Study On The Preparation And Property Tuning Of Visible-Infrared Functional Materials Based On The 4A Zeolite

With the rapid development of new optical detection technologies,traditional camouflage materials have become easy to detect and identify.For the purpose of resisting the infrared and hyperspectral detection,the development of corresponding radiative cooling materials and bionic vegetation materials has become of great significance for improving the camouflage level.In this work,we take the 4A zeolite as the research material.First,we studied its spectral reflectance formation mechanism and radiative cooling performance.Further,a dark cooling coating based on ultramarine blue was prepared by doping chromogenic groups into the pores of the zeolite.Finally,ultramarine green was prepared based on 4A zeolite and was applied to simulate the spectrum of green vegetation.Overall,we believe this paper has important reference value for promoting the application of zeolite materials in the field of optical and infrared camouflage.First,we studied the spectrum’s forming mechanism of the zeolite and the radiative cooling characteristics of 4A zeolite.By studying the influence of the pore size and heat treatment on the spectrum of the zeolites,it was found that the zeolites’adsorption capacity for water is the key to with regard to affecting the near-infrared spectrum.Then,we synthesized the 4A zeolite by low temperature hydrothermal method,and analyzed the effects of crystallization temperature and crystallization time on its spectrum.By comparing the 4A zeolites going through a heat treatment at 600-1000℃,it was found that after heat treatment of 800℃（4A-800）,the structure of 4A zeolite changed from LTA to Low-carnegieite Na Al Si O₄,while its reflectivity in solar spectral band increased from 89%to 92%,and the emissivity in infrared band decreased from 0.95 to 0.86.Then,we prepared the radiative cooling coating by using 4A-800 as the functional material and PVDF as the film-forming material.The cooling effect of 4A-800 coating was tested with a home-made device.The results showed that the temperature of the device coated with a 4A-800 coating can be 4℃lower than that of the Ti O₂coating.Compared with the 4A zeolite coating,the temperature of the 4A-800 coating can be dropped by 2°C at most.At night,the temperature of the 4A-800 coating is 5°C lower than ambient.Ultramarine blue pigments with high near-infrared reflectivity were prepared by doping sulfide ions into the cages of 4A zeolite,and the cooling performance of the ultramarine blue coating was tested.Firstly,we analyzed the chromogenic mechanism of doping the sulfide ions into the cage structure of zeolite.S₂^-and S₃^-groups were the main factors affecting the color of synthetic ultramarine blue.Then we synthesized the ultramarine blue pigment based on the 4A zeolite,and analyzed the influence of Na₂CO₃content on the color and spectrum of the sample.With the increase of the Na₂CO₃,the color of ultramarine change from yellow to green,and finally to blue.When the mass fraction of Na₂CO₃in the raw material was 8.7%,the average reflectivity of the ultramarine blue in the near-infrared band reached 88.1%.Afterward,the thermal stability of the synthetic ultramarine blue was tested by TG-DSC,and it was found that the CIE parameters of the synthetic ultramarine blue changed little after treatment at 800°C for 2 h.Its L*value decreased by 1.3,a*value increased by 2.5,and-b*value increased by 3.5.Finally,based on the synthesized ultramarine blue pigment,an ultramarine blue coating with high near-infrared reflectivity was prepared and its cooling effect was tested.The temperature of the synthesized ultramarine blue coating can be dropped by 2℃when compared with the commercial ultramarine blue coating.We simulated the solar spectral reflection characteristics of green vegetation based on the ultramarine green pigment.Firstly,we studied the spectral characteristics of green vegetation,and it can be summarized as:the green peak near 550 nm,the“red edge”near 700 nm,the“near-infrared plateau”in the 780-1100 nm band,and the water peaks at wavelengths of 1450 nm and 1930 nm.Then,the Orthogonal experiment was designed and the experimental conditions for preparing the ultramarine green pigment were optimized as follows:holding time 2 h,temperature 800℃,mass fraction of Na₂CO₃is 1.5%.Secondly,bionic leaves were prepared by setting the ultramarine green as the green pigment,PVDF as the film-forming material and Li Cl as the hygroscopic agent,and their optical constants were calculated according to the four-flow model.It was found that the ultramarine green pigment mainly affected the spectrum in the ultraviolet-visible band,while Li Cl mainly affected the spectrum in the near-infrared band.It was determined that the optimal mass fractions for preparing bionic leaves was28.6%ultramarine green and 9%lithium chloride respectively,in which case the spectral similarity coefficient between the obtained bionic leaves and the Scindapsus aureus leaves reached 0.91.Finally,the relevant application characteristics of the bionic leaves were studied.After 48 h treatment in a simulated tropical rain forest environment（The humidity was 90%and the temperature was 30℃）,the spectral similarity coefficient of bionic leaves increased to 0.94.In addition,by analyzing the surface hydrophobic properties of the bionic leaves（The contact angle was 82.94°）and carrying out the infrared radiation temperature test（The temperature difference between the leaves and the Scindapsus aureus leaves was less than 0.5 after being placed outdoors for 4 h）,it was found that the bionic leaves prepared based on ultramarine green had great potential in simulating green vegetation spectrum.