Thermal, solution and reductive decomposition of Cu–Al layered double hydroxides into oxide products

Abstract

Cu–Al layered double hydroxides (LDHs) with [Cu]/[Al] ratio 2 adopt a structure with monoclinic symmetry while that with the ratio 0.25 adopt a structure with orthorhombic symmetry. The poor thermodynamic stability of the Cu–Al LDHs is due in part to the low enthalpies of formation of Cu(OH) 2 and CuCO 3 and in part to the higher solubility of the LDH. Consequently, the Cu–Al LDH can be decomposed thermally (150 °C), hydrothermally (150 °C) and reductively (ascorbic acid, ambient temperature) to yield a variety of oxide products. Thermal decomposition at low (400 °C) temperature yields an X-ray amorphous residue, which reconstructs back to the LDH on soaking in water or standing in the ambient. Solution decomposition under hydrothermal conditions yields tenorite at 150 °C itself. Reductive decomposition yields a composite of Cu 2O and Al(OH) 3, which on alkali-leaching of the latter, leads to the formation of fine particles of Cu 2O (<1 μm).