Catalytic Activity of Co3O4 Nanomaterials with Different Morphologies for the Thermal Decomposition of Ammonium Perchlorate

Abstract

Nano-Co3O4 with different morphologies was successfully synthesized by annealing CoC2O4·2H2O precursors. The as-obtained samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and low-temperature nitrogen adsorption-desorption. It was found that the volume ratio of N,N-dimethylformamide (DMF) and water played an important role in the formation of cobalt oxalate precursors with different morphologies. After calcination in air, cobalt oxalate precursors converted to Co3O4 nanomaterials while their original morphologies were maintained. The catalytic effect was investigated for nano-Co3O4 with different morphologies on the thermal decomposition of ammonium perchlorate (AP) by differential scanning calorimeter (DSC). The results indicated that all products showed excellent catalytic activity for thermal decomposition of AP and the Co3O4 nanorods with larger BET surface area and pore volume had the highest catalytic activity.

Li-Na Jin 1 and Jian-Guo Wang 1 and Xin-Ye Qian 1 and Dan Xia 2 and Ming-Dong Dong 2

Academic Editor:P. Davide Cozzoli

1, Institute for Advanced Materials and School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China
2, Center for DNA Nanotechnology (CDNA), Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000 Aarhus, Denmark

Received 9 March 2015; Accepted 20 April 2015; 5 October 2015

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Morphology-controlled synthesis of inorganic nanomaterials is of extensive research interest in materials science because the electronic, optical, magnetic, and catalytic properties of nanocrystals are highly dependent on not only their composition, but also their structure [1], shape [2], and size [3]. Therefore, many efforts have been made to develop cost-effective synthesis methods of nanomaterials with different structures and morphologies for enabling novel intrinsic properties and applications of nanomaterials.

Co₃ O₄ , as one of the most intriguing magnetic p-type semiconductors, is of special interest due to its potential applications in heterogeneous catalyst [4], lithium-ion battery [5], supercapacitor [6], gas sensor [7], and many other aspects [8]. Up to now, shape-controlled Co₃ O₄ nanostructures have been prepared by various approaches, in which morphology-conserved transformation of precursors has proved to be a promising approach for the synthesis of Co₃ O₄ nanostructures [9-12]. For example, Zhu et al. reported the shape-controlled synthesis of cobalt carbonate/hydroxide intermediates via a solvothermal method at 220°C for 18 h [9]. Hu et al. synthesized β -Co(OH)₂ nanosheet at 180°C for 12 h and Co(CO₃ )_0.5 (OH)_0.11 H₂ O nanobelt at 140°C for 12 h via a solvothermal method [10]. Wang et al. prepared one-dimensional and layered parallel folding of cobalt oxalate nanostructures using N,N-dimethylacetamide (DMA) and dimethyl sulfoxide (DMSO) as solvents at ambient temperature [11]. In our past work, we prepared shape-controlled synthesis of Co₃ O₄ nanostructures derived from coordination polymer precursors [12]. However, for some shape-controlled synthesis methods, special instruments, complicated processes, long reaction times, and relatively high temperatures are required. Therefore, it is important to design a simple, rapid, low-temperature, and low-cost synthesis route to synthesize morphology-controlled cobalt precursors.

Over the past decades, ammonium perchlorate (AP) has received considerable attention because AP is an important oxidizer in solid composite propellants for solid fueled rockets and the combustion behavior of propellants is highly relevant to the thermal decomposition of AP. The lower the temperature at which AP begins to decompose, the higher the burning rate of propellants [13-15]. Recently, Co₃ O₄ nanomaterials with various morphologies have been used as effective catalyst to accelerate thermal decomposition of AP [12, 16-19].

In the present work, we report morphology-controlled preparation of cobalt oxalate precursors from the reaction of cobalt(II) nitrate hexahydrate and oxalic acid under mild conditions. It was found that the volume ratio of N,N-dimethylformamide (DMF) and water played a crucial role in the formation of cobalt oxalate with different morphologies. After calcination in air, the as-prepared cobalt oxalate precursors subsequently converted to porous Co₃ O₄ nanomaterials while their original morphologies had been well maintained. To study their potential applications, the as-prepared nano-Co₃ O₄ with different morphologies had been applied in the thermal decomposition of AP, which exhibited good activity.

2. Experimental

All chemicals and solvents are of analytical grade and were used as received without further purification. In a typical experiment, 1 mmol Co(NO₃ )₂ [figure omitted; refer to PDF] 6H₂ O was dissolved in a mixed solution of DMF and deionized water at room temperature (the total volume is 20 mL), followed by addition of 1 mmol H₂ C₂ O₄ [figure omitted; refer to PDF] 2H₂ O under vigorous stirring. After 5 min, the as-obtained precipitates were centrifuged, washed with distilled water and absolute ethanol several times, and dried in vacuum at 60°C for 5 h. In addition, a calcination process (350°C for 1 h in air with a heating rate of 2°C min^-1 ) was performed to transform cobalt oxalate to black Co₃ O₄ crystals. In the experiments, to obtain products with different morphologies, the volume ratio of DMF and water was adjusted while all other conditions were keeping unaltered.

The products were characterized by powder X-ray diffraction (XRD) on a Rigaku D/max 2500PC diffractometer with graphite monochromator and Cu K _α radiation (λ = 0.15406 nm) at a step width of 0.02°. SEM images of the products were obtained on scanning electron micro analyzers (HITACHI S-3400N,). Nitrogen adsorption-desorption isotherms, pore size distributions, and surface areas of the samples were measured by the instrument of NOVA 2000e using N₂ adsorption.

To test the catalytic effect of Co₃ O₄ nanostructures with different morphologies on the thermal decomposition of AP, the mixture of AP and Co₃ O₄ was ground carefully for 10 min and was detected by a differential scanning calorimeter (DSC) using STA 449C thermal analyzer with a heating rate of 10°C min^-1 in N₂ atmosphere over the temperature range of 30-500°C. The mass percentage of Co₃ O₄ nanostructures to AP in the mixture was 2%.

3. Results and Discussion

Figure 1 shows the XRD patterns of the precursors prepared under the different volume ratio of DMF and water. All of the diffraction peaks in Figure 1(a), 1(b), 1(c), and 1(d) can be indexed as the orthorhombic phase of CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O by comparison with the data of JCPDS card files number 25-0250. No impurity peaks are detected in the XRD pattern.

Figure 1: XRD patterns of the as-prepared precursors under the different volume ratio of DMF and water: (a) 0 : 20, (b) 4 : 16, (c) 8 : 12, and (d) 12 : 8.

[figure omitted; refer to PDF]

Morphologies of all the precursors were characterized by SEM and the images of the samples are shown in Figure 2. When 20 mL of H₂ O was used without addition of DMF, the result shown in Figure 2(a) reveals that sample is composed of CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O microrods with diameter of about 2-5 μ m. When 16 mL of H₂ O and 4 mL of DMF were used, spindle-like CoC₂ O₄ ·2H₂ O nanostructures were obtained, shown in Figure 2(b). Figure 2(c) shows the morphology of sample prepared in the presence of 12 mL of H₂ O and 8 mL of DMF. It was observed that the sample consisted of nanorod bundles. Figure 2(d) illustrates nanorods in sample prepared by using 8 mL of H₂ O and 12 mL of DMF. In addition, when 4 mL of H₂ O and 16 mL of DMF were used or 20 mL of DMF was used without addition of H₂ O, no products could be obtained. The above facts showed that DMF/water volume ratio played an important role in the information of CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O. According to the previously reported studies, when only water was used as solvent, CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O microrods were obtained because the ion-exchange reaction between the cobalt ion and the oxalate ion was very rapid in aqueous solution. In organic solvent medium, oxalic acid is a weak electrolyte that cannot be electrolytically dissociated into ions, so the cobalt ion and the oxalic acid do not react immediately. Therefore, when DMF and water were used, the reaction rate slowed down leading to smaller products, including spindle-like architectures, nanorod bundles, and nanorods. Furthermore, when the amount of DMF was increased to 16 mL or 20 mL, no products were obtained because the ion-exchange reaction was restrained [11].

Figure 2: SEM images of the as-prepared cobalt oxalate precursors and Co₃ O₄ nanostructures: (a, e) microrods, (b, f) spindle-like architectures, (c, g) nanorod bundles, and (d, h) nanorods.

[figure omitted; refer to PDF]

The thermal behavior of CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O microrods was investigated by thermogravimetric analysis (TGA) in static air atmosphere. From Figure 3, it can be seen that there are two distinct weight loss steps. The first weight loss occurs at 110-220°C, which corresponds to the evaporation of crystallized water. When the temperature is above 300°C, the second weight loss was observed, which is attributed to the decomposition of anhydrous oxalate into Co₃ O₄ . The weight loss of two steps is about 19.7% and 53.3%, which is close to the theoretical value. The decomposition of CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O can be expressed as the following reaction: [figure omitted; refer to PDF]

Figure 3: TGA curve of the as-obtained CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O microrods.

[figure omitted; refer to PDF]

According to the results of TGA, the thermal decomposition of the corresponding CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O was performed at 350°C. After being annealed at 350°C for 1 h in air, the as-synthesized CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O with different morphologies were completely converted to phase-pure spinel Co₃ O₄ . The morphology of the Co₃ O₄ products is shown in Figures 2(e)-2(h), from which it can be seen that the original shape has been maintained after calcination. The crystallographic phase of all the samples is again examined by XRD (Figure 4). All diffraction peaks can be well indexed to the pure cubic phase of Co₃ O₄ (JCPDS 43-1003), indicating that the pure phase of Co₃ O₄ was obtained by annealing CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O precursor directly. Figure 5 shows TEM images of the Co₃ O₄ products, revealing that the Co₃ O₄ products were composed of numerous Co₃ O₄ nanoparticles with a size of several tens of nanometers and abundant pore structures were formed among the nanoparticles.

Figure 4: XRD patterns of the as-prepared Co₃ O₄ nanostructures: (a) microrods, (b) spindle-like architectures, (c) nanorod bundles, and (d) nanorods.

[figure omitted; refer to PDF]

Figure 5: TEM images of the as-prepared Co₃ O₄ nanostructures: (a) microrods, (b) spindle-like architectures, (c) nanorod bundles, and (d) nanorods.

[figure omitted; refer to PDF]

Nitrogen adsorption-desorption isotherms of nano-Co₃ O₄ are shown in Figure 6, and the insets illustrate the corresponding Barrett-Joyner-Halenda (BJH) pore size distribution plots. The isotherms can be categorized as type IV with an H3 hysteresis loop, which is characteristic of mesoporous materials. The BJH pore size distribution indicates that all of the samples contain mesoscale pores. The Brunauer-Emmett-Teller (BET) surface areas and pore volumes of the samples are 42 m² /g and 190.3 mm³ /g, 61 m² /g and 226.3 mm³ /g, 62 m² /g and 241.3 mm³ /g, and 83 m² /g and 277.1 mm³ /g for the Co₃ O₄ with microrods, spindle-like architectures, nanorod bundles, and nanorods, respectively.

Figure 6: N₂ adsorption-desorption isotherms of as-prepared Co₃ O₄ nanostructures at 77 K: (a) microrods, (b) spindle-like architectures, (c) nanorod bundles, and (d) nanorods. Inset in each isotherm is the corresponding pore size distributions.

(a) [figure omitted; refer to PDF]

(b) [figure omitted; refer to PDF]

(c) [figure omitted; refer to PDF]

(d) [figure omitted; refer to PDF]

Considering the porous structures and high BET surface area, we investigated the application of the synthesized nano-Co₃ O₄ for the thermal decomposition of AP. Figure 7 shows DSC curves for thermal decomposition of pure AP and its mixture with nano-Co₃ O₄ with different morphologies. For pure AP, an endothermic peak was observed at about 250°C, which is due to the crystal transformation of AP from orthorhombic to cubic phase (Figure 7(e)) [13]. When nano-Co₃ O₄ with different morphologies as catalyst was added to AP, all samples have similar endothermic peaks at about 250°C, indicating that the catalysts have little effect on the crystallographic transition temperature of AP. However, in the relatively high temperature region, the samples containing catalysts have dramatic changes in the exothermic peaks of AP decomposition. When 2 wt% catalysts were added to AP, the original exothermic peak of pure AP at 445.0°C disappeared and only one exothermic peak was observed. The exothermic peak temperature was 305.1, 299.7, 297.4, and 296.2°C for Co₃ O₄ microrods, spindle-like architectures, nanorod bundles, and nanorods, respectively (Figure 7(a)-7(d)). The present catalytic activity of Co₃ O₄ nanorods was higher than Co₃ O₄ nanoparticles, nanosheets, and octahedral particles [12, 18, 19]. The above results indicate that Co₃ O₄ particles have a significant effect on the decomposition temperature of AP and Co₃ O₄ nanomaterials with different morphologies for decreasing the decomposition of AP are proportional to their BET surface area and pore volume. It is known that specific surface area and pore volume can be the primary reasons for the catalytic role, since more reactive sites can be generated [12, 20, 21]. Thus, Co₃ O₄ nanorods with larger BET surface area and pore volume have the most effective catalytic activity and the thermal decomposition temperature of AP shifted downward about 148.8°C.

Figure 7: DSC curves of the AP samples after addition of various Co₃ O₄ nanostructures: (a) 2 wt% Co₃ O₄ microrods, (b) 2 wt% Co₃ O₄ spindle-like architectures, (c) 2 wt% Co₃ O₄ nanorod bundles, (d) 2 wt% Co₃ O₄ nanorods, and (e) pure AP.

[figure omitted; refer to PDF]

4. Conclusions

In summary, we synthesized porous nano-Co₃ O₄ with different morphologies via annealing CoC₂ O₄ [figure omitted; refer to PDF] 2H₂ O precursors prepared under ambient condition without the assistance of template or surfactant. The as-prepared porous nano-Co₃ O₄ with different morphologies have good catalytic properties for the thermal decomposition of AP due to their large BET surface area and pore volume. Co₃ O₄ nanorods with larger BET surface area and pore volume show better catalytic activity than others and shifted the AP thermal decomposition temperature downwardly to about 148.8°C.

Acknowledgments

The authors acknowledge the financial support by National Natural Science Foundation of China (no. 21401081), China Postdoctoral Science Foundation (no. 2014M560397), Jiangsu Natural Science Funds for Distinguished Young Scholars (no. BK20140013), Jiangsu Postdoctoral Science Foundation (no. 1401051C), and the Senior Intellectuals Fund of Jiangsu University (nos. 14JDG058 and 11JDG098).

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

References

[1] Q. Hua, T. Cao, X.-K. Gu, J. Lu, Z. Jiang, X. Pan, L. Luo, W.-X. Li, W. Huang, "Crystal-plane-controlled selectivity of Cu₂ O catalysts in propylene oxidation with molecular oxygen," Angewandte Chemie-International Edition , vol. 53, no. 19, pp. 4856-4861, 2014.

[2] Y. Zhong, J. Wang, R. Zhang, W. Wei, H. Wang, X. Lü, F. Bai, H. Wu, R. Haddad, H. Fan, "Morphology-controlled self-assembly and synthesis of photocatalytic nanocrystals," Nano Letters , vol. 14, no. 12, pp. 7175-7179, 2014.

[3] Y. Li, Y. Huang, "Morphology-controlled synthesis of platinum nanocrystals with specific peptides," Advanced Materials , vol. 22, no. 17, pp. 1921-1925, 2010.

[4] L. Chen, J. Hu, R. Richards, S. Prikhodko, S. Kodambaka, "Synthesis and surface activity of single-crystalline Co₃ O₄ (111) holey nanosheets," Nanoscale , vol. 2, no. 9, pp. 1657-1660, 2010.

[5] B. Yan, L. Chen, Y. Liu, G. Zhu, C. Wang, H. Zhang, G. Yang, H. Ye, A. Yuan, "Co₃ O₄ nanostructures with a high rate performance as anode materials for lithium-ion batteries, prepared via book-like cobalt-organic frameworks," CrystEngComm , vol. 16, no. 44, pp. 10227-10234, 2014.

[6] H. Wang, L. Zhang, X. Tan, C. M. B. Holt, B. Zahiri, B. C. Olsen, D. Mitlin, "Supercapacitive properties of hydrothermally synthesized Co₃ O₄ nanostructures," The Journal of Physical Chemistry C , vol. 115, no. 35, pp. 17599-17605, 2011.

[7] Y. Lü, W. Zhan, Y. He, Y. Wang, X. Kong, Q. Kuang, Z. Xie, L. Zheng, "MOF-templated synthesis of porous Co₃ O₄ concave nanocubes with high specific surface area and their gas sensing properties," ACS Applied Materials and Interfaces , vol. 6, no. 6, pp. 4186-4195, 2014.

[8] Y. Du, W. Huang, Z. Hua, Y. Wang, X. Cui, M. Wu, Z. Shu, L. Zhang, J. Wang, H. Chen, J. Shi, "A facile ultrasonic process for the preparation of Co₃ O₄ nanoflowers for room-temperature removal of low-concentration NO_x ," Catalysis Communications , vol. 57, pp. 73-77, 2014.

[9] T. Zhu, J. S. Chen, X. W. Lou, "Shape-controlled synthesis of porous Co₃ O₄ nanostructures for application in supercapacitors," Journal of Materials Chemistry , vol. 20, no. 33, pp. 7015-7020, 2010.

[10] L. Hu, Q. Peng, Y. Li, "Selective synthesis of Co₃ O₄ nanocrystal with different shape and crystal plane effect on catalytic property for methane combustion," Journal of the American Chemical Society , vol. 130, no. 48, pp. 16136-16137, 2008.

[11] D. Wang, Q. Wang, T. Wang, "Morphology-controllable synthesis of cobalt oxalates and their conversion to mesoporous Co₃ O₄ nanostructures for application in supercapacitors," Inorganic Chemistry , vol. 50, no. 14, pp. 6482-6492, 2011.

[12] L.-N. Jin, Q. Liu, W.-Y. Sun, "Shape-controlled synthesis of Co₃ O₄ nanostructures derived from coordination polymer precursors and their application to the thermal decomposition of ammonium perchlorate," CrystEngComm , vol. 14, no. 22, pp. 7721-7726, 2012.

[13] S. Chaturvedi, P. N. Dave, "A review on the use of nanometals as catalysts for the thermal decomposition of ammonium perchlorate," Journal of Saudi Chemical Society , vol. 17, no. 2, pp. 135-149, 2013.

[14] W. Wang, J. Yao, "Catalytic activity of magnetite with different shapes for the thermal decomposition of ammonium perchlorate," Chemistry Letters , vol. 43, no. 10, pp. 1554-1556, 2014.

[15] L.-N. Jin, Q. Liu, W.-Y. Sun, "Room temperature solution-phase synthesis of flower-like nanostructures of [Ni₃ (BTC)₂ ·12H₂ O] and their conversion to porous NiO," Chinese Chemical Letters , vol. 24, no. 8, pp. 663-667, 2013.

[16] S. Jamil, M. R. Janjua, T. Ahmad, "The synthesis of flower shaped microstructures of Co₃ O₄ by solvothermal approach and investigation of its catalytic activity," Solid State Sciences , vol. 36, pp. 73-79, 2014.

[17] X. Guan, G. Li, L. Zhou, L. Li, X. Qiu, "Template-free approach to core-shell-structured Co₃ O₄ microspheres," Chemistry Letters , vol. 38, no. 3, pp. 280-281, 2009.

[18] E. Alizadeh-Gheshlaghi, B. Shaabani, A. Khodayari, Y. Azizian-Kalandaragh, R. Rahimi, "Investigation of the catalytic activity of nano-sized CuO, Co₃ O₄ and CuCo₂ O₄ powders on thermal decomposition of ammonium perchlorate," Powder Technology , vol. 217, pp. 330-339, 2012.

[19] H. Zhou, B. Lv, D. Wu, Y. Xu, "Synthesis and properties of octahedral Co₃ O₄ single-crystalline nanoparticles enclosed by (111) facets," CrystEngComm , vol. 15, no. 41, pp. 8337-8344, 2013.

[20] X. Guan, L. Li, J. Zheng, G. Li, "MgAl₂ O₄ nanoparticles: a new low-density additive for accelerating thermal decomposition of ammonium perchlorate," RSC Advances , vol. 1, no. 9, pp. 1808-1814, 2011.

[21] X.-J. Shen, J.-P. Yang, Y. Liu, Y.-S. Luo, S.-Y. Fu, "Facile surfactant-free synthesis of monodisperse Ni particles via a simple solvothermal method and their superior catalytic effect on thermal decomposition of ammonium perchlorate," New Journal of Chemistry , vol. 35, no. 7, pp. 1403-1409, 2011.