Hybrid NiAl layered double hydroxide: Characterization and in situ synchrotron XRD and vibrational spectroscopic studies under high-pressure

Abstract Anions from 2-aminoterephthalic acid (ATA), an aniline derivative, were intercalated into layered double hydroxide (LDH), and submitted to high-pressures by using a diamond anvil cell to access possible transformations of guest species in confined environment. The hybrid material, constituted by Ni2+ and Al3+ in a molar ratio equal to 2 (Ni2Al-ATA), was characterized by mass spectrometry coupled thermal analysis (TGA-DSC-MS), X-ray diffractometry (XRD) and vibrational spectroscopy (infrared and Raman) at ambient pressure. The response of Ni2Al-ATA to the pressure stimuli was monitored by in situ synchrotron XRD and in situ vibrational spectroscopies (infrared and Raman), during the compression-decompression cycle up to 14–16 GPa. XRD reflections related to (00l) stacking planes of hybrid material presented broadening and intensities decreasing, pointing out a pressure-induced amorphization. XRD profile of Ni2Al-ATA was not recovered after decompression, indicating that the structural modification promoted by the pressure to the inorganic matrix is irreversible. In-situ vibrational spectroscopy as a function of pressure revealed a minor modification in the spectrum of ATA anion confined into LDH (for example, the Raman intensity decreasing (without shift) of the 1612 cm−1 band). Spectral features were recovered after the decompression, suggesting no decomposition or reactivity of the organic guest species between the LDH layers. On the other hand, Raman spectrum of 2-aminoterephthalic acid (non-intercalated) changed expressively during the decompression step and sample become completely luminescent at 1.7 GPa and at ambient pressure. Probably LDH decreases the guest reactivity by a steric blockage imposed by ATA arrangement in the confined environment, which can improve the guest stability submitted to high-pressure stimulus.