Preparation And Properties Of High Efficiency Solar Absorbing Coating

With the development of the industry and the rise of the low-carbon trend,the current energy structure needs to be adjusted and upgraded urgently.As a clean and abundant green energy,solar energy occupies a very important position in the new energy industry which products have penetrated into every aspect of people’s lives.Compared with photovoltaic applications of solar energy,solar thermal applications with broad-spectrum absorption can utilize solar energy more efficiently.The most widely used product among them should be solar collectors.As a high-efficiency light-to-heat conversion device,its core component is a dark absorbing plate equipped with a solar selective absorbing coating.Considering factors such as cost-effectiveness,operation process and commercial feasibility,the solar selective absorption coating of composite matrix resin and functional powder prepared by coating method is more popular in the market.However,problems such as the emission of organic solvents during the resin production process,the poor water and high temperature resistance of the resin,the immature preparation process of functional powders restrict the development of solar selective absorbing coatings to a certain extent.Based on this,this article starts from two aspects of matrix resin and functional powder to further optimize and improve the photothermal performance of the coating in outdoor scenes,aiming to obtain efficient solar selective absorption coating materials.The primary focus of the paper’s research is as follows:The first part:Synthesis and performance research of fluorine-modified UV-curable waterborne star polyurethane.Firstly,the fluorine-containing diol monomer（FMPG）was self-made by perfluorooctanoic acid（PFOA）and 2-amino-2-methyl-1,3 propanediol（AMPG）under the action of amidating reagent（EEDQ）;The addition reaction between the functional HDI trimer（HDT）and the difunctional diethanolamine（DEOA）synthesized a polyol（HDPO）containing six hydroxyl groups;the above two products were introduced into the polyurethane system.Combining main raw materials such as isophorone diisocyanate（IPDI）,HDPO,polycarbonate diol（PCDL）,FMPG,dimethylolpropionic acid（DMPA）and pentaerythritol triacrylate（PETA）to synthesize a series of fluorine Modified UV-curable star-shaped waterborne polyurethane（WFPU）,and then explored the effect of FMPG content on the performance of waterborne polyurethane.The research results indicate that the introduction of fluorine-containing side chains FMPG has significantly improved the water resistance drawback of waterborne polyurethane coatings.The water contact angle of the coating film has increased from 70.2°to 101.5°and the water absorption rate（soaked in water for 24 hours）has decreased from 15.80%.to 6.1%.Smaller fluorine atoms have little effect on the light transmittance of the coating,and the light transmittance of a series of coatings with different FMPG content is above 90%,which can be adapted to the use of solar coating resins.The incorporation of FMPG content was observed to lead to a decrease in the rate of thermal weight loss for the material,this trend indicates that the introduction of fluorine modification can enhance the material’s thermal stability to some extent.Both adhesion and tensile properties are improved.After considering factors such as water resistance,light transmittance,thermal stability and storage stability of the coating,8%FMPG is selected as the optimal addition amount.In this case,the overall performance of the coating is the best,which can meet the requirements of the resin part of the solar absorbing coating material.The second part:Preparation and properties research of metal-doped Fe Cu Mn O_x solar energy selective absorption powders and corresponding coatings.With Cu（NO₃）₂·3H₂O,Mn（NO₃）₂·4H₂O,Fe（NO₃）₃·9H₂O,Cr（NO₃）₃·9H₂O,Co（NO₃）₂·6H₂O,Ni（NO₃）₂·6H₂O and Na OH as the main raw material,a series of metal（Cr,Co,Ni）doped Fe Cu Mn O_x quaternary transition metal oxide absorption powders were prepared by co-precipitation calcination method.using the polyurethane prepared in the first part as a film-forming agent,a series of solar selective absorbing coatings were prepared by spraying method.It was determined that Cr would be the most suitable metal for doping,and additional experiments were conducted to investigate the impact of varying levels of Cr doping and calcination procedures on the coating’s properties.The research results show that when the doping content of Cr is higher than 10%,the amount of Cr in the spinel structure will reach saturation.When the molar ratio of Cr,Fe,Cu and Mn is 0.5:1:3:3,the coating has the highest solar absorption rate（α_s）which is 95.94%.The calcination temperature and calcination time will affect the powder morphology.As the calcination temperature and time increase,the octahedral shape and size of the powder become more obvious.The powder coating prepared by calcination at 600℃for 3 hours has the best solar absorption performance.In such a case,the emissivity（ε_T）of Cr Fe Cu Mn O_x coating is24.31%,the quality factor（α_s/ε_T）reaching a maximum of 3.95,and the final stable temperature is 83.5℃under the solar simulator.The third part:Preparation and properties research of Mo S₂@Cr Fe Cu Mn O_x solar absorption powders and corresponding coatings.Using ammonium molybdate tetrahydrate and thiourea as raw materials,petal-shaped Mo S₂ absorbing powder was prepared by hydrothermal calcination method.With the help of highly adhensive polydopamine,Mo S₂@Cr Fe Cu Mn O_xwas prepared by loading previously synthesized Cr Fe Cu Mn O_x on Mo S₂.Through optimizing the reaction p H,calcination process,doping PDA and changing the loading content of Cr Fe Cu Mn O_x,a series of solar selective absorbing coatings were prepared by spraying the polyurethane prepared in the first part as a film-forming agent.The findings indicate that when contrasted with the single Cr Fe Cu Mn O_x coating,Mo S₂@Cr Fe Cu Mn O_x has better solar energy absorption efficiency in the 300-2000 nm of solar spectrum,and the modified material reduces its own optical band gap,which is beneficial for the absorption of spectra and increase the concentration of free electrons in the material,thereby promoting the material’s photothermal conversion performance.When the calcination temperature is 260°C and the calcination time is 3h can achieve the purest Mo S₂.When the p H of the reaction system is 2,the spatial morphology of the powder is the most complex and diverse,its structure can perform multiple diffuse reflections on light which can enhance the ability to absorb light.Tetramethylpiperidinium oxide（TEMPO）doped PDA can use the method of constructing donor-acceptor pairs to reduce the band gap of the material to enhance the light absorption ability,under the doping of 20%TEMPO,the solar absorption rate of the coating can reach96.95%.The Mo S₂@Cr Fe Cu Mn O_x absorption coating with 40%Cr Fe Cu Mn O_x content has the best light-to-heat conversion effect,and finally reaches a stable temperature of 86.3°C under the solar simulation device.