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Template-free hydrothermal method for the synthesis of multi-walled CuO nanotubes
Materials Letters 130 (2014) 68–70
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Template-free hydrothermal method for the synthesis of multi-walled CuO nanotubes Tuğba İpeksaç a,b, Figen Kaya a, Cengiz Kaya a,n a Faculty of Chemical and Metallurgical Engineering, Department of Metallurgical and Materials Engineering, Yildiz Technical University, Esenler, Istanbul, Turkey b Institute of Chemistry, TUBITAK Marmara Research Center, Gebze 41470, Turkey
art ic l e i nf o
a b s t r a c t
Article history: Received 31 January 2014 Accepted 10 May 2014 Available online 16 May 2014
Multi-walled CuO nanotubes (NTs) were prepared by a simple hydrothermal method followed by a low temperature thermal oxidation process without the use of any catalysts, surfactants or substrates. Pure multi-walled CuO NTs were obtained after hydrothermal treatment at 100 1C followed by a calcination process at 400 1C. It was shown that the obtained multi-walled CuO NTs with high purity and crystallinity had 3 nm inner and 7 nm outer diameters and showed a strong antibacterial effect against Staphylococcus aureus bacteria. & 2014 Elsevier B.V. All rights reserved.
Keywords: CuO nanotubes Hydrothermal synthesis Antibacterial
1. Introduction
2. Experimental work
Nano-sized metal oxides with controlled morphology, structure and size have gained significant technological and scientific interest because of their unique optical, electronic, physical and chemical properties that are neither characteristics of the individual atoms nor of the bulk counterparts due to the large surface area to volume ratio of nano-structures [1,2]. Recently, one-dimensional (1D) nanostructures such as wires, belts, rods, ribbons, cubes, dandelions and tubes have been a subject of extensive research because of their potential applications in various fields [1]. Recent studies have shown that copper oxide-based nanoparticles (NPs), in the form of cupric oxide (CuO) and cuprous oxide (Cu2O) in particular, are industrially important materials that can be widely used in applications, such as magnetic storage media, solar energy transformation, gas sensors, anode electrodes for batteries, electrical contacts in nanoelectronics, ferromagnetics, superconductors and catalysts [1–10]. There is limited research on the synthesis of CuO NTs and the current techniques used for this aim, such as anodic aluminum oxide membrane template methods, hydrothermal treatment of the Cu (OH)24 , and direct thermal oxidation of copper metal method, are expensive and complex processes [2–4]. Therefore, in the present work, an efficient and practical approach comprising hydrothermal synthesis followed by a low temperature thermal oxidation process is introduced to produce pure multi-walled CuO NTs without using any template.
Copper (II) nitrate trihydrate (Cu(NO3)2 3H2O, Merck), Sodium hydroxide (NaOH, Merck), ethylenediamine (EDA, C2H4(NH2)2, Merck) and hydrazine hydrate (N2H4 H2O, Fluka) were used in the experiments. To prepare CuO NTs, 10 M NaOH solution was added into 10 M (Cu(NO3)2 3H2O) solution and then magnetically stirred at room temperature for 5 min. After stirring, 2 mL EDA and 1 mL N2H4 H2O were added and further stirred for 4 h. 40 mL of homogeneous liquid mixture was then placed into a 50 mL Teflonlined stainless steel autoclave. The autoclave was sealed and maintained at 100 1C for 24 h. The resulting product was washed several times with centrifugation and the obtained precipitates were dried at 75 1C. Finally, CuO NTs were obtained after calcination of the dried precipitates at 400 1C for 5 h. The antibacterial effect of CuO NTs against Staphylococcus aureus bacteria was examined under dark ambiance using the MTT technique (using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay) [11]. CuO NT powders were suspended in distilled water (in a range between 1 and 1000 mg/mL) and anti-bacterial assay is given as a comparative depending on the concentration of bacteria at the end of 24 h. A Miniflex600 desktop X-ray diffractometer by Rigaku was used for the X-ray scans at a fixed voltage of 40 kV and current of 15 mA. The morphology of the synthesized CuO NTs was investigated by high resolution transmission electron microscopy using a JEOL 2100 LaB6 HRTEM. The morphology of the as-synthesized precipitants before calcination was viewed by the scanning electron microscope using a JEOL JSM 6335F FEG-SEM. Cell viability values were determined quantitatively using a Thermo-Labsystems Fluoroskan Ascent microplate reader.
n
Corresponding author. Tel.: þ 90 2123834713; fax: þ90 2123834665. E-mail address: [email protected] (C. Kaya).
http://dx.doi.org/10.1016/j.matlet.2014.05.059 0167-577X/& 2014 Elsevier B.V. All rights reserved.
T. İpeksaç et al. / Materials Letters 130 (2014) 68–70
69
Fig. 1. TEM images of as-prepared multi-walled CuO nanotubes: the length of the tubes (a), the cross section of the CuO nanotubes (b).
Fig. 2. FEG SEM micrographs of synthesized CuO nanotubes indicating the overview (a) and detail (b) structure of the nanotubes.
3. Results and discussion The TEM images of as-prepared CuO NTs are shown in Fig. 1. The lengths of the nanotubes were determined to be in the range of 20–120 nm, as shown in Fig. 1(a). The detailed TEM microstructures of the cross-sectional view of the synthesized CuO NTs with inner and outer diameters of 3 nm and 7 nm are also given in Fig. 1(b). Fig. 1 (b) clearly proves that the final CuO NTs had a multi-walled structure and were in nearly spherical shape. The overview of the CuO nanotubes was also determined by SEM as shown in Fig. 2(a) and (b). Fig. 2 indicates that the average nanotube length is 350 nm and the average diameter is 9 nm and these values are also confirmed by particle size measurements. However, it is also seen in Fig. 2(a) and (b) that there are some CuO nanotubes with a length of 450 nm and diameter of 30 nm (see Fig. 2b) as well as some degree of nanotube agglomerations. The XRD patterns of the obtained CuO NTs before and after calcination at 400 1C for 5 h are shown in Fig. 3, which is matched with the standard data of the copper (II) oxide monoclinic phase (DB card no. 70-6828) [5]. The peak intensities and widths indicate that the obtained CuO NTs were in highly crystalline form. Noncalcinated pattern had Cu2O peaks beside the CuO peaks, the SEM and TEM images of which are given in Fig. 4. The peaks of Cu2O determined at 29.71, 36.61, 42.41 (DB card no. 71-4310) and the corresponding planes are (110), (111), (200). In this study it is highly believed that the presence of Cu2O led to transformation of wire structures to the CuO NTs by Kinkendall effect. It is important to understand the formation of CuO NTs without the formation of any
Fig. 3. XRD patterns of the non-calcinated samples and obtained CuO nanotubes after calcination.
by-products based on the reactions of the starting chemicals and thermal oxidation so that pure stoichiometric CuO can be obtained. The formation of CuOþCu2O during hydrothermal synthesis was considered to follow a precipitation and a dehydration process [12,13]. On the other hand, the ratio of CuO/Cu2O after hydrothermal processing is determined to be 96.3/3.7 (weight percent) by XRD. The SEM image of CuO þCu2O compound is given in Fig. 4 (a) and the TEM image of the compound with an average diameter of 8 nm is given in Fig. 4(b). The sample was calcinated after the
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T. İpeksaç et al. / Materials Letters 130 (2014) 68–70
Fig. 4. SEM image (a) and TEM image (b) of the hydrothermally prepared nanowire structure.
Fig. 5. Antibacterial effect of the CuO nanotubes (a) and CuO nanowires (b) on S. aureus bacteria.
wire formation and formation of CuO NTs occurred by Kirkendall type diffusion. The Kirkendall type diffusion is a mechanism used for the explanation of nanotube formation from nanowires [14,15]. In the Kirkendall effect, diffusion of atoms causes oversaturation of lattice voids. It is thought that this oversaturation causes condensation of more voids (Kirkendall voids) close to the interface. Therefore, these Kirkendall voids damage interfacial properties and force to form multi-walled nanotubes. When CuO þCu2O nanowires were calcinated at 400 1C, the Cu2O compound transformed to CuO by reacting with O2 and the Kirkendall voids are formed. Therefore it is proposed that the wire-like structure of the CuO þ þ Cu2O is converted to multi-walled CuO NTs directly through calcination at 400 1C without creating any transitional phases, such as Cu2O, based on the XRD pattern, reactions given above and the results presented in Fig. 1(a and b). Antibacterial effect of the CuO nanotubes (a) and CuO nanowires (b) on S. aureus bacteria is shown in Fig. 5. For CuO nantubes, depending on the concentration of CuO NTs, bacterial growth at the end of the 24th h decreased approximately two-fold in a dark ambiance and the number of bacteria was determined to be 1,400,000 for a CuO concentration of 50 mg/mL, while the number of bacteria was decreased to 600,000 for a CuO concentration of 1000 mg/mL, as shown in Fig. 5a. However, the number of bacteria was decreased to 1,000,000 and 1,200,000 for CuO nanowire and CuO nanotube concentrations of 100 mg/mL indicating that nanowire structure is more effective than nanotubes against bacteria. 4. Conclusions Overall, it is shown that multi-walled CuO NTs can be prepared by a simple hydrothermal treatment at 100 1C followed by a low temperature thermal oxidation process at 400 1C without the use
of any catalysts, surfactants or substrates. It is also shown that the obtained multi-walled CuO NTs had high crystallinity with 3 nm inner and 7 nm outer diameters with the presence of no other phases. Although the mechanism of nanowires formation is not completely understood, the mechanism of nanotube formation from nanowires was clarified.
Acknowledgment Financial support from TUBITAK-COST under the contract number 109R007 and YTU Scientific Research Fund (Grant nos. 2013-07-02KAP06, 2012-07-02-KAP01) is greatly appreciated. References [1] Zhang K, Rossi C, Tenailleau C, Alphonse P, Chane-Ching J. Nanotechnology 2007;18:275607–14. [2] Cao M, Hu C, Wang Y, Guo Y, Guo C, Wang EA. Chem Commun 2003;15:1884–5. [3] Cho Y, Huh Y. Bull Korean Chem Soc 2008;29:2525–7. [4] Malandrino G, Finocchiaro ST, Nigro R, Bongiorno C, Spinella C, Fragala IL. Chem Mater 2004;16:5559–61. [5] Karthik K, Jaya NV, Kanagaraj M, Arumugam S. Solid State Commun 2011;151:564–8. [6] Zhang M, Xu X, Zhang M. Mater Lett 2008;62:385–8. [7] Jiang X, Herricks T, Xia Y. Nano Lett 2002;2:1333–8. [8] Scalza A. University of New Haven, Department of Chemical Engineering; 2010. [9] Reitz JB, Solomon EI. J Am Ceram Soc 1998;120:11467–78. [10] Feng Y, Zheng X. Nano Lett 2010;10:4762–6. [11] Allahverdiyev AM, Abamor ES, Bagirova M, Kaya F, Kaya C, Ustundag CB. Int J Nanomed 2011;6:2705–14. [12] Wu H, Wei X, Shao M, Gu J, Qu M. Chem Phys Lett 2002;364:152–6. [13] Li J, Xiong S, Pan J, Qian YJ. Phys Chem C 2010;114:9645–50. [14] Nyquist RA, Kagel RO. Infrared spectra of inorganic compounds. Elsevier; 1971. [15] Ipeksac T. [M.Sc. thesis]. Yildiz Technical University, Istanbul; 2012.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Template-free hydrothermal method for the synthesis of multi-walled CuO nanotubes Tuğba İpeksaç a,b, Figen Kaya a, Cengiz Kaya a,n a Faculty of Chemical and Metallurgical Engineering, Department of Metallurgical and Materials Engineering, Yildiz Technical University, Esenler, Istanbul, Turkey b Institute of Chemistry, TUBITAK Marmara Research Center, Gebze 41470, Turkey
art ic l e i nf o
a b s t r a c t
Article history: Received 31 January 2014 Accepted 10 May 2014 Available online 16 May 2014
Multi-walled CuO nanotubes (NTs) were prepared by a simple hydrothermal method followed by a low temperature thermal oxidation process without the use of any catalysts, surfactants or substrates. Pure multi-walled CuO NTs were obtained after hydrothermal treatment at 100 1C followed by a calcination process at 400 1C. It was shown that the obtained multi-walled CuO NTs with high purity and crystallinity had 3 nm inner and 7 nm outer diameters and showed a strong antibacterial effect against Staphylococcus aureus bacteria. & 2014 Elsevier B.V. All rights reserved.
Keywords: CuO nanotubes Hydrothermal synthesis Antibacterial
1. Introduction
2. Experimental work
Nano-sized metal oxides with controlled morphology, structure and size have gained significant technological and scientific interest because of their unique optical, electronic, physical and chemical properties that are neither characteristics of the individual atoms nor of the bulk counterparts due to the large surface area to volume ratio of nano-structures [1,2]. Recently, one-dimensional (1D) nanostructures such as wires, belts, rods, ribbons, cubes, dandelions and tubes have been a subject of extensive research because of their potential applications in various fields [1]. Recent studies have shown that copper oxide-based nanoparticles (NPs), in the form of cupric oxide (CuO) and cuprous oxide (Cu2O) in particular, are industrially important materials that can be widely used in applications, such as magnetic storage media, solar energy transformation, gas sensors, anode electrodes for batteries, electrical contacts in nanoelectronics, ferromagnetics, superconductors and catalysts [1–10]. There is limited research on the synthesis of CuO NTs and the current techniques used for this aim, such as anodic aluminum oxide membrane template methods, hydrothermal treatment of the Cu (OH)24 , and direct thermal oxidation of copper metal method, are expensive and complex processes [2–4]. Therefore, in the present work, an efficient and practical approach comprising hydrothermal synthesis followed by a low temperature thermal oxidation process is introduced to produce pure multi-walled CuO NTs without using any template.
Copper (II) nitrate trihydrate (Cu(NO3)2 3H2O, Merck), Sodium hydroxide (NaOH, Merck), ethylenediamine (EDA, C2H4(NH2)2, Merck) and hydrazine hydrate (N2H4 H2O, Fluka) were used in the experiments. To prepare CuO NTs, 10 M NaOH solution was added into 10 M (Cu(NO3)2 3H2O) solution and then magnetically stirred at room temperature for 5 min. After stirring, 2 mL EDA and 1 mL N2H4 H2O were added and further stirred for 4 h. 40 mL of homogeneous liquid mixture was then placed into a 50 mL Teflonlined stainless steel autoclave. The autoclave was sealed and maintained at 100 1C for 24 h. The resulting product was washed several times with centrifugation and the obtained precipitates were dried at 75 1C. Finally, CuO NTs were obtained after calcination of the dried precipitates at 400 1C for 5 h. The antibacterial effect of CuO NTs against Staphylococcus aureus bacteria was examined under dark ambiance using the MTT technique (using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay) [11]. CuO NT powders were suspended in distilled water (in a range between 1 and 1000 mg/mL) and anti-bacterial assay is given as a comparative depending on the concentration of bacteria at the end of 24 h. A Miniflex600 desktop X-ray diffractometer by Rigaku was used for the X-ray scans at a fixed voltage of 40 kV and current of 15 mA. The morphology of the synthesized CuO NTs was investigated by high resolution transmission electron microscopy using a JEOL 2100 LaB6 HRTEM. The morphology of the as-synthesized precipitants before calcination was viewed by the scanning electron microscope using a JEOL JSM 6335F FEG-SEM. Cell viability values were determined quantitatively using a Thermo-Labsystems Fluoroskan Ascent microplate reader.
n
Corresponding author. Tel.: þ 90 2123834713; fax: þ90 2123834665. E-mail address: [email protected] (C. Kaya).
http://dx.doi.org/10.1016/j.matlet.2014.05.059 0167-577X/& 2014 Elsevier B.V. All rights reserved.
T. İpeksaç et al. / Materials Letters 130 (2014) 68–70
69
Fig. 1. TEM images of as-prepared multi-walled CuO nanotubes: the length of the tubes (a), the cross section of the CuO nanotubes (b).
Fig. 2. FEG SEM micrographs of synthesized CuO nanotubes indicating the overview (a) and detail (b) structure of the nanotubes.
3. Results and discussion The TEM images of as-prepared CuO NTs are shown in Fig. 1. The lengths of the nanotubes were determined to be in the range of 20–120 nm, as shown in Fig. 1(a). The detailed TEM microstructures of the cross-sectional view of the synthesized CuO NTs with inner and outer diameters of 3 nm and 7 nm are also given in Fig. 1(b). Fig. 1 (b) clearly proves that the final CuO NTs had a multi-walled structure and were in nearly spherical shape. The overview of the CuO nanotubes was also determined by SEM as shown in Fig. 2(a) and (b). Fig. 2 indicates that the average nanotube length is 350 nm and the average diameter is 9 nm and these values are also confirmed by particle size measurements. However, it is also seen in Fig. 2(a) and (b) that there are some CuO nanotubes with a length of 450 nm and diameter of 30 nm (see Fig. 2b) as well as some degree of nanotube agglomerations. The XRD patterns of the obtained CuO NTs before and after calcination at 400 1C for 5 h are shown in Fig. 3, which is matched with the standard data of the copper (II) oxide monoclinic phase (DB card no. 70-6828) [5]. The peak intensities and widths indicate that the obtained CuO NTs were in highly crystalline form. Noncalcinated pattern had Cu2O peaks beside the CuO peaks, the SEM and TEM images of which are given in Fig. 4. The peaks of Cu2O determined at 29.71, 36.61, 42.41 (DB card no. 71-4310) and the corresponding planes are (110), (111), (200). In this study it is highly believed that the presence of Cu2O led to transformation of wire structures to the CuO NTs by Kinkendall effect. It is important to understand the formation of CuO NTs without the formation of any
Fig. 3. XRD patterns of the non-calcinated samples and obtained CuO nanotubes after calcination.
by-products based on the reactions of the starting chemicals and thermal oxidation so that pure stoichiometric CuO can be obtained. The formation of CuOþCu2O during hydrothermal synthesis was considered to follow a precipitation and a dehydration process [12,13]. On the other hand, the ratio of CuO/Cu2O after hydrothermal processing is determined to be 96.3/3.7 (weight percent) by XRD. The SEM image of CuO þCu2O compound is given in Fig. 4 (a) and the TEM image of the compound with an average diameter of 8 nm is given in Fig. 4(b). The sample was calcinated after the
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Fig. 4. SEM image (a) and TEM image (b) of the hydrothermally prepared nanowire structure.
Fig. 5. Antibacterial effect of the CuO nanotubes (a) and CuO nanowires (b) on S. aureus bacteria.
wire formation and formation of CuO NTs occurred by Kirkendall type diffusion. The Kirkendall type diffusion is a mechanism used for the explanation of nanotube formation from nanowires [14,15]. In the Kirkendall effect, diffusion of atoms causes oversaturation of lattice voids. It is thought that this oversaturation causes condensation of more voids (Kirkendall voids) close to the interface. Therefore, these Kirkendall voids damage interfacial properties and force to form multi-walled nanotubes. When CuO þCu2O nanowires were calcinated at 400 1C, the Cu2O compound transformed to CuO by reacting with O2 and the Kirkendall voids are formed. Therefore it is proposed that the wire-like structure of the CuO þ þ Cu2O is converted to multi-walled CuO NTs directly through calcination at 400 1C without creating any transitional phases, such as Cu2O, based on the XRD pattern, reactions given above and the results presented in Fig. 1(a and b). Antibacterial effect of the CuO nanotubes (a) and CuO nanowires (b) on S. aureus bacteria is shown in Fig. 5. For CuO nantubes, depending on the concentration of CuO NTs, bacterial growth at the end of the 24th h decreased approximately two-fold in a dark ambiance and the number of bacteria was determined to be 1,400,000 for a CuO concentration of 50 mg/mL, while the number of bacteria was decreased to 600,000 for a CuO concentration of 1000 mg/mL, as shown in Fig. 5a. However, the number of bacteria was decreased to 1,000,000 and 1,200,000 for CuO nanowire and CuO nanotube concentrations of 100 mg/mL indicating that nanowire structure is more effective than nanotubes against bacteria. 4. Conclusions Overall, it is shown that multi-walled CuO NTs can be prepared by a simple hydrothermal treatment at 100 1C followed by a low temperature thermal oxidation process at 400 1C without the use
of any catalysts, surfactants or substrates. It is also shown that the obtained multi-walled CuO NTs had high crystallinity with 3 nm inner and 7 nm outer diameters with the presence of no other phases. Although the mechanism of nanowires formation is not completely understood, the mechanism of nanotube formation from nanowires was clarified.
Acknowledgment Financial support from TUBITAK-COST under the contract number 109R007 and YTU Scientific Research Fund (Grant nos. 2013-07-02KAP06, 2012-07-02-KAP01) is greatly appreciated. References [1] Zhang K, Rossi C, Tenailleau C, Alphonse P, Chane-Ching J. Nanotechnology 2007;18:275607–14. [2] Cao M, Hu C, Wang Y, Guo Y, Guo C, Wang EA. Chem Commun 2003;15:1884–5. [3] Cho Y, Huh Y. Bull Korean Chem Soc 2008;29:2525–7. [4] Malandrino G, Finocchiaro ST, Nigro R, Bongiorno C, Spinella C, Fragala IL. Chem Mater 2004;16:5559–61. [5] Karthik K, Jaya NV, Kanagaraj M, Arumugam S. Solid State Commun 2011;151:564–8. [6] Zhang M, Xu X, Zhang M. Mater Lett 2008;62:385–8. [7] Jiang X, Herricks T, Xia Y. Nano Lett 2002;2:1333–8. [8] Scalza A. University of New Haven, Department of Chemical Engineering; 2010. [9] Reitz JB, Solomon EI. J Am Ceram Soc 1998;120:11467–78. [10] Feng Y, Zheng X. Nano Lett 2010;10:4762–6. [11] Allahverdiyev AM, Abamor ES, Bagirova M, Kaya F, Kaya C, Ustundag CB. Int J Nanomed 2011;6:2705–14. [12] Wu H, Wei X, Shao M, Gu J, Qu M. Chem Phys Lett 2002;364:152–6. [13] Li J, Xiong S, Pan J, Qian YJ. Phys Chem C 2010;114:9645–50. [14] Nyquist RA, Kagel RO. Infrared spectra of inorganic compounds. Elsevier; 1971. [15] Ipeksac T. [M.Sc. thesis]. Yildiz Technical University, Istanbul; 2012.