Regeneration mechanism, modification strategy, and environment application of layered double hydroxides: Insights based on memory effect

Layered double hydroxides (LDHs), are ideal inorganic materials for versatile fields, such as catalysis, energy, and medicine. Memory effect means the ability of reconstruction into their initial structure after decomposition treatment for some special materials. Based on the unique property, the layered structure can be regenerated from the calcined LDHs (layered double oxide, LDO) in an aqueous solution or moist air. This effect provides a new paradigm for modification of LDHs, increasing the abundance of active sites in LDHs as well as preserves original active sites for multifunctional environmental applications. Therefore, this review summarizes the memory effect of LDHs from basic mechanisms to real applications. Firstly, various kinds of active sites on LDHs/LDOs and the importance of sites structure are concluded. Secondly, the modification methods of LDHs are briefly introduced and the characteristics of memory effect are summarized. Then, the mechanism of chemical reaction, topology, and thermodynamics of memory effect are discussed as well as the microscopic mechanism of memory effect through theoretical chemical calculation. The influencing factors and applications in environmental remediation are also presented. Finally, the challenges and prospects of memory effect-based LDHs are proposed. We hope the review could open a new path for the environmental application of memory effect-based LDHs.