Study On The Preparation Of Simulation Material Of Green Vegetation Spectrum By The Organic Anions Intercalated LDHs

The rapid development of new reconnaissance technology represented by hyperspectral remote sensing imager has brought great challenges to optical camouflage technology since the1980s.The core of hyperspectral remote sensing technology is using the slight difference between the target and the background in the visible light and near infrared?VIS-NIR?band spectra to detect and identify the target,which makes it difficult for the existing optical camouflage materials to compete with it.In this paper,the layered double hydroxide?LDHs?which rich in hydroxyl groups and water molecules was used as the matrix material.And then the controllable regulation of the VIS-NIR spectral reflectance was realized through adjusting electronic structure and intercalated layer board anionic organic pigments and other methods based on the mechanism of VIS-NIR spectra of natural green vegetation.Preparing LDHs pigment which have high spectral similarity with natural green plants.in order to be applied in camouflage coating for confronting hyperspectral reconnaissance.Specific research work includes:First of all,the colored M²⁺,M³⁺metal cations are introduced in the layer board for curbing high reflection in visible light spectrum of MgAl-LDHs,so as to enhance the visible light absorption and change the sample color through regulating the electronic structure of materials.Meanwhile,the influence of the LDHs layer board cations(M²⁺/M³⁺)type and ratio on the structure and optical properties are studied.The results show that the color of LDHs can be significantly changed by assembling the colored cations into its laminate.However,the electron transition absorption of some colored cations(such as Fe³⁺and Ni²⁺)significantly enhanced the spectral absorption intensity of band 800¹350 nm,it result in the spectral similarity with green vegetation in near-infrared band reducing at the same time.In contrast,the MgCr-LDHs sample has a typical spectral shape similar to green vegetation,but there are some differences in the location and intensity of these spectral features.On the other hand,when the ratio of cations(Mg²⁺/Al³⁺)is in the range of 2 to 4,the change of spectral properties of the products is mainly related to the purity of LDHs.Secondly,the influence of hydrothermal processing parameters such as crystallization temperature,crystallization time and pH on material composition,morphology,color and VIS-NIR spectral characteristics was systematically studied.The results show that increasing the crystallization temperature and prolonging the hydrothermal time could increase the particle size,the layered structure was more orderly at the same time,which result in the increase of the product reflectivity in the whole near-infrared band.In contrast,the particles prepared at a lower crystallization temperature have an obvious agglomeration phenomenon,which increases the content of physically adsorbed water in the samples,thus the intensity of the spectral absorption peak in the near-infrared band is enhanced.On the other hand,the crystallinity and crystal structure parameters of the product changed little when the pH value was set between 9 and 12,and there was no significant influence on the intercalation efficiency and spectral absorption effect of organic pigments.Afterwards,in order to further increase the similar degree of spectra between the sample and natural plant based on the interlayer anion exchange property of LDHs,the effect of the interlayer colored anions on the structure and optical properties of MgAl–LDHs is studied.The color of samples is continuous controlled from blue to green within the scope of regulation through reasonably selecting organic pigment types and optimizing the concentration and ratio of intercalated anions.The VIS-NIR spectra of Organic-LDHs samples and natural green plants can get to 97.2%.Finally,the thermal decomposition behavior of Organic-LDHs is studied,and the correlation between material components and VIS-NIR spectra was preliminarily analyzed to explore the fine regulation method of VIS-NIR spectra.Spectral absorption in visible light band is mainly influenced by interlayer organic pigments.And the absorption characteristics in near-infrared band are determined by physical adsorption water,interlayer crystallinity water and lamellar hydroxyl.The XRD and FT-IR test results show that LDHs could maintain the original phase structure at 300°C with only a small part water molecules losing,so as to the spectral characteristics are not changed significantly.However,the absorption peak in the near-infrared band of LDHs was significantly reduced which due to the removal of interlayer water and hydroxyl groups after the heat treatment at 400⁶00°C.It is also found that the intercalation of organic anions can improve the temperature resistance of LDHs matrix structure.