Silica-supported Ni and Co nanooxides: Colloidal properties and interactions with polar and nonpolar liquids

Binary and ternary mixed oxides composites (NiO/SiO2, Co3O4/SiO2, and NiO/Co3O4/SiO2) were synthesized using a method of solvate-stimulated modification of the fumed silica with Ni and Co nitrate hexahydrates for further thermal decomposition and formation of the crystalline NixOy, CoxOy or NixOy/CoxOy oxides. Synthesized composites were examined using IR spectroscopy, argon adsorption-desorption, microcalorimetry, and photon correlation spectroscopy. A two-stage method used for the synthesis of composites showed high potential in order to prepare ultra-dispersed solids with a high interfacial area of 246–255 m2/g, which is close to that of the initial fumed silica used as support. According to the results of the XRD analysis, 15 nm NiO and 14 nm Co3O4 crystallites were formed within the composite structure. As compared with the initial silica, the secondary particles (aggregates) of metal oxides in the aqueous medium have a large size of 100–180 nm while agglomerated particles are in the range from 1.1 to 1.3 μm. Hydrophilic properties of the synthesized composites are close to the initial silica, the hydrophilicity index varies from 2.4 to 2.6, according to the measured heats of immersion in water and n-decane.