Preparation And Water Treatment Application Of Ti₃C₂T_x MXene-Based Solar-Driven Interfacial Evaporation Photothermal Membrane

In recent years,solar-driven interfacial evaporation technology has become one of the potential methods of seawater desalination and sewage purification due to its advantages of zero energy consumption,green environmental protection,and low cost.At present,the factors restricting the commercialization of this technology mainly include:low evaporation performance,short life and high cost.The traditional photothermal materials（nobel metals and carbon nanotubes,etc.）have many shortcomings,such as unsatisfactory water transport channels and low photothermal conversion efficiency,which restricts the further development of this new technology.Two-dimensional（2D）Ti₃C₂T_x MXene have attracted extensive attention in water treatment due to their unique layered structure,excellent photothermal conversion performance,and selective adsorption of heavy metal ions.In this paper,based on Ti₃C₂T_x MXene nanosheets,two solar interfacial evaporative photothermal membranes were prepared,namely:MXene/copper indium selenide（CIS）nanoparticle composite photothermal membrane and Ti₃C₂T_x-NH₂/nonwoven fiber three-dimensional（3D）photothermal membrane.The physical and chemical properties and water treatment performance of the two photothermal materials were systematically studied,including:（1）The MXene nanosheets and CIS nanoparticles were composited in different proportions and vacuum filtered onto the PVDF membrane to form a composite photothermal membrane.The introduction of CIS can effectively improve the microstructure of MXene nanosheets,increase the interlayer spacing of MXene nanosheets to prevent the re-stacking of MXene nanosheets,strengthen the spatial accessibility and wettability of the photothermal membrane,and enhance the light absorption capacity of the photothermal membrane.At the same time,a Schottky junction may be formed between MXene and CIS,which promotes the separation of photogenerated carriers and improves the photothermal conversion efficiency.The optimal evaporation rate and evaporation efficiency of the MXene/CIS nanocomposite photothermal membrane were 1.434 kgm^-2h^-1 and 90.04%,respectively,which were significantly better than the 1.278 kgm^-2h^-1 and 80.24%of the pure MXene photothermal membrane,and pure CIS 1.204 kgm^-2h^-1 and 75.57%.Moreover,the MXene/CIS composite photothermal membrane was very cost-effective,demonstrating good light intensity adaptability and durability.Finally,the removal rates of organic dyes,salt ions,and heavy metal ions by the composite photothermal membrane were 100%,98%,and 99%,respectively.（2）Compared with the pre-grafted MXene nanosheets,Ti₃C₂T_x-NH₂ nanosheets had significantly increased interlayer spacing,increased specific surface area,stronger light absorption ability and more hydrophilic.The decontaminated 5×5 cm nonwoven fibers were soaked in Ti₃C₂T_x-NH₂ nanosheet solution for 3 h,and dried to form a Ti₃C₂T_x-NH₂/nonwoven fiber 3D evaporator.As compared to the MXene/CIS nanocomposite photothermal membrane,the 3D evaporator has more water transport channels and gas escape sites,not only the evaporation performance is enhanced,the salt tolerance is improved,but also the removal performance of organic dyes,salt ions and heavy metal ions is better.The evaporation rate and evaporation efficiency of Ti₃C₂T_x-NH₂/nonwoven fiber3D evaporator were as high as 1.457 kgm^-2h^-1 and 91.48%,respectively,while the Ti₃C₂T_x/nonwoven fiber 3D evaporator is only 1.240 kgm^-2h^-1 and 77.82%.After ten performance cycle tests,the performance of the 3D evaporator did not decrease significantly,and there was no obvious salt crystallization on the surface of the evaporator.In addition,the 3D evaporator showed good environmental adaptability,and there was no obvious change after being placed in pure water,strong acid,and strong alkali solution for a week.Finally,the removal rates of organic dyes,salt ions,and heavy metal ions by the 3D photothermal evaporator were 100%,99.8%,and 99.9%,respectively.In this study,two novel photothermal filter membranes were prepared based on Ti₃C₂T_xMXene,which was expected to promote the commercialization of solar interfacial evaporation technology.The design ideas may also have certain reference for other types of m technologies.