Controllable Preparation And Selective IR Absorption Properties Of Large-Sized Layered Double Hydroxides

Sunlight is the primary source of energy of life on Earth, and infrared is the major component of the solar spectrum. Infrared provides energy for life and is of great significance for the continuation of life. The wavelength of infrared between 8～14 μm is called life ray, which can enhance human immunity, and plays an important role in plant growth. Therefore, research on the infrared selective absorption material is of great significance.Layered double hydroxides (LDHs) are a class of anionic clays and the laminar structure of LDHs and high charge density of their sheets are responsible for their anionic exchange and intercalation abilities which give them extremely varied potential technological applications in fields such as infrared absorption. It should be possible to take advantage of their anionic exchange ability to incorporate anions which have strong infrared absorption in the required range. LDHs is a kind of green environmental friendly material, accord with the requirement of the state environmental protection department for environmental protection. According to the law of Mie, the particle size of material has an important influence on the infrared absorption except for the chemical composition and chemical structure. Hence, to study the effect of material particle size on the infrared absorption is necessary. The results are as follows:(1) Large-sized MgAl-CO3-LDHs is prepared by using the homogeneous precipitation method. MgAl-CO3-LDHs strongly absorb infrared radiation in the range 7～14μm, which has the largest infrared extinction coefficient(IEC) value 0.122 m2·g-1 at the diameter of 7.5 μm. Sodium stearate is used as surface modification agent for modification of LDHs, and the IEC value is 0.132 m2·g-1 after modification steps. The IEC value of LDHs prepared by engineering experiments is 0.130 m2·g-1. The change rule of particle size is that the proportion of precipitation agent and concentration is inversely proportional to the particle size, on the other hand when the HMT as precipitant the diameter increased twice its size than that HMT/Na2CO3 as precipitant. According to the data of LDHs, growth mechanism are discussed in this paper which explains the rules of the hexagonal platelet shape and irregular hexagonal platelet shape.(2) Large-sized MgAl-H2PO4-LDHs was synthesised by ion exchange method, and H2PO4- was intercalated into the interlayer spacings of MgAl-CO3-LDHs. Sodium stearate is used as surface modification agent for modification of LDHs, and the IEC value between 7～14 μm is 0.143 m2·g-1 after modification steps. The IEC value of LDHs prepared by engineering experiments is 0.139 m2·g-1(3) LDHs@C composites infrared absorption material is based on MgAl-CO3-LDHs and graphite. MgAl-CO3-LDHs sheet structure grow on the graphite surface and cross section, and the section is coated with LDHs. The infrared extinction coefficient of Obtained LDHs@C composites in 1500～700cm-1 range is 0.140 m2·g-1 greater than that of MgAl-CO3-LDHs’ 0.132 m2·g-1. LDHs@C composites have good insulating performance.