Nanocomposites and nanomaterials

Synthesis and catalytic properties of complex oxide compositions of cobalt-manganese and cerium-zirconium
O.P. Ivanenko1, T.V. Pavlenko1, Yu.V. Pohorenko1, A.O. Omelchuk1, V.M. Bykov2
1Vernadsky Institute of General and Inorganic Chemistry, NAS of Ukrainian, prospekt Palladina 32/34, 03142 Kyiv, Ukraine, ivanenko@ionc.kiev.ua
2Institute of Physics, NAS of Ukrainian, avenu Nauki 46, 03028 Kyiv, Ukraine

Cobalt and manganese nanoparticles were prepared by sol-gel method in ammonia or hexamethyltetraamine (HMTA) solutions. The samples were heat treated at 80 °C (4-7 h) and 400 °C (2 h). The compounds dried and roasted in this way precipitated cerium-zirconium oxides in an equimolar ratio of 5-20 mol% relative to the initial sample followed by heat treatment. X-ray investigations of the roasted samples as starting compounds and with the Ce-Zr oxides deposited on them show the formation mixed oxides Co3O4 and Mn3O4. Calculated by the Sherer equation, the particle size was 6-18 nm.
The catalytic properties of the synthesized samples as the initial oxides of cobalt and manganese, as well as with those deposited on them by Ce-Zr oxides, were investigated in the decomposition of hydrogen peroxide. 
It was found that the duration of the H2O2 decomposition with the participation of the samples obtained in the ammonia environment was completed within 5-6 days, while the catalytic activity of the samples synthesized in the HMTA medium did not end even after 14 days of the experiment. At the same time, the highest ability for catalysis showed a sample of Co3O4 + 10 mol% (CeO2 + ZrO2), 1 g of which decomposes 3,4 dm3 H2O2.
The study of surface characteristics indicates the higher values of the specific surface area, pore volume and size for pure cobalt oxide obtained using an ammonia solution compared to the analogue obtained from the solution of HMTA. In the transition to complex oxide compositions fried at 400 °C, their surface characteristics have the following values: specific surface (50-77 m2/g), pore volume (0.21-0.3 cm3/g), pore size (60-78 Å). The spatial structure of cobalt oxide particles obtained under different conditions was investigated by scanning electron microscopy. It has been found that, regardless of the conditions of precipitation and heat treatment of particles of cobalt oxide, they form 2D structures, which, when deposited from the solution of ammonia, are agglomerated into spherical globules. Thermal treatment helps to destroy the created globules. The solution of HMTA contributes to the formation of flat layered structures formed by plates of cobalt oxide, which are closely adjacent to each other. Heat treatment contributes to the stratification of such structures.