Micrometer-sized dihydrogenphosphate-intercalated layered double hydroxides: synthesis, selective infrared absorption properties, and applications as agricultural films.

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 (CO-LDH) precursors of sizes ranging from 1.32 μm to 8.64 μm by simply adjusting the feeding Mg concentration from 0.80 mol L to 0.20 mol L. From these pristine LDH materials, μm-sized dihydrogenphosphate-intercalated LDHs (HPO-LDHs) were prepared by an anion-exchange method. The structure, the platelet size, and the associated selective IR absorption properties of the HPO-LDH and the derivative HPO-LDH/EVA composite as well as the related visible transmittance and the photostability of the HPO-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 HPO-LDHs and HPO-LDH/EVA composites depends on the corresponding number-averaged particle size of HPO-LDH in the range of 2.01 μm to 8.80 μm. Compared with EVA, the HPO-LDH/EVA composites demonstrate a significant improvement of selective IR absorption, while maintaining acceptable visible transmittance, and similar photostability. An optimized particle size of HPO-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.