Large-scale synthesis of hierarchical alpha-FeOOH ... - Springer Link

7 downloads 160 Views 558KB Size Report
May 7, 2010 - mental friendly ultrasonic-assisted hydrothermal route for preparation of ..... W.S. Seo, H.H. Jo, K. Lee, B. Kim, S.J. Oh, J.T. Park, Angew. Chem.
J Mater Sci: Mater Electron (2011) 22:252–259 DOI 10.1007/s10854-010-0124-9

Large-scale synthesis of hierarchical alpha-FeOOH flowers by ultrasonic-assisted hydrothermal route H. F. Chen • G. D. Wei • X. Han • S. Li P. P. Wang • M. Chubik • A. Gromov • Z. P. Wang • W. Han



Received: 31 January 2010 / Accepted: 20 April 2010 / Published online: 7 May 2010 Ó Springer Science+Business Media, LLC 2010

Abstract In this paper, we report a facile, an environmental friendly ultrasonic-assisted hydrothermal route for preparation of goethite flower structures using Fe nanopowders at low temperature (85°C). The flower structure consisted of tens of hundreds of nanowires and such structures can further self-assemble with the flake with micro size area. Structural, morphological, and elemental analysis revealed that the products consisted of flower-like structures with high structural uniformity, good crystal quality, and high yields. Influencing factors such as the reaction temperature, pH value, and the deposition time were systematically investigated. A possible formation mechanism was proposed on the basis of the experimental results. Magnetic measurements showed that the as-obtained goethite flowers exhibited weakly ferromagnetic characteristics at room temperature, which were quite different from those of the corresponding bulk materials.

H. F. Chen  X. Han  S. Li  P. P. Wang  W. Han (&) College of Physics, Jilin University, 130021 Changchun, People’s Republic of China e-mail: [email protected] G. D. Wei (&) College of Science, Ningbo University of Technology, 315016 Ningbo, People’s Republic of China e-mail: [email protected] Z. P. Wang Siping Gao Sida Nano Material & Equipment Ltd, Siping, People’s Republic of China M. Chubik  A. Gromov Tomsk Polytechnic University, 634050 Tomsk, Russia

123

1 Introduction Iron oxyhydroxide (FeOOH) is one of the most abundant and important mineral in natural and has distinctive properties with many industrial applications [1–4]. Among the well known iron oxyhydroxides, goethite (a-FeOOH) with nontoxicity, high resistance to corrosion, low cost, and interesting magnetic properties represents the most stable polymorphs of iron oxyhydroxide and the most important precursor in the synthesis of iron oxide such as hematite (a-Fe2O3) and maghemite (c-Fe2O3). In addition, goethite as pigment is widely used in various compositions of house paints or fine colors for painting. Therefore, goethite with the excellent properties is a very attractive material and has received increasing attention because of its extensive applications in magnetic recording media [5], catalysts [6], pigments [5], electrode materials [7], absorptions of metal ion [8, 9], precursors in lithium batteries [10], and sensors [11]. One-dimensional (1D) a-FeOOH nanostructure with its anisotropic morphologies and excellent structure has outstanding physical and chemistry properties, especially distinct magnetic properties, which is quite different from its bulk [12, 13]. Stimulated by its potential applications, many efforts have been directed toward the fabrication of 1D a-FeOOH nanostructures. Up to now, hydrothermal process with diverse reaction raw materials was adopted for the synthesis of 1D a-FeOOH nanostructures to enhance their performance and find novel properties, which appears to have some advantages, including mild synthetic conditions, simple manipulation, and good crystallization of the products. A number of 1D a-FeOOH nanostructured materials with various geometrical morphologies such as nanorods [10, 13, 14], nanowires [15], nanotubes [16], and nanobundles [17], were synthesized by the hydrothermal

J Mater Sci: Mater Electron (2011) 22:252–259

processes. Tang et al. and Shao et al. have successfully synthesized a-FeOOH nanorods via a hydrothermal method, respectively [12, 13]. In their papers, they all pointed out that the nanorods had distinctive magnetic properties with quite different from that of their bulk. In recent days, the design and synthesis of hierarchical self-assembled and patterned superstructures from 1D nanostructures (building blocks) have been important research subjects in nanoscience and nanotechnology [18]. As an important step in research and development of 1D a-FeOOH nanostructure for the nanodevices and nanotechnology, it is a fundamental and challenging work to control the oriented growth and self-assembled of 1D a-FeOOH nanostructures. However, to the best of our knowledge, the assembly of 1D a-FeOOH nanostructures building blocks into three-dimensional (3D) superstructures and even more complex structures are still a challenge work in the realization of advanced nanodevices and applied nanotechnology. In our present work, we have successfully fabricated the a-FeOOH flower structures via ultrasonic-assisted hydrothermal route with used Fe nanopowders at low temperature. By using such new synthesis method, we can achieve the facile, environmental friendly synthesis process and the morphology control of a-FeOOH flowers at lower temperature, whereas the reaction temperature of hydrothermal method is always more than 100°C according to literatures [13, 16, 19]. More important is that the uniform a-FeOOH flowers could be obtained with high yield, good crystal quality and good reproducibility. The effects of different reaction parameters on the evolution of a-FeOOH were investigated and the possible formation mechanism of the morphologies was also discussed here. Magnetic measurements showed that the as-obtained a-FeOOH nanorods exhibited weakly ferromagnetic characteristics at room temperature, which was quite different from the behavior of the corresponding bulk material.

2 Experimental details All the used chemical reagents in this work, such as hydrochloric acid, nitric acid and sodium hydroxide were of analytical grade without any further purification. High purity Fe nanopowders with the diameter of *60 nm were synthesized in our lab by wire electrical explosion method as described in detail elsewhere [20]. 2.1 Preparation of goethite (a-FeOOH) In a typical procedure, 0.8 g Fe nanopowders were immersed into 200 mL distilled water kept in a beaker under ultrasonically treatment at 85°C. Subsequently, 4.5 g

253

HNO3 (65–68%) solution was dropped into the mixed solution at a constant flow rate of 1 mL min-1. After the above solution was ultrasonically treated for 1 h, 8 g NaOH powders were added into the solution to make the concentration of NaOH in the solution at 1 mol/L. After ultrasound vibration for another 1 h, turned off the ultrasound generator and kept the solution still staying in the water bath for 6 h. Then, the solution was taken out from the water bath and let the product of deposition at room temperature for 24 h. Finally, the resulting solid products were obtained with filtered off from the solution, washed with distilled water for several times, and dried in the vacuum dry chamber at 60°C for 6 h. 2.2 Characterization The crystal structures and phase purity of the products were characterized by X-ray powder diffraction (XRD, Rigaku ˚ ). A scanD/max-RA) with CuKa radiation (k = 1.5418 A ning rate of 5°/min was applied to record the pattern in the 2h range of 10–70°. The size and morphology of the products were investigated by scanning electron microscopic (SEM, JEOL, JSM-6480LV) equipped with energy-dispersive X-ray spectroscopy (EDS). The products were further investigated by using Fourier transform infrared spectroscopy (FT-IR, AVATAR 370 DTGS). The magnetic properties of the a-FeOOH products were examined using a Lake Shore 7307 vibrating sample magnetometer at room temperature.

3 Results and discussion 3.1 Morphology and structures analysis Compared with that of Fe bulk and another Fe salts, it is well known that metal Fe nanopowders have high surface energy and even can take place spontaneous combustion in air. Thus, it can short the reaction time, decrease the synthesized temperature, and enhance the production yield. More importantly, it can avoid another element introduced (such as Cl-, SO4-) in the synthesis process, which can greatly influence the properties of the samples. The above mentioned merits for Fe nanopowders have inspired us to find a green, facile and simple hydrothermal route to synthesize a-FeOOH 1D nanostructure. In the present work, it is proved that a-FeOOH nanostructures is affected by a series of reaction parameters, such as reaction time, growth temperature, deposition time and the amount of NaOH. When fixing the experiment parameters according to that described in experiment section, flower-like a-FeOOH nanostructures can be successfully synthesized with largescale yield.

123

254

The morphology characteristics of the obtained products were first analyzed by using SEM. Figure 1a displays a low magnification SEM image of the as-prepared products, which reveals that the products are consisted of well-grown flower-like structures with a uniform morphology. The assembly of flower-like nanostructures consisted of tens of hundreds of nanowires. The nanowires with typical lengths are in the range of one to ten micrometers and diameters are several tens to several hundreds of nanometers, respectively. Figure 1b and c show high-magnification SEM images of an individual flower-like. It is noted that these nanowires look seemingly growing from the inside particles and such flower-like structures can be selfassembled into more complex structures. In our as-synthesized products, we found that these flower-like structures could be further self-assembled a three dimension flat structure, which even can be seen by naked eye. Figure 1d presents three very big flats with several 100 lm in length and several 10 lm in width and about 10 lm in thickness. Thus, flower-like nanostructures as the nanoscale building blocks could be large-scale self-assembled into more complex structures and such large dimension structure can be well applied in many fields. The composition and crystalline phase purity of the as prepared products were further examined by XRD. As shown in Fig. 2a, all of the diffraction peaks can be Fig. 1 Different magnification of SEM images of the products obtained after hydrothermal reaction

123

J Mater Sci: Mater Electron (2011) 22:252–259

indexed to a pure orthorhombic a-FeOOH phase, which agree well with the reported data (a-FeOOH, JCPDS No. 81-0463), and no other obvious XRD peaks due to impurities were found in the XRD patterns. The broadening of the diffraction peaks could be attributed to the small particle size and overlapping of the diffraction peaks. The strong and sharp diffraction peaks can also demonstrate the as-synthesized products with good crystal quality. However, due to XRD is less accurate quantitatively when the material content is less than 2%, we use FT-IR technique to identify goethite compositions, especially checking out whether low content goethite derivatives, such as the phases of a-Fe2O3, a-FeOOH, and Fe3O4 are exist or not. Incidentally, FT-IR spectroscopy is a very useful technique in detecting a-FeOOH or b-FeOOH phases present in small fractions. The representative FT-IR spectrum (Fig. 2b) of the products indicates the formation of FeOOH since the main absorption bands are in good agreement with that of the standard spectrum of a-FeOOH. Absorption bands centered at 3,403 and 1,556 cm-1 in the spectra can be identified to the H2O stretching and bending modes resulted from the presence of adsorption water molecule on the hydroxylated goethite surfaces [21]. Iron oxides, especially at the nanoscale, have a very high affinity for water, adsorbing up to one mole of excess H2O per mole of iron oxide. From previous investigations by Cambier and

J Mater Sci: Mater Electron (2011) 22:252–259

255

3.2.1 Effect of the reaction temperature

Fig. 2 XRD pattern (a) and FT-IR spectra (b) of goethite a-FeOOH flowers, respectively

Cwiertny [22, 23], the bands centered at 1,346, 979, and 619 cm-1 can be all identified to the Fe–O vibrational modes in FeOOH, and the band centered at 3,129 cm-1 can be attributable to O–H stretching mode in the goethite structure. The bands at 894 and 800 cm-1 are characteristic of a-FeOOH, and thus they can be assigned to Fe–O–OH bending vibrations modes in a-FeOOH [23, 24]. Based on the above analysis and discussion, the FT-IR studies combined with the XRD results indicate that the obtained goethite flowers were high pure and good crystallizability of a-FeOOH. 3.2 Growth mechanism of the flower-like The size, morphology, structure, and even phase of the asprepared structures are very sensitive to the reaction conditions, such as temperature, concentration of NaOH, and deposition time. Thus, in order to understand the reactions process and growth mechanism of goethite flowers, a number of controlled experiments were performed.

Oxyhydroxides are normally obtained by precipitation from an aqueous solution. The particle size is controlled by initial iron concentration, organic additives, solution pH, and reaction temperature. It is well known that the temperature is a key factor for hydrothermal reaction, especially for goethite. Thus, to investigate the growth mechanism and reveal the generation process of the structures, reaction temperature dependent experiments were firstly carried out at different reaction temperature in the cases of 65, 75, and 95°C, respectively. As shown in Fig. 3a, at low reaction temperature (65°C), the products are consisted of many agglomerate particles with anomalous shapes. There are only few rod-like structures on the surface of the agglomerate particles with several 100 nm in length and *100 nm in width. By increasing the reaction temperature to 75°C, as shown in Fig. 3b, the rod-like a-FeOOH products largely appears with much longer length scale. The XRD pattern also confirmed that a-FeOOH phase was the main phase in these products. When the reaction temperature increases to 85°C, all products were transferred into a-FeOOH flower (Fig. 3c). As shown in Fig. 3d, when the reaction temperature increases to 95°C, the a-FeOOH are consisted of nanowires with several tens of micrometer in length and several hundreds of nanometers in width. It is noted that the nanowires can also self-assemble into flower structures. Obviously, from these images, the experimental results showed that the reaction temperature had a remarkable influence on the phase structure and the final morphology of the product. 3.2.2 Effect of the NaOH concentration In addition to the reaction temperature, the concentration of the NaOH solution also plays a very important role in the formation of such flower structures. As shown in Fig. 4a, when the concentration of the NaOH solution is kept at 0.5 mol/L, the products are mainly consisted of agglomerate particles and there are only few pine needle structures on the surface of these particles. However, when the concentration of the NaOH solution was increased to 2.0 mol/L, the flower structures completely disappeared and there were only belt structures in the products with several tens of micrometer in length and *1–2 lm in width (Fig. 4b). Obviously, the sizes of the structures are quite bigger than that of flowers growing in the NaOH solution of 1.0 mol/L. It is noted that the belts can be form arrays in micro-size area and have the similar growth direction as shown in Fig. 4b. Thus, from these images, the amount of NaOH in the solution also can significantly influence the morphology of the products.

123

256

J Mater Sci: Mater Electron (2011) 22:252–259

Fig. 3 SEM images of the samples obtained at different hydrothermal reaction temperatures: a 65°C, b 75°C, c 85°C, and d 95°C

Fig. 4 SEM images of the samples obtained at different concentrations of the NaOH solution: a 0.5 mol/L, and b 2 mol/L

3.2.3 Effect of the deposition time To date, a lot of reports reported that the goethite a-FeOOH nanostructures were generally obtained by deposition in their corresponding ion solution. Thus, deposition time also played an important role in the formation of the final goethite nanostructures. In order to reveal the evolution process of the assembled 3D superstructures, the deposition time dependent experiments were investigated by the different deposition time in the cases of 0, 24, and 48 h, respectively. As shown in Fig. 5a, the goethite a-FeOOH nanostructures with flower-like structures (deposition time

123

is zero) have already grown on the surface of the agglomerate particles. When the deposition time is increased 24 h, as shown in Fig. 5b, all the products are consisted of the goethite a-FeOOH nanostructures with better crystalline and clear flower-like morphology. However, when the deposition time is increased to 48 h, the flower structures completely disappeared and the products are consisted of a-FeOOH nanowires with several tens of micrometers in length. Only few dandelion structures could be found in the products. On the basis of the above experiment results and discussion, the growth mechanism of the flowers is proposed

J Mater Sci: Mater Electron (2011) 22:252–259

257

Fig. 5 SEM images of the samples obtained at different deposition time: a 0 h, b 24 h, and c 48 h

as illustrated in Fig. 6. First, at an early reaction stage, Fe ion can be produced from the surface of these Fe nanoparticles through the chemical reactions Eq. 1. Once NaOH was added, the Fe irons transferred into Fe(OH)2 nuclei were formed through conventional nucleation on their surface. Meanwhile, the small crystals or nuclei grow at various positions of the Fe particle’s surface and have random crystallographic orientations (Fig. 6c). Then, the

small Fe(OH)2 grains further gradually evolved to 3D flower-like superstructures through oriented aggregation and oriented-attachment and the synthesis process approaches completion (Fig. 6d). Finally, Fe(OH) 2 was gradually oxidized into a-FeOOH. All the reactions may be formularized as follows: 3Fe þ 8HNO3 ! 3FeðNO3 Þ2 þNO " þ4H2 O

ð1Þ

FeðNO3 Þ2 þ 2NaOH ! 2NaNO3 þ FeðOHÞ2

ð2Þ

4FeðOHÞ2 þ O2 ! 4FeOOH þ 2H2

ð3Þ

In brief, the formation process of the assembled 3D superstructures can be described as the assembly route: 0D?1D?3D. 3.3 Magnetic property of the as-synthesized flowers

Fig. 6 Schematic illustration of the formation process of a-FeOOH flowers

Goethite is antiferromagnetic in the bulk state and has Tc = 393 K [25]. Although the bulk a-FeOOH is antiferromagnetic, according to reports, the magnetic properties of iron oxides nanomaterials can exhibit unusual magnetic behaviors (low coercive force), which are quite different from those of conventional bulk materials [12, 13]. 1D a-FeOOH nanostructures have increased anisotropies in both the shape anisotropy and magneto crystalline anisotropy, which exert influence on their magnetic properties [26, 27]. Herein, we investigated the magnetic property of the assynthesized goethite flowers, which are self-assembled with hundreds of 1D nanowire. A typical magnetization curve as a function of applied field at room temperature (300 K) is shown in Fig. 7. The remnant magnetization and coercive

123

258

J Mater Sci: Mater Electron (2011) 22:252–259

To sum up the above arguments, goethite flowers may have novel properties and have potential applications in many technological fields because of structure–property relationship in nanostructure. These flower-like structures will offer more opportunities for both fundamental research and a crucial object for building blocks for nanodevices in the future. Additionally, the present route may provide a general method for the synthesis of other material nanostructures with special morphologies by used other metal nanopowders. Acknowledgments Financial support from the National 863 Program of China (Grant No. 2007AA068316), Scientific and Technological Planning Project of Jilin Province (Grant No. 20086001) and National Found for Fostering Talents of basic Science (Grant NO. J0730311) are gratefully acknowledged. Fig. 7 Magnetic hysteresis loop of the as-synthesized sample at room temperature

force are 27.13 emu/g and 185.68 Oe, respectively, which indicates that the goethite flowers are characteristically similar to typical weakly ferromagnetic property at room temperature. No saturation of the magnetization as a function of the applied magnetic field is observed up to the maximum applied magnetic field (15,000 Oe). However, when decreasing the magnetic field, magnetization decreases very fast and remnant magnetization is very low, which reveals that the goethite flowers are hard to be magnetized. This phenomenon possibly resulted from the small size nature of 1D nanowire, which has a nonzero magnetic moment due to the incomplete compensation of the magnetic moments of the sublattices [27, 28]. Herein, we used a simple and high-yield method to obtain goethite flowers with low coercive force, which are quite meaningful for the development of softmagnetic materials and their corresponding devices.

4 Conclusions In conclusion, by used a facile and an environmental friendly ultrasonic-assisted hydrothermal route, goethite flower structures have been obtained with Fe nanopowders at low temperature (85°C). The flowers are consisted of tens of hundreds of nanowires with high structurally uniform, good crystal quality, and high yields and such structures can further construct the flake with micro size area. Influencing factors such as reaction temperature, pH value, and the deposition time were systematically investigated. A possible formation mechanism was proposed for the flowers. Magnetic measurements showed that the as-obtained goethite flower exhibited weakly ferromagnetic characteristics at room temperature, which is quite different from the behavior of the corresponding bulk material.

123

References 1. M. Muruganandham, J.J. Wu, Catal. Commun. 8, 668–672 (2007) 2. J.F. Banfield, S.A. Welch, H. Zhang, T.T. Ebert, R.L. Penn, Science 289, 751–754 (2000) 3. M.M. Benjamin, J.O. Leckie, J. Colloid Interface Sci. 79, 209– 221 (1981) 4. J.A. Davis, J.O. Leckie, J. Colloid Interface Sci. 67, 90–107 (1978) 5. S. Krehula, S. Popovi, S. Musi, Mater. Lett. 54, 108–113 (2002) 6. J.F. Boily, N. Nilsson, P. Persson, S. Sjoberg, Langmuir 16, 5719–5729 (2000) 7. M. Charles, J.R. Flynn, Chem. Rev. 84, 31–41 (1984) 8. M. Petrovic, M. Kastelan-Macan, A.J.M. Horvat, Water Air Soil Pollut. 111, 41–56 (1999) 9. P. Persson, K. Zivkovic, S. Sjo¨berg, Langmuir 22, 2096–2104 (2006) 10. D.E. Zhang, X.J. Zhang, X.M. Ni, H.G. Zheng, Mater. Lett. 60, 1915–1917 (2006) 11. G. Neri, A. Bonavita, S. Galvagno, P. Siciliano, S. Capone, Sens. Actuators, B 82, 40–47 (2002) 12. B. Tang, G. Wang, L. Zhuo, J. Ge, L. Cui, Inorg. Chem. 45, 5196–5200 (2006) 13. M.W. Shao, H.Z. Ban, Y.H. Tong, H. Hu, L.L. Niu, H.Z. Gao, Y. Ye, Mater. Lett. 61, 4318–4320 (2007) 14. B.J. Lemaire, P. Davidson, J. Ferre´, J.P. Jamet, P. Panine, I. Dozov, J.P. Jolivet, Phys. Rev. Lett. 88, 125507 (2002) 15. P. Ou, G. Xu, Z. Ren, X. Hou, G. Han, Mater. Lett. 62, 914–917 (2008) 16. F. Geng, Z. Zhao, J. Geng, H. Cong, H.M. Cheng, Mater. Lett. 61, 4794–4796 (2007) 17. Z. Sun, X. Feng, W. Hou, Nanotechnology 18, 455607 (2007) 18. X. Wen, S. Wang, Y. Ding, Z.L. Wang, S. Yang, J. Phys. Chem. B 109, 215–220 (2005) 19. X. Liu, G. Qiu, A. Yan, Z. Wang, X. Li, J. Alloys Compd. 433, 216–220 (2007) 20. Y.R. Uhm, W.W. Kim, S.J. Kim, C.S. Kim, C.K. Rhee, J. Appl. Phys. 93, 7196 (2003) 21. C. Morterra, A. Chiorlno, E. Borello, Mater. Chem. Phys. 10, 119–138 (1984) 22. P. Cambier, Clay Min. 21, 201–210 (1986) 23. D.M. Cwiertny, G.J. Hunter, J.M. Pettibone, M.M. Scherer, V.H. Grassian, J. Phys. Chem. C 113, 2175–2186 (2009)

J Mater Sci: Mater Electron (2011) 22:252–259 24. S. Musi, S. Krehula, S. Popovi, Mater. Lett. 58, 2640–2645 (2004) 25. C.J.W. Koch, M.B. Madsen, S. Mørup, Hyperfine Interact. 28, 549–552 (1986) 26. S.J. Park, S. Kim, S. Lee, Z.G. Khim, K. Char, T. Hyeon, J. Am. Chem. Soc. 122, 8581–8582 (2000)

259 27. W.S. Seo, H.H. Jo, K. Lee, B. Kim, S.J. Oh, J.T. Park, Angew. Chem. Int. Ed. 43, 1115–1117 (2004) 28. F. Bødker, M.F. Hansen, C.B. Koch, K. Lefmann, S. Mørup, Phys. Rev. B 61, 6826–6838 (2000)

123