Investigation of the formation of nickel and cobalt nanoparticles upon thermal decomposition of Ni,Al-and Co,Al-layered double hydroxides pillared with complexes [Ni(edta)]²⁻ and [Co(edta)]²⁻

Abstract

Double layered hydroxides [M_0.7Al(OH)_3.6] [M(edta)]_0.4·nH₂O (M,Al-M(edta), M = Ni, Co) containing nickel or cobalt edta complexes in the interlayer space were obtained for the first time. Vacuum thermal decomposition of these compounds results in the formation of metal nanoparticles dispersed in an amorphous matrix. Thermal decomposition products were studied by powder X-ray diffraction and ferromagnetic resonance technique. The scheme of structural rearrangements occurring during heating was derived from the data obtained. According to this scheme, below 200°C the interlayer and absorbed water escapes, and at 200–325°C metal-hydroxide layers undergo dehydration. At higher temperatures organic fragment of the complex suffers destruction to yield metal. It is shown that thermal decomposition of Ni, Al-Ni(edta) at 325–340°C gives isotropic nickel nanoparticles, while at higher temperatures the metal consists of a mixture of isotropic and anisotropic particles. Isotropic particles of β-Co formed at 350°C and above are of size 3–4 nm, no anisotropic particles being observed.