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J. Phys. Chem. C 2009, 113, 5960–5966
Nanostructures of Ni and NiCo Amorphous Alloys Synthesized by a Double Composite Template Approach Ming Wen,* Ya-Fen Wang, Fan Zhang, and Qing-Sheng Wu* Department of Chemistry, Tongji UniVersity, 1239# Siping Road, Shanghai 200092, China ReceiVed: October 27, 2008; ReVised Manuscript ReceiVed: February 6, 2009
Two-dimensional handkerchief-like nanostructures of Ni and NiCo magnetic amorphous alloys have been synthesized by a double composite structure-inducing template. High resolution transmission electron microscopy was used to characterize the morphology and the dimensions. The self-assembly of fine handkerchief-like Ni and NiCo nanoalloys is attributed to the cooperation between ion-selected delivery of a hard collodion membrane by nitro-group chemical complexations and the size-controlled action of a reverse microemulsion. Importantly, the coordinations of ethylenediamine with Ni2+ and Co2+ can restrict the structureinducing action. The phase transformation behavior was recorded by differential scanning calorimetry. Substituting Co for Ni can slow phase transformation, and the kinetic ordering temperature increases with the Co concentration increasing. The magnetic property measurement results show that the saturation magnetizations increase as the Co concentration is increased, but the coercivity is not sensitive to the Co concentration and is decided only by the phase structure. 1. Introduction Alloys and intermetallic compound nanomaterials have attracted steadily growing attention because of their surprisingly diverse range of physical properties for potential applications in optics,1 magnetics,2 catalysis activity,3,4 hydrogen storage,5 corrosion resistance,6 electrochemistry,7 and biotechnology,8 etc. The possibility of integrating the well-established properties of alloy with emerging nanotechnological applications has generated a renewed interest in controlling their synthesis. For their utility in future applications, the nanostructure and morphology of multimetallic materials become the important characteristics. Two-dimensional (2D) and one-dimensional (1D) metal nanostructures, such as nanosheet,9 nanomesh,10 nanonetwork,11 nanorings,12 nanochains,13 and nanorods,14 have received alot of attention in recent years because they can give rise to unique potential applications. Among various strategies, structuredirecting template synthesis is a simple and versatile method that allows well-defined templates to control the morphology and size of metal nanostructures.15 Using polymer films as templates, nanostructures of metal nanorods, metal nanotube metal magnetic particle arrays, and porous metal oxide films have been successfully achieved.14,16-21 Because collodion membranes consist of nitrocellulose with a three-dimensional network, they have the capability to incorporate or trap stably several kinds of active materials such as fluorocarbon compounds. Thus, it provides not only a possibility for novel composite membranes but also an opportunity to study the transport mechanism from fundamental standpoint.22 Moreover, reverse microemulsion soft templates are widely employed to fabricate metal nanomaterial.23 The size of micelles is mainly dependent on the molar ratio of water to surfactant in microemulsion and can affect the size of the obtained nanomaterials.24,25 Some metal nanomaterials with different morphologies have been successfully prepared through the soft template-induced * Corresponding author. E-mail:
[email protected] (M.W.); qswu@ tongji.edu.cn (Q.-S.W.), tel: +86-21-65982653 ext 803; fax: +86-2165981097.
technique.26,27 However, efforts to prepare 2D amorphous alloy nanostructures are rare despite their scientific and technological importance. The amorphous metal-metalloid nanoalloys with plenty of dangling bonds have attracted considerable attention because they combine the characteristics of amorphous alloys with chemical disorder structure and nanoscale size. Especially Ni-based alloy nanomaterials are attractive because of their catalytic and magnetic properties for application in magnetic recording media, sensors, catalysts, and nanoelectrodes.28-31 Although alot of studies are concerned with amorphous Ni-based alloy nanomaterials,32-36 the new 2D nanostructure and the relationships between structure/component and property still need to be explored. On the basis of our previous work,37,38 we report here on the 2D handkerchief-like Ni and Ni-Co amorphous magnetic alloys synthesized by a soft-hard double composite template direction in high yield. This kind of nanostructure was directly fabricated in a reaction solution. The various template-assisted routes have been used to investigate the reaction mechanism for nanostructure fabrication. The magnetic property has been also studied based on the measurement results. 2. Experimental Section 2.1. Chemical. Nickel chloride hexahydrate (NiCl2 · 6H2O, 98%), cobalt chloride hexahydrate (CoCl2 · 6H2O, 99%), sodium hydroxide (NaOH, 96%), potassium borohydride (KBH4, 95%), cationic surfactant cetyltrimethyl ammonium bromide (CTAB), n-hexane (C6H14, 97.0%), and ethylenediamine (C2H8N2, 99%) were purchased from Sinopharm Chemical Reagent Co. Ltd. The organic solvents ethanol (C2H5OH, 99.7%), n-hexanol (C6H14O), and collodion were purchased from Shanghai Lingfeng Chemical Reagent Co. Ltd., and all the reagents were used without further purification. The preparation of collodion membrance within a thickness of about 0.18 mm was carried out on a Chemat Technology Spin-Coater KW-4A using a silicon substrate at the rotary speed of 1000 rpm for 15 s. Then the artificial active collodion membrance was allowed to naturally dry and peeling for spare.
10.1021/jp809488t CCC: $40.75 2009 American Chemical Society Published on Web 03/24/2009
Ni and NiCo Amorphous Alloys
J. Phys. Chem. C, Vol. 113, No. 15, 2009 5961 3. Results and Discussion
Figure 1. Schematic view of the experimental setup.
2.2. Synthesis. Figure 1 represents a schematic illustration of the experimental setup which was employed for the synthesis of Ni and Ni-Co alloy handkerchief-like nanostructures. Then 10 mL of NiCl2 (5mmol/L) solution or a 10 mL solution (5 mmol/L) of a NiCl2 and CoCl2 mixture in a molar ratio of 4:1 was added into a glass tube with the bottom sealed by collodion membrance. Then the above-mentioned glass tube was vertically immersed into a beaker filled with 10 mL of KBH4 (50 mmol/ L). The pH of the reaction solution was 12. After 1-2 days reaction, the black products were collected merely from the side of the metal ion solution and thoroughly washed with distilled water and ethanol three times. Then products were dissolved in ethanol for storage. In order to study the double template effect, a reverse microemulsion of Ni2+ and Co2+ was substituted for the metal ion solution and treated as in the above method. A relatively finer silk-rolled-like nanostruture of Ni and Ni-Co can be synthesized. Then ethylenediamine was employed as a ligand to coordinate Ni2+ and Co2+ for restricting the delivery process of M2+ based on the former treatment; it only generates Ni and NiCo nanoparticles. The microemulsion system consisted of CTAB as the surfactant, n-hexanol as the cosurfactant, n-hexane as the continuous oil phase, and a metal ion aqueous solution as the dispersed phase. A W/O microemulsion in which 1.28 g of CTAB, 50 mL of n-hexane, and 2.5 mL of n-hexanol were mixed as the oil phase was prepared. Briefly, the water phase is 2 mL of 0.1mol/L metal ion solution. Then it was subjected to ultrasonic waves for 30 min to eventually form a stable transparent W/O microemulsion. In contrast, Ni and NiCo aggressive nanoparticles were prepared by adding dropwise an aqueous KBH4 (50 mmol/L) solution into an aqueous NiCl2 solution (5 mmol/L) or a solution of NiCl2 and CoCl2 (5 mmol/ L). 2.3. Characterization. The size and morphology of the products were obtained by using a JEOL JEM-1200EX highresolution transmission electron microscope (HRTEM). For the HRTEM investigations, the products were deposited on a copper-grid-supported transparent Formvar foil. The product component measurement was carried out by energy dispersive spectroscopy (EDS) using a Tacnai TF20 high-resolution transmission electron microscope. The X-ray diffraction measurements were performed on a Rigaku Corporation D/max 2550 X-ray diffractometer using Cu KR radiation (λ ) 1.54056 Å). The thermal behaviors of the synthesized nanoproducts were determined on a STA409PC NETZSCH differential scanning calorimeter (DSC). The magnetization was measured on a LakeShore 7307 vibration sample magnetometer (VSM), and the data are summarized in Table 1.
The collodion membrane is commonly used in semipermeable artificial active membrane preparation because of its thickness and superiority of effective aperture that is adjustable from several dozens to hundreds of nanometers. Because of the massive, active nitro groups and the passageways in the membrane, the collodion membrane can be used as a structureintroducing template to direct the fabrication of alloy nanostructure. In the reverse microemulsion system, besides the micelles size can affect the size of the nanoproducts. When the particle size approaches that of the aqueous nucleus, the surfactants are adsorbed on the particle surface, so the merit of microemulsion is that it not only acts as a microreactor for processing reactions but also inhibits the excess aggregation of particles. As a result, the nanostructures obtained in such a medium are generally fine and dispersed.37 Thus, the cooperation of the double composite template between the hard artificial active collodion membrane and soft microemulsion might function to control the nanostructure size and morphology. In this work, 2D handkerchief-like Ni and NiCo amorphous alloys can be induced by the the cooperation of the hard artificial active collodion membrane and the soft reverse microemulsion. The nanostructure morphology and size are easily controlled by the double composite template and the coordination ligand of ethylenediamine. Some conditions are optimized for obtaining handkerchieflike nanostructures of Ni-based alloys in the current experiment. Since the membrane channels are plugged easily in large concentration, and the reaction rate becomes too slow in small concentration, a Mn+ concentration of 5 mmol/L is used to control the reaction rate for suitable ion delivery speed through the membrane. As the membrane effective aperture is reduced as the thickness increases, the optimal thickness of the collision membrane is prepared at about 0.18 mm with an aperture of 60-120 nm in the present experiment. Taking into account the morphology integrity, the reaction is carried out less than 40 h. 3.1. Synthesis and Structure. The experimental setup for the synthesis of Ni and Ni-Co amorphous alloy nanostructures is represented in Figure 1. Regardless of whether the metal ion solution is in the up side or down side of the membrane, the products are generated at the side of metal ion in the double composite template system. When ethylenediamine is employed as coordination ligand for controlling the reaction rate, the products are formed at both sides of the membrane in the single template system and generated at the side of the metal ion in the double composite template system. Figure 2 shows the TEM images of Ni and Ni-Co amorphous alloy nanostructure obtained in different template-assisted routes. In an effort to understand the formation of handkerchief-like nanostructures, the hard collodion membrane and soft reverse microemulsion template, using CTAB as surfactant as well as the coordination ligand of ethylenediamine, are used to affect the nanostructure fabrication. Compared with the agglomerate nanoparticles of Ni and NiCo, which are prepared by directly reducing Ni2+ and Co2+ in aqueous solution without any template (Figure 2e and Figure 3e), the single hard collodion membrane induces the handkerchief-like nanostructure of Ni (Figure 2a) and Ni82Co18 (Figure 3a) at the metal ion side. When the reverse microemulsion substitutes for the metal ion solution, the double composite templates of the hard collodion membrane cooperating with the soft reverse microemulsion gives rise to relatively finer nanostructure of the Ni and NiCo amorphous alloys in the same handkerchief-like morphology, as shown in Figure 2b and Figure 3b. After ethylenediamine is added to the reverse microemulsion
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Figure 2. TEM images of handkerchief-like nanostructure of Ni amorphous alloys: (a) Ni nanostructure fabricated by a single template of the hard collodion membrane (inset: SADP of products); (b) Ni nanostructure directed by a double template of the hard collodion membrane and soft reverse microemulsion; (c) Ni NPs induced by a double composite template of collodion membrane and soft reverse microemulsion with ethylenediamine as ligand; (d) Ni NPs induced by a single template of collodion membrane with ethylenediamine as ligand; (e) Ni NPs obtained in aqueous solution without template.
TABLE 1: Molar Ratios of Metallic Salt in Initial Solution and As-Synthesized Alloy Components with their Ms and Hc of (a) As-Synthesized Ones and (b) Annealed Ones molar ratios of Ni:Co in initial solution component concentration (at.%) Ms (emu/g) Hc (Oe)
a b a b
to control the reaction rate, the double composite template results in the generation of an actinomorphic-like nanosphere assembled
S1
S2
S3
S4
100:0 Ni 0.28 33.84 26.37 71.53
80:20 Ni82Co18 0.45 72.01 23.05 68.03
50:50 Ni52Co48 4.26 76.19 31.18 71.41
25:75 Ni23Co77 4.88 81.17 31.69 77.99
by nanoparticles with a diameter of about 5 nm (Figure 2c and Figure 3c). Is the structure-inducing action of the hard collodion
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Figure 3. TEM images of handkerchief-like nanostructures of Ni82Co18 amorphous alloys: (a) nanostructure fabricated by a single template of hard collodion membrane (inset: SADP of products); (b) nanostructure directed by double a template of hard collodion membrane and soft reverse microemulsion; (c) nanoparticles induced by a double composite template of collodion membrane and soft reverse microemulsion using ethylenediamine as ligand; (d) nanoparticles induced by a single template of collodion membrane using ethylenediamine as ligand; (e) nanoparticles obtained in aqueous solution without template.
membrane restricted by the coordination of ethylenediamine? For a clear understanding of this phenomenon, ethylenediamine is added to a solution of Ni2+ and Co2+ in the single hard collodion membrane system, and then the single collodion membrane template leads to Ni and NiCo nanoparticles with a diameter of about 5 nm in the both sides of membrane, as shown in Figure 2d and Figure 3d. It indicated that the massive, active nitro groups on the membrane porewall lose the activity to act with metal ions after ethylenediamine is coordinated with the metal ions. The TEM images in different template-assisted routes agree with the following reaction mechanism.
We summarize the schematic view of the mechanism in Figure 4. In case a, delivery in channels, metal ions of Ni2+ and Co2+ will coordinate with nitro groups on the porewall of the collodion membrane to form a metal complex. Because of the concentration difference, M2+ and H- from BH4- both have the tendency to spread to the other side, which provides the dynamics driving force for the reduction. The spread rate of Ni2+ and Co2+ become lower than that of the H- ions because of the size differential. However, for the control of the template, nitro groups coordinated to M2+ are still under the attraction of the membrane in the side of the
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Figure 4. Schematic illustration of the reaction mechanism and nitro groups and their chemical complexation of metal ions on the membrane porewall. The reaction adapts to the ion delivery mode in case a, and the coordination of ethylenediamine to metal ions inhibits the structureinducing action in case b.
metal ion solution. When H- ions pass the membrane pole and close to the side of the metal ion solution, H- captures Ni2+ or Co2+ on the porewall and reduces them to metal atoms. Then the structure-inducing membrane assembles the metal atoms to give handkerchief-like nanostructures of Ni and Ni-Co amorphous nanoalloy in the metal ion side of membrane (Figure 2a and Figure 3a). In addition, the reverse microemulsion can act as a microreactor and lead to fine nanostructure. As a result, in contrast to the action of a single hard artificial active collodion template, the cooperation of the hard membrane template to the soft microemulsion template can generate a finer handkerchieflike nanostructure of the Ni and NiCo amorphous alloys in the current experiment (Figure 2b and Figure 3b). Importantly, if ethylenediamine is employed to coordinate with Ni2+ and Co2+, nitro groups cannot bond with Ni2+ and Cu2+ ions on the porewall. The reaction is performed according to case b in Figure 4. The porewall of the collodion membrane will lose ion delivery activity. Under free movement, the spread of Ni(II) and Co(II) complexes will not be controlled by the hard collodion memberane template. Thus, they are directly reduced by H- ions to form Ni nanoparticles in the metal ion side first and then in the other side finally, but NiCo nanoparticles are only formed in the metal ion side because the passage of largesize micelles through the pores is limited. This reaction process can be observed in our experiment. So the nanoparticles can be collected at the both sides of the collodion membrane in a single hard template system but only separated out at the metal ion sides in the hard-soft composite template system, which are consistent with the TEM images in Figure 2c and Figure 3c, Figure 2d, and Figure 3d, respectively. This supports the above mechanistic analysis. Therefore, it is clear that the hard collodion membrane affects the nanostructure morphology, and the soft reverse microemulsion could adjust the size of nanostructures. Moreover, the coordination of ethylenediamine with metal ions inhibits the structure-inducing action. Hence, the nanostructure morphology and size of Ni and NiCo amorphous alloys can be easily controlled by a double composite template and an ethylenediamine coordination ligand in different templateassisted routes.
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Figure 5. EDS spectra of as-synthesized alloys: (a) Ni; (b) Ni82Co18; (c) Ni52Co48; (d) Ni23Co77.
Figure 6. XRD patterns: (a) as-synthesized Ni and Ni-Co amorphous nanoalloys; (b) their annealed specimens.
Composition analysis is measured by EDS, as shown in Figure 5. Strong peaks of Ni and Co undoubtedly confirmed that the synthesized products are Ni (Figure 5a) and NiCo alloys (Figure 5b-d). The observed Ni:Co intensity ratios of peaks are ∼4:1 for Ni82Co18 in Figure 5b, ∼1:1 for Ni52Co48 in Figure 5c, and ∼1:3 for Ni23Co77 in Figure 5d, respectively. It corresponds to the data in Table 1, in which the components Ni and Co are basically consistent with the starting molar ratios of NiCl2 · 6H2O and CoCl2 · 6H2O, and give the final results of Ni, Ni82Co18, Ni52Co48, and Ni23Co77. The structure and phase characterization was measured with XRD. Figure 6 gives the typical XRD patterns for as-synthesized Ni and NiCo amorphous nanoalloys and their annealed alloys at 873 K under argon for 1 h. There is a broad peak at 2θ ) 45° for as-synthesized Ni and Ni-Co alloys in Figure 6a. It indicated that the as-obtained nanoproducts of Ni and Ni-Co are chemically disordered amorphous nanoalloys, which also can be further proved by the selected-area electron diffraction pattern (SADP) in the corner of Figure 2a and Figure 3a. The SADP exhibits a diffuse halo corresponding to the amorphous structure. As the fast reduction cannot offer enough time for metal atoms to arrive at the alloy lattices and results in a disordered amorphous state, the amorphous alloy can thus be generated in chemical solution. After annealing treatment at 873 K for 1 h under argon, three sharp peaks appear in the diffraction patterns in Figure 6b, which could be the results of the alloy phase changing from the amorphous state to the crystal state. The three diffraction peaks that appeared can be indexed to (111) at 2θ ) 44°, (200) at 2θ ) 52°, (220) at 2θ ) 76°, respectively. These crystal planes confirm the FCC structure in Ni and Ni-Co
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Figure 7. DSC curves of as-obtained Ni (a), Ni82Co18 (b), Ni52Co48 (c) and Ni23Co77 (d).
alloy system. The clearly crystallizing behavior also corresponds to the DSC curves in Figure 7. 3.2. Thermal Stability and Crystallization. The thermal stability and crystallization behavior of as-synthesized Ni and Ni-Co amorphous alloys are confirmed with DSC on NETZSCH (STA409PC) at heating rates of 10 °C/min. The DSC diagrams of as-synthesized products are given in Figure 7. The exothermic peaks are identified at 599.5 K and 677.0 K for Ni, 602.0 K and738.0 K for Ni82Co18, 663.9K and 743.0 K for Ni52Co48, and 600.0 K and 727.2 K for Ni23Co77, respectively. It illustrates that the phase transition temperature shifts to a high temperature field in the DSC signals as the Co concentration increases in the Ni-Co alloy system except for Ni23Co77. In view of the feature of atomic clusters in the amorphous structure, the amorphous alloy needs go through the process of structural relaxation in the crystallization transformation. The flat exothermic peaks at lower temperatures of each sample suggest that the alloy might incur structure relaxation at this temperature without a new phase formation. The clear exothermic peaks of each sample at high temperature can be assigned to the structure transition from the amorphous structure to the fcc crystalline structure. So this amorphous structure can exist stably under this high temperture to allow application despite its amorphous physical and chemical properties. These exothermic peaks contributed because of crystallization in agreement with the XRD observation after annealing at 873 K (Figure 6b). Thus, it can be indicated that the effect of Co additions to Ni leads to a kinetic ordering temperature higher than that of Ni as the reason for the multicomponent alloy system having a stronger amorphous formation ability, viz. substitution of Co for Ni leads to a slower phase transformation of the NiCo alloy. In the binary Ni-Co alloys,39 because Co atoms are approximately the same size as Ni atoms, a size argument is not sufficient to explain the observed behavior. Therefore, a chemical component must also contribute to the activation energy. Our DSC measurement results indicate that the additions of Co act to slow the transformation and the increase in Co concentration results in the increase of the kinetic ordering temperature in the Ni-based NiCo alloy system. For the exceptional Ni23Co77 alloy with a kinetic ordering temperature similar to that of Ni82Co18, it belongs to the Co-based CoNi alloy system. Substitution of Ni for Co will also slow the phase transformation of the Co-based CoNi alloy system. Therefore, multicomponent alloy systems of NiCo and CoNi have a stronger amorphous formation ability than Ni and Co and can result in a higher kinetic ordering temperature. 3.3. Magnetic Property. Figure 8 illustrates the hysteresis loops of the obtained products and the annealed products. The hysteresis loops are surveyed at room temperature on a LakeShore 7307 VSM under an applied magnetic field of 5000
Figure 8. Room-temperature magnetic hysteresis loops of Ni, Ni82Co18, Ni52Co48, and Ni23Co77: (a) as-synthesized amorphous nanoalloys; (b) annealed specimens.
G, in which S(a) is the hysteresis loops of as-synthesized products and S(b) is that of annealed products at 873 K. The data of saturation magnetization (Ms) and coercivity (Hc) of Ni and Ni-Co alloy are listed in Table 1. The Ms of as-obtained Ni, Ni82Co18, Ni52Co48, and Ni23Co77 are 0.28 emu/g, 0.45 emu/ g, 4.26 emu/g, and 4.88 emu/g, respectively. The Hc of assynthesized products are 26.37 Oe for Ni, 23.05 Oe for Ni82Co18, 31.18 Oe for Ni52Co48, and 31.69 Oe for Ni23Co77. It illustrates that as-synthesized Ni and Ni-Co alloys possess superparamagnetism. After products were annealed at 873 K for 1 h under argon, the Ms values of Ni, Ni82Co18, Ni52Co48, and Ni23Co77 are up to 33.84 emu/g, 72.01 emu/g, 76.19 emu/g, and 81.17 emu/g, respectively. The Hc are up to 71.53 Oe for Ni, 68.03 Oe for Ni82Co18, 71.41 Oe for Ni52Co48, and 77.99 Oe for Ni23Co77. The Ms increases with the increase of Co concentration. Here the Hc is not sensitive to the Co concentration in the NiCo alloy but has a large increase after phase transformation through annealing treatment, which does not follow the trend of Ms. Thus, the Ms is decided by the components and the Hc is related to alloy phase structure in the Ni-Co alloy system. Annealing caused a nucleation of crystallization, and it eliminated the vacancies and improved long-range order. So the ferromagnetic order inside the product is enhanced which causes increased saturation magnetization and coercivity.
5966 J. Phys. Chem. C, Vol. 113, No. 15, 2009 4. Conclusion Employing the double composite template of a hard collodion membrane and soft reverse microemulsion as the structureinducing template, fine handkerchief-like nanostructure Ni and NiCo amorphous alloys can be fabricated at room temperature. The self-assembly of Ni and NiCo handkerchief-like nanostructures is attributed to the ion-selected delivery of a hard collodion membrane by nitro-group chemical complexation and the sizecontrolled function of reverse microemulsion. The coordination of ethylenediamine with metal ions inhibits the structureinducing action. DSC results show that the substitution of Co for Ni slows phase transformation, and the kinetic ordering temperature increases as the Co concentration in the Ni-based NiCo alloy system increases. In addition, the magnetic property investigation indicates that Ms increases with an increase in Co concentration, and the Hc is not sensitive to the Co concentration but only decided by the phase structure in Nibased Ni-Co alloys. Acknowledgment. This work was financially supported by the NSFC [No.20771085, 50772074], the States Key Project of Fundamental Research (973) [No. 2006CB932302] from China. References and Notes (1) Kelly, K. L.; Coronado, E.; Zhao, L. L; Schatz, G. C. J. Phys. Chem. B 2003, 107, 668. (2) (a) Bautusta, M. C.; Bomati-Miguel, O.; Zhao, X.; Morales, M. P.; Gonzalez-Carreno, T.; de Alejo, R. P.; Ruiz-Cabello, J.; WeintemillasVerghor, S. Nanotechnology 2004, 15, 154. (b) Sun, S.; Murray, C. B.; Weller, D.; Folks, L.; Moser, A. Science 2000, 287, 1989–1992. (c) Goll, D.; Kronmuller, H. Naturewissenschaften 2000, 87, 423–438. (d) Paduani, C. J. Appl. Phys. 2001, 90, 6251. (3) Roucoux, A.; Schulz, J.; Patin, H. Chem. ReV. 2002, 102, 3757. (4) (a) Roucoux, A.; Schulz, J.; Patin, H. Chem. ReV. 2002, 102, 3757– 3778. (b) Casado-Rivera, E.; Gal, Z.; Angelo, A. C. D.; Lind, C.; DiSalvo, F. J.; Abruna, H. D. ChemPhysChem 2003, 4, 193–199. (c) Casado-Rivera, E.; Volpe, D. J.; Alden, L.; Lind, C.; Downie, C.; Vazquez-Alvarez, T.; Angelo, A. C. D.; DiSalvo, F. J.; Abruna, H. D. J. Am. Chem. Soc. 2004, 126, 4043–4049. (d) Zhang, C. J.; Baxter, R. J.; Hu, P.; Alavi, A.; Lee, M.-H. J. Chem. Phys. 2001, 115, 5272–5277. (e) Mathauser, A. T.; Teplyakov, A. V. Catal. Lett. 2001, 73, 207–210. (5) (a) Kirchheim, R.; Mutschele, T.; Keininger, W.; Gleiter, H.; Birringer, R.; Koble, T. D. Mater. Sci. Eng. 1988, 99, 457–462. (b) Kamakoti, P.; Sholl, D. S. J. Membr. Sci. 2003, 225, 145–154. (6) Lopez, M. F.; Escudero, M. L. Electrochim. Acta 1998, 43, 671– 678. (7) Menon, V. P.; Martin, C. R. Anal. Chem. 1995, 67, 1920. (8) Fritzsche, W.; Taton, T. A. Nanotechnology 2004, 15, 63. (9) H, Y; Wu, X. F.; Lu, G.; Shi, G. Q. Nanotechnology 2005, 16, 791-–796. (10) Schaak, R. E.; Sra, A. K.; Leonard, B. M.; Cable, R. E.; Bauer, J. C.; Han, Y. F.; Means, J.; Teizer, W.; Vasquez, Y.; Funck, E. S. J. Am. Chem. Soc. 2005, 127, 3506–3515.
Wen et al. (11) Shin, H. J.; Ryoo, R.; Liu, Z.; Terasaki, O. J. Am. Chem. Soc. 2001, 123, 1246–1247. (12) Hu, M. J.; Lu, Y.; Zhang, S.; Guo, S. R.; Lin, B.; Zhang, M.; Yu, S. H. J. Am. Chem. Soc. 2008, 130, 11606–11607. (13) Hu, M. J.; Lin, B.; Yu, S. H. Nano Res. 2008, 1, 303–313. (14) Xue, S. H.; Wang, Z. D. Mater. Sci. Eng., B 2006, 135, 74–77. (15) Wang, Q. T.; Wang, G. Z.; Han, X. H.; Wang, X. P.; Hou, J. G. J. Phys. Chem. B 2005, 109, 23326–23329. (16) (a) Wirtz, M.; Yu, S.; Martin, C. R. Analyst 2002, 4, 259. (b) Steinle, E. D.; Mitchell, D. T.; Wirtz, M.; Lee, S. B.; Martin, C. R. Anal. Chem. 2002, 74, 2416. (17) (a) Lee, S. B.; Martin, C. R. J. Am. Chem. Soc. 2002, 124, 11850. (b) Wirtz, M.; Parker, M.; Kobayashi, Y.; Martin, C. R. Chem. Eur. J. 2002, 16, 3572. (18) (a) Lee, S. B.; Mitchell, D. T.; Trofin, L.; Nevanen, T. K.; Martin, C. R. Science 2002, 296, 2198. (b) Martin, C. R. Science 1994, 278, 655. (19) Wirtz, M.; Martin, C. R. AdV. Mater. 2003, 15, 455. (20) Cheng, J. Y.; Jung, W.; Ross, C. A. Phys. ReV. B 2004, 70, 064417. (21) Schattka, J. H.; Wong, E. H.-M.; Antonietti, M.; Caruso, R. A. J. Mater. Chem. 2006, 16, 1414–1420. (22) Yamauchi, A.; Shin, Y.; Shinozaki, M.; Kawabe, M. J. Membr. Sci. 2000, 170, 1–7. (23) Capek, I. AdV. Colloid Interface Sci. 2004, 110, 49–74. (24) Lisiecki, I.; Pileni, M. P. J. Am. Chem. Soc. 1993, 115, 3887. (25) Yadav, O. P.; Palmqvist, A; Cruise, N.; Holmberg, K. Colloids. Surf. A 2003, 221, 131–134. (26) Pileni, M. P. Langmuir 1997, 13, 3226. (27) Maillard, M.; Giorgio, S.; Pileni, M. P. AdV. Mater. 2002, 14, 1084. (28) Foyet, A.; Hauser, A.; Scha¨fer, W. J. Solid State Electrochem. 2008, 12, 47–55. (29) Qin, J.; Nogue´s, J.; Mikhaylova, M.; Roig, A.; Mun˜oz, J. S.; Muhammed, M. Chem. Mater. 2005, 17, 1829. (30) Fert, A.; Piraux, L. J. Magn. Magn. Mater. 1999, 200, 338. (31) Sun, L.; Searson, P. C. Appl. Phys. Lett. 1999, 74, 2803. (32) (a) Pan, H.; Liu, B.; Yi, J.; Poh, C.; Lim, S.; Ding, J.; Feng, Y.; Huan, C. H. A.; Lin, J. J. Phys. Chem. B 2005, 109, 3094–3098. (b) Niu, H.; Chen, Q.; Ning, M.; Jia, Y.; Wang, X. J. Phys. Chem. B 2004, 108, 3996–3999. (33) (a) Chu, S. Z.; Wada, K.; Inoue, S.; Todoroki, S.; Takahashi, Y. K.; Hono, K. Chem. Mater. 2002, 14, 4595–4602. (b) Knez, M.; Bittner, A. M.; Boes, F.; Wege, C.; Jeske, H.; Maib, E.; Kern, K. Nano Lett. 2003, 3, 1079– 1082. (34) (a) Liu, Z. P.; Li, S.; Yang, Y.; Peng, S.; Hu, Z. K.; Qian, Y. T. AdV. Mater. 2003, 15, 1946–1948. (b) Liu, C. M.; Guo, L.; Wang, R. M.; Deng, Y.; Xu, H. B.; Yang, S. H. Chem. Commun. 2004, 2726–2727. (35) Vieyra, M.; Meydan, T.; Borza, F. J. Appl. Phys. 2007, 101, 102. (36) Jana, N. R.; Gearheart, L.; Murphy, C. J. AdV. Mater. 2001, 13, 1389. (37) (a) Wen, M.; Liu, Q. Y.; Wang, Y. F.; Zhu, Y. Z.; Wu, Q. S. Colloids. Surf. A 2008, 318, 238–244. (b) Wen, M.; Li, L. J.; Liu, Q. Y.; Qi, H. Q.; Zhang, T. J. Alloys Compd. 2008, 455, 510–515. (38) (a) Liu, J. K; Wu, Q. S.; Ding, Y. P. Cryst. Growth Des. 2005, 5 (2), 445–449. (b) Liu, J. K; Wu, Q. S.; Ding, Y. P. J. Cryst. Growth 2005, 279 (3-4), 410–414. (c) Duan, S. M.; Wu, Q. S.; Jia, R. P.; Liu, X. B. J. Nanopart. Res. 2008, 10 (3), 525–529. (d) Zhang, Z. L.; Wu, Q. S.; Ding, Y. P. Inorg. Chem. Commun. 2003, 6, 1393–1394. (39) (a) Sangregorioa, C.; Ferna´ndez, C. d. J.; Battaglinc, G.; Gatteschia, G.; De, D.; Mattei, G.; Mazzoldib, P. J. Magn. Magn. Mater 2004, 272276, 1251–1252. (b) Fenineche, N. E.; Hamzaoui, R.; Kedim, O. E. Mater. Lett. 2003, 57, 4165–4169. (c) Liu, X. M.; Fu, S. Y.; Huang, C. J. Mater. Lett. 2005, 59, 3791–3794.
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