Direct Laser Writing Carbonization Of Polyimide For The Fabrication Of Multilayered Photothermal Films And Their Use For Intcrfacial Solar-driven Water Evaporation

Developing a stable,sustainable,and cost-effective way to produce clean water has become an increasingly urgent issue due to the increasing global water scarcity.In recent years,due to the expansion of solar thermal technology in compact,self-contained and portable systems,the interfacial evaporation method has received extensive attention.Compared with the traditional integral heating method of directly heating water bodies,the interfacial heating-based solar water evaporation technology integrates solar energy.The conversion takes place at the vapor/liquid interface of the device,increasing the solar-to-steam conversion of the system by efficiently heating the water at the device interface.On this basis,the researchers enhanced the solar light conversion efficiency of the interface by preparing photothermal materials with high photothermal conversion efficiency and adding thermal insulation devices to reduce the energy dissipation of interface conversion to the environment.These two measures have been proved to be effective in improving the evaporation efficiency of the system.Even so,in the integrated interface seawater desalination device,energy utilization rate,low freshwater production,and the device’s stability under long-term use are still the research problems of solar water evaporation technology.Carbon-based materials have been shown to exhibit high mechanical and chemical stability and broadband solar absorption,therefore,they have great application potential,but current methods to fabricate/integrate/assemble high-efficiency water evaporation systems based on carbon-based materials usually involve a tedious multi-step process in which light-absorbing materials are separately prepared by complex wet-chemical methods and then integrated with the underlying thermal insulation layer.Therefore,in this paper,using the new carbonization technology of laser direct writing,and using polyimide(PI),a common polymer material,as a precursor,carbon materials with high light and heat absorption efficiency were prepared in situ.Moreover,the hydrophilicity of the carbon layer was further adjusted by HNO3 treatment,and an interfacial evaporation system with high efficiency,broad-spectrum solar light absorption efficiency,desalination performance and long-term stability was developed.The purpose is to solve the key problems of low solar light band absorption,energy dissipation and high durability of interfacial solar desalination systems.1.The two sides of the PI film were carbonized by CO2 laser with a wavelength of 10.6 μm,and a tri-layer structure containing carbon/polyimide/carbon was prepared.Converting the effect of the light conversion rate of carbon materials,carbon materials with an average light absorbance of 96%in the solar band of 200-2500 nm were prepared.Since the preparation parameters,namely laser processing power,whether the carbon material is subjected to hydrophilic treatment,and whether the polyimide precursor is punched or not,will be introduced in the process of assembling the solar desalination device,these conditions will vary to varying degrees.Affects the desalination rate of seawater.Using the experimental design software Design Expert?,this project successfully obtained the process combined with the highest desalination rate and obtained the experimental condition that has the greatest impact on the desalination rate of the polyimide precursor:hole.The vapor/liquid interface seawater desalination system obtained by compounding the prepared photothermal absorber,filter paper and polyurethane foam has a capacity of 1.61 kg m-2 h-1 under a simulated sun,and the seawater evaporation efficiency reaches 93.2%,but this system haspoor desalination performance.We used a three-layer composite membrane with double-sided hydrophilic and hydrophobic anisotropy designed by Janus.The seawater desalination rate has been kept at 1.43 kg m-2 h-1 in the 8 h test,and the durability of the composite membrane in planar configuration was tested.It also confirms the excellent robustness of the laser carbon carbide film.2.Using the PI film folded from the middle as the precursor for laser processing,a laser carbonized PI layer-polyimide layer bilayer structure with an inverted V configuration was prepared after unfolding,which is different from the laser carbonization of the planar configuration.The inverted V carbon film is also treated in HNO3,so,the light-to-heat conversion layer and the water transport layer can be perfectly integrated.When assembling the inverted V carbon film into an interface seawater desalination device,only the bottom of the film needs to be inserted into the polyurethane foam,the heat dissipation of the light-to-heat conversion layer is limited due to the reduction of the contact area with the bulk water and the air barrier between the inverted V device and the bulk water,and the test of the seawater evaporation rate was 1.73 kg m-2 h-1.The inverted V system not only has larger evaporation rate than the plane configuration,but also has higher desalination rate.In addition,the design of the inverted V structure makes salt can be deposited on top of the structure.The salt that accumulates at the top of the structure can dissolve on its own in the dark.These characteristics above solve many problems caused by the accumulation of salt in the interfacial water evaporation device.So,the long-term performance of the carbon-polyimide bilayer inverted V structure is greatly improved.