Article pubs.acs.org/Langmuir
Preparation of Dendritic Nanostructures of Silver and Their Characterization for Electroreduction Xia Qin, Zhiying Miao, Yuxin Fang, Di Zhang, Jia Ma, Lu Zhang, Qiang Chen,* and Xueguang Shao The Key Laboratory of Bioactive Materials, Ministry of Education, College of Life Science, Nankai University, Tianjin 300071, China College of Chemistry, Nankai University, Tianjin 300071, China S Supporting Information *
ABSTRACT: Silver nanostructures of different morphologies including well-defined dendrites were synthesized on an Au substrate by a simple surfactant-free method without using any template. The morphology of the material was investigated by field-emission transmission electron microscopy and scanning electron microscopy. The crystal nature of the dendritic nanostructure was revealed from their X-ray diffraction and electron diffraction patterns. Effects of applied potential, electrolysis time, and the solution concentration were studied. The possible formation mechanism of the dendritic morphology was discussed from the aspects of kinetics and thermodynamics based on the experiment results. The H2O2 electroreduction ability of the dendritic materials was characterized. Use of silver dendrite-modified electrode as H2O2 sensor was also demonstrated.
1. INTRODUCTION Because of their remarkable physicochemical properties and numerous applications, noble metal nanostructures have attracted considerable attention and have been widely exploited.1,2 It has also been well-established that the size, shape, and morphology of metal nanostructures are favorable for their properties and applications, and therefore the design of nanocrystals with well-defined sizes, shapes, and morphologies has received great interest.3−7 Among various specific nanostructures, dendritic materials with self-assembled hierarchical and repetitive superstructures are fascinating.8−10 The essential pattern observed in nonequilibrium growth processes not only provides a natural framework for the study of disordered systems but also possesses promising complex functions which are highly dependent on the morphology of the structures.11,12 To date, many methods by which dendritic nanostructures of noble metal can be obtained are founded mainly on electrochemical, chemical, and physical meansfor instance, electrochemical metallic deposition,13,14 γ-irradiation using isopropyl alcohol as a protecting agent,15 ultraviolet irradiation photoreduction using poly(vinyl alcohol) as a protecting agent,8 Raney nickel-assisted template method,12 solvothermal methods using poly(vinylpyrrolidone) as an adsorption agent and architecture soft template,16 wet-chemical route using p-phenylenediamine or zinc microparticles as a reducing agent,10,17 acetone-based mixed solvent route,18 and so forth. It is not difficult to find that most of the syntheses are carried out in the presence of additional reagents like surfactants/polymers or templates which are required as shape-directing agents. However, the surfactants used for morphology control usually adsorb strongly on the surfaces © 2012 American Chemical Society
of products, introducing heterogeneous impurities or significant interference for some special applications such as surfaceenhanced Raman scattering (SERS), biosensing, and catalysis, thus limiting their applications.19−21 Also, the use of templates may complicate the synthetic procedure and limit the synthesis of nanostructured materials in large quantities.22,23 Therefore, development of template- and surfactant-free method is of great importance. Moreover, a simple morphology-controllable and large-scale synthesis route continues to be highly expected. Electrodeposition has been demonstrated to be a good alternative strategy for the one-step synthesis of hierarchical micro/nanostructures of various metals grown on a substrate with high yields.9,24 This method makes it possible to modify the morphology and/or structure of deposits by adjusting the preparation conditions, while working both at ambient pressure and temperature, thus requiring relatively inexpensive equipment. And, no additional procedure is required to immobilize the materials onto a solid substrate, and the high surface area electrodes with the assemblies can be used directly for various applications such as in the fields of SERS, catalysis, and so on. However, surfactants or templates are often introduced in the process of electrodeposition.22,25−28 As for Ag dendrites, a template- and surfactant-free electrodeposition route general to the preparation of the nanostructure is highly desirable. Furthermore, the growth mechanism is needed to be clarified and the study of the electrocatalytic activity of the as-prepared Ag dendrites remains very limited. Received: November 15, 2011 Revised: February 28, 2012 Published: February 29, 2012 5218
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materials toward hydrogen peroxide. The electrodes modified with Ag dendrites were obtained at different conditions. After the electrolysis, the electrode was moved out from the aqueous solution and washed by the deionized water. The electrode was put into the three-electrode cell to characterize its electrochemical properties. Coiled Pt wire electrode and Ag/AgCl (saturated with KCl) were applied as the auxiliary electrode and reference electrode, respectively. Later, the electrode was put into a stirring cell filled with 20 mL of 0.1 M phosphate buffer saline (PBS, pH 7.0) to check the electroreduction ability to hydrogen peroxide. The CV scanning rate was set to be 50 mV/s. For amperometric measurements, the electrochemical workstation and the three-electrode configuration were used as described above. As a working electrode, Au foil modified by Ag dendrites was obtained by the electrolysis at the potentials of −0.3 V for 60 s with silver ion concentration of 20 mM. After washing, the electrode was put into a 20 mL aqueous solution of 0.1 M PBS (pH 7.0) as the electrolyte. The chronoamperometry technique was applied to electrolyze the solution. The potential was set to be −0.2 V (vs Ag/ AgCl). Various amounts of stock hydrogen peroxide solution were added into the cell with certain time intervals to show the electrode response to the different hydrogen peroxide concentrations.
In our previous work, using glassy carbon electrode as the substrate, a dendritic nanostructure of silver was obtained by means of electrodeposition,29 which provides a straightforward and robust protocol for preparing dendritic Ag nanostructure. Herein, we show in detail and study systematically that silver dendritic nanostructures with various morphologies can be fabricated directly on the surface of Au foil in AgNO3 aqueous solution at room temperature. The synthetic process is very facile and controllable. The dendrites with “clean” surfaces are obtained with the chronoamperometry technique from an aqueous solution without introducing any template, surfactant, or modification of electrode surfaces. Effect of different parameters (electrolysis time, working electrode potential, and silver ion concentration) on the morphologies of the resulting Ag nanostructures is studied. A possible mechanism for electrochemically induced growth of the Ag dendrites is suggested based on the experimental results. The H2O2 electroreduction ability of the materials is also demonstrated. The as-prepared dendrites have very pure surface and unique local morphology, both of which will make them find applications in SERS, biosensing, and catalysis.
3. RESULTS AND DISCUSSION Preparation and Characterization of Silver Dendritic Structures. Figure 1a shows a typical SEM image of the dendritic nanostructure obtained with 20 mM AgNO3. It is clearly seen that the silver dendrites look like metasequoiases
2. EXPERIMENTAL SECTION Preparation and Characterization of Silver Dendritic Structures. The electrodeposition of Ag was performed in a threeelectrode cell using a 283 potentiostat−galvanostat electrochemical workstation (EG&G PARC with M270 software). Au foil (EG&G Co.) was used as the substrate for the electrodeposition, and the area of the electrode dipped into the electrolyte solution was 0.196 cm2. A bulk Ag electrode was used for comparison, and its area of was 0.0707 cm2. A coiled Pt wire electrode was used as the auxiliary electrode, and an Ag/AgCl (saturated with KCl) electrode was used as reference electrode. All the potentials reported in this work were quoted with Ag/AgCl as the reference electrode unless otherwise specified. A 20 mL mixture solution containing 0.1 M KNO3 and (e.g., 1, 5, or 10 mM) AgNO3 (Tianjin Yingda Rare Chemical Reagent Co.) was added into cell for the electrolysis. Chronoamperometry was applied to obtain the deposits from the mixture solution using different potentials (e.g., 0, −0.3, or −0.6 V). Electrodeposition was carried out in a stationary electrolyte solution without any stirring or protective gas bubbling. After certain time (e.g., 10, 60, or 120 s) of electrolysis, the electrode was taken out and washed with deionized water several times. Special care was taken when the electrode was removed from solution, so that the shear force between the solution and electrode surface did not break the dendrites. The X-ray diffraction (XRD) patterns recorded using a Rigaku D/ max-rA with Cu Kα radiation (λ = 1.5418 Å) on a diffractometer (Rigaku, Japan) was used to determine the metallic nature of the deposited Ag nanostructures. Electron diffraction (ED, Philips, Tecnai G2 F20) was applied to analyze the crystal structure of the deposits at the edges of the dendrite. The morphologies of the samples were studied by a scanning electron microscope (SEM, FEI Co., QUANTA 200) and a field-emission transmission electron microscope (FE-TEM, Philips, Tecnai G2 F20) equipped with an energy-dispersive X-ray spectroscopy analyzer. For TEM and XRD, the deposits were removed from the Au substrate by ultrasonication for 10 min. A small amount of the sample was dispersed in ethanol, and then a drop of this suspension was deposited on an amorphous carbon film on Cu grid for TEM observation. XRD characterization was carried out by placing 20 μL of the sample on a glass slide to avoid the influence of the Au substrate. Electrochemical Measurements. Electric signals were measured and recorded with a 283 potentiostat−galvanostat electrochemical workstation (EG&G PARC with M270 software). Solutions were deaerated by purging with nitrogen gas for 10 min prior to the electrochemical experiments. Cyclic voltammetric (CV) experiments were carried out to show the electroreduction ability of Ag dendritic
Figure 1. (a) Typical SEM image of the dendritic Ag nanostructure. (b) XRD pattern of the bulk dendrites. The sample was obtained at the applied potential of −0.3 V with an electrolysis time of 60 s in aqueous solution containing KNO3 (0.1 M) and AgNO3 (20 mM). 5219
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Figure 2. EDS of the Ag dendritic nanostructure.
Figure 4. Schematic representation of the proposed morphological and structural evolution during a silver dendrite growth.
Figure 3. (a) Low-magnification TEM image of a typical Ag dendrite. (b) The corresponding SAED pattern. (c, d) Higher magnification TEM image of a subbranch of the Ag dendrite in (a). The sample was obtained at the applied potential of −0.3 V with an electrolysis time of 60 s and silver ion concentration of 20 mM. Figure 5. I−t curves of the different potentials of (a) 0, (b) −0.3, and (c) −0.6 V (vs Ag/AgCl) with silver ion concentration of 20 mM for an electrolysis time of 60 s.
with multilevel structure, namely a long main trunk with short side branches all decorated by small leaves. The overall length of the dendrite is about 8 μm, and both the trunk and the branches are 70−80 nm in diameter. For the higher-order branches (leaves), the dimension can reach as small as a few nanometers. Surprisingly and interestingly, all the side branches grow from the main trunk with an angle of ca. 60°, implying that the silver dendritic crystals grow along a preferential direction. Figure 1b shows the XRD patterns of the as-prepared samples. All the diffraction peaks observed could be indexed to the (111), (200), (220), (311), and (222) diffraction peaks of the cubic structure of metallic Ag, respectively, indicating that the dendrite is crystalline Ag.16 The chemical composition of the dendrites was also examined by the technique of energy-dispersive X-ray spectroscopy. As can be seen in Figure 2, the energy-dispersive Xray spectrum (EDS) collected from the as-prepared nano-
dendrites shows the peak of Ag appear at about 3, 22 and 25, confirming that the products have a “clean” surface and these nanosturctures are comprised only of pure silver (C and Cu peaks can be assigned to the carbon film Cu grid). A further insight into the morphology of the nanodendrites is gained from a TEM image, as shown in Figure 3a, confirming the dendrite-like structure. As can be seen from Figure 3b, the selected area electron diffraction (SAED) pattern displays discontinuous concentric rings characteristic of the cubic Ag, indicating that although the whole Ag nanodendrite is not a perfect single crystal, it has a high extent of preferential crystal orientation. Figure 3c is a higher magnification TEM image from a subbranch (i.e., the third genaration) of the Ag dendrite, 5220
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Figure 6. Typical SEM images of Ag nanostructures obtained at different potentials: (a, b) 0, (c, d) −0.3, and (e, f) −0.6 V vs Ag/AgCl. The electrolysis was carried out for 60 s with silver ion concentration of 10 mM.
shows some misorientations originating from the imperfect assembling among small aggregates. From the above depiction, it suggests that the dislocations are once formed in selfassembling process, then the former interface between two aggregates nearly disappears, and the two aggregates share the same single crystallographic orientation. As a result, the polycrystalline aggregates transform to a single crystal. Thus, it is reasonable to believe that the imperfect dendrite is polycrystalline due to the shorter growth time and the oriented attachment is responsible for the crystal growth. The driving force for the spontaneous oriented attachment is the elimination of the high-energy surfaces, which will lead to a substantial reduction in the surface free energy from the thermodynamic viewpoint.30 In the initial situation of the growth process, the small aggregates just attached randomly on the lateral of silver dendrites as shown in Figure S2 of the Supporting Information. As the reaction proceeds, the small grains may have sufficient time to rotate and relax to minimum energy position, thus contributing to the formation of singlecrystal silver nanostructure as shown in Figure S1b. Figure 4 gives a schematic representation of the proposed morphological
which shows a robust structure and glossy surface except some nanoparticles adhered. The further crystal structure information comes from high-resolution transmission electron microscopy (HRTEM) analysis. Figure S1 (Supporting Information) is a HRTEM study of the dendrite in Figure 3c. Figure S1a shows a joint between a leaf and the subbranch, and the interface area is marked by a white rectangle, revealing a robust connection that the aggregates belong to the same crystal system with the same crystal orientation (marked by a white arrow). Figure S1b shows a single leaf; it can be seen that the crystals share nearly the same crystallographic orientation attached by a group of small particles with slight misorientation on the tip. So, it suggests that the silver aggregation is not simply a physical contact but rather an epitaxial growth. The TEM image in Figure 3d shows another subbranch which is on the tip of a branch in the same Ag dendrite. However, the crystallinity is relatively poor, and it looks like incompact composition of very small nanocrystals with incontinuous joints between adjacent surfaces, which is further evidenced by Figure S2. A higher magnification TEM image of a leaf is shown in Figure S2a, from which the polycrystalline character is confirmed. Figure S2b 5221
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Figure 7. Typical SEM images of Ag nanostructures obtained at different silver ion concentrations: (a, b) 1 mM, (c, d) 5 mM, (e, f) 20 mM. The electrolysis was carried out for 60 s at the potential of −0.3 V vs Ag/AgCl.
and structural evolution during a silver dendrite growth, including the aggregates attachment, grains rotation, and grains relaxation. We also investigated the relations between the morphology of the silver nanostructures and various electrolysis parameters including the applied potentials and silver ion concentrations. Product morphology is highly determined by the applied potential, since it controls the electrochemical driving force in the constant potential mode.25 More precisely, the applied potential via the Nernst equation controls the relative surface concentration of the electroactive species and thus the rate of the electrodeposition process. Figure 5 shows the I−t curves with the different electrolysis potentials. From the curves, it is obvious that the more negative potential will result in the larger reduction current. During the electrolysis process, the applied potentials (0, −0.3, and −0.6 V) were sufficient for the reaction Ag+ + e = Ag (E° = 0.799 V vs SHE) to take place on the working electrode. The SEM images of the samples obtained at different potentials with a constant silver ion concentration (10 mM) are clearly illustrated in Figure 6. For different potentials, the coexistence of spherical and dendritic structures is
exhibited, with certain differences. For the materials obtained at lower potential of 0 V vs Ag/AgCl, which can be seen in Figure 6a,b, the density of the deposits is very low; only smaller dendrites are observed, and most of the particles obtained are spherical. At the more negative potential of −0.3 V (Figure 6c,d), more and larger dendritic structures with well-defined morphology are realized. When the potential is further increased to −0.6 V (Figure 6e,f), high-density yet irregular dendritic silver crystals were formed. The typical SEM images of the samples obtained at different silver ion concentrations at a fixed electrolysis time (60 s) and potential (−0.3 V vs Ag/AgCl) are shown in Figures 6c,d and 7. Spherical particles are observed at lower concentration of 1 mM, while some crystals tend to aggregate (Figure 7a,b). The material obtained with ion concentration of 5 mM (Figure 7c,d) appears nonuniform and consists of sparse and imperfect dendrites. At the concentration of 10 mM, the density of nanodendritic structures is still low, and the dimension of the structures is small (Figure 6c,d), while more dense silver dendrites with larger dimensions and complex dendrites with numerous side branches are observed when the concentration 5222
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Figure 8. Typical SEM images of Ag nanostructures obtained at a potential of −0.3 V vs Ag/AgCl with silver ion concentration of 10 mM for different electrolysis times: (a, b) 10, (c, d) 30, (e, f) 120, (g, h) 240 s.
model32 have been widely used to interpret and analyze these fractal phenomena. In the electrodeposition methods, some processes such as kinetic anisotropy in the reduction of silver ions28 and the lack of electrolyte play an important role in the formation of Ag dendrites.33 How does the anisotropic dendritic Ag nanostructure form in the present case? In order to understand the formation process, the time-dependent shape
is increased to 20 mM (Figure 7e,f). These results demonstrate that the concentration of silver ions plays a significant role in the formation and growth of the silver nanoparticles, which can be further evidenced by TEM images in Figure S3 and Figure 3a. Dendritic fractals are phenomena generally observed in nonequilibrium and anisotropic growth; the diffusion-limited aggregation model31 and the cluster−cluster aggregation 5223
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Figure 9. Schematic illustration of the formation process of silver dendrites on a substrate.
Figure 11. Cyclic voltammograms for Ag dendrite-modified Au electrode in 1 mM H2O2 in 0.1 M pH 7.0 PBS at a scan rate of 50 mV/ s. (A) The Ag dendrite-modified Au electrodes were obtained at the potential of −0.3 V with an electrolysis time of 60 s in aqueous solution containing different silver ion concentrations ((a) 5, (b) 10, (c) 20 mM). (B) The Ag dendrite-modified Au electrodes were obtained at different potentials ((a) 0, (b) −0.3, (c) −0.6 V vs Ag/ AgCl) with the electrolysis time of 60 s in silver ion concentration of 20 mM.
Figure 10. Cyclic voltammograms for (a) bare Ag electrode, (b) Au electrode, and (c) Ag dendrite-modified Au electrode in 1 mM H2O2. Inset: cyclic voltammograms of Ag dendrite-modified Au electrodes at different concentrations ((a′) 1, (b′) 2, (c′) 3, (d′) 4, (e′) 5 mM) of H2O2 in 0.1 M pH 7.0 PBS at a scan rate of 50 mV/s.
evolution process is also carried out by careful examinations of the intermediates. The morphologies obtained with different electrolysis times at a potential of −0.3 V vs Ag/AgCl with concentration of 10 mM are shown in Figures 6c,d and 8. The material obtained with the shortest electrolysis time of 10 s as shown in Figure 8a,b appears spherical crystals without any dendrites. When the electrolysis time increased to 30 s, quasi-dendritic structures appear (Figure 8c,d), though most are still spherical and nanorod structures, which may further develop into dendrites. The nanorods grow larger, and branches of the crystals grow with increasing growth time, forming the dendritic structures, which can be verified in (Figures 6c and 8e). For the longer electrolysis time, the dendrites are more uniform (Figure 8g,h), and the dendrite coverage on the electrode surface is so high and the perfect dendritic structure with large dimensions is observed. Based on the experiments above, a plausible formation process is speculated. In this approach, the electrochemical reaction (or electron transfer) and crystallization (nucleation and growth) coexist, and the formation of Ag dendrites involves
the following stages: (1) AgNO3 is rapidly reduced to form Ag adatoms (Ag0) via electron transfer reaction under an appropriate driving force (the applied potential) when the process happened initially. Because the initial concentration of the silver salt is very high, concentrated silver atoms are produced. (2) Large quantities of silver nucleus will then be instantaneously formed at random positions on the bare Au substrate due to the surface diffusion of adatoms, and a subsequent growth phase in which free Ag atoms will be captured to incorporate into the already preformed silver nuclei by direct transfer from solution as well as surface diffusion on the Au substrate. (3) With prolonging of the reaction duration, the already existing nuclei will grow into the somewhat fragmented looking nanostructures or a chainlike network, yielding an initial aggregate of Ag nanoparticles. Other free nanoparticles will diffuse continually toward the aggregate and further be immobilized, forming a larger aggregate. (4) With elapsed time, the concentrations of the silver salt greatly decrease, the growth is mainly driven by decreasing surface 5224
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obvious cathodic current increment is observed for the silver dendrite-modified electrode, and the peak appears near −0.35 V, which is ascribed to the reduction of H2O2. The response of H2O2 for the bare Ag and Au electrode was weak without any peaks for H2O2 reduction and could be disregarded. The CV curves of silver dendrite-modified electrodes at different concentrations of H2O2 are shown in the inset of Figure 10, which can be seen that the cathodic current increases with the increase of H2O2 concentration. These results are clear evidence for the catalytic effects of the Ag dendrites toward the reduction of H2O2. The H2O2 electrocatalytic ability of the Ag dendrite-modified electrodes obtained at different electrolysis parameters was also evaluated. Figure 11A shows CV curves for the modified electrodes obtained at different silver ion concentrations (5, 10, and 20 mM) at potentials of −0.3 V (vs Ag/AgCl) with electrolysis time of 60 s in 1 mM H2O2. As predicted previously, the electrodes modified with Ag materials obtained at higher silver ion concentrations result in a larger peak current. Figure 11B shows CV curves for the modified electrodes obtained at different potentials of 0, −0.3, and −0.6 V (vs Ag/AgCl) with electrolysis time of 60 s at silver ion concentration of 20 mM. From the CV curves, it is obvious that the electrodes modified at more negative potentials produce a larger peak current, which is consistent with the result in Figure 5. These results are attributed to the differences in the surface area of the working electrode. When a higher potential or a higher silver ion concentration is applied to obtain Ag materials in a larger surface coverage with the same electrolysis time, the larger surface coverage allows a more effective electroreduction, which is manifested in its reduction peak current. After confirming the H2O2 electroreduction ability, the Ag dendrite-modified Au electrode was fabricated as the H2O2 detector in aqueous solution. The electrode was modified at −0.3 V for 60 s in a mixture solution containing 0.1 M KNO3 and 20 mM AgNO3. Amperometry with the potential of −0.2 V was applied to check the electrode response to the different concentrations of H2O2, which can be seen in Figure 12. Compared with the bare silver electrode, the dendrite-modified electrode is more sensitive to H2O2, which could be due to the excellent catalytic activity of Ag dendrites with large surface areas. Research is being conducted on the detailed relationship among deposition potential, electrolysis time, dendrite size, and the sensitivity to H2O2 and other organic compounds.
Figure 12. Amperimetric responses at bare Ag electrode (a) and Ag dendrite-modified Au electrode (b) upon increasing the concentration of H2O2 in steps of 1 mM in 0.1 M pH 7.0 PBS at −0.2 V vs Ag/AgCl. Inset: amplification of curve (a).
energy, and newly arriving silver atoms are continuously attached onto the surfaces of the silver nanostructures in an oriented attachment that leads to the formation of dendrites. This is because an appropriate driving force for the spontaneous oriented attachment is the elimination of the high-energy surfaces which will adjust growth rate differences due to surface energy differences on different crystallographic directions, leading to a geometrical anisotropy with substantial reduction of the surface free energy.30,34 To conclude, at relatively short reaction time with a higher silver ion concentration, the growth process is mainly controlled by a kinetic factor which is determined by the rate of incorporation of new Ag0 adatoms. While at longer reaction time with a low silver ion concentration, thermodynamic factor is favorable thus a relatively stable dendritic silver nanostructure is obtained. Figure 9 shows a schematic diagram to illustrate the possible electrochemical formation process of Ag dendrites in this synthesis. Hydrogen Peroxide Electroreduction Ability of Ag Dendritic Material Based on Electrochemical Measurements. To evaluate the Ag dendrite as an electrode material for practical application, we studied the electroreduction ability of the Ag dendrite-modified electrode toward hydrogen peroxide (H2O2) in aqueous solution. Determination of H2O2 is of practical importance in chemical, biological, clinical, environmental, and many other fields.35,36 Reduction of H2O2 by electrochemical methods has attracted considerable attention compared to traditional H2O2 oxidation which requires high overpotentials, thus arising interferences from common electroactive species.37 Noble metals such as platinum, gold, and palladium have been widely used as nanoparticles for the reduction of H2O2.38−40 As a test of the good electrocatalytic properties of the Ag nanodendrites, cyclic voltammetry (CV) is a useful tool to characterize the sensing behavior of the electroactive species on the electrode surface. A comparison of the H2O2 electroreduction ability among bare Ag electrode (a), Au foil (b), and Ag dendrite-modified electrode (c) is investigated by CV, as shown in Figure 10. The modified electrode was obtained with the silver ion concentration of 20 mM at potentials of −0.3 V vs Ag/AgCl with electrolysis time of 60 s. It can be seen that an
4. CONCLUSIONS Ag materials with a novel nanostructure have been synthesized on an Au foil by a very facile, rapid and cost-effective chronoamperometry technique without introducing any template, surfactant or modification of electrode surfaces. The density and the morphology of the Ag nanostructures can be easily controlled by changing electrolysis parameters, such as the applied potential, precursor concentration, and electrolysis time. The electrochemically induced formation of the Ag dendrites is suggested to result from instantaneous nucleation and anisotropic growth of silver, which sensitively depends on the deposition parameters. The obtained dendritic nanostructures with high surface areas exhibit high electrocatalytic ability for H2O2 reduction and could be a good candidate for application of sensors in analytical detection. 5225
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(29) Qin, X.; Wang, H. C.; Wang, X. S.; Miao, Z. Y.; Fang, Y. X.; Chen, Q.; Shao, X. G. Electrochim. Acta 2011, 56, 3170. (30) Alivisatos, A. P. Science 2000, 289, 736. (31) Witten, T. A. Jr.; Sander, L. M. Phys. Rev. Lett. 1981, 47, 1400. (32) Kolb, M.; Botet, R.; Jullien, R. Phys. Rev. Lett. 1983, 51, 1123. (33) Zheng, X. J.; Jiang, Z. Y.; Xie, Z. X.; Zhang, S. H.; Mao, B. W.; Zheng, L. S. Electrochem. Commun. 2007, 9, 629. (34) Tang, S. C.; Meng, X. K.; Wang, C. C.; Cao, Z. H. Mater. Chem. Phys. 2009, 114, 842. (35) Bartlett, P. N.; Birkin, P. R.; Wang, J. H.; Palmisano, F.; Benedetto, G. D. Anal. Chem. 1998, 70, 3685. (36) Wang, J.; Lin, Y. H.; Chen, L. Analyst 1993, 118, 277. (37) Welch, C. M.; Banks, C. E.; Simm, A. O.; Compton, R. G. Anal. Bioanal. Chem. 2005, 382, 12. (38) Niazov, T.; Shlyahovsky, B.; Willner, I. J. Am. Chem. Soc. 2007, 129, 6374. (39) Qiu, J.; Peng, H.; Liang, R.; Li, J.; Xia, X. Langmuir 2007, 23, 2133. (40) Huang, J.; Wang, D.; Hou, H.; You, T. Adv. Funct. Mater. 2008, 18, 441.
ASSOCIATED CONTENT
S Supporting Information *
HRTEM images of the Ag nanodendrite in Figure 3 and TEM images of Ag nanostructures obtained at different silver ion concentrations. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are grateful to the financial support from National Natural Science Foundation of China (Grants 81127001 and 30900325) and Natural Science Foundation of Tianjin (Grant 11ZCGHHZ01300).
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REFERENCES
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dx.doi.org/10.1021/la300311v | Langmuir 2012, 28, 5218−5226
