Preparation Of Photothermal Conversion Film Of Polyaniline/Polyurethane Sponge And Its Application In Interfacial Evaporation

When using solar energy for photothermal conversion,the desire to obtain highphotothermal conversion efficiency depends not only on the properties of the material,but also on the structure of its surface.Therefore,the development of a structure that facilitates light absorption is the focus of this paper.Polyurethane sponge（PU）has a large specific surface area and stable physical and chemical properties,and its unique porous structure makes it different from other conventional water treatment materials.Therefore,polyaniline（PANI）is considered as the basis of this paper because of its high photothermal conversion efficiency and low thermal conductivity.The polyurethane sponge was modified by using polyaniline,and the water supply was carried out by attaching black polyaniline to the sponge skeleton for restricted domain capillary action to improve the hydrophilicity of the polyurethane sponge and increase its evaporation efficiency.The first step is to improve the evaporation efficiency of polyurethane sponges.The polyaniline/polyurethane sponge photothermal conversion film material（MPANI）was prepared by depositing polyaniline onto a three-dimensional structured polyurethane sponge using the impregnation method,as well as exploring its application in solar interfacial evaporation.The experimental results show that the average absorbance of the original sponge is 0.33.When the concentration of polyaniline is 0.6 g,the average absorbance of the film is 1.04,which is 3.14 times that of M0.The average membrane surface temperature could reach 58.3°C,the evaporation rate could reach 1.1 kg·m^-2·h^-1and the solar-vapour conversion efficiency reached 52.8%.After 20 cycles,the evaporation efficiency of the membranes was above 1.01 kg·m^-2·h^-1,but with the appearance of salt crystals.The experimental results can show that the MPANI membrane prepared by the impregnation method has the function of photothermal conversion.Then,to further improve the photothermal conversion performance,the polyaniline/polyurethane sponge film material（NPANI）was made by changing the method and using non-solvent-induced phase separation（NIPS）.Its systematic study was carried out by SEM,EDX,FTIR,XRD and water contact angle.The results showed that the average absorbance of the film at a concentration of 1.86 g was 4.27 times that of the original.Under one sunlight,the evaporation rate of the membrane was 1.38 kg·m^-2·h^-1,and the solar energy conversion efficiency was 67.1%.The evaporation efficiency remained at 1.12 kg·m^-2·h^-1after 20 cycles were carried out,and the surface salt precipitation after 20 h was less than that of the M2 membrane,which had high stability and high evaporation performance.Finally,polyaniline/polyurethane sponge membrane materials were modified for salt resistance using polydimethylsilane（PDMS）.The effect of the concentration of PDMS on the membrane was investigated.It was shown that the water contact angle of the membranes gradually increased with increasing concentration of the added PDMS compared to the modified membranes without PDMS,with a maximum water contact angle of 138.8°.The difference in solar energy absorption capacity was not significant.The evaporation rate of the membrane reaches 1.39 kg·m^-2·h^-1at a PDMS concentration of 1.5g.After 20 cycles,the evaporation rate of the membrane can be maintained between 1.03kg·m^-2·h^-1and 1.28 kg·m^-2·h^-1,and the retention rate can still be maintained above 99.9%.The amount of surface salt deposition is greatly reduced and is smaller than the amount of salt deposited on the surface of the N4 membrane,with only a small percentage occurring at the edges.This indicates that the introduction of PDMS has successfully improved the salt resistance of the membrane.