ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 11, pp. 1798!1803. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + I.A. Farbun, I.V. Romanova, T.E. Terikovskaya, D.I. Dzanashvili, S.A. Kirillov, 2007, published in Zhurnal Prikladnoi Khimii,
2007, Vol. 80, No. 11, pp. 1773!1778.
AND INDUSTRIAL INORGANIC CHEMISTRY
Complex Formation in the Course of Synthesis of Zinc Oxide
from Citrate Solutions
I. A. Farbun, I. V. Romanova, T. E. Terikovskaya, D. I. Dzanashvili, and S. A. Kirillov
Institute of Sorption and Problems of Endoecology, National Academy of Sciences of Ukraine, Kiev, Ukraine
Institute of Inorganic Chemistry and Electrochemistry, Tbilisi, Georgia
Received September 29, 2006; in final form, April 2007
Abstract-Complex formation of zinc(II) with citric acid in acidic medium was studied by pH-potentiometric
titration at various metal to acid ratios. The speciation diagrams of the complexes in relation to pH were
plotted, and the stability constants of the complexes were determined. Precursors of the synthesis of metal
oxide materials were prepared at two reactant ratios. A scheme of the precursor thermal decomposition based
on data of derivatography and IR spectroscopy was suggested, and the compositions of compounds formed
during decomposition were determined.
Transition metal oxides and materials based on
them attract researchers’ interest for a long time due
to a wide set of possibilities of their use as cathode
masses for chemical power sources, catalysts and
photocatalysts, highly selective sorbents, semicon-
ductors, and magnetic materials . Previously
these materials were usually prepared by sintering of
oxides or thermal decomposition of hydroxides or
metal salts (nitrates, acetates, carbonates, oxalates).
In the case of poorly soluble salts, their precipitation
or coprecipitation preceded thermal decomposition.
A new step in the development of the synthesis of
oxide materials is connected with the use of polybasic
hydroxy carboxylic acids. Concentrated solutions
containing metal salts and the above acids tend to
form sols and then gels (or glasses). This procedure
differs from traditional sol3gel methods in that the
agent forming the polymeric matrix is polybasic hy-
droxy carboxylic acid and not hydrated silicon, titani-
um, zirconium, etc. species tending to form H-bond
network, which significantly extends the range of
objects that can be involved in the process. Precursors
containing metal salts and excess acid are formed
when the major fraction of water is removed from gels
(glasses). Their further thermal treatment gives homo-
geneous oxide materials.
In , we suggested an optimized method for pre-
paring oxide materials, which was tested with zinc,
nickel, copper, manganese, and cerium salts. Many of
the materials obtained showed high activity in catalyt-
ic oxidation of CO  and of volatile organic com-
pounds: paraffin and aromatic hydrocarbons ,
alcohols, ethers, and esters .
Complex compounds are formed in the solution
when the initial metal salts are mixed with the acid.
Their composition and stability determine the com-
position of the precursor, pathway of its thermal
decomposition, and parameters of the oxide material
formed (crystal dimensions, specific surface area,
porosity, etc.). These questions have not been ad-
equately discussed in the literature .
In this study, with the Zn
3citric acid (C
system as example, we examined complex formation
in solution at various pH values and metal to acid
ratios, determined the compositions of complexes
formed in solution, prepared the precursors, and
analyzed pathways of their decomposition. Zinc was
chosen because it does not undergo redox transforma-
tions which could complicate the precursor decom-
position. In addition, zinc oxide has been actively
studied recently for various applications [13, 14].
All chemicals used were of chemically pure grade
and were used without additional purification. The
metal and acid concentrations were determined by
complexometric and acid3base titration [15, 16].