| dc.description.abstract | Transition metal oxides are important materials that have found many applications,
as capacitors, sensors or in energy storage [1]. Synthesis of these compounds
has been realized by various methods, such as hydro(solvo)thermal synthesis,
precipitation, microwave synthesis or sol-gel synthesis [2]. Recently, the thermolysis
of coordination compounds as precursors has been considered as a new approach in
obtaining functional nanosized materials. [3]. In this way, by selecting the proper
precursor, it is possible to control the phase composition, morphology and particle
size of a resulting material [3].
The biphasic powder composed of ZnO (zincite) and ZnMn2O4 (hetaerolite), (I) has been
obtained by thermolysis of bimetallic complex [MnZn2(dipya)3(tpht)3(H2O)4]·2H2O
(dipya = 2,2’-dipyridylamine, tpht = dianion of 1,4-benzenedicarboxylic acid) at
450 °C during 1 h in air atmosphere. Scanning Electron Microscopy (SEM) was
used to investigate the morphology of I (Figure 1). It can be observed that the
morphology consists of deformed spherical grains of ZnO with an average diameter
of 67 nm and elliptical grains of hetaerolite whose average diameter and length
were 156 and 290 nm, respectively. The X-ray powder diffraction (XRPD) was
applied to investigate the structure of I. In Figure 2 two-phase Rietveld refinement
Electron Microscopy of Nanostructures ELMINA 2018, August 27-29, 2018
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pattern of I is presented (ZnO to ZnMn2O4 phase-ratio of 62:38 wt. %). The main
crystallographic data and Rietveld refinement parameters for ZnO phase are:
hexagonal, space group P63mc, a = 3.2574(1), c = 5.2175(2) Å, V = 47.945(3) Å3
; for
ZnMn2O4 phase are: tetragonal, space group I41/amd, a = 5.7299(3), c = 9.3000(8) Å,
V = 305.34(3) Å3
; Rwp = 4.80 %, Rp = 3.82 %, Rexp = 3.80 % and χ2
= 1.5960. UV-
Vis-NIR absorption spectrum was measured in order to investigate the direct band
gap (Eg) of I. Due to the existence of two phases in I, two different Eg values of
2.4 and 3.3 eV for ZnMn2O4 and ZnO phase, respectively, were determined using
Kubelka-Munk function. The mean size, polydispersity index (PDI) and zeta
potential of spherical grains were measured using Zetasizer Nano Series, Nano ZS.
The mean size was 418.6±53.1 nm while PDI value was found to be 0.354±0.099.
Relatively high values of PDI and low apostate value of zeta potential (–6.55 mV)
are indications of incipient instability of colloidal dispersion of I, probably due to the
formation of agglomerates [4, 5]. Photoluminescence measurements were carried
out at room temperature on Fluorolog-3 Model FL3-221 spectrofluorimeter system
upon excitation at 350 nm, in order to study the optical properties of I. This analysis
revealed one band centred at 422 nm in the blue region of the visible part of the
spectrum, which can possibly be associated with defects in the crystal structure of
the ZnO phase [6].
References:
[1] C Yuan et al, Angewandte Chemie International Edition 53 (2014), 1488.
[2] CNR Rao and B Raveau in “Transition Metal Oxides: Structure, Properties, and
Synthesis of Ceramic Oxides” 2nd edition (WILEY-VCH, New York).
[3] MY Masoomi and A Morsali, Coordination Chemistry Reviews 256 (2012),
2921.
[4] R Greenwood and K Kendall, Journal of the European Ceramic Society 19
(1999), 479.
[5] M Staiger et al, Journal of Dispersion Science and Technology 23 (2002), 619.
[6] H Zeng et al, Advanced Functional Materials 20 (2010), 561.
[7] The authors acknowledge funding from the Ministry of Education, Science and
Technological Development of the Republic of Serbia, Grant Number III45007. | sr |
