In situ XRD reveals terephthalate incorporation and phase evolution during reconstruction of zinc/aluminium and magnesium/aluminium layered double oxides under open air

This study examined the reconstruction of calcined layered double oxides, a widely used route for introducing bulky organic anions into layered double hydroxides. The timing of guest participation during initial layer reformation or later anion exchange remains unclear. This question is particularly relevant to practical open air processing, where atmospheric carbon dioxide introduces carbonate as a competing species that can redirect the reconstruction pathway. In this study, terephthalate (TPA) was used as a model dianion to compare zinc/aluminium (ZnAl) and magnesium/aluminium (MgAl) systems under stirred and static contact. Time resolved synchrotron X-ray diffraction (XRD), supported by ex situ XRD, attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy, and quantification of recoverable TPA, revealed distinct phase sequences. ZnAl rapidly developed a TPA expanded layered phase, while carbonate associated ordering became detectable when solution renewal was restricted. MgAl reconstructed more slowly, first forming carbonate associated ordering and developing the TPA expanded phase only at later times. Under nitrogen protection or after mild nitric acid pretreatment, the TPA expanded reflections appeared earlier in the MgAl system. These results identify the early period of layer reformation as the critical stage for bulky guest access and phase selection. They further show that host system, precursor condition, carbonate availability, and local transport shape the accessible reconstruction pathway. The findings provide practical guidance for promoting bulky functional anion incorporation during simple open air reconstruction in carbonate containing environments.