Large oriented mesoporous self-supporting Ni–Al oxide films derived from layered double hydroxide precursors

Abstract

Large (~1 cm²) transparent highly (111)-oriented mesoporous self-supporting Ni–Al oxide films of uniform small nanoparticles have been prepared using an Ni₂Al(OH)₆(NO₃)·2.1H₂O layered double hydroxide (LDH) as a single precursor. The monodisperse small LDH nanoparticles (about 20 nm in diameter) are first cast as an oriented assembly on a glass substrate to form large transparent self-supporting (00l)-oriented LDH films. Subsequent heating in air affords (111)-oriented mesoporous Ni–Al oxide films preserving the shape, dimensions and optical transparency of the films. The process involves a topotactic transformation from the LDH (00l) facet to the NiO and NiAl₂O₄ spinel (111) facets, demonstrated here for the first time, and does not require any template, structure-directing agent, or lattice-matched single crystal substrate. The nanostructures of the resulting mixed metal oxide films can be controlled by changing the calcination temperature: Al-doped NiO and composite NiO/NiAl₂O₄ films of uniform small nanoparticles have been obtained at 500 °C and 900 °C respectively. The pore size and pore size distribution increase monotonically with temperature due to the increased sintering of the nanoparticles at higher temperatures. The resulting large transparent Ni–Al oxide films have a narrow distribution of mesopores (<10 nm) and high thermal stability, suggesting their potential application as catalysts or catalyst supports, in sensors, and as ultrafiltration membranes in harsh environments.