Synthesis and characterisation of aqueous miscible organic-layered double hydroxides

Abstract

We report the synthesis and characterisation of a new family of layered double hydroxides entitled Aqueous Miscible Organic Layered Double Hydroxide (AMO-LDH). AMO-LDHs have the chemical composition [M^z+_1−xM′^y+_x(OH)₂]^a+(Xⁿ⁻)_a/r·bH₂O·c(AMO-solvent) wherein M and M′ are metal cations, z = 1 or 2; y = 3 or 4, 0 < x < 1, b = 0–10, c = 0–10, X is an anion, r is 1–3 and a = z(1 − x) + xy − 2. The role of the AMO-solvents such as acetone (A) or methanol (M) in the LDH synthesis is discussed. The distinguishing features between AMO, and conventional or commercial LDHs are investigated using X-ray diffraction, infrared spectroscopy, electron microscopy, thermal analysis, adsorption and powder density studies. These experiments show that AMO-LDHs are highly dispersed and exhibit significantly higher surface areas and lower powder densities than conventional or commercially available LDHs. AMO-LDHs can exhibit N₂ BET surface areas in excess of 301 m² g⁻¹ compared to 13 m² g⁻¹ for the equivalent LDHs prepared by co-precipitation in water. The Zn₂Al–borate LDH exhibits a pore volume of 2.15 cm³ g⁻¹ which is 2534 times higher than the equivalent conventionally prepared LDH.