Preparation Of Ti₃C₂ And Wood Charcoal Based Photothermal Devices And The Performance In Solar Interfacial Water Evaporation And Electricity Production

Solar interfacial water evaporation technology is a promising approach to solve clean water scarcity.However,as the core part of the solar interface water evaporation technology,the photothermal devices are facing the following problems:The optical loss,insufficient water transport,and heat loss of the photothermal devices cause the low photothermal evaporation efficiency;The poor thermal stability and salt crystallization problem of photothermal devices make it impossible to maintain long-term efficient water evaporation;The traditional photothermal devices can only take advantage of the heat energy during the solar interfacial water evaporation and ignore the accompanying other forms of energy,resulting in a low overall utilization of the solar energy.In response to the above problems,the photothermal evaporation efficiency of photothermal devices can be improved by optimizing the physical structure of the photothermal devices to enhance the light absorption and control water transportation,and optimizing the thermal structure of the photothermal devices to reduce heat loss.The long-term efficient water evaporation can be realized by strengthening the thermal stability and salt resistance of photothermal devices.The multiple utilization of energy can be achieved by designing the multifunctional photothermal devices.The main content and results are shown as follows:（1）Ti₃C₂-based aerogels with vertical pore channel structure（Janus VA-MXA）were fabricated by the directional freeze-drying technology.The effects of the optical properties of photothermal conversion materials and the structure of vertical pore channels on the photothermal evaporation performance were investigated.The results showed that the photothermal evaporation efficiency can be improved by adjusting the size of the vertical pore channel to match the water transport amount and water evaporation amount,enhancing the light absorption by multiple scattering of incident light inside the vertical pore channel and the excellent photothermal conversion performance of Ti₃C₂ materials.The vertical pore channel size of photothermal devices can be adjusted from 5μm to 35μm by changing the concentration of Ti₃C₂ dispersion solution.When the pore channel size decreased from 35μm to 5μm,the water transport rate of Janus VA-MXA increased from 0.29 g·min^?1 to 0.63g·min^?1.The photothermal device with the pore size of 15μm(Janus VA-MXA₁₅)showed the optimal matching of water transport rate and evaporation rate,and its light absorption was96.1%.The photothermal evaporation efficiency of Janus VA-MXA₁₅ can reach 87.3%,which was 14%higher than that of the Ti₃C₂ device with disordered porous structure.（2）The Ti₃C₂-based cotton fabric was prepared by coating technology（SMF）.The effect of heat loss on the photothermal evaporation performance of hanging SMF and floating SMF was investigated.The results showed that the hanging evaporation can reduce the heat conduction loss from the light absorption layer of the photothermal devices to the bottom bulk water through the indirect contact,thus realizing the improvement of the photothermal evaporation efficiency.The total heat loss of the hanging SMF was 11.4%,which only accounted for 1/5 that of the floating SMF.This can be explained by that the hanging evaporation can reduce the heat conduction loss from 48.4%（floating SMF）to 1.4%,which accounted for a large proportion of the total heat loss.By reducing the heat loss of photothermal devices,the photothermal evaporation efficiency was increased from 40.8%（floating SMF）to 81.3%（hanging SMF）.（3）The Ti₃C₂-based sponges（Sn O₂-SPM）coated by Sn O₂ thin film was prepared by high-temperature calcination and dip coating technologies.The Sn O₂ thin film formed a physical barrier to isolate oxygen,thus avoiding the oxidation of Ti₃C₂ and promoting the long-term efficient utilization of solar energy.The photothermal evaporation performance was regulated by adjusting the thickness of Sn O₂ thin film,and the thermal stability of Sn O₂-SPM was investigated.When the thickness of Sn O₂ thin film decreased from 11.2 nm to 2.1 nm,the light absorption increased from 88.3%to 95.4%,and the photothermal evaporation efficiency increased from 64.7%to 84.8%.After 12 h of light irradiation,the light absorption of the Sn O₂-SPM was still above 90%,and the water evaporation rate remained stable(1.41kg·m^-2·h^-1).The light absorption of SPM decreased to 17%and the water evaporation rate decreased by 65%because of the oxidation of Ti₃C₂ on the SPM surface.After 30 days of long-term operation,the light absorption,the structure and the solar photothermal evaporation performance of Sn O₂-SPM remained stable.（4）To relieve the salt crystallization of photothermal devices during the photothermal evaporation,a carbonized wood（ACW）modified with oxygen-containing groups were prepared by the high-temperature carbonization technology and the acid oxidation treatment.The salt resistance can be enhanced by relieving the precipitation of salt crystals based on the principle of real time dynamic separation of anions and cations induced by electric field.The ACW was used as cathode applying the negative voltage.The effect of electric field on the salt resistance of ACW was investigated.The water evaporation rate（5.0 wt%,Na Cl solution）of ACW increased from 2.94 kg·m^-2·h^-1 to 3.89 kg·m^-2·h^-1 with negative voltage（cell voltage）increased from-1.0 V to-3.0 V under 3-sun.This can be explained by that the increase of voltage can enhance the dynamic separation of anions and cations.The results of long-term operation showed that the water evaporation rate（5.0 wt%of Na Cl solution）of the electro-assisted ACW remained stable after the photothermal evaporation for 10 h,while the water evaporation rate of the ACW without the electro-assistance decreased by 46.3%.Moreover,the salt crystals were found in the surface and internal pore channels of the ACW without the electro-assistance after photothermal evaporation.（5）To realize the co-generation of water and electricity by utilizing the temperature difference during the photothermal evaporation,a composite energy collection device（B-MXM）was designed by Ti₃C₂-based devices with the n-type and p-type Si slices.The clean water and electricity can be obtained simultaneously by the temperature difference between the light absorption layer of photothermal devices and the bottom water in storage tank,which realized the multi-effect utilization of energy.The effects of light radiation intensity on photothermal evaporation performance and temperature-difference-induced electricity performance were investigated.When the light radiation intensity increased from 1k W·m^?2 to 25 k W·m^?2,the water evaporation rate of B-MXM increased from 1.43 kg·m^-2·h^-1to 30.27 kg·m^-2·h^-1,and the temperature-difference-induced voltage increased from 0.06 V to0.585 V,indicating that the increase of the light radiation intensity can increase the voltage induced by temperature difference.（6）To realize the co-generation of water and electricity by utilizing the ion separation phenomenon during the photothermal evaporation,a multifunctional photothermal device（A-CWA）was prepared by the carbonized wood（the pore channel surface modified with negatively charged groups）and two titanium mesh electrodes.The clean water and electricity can be obtained simultaneously by light-driven ion transport behavior from surface charges control.The photothermal evaporation performance of A-CWA was investigated.The effect of the brine salinity and the charge quantity of ions on the electricity performance was investigated.The results showed that the water evaporation rate of A-CWA was 1.18kg·m^-2·h^-1(1 k W·m^?2).When the salinity of brine increased from 14‰to 89‰,the steady-state voltage of A-CWA increased from 0.35 V to 0.82 V.When the charge quantity of anions in brine was constant,the voltage increased from 0.27 V to 0.67 V with the increase of cation charge quantity(Na⁺,Mg²⁺and Al³⁺).The results indicated that the increase of brine salinity and ion charge can increase ion-induced voltage.In summary,the photothermal evaporation efficiency can be improved by constructing vertical pore channel structure to enhance light absorption and control water transport,and constructing hanging evaporation mode to reduce heat conduction loss.The long-term efficiency of photothermal evaporation can be enhanced by the physical oxygen isolation with Sn O₂ thin film and the dynamic separation of anions and cations with the electro-assistance.The water and electricity co-generation can be realized by the concomitant temperature difference phenomenon and directional separation of charged ions during photothermal evaporation,which realized the multi-stage utilization of energy.This research has an important guiding significance for the design of high-efficiency,stable and multifunctional photothermal devices and the development of solar interfacial water evaporation technologies in the field of water treatment.