Study On The Design,preparation And Performance Of Salt-resistant Solar Photothermal Evaporation Materials

With the rapid population growth and economic development in modern society,the problem of global freshwater scarcity is becoming increasingly serious.Desalination is considered to be one of the most promising solutions to the global freshwater crisis.Traditional desalination me thods often suffer from high energy consumption,high investment costs and low energy conversion efficiency,and so on.Solar photothermal evaporation integrates inexhaustible solar energy and abundant seawater to solve the problem of freshwater shortage.It is of great interest because of its green,non-polluting,low-cost,high energy conversion efficiency and sustainability features.However,due to the deposition of crystalline salt on the surface of the photothermal evaporation material and the water t ransmission channel during the seawater desalination,the light absorption capacity of the photothermal evaporation material is reduced and the water trans portation channel is blocked,and the photothermal evaporation efficiency is reduced during continuous operation.Previous researches have proved that photothermal evaporation materials with large pore size and low tortuosity exhibit outstanding salt resistance.Based on this,the thesis takes the materials with large pore size and low tortuosity as the starting point,aiming to study high-efficiency salt-resistant photothermal evaporation materials.Then,three new photothermal evaporation materials were prepared u sing polypyrrole sponge(PPy sponge),melamine sponge(MS)and glass capillary array(GCA)as raw materials,and their photothermal evaporation performance and salt resistance performance are systematically investigated.The main research contents and conclusions of the thesis are as follows:(1)In this section,PPy sponge is used as the precursor,and the calcium ion cross-linked sodium alginate is used to hydrophilically-modify it to prepare a M-PPy sponge with unique micron-sized pores.M-PPy sponge has excellent thermal insulation,super hydrophilicity and almost 100%light absorption(200-2500 nm).The experimental results show that under 1 k W m^-2 illumination,M-PPy sponge can achieve 84.72%photothermal evaporation efficiency.It can achieve 84.43%p hotothermal evaporation efficiency in high concentration salt solution.The fundamental research based on the PPy bulk material in the field of photothermal evaporation is the first case reported in the literature,which can provide a new research direction for further design and exploration of the preparation of new PPy-based functional materials.(2)From the perspective of sunlight utilization,this section enhances the light absorption capacity of system by supplementing an additional light reflection layer in the photothermal evaporation system.Utilizing MS as the water transportation and thermal insulation medium,reduced graphene oxide(r GO)as the light absorption layer,and aluminum foil as the reflection layer on the bottom of the photothermal material,an efficient salt-resistant solar photothermal evaporator was assembled(r GOMS-Re).r GOMS-Re has excellent thermal insulation performance,fast water transportation performance and high light absorption(the light absorption can reach 92.8%in the wavelength range of 200-2500 nm).The construction of the reflective layer reduces the loss of sunlight in the system and enhances the light utilization efficiency.Compared with the sample without the reflective layer,the photothermal evaporation efficiency of r GOMS-Re is 87.5%under 1 k W m^-2 illumination,an increase of 12.2%.In addition,r GOMS-Re exhibits excellent salt-resistance.r GOMS-Re maintained a high photothermal evaporation efficiency in a high concentration of brine at 20 wt.%.(3)In this section,two solar photothermal evaporators(PDA-GCA,PDN-GCA)were prepared from optimized photothermal material water transportation as the entry point,using the capillary effect of vertically aligned GCA,with GCA as the base material,polydopamine(PDA)and metallic palladium nanoparticles(PDN)coated o n the surface of glass capillary array(GCA)as the photothermal conversion layer and multilayer cotton fibers as the thermal insulation layer.In the photothermal evaporation system,the glass capillary tube utilizes the capillary effect to ensure sufficient water supply and one-dimensional transportation,and the multi-layer cotton fiber serves as the bottom insulation layer to reduce heat loss.The photothermal evaporation efficiency of PDA-GCA and PDN-GCA are84.8%and 89.8%under 1 k W m^-2 illumination,respectively,and the stable photothermal evaporation efficiency can still be maintained within 10 cycles.The photothermal evaporation efficiency of PDN-GCA reached 89%in a highly concentrated of brine at 20 wt.%.In addition,compared with conventional synthetic materials,the GCA-based photothermal evaporators have excellent corrosion resistance and can be used to obtain fresh water in a variety of environments(such as industrial wastewater,sea sand,water-containing wood residue,and sludge-containing water,etc.).