Micrometer-sized dihydrogenphosphate-intercalated layered double hydroxides: synthesis, selective infrared absorption...

High-performance heat-retention agents for multifunctional green agricultural films are today largely suitable to increase the production yield as well as to save energy. Here, an adapted ammonia releasing hydrothermal method was used to produce a series of micrometer-sized carbonate-layered double hydroxide (CO₃-LDH) precursors of sizes ranging from 1.32 μm to 8.64 μm by simply adjusting the feeding Mg²⁺ concentration from 0.80 mol L^-1 to 0.20 mol L^-1. From these pristine LDH materials, μm-sized dihydrogenphosphate-intercalated LDHs (H₂PO₄-LDHs) were prepared by an anion-exchange method. The structure, the platelet size, and the associated selective IR absorption properties of the H₂PO₄-LDH and the derivative H₂PO₄-LDH/EVA composite as well as the related visible transmittance and the photostability of the H₂PO₄-LDH/EVA film were investigated. The results show that the selective IR absorption in the wavelength range of 7-14 μm enabling the heat retention of the H₂PO₄-LDHs and H₂PO₄-LDH/EVA composites depends on the corresponding number-averaged particle size of H₂PO₄-LDH in the range of 2.01 μm to 8.80 μm. Compared with EVA, the H₂PO₄-LDH/EVA composites demonstrate a significant improvement of selective IR absorption, while maintaining acceptable visible transmittance, and similar photostability. An optimized particle size of H₂PO₄-LDH of ca. 5.85 μm leads to 60% selective IR absorption and 64% selective IR absorption when dispersed in EVA, while the polymer free of filler exhibits less than 50% absorption in the 7-14 μm IR domain.