Inclusion/energy transfer/release of L-ascorbate in the interlayer gallery of layered yttrium hydroxide

Abstract

L-ascorbate (AS, Vitamin C) was intercalated into the interlayer gallery of layered yttrium hydroxide (LYH), a representative member of the layered rare earth hydroxide series (LRHs), through an ion-exchange reaction in an aqueous solution of sodium ascorbate. Based on the expansion of the interlayer space of the resulting AS-LYH hybrid, it is suggested that AS anions vertically oriented to hydroxide layers would be arranged to form a partially interdigitated bilayer in the interlayer space of LYH with a high loading capacity and density of AS. This arrangement is different from the antiparallel monolayer configuration of AS anions that are horizontally or vertically oriented to the layer of classical layered double hydroxides (LDHs). The durability of AS against light and oxidation was sufficiently enhanced in the interlayer gallery of LYH so that no degradation occurred after exposure to simulated sunlight or heating at 60 °C for a long time. Practically no release of AS from AS-LYH was observed in a saline solution and simulated sea water, whereas a sustained release of AS occurred selectively in a phosphate buffer solution, with a release process best described by the first-order model. When LYH was doped with Tb3+ activator to give it photoluminescence ability, the UV light energy absorbed for the π → π* transition of AS was efficiently transferred to Tb3+, leading to strong green emission attributed to its 5D4 → 7F5 transition.