Preparation Of MXene Materials And Study On Photothermal Conversion Properties

As strategic economic resources and basic natural resources,water resource is the key control factor of ecological environment and the material basis for life to survive.With the rapid development of modern industry,water shortage caused by increasingly serious environmental pollution has become a major obstacle to the sustainable development of human health,economy and society.Using solar-driven interface evaporation technology（SSG）to desalination seawater or other non-potable water resources to produce clean water is one of the effective ways to solve the shortage of fresh water resources,and has become a research hotspot in this field in recent years.The design of solar steam generator is the research foundation and key problem of solar driven interfacial evaporation system.As the core of solar driven evaporation photothermal material（PCMs）has been used to prepare solar steam generator.In recent years,with the rapid development of solar-driven interface evaporation technology,solar photohot water evaporation method is no longer limited to the simple solar desalination,but derived a lot of solar photothermal materials combined with seawater desalination and applied in such fields as:sewage（waste）water treatment,adsorption,antibacterial and catalysis.As far as the reported photothermal materials are concerned,most of them are composed of biomass carbon-based materials,composite materials and conductive polymer materials.Although they all have excellent photothermal evaporation performance,due to the limitations of the material itself and the preparation method,it is still difficult to realize efficient photothermal evaporation and purification of polluted（waste）water in the same material at the same time.MXene（Ti₃C₂）is a new type of 2D transition metal carbide.Due to its advantages of strong designability,high surface area,excellent metal conductivity,abundant metal hydroxide active sites,and easy functionalization,MXene has attracted wide attention in the fields of energy storage,catalysis and environmental remediation.In view of the deficiencies in the current research field of photothermal materials for solar driven interface evaporation,this paper takes the development of multifunctional photothermal materials as the starting point,through reasonable design,MXene as the main material,to prepare a series of multi-functional MXene-based photothermal materials.The regulation and strengthening of photothermal conversion properties such as light absorption,water molecular transport,heat insulation and desalting,photocatalytic degradation and antibacterial properties of these materials in oily wastewater,dye wastewater and seawater desalination have been systematically studied,laying a preliminary foundation for exploring the preparation of new photothermal materials and their applications in solar desalination,pollution（waste）treatment and purification.At the same time,it can provide new ideas for the design of new photothermal materials in the future.The main contents and conclusions of this paper are as follows:（1）Kapokay fiber（KFs）and sodium alginate（SA）as aerogels base,impregnated in MXene suspension,prepared a new flake solar steam generator derived from Kapokay fiber Wiki MXene composite aerogels（named KFs-MXene）.It benefits from excellent light absorption（about 97%）,good heat insulation(thermal conductivity0.05039 W m^-1 K^-1),abundant porosity（95.60%）and fast water transfer.KFs-MXene exhibited excellent solar interfacial evaporation（ISSG）performance,with a water evaporation rate of 1.47 kg m^-2 h^-1 and an evaporation efficiency of up to 90.4%at a light intensity of 1 k W m^-2.In order to improve the antifouling performance of KFs-MXene,chemical hydrophilic and oil-phobic modifications were adopted,so that KFs-MXene can be widely used in oily wastewater.Under the irradiation of 1 k W m^-2,after hydrophilic and oleophobic modification of KFs-MXene（named O-KFs-MXene）.The evaporation rate and energy conversion efficiency can reach 1.40 kg m^-2 h^-1 in 1wt%oily water,and the evaporation efficiency and rate of O-KFs-MXene remain stable during 6 hours of continuous solar-driven interfacial evaporation.（2）With melamine foam（MF）as the base,MXene as the absorption layer and the bridge between polypyrrole（PPy）and MF,PPy as a photocatalytic active agent,through simple impregnation and in situ polymerization successfully prepared a new multifunctional MXene/PPy coated melamine foam（MF）,named as MF-MXene/PPy.MF-MXene/PPy has abundant porosity（89.13%）,good water molecular transport channel,excellent light absorption capacity（about 94%）,low thermal conductivity(0.1047 W m^-1 K^-1),and shows excellent performance in solar desalination,wastewater purification and organic dye photodegradation.The solar energy conversion and efficiency of MF-MXene/PPy reached 1.5174 kg m^-2 h^-1 and 91.24%under 1 k W m^-2irradiation.In addition,MF-MXene/PPy showed good salt tolerance even after 8 h continuous evaporation in 20 wt%Na Cl due to its regular pore size.After continuous evaporation in 70 m L 20 wt%Na Cl for 8 h,the amount of salt collected can reach 0.2g.In addition,MF-MXene/PPy also has excellent visible light degradation ability for organic dyes,such as methylene blue（MB）,Rhodamine B（Rh B）and methyl orange（MO）degradation rates of 92.38%,88.92%and 91.75%,respectively.（3）Polyvinylidene fluoride（PVDF）,carbon black（CB）as film plate,calcium carbonate（Ca CO₃）and hydrochloric acid（HCl）as pore-forming agent,and MXene/Ag₃PO₄ as photocatalyst were used to prepare the heterogeneous composite polyvinylidene fluoride（PVDF）mixed film（PCC-MXene/Ag₃PO₄）.PCC-MXene/Ag₃PO₄ has abundant porosity（80.64%）,good water molecular transport channel,good light absorption capacity（about 90%）,low thermal conductivity(0.15178 W m^-1 K^-1),and excellent performance in solar interfacial evaporation,photodegradation and antibacterial properties.With the help of a porous PU sponge,the double-layer solar evaporator showed a high evaporation rate and efficiency of 1.4736kg m^-2 h^-1 and 83%under 1 k W m^-2 solar irradiation,as well as excellent evaporation stability and salt resistance.In addition,PCC-MXene/Ag₃PO₄ had excellent antibacterial properties and photodegradation ability of organic dyes,and the degradation rates of methylene blue（MB）,Rhodamine B（Rh B）and methyl orange（MO）were 95.06%,96.9%and 74.23%,respectively.