Preparation Of P(AM-DMDAAC)-graphene Based Janus Material And Its Photothermal Evaporation/photothermal Degreasing Performance

The shortage of fresh water resources is one of the major problems facing the development of human society,and desalination is an effective means to alleviate water shortage.Reverse osmosis is the main method of desalination,but the technology consumes high energy and is easy to cause membrane contamination,so there is an urgent need to develop new desalination technology.At the same time,the frequent occurrence of marine oil spills has greatly affected the quality of seawater,which in turn has affected the operation of desalination and water quality,and how to effectively recover marine oil spills is an urgent problem.In response to the above problems,this study,based on the review of a large amount of relevant literature at home and abroad,constructs aerogel materials with Janus structure for solar-driven interfacial evaporation desalination and marine oil spill treatment by using graphene oxide(GO)as the basic carbon skeleton and P(AM-DMDAAC)as the modified material through a one-step hydrothermal freeze casting method,and the main research contents are as follows:(1)A kind of Janus aerogel with both hydrophobic upper surface and hydrophilic underwater surface was prepared by a one-step hydrothermal freeze casting method using P(AM-DMDAAC)and graphene oxide(GO)as raw materials.Using the upper surface water contact angle as the main index,the effects of GO dispersion concentration,pH,P(AM-DMDAAC)dosage and the placement of the material during the freeze-drying process on its performance were investigated to determine the optimal preparation process for P(AM-DMDAAC)/graphene-based Janus aerogel(JPGA):the concentration of GO dispersion is 6 mg mL-1,pH is 9,the concentration of P(AM-DMDAAC)solution is 4 mg mL-1,and the lyophilization is performed by vertical placement(the lower surface of the material touched the bottom of the container).The JPGAs prepared under these conditions had water contact angles of 133.6° on the upper surface and 0° on the lower surface,demonstrating the successful fabrication of the Janus structure.At the same time,it is proved that P(AM-DMDAAC)has been successfully introduced into the graphene sheet in the form of hydrogen bond by Fourier transform infrared spectroscopy.The upper and lower surface morphology of the material was analyzed by CLSM and SEM tests,and it is found that there are abundant reticular macropores on the upper surface of JPGA while the lower surface was smooth.Compression experiments show that JPGA has strong compressive properties,with a maximum compressive stress of 5.8 kPa at 60%strain.(2)The temperature of upper surface can reach 76.3℃ under one solar intensity irradiation and 41.6℃ even under humid conditions,indicating that it has excellent photothermal conversion performance.The DSC test shows that JPGA can convert free water into intermediate water to reduce the energy needed for evaporation and carry out efficient evaporation.Under the best preparation conditions,the evaporation rate of JPGA to pure water under one sunlight intensity is 3.65 kg m-2 h-1,and the photothermal conversion efficiency is as high as 98.9%.In the process of investigating the effects of GO dispersion concentration,pH.P(AM-DMDAAC)dosing and the placement of the material during the freeze-drying process on the evaporation performance of aerogels,it was found that the hydrophobicity of the upper surface followed the same trend as the evaporation rate.At the same time,the hydrophobic upper surface of JPGA cannot be infiltrated by the water body due to its unique Janus structure,thus effectively reducing the generation of salt crystals in the face of high salinity water bodies.Under the capillary force,the salt crystals can be dissolved back to the aqueous body by convection.As a result,JPGA exhibits strong salt tolerance and self-cleaning,properties,and is capable of long-term stable desalination and high salinity water purification processes,with removal rates of more than 99%for various ions(Na+,K+,Ca2+,Mg2+)in water bodies.(3)The oil-water separation results showed that JPGA exhibited excellent oil-water separation ability as well as photothermal oil removal and purification performance.Up to 65%improvement in the adsorption of Janus aerogels compared to non-Janus structured aerogels for organic solvents with lower viscosity.At the same time.JPGA aerogel has the ability of continuous and stable dynamic oil-water separation process.With the excellent photothermal conversion performance of the material itself,JPGA can quickly heat the high viscosity oil and improve its fluidity,thus completing the adsorption process.The prewetting operation can help JPGA realize the hydrophilic and hydrophobic conversion of its interfacial wettability for different oil-water systems.For more complex emulsion oil-water systems,solar energy can also be used as a driving force to realize the demulsification and evaporation purification treatment of oil-in-water emulsion,and the TOC removal rate of soybean oil,n-octane water-in-oil emulsion and actual ballast water wastewater can reach more than 90%.