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AZ9RBAYCAN KIMYA JURNALI № 2 2018
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
2+
Co and Al nitrates in
UDC 661.847.92
OBTAINING OF NANODIMENSIONAL POWDERS BY METHOD OF HYDROTHERMAL DECOMPOSITION OF Cu, Co, AND Al NITRATES IN POLYOLIC
ENVIRONMENT
S.T.Jafarova, A.A.Medjidov, M.M.Ahmadov, B.Yalcin*, P.A.Fatullayeva, S.A.Agayeva,
M.G.Abbasov
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan * Faculty of Arts and Sciences Department of Chemistry of Marmara University, Turkey
rsevil [email protected] Received 05.02.2018
The hydrothermal reductive decomposition of Cu2+, Co2+ and Al3+ nitrates in the temperature range of 220-3500C in the presence of polyols (ethylene glycol and glycerol) was investigated. It has been established, that depending on the synthesis conditions the forming of highly dispersed oxide systems of Cu-Co-Al and/or with admixture of metallic copper are possible. The products of reaction by physicochemical methods: XRF, SEM, spectroscopy in the IR and UV ranges are characterized. A correlation between the reaction conditions and the physical and chemical properties of the nanopowders was established. A possible scheme for the flow of reaction is proposed.
Keywords: nanoparticles, ethylene glycol, glycerol, hydrothermal conditions.
In recent years interest of researchers to obtaining of oxide nanomaterials for various purposes strongly has grown. They find application as efficient sorbents, catalysts, sensory sensors, metal-ceramic products, etc. [1-4]. The special place among in practical application of such materials occupies catalysis. There are numerous literary data on the methods for their obtaining, forming of structure, physical and chemical properties and also working (production) characteristics. One of the promising methods for obtaining of metal and metal oxide powders with highly dispersed particles is hydrothermal synthesis. By hydrothermal decomposition of metal nitrates in supercritical temperatures were obtained their oxides [5]. During realization of hydrothermal treatment of nitrates in the presence of di- and triols and other reducing agents were obtained highly dispersed compositions, containing simultaneously metals, metal oxides and carbonates [6]. By using various methods of synthesis of nanoparticles of the same composition differences in their structure, morphology and properties are observed. In this regard, the study of influence of various factors on the phase formation mechanism and the physical and chemical properties of nanoparticles obtained in the presence of polyols under hydrothermal conditions is represented interesting.
This work is devoted to identification of regularity of the process of hydrothermal de-
composition of Cu the presence of ethylene glycol and glycerole and to studying of properties of the received nanoparticles.
Experimental part
Materials for synthesis. The following reagents were used for synthesis: Cu(NO3)23H2O (analytical reagent grade a.r.g.); Co(NO3)26H2O (a.r.g.); Al(NO3V9H2O (a.r.g.); ethylene glycol (a.r.g.); glycerol (analytical reagent quality).
The course of synthesis. The dissolved in water mixture of starting materials was mixed and loaded into the reaction volume. The initial mixture had the typical composition, similarly to given in [7], with some modification: metal nitrates was taken in weight proportion 1:1:3 and volume ratio ethylene glycol (or glycerol): water =1.2.
Experiments on hydrothermal synthesis were carried out in autoclaves which made of stainless steel 09X18H10T with an internal reactionary volume of 120 ml, with a filling factor of the initial mixture 0.5-0.8. The equipped with manometr for measuring the internal pressure autoclave was heated to the required temperature at a rate of 500C/min and kept under isothermal conditions for 6 hours. The autoclave was then cooled to room temperature, the reaction vessel was removed from the autoclave, the solid powder products were
АЗЕРБАЙДЖАНСКИМ ХИМИЧЕСКИМ ЖУРНАЛ № 2 2018
separated from the mother liquor by filtration on a glass filter, thoroughly washed with distilled water and powders dried at temperature of 600C. In some experiments, the residues of the reaction solutions were subjected to analysis. Each experiment was carried out twice.
Methods of analysis. The products of reaction were studied with using of a complex of instrumental methods: XRD, SEM, UV, IR spectroscopy. Samples of the synthesized powders were studied by the XRD method with diffractometer "D2 Phaser" ("Bruker", Germany, Cu-Xa-radiation, ^ = 154 A, nickel filter). The database of ICPDS for to identify the X-ray diffractogram was used. The research by electron microscopy was carried by SEM "SigmaVP" CarlZeiss (Germany), where the source of electrons is a cathode with field emission (cathode of Schottky) with the possibility of varying the accelerating voltages from 0.2 to 30 kV. The spectra of the solutions of reaction in the IR and UV regions were recorded by spectrometer "Ni-coletiS10" and spectrophotometer "Evolution 60S" (Thermo Scientific Spectronic firm, USA).
Results and discussion
On the process of interaction of metal nitrates with the ethylene glycol and glycerol water solutions the temperature and nature of the reducing agent have a significant influence. In this paper, the influence of the above mentioned experimental conditions on the phase composition, morphology, and elemental composition of the
surface of synthesized samples was investigated; in some experiments reactionary solutions was studied by IR and UV spectroscopy for finding out the possible mechanism of reaction.
To determine the effect of the reducing agent nature and to elucidate of the minimum synthesis temperature under hydrothermal conditions, a series of experiments was performed in the presence of ethylene glycol and glycerol at different temperatures on the example of the Cu-Co-Al systems, which are the most widely used in catalytic processes.
Figure 1 presents the results of X-ray phase analysis of the product hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates in the presence of water solutions of ethylene gly-col and glycerol at various temperatures. The carried out analysis of reaction products of the threefold mix metal nitrates with ethylene glycol at the temperature 2300C showed presence in them of Cu(II) hydrate oxalate CuC2O4H2O and Co(II) dihydrate oxalate C2CoO4^^O-pC2CoO4-2H2O, which at the 2800C turn to cobalt oxalate CoC2O4 p-C2O4Co. In contrast, in water solution of glycerol at the temperature 2800C Co(II) dihydrate oxalate M2O42H2O is still present, which is converted to spinel Co2 88O4 at 3300C. At this temperature (3300C) in products of reaction the phases of inorganic compounds: metallic copper and cobalt and aluminium oxides are present.
Fig. 1. X-ray powder diffraction patterns of the products of hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates in the presence of ethylene glycol (glycerol) at temperatures: a (e) - 230, b (f) 280, c (g) - 330, d (h) - 3500C. 1 - CUC2O4 H2O, 2 - C2CoO4-2H2O. P-C2CoO4-2H2O, 3 -Cu2(HCOO)4((CH3)2NCHO)2, 4 - Cu, 5 -CoC2O4p-C2O4Co, 6 - Al(OH)3, 7 -CoC2O42H2O, 8 - Al2O3; 9 - Cu2+1O, 10 - CoZ88O4, 11 - M2O3. * - [No 01-075-4529].
For the study of morphology of the received powders products electron-microscopic studies were carried out. Figure 2 shows SEM images of the powder reaction products, which were obtained at different temperatures in the
presence ethylene glycol (glycerol) at various magnification. In Figure 2(a, a*) images of the reaction product of reductive decomposition of metal nitrate mix at the temperature 2800C are shown.
Fig. 2. Morphology of powder products of hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates of in the presence of ethylene glycol (glycerol) at various temperatures: a and a* (d) - 280; b, b* and b** (e and e*) - 330; c (f) - 3500C.
АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 2 2018
The presence of amorphous formations of aluminium hydroxide is clearly visible, though the characteristic peaks of this phase is absent on the diffractograms (Figure 1). In the case of glycerol, the thin films of aluminium hydroxide (Figure 2 (d, e)) are observed; the surface is more loose structure and porous. In the presence an ethylene glycol by increase in temperature the surface of film becomes granular (Figure 2 (b, b*), whereas in the presence of glycerol no significant morphological differences are observed. Grains have an average size of particle ~240 nm. So the grains acquire a kind of dendritic form, which can indicate the fact that each grain is formed by the association of a few nano-particales into one. The further in rise temperature leads to an increase in the density of the surface and it becomes more homogeneous, which, is probably, explained by the decrease of the grain sizes of the powder. In the case of glycerol, large agglomerates are formed, that have not precisely chiseled borders.
The results of the energy-dispersive analysis, carried out by means of a scanning electron microscope, are presented in the table. It can be seen from the table data that at the realization of the reaction in water solution of ethylene glycol in the surface layer a uniform and predominant distribution of Al is observed. It coincides with electron microscopic analysis of the image of morphology of the powder surface (Figure 2). On the surface of the first sample the d-elements have non-uniform, while in a spectrum 2 of Co (27.8 wt %) prevails and in the spectrum 3-Cu (36.6 wt %) does. The rise in temperature of synthesis promotes a relatively uniform distribution of the elements over the area (spectra 1 and 2), with a small difference of Cu (11.1
and 2.1 wt %, respectively). At the realization of the reaction in water solution of glycerin, regardless of the synthesis temperature, a uniform distribution of all elements over the surface area of the samples is observed.
Thus, the conducted studies have shown that at hydrothermal decomposition of metal nitrates in the presence of polyols the responsible for the reducing ability of polyols has main factor is the temperature. At present, the mechanism of the reaction of decomposition of nitrates in the presence of polyols has been sufficiently studied. The spectra of reactionary water solution in the IR and UV spectral range were taken off to reveal the nature of the substances present in the reaction solutions.
On Figure 3 electronic spectra in the UV area of reactionary solutions are presented. From him it is visible, that in spectrum of the obtained at low-temperature reduction by glyc-erol (2300C) liquid reactionary residues the absorption band at 260 nm (c.6) is observed. Analogical band is absent, when it was used eth-ylene glycol. By using ethylene glycol very weak absorption band at 2800C (c. 1) appears, which intensity at increase of temperature to 3300C. The recorded spectrums of oxalic acid absorption (c.7) allows us related the absorption bands with a maximum at 260 nm to the presence of oxalic acid in the solution. Further increase of the reduction temperature complicates the form of the electronic spectrums (c.3 and 5) of the reactionary solutions. On the spectrum 3 visible a relatively narrow peak at 205 nm, absent on the c.5, and a slight bend in the area of 220 nm, and also band of absorption with a maximum at 275 nm, which on c.5 is less intensive.
Polyol Sample Temperature of process, 0C Spectrum Elements Total
Al Co Cu O C
Ethylene glycol 1 330 1 37.6 3.6 2.8 41.6 14.4 100
2 20.0 27.8 1.9 37.7 12.5 100
3 21.2 6.2 36.6 26.7 9.3 100
2 350 1 27.8 9.2 11.1 40.9 11.0 100
2 27.2 5.3 2.1 46.6 18.8 100
Glycerol 3 300 1 12.1 14.8 15.7 38.6 18.8 100
2 12.5 29.0 12.2 29.8 16.5 100
4 330 1 17.2 13.8 2.6 35.9 30.2 99.7
2 20.0 15.3 7.3 35.2 22.1 99.9
Distribution of elements over the surface area of powders, obtained by hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates , depending on the temperature of reaction
Fig. 3. UV spectra of reactionary solution after the hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates at different temperatures in the presence of ethylene glycol (curves: 1 - 280, 2 -330, 3 - 3500C) and glycerol (curves: 4 -280, 5 - 350, 6 - 2300C); curve 7 is oxalic acid.
200
250
300
350
400
Wave length, nm
The bands of absorption in area of 200*
210 nm is accorded to the n^-rc transition in carboxylic acids, but at 280 nm accord to the excitation of the rc-electrons of the free electron pair of oxygen of the carbonyl group C=O.
The registered at the same experimental conditions UV VIS spectrum of oxalates of copper and cobalt allow are identified the entire set of all bands of absorption as belonging these compounds. Thus, the complication of electronic spectra, some displacement of individual bands and a change in intensities are possibly caused by the presence of intermolecular interactions in the solution under study.
On Figure 4 IR spectra of the reactionary
are given. On the spectrums of reactionary solution there is an intense and wide band of absorption in area of 3300-3500 cm-1 with maxima at 3424 and 3385 cm-1, according to the vibrations of the free hydroxyl group, and in area of 2400-3000 cm-1 with maxima at 2881, 2946 and 2957 cm-1 connected by a hydrogen bond to a carboxyl group. The bands of absorption with maxima at 1637 and 1363, 1332 cm-1 is according to asymmetric and symmetric vibrations of the anion of the COO- group in salts of acids, the excitation of a free electron pair of oxygen that of was observed as an of band an absorption on the spectrums in the UV areas with a maximum at 280 nm.
solution after the hydrothermal decomposition
/
wave number, sin "1
Fig. 4. IR spectra of reactionary solution after the hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates at the temperature 3300C in the presence of glycerol (a) and ethylene glycol (b).
A3EPEAH#^AHCKHH XHMHHECKHH ^YPHAH № 2 2018
Thus, on the basis of the results obtained by interpreting of the spectra of absorption in the IR and UV spectral areas, it was established that regardless by the nature of the polyol a basic organic product in reactionary solution are oxalic
acid and its salts. Consequently, ethylene glycol is oxidized to oxalic acid with the release of carbon dioxide, which is agreement with the work [8]. The scheme of oxidation of ethylene glycol to oxalic acid can be represented as follows:
According to experimental data, the further mechanism of reaction can be represented as follows. The complex cations of metals [Cu(H2O)3]2+ and [Co(H2O)6]2+, present in solution during in the process of dissociation of the corresponding salts, interact with the dianion C2O42- formed from double deprotonation of oxalic acid to form hydrates of metal oxalate on the reaction:
C2O42- + [Me(H2O)x]2+ ^ MeC2O4 «H2O + (x-n)HO, Me - Cu, Co.
The rise in temperature of reaction promotes at first dehydrations of hydrate of cobalt oxalate, and further increase of temperature to decomposition of the formed oxalate to an oxide:
CoC2O4-2H2O^CoC2O4+ 2H2O, CoC2O4 ^CoxOy+ 2CO2T.
Unlike CuC2O4H2O for which is removal of water takes place simultaneously with the decomposition of oxalate to the metal:
CuC2O4-H2O^Cu|+ 2CO2T+ 2H2O.
At a low temperature in the presence of glycerol, decomposition proceeds with formation
of an oxide:
CuC2O4-H2O^CuO|+ 2CO2T+ 2H2O.
For removal of residual carbon, the products of hydrothermal cooperative decomposition of nitrates of Cu, Co, and Al in polyol environment were calcined at temperature of 5000C (Figure 5). After calcining of products at 5000C, on the diffractions patterns there are observed the reflections only of cubic Co3O4 and monoclinic CuO. The synthesized systems can be promising as catalysts for the production of hydrogen.
Thus, on the basis of a large number of experimental data, it has been established that the process of cooperative decomposition of Cu2+, Co2+ and Al3+ nitrates in the temperature range 230-3500C in the presence of polyols under hydrothermal conditions proceeds through the formation of predominantly of oxalates of metals with further decomposition. The final products of the process are grains with an average size of particles of 220-400 nm. It has been shown that this method can be used for producing highly disperse oxide powders.
10 20 30 40 50 60 70 80*
2 Thcta Scale
Fig. 5. Powder diffraction patterns of the products of hydrothermal decomposition of Cu2+, Co2+ and Al3+ nitrates are calcined at 5000C: 1 - Co3Û4, 2 - CuO.
The work was carried out with the financial support of "SOCAR" (Grant No. 07 for 2014-2016, the title of the project: "Synthesis of catalysts for hydrogen production and purification for fuel cells").
References
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2. Rempel A.A. Nanotekhnologii, svoistva i primenenie nanostrukturirovannykh materialov // Uspehi himii. 2007. T. 76. № 5. S. 474-500.
3. Gusev A.I. Nanokristallicheskie materialy: metody polucheniia i svoistva. M.: Fizmatlit, 2005. 199 s.
4. Andrievskif R.A. Nanostrukturny'e materialy'. M: Izdat. centr "Akademiia", 2005. 192 s.
5. Hayashi H., Hakuta Y. Hydrothermal Synthesis of Metal Oxide Nanoparticles in Supercritical Water // Materials, 2010, V. 3. P. 3794-3817.
6. Yadong Li, Junwei Wang, Zhaoxiang Deng, Yiy-ing Wu, Xiaoming Sun, Dapeng Yu, Peidong Yang. Bismuth Nanotubes: A Rational Low-Temperature Synthetic Route // J. Am. Chem. Soc. 2001. V. 123. P. 9904-9905.
7. Medjidov A.A., Fatullayeva P.A., Agayeva S.A., Yalcin B., Jafarova S.T., Ahmedov V.M., Ab-basovM.G. Reduction of metal nitrates by formaldehyde, ethyleneglycole and glycerol under hydrothermal conditions // Azerb. Chem. J. 2016. № 3. P. 75-81.
8. Liu, Z., Jackson, G. S., Eichhorn B. W. Tuning the CO-tolerance of Pt-Fe bimetallic nanoparticle electrocatalysts through architectural control // Energy Environ. Sci. 2011. Issue 4. P. 1900-1903.
POLÍOL MÜHÍTÍNDO Cu, Co VO Al NÍTRATLARIN BÍRGO HÍDROTERMAL DEKOMPOZÍSÍYA ÜSULU ÍLO NANOÖLCÜLÜ TOZLARIN ALINMASI
S.T.Cafarova, O.O.Macidov, M.M.Ohm3dov, B.Yalcin, P.O.Fatullayeva, S.A.Agayeva, M.H.Abbasov
Cu2+, Co2+ и Al3+ nitratlann 220-3500С temperatur intervalinda poliol mühitinda (etilenqlikol va qliserin) hidrotermal-reduksion dekompozisiyasi tadqiq edilmiçdir. Sintez çaraitindan asili olaraq yüksak dispersli Cu-Co-Al oksid va/va ya mis metal qançigi olan sistemlarin formalaçmasinin mümkünlüyü müayyan edilmiçdir. Reaksiya mahsullari UF va ÍG spektroskopiya, RFA, SEM fiziki-kimyavi üsullan ila xarakteriza edilmiçdir. Nanotozlann fiziki-kimyavi xassalari ila sintez çaraiti arasinda korellasiyasi mûayyanlaçdirilmiçdir. Reaksiyanin gediçi haqqinda mümkün ola bilan sxem taklif olunmuçdur.
Açar sözlar: nanohissaciklar, etilenqlikol v3 qliserin, hidrotermal §3rait
ПОЛУЧЕНИЕ НАНОРАЗМЕРНЫХ ПОРОШКОВ МЕТОДОМ ГИДРОТЕРМАЛЬНОГО СОВМЕСТНОГО РАЗЛОЖЕНИЯ НИТРАТОВ Cu,Co И Al В ПОЛИОЛЬНОЙ СРЕДЕ
С.Т.Джафарова, А.А.Меджидов, М.М.Ахмедов, Б.Ялчин, П.А.Фатуллаева, С.А.Агаева, М.Г.Аббасов
Исследовано гидротермальное восстановительное разложение нитратов Cu2+, Co2+ и Al3+ в интервале температур 220-3500С в присутствии полиолов (этиленгликоля и глицерина). Установлено, что в зависимости от условий синтеза возможно формирование высокодисперсных Cu-Co-Al-оксидных систем с примесью и без металлической меди. Продукты реакции охарактеризованы физико-химическими методами: РФА, СЭМ, спектроскопия в ИК- и УФ-областях. Установлена корреляция между условиями реакции и физико-химическими свойствами нанопорошков. Предложена возможная схема протекания реакции.
Ключевые слова: наночастицы, этиленгликоль, глицерин, гидротермальные условия.
AЗЕPБAЙДЖAHCKИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 2 2018
