Nanocomposites based on opal matrices and iron subgroup metal nanoparticles

Three-dimensional nanocomposites based on ordered opal matrices (OMs) and metal nanoparticles were prepared by the reduction of salts and oxides of iron subgroup metals (M = Ni, Co, and Fe) and their binary and ternary mixtures with isopropanol in a supercritical state. The effect of the composition of the initial salts (nitrates or chlorides) on the phase composition of OM/M composites was determined. For a binary system of Ni and Co nitrates (1 : 1), the particles of a NiCo solid solution in a cubic modification were formed in an opal matrix after treatment in supercritical isopropanol. For the Ni-Fe and Co-Fe systems, the nanoparticles of solid solutions based on nickel or α-, β-cobalt metal and also oxides or an MFe2O4 phase with the spinel structure were formed in opal matrices with the use of iron trichloride. The nanoparticles of iron metal and Ni3Fe, NiFe, and CoFe intermetallic compounds with regular distributions of metal atoms were detected for the first time in addition to spinel phases upon the reduction of composites with Fe, Ni-Fe, and Co-Fe nitrates with supercritical isopropanol. The reduction of composites obtained by the thermal treatment of a ternary mixture of nickel and cobalt nitrates and iron chloride in supercritical isopropanol led to the formation of solid solution nanoparticles based on Ni, Co, and Fe with an fcc structure and an oxide phase with the spinel structure in the voids of opal matrices. In the composite based on an opal matrix and a ternary system of Ni-Co-Fe nitrates (1 : 1 : 1), the complete reduction of spinel phases to the intermetallic phases of Ni3Fe, NiFe, and CoFe was noted.