 3D porous materials in emulsion treatment and laid a foundation for exploring the demulsification mechanism of 3D porous materials.