Insights into memory effect mechanisms of layered double hydroxides with solid-state NMR spectroscopy

The memory effect of layered double hydroxides (LDHs) plays a critical role in their applications, yet the details of the mechanism are still under debate. Here authors reveal the nature of the memory effect with ex situ and in situ solid-state NMR spectroscopy. Layered double oxides (LDOs) can restore the parent layered double hydroxides (LDHs) structure under hydrous conditions, and this memory effect plays a critical role in the applications of LDHs, yet the detailed mechanism is still under debate. Here, we apply a strategy based on ex situ and in situ solid-state NMR spectroscopy to monitor the Mg/Al-LDO structure changes during recovery at the atomic scale. Despite the common belief that aqueous solution is required, we discover that the structure recovery can occur in a virtually solid-state process. Local structural information obtained with NMR spectroscopy shows that the recovery in aqueous solution follows dissolution-recrystallization mechanism, while the solid-state recovery is retro-topotactic, indicating a true memory effect. The amount of water is key in determining the interactions of water with oxides, thus the memory effect mechanism. The results also provide a more environmentally friendly and economically feasible LDHs preparation route.

Automated summary

In this study, the authors investigate the memory effect mechanism of layered double hydroxides (LDHs) using solid-state NMR spectroscopy. They discover that the structure recovery can occur in a virtually solid-state process, providing a more environmentally friendly and economically feasible preparation route for LDHs.