| With the rapid development of society,the shortage of fresh water has become a global concern.Although traditional seawater desalination technology can relieve the pressure of fresh water shortage to a certain extent,in the long run,its environmental pollution and rapid energy consumption cannot be ignored.Therefore,it is necessary to find a cleaner way to desalinate water.Solar energy is a kind of green energy,and the interfacial water evaporation technology driven by solar energy has been deeply studied,because it can realize the replenishment of fresh water resources in a green and sustainable way,which is considered to be one of the most effective ways to alleviate the freshwater crisis.As a mature technology,the fiber produced by electrospinning technology has the advantages of softness,light weight,high specific surface area and high porosity,etc.It has excellent application prospect in the field of water evaporation driven by solar energy,and is one of the ideal substrates for photothermal conversion of evaporator.Therefore,in this work,recycled mineral water bottle（mainly composed of polyethylene terephthalate,shortened to r PET）as the base material,combined with carbon nanotubes（CNTs）and low-cost carbon black（CB）,using electrospinning technology and folding technology,designed the top hydrophobic,bottom hydrophilic double-layer plane structure and 3D folding structure.Therefore,the effective illumination area and utilization rate of the evaporator are improved.Finally,the evaporation performance of the evaporator and the application of seawater desalination as well as the relationship between different folding structures and evaporation performance are explored.The specific research contents are as follows:（1）Firstly,CNTs and r PET were used as raw materials to prepare the mixed solution,and air-laid paper was used as the receiver to prepare the double-layer film CNTs@r PET-P by electrospinning technology（P is short for air-laid paper）.The bottom of CNTs@r PET-P is air-laid paper,which has excellent hydrophilicity,and conducive to sending water from the bottom up to the photothermal layer,and convenient for the photothermal layer to evaporate water;The top layer of photothermal layer is CNTs@r PET.Thanks to the good hydrophobic property of PET,it can prevent salt deposition on the surface of CNTs@r PET and affect the light absorption performance.Finally,a 2D evaporation system is assembled by taking CNTs@r PET-P as the evaporator,the air-laid strip as the water transport channel,and the polystyrene（PS）foam as the insulation layer and the supporting structure.The microscopic morphology,mechanical properties,flexibility,physicochemical stability of CNTs@r PET-P and the photothermal and evaporative properties of CNTs@r PET-P-N（N is the concentration of CNTs,0.5,2,3.5,5 wt%）under a solar intensity(1 k W m-2)were explored.The results show that the size of CNTs@r PET-P fiber is uniform,and has good mechanical properties,physicochemical stability and flexibility.In terms of photothermal conversion performance,with the increase of CNTs concentration,the photothermal performance of CNTs@r PET-P first increased and then leveled off.Finally,the photothermal conversion efficiency of CNTs@r PET-P-3.5%reached 45.4%,slightly lower than that of CNTs@r PET-P-5%（50.1%）.（2）The folding structure can improve the light absorption,and thus improve the photothermal conversion efficiency.Therefore,in order to improve the photothermal conversion efficiency,we converted the above CNTs@r PET-P into a 3D structure,that is,CNTs@r PET-P was folded to obtain a 3D evaporator（F-N,N is the concentration of CNTs）,and an evaporation system was assembled with air-laid paper water transport channel and PS thermal insulation foam.The photothermal conversion performance,evaporation stability and seawater desalination performance of F-N evaporator were investigated.The results show that the photothermal conversion efficiencies of F-3.5%and F-5%are 85.8%and 89.6%,respectively,and the evaporation rates are 1.34 kg m-2 h-1 and 1.39 kg m-2 h-1,respectively under 1 k W m-2.And the conversion efficiency remains basically stable after11 cycles in seawater.In addition,the concentration of ions in the purified water collected after desalination is two to three orders of magnitude lower than that of the seawater before desalination,which meets the drinking water requirements of the World Health Organization（WHO）and the US Environmental Protection Agency（EPA）.（3）Among carbon-based materials,in addition to CNTs,CB is also one of the photothermal materials commonly used for solar photothermal conversion,and its cost is lower than CNTs.Therefore,considering the cost,we kept the r PET base material unchanged,took CB as the photothermal material,spun on the air-laid paper by electrospinning technology,and got CB@r PET-P double layer film.According to the results of the previous chapter,folding structure can improve the photothermal conversion efficiency.Therefore,3D evaporator F-M is prepared in the same folding way（M is the concentration of CB,1,3,5,6 wt%）,and assembled with the air-laid strip and PS insulation foam to form an evaporation system.Finally,we explore the microstructure,mechanical properties and stability of CB@r PET-P,as well as the photothermal conversion performance,photothermal stability and seawater desalination performance of F-M evaporator.The results show that CB@r PET-P fiber has smooth surface and uniform diameter,as well as good stability and mechanical properties.In terms of photothermal performance,the photothermal conversion efficiency of F-5%evaporator and F-6%evaporator is 90.98%and 93.91%,and the evaporation rate is 1.41 kg m-2 h-1 and 1.46 kg m-2 h-1,respectively at 1 k W m-2.In addition,we also explored its seawater desalination performance under one sunlight intensity,and found that the ion concentration of purified water after desalination was 3-4 orders of magnitude lower than that of seawater before desalination,meeting the water quality requirements of WHO and EPA.It shows that the conversion efficiency can be higher than that in the previous chapter under the condition of lower cost,which indicates that we have successfully prepared a 3D evaporator with low cost,high photothermal conversion efficiency and seawater desalination performance,which provides ideas for the preparation of low cost and high photothermal conversion performance of evaporator,and also provides a new way for the recycling of waste plastics.（4）Combined with the experimental results in the previous chapters,we found that compared with the material,the structure has a greater degree of optimization for the photothermal conversion performance.In addition,we also observed that the evaporation efficiency of F-M gradually increased with the increase of CB concentration,and the change gradually decreased,indicating that even if the CB concentration was increased again,the improvement of photothermal conversion performance was little,which may be related to the degree of dispersion of CB particles.Therefore,CB@r PET-P-6%was folded into different structures of the evaporator F@K（K is the number of folded petals,which are 0,4,8 and 16）,and the relationship between the photothermal conversion performance and the structure was explored.The results showed that the photothermal conversion efficiency increased first and then decreased with the increase of the number of folded petals.In addition,we also introduce the quality factor as a comprehensive index to evaluate the photothermal performance of the evaporator,which is mainly related to the photothermal conversion efficiency and cost.The larger the quality factor,the better the comprehensive performance of evaporator. |
