Preparation Of Oil-repellent And Salt-tolerant Porous Materials And Their Solar Interface Evaporation Performance

The shortage of fresh water resources has become a bottleneck restricting social and economic development.Solar-driven interfacial evaporation（SSG）,as one of the most effective technologies to solve the shortage of fresh water resources,has attracted extensive attention of researchers.Solar-driven interface evaporation technology uses clean solar energy as energy input,which is a promising photothermal evaporation technology,and can effectively obtain fresh water resources,thus alleviating the shortage of fresh water resources.In this paper,the channel structure and surface wettability of photothermal materials are designed to improve the salt resistance and oleophobic performance of interfacial steam generator,which can be widely used in oily wastewater,dye wastewater,seawater desalination and other aspects.Due to the complicated environment of fresh water source produced by solar evaporation in practical application,in reality,seawater,industrial sewage and other water bodies contain inorganic salts and oil stains at the same time.Inorganic salts and oil stains in the wastewater can easily block the water transmission channel of photothermal materials,seriously affecting their photothermal conversion efficiency,which puts forward higher requirements for the salt-resistant stability and oleophobicity of photothermal conversion materials under harsh conditions.Based on this,from the practical application point of view,on the premise of maintaining the efficient evaporation efficiency of solar-driven interface evaporator,this paper also pays attention to the improvement of the salt-resistant and oleophobic properties of photothermal materials,so that the prepared interface evaporator can be widely used in the actual water environment.In this paper,three kinds of raw materials with low cost,abundant reserves and no pollution are selected,and the photothermal materials with good oleophobic and salt-resistant properties are obtained by simple preparation process.The photothermal properties of these materials in oily wastewater,dye wastewater and seawater desalination are systematically studied by using the solar-driven interface evaporation experimental device.The research in this paper can not only provide new research ideas for further designing and exploring the preparation of new and high-performance photothermal materials,but also provide a class of high-performance photothermal materials with potential application value in solar energy utilization,and provide new solutions for solar interfacial evaporation in oily sewage,dye wastewater and seawater desalination.The main contents and conclusions of this paper are as follows:（1）Graphene oxide（GO）was prepared by using graphite powder as raw material,and then using GO as matrix material and polyvinyl alcohol（PVA）as cross-linking agent,a new type of graphite oxide with special arrangement of channels was prepared by directional freezing and simple carbonization Alkenyl-based solar steam generators（GO-SSGs）.Through testing and characterization,it is found that GO-SSGs has excellent light absorption performance（the light absorption efficiency exceeds 94%）and good heat insulation performance(the thermal conductivity is 0.259 W m^-1 K^-1),and the special porous structure is conducive to rapid water transportation.Under the irradiation test condition of 1 k W m^-2,the photothermal conversion efficiency of GO-SSGs is as high as 92%,showing excellent photothermal evaporation performance.In addition,the unique arrangement channel makes GO-SSGs have good salt resistance.In the salt solution with the concentration of 20 wt.%Na Cl,KCl and Mg Cl₂,the photo-thermal conversion efficiency of GO-SSGs can reach over 85%.In order to improve the antifouling performance of interfacial evaporator,the surface of interfacial evaporator was modified by hydrophilic and oleophobic.The test results show that in the oil-water mixture containing 10 wt.%n-hexadecane,the photothermal conversion efficiency can reach to 84%,showing good oleophobic performance and stable operation in oily wastewater.（2）After mixing halloysite and chitosan solution,direct directional freezing by liquid nitrogen,and then simple carbonization in nitrogen atmosphere to prepare a halloysite-based interface steam generator（H1）with neatly arranged channels.Hydrophilic and oleophobic solar interface steam generator H2 was obtained by oleophobic modification on the side and lower surface of H1.H1 has high light absorptivity（Ca.97.4%）,good heat insulation performance（in dry state）,thermal conductivity of 0.086 W m^-1 K^-1 and abundant porosity（84.2%）.H1 with neatly arranged channels can ensure timely water transmission.The test results show that the evaporation efficiency is as high as 1.58 kg m^-2 h^-1 under the test condition of 1 k W m^-2,and the relative photothermal conversion efficiency is 95.5%.In addition,H1 shows excellent salt tolerance in high-concentration brine,and has a good desalination effect on artificial simulated seawater.The purified water collected after evaporation can meet the World Health Organization standard for drinking water.In addition,the oleophobic modified H2 also shows excellent photothermal evaporation performance in oil and water,and its photothermal conversion efficiency can reach 86.0%.（3）A double-layer solar-driven interfacial evaporator（M-SSGs）with self-desalting and oleophobicity was prepared with carbon black（CB）,polyvinylidene fluoride（PVDF）and nano sponge.The light absorption rate of the prepared M-SSGs can reach 90%,and the photothermal conversion efficiency is 81.7%-83.1%.The superhydrophilicity and self-floating property of M-SSGs enable nano sponge to continuously transport water and effectively promote the dissolution of inorganic salts.For example,if 1 g Na Cl crystal salt is placed on PVDF composite membrane,the crystal salt can be completely dissolved in a short time.In 20 wt.%Na Cl,the photothermal conversion efficiency of M-SSGs is 78.9%-79.2%,and its photothermal conversion efficiency can reach 80.4%in the oil-water mixture containing 6 wt.%n-hexadecane.Compared with most existing interface evaporation systems,M-SSGs has the advantages of simple manufacture,high efficiency,stability and portability.