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UDK 541.1
REDUCTION OF METAL NITRATES BY FORMALDEHYDE, ETHYLENEGLYCOLE AND GLYCEROL UNDER HYDROTHERMAL CONDITIONS
A.A.Medjidov, P.A.Fatullayeva, S.A.Agayeva, B.Yalcin*, S.T.Jafarova, V.M.Ahmedov,
M.G.Abbasov
Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan *Faculty of Arts and Sciences Department of Chemistry of Marmara University, Goztepe,
Istanbul- Turkey
ajdarmedjidov@gmail.com
Received 28.04.2016
The reduction of cobalt, nickel, copper, zinc and aluminum nitrates by formaldehyde, ethylene glycol and glycerol under hydrothermal conditions at temperatures of 220-3200C was studied. It is shown that the metal carboxylates (oxalates, formates) can be obtained at temperatures below 2400C, while the oxides and metal carbonates form at higher temperatures. The reduction of copper nitrate formed a metallic powder under these conditions. Under certain conditions metallic cobalt and nickel can be obtained as well. Calcination samples received at temperatures up to 2400C, at 5000C leads to formation of nano-powders of metal oxides with an average size of particles about 30-60 nanometers.
Keywords: hydrothermal reduction, metal nitrates, nanoparticles.
Introduction
The hydrothermal method is one of the most effective ways to produce the nanodimen-sional powders of metals, their oxides and carbonates. This method is performed by: 1) decomposition of metal salts in water solutions at supercritical temperatures; 2) single-stage hydrothermal redox-reaction of metal salts (particularly of metalnitrates) with various reducers; 3) forming of nanoparticles at hydrothermal conditions; 4) hydrothermal flow method.
The essence of hydrothermal method at supercritical temperatures consists in hydrolysis of metal salts into metal oxides [1-10]. This method allows obtaining the multimetal oxides [1]. In fact, the hydrothermal flow method does not differ from the stationary hydrothermal method, but has technological advantages [11-19].
The synthesis of nanoparticles by hydrothermal method is carried out, as a rule, at two stages. At the first stage, the chemical reaction takes place (hydrolysis, substitution, etc.); then (a second step), the reaction mass is subjected to a hydrothermal treatment [20-23].
Single-stage reduction of metal nitrates with diols, triols and other reducers in hydrothermal conditions allows receiving the high-dispersing compositions consisting the metal particles, metal oxides and carbonates [24, 25].
Experimental part
Reactions of metal nitrates -Co(NO3)2-6H2O, M(NOb)2-6H2O, CU(NOB)23H2O and Al(NO3)3-9H2O with formaldehyde ethylene glycol and glycerol were carried out in the steel autoclave at temperatures of 240-3200C. Formaldehyde was used in the form of 40% water solution.
The following experimental conditions were used for a typical run: 2 g of copper nitrate and 2 g of cobalt nitrate were dissolved in 10 ml water and then 10 ml of ethylene glycol was added. The mixture was poured in a glass tube placed in the steel autoclave. Autoclave was heated at 2700C within 4 hours. Pressure in autoclave reached 70 atmospheres during reaction. Then the reaction mixture was filtered, washed by water and dried at 700C. Water was removed from filtrate, then the rest (residue) was analyzed by IR and UV VIS spectroscopy. The obtained samples were exposed to calcination at 5000C.
The phase structure, size and form of particles before and after calcination were characterized by X-ray diffraction (XRD) (Bruker-D2 Phaser, Germany), Fourier transform infrared spectroscopy (Nicolet-AS10, USA) and the scanning electronic microscope Sigma VP (Carl Zeiss Jena).
Discussion
We have studied the reduction of individual metal nitrates and their double and threefold composition in the range of 200-3 200C using formaldehyde, ethylene glycol and glycerol as reducers. A reaction of metal nitrates under hydrothermal conditions proceeds rather softly in comparison with combustion method. Thus pressure in the course of reaction changes smoothly and as a rule does not exceeds 150 atm. Reduction of individual Cu(II), Ni(II) and Co(II) at 3200C leads to the formation of metallic particles. A reaction of the stoichiometric quantities of oxidizer (metal nitrate) and reducer (ethylene glycol and glycerol) proceeds according to the equations:
5M(NOb)2 + 6HOCH2-CH2OH ^ 5M0 + 12CO2 + 5N2 + 18H2O,
7M(NOB)2 + 6HOCH2CHOHCH2OH ^ 7M0 + 18CO2 + 7N2 + 24H2O.
It was observed that the complete recovery is realized only in some cases in the temperature range of 230-3200C.
Possibility of metal ions' reduction to the metallic state depends on natures of metal and reducer and temperature of process. In the presence of glycerol, a metallic copper is formed at 2400C, while a temperature higher than 3000C is necessary for the reduction of cobalt ions.
The mixture of cobalt and nickel nitrates. The X-ray diffraction pattern of the obtained compounds reveals that the reduction of mixture of cobalt and nickel nitrates by formaldehyde at 2200C yields cobalt oxide (Co3O4) and nickel oxide (NiO) (Figure 1).
The reduction of binary mixture of cobalt and nickel nitrates by glycerol at temperatures of 220-2500C gives a mixture of cobalt and nickel oxalates, and also nitrogen-containing organic compounds. Increasing temperature up to 300-3200C leads to the formation of nanome-tallic cobalt and nickel particles (~55 nm) with a small amount of intermetallic compound -Co3Ni7. Calcination of received in autoclave samples in air within 2 hours at 5000C yields nickel and cobalt oxides (NiO and Co3O4) with average size of particles 30-60 nm.
a - Co3O4 b - NiO
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иглу™ Uli Ц.Т
2-Theta-Scale
Fig. 1. XRD pattern of the sample received by reduction of the cobalt and nickel nitrates mixture by formaldehyde at 2200C.
a
b
a
a
a
a
The mixture of cobalt and copper nitrates. The reduction of the mixture of cobalt and copper nitrates by glycerol at temperatures of 220-25 00C yields metallic copper particles and cobalt oxalate dihydrate Co(C2O4)^2H2O. Increasing temperature up to 3000C allows the formation of metallic copper and cobalt oxide Co3O4. Calcination of obtained products in air 2 hours at 5000C yields copper oxide (CuO -tenorite) and cobalt oxide Co3O4.
The mixture of aluminum, copper and cobalt nitrates. We have not observed the formation of noticeable metallic phases during reduction of the mixture of aluminum-, copper-and cobalt nitrates by formaldehyde at 230-
Fig. 2. The electron microscopic image of the particles received by reduction of the cobalt, copper and aluminum nitrates mixture by formaldehyde at
temperature of 230"C.
3000C. The XRD pattern of the obtained compounds reveals no phases of aluminum oxide and aluminum hydroxide. At the same time, the electron microscopic image shows of the considerable amount of aluminum indicating the high dispersion (amorphous) of the formating aluminium compounds (Figure 2).
IR spectrum of the product allocated from solution after reaction of cobalt, copper and aluminum nitrates mixture by formaldehyde contains the absorption bands at 1636 and 1363 cm-1 relating to antisymmetric and symmetric vibrations of carboxylate groups, indicating the presence of copper(II) and cobalt(II) oxalates (Figure 4) as the main product of reaction.
Fig. 3. The content of elements in the samples received in reduction of the cobalt, copper and aluminum nitrates at temperature of 2300C by formaldehyde.
v, cm
Fig. 4. IR spectrum of the product allocated from solution after reaction of cobalt, copper and aluminum nitrates mixture with formaldehyde.
11 Я 3D 40 50 BD 70
2-TTieta - Scale
Fig. 5. The XRD pattern of the compounds received after calcination at 5000C of triple nitrates system reduced by formaldehyde: at 2500C (line 1), at 3000C (line 2) and at 3200C (line 3).
Fig. 6. The electron microscopic image of the sample received by reduction of copper and cobalt nitrates after calcination at 5000C.
The XRD pattern of the compounds received after calcination at 5000C of the triple nitrates system reduced by formaldehyde reveals the formation of copper and cobalt oxides (Figure 5).
Electron microscopic measurements indicate high dispersion of the oxides which are
formed in the course of calcination. From the presented on Figure 6, it can be identified the average particle sizes (29.5 nm) and high uniformity of particles.
It should be noted that despite the absence of X-ray diffractogram of crystallic phases of aluminium compounds, diffraction of secondary
electrons indicates presence of significant amount of aluminium in samples (Figure 7). It can indicate the high dispersion (amorphous) of the phases containing of aluminum compounds.
Reduction of this system by ethylene glycol at 2300C leads to formation of cobalt oxalate dehydrate - Co(C2O4)-2H2O and copper oxalate hydrate (Figure 8.)
The metallic copper, cobalt oxalate hydrate and a small amount of aluminium oxide
was observed in products of reduction of nitrates mixture by glycerine at 2800C (Figure 9).
The X-ray diffractogram of both reduced samples after calcination at 5000C within 2 hours in air reveals the formation of copper oxide (CuO ) and Co3O4. When reaction is carrying at 2500C the nitrogen-containing compounds (dicyaneimide, dimethylformamide) are obtained along with cobalt and copper oxalates.
Fig. 7. The content of elements in the samples after calcination received by reduction of the of cobalt, copper and aluminium nitrates mixture at temperature 2300C by formaldehyde.
Fig. 8. XRD pattern of the sample received by reduction of the copper, cobalt and aluminium nitrates mixture by ethylene glycol at 2500C.
a, c
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a, c
b b
w
b, c
a, c
b b b
2Theta (Coupled TwoTheta/Theta) WL=1.54060
Fig. 9. XRD pattern of the sample received by reduction of the copper-, cobalt- and aluminium nitrates mixture by glycerine at 2800C: a - cobalt oxalate hydrate, b - aluminum oxide, c - metallic copper.
Thus it is shown that either metal car-boxylates (lower than 2400C) or oxides can be formed depending on temperature of hydrothermal reduction of metal nitrates by formaldehyde, ethylene glycol and glycerol. The metal oxides are formed at more high temperatures of process. Copper nitrate can be reduced to metallic state at temperature 2400C. Calcination of reduction products leads to the formation of na-nosize metal oxides particles (~30 nm).
This work was supported by SOCAR Scientific Fond (Grant № 07 from 15.10.2014) and Scientific Research Projects Unit of Marmara University (Project Number -FEN-A-120514-0152).
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HÍDROTERMAL §ORAÍTDO METAL NÍTRATLARIN FORMALDEHÍD, ETÍLENQLÍKOL VO
QLÍSERÍNLO REDUKSÍYASI
O.e.Macidov, P.O.Fatullayeva, S.A.Agayeva, B.Yalcin, S.T.Cafarova, V.M.Ohmadov, M.H.Abbasov
Hidrotermal üsulla 220-2300C-da kobalt, nikel, mis, sink va alüminium nitratlann formaldehid, etilenqlikol va qliserinla reduksiyasi ôyranilmiçdir. Gôstarilmiçdir ki, 2400C-dan açagi temperaturda metal karboksilatlan (oksalatlan, formiatlan) alinir. Nisbatan yüksak temperaturlarda metal oksidlari va karbonatlan alinir. Xüsusi çaraitda Cu va Ni yüksak dispers metallik tozlanni almaq olur. 2400C-dak alinmiç nümunalarin sonradan 5000C-dak qizdirilmasi orta ôlçûsû 30-60 nm olmaqla metal oksidlarinin nanotozlanmn alinmasi ila naticalanir.
Açar sözlar: hodrotermal reduksiya, metal nitratlari, nanohiss3cikhr.
ВОССТАНОВЛЕНИЕ НИТРАТОВ МЕТАЛЛОВ ФОРМАЛЬДЕГИДОМ, ЭТИЛЕНГЛИКОЛЕМ И ГЛИЦЕРИНОМ В ГИДРОТЕРМАЛЬНЫХ УСЛОВИЯХ
А.А.Меджидов, П.А.Фатуллаева, С.А.Агаева, Б.Ялчин, С.Т.Джафарова, В.М.Ахмедов, М.Г.Аббасов
Изучено восстановление нитратов Co(II), Ni(II), Cu(II), Zn(II) и Al(III) формальдегидом, этиленгликолем и глицерином в гидротермальных условиях при температурах 220-3200С. Показано, что при температурах ниже 2400С образуются карбоксилаты металлов (оксалаты и формиаты), в то время как при более высоких температурах образуются оксиды и карбонаты металлов. В определенных условиях можно получить высокодисперсные металлические порошки Cu и Ni. Прокалка при 5000С образцов, полученных в автоклаве, приводит к образованию нанопорошков оксидов металлов со средним размером частиц порядка 30-60 нм.
Ключевые слова: гидротермальные реакции, нитраты металлов, наночастицы.
