Effect of relative humidity on the interlayer spacing of phosphate intercalated Mg, Al layered double hydroxide (hydrotalcite-like) crystals

The availability of water and the type of interlayer anions present affect the arrangement and interlayer spacing of layered double hydroxide (LDH). A systematic study of the effect of relative humidity (RH) on the basal spacing of phosphate intercalated, magnesium aluminum LDHs (MgAl–PO₄ LDH) was conducted, confirming that MgAl-PO₄ LDH exhibit distinct interlayer spacing corresponding to separate low- and high-hydration states produced when exposed to low and high humidity conditions. The transition from the low- to high-hydration form begins when RH exceeds 33% and is accompanied by the transition from one to two interlayers of water. An improved understanding of the effect of RH on MgAl–PO₄ LDHs will enable more accurate atomistic modeling and experimental characterization of MgAl–PO₄ LDHs and may lead to improvements in the tunability of MgAl-PO₄ LDHs for commercial applications such as slow-release fertilizer.