- Email: [email protected]
Preparation of porous zinc oxide-nickel oxide nanocomposites by facile one-pot solution process
Ceramics International xx (xxxx) xxxx–xxxx
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Preparation of porous zinc oxide-nickel oxide nanocomposites by facile one-pot solution process ⁎
Kyung Ho Kim , Yuya Yoshihara, Yoshio Abe, Midori Kawamura, Takayuki Kiba Department of Materials Science and Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
A R T I C L E I N F O
A BS T RAC T
Keywords: ZnO NiO Sphere-like structures Nanolayered structures Nanocomposites
Porous zinc oxide (ZnO)-nickel oxide (NiO) nanocomposites were fabricated via a one-pot process using aqueous solutions of zinc nitrate hexahydrate (Zn(NO), 10 mM), hexamethylenetetramine (HMT, 10 mM), and nickel acetate tetrahydrate (Ni(Ac), 7 mM (7NZO), 10 mM (10NZO)). The structural and morphological properties of these nanocomposites were investigated and compared to those of pure ZnO nanostructures. Rodtype nanostructures were observed in the pure ZnO sample, while porous sphere-like structures and continuous nanolayered structures were observed in the 7NZO and 10NZO samples, respectively. This difference in morphology might be due to the growth of the non-polar plane instead of the polar plane of ZnO in the clusters. The nanocomposites were composed of Ni, Zn, and O, which were homogeneously distributed. Distinct morphologies of the ZnO-NiO nanocomposites were obtained via a facile one-pot solution process.
1. Introduction
2. Experimental
Significant efforts have been devoted to the development of nanostructured metal oxides with unique structural morphologies that find potential applications in a wide range of electronic and optoelectronic devices [1–3]. One such metal oxide, zinc oxide (ZnO), with a wide band gap energy (3.37 eV) and large exciton binding energy (60 meV), has been of strong research interest as a typical n-type oxide semiconductor [1,2]. The electrical and optical properties of ZnO can be modified by the incorporation of dopants (Al, Ga, Sn, etc.) into its lattice in order to meet the requirements for nanotechnology applications [4–6]. Meanwhile, nickel oxide (NiO) as a p-type oxide semiconductor has been used in drug delivery systems, photocatalysts, battery cathodes, magnetic materials, electrochemical capacitors, and electrochromic films [7,8]. ZnO-based mixed nanocomposites, i.e., ZnO-SnO2, ZnO-NiO, ZnOCuO, exhibit superior functional performance compared to singlephase metal oxides [8–12]. This study has mainly focused on the control of the dimensions and morphology of such mixed oxides, as well as use of simple, cost-effective processing methods that do not require sophisticated equipment [8,10,11]. In this study, we prepared unique porous ZnO-NiO nanocomposites via a facile one-pot solution process and compared their structural and morphological properties with those of pure ZnO nanostructures.
For the ZnO sample, an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O; Zn(NO), 10 mM) and hexamethylenetetramine (HMT, C6H12N4, 10 mM) was stirred for 1 h at room temperature. The transparent aqueous solution was kept in a dry oven at 90 °C for 6 h. After reaction, the whitish powder was centrifuged and then dispersed in ethanol (C2H6O). The resulting solution was dropped on a substrate and dried at 120 °C for 10 min, in air. It was finally annealed at 500 °C for 1 h at a heating rate of 10 °C/min, in air. For the ZnO-NiO sample, nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O; Ni(Ac), 7–10 mM) was added to the ZnO solution; this is a simple condition for the synthesis of ZnO-NiO nanocomposites [8,10,11]. The other parameters were kept the same as those for the ZnO synthesis. Samples without Ni(Ac), and those with 7 mM and 10 mM Ni(Ac) were indexed as 0NZO, 7NZO, and 10 NZO, respectively. The crystalline structure and phase of the samples were identified using X-ray diffraction (XRD, D8ADVANCE) at acceleration voltage and current of 40 keV and 40 mA, respectively, with a scanning step of 0.01°. Sample morphologies were observed by a field emission scanning electron microscopy (FESEM, JSM-6701) attached with an energy dispersive X-ray (EDX).
⁎
Corresponding author. E-mail address: [email protected] (K.H. Kim).
http://dx.doi.org/10.1016/j.ceramint.2016.10.086 Received 19 September 2016; Received in revised form 11 October 2016; Accepted 13 October 2016 Available online xxxx 0272-8842/ © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Kim, K.H., Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.10.086
Ceramics International xx (xxxx) xxxx–xxxx
K.H. Kim et al.
Fig. 1. XRD patterns of (a) 0NZO, (b) 7NZO, and (c) 10NZO samples.
[15]. It was known that one-dimensional (1D) rod-type nanostructures are easily grown because of the surface energy difference between the polar and non-polar planes of ZnO [14,16,17]. Nanostructures with an interesting morphology were observed when Ni(Ac) was added to the ZnO solution. Three-dimensional (3D) sphere-like structures assembled with interwoven nanowalls were observed in the 7NZO sample, as shown in Fig. 2(c). The average diameter of the sphere-likes structures was around 3 µm, and they are uniformly distributed, as shown in Fig. S3(a). From the high-magnificent image (Fig. 2(d)), the thickness of the nanowalls was found to be around 25 nm. The Ni ions might have lowered the surface energy difference between the polar and nonpolar planes, leading to a distinct morphology [18]. As a result, individual clusters with interconnected nanostrings formed nanowalls rather than rods. Further studies are underway to understand the growth mechanism of the nanostructures. It is noteworthy that individual nanowalls are embedded with nanoparticles that are ~10 nm in diameter (Fig. 2(d)). Similar sphere-like structures have been reported in the other papers on ZnO, NiO, or nickel hydroxide (NiOH) [19–22]. However, this morphology is unique among ZnO-based mixed nanocomposites [10,11]. Porous nanostructures with a large surface area are important for a wide range of applications [23,24]. With an increase in the amount of Ni(Ac) in the ZnO solution to 10 mM (Fig. 2(e,f)), individual sphere-like structures that were interconnected without clear boundaries formed continuous nanolayered structures (Fig. S3(b)). The high-magnification image (Fig. 2(f)) revealed that the continuous nanolayered structures consisted of embedded nanoparticles. Fig. 3 shows the electron image (a), EDX elemental maps (b–d), and spectrum (e) of the 10NZO sample. These images confirmed that the nanocomposites were composed of Ni, Zn, and O, which were uniformly distributed. From XRD and EDX analyses, it could be confirmed that porous ZnO-NiO nanocomposites were formed via the facile one-pot solution process.
3. Results and discussion Fig. 1 shows the XRD patterns of the 0NZO (a), 7NZO (b), and 10NZO (c) samples. Detailed peak positions and lattice parameters are summarized in Table S1 in Supporting Information. In the case of the 0NZO sample (Fig. 1(a)), all the diffraction peaks could be indexed to wurtzite hexagonal structured ZnO (JCPDS card no. 36–1451). The calculated lattice parameters of the 0NZO sample were a=3.24 Å and c=5.20 Å. When Ni(Ac) was added, a (111) diffraction peak due to NiO (JCPDS card no. 47-1049) as a secondary phase, as well as peaks due to ZnO, were observed in the spectra of the 7NZO and 10NZO samples (Fig. 1(b) and (c)). As expected, an excess of Ni led to the formation of the oxide phase. In the 7NZO and 10NZO samples, diffraction peaks indexed to ZnO were shifted to higher 2θ values as compared to those for the pure ZnO sample (0NZO). This was due to the differences in the ionic radii of Zn2+(0.74 Å) and Ni2+(0.69 Å) [13], indicating that smaller Ni ions were incorporated into the ZnO lattice and caused a reduction in the lattice parameters. Meanwhile, the NiO (111) diffraction peak of the 7NZO sample was shifted to the lower 2θ values as compared to that of the 10NZO sample. Thus, it could be concluded that Ni-doped ZnO and Zn-doped NiO composites were prepared via a facile one-pot solution process, in the 7NZO and 10NZO samples. Fig. 2 shows the FESEM images of ZnO samples with various Ni(Ac) contents. As shown in Fig. 2(a) and (b), the 0NZO sample had a flower-like structure assembled from rods and individually distributed rods. The length and width of the rods were irregular. The surface of the rods was very smooth (Fig. 2(b)). The morphology of the nanostructures was influenced by the nucleation and growth process in aqueous solution [14]. FESEM images of the 0NZO sample reacted at 90 °C for 1 h are shown in Fig. S1. It could be seen that rod-type nanostructures (Fig. S1(b)) spouted from ball-like clusters of the assembled nanostrings with a thickness of ~10 nm. After reaction for 2 h, the rods from the clusters increased in length, as shown in Fig. S2. This result is in good agreement with the study reported by Liu et al.
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Fig. 2. FESEM images of NZO samples with various Ni(Ac) contents: (a, b) 0 mM (0NZO), (c,d) 7 mM (7NZO), (e,f) 10 mM (10NZO). (a,c,e) Low-magnification images, (b,d,f) highmagnification images of the areas marked by squares in (a,c,e), respectively.
Porous sphere-like structures assembled with interwoven nanowalls were observed in the 7NZO sample, while, the continuous nanolayered structures consisting of embedded nanoparticles were observed in the 10NZO sample. EDX results showed that Ni, Zn, and O were homogeneously distributed on the sample surface, thus indicating that the ZnO and NiO nanoparticles were well distributed in the nanocomposites.
4. Conclusions We fabricated porous ZnO-NiO nanocomposites via a simple onepot process using an aqueous solution of Zn(NO), Ni(Ac), and HMT. We compared the structural and morphological properties of these nanocomposites to those of pure ZnO nanostructures. XRD results confirmed that the ZnO and NiO nanocrystalline structures were formed in the 7NZO and 10NZO samples, without any other phases.
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Fig. 3. (a) Electron image and (b–d) EDX elemental mapping images of (b) Ni-Kα, (c) Zn-Kα, (d) O-Kα, and (e) EDX spectrum of the 10NZO sample. sensors, Mater. Sci. Eng. B 176 (2011) 1409–1421. [3] X. Wang, C. Hu, H. Liu, G. Du, X. He, Y. Xi, Synthesis of CuO nanostructures and their application for nonenzymatic glucose sensing, Sens. Actuators B: Chem. 144 (2010) 220–225. [4] M.-C. Jun, S.-U. Park, J.-H. Koh, Comparative studies of Al-doped ZnO and Gadoped ZnO transparent conducting oxide thin films, Nanoscale Res. Lett. 7 (2012) (639-1-6). [5] R. Jothi Ramalingam, G.S. Chung, Polymer assisted Ga doped ZnO nanodisk/ nanorod structures prepared by a low temperature one-pot hydrothermal method, Mater. Lett. 68 (2012) 247–250. [6] C. Wu, L. Shen, H. Yu, Q. Huang, Y.C. Zhang, Synthesis of Sn-doped ZnO nanorods and their photocatalytic properties, Mater. Res. Bull. 46 (2011) 1107–1112.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.ceramint.2016.10.086. References [1] Z.L. Wang, Zinc oxide nanostructures: growth, properties and applications, J. Phys.:Condens. Matter 16 (2004) R829–R858. [2] A. Wei, L. Pan, W. Huang, Recent progress in the ZnO nanostructure-based
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(2004) 975–977. [17] L.E. Greene, M. Law, D.H. Tan, M. Montano, J. Goldberger, G. Somorjai, P. Yang, General route to vertical ZnO nanowire arrays using textured ZnO seeds, Nano Lett. 5 (2005) 1231–1236. [18] S.H. Chiu, J.C.A. Huang, Chemical bath deposited of ZnO and Ni doped ZnO nanorod, J. Non-Cryst. Solids 358 (2012) 2453–2457. [19] J. Qiu, B. Weng, L. Zhao, C. Chang, Z. Shi, X. Li, H.-K. Kim, Y.-H. Hwang, Synthesis and characterization of flower-like bundles of ZnO nanosheets by a surfactant-free hydrothermal, J. Nanomater. 11 (2014) (Article ID 281461). [20] R. Miao, W. Zeng, Hydrothermal synthesis of flake-flower NiO architectures: structure, growth and gas-sensing properties, Mater. Lett. 171 (2016) 200–203. [21] Q. Li, Y. Chen, T. Yang, D. Lei, G. Zhang, L. Mei, L. Chen, Q. Li, T. Wang, Preparation of 3D flower-like NiO hierarchical architectures and their electrochemical properties in lithium-ion batters, Electrochim. Acta 90 (2013) 80–89. [22] Z. You, K. Shen, Z. Wu, X. Wang, X. Kong, Electrodeposition of Zn-doped α-nickel hydroxide with flower-like nanostructure for supercapacitors, Appl. Surf. Sci. 258 (2012) 8117–8123. [23] X. Wang, W. Liu, J. Liu, F. Wang, J. Kong, S. Qiu, C. He, L. Luan, Synthesis of nestlike ZnO hierarchically porous structures and analysis of their gas sensing properties, ACS Appl. Mater. Interfaces 4 (2012) 817–825. [24] J. Chang, M.Z. Ahmad, W. Wlodarski, E.R. Waclawik, Self-assembled 3D ZnO porous structures with exposed reactive {0001} facets and their enhanced gas sensitivity, Sensors 13 (2013) 8445–8460.
[7] P.P. Dorneanu, A. Airinei, N. Olaru, M. Homocianu, V. Nica, F. doroftei, Preparation and characterization of NiO, ZnO and NiO-ZnO composite nanofibers by electrospinning method, Mater. Chem. Phys. 148 (2014) 1029–1035. [8] L. Xu, R. Zheng, S. Liu, J. Song, J. Chen, B. Dong, H. Song, NiO@ZnO heterostructured nanotubes: coelectrospinning fabrication, characterization, and highly enhanced gas sensing properties, Inorg. Chem. 51 (2012) 7733–7740. [9] A. Hamrouni, H. Lachheb, A. Houas, Synthesis, characterization and photocatalytic activity of ZnO-SnO2 nanocomposites, Mater. Sci. Eng. B 178 (2013) 1371–1379. [10] B. Li, Y. Wang, Facile synthesis and photocatalytic activity of ZnO-CuO nanocomposite, Superlattices Microstruct. 47 (2010) 615–623. [11] R.K. Sharma, D. Kumar, R. Ghose, Synthesis of nanocrystalline ZnO-NiO mixed metal oxide powder by homogeneous precipitation method, Ceram. Int. 42 (2016) 4090–4098. [12] A.A. Kovalenko, A.N. Baranov, G.N. Panin, Synthesis of ZnO/NiO nanocmoposties from ethanol solutions, Russ. J. Inorg. Chem. 53 (2008) 1546–1551. [13] L. Yang, Y. Zhao, R. Yin, F. Li, Synthesis of Ni2+-doped ZnAl2O4/ZnO composite phosphor film with largely enhanced polychromatic emission via a simple-source precursor, J. Am. Ceram. Soc. 97 (2014) 1123–1130. [14] W. Peng, S. Qu, G. Cong, Z. Wang, Synthesis and structures of morphologycontrolled ZnO nano- and microcrystals, Cryst. Growth Des. 6 (2006) 1518–1522. [15] Y. Liu, W. Gao, Growth process, crystal size and alignment of ZnO nanorods synthesized under neutral and acid conditions, J. Alloy. Compd. 629 (2015) 84–91. [16] X.Y. Kong, Z.L. Wang, Polar-surface dominated ZnO nanobelts and the electrostatic energy induced nanohelixes, nanosprings, and nanospirals, Appl. Phys. Lett. 84
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Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Preparation of porous zinc oxide-nickel oxide nanocomposites by facile one-pot solution process ⁎
Kyung Ho Kim , Yuya Yoshihara, Yoshio Abe, Midori Kawamura, Takayuki Kiba Department of Materials Science and Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
A R T I C L E I N F O
A BS T RAC T
Keywords: ZnO NiO Sphere-like structures Nanolayered structures Nanocomposites
Porous zinc oxide (ZnO)-nickel oxide (NiO) nanocomposites were fabricated via a one-pot process using aqueous solutions of zinc nitrate hexahydrate (Zn(NO), 10 mM), hexamethylenetetramine (HMT, 10 mM), and nickel acetate tetrahydrate (Ni(Ac), 7 mM (7NZO), 10 mM (10NZO)). The structural and morphological properties of these nanocomposites were investigated and compared to those of pure ZnO nanostructures. Rodtype nanostructures were observed in the pure ZnO sample, while porous sphere-like structures and continuous nanolayered structures were observed in the 7NZO and 10NZO samples, respectively. This difference in morphology might be due to the growth of the non-polar plane instead of the polar plane of ZnO in the clusters. The nanocomposites were composed of Ni, Zn, and O, which were homogeneously distributed. Distinct morphologies of the ZnO-NiO nanocomposites were obtained via a facile one-pot solution process.
1. Introduction
2. Experimental
Significant efforts have been devoted to the development of nanostructured metal oxides with unique structural morphologies that find potential applications in a wide range of electronic and optoelectronic devices [1–3]. One such metal oxide, zinc oxide (ZnO), with a wide band gap energy (3.37 eV) and large exciton binding energy (60 meV), has been of strong research interest as a typical n-type oxide semiconductor [1,2]. The electrical and optical properties of ZnO can be modified by the incorporation of dopants (Al, Ga, Sn, etc.) into its lattice in order to meet the requirements for nanotechnology applications [4–6]. Meanwhile, nickel oxide (NiO) as a p-type oxide semiconductor has been used in drug delivery systems, photocatalysts, battery cathodes, magnetic materials, electrochemical capacitors, and electrochromic films [7,8]. ZnO-based mixed nanocomposites, i.e., ZnO-SnO2, ZnO-NiO, ZnOCuO, exhibit superior functional performance compared to singlephase metal oxides [8–12]. This study has mainly focused on the control of the dimensions and morphology of such mixed oxides, as well as use of simple, cost-effective processing methods that do not require sophisticated equipment [8,10,11]. In this study, we prepared unique porous ZnO-NiO nanocomposites via a facile one-pot solution process and compared their structural and morphological properties with those of pure ZnO nanostructures.
For the ZnO sample, an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O; Zn(NO), 10 mM) and hexamethylenetetramine (HMT, C6H12N4, 10 mM) was stirred for 1 h at room temperature. The transparent aqueous solution was kept in a dry oven at 90 °C for 6 h. After reaction, the whitish powder was centrifuged and then dispersed in ethanol (C2H6O). The resulting solution was dropped on a substrate and dried at 120 °C for 10 min, in air. It was finally annealed at 500 °C for 1 h at a heating rate of 10 °C/min, in air. For the ZnO-NiO sample, nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O; Ni(Ac), 7–10 mM) was added to the ZnO solution; this is a simple condition for the synthesis of ZnO-NiO nanocomposites [8,10,11]. The other parameters were kept the same as those for the ZnO synthesis. Samples without Ni(Ac), and those with 7 mM and 10 mM Ni(Ac) were indexed as 0NZO, 7NZO, and 10 NZO, respectively. The crystalline structure and phase of the samples were identified using X-ray diffraction (XRD, D8ADVANCE) at acceleration voltage and current of 40 keV and 40 mA, respectively, with a scanning step of 0.01°. Sample morphologies were observed by a field emission scanning electron microscopy (FESEM, JSM-6701) attached with an energy dispersive X-ray (EDX).
⁎
Corresponding author. E-mail address: [email protected] (K.H. Kim).
http://dx.doi.org/10.1016/j.ceramint.2016.10.086 Received 19 September 2016; Received in revised form 11 October 2016; Accepted 13 October 2016 Available online xxxx 0272-8842/ © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Kim, K.H., Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.10.086
Ceramics International xx (xxxx) xxxx–xxxx
K.H. Kim et al.
Fig. 1. XRD patterns of (a) 0NZO, (b) 7NZO, and (c) 10NZO samples.
[15]. It was known that one-dimensional (1D) rod-type nanostructures are easily grown because of the surface energy difference between the polar and non-polar planes of ZnO [14,16,17]. Nanostructures with an interesting morphology were observed when Ni(Ac) was added to the ZnO solution. Three-dimensional (3D) sphere-like structures assembled with interwoven nanowalls were observed in the 7NZO sample, as shown in Fig. 2(c). The average diameter of the sphere-likes structures was around 3 µm, and they are uniformly distributed, as shown in Fig. S3(a). From the high-magnificent image (Fig. 2(d)), the thickness of the nanowalls was found to be around 25 nm. The Ni ions might have lowered the surface energy difference between the polar and nonpolar planes, leading to a distinct morphology [18]. As a result, individual clusters with interconnected nanostrings formed nanowalls rather than rods. Further studies are underway to understand the growth mechanism of the nanostructures. It is noteworthy that individual nanowalls are embedded with nanoparticles that are ~10 nm in diameter (Fig. 2(d)). Similar sphere-like structures have been reported in the other papers on ZnO, NiO, or nickel hydroxide (NiOH) [19–22]. However, this morphology is unique among ZnO-based mixed nanocomposites [10,11]. Porous nanostructures with a large surface area are important for a wide range of applications [23,24]. With an increase in the amount of Ni(Ac) in the ZnO solution to 10 mM (Fig. 2(e,f)), individual sphere-like structures that were interconnected without clear boundaries formed continuous nanolayered structures (Fig. S3(b)). The high-magnification image (Fig. 2(f)) revealed that the continuous nanolayered structures consisted of embedded nanoparticles. Fig. 3 shows the electron image (a), EDX elemental maps (b–d), and spectrum (e) of the 10NZO sample. These images confirmed that the nanocomposites were composed of Ni, Zn, and O, which were uniformly distributed. From XRD and EDX analyses, it could be confirmed that porous ZnO-NiO nanocomposites were formed via the facile one-pot solution process.
3. Results and discussion Fig. 1 shows the XRD patterns of the 0NZO (a), 7NZO (b), and 10NZO (c) samples. Detailed peak positions and lattice parameters are summarized in Table S1 in Supporting Information. In the case of the 0NZO sample (Fig. 1(a)), all the diffraction peaks could be indexed to wurtzite hexagonal structured ZnO (JCPDS card no. 36–1451). The calculated lattice parameters of the 0NZO sample were a=3.24 Å and c=5.20 Å. When Ni(Ac) was added, a (111) diffraction peak due to NiO (JCPDS card no. 47-1049) as a secondary phase, as well as peaks due to ZnO, were observed in the spectra of the 7NZO and 10NZO samples (Fig. 1(b) and (c)). As expected, an excess of Ni led to the formation of the oxide phase. In the 7NZO and 10NZO samples, diffraction peaks indexed to ZnO were shifted to higher 2θ values as compared to those for the pure ZnO sample (0NZO). This was due to the differences in the ionic radii of Zn2+(0.74 Å) and Ni2+(0.69 Å) [13], indicating that smaller Ni ions were incorporated into the ZnO lattice and caused a reduction in the lattice parameters. Meanwhile, the NiO (111) diffraction peak of the 7NZO sample was shifted to the lower 2θ values as compared to that of the 10NZO sample. Thus, it could be concluded that Ni-doped ZnO and Zn-doped NiO composites were prepared via a facile one-pot solution process, in the 7NZO and 10NZO samples. Fig. 2 shows the FESEM images of ZnO samples with various Ni(Ac) contents. As shown in Fig. 2(a) and (b), the 0NZO sample had a flower-like structure assembled from rods and individually distributed rods. The length and width of the rods were irregular. The surface of the rods was very smooth (Fig. 2(b)). The morphology of the nanostructures was influenced by the nucleation and growth process in aqueous solution [14]. FESEM images of the 0NZO sample reacted at 90 °C for 1 h are shown in Fig. S1. It could be seen that rod-type nanostructures (Fig. S1(b)) spouted from ball-like clusters of the assembled nanostrings with a thickness of ~10 nm. After reaction for 2 h, the rods from the clusters increased in length, as shown in Fig. S2. This result is in good agreement with the study reported by Liu et al.
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Fig. 2. FESEM images of NZO samples with various Ni(Ac) contents: (a, b) 0 mM (0NZO), (c,d) 7 mM (7NZO), (e,f) 10 mM (10NZO). (a,c,e) Low-magnification images, (b,d,f) highmagnification images of the areas marked by squares in (a,c,e), respectively.
Porous sphere-like structures assembled with interwoven nanowalls were observed in the 7NZO sample, while, the continuous nanolayered structures consisting of embedded nanoparticles were observed in the 10NZO sample. EDX results showed that Ni, Zn, and O were homogeneously distributed on the sample surface, thus indicating that the ZnO and NiO nanoparticles were well distributed in the nanocomposites.
4. Conclusions We fabricated porous ZnO-NiO nanocomposites via a simple onepot process using an aqueous solution of Zn(NO), Ni(Ac), and HMT. We compared the structural and morphological properties of these nanocomposites to those of pure ZnO nanostructures. XRD results confirmed that the ZnO and NiO nanocrystalline structures were formed in the 7NZO and 10NZO samples, without any other phases.
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Fig. 3. (a) Electron image and (b–d) EDX elemental mapping images of (b) Ni-Kα, (c) Zn-Kα, (d) O-Kα, and (e) EDX spectrum of the 10NZO sample. sensors, Mater. Sci. Eng. B 176 (2011) 1409–1421. [3] X. Wang, C. Hu, H. Liu, G. Du, X. He, Y. Xi, Synthesis of CuO nanostructures and their application for nonenzymatic glucose sensing, Sens. Actuators B: Chem. 144 (2010) 220–225. [4] M.-C. Jun, S.-U. Park, J.-H. Koh, Comparative studies of Al-doped ZnO and Gadoped ZnO transparent conducting oxide thin films, Nanoscale Res. Lett. 7 (2012) (639-1-6). [5] R. Jothi Ramalingam, G.S. Chung, Polymer assisted Ga doped ZnO nanodisk/ nanorod structures prepared by a low temperature one-pot hydrothermal method, Mater. Lett. 68 (2012) 247–250. [6] C. Wu, L. Shen, H. Yu, Q. Huang, Y.C. Zhang, Synthesis of Sn-doped ZnO nanorods and their photocatalytic properties, Mater. Res. Bull. 46 (2011) 1107–1112.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.ceramint.2016.10.086. References [1] Z.L. Wang, Zinc oxide nanostructures: growth, properties and applications, J. Phys.:Condens. Matter 16 (2004) R829–R858. [2] A. Wei, L. Pan, W. Huang, Recent progress in the ZnO nanostructure-based
4
Ceramics International xx (xxxx) xxxx–xxxx
K.H. Kim et al.
(2004) 975–977. [17] L.E. Greene, M. Law, D.H. Tan, M. Montano, J. Goldberger, G. Somorjai, P. Yang, General route to vertical ZnO nanowire arrays using textured ZnO seeds, Nano Lett. 5 (2005) 1231–1236. [18] S.H. Chiu, J.C.A. Huang, Chemical bath deposited of ZnO and Ni doped ZnO nanorod, J. Non-Cryst. Solids 358 (2012) 2453–2457. [19] J. Qiu, B. Weng, L. Zhao, C. Chang, Z. Shi, X. Li, H.-K. Kim, Y.-H. Hwang, Synthesis and characterization of flower-like bundles of ZnO nanosheets by a surfactant-free hydrothermal, J. Nanomater. 11 (2014) (Article ID 281461). [20] R. Miao, W. Zeng, Hydrothermal synthesis of flake-flower NiO architectures: structure, growth and gas-sensing properties, Mater. Lett. 171 (2016) 200–203. [21] Q. Li, Y. Chen, T. Yang, D. Lei, G. Zhang, L. Mei, L. Chen, Q. Li, T. Wang, Preparation of 3D flower-like NiO hierarchical architectures and their electrochemical properties in lithium-ion batters, Electrochim. Acta 90 (2013) 80–89. [22] Z. You, K. Shen, Z. Wu, X. Wang, X. Kong, Electrodeposition of Zn-doped α-nickel hydroxide with flower-like nanostructure for supercapacitors, Appl. Surf. Sci. 258 (2012) 8117–8123. [23] X. Wang, W. Liu, J. Liu, F. Wang, J. Kong, S. Qiu, C. He, L. Luan, Synthesis of nestlike ZnO hierarchically porous structures and analysis of their gas sensing properties, ACS Appl. Mater. Interfaces 4 (2012) 817–825. [24] J. Chang, M.Z. Ahmad, W. Wlodarski, E.R. Waclawik, Self-assembled 3D ZnO porous structures with exposed reactive {0001} facets and their enhanced gas sensitivity, Sensors 13 (2013) 8445–8460.
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