Preparation Of Super-infiltrating Porous Materials And Its Photothermal Conversion Properties

Pollution-free and efficient solar desalination is of great significance to alleviate the traditional energy crisis,reduce water pollution and promote environmental protection.However,as the core component of solar steam generation system,there are still many complex challenges in the actual operation of the existing photothermal materials,such as low photothermal conversion efficiency,high raw material cost,tedious preparation process and so on.Thus limiting its large-scale commercial application.In view of the low energy efficiency,the current academic research is mainly focused on improving the light absorption of photothermal materials evaporated at the solar interface,reducing heat loss and optimizing water supply so as to further improve the water vapor production rate and solar energy conversion rate.Combined with the above situation,the main purpose of this study is to develop new and efficient solar interface evaporation photothermal materials,and the focus of the research is to regulate the surface wettability of porous photothermal materials.In order to achieve water transport optimization and improve solar energy conversion efficiency.At the same time,in the preparation of photothermal materials and the selection of substrates,the compression cost is considered and the process is simplified to facilitate large-scale application.Specifically,in this paper,using commercial polyurethane sponges and prepared manganese dioxide nanowires as substrates,two new types of super-infiltrating solar interface evaporation photothermal materials were prepared according to different methods,and a series of factors affecting the solar vapor efficiency of photothermal materials were studied systematically.The research results not only provide a new research idea for the preparation of super-infiltrating photothermal materials in the future,but also provide a new way for the design and optimization of solar interface evaporation photothermal conversion system.The main contents and conclusions of this paper are as follows:?1?Based on the commercial polyurethane sponge,three kinds of solar photothermal steam generation systems with double-layer structure were designed and prepared by simple one-step impregnation method:the top layer was coated with graphite powder modified by polydimethylsiloxane,the top layer was coated with silver nanoparticles with the size of 5-6nm,and the top layer was etched with nitric acid and then attached silver nanoparticles as photothermal conversion layer,The th ree photothermal conversion layers all show a strong absorption of more than 80%of the solar spectrum,while the lower layer is a polyurethane sponge hydrophilically treated with concentrated sulfuric acid and ammonium persulfate,in order to continuously transport water molecules upward and prevent the heat absorbed by the top layer from losing to the water body(the thermal conductivity of the polyurethane sponge in the wet state is 0.13882 W m^-1 K^-1).In addition,the coated graphite powder has strong hydrophobicity?the water contact angle is about 148°?due to the treatment of polydimethylsiloxane,so that the photothermal conversion layer can float on the water surface,which can further reduce the heat loss and benefit the practical application.The results show that based on the inherent porous structure of the polyurethane sponge,its low thermal conductivity,and the rapid transmission of water molecules after hydrophilic treatment,it is coated with polydimethylsiloxane under 1 kW m^-2 sunlight.The energy conversion efficiency of the graphite powdered polyurethane sponge is73.3%,which is much higher than that of the untreated polyurethane sponge?energy conversion efficiency is 36.0%?.In addition,four different thicknesses of polyurethane sponges under different light intensities are also studied.Energy conversion efficiency to explore the effect of bottom thickness on final efficiency.The energy conversion efficiency of the polyurethane sponge with silver nanoparticles on the surface and the polyurethane sponge with silver nanoparticles after etching is 65.3%and 69.2%,respectively,under the solar light intensity of 1 kW m^-2.There have been few reports on the application of polyurethane sponges to solar light and heat-driven steam generation through surface treatment,and the prepared samples have good stability.No significant change in energy conversion efficiency was observed even after long-term immersion in water.?2?Firstly,the prepared manganese dioxide nanowires were modified by s uper-hydrophilicity,then doped with graphene oxide,reduced by hydrazine hydrate steam,and freeze-dried to form an integrated aerogel block.Then polypyrrole was in-situ coated on the aerogel surface to construct a photothermal conversion layer,so as to achieve efficient solar photothermal steam production.The analysis of the internal morphology and porosity of the aerogel shows that the internal pore size of the aerogel is staggered,thus showing a lower density(0.127 g cm^-3)and a larger specific surface area(1142.7 m² g^-1).At the same time,it also endows itself with good thermal insulation properties(low thermal conductivity of 0.21882 W m^-1 K^-1 in wet state),self-floating and fast water transport.Thanks to the polypyrrole coating on the surfac e,the aerogel shows nearly 100%super light absorption to the solar spectrum.After the introduction of super-hydrophilic manganese dioxide nanowires,the overall wettability of the aerogel was greatly improved,and the addition of the nanowires also enab led the aerogel to maintain a certain mechanical strength?the compressive strength was0.08 MPa at 30%deformation?,thus improving the chance of survival in a harsh environment.Combined with the above advantages,the energy conversion efficiency of our aerogel under 1 kW m^-2 sunlight is 93.8%,which is 4.9 times higher than that of pure water?19.1%?under the same light conditions.In addition,the aerogel also showed excellent salt isolation ability and treatment ability to dye wastewater,as well as excellent stability,and its energy conversion efficiency remained almost unchanged in ten consecutive tests.