Preparation Of Mixed Dimensional Clay-based Photothermal Conversion Film And Their Solar Interfacial Evaporation Performance

As a new technology for obtaining freshwater resources,solar interface evaporation technology has gained rapid development in recent years,which evaporators prepared from various materials have been applied in solar interface evaporation technology.However,all these materials have problems such as high cost,high energy consumption for preparation,salt deposition during long operation and organic dye contamination of materials,which limit the application of solar interface evaporation technology.Therefore,the development of the preparation process is simple,green,high evaporation rate,high photothermal conversion efficiency of photothermal conversion materials,which applied to the solar interface evaporator upper layer of the absorption layer of the film material has become a research hot spot in recent years.Mixed-dimensional clay（MD-clay）is an inorganic non-metallic material composed of a variety of clays such as one-dimensional attapulgite,two-dimensional montmorillonite,illite and illite-montmorillonite mixed layer.The low thermal conductivity can effectively reduce the heat loss of photothermal conversion,and the acid and alkali resistance is also better than synthetic materials and biomass materials.In this paper,three kinds of photothermal conversion film were prepared by adding polypyrrole（PPy）,reduced graphene oxide（r GO）and MXene,using cheap mixed-dimensional clay as raw material,polyvinylidene fluoride（PVDF）and polyvinyl alcohol（PVA）as base film.The surface of polypropylene plastic foam（PP）was coated with hydrophilic gauze as the lower insulation layer of the evaporator,and the photothermal conversion film as the upper absorption layer of the evaporator.A solar evaporator with double-layer structure was prepared,and its solar interfacial evaporation performance and salt resistance in high concentration brine were studied.The main research elements and conclusions are as follows:（1）The 2D-clay was modified by polyaniline intercalation method,which was added into the PVDF casting solution.After polyvinylpyrrolidone（PVP）cross-linking the casting solution to make holes,the base film was formed by spinning the casting solution,which 2D MD-clay photothermal conversion film（PPy/PANI/MD-clay）was prepared by spraying PPy.A water droplet was completely infiltrated on the PPy/PANI/MD-clay film surface within 1.5 s;the strain at break was 5.6%at a tensile strength of 1.1 MPa;and the PPy/PANI/MD-clay film had a low thermal conductivity(0.0999 W m^-1 K^-1).The evaporation rate and energy conversion of the PPy/PANI/MD-clay evaporator were 1.4754 kg m^-2 h^-1 and 93.6%under a standard simulated solar(1k W m^-2)irradiation.The evaporation rate of the PPy/PANI/MD-clay evaporator in 15%Na Cl solution within 6 h was not significantly different from that of pure water,and0.2 g Na Cl was completely dissolved on the evaporator surface within 50 min,indicating that the prepared evaporator has excellent salt resistance and salt self-cleaning ability.At the same time,the PPy/PANI/MD-clay evaporator purifies simulated seawater with a concentration of major ions that meets prescribed drinking water standards,which has a good desalination capacity for seawater.（2）The r GO/MD-clay/PVA photothermal film was prepared by’salt-assisted’freeze-drying method after the composite of GO prepared by modified Hummers and mixed dimension clay was added into PVA casting solution.The r GO/MD-clay/PVA film has excellent photothermal conversion performance as GO is black after reduction by hydrazine hydrate,which is beneficial to light absorption.The r GO/MD-clay/PVA film has a low thermal conductivity(0.1574 W m^-1 K^-1)and excellent light absorption（～90%）in the wetted state,with a water droplet taking only 0.532 s to fully wet the surface of the r GO/MD-clay/PVA film.The evaporation rate of the prepared r GO/MD-clay/PVA evaporator was 1.5714 kg m^-2 h^-1 at 1 k W m^-2,with an energy conversion efficiency of 88.9%.In the experimental salt tolerance test,the energy conversion efficiency decreased by only 8%during the concentration of Na Cl solution from 0%to20%,while the ion concentration of the purified simulated seawater was tested to meet human drinking water standards,which has good potential for practical applications in seawater desalination.（3）The MXene/MD-clay/PVA film was prepared by self-assembly of modified mixed clay and MXene material into PVA casting solution using KH550 modified MD-clay as raw material.The MXene/MD-clay/PVA film has a low thermal conductivity(0.2406 W m^-1 K^-1);a breaking strain of 7.8%at the tensile strength of 0.7 k Pa;and a complete infiltration of a water droplet on the surface of the r GO/MD-clay/PVA film taking only 0.133 s.The prepared MXene/MD-clay/PVA evaporator showed an evaporation rate of 1.6026 kg m^-2 h^-1 at 1 k W m^-2 with an energy conversion efficiency of 91.7%,and the evaporation rate in 15%Na Cl solution was 1.4904 kg m^-2 h^-1.The MXene/MD-clay/PVA evaporator also achieved 97%removal of organic dyes in MB solution and has good purification capacity in industrial dye wastewater.