Supercapacitive properties of Mn₃O₄ nanoparticles bio-synthesized from banana peel extract

Abstract

A green approach to the synthesis of Mn₃O₄ nanoparticles using banana peel extract as both reducing and capping agent has been described. The as-obtained Mn₃O₄ electrode exhibits acceptable electrochemical performance (216 F g⁻¹ at 0.3 A g⁻¹, 93% capacity retention after 2000 cycles).

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In recent years, the preparation of manganese oxide nanostructures has been the target of scientific interest due to their various intriguing physical and chemical properties.^1–5 Among the varieties of manganese oxides explored, hausmannite Mn₃O₄, which is one of the most stable oxides of manganese, is particularly interesting because of their broad range of applications such as batteries, catalysts, supercapacitors, ion-exchange, high density magnetic storage medium, molecular adsorption etc.^6,7

Various synthesis methods have been developed to prepare Mn₃O₄ nanostructures, including sol–gel technique,⁸ hydrothermal treatment,⁹ thermal decomposition,¹⁰ co-precipitation,⁶ microwave irradiation synthesis,¹¹ etc. However, these methods usually require special equipment, high temperature or high energy and hard to produce in large-scale. More importantly, these common methods involve toxic, corrosive and flammable chemical substances, which are often potentially dangerous to the human health and environment. For this reason, more and more attentions have been recently focused on the development green chemistry and biological synthetic processes to prepare metal or metal oxide nanostructure by using microorganisms, enzymes, fungi, fruits, plant extracts or even agricultural waste. For example, Xie et al. reported the preparation of single-crystalline Ag nanoplates using the extract of unicellular green alga Chlorella vulgaris.¹² Spherical shape platinum with diameter of less than 4 nm have been synthesized using an extract of Terminalia chebula as reducing and capping agent.¹³ Zirconia nano-chains with an average size ranged from 41 to 45 nm have been synthesized using Curcuma longa tuber extract by Sathishkumar and co-worker.¹⁴ In addition, bio-conjugated Ag-nanoparticle has been synthesized using Ocimum sanctum leaves extract by Zaheer and Rafiuddin.¹⁵

Banana is always a favourite fruit world-wide. According to incomplete statistics, more than 100 million tons of banana are consumed every year in the word¹⁶ and the peels are usually discarded. In the literature, there are several applications of banana peel extract for formation of nano metal or metal oxide. Venkateswarlu reported the synthesis of nano size Fe₃O₄ using plantain peel extract and its magnetic properties was studied.¹⁶ Bankar et al. have prepared gold¹⁷ and palladium¹⁸ nanoparticles by a novel banana peel extract mediated route.

In this paper, we present a room temperature process for preparation of Mn₃O₄ nanoparticles by using naturally banana peel. This abundantly available agricultural waste is composed of polymers such as pectin, cellulose, polyphenols and carbohydrates,^16–18 which can act as both reducing and capping agents in the preparation of Mn₃O₄. This novel method has various advantages including low cost, simplicity and potential for large-scale production, green and eco-friendly method without using any toxic chemicals. The pseudocapacitive behaviors of as-prepared Mn₃O₄ are further evaluated by cyclic voltammograms and galvanostatic charge–discharge measurements and the maximum specific capacitance of 216 F g⁻¹ is delivered at 0.3 A g⁻¹ current density.

The detailed synthesis procedures are described in the Experimental section of the ESI.† The morphology of the sample was firstly determined by FESEM. As shown in Fig. 1(a), it can be clearly seen that the as-obtained product is made up of agglomerate particles with diameters of 20–50 nm. Fig. 1(b) illustrates the XRD pattern of the product. All the diffraction peaks can be recognized as the tetragonal hausmannite of Mn₃O₄ (JCPDS 75-1560), indicating the high purity and crystallinity. The above results suggest that the Mn₃O₄ nanostructure have been successfully synthesized for the first time in a facile and green way by using agricultural waste extract.

Fig. 1 (a) SEM image; (b) X-ray diffraction pattern of the as-obtained Mn₃O₄; the inset is optical pictures of the banana peel (left) and banana peel extract (right).

FT-IR and XPS were used to further characterize the product. Fig. 2(a) displays the FT-IR spectrum of the sample. The vibration frequencies at 623 and 525 cm⁻¹ can be assigned to the Mn–O stretching modes in tetrahedral sites and the distortion vibration of Mn–O in an octahedral environment, respectively. Another absorption peak at 421 cm⁻¹ is attributed to the vibration of manganese species (Mn³⁺) in an octahedral site.¹⁹ The absorption peaks situated at 3450, 2334, 1637, 1384 cm⁻¹ are related to adsorbed and/or crystalline water.²⁰

Fig. 2 (a) FT-IR spectrum; (b) Mn 2p and (c) Mn 3s of XPS spectra for Mn₃O₄.

The binding energy in the XPS analysis was corrected for specimen charging by referencing the C 1s to 284.8 eV. The Mn 2p spectrum is shown in Fig. 2(b), the binding energy value of Mn 2p3/2 is 641.7 eV, and the observed spin-spitting between the Mn 2p3/2 and Mn 2p1/2 is 11.8 eV, which well matches with the previously reported values for hausmannite.²¹ Furthermore, the multiple splitting of the Mn 3s is 5.25 eV (Fig. 2(c)), which exactly matches with the reported values of Mn₃O₄ compound.²² Therefore, both FT-IR and XPS results further confirm that the as-obtained materials is Mn₃O₄, which well agree with the XRD result.

Fig. 3(a) presents the CV curves for the Mn₃O₄ electrode at various scan rates in the potential window of −0.2 to 0.8 (vs. SCE) in the Na₂SO₄ aqueous solution. All of the CV profiles of Mn₃O₄ electrode show the rectangular and symmetric current-potential characteristics, indicating high electrochemical reversibility of the as-prepared sample. Even the scan rate up to 100 mV s⁻¹, only a slight distortion from the ideal symmetrical rectangle shape can be found from this CV curve, which strongly suggests the electrode has excellent power performance.²³ For further evaluating the capacitive properties of Mn₃O₄, galvanostatic charge–discharge measurements were performed (Fig. 3(c)). The linear and symmetric charge–discharge curves show superior capacitive and revisable behavior. The specific capacitance of Mn₃O₄ electrode is calculated to be 216, 203, 168, 162 F g⁻¹ at the current densities of 0.3, 0.5, 0.8 and 1 A g⁻¹, respectively. The current density dependence of the specific capacitance of the electrode is shown in Fig. 3(c). The cycling stability of the electrode was conducted by charge–discharge at a current density of 0.3 A g⁻¹. As seen in Fig. 3(d), about 93% of initial SC is maintained after a cycle number of 2000 charge–discharge process, suggesting superior stability of Mn₃O₄ electrode and be suited for the practical application. The remarkably similar electrochemical impedance spectroscopy (EIS) curves (Fig. 3(e)) before and after 2000 cycling test further demonstrate the high stability of the electrode.

Fig. 3 Electrochemical evaluations of Mn₃O₄ electrode: (a) cyclic voltammograms curves at different scan rates; (b) charge–discharge profiles at various current densities; (c) specific capacitance as a function of current density; (d) cycle performance during 2000 cycles at a current density of 0.3 A g⁻¹ (the inset shows charge–discharge curves for the first (left) and last (right) five cycles).

There are several methods reported on synthesis Mn₃O₄ nanostructures for supercapacitor applications in the references. For instance, a oxidation-precipitation approach have been developed to preparation of Mn₃O₄ nanoparticles, using H₂O₂ as oxidizing agent and the as-obtained sample exhibited a specific capacitance of 172 F g⁻¹ at 10 mV s⁻¹ (loading mass of active materials is 1.5 mg cm⁻²).²⁴ A stacked Mn₃O₄ nanosheets films on Ti substrate has been prepared by Dubal et al. by a chemical bath deposition (CBD) method using hexamethylenetetramine (HMT) as a starting material and the films delivered a high specific capacitance of 398 F g⁻¹ at a scan rate of 5 mV s⁻¹(ref. 25) (loading mass of Mn₃O₄ is 23 mg cm⁻²). However, the hexamethylenetetramine is toxic to humans and can cause long-term harm to the environment. In addition, spherical Mn₃O₄ nanoparticles with diameter range from 60 to 200 nm have been prepared by a microwave assisted reflux method and the sample displayed a specific capacitance of 103 F g⁻¹ at 0.5 mA cm⁻² in 1 M NaNO₃ solution (loading mass of active materials is 0.8 mg cm⁻²).²⁶ Obviously, the current work have many advantages over the previous routes, such as low cost, simplicity and potential for large-scale production, green and eco-friendly method without using any toxic chemicals and the acceptable specific capacitance.

In summary, a green route has been successfully developed to prepare Mn₃O₄ nanoparticle by using banana peel extract as both reducing and capping agent. The as-prepared Mn₃O₄ has spheroid morphology with 20–50 nm in diameter. A specific capacitance of 216 F g⁻¹ is observed at the current density of 0.3 A g⁻¹ for the Mn₃O₄ electrode. In addition, the specific capacitance retention is 97.5% after 500 cycles at 0.3 A g⁻¹, indicating a preferable cycling stability. This novel method has many advantages including low cost, simplicity and potential for large-scale production, green and eco-friendly method without using any toxic chemicals.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Nos 21176051 and 61166008), Guangxi Natural Science Foundation (Nos 2012GXNSFFA060002, 2013GXNSFAA019294 and 2013GXNSFBA019234). This research was jointly sponsored by Guangxi Key Laboratory of Information Materials (Guilin University of Electronic Technology), China (Nos 1110908-02-K, 1110908-05-K), Educational Commission of Guangxi Province of China (no. 201101ZD007), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing (Wuhan University of Technology) (2012-KF-7) and Guangxi Experiment Center of Information Science, Guilin University of Electronic Technology (20130322).

Notes and references

1. M. J. Deng, P. J. Ho, C. Z. Song, S. A. Chen, J. F. Lee, J. M. Chen and K. T. Lu, Energy Environ. Sci., 2013, 6, 2178–2185.
2. M. Kundu, C. C. A. Ng, D. Y. Petrovyky and L. F. Liu, Chem. Commun., 2013, 49, 8459.
3. D. L. Yan, Z. L. Guo, G. S. Zhu, Z. Z. Yu, H. R. Xu and A. B. Yu, J. Power Sources, 2012, 199, 409.
4. R. F. Zhou, C. Z. Meng, F. Zhu, Q. Q. Li, C. H. Liu, S. S. Fan and K. L. Jiang, Nanotechnology, 2010, 21, 345701.
5. X. Y. Lang, A. Hirata, T. Fujita and M. W. Chen, Nat. Nanotechnol., 2011, 6, 232.
6. H. Q. Wang, Z. S. Li, J. H. Yang, Q. Y Li and X. X. Zhong, J. Power Sources, 2009, 194, 1218.
7. D. L. Yan, H. Zhang, S. C. Li, G. S. Zhu, Z. M. Wang, H. R. Xu and A. B. Yu, J. Alloys Compd., 2014, 607, 245.
8. N. Wang, L. Guo, L. He, X. Cao, C. P. Chen, R. M. Wang and S. H. Yang, Small, 2007, 3, 606.
9. H. Jian, T. Zhao, C. Y. Yan, J. Ma and C. Z. Li, Nanoscale, 2010, 2, 2195.
10. W. S. Seo, H. H. Jo, K. Lee, B. S. Kim, S. J. Oh and J. T. Park, Angew. Chem., Int. Ed., 2004, 43, 1115.
11. J. G. Song, G. C. Ji, S. B. Li, D. M. Du and F. Wang, Int. J. Mater. Res., 2013, 12, 93.
12. J. P. Xie, J. Y. Lee, D. I. C. Wang and Y. P. Ting, ACS Nano, 2007, 1, 429.
13. K. M. Kumar, B. K. Mandal and S. K. Tammina, RSC Adv., 2013, 3, 4033.
14. M. Sathishkumar, K. Sneha and Y. S. Yun, Mater. Lett., 2013, 98, 242–245.
15. Z. Zaheer and R. Rafiuddin, Colloids Surf., B, 2013, 108, 90.
16. S. Venkateswarlu, Y. S. Rao, T. Balaji, B. Prathima and N. V. V. Jyothi, Mater. Lett., 2013, 100, 241.
17. A. Bankar, B. Joshi, A. R. Kumar and S. Zinjarde, Colloids Surf. B, 2010, 80, 45.
18. A. Bankar, B. Joshi, A. R. Kumar and S. Zinjarde, Mater. Lett., 2010, 64, 1951.
19. R. Song, S. H. Feng, H. J. Wang and C. M. Hou, J. Solid State Chem., 2013, 202, 57.
20. D. L. Yan, Z. L. Guo, G. S. Zhu, H. J. Yang, R. H. Wei, H. R. Xu and A. B. Yu, Mater. Lett., 2012, 82, 156.
21. A. M. E. Raj, S. G. Victoric and V. B. Jothy, Appl. Surf. Sci., 2010, 256, 2920.
22. S. K. Apte, S. D. Naik, R. S. Sonawane, B. B. Kale, N. Pavaskar, A. B. Mandale and B. K. Das, Mater. Res. Bull., 2006, 41, 647.
23. D. L. Yan, S. C. Li, G. S. Zhu, Z. M. Wang, H. R. Xu and A. B. Yu, Mater. Lett., 2013, 95, 164.
24. S. T. Xing, Z. C. Zhou, Z. C. Ma and Y. S. Wu, Mater. Lett., 2011, 65, 517.
25. D. P. Dubal and R. Holze, J. Power Sources, 2013, 238, 274.
26. K. V. Sankar, S. T. Senthilkumar, L. J. Berchmans, C. Sanjeeviraja and R. K. Selvan, Appl. Surf. Sci., 2012, 259, 624.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra02603a

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