Synthesis and characterisation of layered double hydroxides with varying divalent metal cations: Mg2+, Zn2+, Ca2+

Abstract

This study aims to investigate the physicochemical properties of layered double hydroxides (LDH) with different divalent metal (M2+) cations. A series of nitrate-based LDH materials was synthesised by using aluminium (Al3+) as a trivalent cation (M3+) with varying M2+ cations such as magnesium (Mg2+), zinc (Zn2+), and calcium (Ca2+) ions to prepare magnesium–aluminium-layered double hydroxide (MgAl-LDH), zinc–aluminium-layered double hydroxide (ZnAl-LDH), and calcium–aluminium-layered double hydroxide (CaAl-LDH), respectively. MgAl-LDH and ZnAl-LDH were synthesised by the co-precipitation method, whereas CaAl-LDH was prepared by the hydrothermal method. The samples were characterised by powder X-ray diffraction (PXRD), Fourier transform infrared spectra (FTIR), thermogravimetric and differential thermogravimetric analysis (TGA/DTG), field emission scanning electron microscope (FESEM), and accelerated surface area and porosity (ASAP) analysis. The PXRD patterns show that MgAl-LDH (9.8 Å) had the greatest interlayer spacing, followed by ZnAl-LDH (8.9 Å), and CaAl-LDH (8.7 Å). The FTIR spectra clearly confirms the presence of nitrate ions in the LDH structure. Two-step degradation behaviour of the samples was observed in the TGA curve. The LDHs exhibit Type IV isotherms and hexagonal structures were observed on the FESEM images.