Study on Surface Wettability Design and Regulation of Porous Substrates for Oil-water Separation

Author:Zeng Xin Juan

Supervisor:wen xiu fang


Degree Year:2019





Frequent oil spills,the rapid increase of industrial oily wastewater and domestic oily sewage have caused serious pollution,which becomes an increasing worldwide subject and challenge to clean and recycle oily wastewater effectively.In recent years,the special wettability materials designed by combination of surface chemical composition and surface roughness have been widely studied to solve oil pollution issue on the basis of the interfacial phenomenon of oil and water,and proved to be convenient and effective.Inspired by bionics,some special wettable surfaces were constructed on porous substrates by designing and controlling the surface microstructure and chemical composition,and has realized the separation of various oil-water mixture systems.The main research contents are as follows:The industrialized,inexpensive thermoplastic acrylic resin and hydrophobic SiO2nanoparticles were sequentially modified onto stainless steel mesh surface by simple spray-coating method.The thermoplastic thermoplastic acrylic resin was infiltered into macrovoids among hydrophobic SiO2 nanoparticles during annealing based on an under-saturated capillary rise infiltration mechanism to obtain a superhydrophobic and superoleophilic polymer-infiltrated nanoparticle film coated stainless-steel mesh(PINF-SSM).PINF-SSM had the best porosity and superhydrophobic properties with the spray-coating two layers of SiO2 nanoparticles.The obtained PINF-SSM showed robust superhydrophobicity,excellent easy repairability and storage stability.Furthermore,the as-prepared PINF-SSM was successfully used to separate various oil/water mixtures with separation efficiency high up to99.0%.The oil collector made by a large-size PINF-SSM could realize the rapid and efficient continuous collection of oil slick,exhibiting excellent application potential.The robust superhydrophobic meshes with WCA=156°and SA=2.5°were prepared by using the cured thermoset phenolic resin(TPR)to anchor the hydrophobic SiO2nanoparticles on stainless-steel mesh surface(SiO2@TPR-SSM).The obtained superhydrophobic SiO2@TPR-SSM exhibited excellent mechanical stability which could resistance to violent hand kneading,and it would not cause effect on its wettability with immersion in various organic solvents,or strong acid and high-concentration salt solution for192 h.Even in boiling water or in the environment of 0°C to 240°C,the SiO2@TPR-SSM still could retain its superhydrophobicity.Moreover,the obtained superhydrophobic SiO2@TPR-SSM showed high separation capability in separating various water/oil mixtures and the separation cycles were larger than 200.And it also demonstrated high separation capability for boiling strong acid,base and high-concentration salt water/oil mixtures,which makes the SiO2@TPR-SSM into a promising material in industrial separation practice under harsh conditions.Thiol-functionalized fabric was first obtained through decorating PDA and grafting cystamine dihydrochloride on cotton fabrics.And then,hydrophobic SMA and pH-responsive undecylenic acid were introduced onto the thiol-functionalized fabric via efficient photo-induced thiol-ene click coupling chemistry.The obtained fabric exhibited switchable wettability between superhydrophobicity and superhydrophilicity depending on the contacting liquid pH value with great pH-response abililty,and its tensile breaking strength was stronger than that of the pristine fabric.After 500 peeling experiments,the pH-responsive fabric had excellent superhydrophobicity.More importantly,the as-prepared fabric not only could realize the separation of oil/water/oil ternary mixtures,self-clean and repel oil fouling during separation process,but also could easily remove oil on water or underwater and realize controllable separation of heavy and light oil-water mixtures efficiently.This cost-effective smart cotton fabric exhibits significant potential in satisfying the different separation purposes under complicated conditions.Inspired by the water collecting mechanism of Stenocara beetle’s back structure,a superhydrophilic bumps-superhydrophobic/superoleophilic(SBS)surface was designed.Specifically,hydrophilic silica microparticles were assembled on the as-cleaned substrate surface,which were followed by further spin-coating fluoropolymer/SiO2 nanoparticles solution with carefully selected rotational speed and spin time to control the thickness of the flouoropolymer/SiO2 layer.We systematically studied the water droplet collecting performance of the SBS coating in the oil and proposed the mechanism of water droplets aggregation,that is,the unique superhydrophilic and superhydrophobic topography generates a sharp surface energy gradient,which drives tiny water droplets in the oil toward the isolated superhydrophilic domains on the continuous superhydrophobic surface.The superhydrophilic bumps-superhydrophobic/superoleophilic surface was decorated onto stainless steel mesh with 10μm pore size(SBS-SSM)to separation of water-in-oil emulsions.The superhydrophilic bumps can destabilize and capture emulsified water droplets under the steep surface energy gradient across the superhydrophobic and superoleophilic domains.These captured water droplets could further extract water from emulsion,coalesce,and grow around the superhydrophilic bumps into much larger sizes that can be blocked by the pores of the underlying mesh film,while purified oil permeates through.SBS-SSM filters showed higher separation efficiency for water-in-oil emulsions than the traditional superhydrophobic/superoleophilic stainless steel mesh(S-SSM)filter.The oil purity in the SBS-SSM filtrate could reach up to 99.95 wt%,and the extracted water contents from surfactant-stabilized water-in-oil emulsions was 10-20 fold higher than traditional S-SSM,showing great application potential for oil purification.