TY  - CONF
AU  - Vojisavljević, Katarina
AU  - Benčan Golob, Andreja
AU  - Cilenšek, Jena
AU  - Malič, Barbara
PY  - 2015
UR  - http://rimsi.imsi.bg.ac.rs/handle/123456789/3025
AB  - Over the past two decades, a considerable effort has been devoted to research of the p-type semiconducting materials, which found diverse applications in industry. As the p-type material with a spinel AB2O4 structure and direct optical band gap of 2.19 eV, cobalt oxide, Co3O4 has drawn special interests in gas-sensing and solar energy absorption research community. At the same time, it has found the usage as an electrode material in lithium ion batteries, catalyst, ceramic pigment, field-emission and magnetic material. A powerful strategy to improve the Co3O4 performances in some of the mentioned applications is the utilization of a nanocrystalline powder with a high surface to volume ratio, which can be successfully produced by self-propagation combustion reaction.
In this work, cobalt nitrate (oxidizer) and glycine (fuel) of required amounts were dissolved in the minimum amount of deionized water to obtain a clear solution. According to the rules of propellant chemistry, the glycine/metal ion ratio was adjusted to provide stoichiometric or fuel-lean conditions of the redox reaction. The sols were dried at 80 oC to obtain the gels, and then subjected to the rapid heating, where the gels auto-ignited at approximately 250 oC (depending on the amount of the fuel) and spontaneously underwent a smouldering combustion with evolution of large amounts of gases, subsequently forming a voluminous nanosized Co-oxide powder. 
It is worth to mention that the dual role of the glycine (chelating agent and fuel) in this synthesis was of great importance in preventing the precipitation of the solution during rapid heating, and in liberation of the required energy for the synthesis of the Co3O4 powder with desired Co+2/Co+3 oxidation state, necessary for its further use in production of gas sensors and catalysts. The processes involved in formation of the pure Co3O4 powder and especially the exothermicity of the reaction, were followed by simultaneous thermal analysis (thermogravimetric and differential thermal analysis coupled with evolved gas analysis). According to the X-ray diffraction analysis the phase-pure Co3O4 was obtained only when the precursor powder was prepared from the fuel-lean redox reaction. The field emission scanning electron micrographs revealed the spongy aspect of the calcined powder, where small primary particles formed the agglomerates. The transmission electron microscopy was used to get deeper insight in the particle size and purity of the as prepared nanosized powders. The formation of the single Co3O4 powder from the solution to the combusted powder was also analysed by Fourier transformed infra-red spectroscopy.
PB  - Central and Eastern European Committee for Thermal Analysis and Calorimetry, cop. 2015
C3  - 3rd Central and Eastern European Conference on Thermal Analysis and Calorimetry
T1  - Synthesis of nanocrystalline Co3O4 nanopowders via self-propagation combustion reaction
EP  - 281
SP  - 281
UR  - https://hdl.handle.net/21.15107/rcub_rimsi_3025
ER  - 

@conference{
author = "Vojisavljević, Katarina and Benčan Golob, Andreja and Cilenšek, Jena and Malič, Barbara",
year = "2015",
abstract = "Over the past two decades, a considerable effort has been devoted to research of the p-type semiconducting materials, which found diverse applications in industry. As the p-type material with a spinel AB2O4 structure and direct optical band gap of 2.19 eV, cobalt oxide, Co3O4 has drawn special interests in gas-sensing and solar energy absorption research community. At the same time, it has found the usage as an electrode material in lithium ion batteries, catalyst, ceramic pigment, field-emission and magnetic material. A powerful strategy to improve the Co3O4 performances in some of the mentioned applications is the utilization of a nanocrystalline powder with a high surface to volume ratio, which can be successfully produced by self-propagation combustion reaction.
In this work, cobalt nitrate (oxidizer) and glycine (fuel) of required amounts were dissolved in the minimum amount of deionized water to obtain a clear solution. According to the rules of propellant chemistry, the glycine/metal ion ratio was adjusted to provide stoichiometric or fuel-lean conditions of the redox reaction. The sols were dried at 80 oC to obtain the gels, and then subjected to the rapid heating, where the gels auto-ignited at approximately 250 oC (depending on the amount of the fuel) and spontaneously underwent a smouldering combustion with evolution of large amounts of gases, subsequently forming a voluminous nanosized Co-oxide powder. 
It is worth to mention that the dual role of the glycine (chelating agent and fuel) in this synthesis was of great importance in preventing the precipitation of the solution during rapid heating, and in liberation of the required energy for the synthesis of the Co3O4 powder with desired Co+2/Co+3 oxidation state, necessary for its further use in production of gas sensors and catalysts. The processes involved in formation of the pure Co3O4 powder and especially the exothermicity of the reaction, were followed by simultaneous thermal analysis (thermogravimetric and differential thermal analysis coupled with evolved gas analysis). According to the X-ray diffraction analysis the phase-pure Co3O4 was obtained only when the precursor powder was prepared from the fuel-lean redox reaction. The field emission scanning electron micrographs revealed the spongy aspect of the calcined powder, where small primary particles formed the agglomerates. The transmission electron microscopy was used to get deeper insight in the particle size and purity of the as prepared nanosized powders. The formation of the single Co3O4 powder from the solution to the combusted powder was also analysed by Fourier transformed infra-red spectroscopy.",
publisher = "Central and Eastern European Committee for Thermal Analysis and Calorimetry, cop. 2015",
journal = "3rd Central and Eastern European Conference on Thermal Analysis and Calorimetry",
title = "Synthesis of nanocrystalline Co3O4 nanopowders via self-propagation combustion reaction",
pages = "281-281",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_3025"
}

Vojisavljević, K., Benčan Golob, A., Cilenšek, J.,& Malič, B.. (2015). Synthesis of nanocrystalline Co3O4 nanopowders via self-propagation combustion reaction. in 3rd Central and Eastern European Conference on Thermal Analysis and Calorimetry
Central and Eastern European Committee for Thermal Analysis and Calorimetry, cop. 2015., 281-281.
https://hdl.handle.net/21.15107/rcub_rimsi_3025

Vojisavljević K, Benčan Golob A, Cilenšek J, Malič B. Synthesis of nanocrystalline Co3O4 nanopowders via self-propagation combustion reaction. in 3rd Central and Eastern European Conference on Thermal Analysis and Calorimetry. 2015;:281-281.
https://hdl.handle.net/21.15107/rcub_rimsi_3025 .

Vojisavljević, Katarina, Benčan Golob, Andreja, Cilenšek, Jena, Malič, Barbara, "Synthesis of nanocrystalline Co3O4 nanopowders via self-propagation combustion reaction" in 3rd Central and Eastern European Conference on Thermal Analysis and Calorimetry (2015):281-281,
https://hdl.handle.net/21.15107/rcub_rimsi_3025 .

TY  - CONF
AU  - Vojisavljević, Katarina
AU  - Stojanović, Biljana
AU  - Kmet, Brigita
AU  - Cilenšek, Jena
AU  - Malič, Barbara
PY  - 2013
UR  - http://rimsi.imsi.bg.ac.rs/handle/123456789/2917
AB  - Recently, a considerable effort has been devoted to research and improvement of both dielectrics and wide band-gap semiconductors for the realization of fully transparent devices. Due to the lack of available p-type transparent conducting oxide (TCO) materials, special attention was paid to production of delafossite structured CuMO2 (M = Al, Cr or Y), which exhibit sufficiently large energy gap, required for transparency across the full visible spectrum, and high enough concentration of holes with sufficiently large mobility. Those materials are considered to be good candidates for p-type TCOs. Among them, the CuAlO2 seems to be the most promising candidate to fulfill the demands for technical application. 
However, related studies on CuAlO2 are interested not only in examination of the transparent conducting oxides properties, but also in exploring its applications as a catalyst for the conversion of solar power to hydrogen energy, catalysts for steam reforming process and exhaust gas purification, room temperature ozone sensors, or thermoelectric devices. The performance of CuAlO2 in some of the mentioned applications could be optimized by increasing surface area and decreasing its particle size. Therefore, the synthesis of nanocrystalline CuAlO2 has been a hot topic for material chemists.
The nanocrystalline delafossite CuAlO2 powder was synthesised by a sol-gel nitrate-citrate self-sustained combustion route. Citric acid was introduced both as the chelating and reducing agent or fuel. The citric acid/metal ion ratio was adjusted to provide fuel-lean, stoichiometric or fuel-rich conditions of the redox reaction. Equimolar amounts of copper and aluminium nitrates and the citric acid were dissolved in deionized water. The solution was agitated at room temperature for 1 h, and then neutralized to increase the efficiency of chelating agent. After several hours of drying in temperature range 60 oC – 80 oC, the sol was turned to homogeneous viscous gel. During the rapid heating, the gels auto-ignited at approximately 250 oC (depending on the amount of the fuel) and underwent smouldering combustion spontaneously with the evolution of large amounts of gases, subsequently forming the grey-black voluminous precursor powders. 
According to the X-ray diffraction analysis the phase pure delafossite was obtained only when the precursor powder was prepared from the stoichiometric redox reaction, and after the calcination at 920 oC for 4 h in Ar atmosphere. The field emission scanning electron micrographs revealed the cauliflower aspect of the calcined powder, where small primary particles formed the agglomerates. The formation of the phase pure CuAlO2 powder was also confirmed by Fourier transformed infrared spectroscopy. 
Compared with the solid state synthesis where high processing temperatures (1100 oC) and long reaction times (96 h) have been used to obtain single-phase delafossite CuAlO2 [1, 2], both the calcination temperature and the dwell time are certainly lowered by the proposed citrate-nitrate combustion route.

References: 
[1] Liou, Y.C.; Lee, U.R. J. Alloys Comp. 467,:496(2009).
[2] Zheng, X.G.; Taniguchi, K.; Takahashi, A.; Liu, Y.; Xu, C.N. Appl. Phys. Lett. 85, 1728(2004).

Acknowledgments:
We acknowledge the financial support of the Slovenian research agency (research programme P2-0105 and projects J2-4273) and the EC within the 7FP ORAMA project: Oxide materials for electronics applications, Grant Agreement NMP3-LA-2010-246334.
PB  - Ljubljana : Jožef Stefan Institute, 2013
C3  - SLONANO
T1  - Self-sustained combustion synthesis of the p-type nanocrystalline CuAlO2 powder
EP  - 79
SP  - 79
UR  - https://hdl.handle.net/21.15107/rcub_rimsi_2917
ER  - 

@conference{
author = "Vojisavljević, Katarina and Stojanović, Biljana and Kmet, Brigita and Cilenšek, Jena and Malič, Barbara",
year = "2013",
abstract = "Recently, a considerable effort has been devoted to research and improvement of both dielectrics and wide band-gap semiconductors for the realization of fully transparent devices. Due to the lack of available p-type transparent conducting oxide (TCO) materials, special attention was paid to production of delafossite structured CuMO2 (M = Al, Cr or Y), which exhibit sufficiently large energy gap, required for transparency across the full visible spectrum, and high enough concentration of holes with sufficiently large mobility. Those materials are considered to be good candidates for p-type TCOs. Among them, the CuAlO2 seems to be the most promising candidate to fulfill the demands for technical application. 
However, related studies on CuAlO2 are interested not only in examination of the transparent conducting oxides properties, but also in exploring its applications as a catalyst for the conversion of solar power to hydrogen energy, catalysts for steam reforming process and exhaust gas purification, room temperature ozone sensors, or thermoelectric devices. The performance of CuAlO2 in some of the mentioned applications could be optimized by increasing surface area and decreasing its particle size. Therefore, the synthesis of nanocrystalline CuAlO2 has been a hot topic for material chemists.
The nanocrystalline delafossite CuAlO2 powder was synthesised by a sol-gel nitrate-citrate self-sustained combustion route. Citric acid was introduced both as the chelating and reducing agent or fuel. The citric acid/metal ion ratio was adjusted to provide fuel-lean, stoichiometric or fuel-rich conditions of the redox reaction. Equimolar amounts of copper and aluminium nitrates and the citric acid were dissolved in deionized water. The solution was agitated at room temperature for 1 h, and then neutralized to increase the efficiency of chelating agent. After several hours of drying in temperature range 60 oC – 80 oC, the sol was turned to homogeneous viscous gel. During the rapid heating, the gels auto-ignited at approximately 250 oC (depending on the amount of the fuel) and underwent smouldering combustion spontaneously with the evolution of large amounts of gases, subsequently forming the grey-black voluminous precursor powders. 
According to the X-ray diffraction analysis the phase pure delafossite was obtained only when the precursor powder was prepared from the stoichiometric redox reaction, and after the calcination at 920 oC for 4 h in Ar atmosphere. The field emission scanning electron micrographs revealed the cauliflower aspect of the calcined powder, where small primary particles formed the agglomerates. The formation of the phase pure CuAlO2 powder was also confirmed by Fourier transformed infrared spectroscopy. 
Compared with the solid state synthesis where high processing temperatures (1100 oC) and long reaction times (96 h) have been used to obtain single-phase delafossite CuAlO2 [1, 2], both the calcination temperature and the dwell time are certainly lowered by the proposed citrate-nitrate combustion route.

References: 
[1] Liou, Y.C.; Lee, U.R. J. Alloys Comp. 467,:496(2009).
[2] Zheng, X.G.; Taniguchi, K.; Takahashi, A.; Liu, Y.; Xu, C.N. Appl. Phys. Lett. 85, 1728(2004).

Acknowledgments:
We acknowledge the financial support of the Slovenian research agency (research programme P2-0105 and projects J2-4273) and the EC within the 7FP ORAMA project: Oxide materials for electronics applications, Grant Agreement NMP3-LA-2010-246334.",
publisher = "Ljubljana : Jožef Stefan Institute, 2013",
journal = "SLONANO",
title = "Self-sustained combustion synthesis of the p-type nanocrystalline CuAlO2 powder",
pages = "79-79",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2917"
}

Vojisavljević, K., Stojanović, B., Kmet, B., Cilenšek, J.,& Malič, B.. (2013). Self-sustained combustion synthesis of the p-type nanocrystalline CuAlO2 powder. in SLONANO
Ljubljana : Jožef Stefan Institute, 2013., 79-79.
https://hdl.handle.net/21.15107/rcub_rimsi_2917

Vojisavljević K, Stojanović B, Kmet B, Cilenšek J, Malič B. Self-sustained combustion synthesis of the p-type nanocrystalline CuAlO2 powder. in SLONANO. 2013;:79-79.
https://hdl.handle.net/21.15107/rcub_rimsi_2917 .

Vojisavljević, Katarina, Stojanović, Biljana, Kmet, Brigita, Cilenšek, Jena, Malič, Barbara, "Self-sustained combustion synthesis of the p-type nanocrystalline CuAlO2 powder" in SLONANO (2013):79-79,
https://hdl.handle.net/21.15107/rcub_rimsi_2917 .

TY  - CONF
AU  - Vojisavljević, Katarina
AU  - Stojanović, Biljana
AU  - Kmet, Brigita
AU  - Cilenšek, Jena
AU  - Malič, Barbara
PY  - 2013
UR  - http://rimsi.imsi.bg.ac.rs/handle/123456789/2901
AB  - The nanocrystalline delafossite CuAlO2 powder was synthesised by a sol-gel nitrate-citrate self-combustion route. Citric acid was introduced both as the chelating and reducing agent or fuel. The citric acid/metal ion ratio was adjusted to provide fuel-lean, stoichiometric or fuel-rich conditions of the redox reaction. Equimolar amounts of copper and aluminium nitrates and the citric acid were dissolved in deionized water. The sol was dried at 80 oC to obtain the gel. By increasing the temperature above 250 oC, the gel immediately ignited, forming the precursor powder. According to the X-ray diffraction analysis the phase pure delafossite was obtained only when the precursor powder was prepared from the stoichiometric redox reaction, and after the calcination for 4 h in Ar atmosphere at 920 oC. The field emission scanning electron micrographs revealed the cauliflower aspect of the calcined powder, where small primary particles formed the agglomerates. The formation of the phase pure CuAlO2 powder was also confirmed by Fourier transformed infrared spectroscopy.
PB  - Maribor : Fakulteta za kemijo in kemijsko tehnologijo
C3  - Slovenski kemijski dnevi 2013
T1  - Chemical synthesis of nanocrystalline CuAlO2 via nitrate-citrate combustion route
IS  - 7
UR  - https://hdl.handle.net/21.15107/rcub_rimsi_2901
ER  - 

@conference{
author = "Vojisavljević, Katarina and Stojanović, Biljana and Kmet, Brigita and Cilenšek, Jena and Malič, Barbara",
year = "2013",
abstract = "The nanocrystalline delafossite CuAlO2 powder was synthesised by a sol-gel nitrate-citrate self-combustion route. Citric acid was introduced both as the chelating and reducing agent or fuel. The citric acid/metal ion ratio was adjusted to provide fuel-lean, stoichiometric or fuel-rich conditions of the redox reaction. Equimolar amounts of copper and aluminium nitrates and the citric acid were dissolved in deionized water. The sol was dried at 80 oC to obtain the gel. By increasing the temperature above 250 oC, the gel immediately ignited, forming the precursor powder. According to the X-ray diffraction analysis the phase pure delafossite was obtained only when the precursor powder was prepared from the stoichiometric redox reaction, and after the calcination for 4 h in Ar atmosphere at 920 oC. The field emission scanning electron micrographs revealed the cauliflower aspect of the calcined powder, where small primary particles formed the agglomerates. The formation of the phase pure CuAlO2 powder was also confirmed by Fourier transformed infrared spectroscopy.",
publisher = "Maribor : Fakulteta za kemijo in kemijsko tehnologijo",
journal = "Slovenski kemijski dnevi 2013",
title = "Chemical synthesis of nanocrystalline CuAlO2 via nitrate-citrate combustion route",
number = "7",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2901"
}

Vojisavljević, K., Stojanović, B., Kmet, B., Cilenšek, J.,& Malič, B.. (2013). Chemical synthesis of nanocrystalline CuAlO2 via nitrate-citrate combustion route. in Slovenski kemijski dnevi 2013
Maribor : Fakulteta za kemijo in kemijsko tehnologijo.(7).
https://hdl.handle.net/21.15107/rcub_rimsi_2901

Vojisavljević K, Stojanović B, Kmet B, Cilenšek J, Malič B. Chemical synthesis of nanocrystalline CuAlO2 via nitrate-citrate combustion route. in Slovenski kemijski dnevi 2013. 2013;(7).
https://hdl.handle.net/21.15107/rcub_rimsi_2901 .

Vojisavljević, Katarina, Stojanović, Biljana, Kmet, Brigita, Cilenšek, Jena, Malič, Barbara, "Chemical synthesis of nanocrystalline CuAlO2 via nitrate-citrate combustion route" in Slovenski kemijski dnevi 2013, no. 7 (2013),
https://hdl.handle.net/21.15107/rcub_rimsi_2901 .