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CHEMICAL PROBLEMS 2022 no. 1 (20) ISSN 2221-8688 35
UDC 546
INTERACTION OF COBALT AND MANGANESE NITRATES WITH GRAPHITE UNDER HYDROTHERMAL CONDITIONS
A.A. Mammadova
Acad. M. Nagiyev Institute of Catalysis and Inorganic Chemistry National Academy of Sciences of Azerbaijan AZ1143 Baku, H. Javid Ave., 113; e-mail: aygul.mamdova@gmail.com
Received 12.10.2021 Accepted 04.03.2022
Abstract: The hydrothermal reduction of cobalt and manganese nitrates with graphite in the temperature range of250-3500C has been investigated to obtain nanosized spinel structures. As a result, Co2Mn3O8 and (Co,Mn)(Co,Mn)2O4 spinel phases with average particle sizes of 42 nm and 66 nm have been obtained depending upon reaction conditions (temperature, reaction time and ratio of reagents). The compounds had the following compositions in accordance with the data of energy dispersive analysis (EDA): C-graphite - 86.2%, Co2Mn3O8 - 13.8%, and C-graphite - 93.2%; (Co,Mn)(CoMn)2O4 - 4.8%, Mn3O4 - 1.6%, Co3O4 - 0.5%.
Keywords: hydrothermal synthesis, oxides, graphite, spinel structures. DOI: 10.32737/2221-8688-2022-1-35-39
Introduction
The hydrothermal method is a method of obtaining various chemical compounds and materials (solid-phase substances) based on chemical processes in closed systems that occur in aqueous solutions (as a solvent) at temperatures above 100°C and inder pressures above 1 atmosphere and is one of the most effective methods obtaining single crystals, porous and layered materials, various silicate materials, films and coatings, highly dispersed nanosized powders of metals, their oxides and carbonates [1-3].
The pressure, presence of various reducing agents, temperature, synthesis time, nature of the initial reagents, concentration of the solution, presence of the organic templates, and a number of other parameters [4-6] have their influence on the process of hydrothermal crystallization.
Spinel type structures with a chemical formula of AB2O4 (A, B = Ni, Co, Mn, etc.) are widely used in electronics, catalysis, magnetism and energy storage devices. In the crystal structure of AB2O4 spinel, oxygen anions are closely packed in a face-centered cubic
configuration with 1/8 tetrahedral sites occupied by the A cation and 1/2 octahedral sites occupied by the B cation. Many types of cations can be inserted into the spinel framework by chemical modification. The cations in A and B sites can have oxidation states of +2 to +3 and +2 to +4, respectively.
Mixed transition metal oxides capable of forming spinel structures are playing an increasingly important role in various applications [7].
Metal nitrates form mixed oxide systems interacting with various reducing agents (ethylene glycol, glycerin, formic acid, etc.) under hydrothermal conditions. Cobalt and manganese oxides are able to form spinel structures.
We have previously studied reactions of cobalt and manganese nitrate with various reducing agents under hydrothermal conditions in order to obtain nanosized spinel structures [8].
It ought to be noted that hydrothermal synthesis is a very complex multifactorial process. Advantages of the hydrothermal
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CHEMICAL PROBLEMS 2022 no. 1 (20)
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method in comparison with other methods are that it is a one-stage method and it is possible to carry out the reaction in aqueous solutions at temperatures from 100°C-370°C. It also allows producing metastable compounds and metastable phases, provides the possibility of controlling the morphology, particle size and phase composition of the resulting products.
The investigation of the reaction of graphite with various compounds is of interest from the obtaining intercalates standpoint which can be used as lubricants in chemically
aggressive media and protectors of aggressive substances [9-12].
In this work, we studied the reaction of metal nitrates with graphite in an aqueous medium and obtained Co2Mn3O8 and (Co,Mn)(Co,Mn)2O4 spinel phases. This system can be used in a variety of applications such as electronics, energy storage devices and medical procedures.
It should be noted that the use of graphite as a reducing agent was carried out for the first time in this work
Experimental part
Synthesis technique:
All used reagents corresponded to the analytical grade. The synthesis was carried out in an autoclave made of stainless steel into which a glass ampoule was inserted. A typical experimental technique is shown below:
Obtaining dicobalttrimanganate (IV) oxide Co2Mn3O8:
A glass tube was loaded with 0.72 g of cobalt nitrate Co(NO3)2 , 0.71g of manganese nitrate Mn(NO3)2, 4g of finely ground graphite and 6 ml of distilled water. The autoclave was placed in an oven and kept at a certain temperature from 2500C to 3500C (in different experiments) for 2-12 hours (in different experiments). The resulting precipitate was separated from the reaction solution, washed with water and dried at 700C.
Obtaining cobalt manganese oxide (Co,Mn)(Co,Mn)2O4:
A glass tube was loaded with 0.72 g of cobalt nitrate Co(NO3)2, 0.71g of manganese nitrate Mn(NO3)2, 2g of finely ground graphite and 6 ml of distilled water. The autoclave was
placed in an oven and kept at a temperature of 2700 C for 6 hours (in another experiment, it was kept at a temperature of 3500 C for 3 hours). The resulting precipitate was separated from the reaction solution, washed with water and dried at 700C.
The reaction solution was evaporated in vacuum and the residue studied using IR and UV spectrometry. The phase composition, size and configuration of the particles were examined using a Bruker D2 Phaser X-ray diffractometer (Germany); IR spectra and Electronic Absorption Spectra which were recorded on an FT Nicolet-AS10 Spectrometer (USA) and An Evolution 60s Spectrophotometer, respectively.
The particle size was estimated using the Debye equation:
D=kX/ß cos9 where D- is the particle diameter, X -is the wavelength of X-ray radiation, ß -is the peak width at half maximum, k- is the Scherrer constant equal to 0.89.
Results and their discussion
Previously, we studied the reactions of cobalt and manganese nitrate with various reducing agents - formic acid, ethylene glycol and glycerol under hydrothermal conditions at temperatures of 180-2700C. It was of interest to study the conversion of metal nitrates using graphite as a reducing agent.
We have studied the conversion of cobalt and manganese nitrates in the presence of
graphite (as a reducing agent) at temperatures of 250-3500C under hydrothermal conditions.
When using glycols, reductive decomposition of cobalt and manganese nitrates occur through the stages of formation of oxalates, carbonates, and, ultimately, metal oxides. It revealed that the calcination of samples obtained by hydrothermal reduction of a mixture of cobalt and manganese nitrates with
ethylene glycol leads to the formation of nanosized (20-40nm) spinel powders with the composition (Co,Mn)(Co,Mn)2O4. In most cases, the formation of the (Co,Mn) (Co,Mn) 2O4 phase was observed along with other phases (CoMn2O4, MnOOH, MnCO3).
The X-ray diffraction measurement of the samples obtained by the reduction of nitrates with finely ground graphite (4g) and 2-ethylene glycol (2g) at a temperature of 2500C for 6 hours is indicative that 13.8% Co2Mn3O8 of dicobalttrimanganese (IV) oxide was obtained. In another experiment, 4g of finely ground graphite was used as a reducing agent without changing the composition of the starting products. In this case, 2.1% Co2Mn3O8 of dicobalttrimanganese (IV) oxide was obtained with an average particle size of 42 nm was formed.
It revealed that when the reaction was carried out without a reducing agent (graphite), no changes in the composition of the starting
materials of nitrates were observed; i.e. they were not decomposed or restored. In order to obtain nanosized spinel structures, we changed the initial composition and reaction time. The highest yield of the spinel phase (Co,Mn)(Co,Mn)2O4 (4.8%) with an average particle size of 66 nm -73 nm was observed at a temperature of 2700C and here, a reaction time of 6 hours (Fig. 1).
In the IR spectrum of graphite after the reaction with cobalt and manganese nitrates, an absorption band was observed at 1694 cm-1 which referred to the absorption of the C=O carbonyl group.
The characteristic absorption bands of the benzene ring were observed at ~ 208 and 255 nm in the electronic spectra of reaction solutions (Fig. 2). The band observed at 255 nm contained an electron-vibrational structure which unequivocally, together with the band at 208 nm, revealed the presence of a benzene ring.
Fig. 1. Diffraction pattern of a sample obtained by hydrothermal conversion of cobalt and manganese nitrates mixture in the presence of graphite at a temperature of 270°C.
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A.A. MAMMADOVA
3,5
2,5
1,5
0,5
200 220 240 260 280 300 320 340 360 380 400
X, nm
Fig. 2. UV spectrum of a sample obtained by hydrothermal conversion of a mixture of cobalt and manganese nitrates in the presence of graphite at a temperature of 270°C for 6 hours.
3
2
1
0
Thus, it found that graphite can be used as a reducing agent for cobalt and manganese nitrates under hydrothermal conditions. In this
case, spinel phases are formed in the form of Co2Mn3O8, (Co,Mn)(Co,Mn)2O4 with an average particle size of 42-66 nm.
References
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KOBALT Vd MANQANNiTRATLARIN QRAFiTLB HiDROTERMAL
SdRAiTDd REDUKSiYASI
A.A. Мэттэйоуа
Azdrbaycan Milli Elmldr Akademiyasi akad. M.Nagiyev adina Kataliz vd Qeyri-üzvi Kimya institutu AZ1143 Baki, H.Cavidpr. 113; e-mail: aygul.mamdova@gmail.com
Xülasd: Nanoôlçûlû spinel qurulu§larin alinmasi msqssdi ils 250-3500С temperatur intervalinda kobalt vs manqan nitratlarin qrafitld hidrotermal reduksiyasi ara§dirilmi§dir. Nstics olaraq, reaksiyanin aparilma §sraitindsn asili olaraq (temperatur, zaman va reaktivlsrin nisbstindsn) hisssciyin orta olçûsû 42 - бб nm olan Со2Mn3O8 vs (Co,Mn)(Co,Mn)2O4 §pinel fazalari alinmi§dir. Birls§mslsr enerji dispersiya analizinin nsticslsrins uygun olaraq a§agidaki tsrkiblsrs malikdir: C-qrafit- 86.2%, Со2Mn3O8- 13,8% vs C-qrafit - 93.2% ; (Co,Mn)(Co,Mn)2O4 - 4.8%, Mn3O4- 1.б%, Co3O4- 0.5% .
Açar sözlw. hidrotermal sintez, oksidlsr, qrafit, §pinel qurulu§lar.
ВЗАИМОДЕЙСТВИЕ НИТРАТОВ КОБАЛЬТА И МАРГАНЦА С ГРАФИТОМ В
ГИДРОТЕРМАЛЬНЫХ УСЛОВИАХ А.А. Маммадова
Институт Катализа и Неорганической Химии им. акад. М.Нагиева
Национальной АН Азербайджана AZ1143 Баку, пр.Г.Джавида, 113; e-mail: aygul. mamdova@gmail. com
Аннотация: Исследовано гидротермальное восстановление нитратов кобальта и марганца графитом в интервале температур 250-3500С с целью получения наноразмерных шпинельных структур. В результате, в зависимости от условий проведения реакции (температура, времени и соотношения реагентов) были получены Со2Мп3й8 и (Co,Mn)(Co,Mn)2Ü4 шпинельные фазы со средними размерами частиц 42нм и 66нм. Соединения в соответствии с данными энергодисперсионного анализа (ЭДА) имели следующие составы: С-графит-86.2%, Со2Мп3й8-13,8% и С-графит - 93.2%; (Co,Mn)(Co,Mn)2O4- 4.8%, Mn3O4- 1.6% Co3O4- 0.5%. Ключевые слова: гидротермальный синтез, оксиды, графит, шпинельные структуры.
