High-Yield Seedless Synthesis of Triangular Gold Nanoplates through

Subscriber access provided by University of South Dakota

Communication

High-Yield Seedless Synthesis of Triangular Gold Nanoplates through Oxidative Etching Lei Chen, Fei Ji, Yong Xu, Liu He, Yifan Mi, Feng Bao, Baoquan Sun, Xiaohong Zhang, and Qiao Zhang Nano Lett., Just Accepted Manuscript • DOI: 10.1021/nl504126u • Publication Date (Web): 20 Nov 2014 Downloaded from http://pubs.acs.org on November 21, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Nano Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

High-Yield Seedless Synthesis of Triangular Gold Nanoplates through Oxidative Etching Lei Chen,†,§ Fei Ji†,§ Yong Xu,† Liu He,†,‡ Yifan Mi,† Feng Bao,† Baoquan Sun,† Xiaohong Zhang,† Qiao Zhang*,† †

Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou 215123, P. R.

China ‡

Department of Mechanical and Mechatronics Engineering, Waterloo University, Waterloo, Ontario N2L

3G1, Canada.

ABSTRACT We demonstrate that monodispersed triangular gold nanoplates with high morphological yield (>90%) can be synthesized through a rapid one-pot seedless growth process. The edge length of triangular Au nanoplates can be readily tuned between 40 and 120 nm by varying the reaction parameters. Systematic studies reveal that distinct from previous hypothesis that the formation of nanoplates is mainly determined by the selective binding of iodide ions, our results show that iodide ions could have dual functions: it can selectively bind to the Au {111} facets and also selectively remove other less stable shape impurities through oxidative etching by forming tri-iodide ions (I3-), thus facilitating the formation of nuclei with dominant planar structure. This new synthetic route will not only help to better understand the growth mechanism of triangular gold nanoplates but also promote the research in anisotropic noble metal nanostructures. KEYWORDS: Gold nanoplates; Seedless growth; Surface Plasmon Resonance; SERS

1 Environment ACS Paragon Plus

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Colloidal plasmonic nanoparticles, especially gold and silver, have drawn much attention because of their localized surface plasmon resonance (LSPR) property and the resulting applications in many fields, including surface enhanced Raman scattering (SERS),1,2 biosensing,3 plasmonics,4-7 catalysis,8 biomedicine,9,10 etc. Since the LSPR of metal nanoparticles is highly dependent on particle shape, great effort has been devoted to controlling the morphology of those plasmonic nanoparticles. Among various synthetic approaches developed to date, wet chemical synthesis has proven to be one of the most versatile methods for producing plasmonic nanoparticles with desired morphology and LSPR properties.11,12 For example, a library of gold nanostructures, such as nanorods,13-17 nanoplates,18-20 nanoribbons,21 and nanowires,22-24 have been synthesized through colloidal approaches and the LSPR wavelength can be fine-tuned from visible to near-infrared region by carefully tailoring the shape and size of nanoparticle. Recently, triangular gold and silver nanoplates have attracted increased attention due to their extremely high anisotropy and excellent LSPR property.25-28 Although impressive progress has been achieved in the synthesis of silver nanoplates,29-31 it has been difficult to produce highly monodispersed gold nanoplates, in particular those with edge length less than 100 nm.19 The first report on the synthesis of triangular Au plates dates back to the 1960s when Milligan and Morriss prepared large Au “trigons” by using a thermal reduction method with citric acid as the reducing agent.32 Due to the large dimension and low yield of the “trigons”, only a broad LSPR band centered around 530 nm was observed. The Sastry group prepared large Au plates (edge length around 0.5~1.0 µm) by using the extract of the plant lemongrass.33 In 2005, Mirkin and co-workers successfully prepared colloidal gold nanoplates with edge length of around 100-200 nm through a seeded growth method.18 The as-prepared gold nanoplates show superior LSPR property with distinct dipolar and quadrupolar plasmon resonances. Since then, many synthetic


Page 2 of 20

Page 3 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

strategies have been developed to synthesize gold nanoplates, including seeded-growth method,19,34,35 thermal reduction approach,36 electrochemical approach,37 and photocatalytic approach,38 among which the seeded growth method is still the most popular one because of its simple setup and relatively higher throughput. Despite the pioneering work in the synthesis of gold nanoplates, lots of challenges still remain, including the lack of a clear understanding of the growth mechanism, low morphological yield (lower than 70%), as well as the difficulty in synthesizing small nanoplates (edge length < 100 nm), etc., all of which have seriously impeded the development of triangular gold nanoplates for practical applications. Since the bulk crystal structures of both gold and silver are face-centered cubic (fcc), the formation of highly anisotropic nanoplate is not thermodynamically favored.

It has been

gradually realized that both the capping ligand and the crystal symmetry of the nuclei are critical to the formation of anisotropic nanostructures, as the capping ligand alone cannot guarantee the symmetry breaking.39 For example, Xia and co-workers have used oxidative etching to promote the formation of various anisotropic nanostructures.40-43 Yin et al. discovered that hydrogen peroxide is the key factor for the formation of silver nanoplates, as it can induce the formation of planar twinned defects and remove other less stable structures.31,44 However, due to the higher chemical stability of gold relative to silver and palladium, there are not many reports on the controllable synthesis of gold anisotropic nanostructures through controlled chemical etching of seed particles. In this work, we report a rapid one-pot seedless growth process to prepare monodispersed triangular gold nanoplates with high morphological yield (>90%) and broadly tunable edge length (from ~45 nm to ~ 120 nm) by harnessing the oxidative power of tri-iodide ions. A systematic study has been carried out to investigate the growth mechanism of gold nanoplates.


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 20

Distinct from previously proposed mechanism that iodide ions act solely as the facet-selective species, we show that iodide ions act as a dual-functional reagent: not only can it facilitate the formation of nanoplates through selective binding on the Au {111} facets, but also it forms I3- to selectively remove other shaped impurities at an early stage through chemical etching, in line with the silver nanoplate synthesis where H2O2 has been used as an etchant to facilitate the formation of silver nanoplates.31 Compared to traditional seeded-growth protocols, this simple method has several advantages. First, the seedless growth process can be completed within 10 min, which is much faster than the seeded growth process that takes at least several hours. Second, the reproducibility of the seedless growth is much better than that of seeded growth process which has been limited by the multi-step process. For example, it has been found that the yield of anisotropic nanostructures is determined by the quality of seeds, which is affected by various factors, such as the aging time, the injection rate of reducing agent (NaBH4 in most cases), the reaction temperature, the concentration of reagents, etc. Additionally, the injection rate of seed solution into growth solution and the interval between each seeded step are also critical to the quality of the final product.19 Third, all of the reported protocols can only yield less than 70% of Au nanoplates and a purification step is necessary to obtain monodispersed product.19,45

The proposed seedless growth process can produce more than 90% of

monodispersed Au nanoplates and no purification step is needed. As a result, this rapid seedless growth process is more cost-effective towards practical applications. The seedless growth process is illustrated in Figure 1a. Hexadecyltrimethyl ammonium chloride (CTAC) is explored as the surfactant, and iodide ions are used as the shape-directing agent.

Sodium hydroxide is used to adjust the pH of the growth solution.

In a typical

experiment, CTAC is first mixed with potassium iodide (KI), followed by the addition of sodium


Page 5 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

tetrachloroaurate solution (obtained by mixing chloroauric acid and NaOH in a 1:1 ratio). Upon the addition of ascorbic acid, Au3+ is quickly reduced to Au+, as evidenced by the color change of solution from light yellowish to colorless. Finally, certain amount of NaOH is rapidly injected into the solution to initiate the reduction of Au+. The pH value is around 8.0. The color of the solution changes gradually from colorless to red, purple, and eventually blue, indicating the formation of anisotropic gold nanostructures. The blue colloidal solution is shown in the digital image (inset of Figure 1b). Neither precipitate nor strong scattering can be observed, implying the small size of nanoparticles.

The reaction can be completed within 10 min.

UV/vis

spectrometer has been used to characterize the obtained product. As shown in Figure 1b, the product has a sharp extinction band located around 655 nm and a weak shoulder around 570 nm, which can be attributed to the in-plane dipole and out-of-plane dipole resonance of gold nanoplates, respectively.18 No obvious peak around 530 nm can be observed, suggesting the high yield of anisotropic nanostructures, which has been further confirmed by the TEM characterization. It should be noted that the TEM image is obtained directly from the original product. No size selection or any other purification process has been applied. As shown in Figure 1d, monodispersed triangular gold nanoplates with sharp tips have been successfully prepared. The average edge length of the obtained nanoplates is 67.30 ± 3.29 nm. From both UV-vis spectrum and TEM characterization, it is determined that the morphological yield of triangular gold nanoplates is over 90%. To our best knowledge, this is the highest yield that can be obtained through a colloidal approach. High-resolution TEM (HRTEM) has been used to characterize the obtained Au nanoplates. As shown in Figure 1e, the lattice distance is 0.237 nm, which is in good agreement with bulk Au (111) spacing (0.236 nm), confirming that the planar facet is (111) facet. The selected area electron diffraction (SAED) pattern in the inset of Figure


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1e confirms the as-prepared gold nanoplate is single crystalline. The appearance of 1/3{422} pattern can be attributed to the parallel stacking faults in the direction.46 The atomic force microscopy (AFM) has been used to evaluate the thickness of gold nanoplates, as shown in Figure 1c. The thickness profile in the AFM image is quite smooth, implying a flat surface. The average thickness is around 15 nm. Since the SPR position is highly sensitive to the aspect ratio, defined as the ratio between the edge length and the thickness of nanoplates, the theoretical absorption of Au nanoplates has been simulated by using the finite-difference time-domain (FDTD) method. As shown in Figure S1, the simulation data agree well with the experimental one, in which a maximum absorption at 647 nm has been obtained when the edge length and thickness are set as 70 nm and 15 nm, respectively. The edge length of gold nanoplates can be easily tailored in the range of ~ 40 nm to ~ 120 nm with this seedless growth process by tuning the concentration of reagents, e.g., ascorbic acid, potassium iodide, and NaOH. It is worth noting that the concentrations of CTAC and Au3+ are kept identical in all the experiments. It is well known that fast nucleation can produce uniform and small sized nanoparticles. As depicted in Figure 2a, because the reduction process is initiated by the addition of NaOH, gold nanoplates with the smallest edge length (45.22 ± 3.38 nm) can be obtained at high pH values when the added NaOH concentration is 0.20 mM, while gold nanoplates with the largest edge length (117.29 ± 5.78 nm, Figure 2f) can be obtained when the added NaOH concentration decreases to 0.10 mM and the other parameters are kept the same. The synthetic conditions have been detailed in the Supporting Information (Table S1). The edge length can also be controlled by tuning the concentration of ascorbic acid. As shown in Figure 2b-2d, the edge length of gold nanoplates can be well tuned from 65.48 ± 2.92 nm to 78.25 ± 3.16 when the concentration of ascorbic acid increases from 0.384 mM to 0.640 mM while the


Page 6 of 20

Page 7 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

other conditions are kept identical. It is worth pointing out that the morphological yield of triangular gold nanoplates is over 90% in all of the reaction conditions, suggesting this seedless growth process is a robust method. Since the optical property of gold nanoplates is very sensitive to the physical dimensions, the SPR peak can therefore be tuned readily by controlling the edge length of gold nanoplates. As plotted in Figure S9, the SPR peak can be tuned within the range of 620 nm to 700 nm. No sharp peak around 530 nm has been observed in all the spectra, further confirming the high yield of triangular gold nanoplates. To figure out the growth mechanism of gold nanoplates, a systematic study has been carried out. Alkyltrimethylammonium halide surfactant (e.g., CTAC, CTAB) has been widely used to make anisotropic gold nanostructures as they can preferentially bind to certain gold facets and protect nanoparticles from aggregation. In the absence of CTAC, only big aggregates can be obtained, confirming the protective effect of CTAC. The optimum concentration of CTAC is around 15-20 mM in the solution. The halide species also play an important role in this process. When CTAC is replaced by CTAB and the other conditions are kept the same, the reaction becomes much slower and takes almost four hours. This phenomenon can be attributed to the higher stability of Au-Br complex.47 Because the nucleation process is so slow, only large Au nanoplates (edge length > 0.5 µm) with relatively low morphological yield (< 50%) can be obtained (Figure S10-11). When HAuCl4 is used directly as the gold source and the other parameters are kept identical, no gold nanoplates can be obtained, which might be attributed to the fast reduction of Au3+ to metallic Au. As iodide appears to be the most critical reagent for the nanoplate formation, we examine its role carefully. In the absence of iodide ions, no nanoplates can be obtained, as indicated by the reddish color of the colloidal products. A broad peak around 590 nm can be observed in the UV-


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 20

vis spectrum (black line in Figure 3a). TEM characterization indicates that the as-prepared products are irregular-shaped nanoparticles with size around 200 nm (Figure 3b). When the concentration of iodide ions is increased to 20 µM, the colloid solution shows a purple color, indicating the formation of some anisotropic nanostructures. Two distinct peaks at ~ 560 nm and 650 nm can be observed in the UV-vis spectrum (magenta line in Figure 3a). The ratio between the intensity of two peaks is around one to one. TEM characterization indicates the product is composed of some triangular nanoplates and some faceted nanoparticles (Figure 3c), suggesting iodide ions played an important role in promoting the formation of nanoplates.

Further

increasing the iodide concentration to 75 µM leads to a blue colored solution and monodispersed triangular gold nanoplates have been successfully prepared (Figure 3d). Only one peak around 650 nm appears in the UV-vis spectrum (red line in Figure 3a). When the concentration of iodide ions is further increased to 150 µM, a broad LSPR band centered at 630 nm can be observed in the UV-vis spectrum (blue line in Figure 3). TEM characterization shows that the major product is truncated small triangular nanoplates with edge length about 40 nm (Figure 3e). The truncation of sharp tips can be attributed to the oxidative etching of gold by iodide ions in the presence of oxygen. Since the reaction solution is basic with pH around 8.0, the reaction can be described as follows:48,49 4I- + O2 + 2H2O = 2I2 + 4OH-

(1)

I2 + I- = I3-

(2)

2Au + I3- + I- + = 2AuI2-

(3)

To further confirm the proposed oxidative etching mechanism, colloidal gold nanoplates is mixed with 5 mM KI solution in air. The color of the solution turns from blue to almost 8 Environment ACS Paragon Plus

Page 9 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

colorless within three hours, implying the dissolution of gold nanoplates (see digital image in Figure S13a). The UV-vis spectra showed that the SPR peak in the long wavelength range disappears gradually along with the decreasing of the total intensity (Figure S13b), further proving the etching effect of KI solution. To investigate the detailed growth process of gold nanoplates, we monitor the change in the SPR band during the nucleation and growth process. Upon the injection of NaOH, the originally colorless solution becomes light reddish immediately, implying the reduction of Au+ to metallic Au. As the growth process continues, the light-reddish solution turns to deep red, purple, and eventually blue, suggesting the formation of anisotropic nanostructures. The change in the color of the colloidal solution is recorded by an in situ UV-vis spectrometer, as plotted in Figure 4. With the formation of metallic gold nanoparticles, a weak shoulder around 550 nm appears, suggesting that some anisotropic nanostructures formed very quickly.

With the reaction

continues, the weak shoulder becomes broaden and red-shifts to longer wavelength range. The intensity of the characteristic peak of anisotropic nanostructures in the long wavelength range increases gradually and reaches its maxima within around 8 min, suggesting the completion of the reaction. It should be noted that the characteristic peak of spherical Au nanoparticles at 530 nm has not been observed during the whole process, implying the high morphological yield of triangular nanoplates. It has been widely accepted that halide ions played a critical role in making gold nanostructures.50 For example, Mirkin and co-workers have proposed that iodide ions can selectively bind to the Au {111} facet and promote the formation of anisotropic nanostructures.34 However, it has been realized recently that the capping ligands alone cannot determine the formation of anisotropic nanostructures as the final morphology of the nanostructures is


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 20

determined by both the seed structure and the ligands.39 On the basis of the above information obtained from the systematic study, we can draw a picture to account for the observations, as illustrated in Scheme 1.

Upon the injection of NaOH solution, there is an explosion of

nucleation which produced small gold nuclei containing many defects, including twinned defects that favor the planar growth into plate shapes. Iodide ion can act as a dual-function reagent in this process: it can not only selectively bind to the Au {111} facets to facilitate the growth of nanoplates, but also remove the relatively unstable nanostructures by oxidizing metallic gold into gold ions through Eq. (1-3). The gold ions can be reduced back to metallic gold by ascorbic acid. In the presence of CTAC and iodide ions, uniform triangular nanoplates can be obtained. To prove our hypothesis, a systematic study has been carried out. We first examine the role of oxygen in this seedless growth process. The reaction solution has been bubbled by nitrogen gas for 30 min to get rid of oxygen. It is found that the yield of triangular gold nanoplates drops dramatically, suggesting the important role of oxygen. Since no gold nanoplates can be obtained in the absence of iodide ions, it can be concluded that both oxygen and iodide ions are critical to the formation of gold nanoplates and iodide ion alone cannot guarantee the high-yield synthesis of gold nanoplates. Furthermore, KI3 solution is prepared by mixing elemental iodine (I2) and potassium iodide (KI) in a 1:1 ratio to make gold nanoplates. The whole reaction solution has been pretreated with nitrogen gas for 30 min to make sure oxygen had been removed. When KI is replaced by KI3 and the other parameters are kept identical, the reaction can still be completed within 10 min and a bluish solution can be obtained with appropriate amount of KI3. As plotted in Figure 5a, anisotropic gold nanostructures with high yield can be prepared in the presence of KI3, evidenced by the sharp peak in the long wavelength range. Without the addition of KI3, only irregular nanoparticle can be obtained. When the concentration of KI3 is 5 µM, a mixture of


Page 11 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

gold nanoplates and irregular nanoparticles can be prepared, as evidenced by the UV-vis spectrum and TEM image (Figure S14).

Careful investigation shows that the optimum

concentration of KI3 falls in the range between 10 µM and 30 µM, supported by the UV-vis spectra and TEM image (Figure 5). Based on the above information, we can conclude that triiodide ion is the critical factor in the synthesis of gold nanoplates as it can selectively remove less stable shaped impurities through oxidative etching. In summary, monodispersed triangular gold nanoplates with tailored edge length and tunable SPR properties have been prepared through a rapid seedless growth process. It is believed that iodide ions can promote the formation of gold nanoplates by both selective binding onto the Au {111} facets and oxidative etching to remove less stable gold nuclei, leaving behind dominant planar structured nuclei. The critical role of tri-iodide ions has been confirmed by a systematic study. Understanding the role of oxidative etching is critical to the achievement of both high yield and uniform morphology in the synthesis of noble metal nanostructures. Such an approach likely can be extended to other gold anisotropic nanostructures to not only improve the yield and uniformity of existing nanostructures but also to achieve cost-effective synthesis for practical applications. ASSOCIATED CONTENT Supporting Information. Chemicals, detailed synthesis protocols, characterization methods, the FDTD simulation process, TEM images, UV-vis spectra, SERS performance and data analysis, could be found in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 20

Corresponding Author * Corresponding author: [email protected] Author Contributions The manuscript was written through contributions of all authors.

All authors have given

approval to the final version of the manuscript. § L.C. and F.J. contributed equally. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We thank the funding support from the National Basic Research Program of China (973 Program, 2012CB932402), the Natural Science Foundation of Jiangsu Province (BK20140304), Jiangsu Key Laboratory for Carbon-based Functional Materials & Devices, and Collaborative Innovation Center of Suzhou Nano Science and Technology. F.J. thanks the funding support from the “Innovation & Entrepreneurship Training Program of Jiangsu College Students” (201410285027Z). We thank Mr. Binghao Wang for AFM measurement.


Page 13 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 1. (a) Schematic illustration of the synthesis process of Au nanoplates using a one-step seedless method; (b) a typical UV-vis spectrum of the obtained Au nanoplates. The inset in (b) shows a digital image of colloidal Au nanoplates solution. (c) The height profile of a gold nanoplate. The scale bar of the inset AFM image is 100 nm. (d) TEM image of the as-obtained Au nanoplates with average edge length of 67.30 ±3.29 nm. (e) High-resolution TEM (HRTEM) image of Au nanoplate; the inset shows the selected area electron diffraction (SAED) pattern.


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 20

Figure 2. TEM images of Au nanoplates with tunable edge length. The average edge length of each sample is: (a) 45.22 ± 3.38 nm; (b) 65.48 ± 2.92 nm; (c) 70.26 ± 3.07 nm; (d) 78.25 ± 3.16 nm; (e) 107.34 ± 8.01 nm; (f) 117.29 ± 5.78 nm. The scale bars are 100 nm.


Page 15 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 3.

UV-vis spectra (a) and TEM images (b-e) of Au nanoparticles obtained in the

presence of various concentrations of iodide ions: 0 µM (black line, b); 20 µM (magenta line, c); 75 µM (red line, d); and 150 µM (blue line, e).


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 20

Figure 4. UV-vis spectra obtained by in situ monitoring the evolution process of Au nanoplates. The interval time is 15 seconds.

Scheme 1. Proposed growth pathway of gold nanoplates through oxidative etching: gold nuclei with various crystal structures are produced at the early stage of nucleation. In the presence of oxygen and iodide, dominant gold nuclei with planar twined structure are left and grow into nanoplates while the other shaped nuclei are oxidized by tri-iodide ions.


Page 17 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 5. (a) UV-vis spectra of gold colloids obtained with different concentration of KI3. From bottom to up: 0 (magenta), 5 (green), 10 (black), 25 (red), and 50 µM (blue). (b) TEM image of gold nanoplates obtained when [KI3] is 25 µM. The average edge length is 87.17 ± 5.54 nm. REFERENCES (1) Herzog, J. B.; Knight, M. W.; Li, Y. J.; Evans, K. M.; Halas, N. J.; Natelson, D. Nano Lett. 2013, 13, 1359-1364. (2) Zhang, P. P.; Yang, S. M.; Wang, L. S.; Zhao, J.; Zhu, Z. C.; Liu, B.; Zhong, J.; Sun, X. H. Nanotech. 2014, 25, 245301. (3) Gao, C. B.; Lu, Z. D.; Liu, Y.; Zhang, Q.; Chi, M. F.; Cheng, Q.; Yin, Y. D. Angew. Chem. Int. Edit. 2012, 51, 5629-5633. (4) Anderson, L. J. E.; Zhen, Y. R.; Payne, C. M.; Nordlander, P.; Hafner, J. H. Nano Lett. 2013, 13, 6256-6261. (5) Sonnichsen, C.; Reinhard, B. M.; Liphardt, J.; Alivisatos, A. P. Nature Biotech. 2005, 23, 741-745. (6) Gao, B.; Arya, G.; Tao, A. R. Nat. Nanotech. 2012, 7, 433-437. (7) Jiang, N. N.; Shao, L.; Wang, J. F. Adv. Mater. 2014, 26, 3282-3289. (8) Christopher, P.; Xin, H. L.; Linic, S. Nat. Chem. 2011, 3, 467-472. (9) Dreaden, E. C.; Alkilany, A. M.; Huang, X. H.; Murphy, C. J.; El-Sayed, M. A. Chem. Soc. Rev. 2012, 41, 2740-2779. (10) Hu, M.; Chen, J. Y.; Li, Z. Y.; Au, L.; Hartland, G. V.; Li, X. D.; Marquez, M.; Xia, Y. N. Chem. Soc. Rev. 2006, 35, 1084-1094. (11) Lohse, S. E.; Murphy, C. J. Chem. Mater. 2013, 25, 1250-1261. (12) Na, K.; Zhang, Q.; Somorjai, G. A. J. Clust. Sci. 2014, 25, 83-114. (13) Jana, N. R.; Gearheart, L.; Murphy, C. J. J. Phys. Chem. B 2001, 105, 4065-4067. (14) Nikoobakht, B.; El-Sayed, M. A. Chem. Mater. 2003, 15, 1957-1962. (15) Ye, X. C.; Jin, L. H.; Caglayan, H.; Chen, J.; Xing, G. Z.; Zheng, C.; Doan-Nguyen, V.; Kang, Y. J.; Engheta, N.; Kagan, C. R.; Murray, C. B. ACS Nano 2012, 6, 2804-2817.


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 20

(16) Ye, X. C.; Gao, Y. Z.; Chen, J.; Reifsnyder, D. C.; Zheng, C.; Murray, C. B. Nano Lett. 2013, 13, 2163-2171. (17) Ye, X. C.; Zheng, C.; Chen, J.; Gao, Y. Z.; Murray, C. B. Nano Lett. 2013, 13, 765-771. (18) Millstone, J. E.; Park, S.; Shuford, K. L.; Qin, L. D.; Schatz, G. C.; Mirkin, C. A. J. Am. Chem. Soc. 2005, 127, 5312-5313. (19) Scarabelli, L.; Coronado-Puchau, M.; Giner-Casares, J. J.; Langer, J.; Liz-Marzan, L. M. Acs Nano 2014, 8, 5833-5842. (20) Huang, X.; Li, S. Z.; Huang, Y. Z.; Wu, S. X.; Zhou, X. Z.; Li, S. Z.; Gan, C. L.; Boey, F.; Mirkin, C. A.; Zhang, H. Nat. Commun. 2011, 2. (21) Payne, C. M.; Tsentalovich, D. E.; Benoit, D. N.; Anderson, L. J. E.; Guo, W. H.; Colvin, V. L.; Pasquali, M.; Hafner, J. H. Chem. Mater. 2014, 26, 1999-2004. (22) Lu, X. M.; Yavuz, M. S.; Tuan, H. Y.; Korgel, B. A.; Xia, Y. N. J. Am. Chem. Soc. 2008, 130, 8900-8901. (23) Huo, Z. Y.; Tsung, C. K.; Huang, W. Y.; Zhang, X. F.; Yang, P. D. Nano Lett. 2008, 8, 2041-2044. (24) Wang, C.; Hu, Y. J.; Lieber, C. M.; Sun, S. H. J. Am. Chem. Soc. 2008, 130, 8902-8903. (25) Pastoriza-Santos, I.; Liz-Marzan, L. M. J. Mater. Chem. 2008, 18, 1724-1737. (26) Millstone, J. E.; Hurst, S. J.; Metraux, G. S.; Cutler, J. I.; Mirkin, C. A. Small 2009, 5, 646664. (27) Sun, Y. G. Adv. Funct. Mater. 2010, 20, 3646-3657. (28) Xue, C.; Metraux, G. S.; Millstone, J. E.; Mirkin, C. A. J. Am. Chem. Soc. 2008, 130, 83378344. (29) Jin, R. C.; Cao, Y. W.; Mirkin, C. A.; Kelly, K. L.; Schatz, G. C.; Zheng, J. G. Science 2001, 294, 1901-1903. (30) Jin, R. C.; Cao, Y. C.; Hao, E. C.; Metraux, G. S.; Schatz, G. C.; Mirkin, C. A. Nature 2003, 425, 487-490. (31) Zhang, Q.; Li, N.; Goebl, J.; Lu, Z. D.; Yin, Y. D. J. Am. Chem. Soc. 2011, 133, 1893118939. (32) Milligan, W. O.; Morriss, R. H. J. Am. Chem. Soc. 1964, 86, 3461-3467. (33) Shankar, S. S.; Rai, A.; Ankamwar, B.; Singh, A.; Ahmad, A.; Sastry, M. Nat. Mater. 2004, 3, 482-488. (34) Millstone, J. E.; Wei, W.; Jones, M. R.; Yoo, H. J.; Mirkin, C. A. Nano Lett. 2008, 8, 25262529. (35) Millstone, J. E.; Metraux, G. S.; Mirkin, C. A. Adv. Funct. Mater. 2006, 16, 1209-1214. (36) Chu, H. C.; Kuo, C. H.; Huang, M. H. Inorg. Chem. 2006, 45, 808-813. (37) Zhu, J.; Jin, X. L. Superlattice Microst. 2007, 41, 271-276. (38) Miranda, A.; Malheiro, E.; Skiba, E.; Quaresma, P.; Carvalho, P. A.; Eaton, P.; de Castro, B.; Shelnutt, J. A.; Pereira, E. Nanoscale 2010, 2, 2209-2216. (39) Xia, Y. N.; Xiong, Y. J.; Lim, B.; Skrabalak, S. E. Angew. Chem. Int. Ed. 2009, 48, 60-103. (40) Wiley, B.; Herricks, T.; Sun, Y. G.; Xia, Y. N. Nano Lett. 2004, 4, 2057-2057. (41) Xiong, Y. J.; Wiley, B.; Chen, J. Y.; Li, Z. Y.; Yin, Y. D.; Xia, Y. N. Angew. Chem. Int. Ed. 2005, 44, 7913-7917. (42) Zettsu, N.; McLellan, J. M.; Wiley, B.; Yin, Y. D.; Li, Z. Y.; Xia, Y. N. Angew. Chem. Int. Ed. 2006, 45, 1288-1292. (43) Xiong, Y. J.; Cai, H. G.; Wiley, B. J.; Wang, J. G.; Kim, M. J.; Xia, Y. N. J. Am. Chem. Soc. 2007, 129, 3665-3675.


Page 19 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

(44) Yu, H.; Zhang, Q.; Liu, H.; Dahl, M.; Joo, J.; Li, N.; Wang, L.; Yin, Y. ACS Nano 2014, 8, 10252-10261. (45) Ha, T. H.; Kim, Y. J.; Park, S. H. Chem. Commun. 2010, 46, 3164-3166. (46) Germain, V.; Li, J.; Ingert, D.; Wang, Z. L.; Pileni, M. P. J. Phys. Chem. B 2003, 107, 87178720. (47) Kelsall, G. H.; Welham, N. J.; Diaz, M. A. J. Electroanal. Chem. 1993, 361, 13-24. (48) Lyday, P. A. In Ullmann's Encyclopedia of Industrial Chemistry; Wiley-VCH Verlag GmbH & Co. KGaA: 2000. (49) Baghalha, M. Hydrometallurgy 2012, 113, 42-50. (50) Langille, M. R.; Personick, M. L.; Zhang, J.; Mirkin, C. A. J. Am. Chem. Soc. 2012, 134, 14542-14554.


Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

SYNOPSIS


Page 20 of 20

High-Yield Seedless Synthesis of Triangular Gold Nanoplates through

Recommend Documents