Study On Interfacial Desalination Of Montmorillonite Nanosheets/MXene Composites

Montmorillonite is an inexpensive and available clay mineral that can be exfoliated into two-dimensional montmorillonite nanosheets after hydration.Its hydrophilic properties and thermal insulation ability will be further improved,but this unique property of montmorillonite is rarely exploited.The shortage of freshwater resources is a serious threat to the survival and development of human beings,and desalination is a necessary means to solve the shortage of freshwater resources today.Solar desalination utilizes inexhaustible solar energy to produce fresh water for energy.It is clean,environmentally friendly,and low-cost,which has attracted much attention.Among them,the solar interface desalination can fix the thermal energy locally at the water-vapor interface,and the energy utilization efficiency is high,which has aroused the interest of the majority of scientific researchers.Many materials and designs have been developed for solar interface desalination,but problems such as low photothermal conversion efficiency,high cost,and salt deposition still exist.In order to solve these problems,this paper uses the characteristics of MXene with broad absorption spectrum and high light absorption rate and montmorillonite with good hydrophilicity and low thermal conductivity to design a composite material for the study of solar interfacial desalination.The mechanism of delithiation hydrophilic modification was calculated by DFT theory.The use of montmorillonite nanosheets for solar interfacial desalination not only expands the application field of montmorillonite and promotes the high-value utilization of montmorillonite,but also provides ideas for solving the shortage of freshwater resources.The main contents of this paper are as follows:1)Preparation of montmorillonite nanosheets/MXene binary films for solar interfacial desalination.Using montmorillonite nanosheets and MXene as raw materials,the montmorillonite nanosheets/MXene binary film was prepared by chitosan modification and cross-linking,and reassembly.The binary film uses MXene as the upper light absorbing material to fully absorb light energy,and uses the montmorillonite film as the base material to provide water transmission channels and thermal insulation effects.The experimental results show that the binary film has good light absorption rate,and under the radiation of a standard sunlight,its evaporation rate is 1.22 kg·m-2·h-1,and the photothermal conversion efficiency is 84.86%.And has good cycle performance.It still has high light-to-heat conversion efficiency under the condition of concentrating light.Moreover,the binary membrane can also desalinate wastewater.(2)Preparation of montmorillonite nanosheets/MXene three-dimensional porous composite gel for solar interfacial desalination.Using montmorillonite nanosheets and MXene as raw materials,MXene and montmorillonite nanosheets were prepared into gels with three-dimensional porous structures,respectively.The upper light-absorbing material is a three-dimensional porous MXene gel,which has a very high light absorption rate(over 94%),and the base material is a montmorillonite gel with three-dimensional water transport channels,and has high thermal insulation properties(thermal conductivity).is 0.04366 W/m K).Contact angle test and water transport test show that the montmorillonite gel has good hydrophilicity and ultrafast water transport rate.In the solar interface desalination test,the material not only has a high water yield of 1.37 kg m-2 h-1,but also has a very high photothermal conversion efficiency(93.7%).The three-dimensional porous composite gel still has extremely high photothermal conversion efficiency under light-converging conditions.Cycling tests and salt blocking tests show that the three-dimensional porous composite gel not only has good cycling stability,but also can transport the salt above the light-absorbing material to the lower seawater through gravity and concentration gradient driving force,which has a good application prospect.3)The mechanism of hydrophilic modification of montmorillonite was studied by DFT calculation.Using density functional theory,the structure of montmorillonite was optimized,and its adsorption configuration was analyzed.It was found that CS has very strong adsorption energy for water molecules,mainly physical adsorption and hydrogen bonding,while montmorillonite and CS have very strong adsorption energy.Chemisorption occurs between them.Thus,the adsorption of montmorillonite to water molecules is enhanced.In addition,the results of charge density and population analysis showed that in the interaction of montmorillonite and chitosan,the charge on the surface of montmorillonite would be transferred to CS,which would lead to the formation of physical adsorption.Thus,the hydrophilicity of CS-modified montmorillonite is increased.