SCIENCE CHINA Technological Sciences • Article •

March 2015 Vol.58 No.3: 1–4 doi: 10.1007/s11431-014-5746-3 doi: 10.1007/s11431-014-5746-3

Formation of copper oxide nanowires and nanoparticles via electrospinning CAI YaNan, WANG Wu, CHEN Zhe, YU JianGang, CHEN AQing & ZHU KaiGui* Department of Physics, Beihang University, Beijing 100191, China Received September 25, 2014; accepted December 9, 2014

Copper oxide nanowires and nanoparticles were fabricated through electrospinning followed by calcinations in different heating conditions. It was found that the solution viscosity and environment humidity had great impact on the morphologies of precursor nanowires, and the parameters of heat treatment, including final temperature and heating rate, significantly affected the product morphologies. electrospinning, copper oxide nanowire, copper oxide nanoparticle Citation:

Cai Y N, Wang W, Chen Z, et al. Formation of copper oxide nanowires and nanoparticles via electrospinning. Sci China Tech Sci, doi: 10.1007/s11431-014-5746-3

1 Introduction

2 Experiment

In the past years, more and more attention has been paid to the fabrication of one-dimensional metal oxide due to its amazing morphologies and distinctive properties compared with metal oxide bulk materials [1–4]. Electrospinning was originally applied to polymer materials [5–7], and its operation of devices can be controlled more simply and easily compared with other methods. As a convenient and effective method to fabricate one-dimensional metal oxide nanomaterials, electrospinning is commonly used to fabricate nanowires such as zinc oxide [8–11], stannic oxide [12–14], and titanium dioxide [15]. However, there are few reports about the fabrication of copper oxide nanowires [16], especially nanoparticles, with this method. In this work, electrospinning method was employed to synthesize copper oxide nanoparticles and nanowires.

Copper oxide nanowires, as well as nanoparticles, were fabricated through electrospinning and followed by calcinations in air. To obtain Cu(NO3)2/PVA precursor nanofibers, a typical procedure [17] was applied. 0.3 g PVA (Poly vinyl alcohol, Mw=89000–98000, Aldrich) was added slowly into 3.45 g deionized water (PVA: 8 wt%). And then the solution was kept under vigorous magnetic stirring for 1 h at 80°C to make PVA dissolve. After that, 0.56 g Copper (II) nitrate hydrate (Mw=187.56, Aldrich) was added in the solution for another 12 h stirring at room temperature. Then a viscous gel suitable for electrospinning was obtained. The as-prepared gel was loaded into a syringe with a stainless steel needle (outside diameter=0.6 mm) connected to a high-voltage power supply for electrospinning. A piece of flat aluminum foil was placed 18 cm from the needle tip. Upon applying a high voltage of 15 kV, a fluid jet was ejected from the needle tip. The solvent evaporated and the charged fibers, the Cu(NO3)2/PVA precursor nanofibers,

*Corresponding author (email: [email protected]) © Science China Press and Springer-Verlag Berlin Heidelberg 2015

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were deposited on the foil. Then the precursor fibers were calcinated in different heating conditions to get copper oxide nanowires and nanoparticles.

3 Results and discussion During the process of synthesizing Cu(NO3)2/PVA precursor nanofibers, different solutions (see Table 1) were prepared to study the influencing factor of viscosity. It was found that the precursor nanofibers electrospun from 6 wt% PVA solution had some nodes as shown in Figure 1(a); similar to the results obtained by Pankaj et al. [18] and Deitzel et al. [19], the 10 wt% ones stuck together (see Figure 1(c)), and the 8 wt% ones were smooth, with an average diameter of about 500 nm (see Figure 1(b)). The effect of environment humidity on the electrospinning process was also considered. The environment humidity was controlled by the humidifier and dryer during the electrospinning process. It was observed that the precursor nanofiders would stand up between the needle and the aluminum foil when the environment humidity exceeded 38%, as shown in Figure 2. When it was less than 22%, the stainless needle was easily stemmed during the electrospinning process, and when the environment humidity was 22%–38%, it was good for electrospinning. During the following calculation process, the reaction equation is as follows:

Figure 1

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Table 1

Different solutions adopted to study the factor of viscosity

Sample

PVA (g)

Deionized water (g)

Cu(NO3)2 (g)

PVA (wt%)

Cu(NO3)2 (wt%)

1

0.3

4.7

0.75

6%

15%

2

0.3

3.45

0.56

8%

15%

3

0.3

2.7

0.45

10%

15%

2Cu(NO3 ) 2  2CuO  4NO 2  O 2 PVA  CO 2  H 2 O

As the decomposition temperature of Cu(NO3)2 and PVA was 170 and 300°C respectively, to get pure copper oxide and learn the effect of heat treatment conditions on CuO morphologies, 4 samples listed in Table 2 were prepared first. It can be seen from Figures 3 and 4 that PVA in sample 2, 3, 4 resolved completely, except sample 1, because sample 1 had a carbon residue as shown in Figure 4(a). Figures 3(b1) and (b2) show good nanowires images of sample 2, although there is some breakage. Sample 3 (Figures 3(c1), (c2)) and sample 4 (Figures 3(d1), (d2)) had good images of nanoparticles, but nanoparticles of sample 4 were smaller than those of sample 3. So it is concluded that copper oxide tends to form nanowires at the final temperature of about 350°C, while to form nanoparticles above 350°C. To learn the effect of heating rate on product morphologies, we prepared another 3 samples, as shown in Table 3.

SEM images of precursor nanofibers from 3 samples in Table 1: (a) 6 wt% PVA; (b) 8 wt% PVA; (c) 10 wt% PVA.

Figure 2

(1)

Eletrospinning process when environment humidity exceeded 38%.

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Table 2 Samples adopted to study the effect of final temperature on the calcination process Sample Heating rate (°C/min) Final temperature (°C) Holding time (h) 1 10 300 2 2 10 350 2 3 10 400 2 4 10 450 2

Table 3 Samples adopted to understand the effect of heating rate on the calcination process Sample 1 2 3

Figure 3

Heating rate (°C/min) 12 7 2

Final temperature (°C) 350 350 350

Holding time (h) 2 2 2

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Figure 5 shows the morphologies of 3 products at different heating rates. Figures 5(a) and (c) suggest that a high heating rate benefits the formation of nanoparticles, while a low heating rate benefits the formation of nanowires. Figure 6 suggests that CuO nanowires at a heating temperature of 350°C and a heating rate of 7°C/min have a good crystallinity. In this pattern, the two strong peaks indicate the crystal orientation of CuO nanowires. In fact, the left weak peaks are also representative CuO phases except for the two tungsten peaks marked in the pattern, because CuO nanowires were collected on the tungsten substrate.

4 Conclusions In this work, we found that the morphologies of

Whole and local SEM images of the 4 samples listed in Table 2. (a1) and (a2) 300°C; (b1) and (b2) 350°C; (c1) and (c2) 400°C; (d1) and (d2) 450°C.

Figure 4

EDX of the 4 samples listed in Table 2. (a) 300°C; (b) 350°C; (c) 400°C; (d) 450°C.

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Figure 5

Figure 6

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SEM images of 3 samples in Table 3. (a) 12°C/min; (b) 7°C/min; (c) 2°C/min.

XRD pattern of CuO after 350°C heating temperature at heating rate of 7°C/min.

Cu(NO3)2/PVA precursor nanofibers prepared via electrospinning were strongly influenced by such parameters as the solution viscosity and environment humidity. For the reagents adopted here, smooth and unique fibers were formed at the PVA content of about 8 wt% and the environment humidity of 22%–38%. It was also found that a final temperature of about 350°C and a low heating rate during the calcinations process were good for the formation of copper oxide nanowires, while a higher final temperature and a higher heating rate were good for the formation of nanoparticles. This work was supported by the National Natural Science Foundation of China (Grant No. 51171006), and the Key Research Project in Science and Technology of Leshan (Grant No. 12GZD066).

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Chen P C, Shen G, Zhou C. Chemical sensors and electronic noses based on 1-D metal oxide nanostructures. IEEE T Nanotechnol, 2008, 7: 668–682 Al-Enizi A M, Elzatahry A A, Abdullah A M, et al. Synthesis and electrochemical properties of nickel oxide/carbon nanofiber composites. Carbon, 2014, 71: 276–283 Li Q, Liu E, Lu Z, et al. HEPES and polyol mediated solvothermal synthesis of hierarchical porous ZnO microspheres and their improved photocatalytic activity. Mater Lett, 2014, 130: 115–119 Teo W E, Inai R, Ramakrishna S. Technological advances in electrospinning of nanofibers. Sci Tech Adv Mater, 2011, 12: 013002 Rieger K A, Schiffman J D. Electrospinning an essential oil: Cinnamaldehyde enhances the antimicrobial efficacy of chitosan/poly (ethylene oxide) nanofibers. Carbohydr Polym, 2014, 113: 561–568 Zheng B, Liu G, Yao A, et al. A sensitive AgNPs/CuO nanofibers non-enzymatic glucose sensor based on electrospinning technology. Sensor Actuat B-Chem, 2014, 195: 431–438

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Lu T, Olesik S V. Electrospun polyvinyl alcohol ultra-thin layer chromatography of amino acids. J Chromatogr B, 2013, 912: 98–104 Jae Y P, Sang S K. Growth of nanograins in electrospun ZnO nanofibers. J Am Ceram Soc, 2009, 92: 1691–1694 Liu M, Wang Y, Cheng Z, et al. Function of NaOH hydrolysis in electrospinning ZnO nanofibers via using polylactide as templates. Mat Sci Eng B-Solid, 2014, 187: 89–95 Lin D D, Wu H, Pan W. Photoswitches and memories assembled by electrospinning aluminum‐doped zinc oxide single nanowires. Adv Mater, 2007, 19: 3968–3972 Wu W Y, Ting J M, Huang P J. Electrospun ZnO nanowires as gas sensors for ethanol detection. Nanoscale Res Lett, 2009, 4: 513–517 Choi J K, Hwang I S, Kim S J, et al. Design of selective gas sensors using electrospun Pd-doped SnO2 hollow nanofibers. Sensor Actuat B-Chem, 2010, 150: 191–199 Li L, Yin X, Liu S, et al. Electrospun porous SnO2 nanotubes as high capacity anode materials for lithium ion batteries. Electro Chem Commun, 2010, 12: 1383–1386 Zhang Y, Li J, An G, et al. Highly porous SnO2 fibers by electrospinning and oxygen plasma etching and its ethanol-sensing properties. Sensor Actuat B-Chem, 2010, 144: 43–48 Lori E G, Matt L, Benjamin D. ZnO-TiO2 core-shell nanorod/P3HT solar cells. J Am Ceram Soc, 2007, 111: 18451–18456 Xu K, Tian X J, Yu H B, et al. Large-scale assembly of Cu/CuO nanowires for nano-electronic device fabrication. Sci China Tech Sci, 2014, 57: 734–737 Wu H, Zhang R, Liu X, et al. Electrospinning of Fe, Co, and Ni nanofibers: Synthesis, assembly, and magnetic properties. Chem Mater, 2007, 19: 3506–3511 Pankaj G, Casey E, Timothy E. Long. Electrospinning of linear homopolymers of poly (methyl methacrylate): Exploring relationships between fiber formation, viscosity, molecular weight and concentration in a good solvent. Polymer, 2005, 46: 4799–4810 Deitzel J M, Kleinmeyer J, Harris D, et al. The effect of processing variables on the morphology of electrospun nanofibers and textiles. Polymer, 2001, 42: 261–272