Nanocomposites and nanomaterials

Features of the technology for obtaining magnetically sensitive catalysts of the core-shell type
Makido O.Yu.1, Khovanets’ G.I.1, Khamar O.О.2
1 Department of Physical Chemistry of Fossil Fuels of the Institute of Physical–Organic Chemistry and Coal Chemistry named after L. M. Lytvynenko NAS of Ukraine.
Naukova Str., 3а, Lviv-79060, Ukraine.
E-mail: khovanets_galyna@ukr.net
2 Ivan Franko National University of Lviv.
Kyryla and Mefodiya str., 6, Lviv-79005, Ukraine.

The creation of catalytic systems based on nanodispersed powders of mixed metal oxides characterized by magnetic properties for easy extraction of them from the reaction medium is relevant both for chemical synthesis and for the purification of natural and sewage.
The synthesis of multilayered nanostructured magnetically sensitive catalysts of the core-shell type is carried out in several stages, the first of which is the synthesis of CoFe2O4 particles forming the magnetically sensitive core of the future catalyst. For ease of practical use, an important condition is the high magnetic sensitivity of the core, which can be achieved by the formation of structured cobalt ferrite CoFe2O4. 
The process of precipitation of CoFe2O4 from solutions of iron and cobalt salts at molar ratio Co : Fe = 1 : 2 by ammonium hydroxide solution at pH = 12 showed that in addition to cobalt ferrite, the formation of the maghemite γ-Fe2O3 mineral is observed, indicating incomplete precipitation of cobalt ions. It is known that with an excess of ammonium hydroxide, cobalt forms stable soluble complex compounds. Therefore, the investigations have been carried out on the effect of the amount of NH4OH on the completeness of precipitation of both pure solutions of Fe(NO3)3, Co(NO3)2, and their mixture at a given molar ratio.
The residual concentration of iron, cobalt and ammonium ions in the solution was determined photometrically using a spectrophotometer UV-visible range Shimadzu UVmini-1240 (Kyoto, Japan). It was established experimentally that soluble cobalt amine complexes are observed at a 20-fold amount of NH4OH in a molar ratio. Therefore, the optimal ratio of the initial reactants at the first stage of the synthesis of the magnetic core was selected (Fe3+ + Co2+) : NH4OH = 1 : 10. 
Carrying out the process of precipitation under selected conditions allowed to obtain cobalt ferrite, the stoichiometric composition of which was confirmed by X-ray analyzer of a scanning electron microscope РЕMMA 102-02.