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Facile size and shape control of templated Au nanoparticles under microwave irradiation
Materials Letters 65 (2011) 2307–2310
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Facile size and shape control of templated Au nanoparticles under microwave irradiation Weibin Liang, Andrew T. Harris ⁎ Laboratory for Sustainable Technology, School of Chemical and Biomolecular Engineering, University of Sydney, NSW, Australia
a r t i c l e
i n f o
Article history: Received 16 November 2010 Accepted 20 April 2011 Available online 28 April 2011 Keywords: Gold Icosahedron Nanoplate Microwave Pluronic P123 Sodium chloride
a b s t r a c t In this work we prepared icosahedral gold particles and gold nanoplates using potassium tetrachloroaurate as precursor and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers as both reductant and capping agent under microwave irradiation. The products were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The size and shape of the resultant nanoparticles could be tuned by changing the chloride ion dosage and reaction temperature. With lower dosage of chloride ion, a lower proportion of irregular shaped nanoparticles and smaller gold decahedra and icosahedra were observed. Increasing the molecular ratio of [AuCl4]/[Cl−] and reaction temperature could increase the proportion of gold nanoplates in the final product. Typically when the reaction proceeded at 120 °C with [AuCl4]/[Cl−] = 10, N 90% of the product was nanoplatelets. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Chemical methods to synthesize metal nanoparticles have been well studied [1]. However, the majority of these necessitate the use of toxic chemicals in the synthesis protocol, including aggressive reducing and capping agents and the use of organic solvents [2]. It is therefore important to develop benign synthesis processes for the fabrication of metal nanoparticles, to address concerns about the toxicity of the reagents used and the resultant toxicity of the nanoparticles in end-use applications [3]. In this respect, integration of the principles of “green chemistry” into nanoscience and nanotechnology has resulted in the development of novel, low impact nanoparticle synthesis protocols. Wallen et al. described the key steps in the “green” preparation of metallic nanoparticles, including the choice of benign solvents, reducing and stabilizing agents [4]. One approach which satisfies these, is the use of non-ionic block copolymers (Poloxamers), materials widely used in dispersion, stabilisation, solubilisation, emulsification and lubrication in the pharmaceuticals and bioprocessing industries [5–7]. Recently, Poloxamers have been used as both a reducing agent and colloidal stabilizer in the synthesis of Au nanomaterials. Depending on the combination of poly(propylene oxide)/poly(ethylene oxide) units, and the molecular weight of the polymer, 10 nm spheres [8] or 100 nm–1 μm icosahedra [9], nanowires and nanosheets [10] were able to be synthesized using water as a solvent.
⁎ Corresponding author. Fax: + 61 2 9351 2854. E-mail address: [email protected] (A.T. Harris). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.04.075
In this work we show it is possible to tune the distribution of Au nanoparticle size and shape, in the presence of a templating Poloxmer (Pluronic P-123), in water under the influence of microwave irradiation. The use of microwave heating has attracted attention as a rapid and effective mode of heating for the generation of nanomaterials [11–14]. 2. Experimental All reagents (Sigma-Aldrich, analytical-grade) were used as received. In a typical procedure, 8 ml of 13 wt.% (~ 2.58 mM) Pluronic P123, 2 ml NaCl (0.005 M, 0.0025 M, 0.0005 M and 0.00025 M) and 0.5 ml 0.01 M KAuCl4 were added to a sealed microwave Teflon pressure vessel followed by heating under irradiation in a commercial microwave system (MDS-10, 2450 ± 45 MHz Shanghai Sineo Microwave Chemistry Technology Co., Ltd.). The power output of the microwave (up to 1 kW) was adjusted to maintain the required reaction temperature using a linear temperature ramp (typically 1 min) and maintained at this temperature for 5 min.Scanning electron microscopy (SEM, Zeiss Ultra + FESEM, 1.5 kV) and transmission electron microscopy (TEM, Phillips CM120 Biofilter, 200 kV) were used to study the size, shape and morphology of the assynthesized reaction products. For SEM and/or TEM analysis, nanoparticles were separated and recovered by centrifugation at 6000 rpm for 20 min, followed by washing in deionised water. This procedure was repeated three times to remove unreacted polymer and ions not attached to the nanoparticle surface. A droplet of the resultant solution was placed onto a {100} silicon wafer and carbon coated copper grid and dried at 40 °C, for SEM and TEM detection respectively. X-Ray diffraction patterns (XRD, Siemens D5000) were measured with CuKα
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radiation by depositing the sample on silicon wafer. The XRD patterns were recorded from 35° to 80° with a scanning rate 0.01°/s. 3. Results and discussion Fig. 1 shows SEM (main) and TEM (inset) images of Au nanoparticles prepared by the reduction of KAuCl4 in an aqueous solution of Pluronic P123 at 60 °C for 5 min. The products are a mixture of spherical nanoparticles and triangular, belt and hexagonal nanoplates. The TEM images suggest that the rod structures are actually the edge of the nanoplates, aligned at 90° to the field of obervation. There are marked differences in the product morphology between Au nanoparticles synthesised under microwave irradiation and those formed during conventional hydrothermal heating. Based on the work of Lee et. al., under hydrothermal heating, without NaCl addition only spherical or quasi-spherical nanoparticles were obtained [15]. However Fig. 1. shows that Au nanoplates were the main product. The preferential formation of nanoplates under microwave heating is likely due to the rapid and homogeneous dielectric heating, which cannot be achieved under traditional hydrothermal conditions. The presence of the electromagnetic field induces the rotation of the water, a polar solvent, converting electromagnetic energy into thermal energy, increasing the rate of nucleation of Au nanoparticles [16]. This in turn promotes homogeneous distribution of the nuclei favoring the presence of planar defects (stacking faults) in the seeds, which can induce 2D anisotropic growth, resulting in the formation of nanoplates. Fig. 2 shows typical SEM images of Au nanoparticles prepared at different temperatures and ratios of [KAuCl4]/[NaCl], in the presence of Pluronic P-123 (13 wt.%). Although a small quantity of irregularly shaped Au nanoparticles are also present (inset of Fig. 2 e and i), the majority of particles are triangular/hexagonal plates, decahedra and icosahedra (Fig. 1), which are mainly caped by the (111) family of planes. The phase purity and high crystallinity of the nanoparticles are supported by X-Ray diffraction (inset, Fig. 1). The sample shows an intense peak at 2θ = 38.2, which corresponds to the (111) lattice plane of face-centered cubic (FCC) metallic Au. Whereras the peaks at 2θ = 44.4 and 64.7, corresponding to the lattice planes (200) and (220), are very weak. The intensity ratio of (200) and (111) is 0.026,
much lower than the conventional value (0.53) for FCC Au. These data indicate that for the as-synthesized nanoparticles the (111) family of planes is dominant. The peak at 2θ ≈ 70° is assigned to the silicon wafer used to support the Au nanoparticles. Lee et. al. reported that increased dosage of [Cl−], resulted in a greater proportion of triangular and hexagonal nanoplates when using Pluronic P123 as reducing and stabilizing agent following heating at 60 °C for 25 min [15]. The use of microwave heating has significantly extended this approach and showed that greater shape and size selectivity is possible, as a function of both temperature and [Cl-]. The presence of [Cl−] is reported to interact with an Au surface to promote the anisotropic growth of Au crystalst [17]. Under microwave irradiation, as the molecular ratio of [AuCl4] −/[Cl−] increased from 1/2 to 10/1, the quantity of Au nanoplates increased (Fig. 2 i, j, k and l). A similar trend was observed with reaction temperature; increasing the temperature from 80 to 120 °C increased the quantity of Au nanoplates. Typically, at 120 °C and R = 10/1, N 90% of the nanoparticles present were Au nanoplates with edge lengths of ~ 1 μm (Fig. 2l). With a lower dosage of [Cl−], a lower proportion of irregular shaped nanoparticles was observed and more uniform icosahedra and decahedra, ~ 180 nm in size, were detected (Fig. 2a, b and c). Increasing the reaction temperature from 80 to 120 °C was effective at reducing the size of the decahedra and icosahedra (from ~ 200 nm to ~ 160 nm) (Fig. 2 c, g and k). This is likely due to higher temperatures promoting the generation of more Au nuclei; under these conditions, with the same quantity of Au available, the average diameter decreased as a result. The Au nanoparticles produced using this technique are potentially applicable as chemical or biological sensors [17], in therapeutics [18], in photothermal cancer therapies [19], in optical coatings [20] and catalysts [21]. 4. Conclusions Icosahedral Au nanoparticles and nanoplates were obtained through a simple and benign method, with water as a solvent under microwave irradiation. The size and shape of the resultant nanoparticles could be tuned by changing the [Cl−] ion dosage and reaction
Fig. 1. (main) SEM image of Au nanoparticles synthesized by the reduction of 0.5 ml 0.01 M KAuCl4 with 8 ml 13 wt.% Pluronic P123 under microwave irirradiation at 60 °C for 5 min, and (inset) typical TEM image and the XRD pattern of nanoparticles produced under the same reaction conditions.
W. Liang, A.T. Harris / Materials Letters 65 (2011) 2307–2310
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Fig. 2. Two dimentional map of Au nanoparticles synthesized at different temperatures and [KAuCl4]/[NaCl] ratios with SEM images showing the reaction products synthesized at the selected reaction conditions: (a) 80 °C and R = 1/2, (b) 80 °C, and R = 1/1, (c) 80 °C and R = 5/1, (d) 80 °C and R = 10/1, (e) 100 °C and R = 1/2, (f) 100 °C and R = 1/1, (g) 100 °C and R = 5/1, (h) 100 °C and R = 10/1, (i) 120 °C and R = 1/2, (j) 120 °C and R = 1/1, (k) 120 °C and R = 5/1, (l) 120 °C and R = 10/1. The insets in (a)-(l) show high magnification images of particles from each experiment. The scale bars in these inset images indicate a length of 200 nm.
temperature. Typically, when the reaction proceeded at 120 °C with [AuCl4] −/[Cl−] = 10, N90% of the product were nanoplatelets. Acknowledgements The authors are grateful to S. Bulcock, P. Trimby and A. Sikorski for assistance with electron microscopy and XRD measurements, respectively. References [1] Xia Y, Xiong Y, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals: simple chemistry meets complex physics? Angew Chem Int Ed 2009;48(1):60–103. [2] Burda C, Chen X, Narayanan R, El-Sayed MA. Chemistry and properties of nanocrystals of different shapes. Chem Rev 2005;105(4):1025–102. [3] Lewinski N, Colvin V, Drezek R. Cytotoxicity of nanopartides. Small 2008;4(1): 26–49. [4] Raveendran P, Fu J, Wallen SL. Completely “green” synthesis and stabilization of metal nanoparticles. J Am Chem Soc 2003;125(46):13940–1. [5] Paterson IF, Chowdhry BZ, Leharne SA. Investigations of naphthalene solubilization in aqueous solutions of ethylene oxide-b-propylene oxide-b-ethylene oxide copolymers. Langmuir 1999;15(19):6187–94.
[6] Kozlov MY, Melik-Nubarov NS, Batrakova EV, Kabanov AV. Relationship between pluronic block copolymer structure, critical micellization concentration and partitioning coefficients of low molecular mass solutes. Macromolecules 2000;33(9):3305–13. [7] Alexandridis P, Yang L. Micellization of polyoxyalkylene block copolymers in formamide. Macromolecules 2000;33(9):3382–91. [8] Sakai T, Alexandridis P. Single-step synthesis and stabilization of metal nanoparticles in aqueous pluronic block copolymer solutions at ambient temperature. Langmuir 2004;20(20):8426–30. [9] Zhang C, Zhang J, Han B, Zhao Y, Li W. Synthesis of icosahedral gold particles by a simple and mild route. Green Chem 2008;10(10):1094–8. [10] Kim JU, Cha SH, Shin K, Jho JY, Lee JC. Preparation of gold nanowires and nanosheets in bulk block copolymer phases under mild conditions. Adv Mater 2004;16(5):459–64. [11] Tsuji M, Hashimoto M, Nishizawa Y, Kubokawa M, Tsuji T. Microwave-assisted synthesis of metallic nanostructures in solution. Chemistry European J 2005;11(2): 440–52. [12] Kundu S, Peng L, Liang H. A new route to obtain high-yield multiple-shaped gold nanoparticles in aqueous solution using microwave irradiation. Inorg Chem 2008;47(14):6344–52. [13] Kundu S, Liang H. Polyelectrolyte-mediated non-micellar synthesis of monodispersed ‘aggregates’ of gold nanoparticles using a microwave approach. Colloids Surf A 2008;330(2–3):143–50. [14] Kundu S, Wang K, Liang H. Size-controlled synthesis and self-assembly of silver nanoparticles within a minute using microwave irradiation. J Phys Chem C 2009;113(1):134–41.
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[15] Lee WK, Cha SH, Kim KH, Kim BW, Lee JC. Shape-controlled synthesis of gold icosahedra and nanoplates using Pluronic P123 block copolymer and sodium chloride. J Solid State Chem 2009;182(12):3243–8. [16] Tompsett GA, Conner WC, Yngvesson KS. Microwave synthesis of nanoporous materials. Chemphyschem 2006;7(2):296–319. [17] Rai A, Singh A, Ahmad A, Sastry M. Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles. Langmuir 2006;22(2): 736–41. [18] Sassaroli E, Li KCP, O'Neill BE. Numerical investigation of heating of a gold nanoparticle and the surrounding microenvironment by nanosecond laser pulses for nanomedicine applications. Phys Med Biol 2009;54(18):5541–60.
[19] Abdulla-Al-Mamun M, Kusumoto Y, Mihata A, Islam MS, Ahmmad B. Plasmoninduced photothermal cell-killing effect of gold colloidal nanoparticles on epithelial carcinoma cells. Photochem Photobiol Sci 2009;8(8):1125–9. [20] Xu X, Stevens M, Cortie MB. In situ precipitation of gold nanoparticles onto glass for potential architectural applications. Chemistry Materials 2004;16(11): 2259–66. [21] Bi Y, Lu G. Morphological controlled synthesis and catalytic activities of gold nanocrystals. Mater Lett 2008;62(17–18):2696–9.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Facile size and shape control of templated Au nanoparticles under microwave irradiation Weibin Liang, Andrew T. Harris ⁎ Laboratory for Sustainable Technology, School of Chemical and Biomolecular Engineering, University of Sydney, NSW, Australia
a r t i c l e
i n f o
Article history: Received 16 November 2010 Accepted 20 April 2011 Available online 28 April 2011 Keywords: Gold Icosahedron Nanoplate Microwave Pluronic P123 Sodium chloride
a b s t r a c t In this work we prepared icosahedral gold particles and gold nanoplates using potassium tetrachloroaurate as precursor and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers as both reductant and capping agent under microwave irradiation. The products were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The size and shape of the resultant nanoparticles could be tuned by changing the chloride ion dosage and reaction temperature. With lower dosage of chloride ion, a lower proportion of irregular shaped nanoparticles and smaller gold decahedra and icosahedra were observed. Increasing the molecular ratio of [AuCl4]/[Cl−] and reaction temperature could increase the proportion of gold nanoplates in the final product. Typically when the reaction proceeded at 120 °C with [AuCl4]/[Cl−] = 10, N 90% of the product was nanoplatelets. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Chemical methods to synthesize metal nanoparticles have been well studied [1]. However, the majority of these necessitate the use of toxic chemicals in the synthesis protocol, including aggressive reducing and capping agents and the use of organic solvents [2]. It is therefore important to develop benign synthesis processes for the fabrication of metal nanoparticles, to address concerns about the toxicity of the reagents used and the resultant toxicity of the nanoparticles in end-use applications [3]. In this respect, integration of the principles of “green chemistry” into nanoscience and nanotechnology has resulted in the development of novel, low impact nanoparticle synthesis protocols. Wallen et al. described the key steps in the “green” preparation of metallic nanoparticles, including the choice of benign solvents, reducing and stabilizing agents [4]. One approach which satisfies these, is the use of non-ionic block copolymers (Poloxamers), materials widely used in dispersion, stabilisation, solubilisation, emulsification and lubrication in the pharmaceuticals and bioprocessing industries [5–7]. Recently, Poloxamers have been used as both a reducing agent and colloidal stabilizer in the synthesis of Au nanomaterials. Depending on the combination of poly(propylene oxide)/poly(ethylene oxide) units, and the molecular weight of the polymer, 10 nm spheres [8] or 100 nm–1 μm icosahedra [9], nanowires and nanosheets [10] were able to be synthesized using water as a solvent.
⁎ Corresponding author. Fax: + 61 2 9351 2854. E-mail address: [email protected] (A.T. Harris). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.04.075
In this work we show it is possible to tune the distribution of Au nanoparticle size and shape, in the presence of a templating Poloxmer (Pluronic P-123), in water under the influence of microwave irradiation. The use of microwave heating has attracted attention as a rapid and effective mode of heating for the generation of nanomaterials [11–14]. 2. Experimental All reagents (Sigma-Aldrich, analytical-grade) were used as received. In a typical procedure, 8 ml of 13 wt.% (~ 2.58 mM) Pluronic P123, 2 ml NaCl (0.005 M, 0.0025 M, 0.0005 M and 0.00025 M) and 0.5 ml 0.01 M KAuCl4 were added to a sealed microwave Teflon pressure vessel followed by heating under irradiation in a commercial microwave system (MDS-10, 2450 ± 45 MHz Shanghai Sineo Microwave Chemistry Technology Co., Ltd.). The power output of the microwave (up to 1 kW) was adjusted to maintain the required reaction temperature using a linear temperature ramp (typically 1 min) and maintained at this temperature for 5 min.Scanning electron microscopy (SEM, Zeiss Ultra + FESEM, 1.5 kV) and transmission electron microscopy (TEM, Phillips CM120 Biofilter, 200 kV) were used to study the size, shape and morphology of the assynthesized reaction products. For SEM and/or TEM analysis, nanoparticles were separated and recovered by centrifugation at 6000 rpm for 20 min, followed by washing in deionised water. This procedure was repeated three times to remove unreacted polymer and ions not attached to the nanoparticle surface. A droplet of the resultant solution was placed onto a {100} silicon wafer and carbon coated copper grid and dried at 40 °C, for SEM and TEM detection respectively. X-Ray diffraction patterns (XRD, Siemens D5000) were measured with CuKα
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W. Liang, A.T. Harris / Materials Letters 65 (2011) 2307–2310
radiation by depositing the sample on silicon wafer. The XRD patterns were recorded from 35° to 80° with a scanning rate 0.01°/s. 3. Results and discussion Fig. 1 shows SEM (main) and TEM (inset) images of Au nanoparticles prepared by the reduction of KAuCl4 in an aqueous solution of Pluronic P123 at 60 °C for 5 min. The products are a mixture of spherical nanoparticles and triangular, belt and hexagonal nanoplates. The TEM images suggest that the rod structures are actually the edge of the nanoplates, aligned at 90° to the field of obervation. There are marked differences in the product morphology between Au nanoparticles synthesised under microwave irradiation and those formed during conventional hydrothermal heating. Based on the work of Lee et. al., under hydrothermal heating, without NaCl addition only spherical or quasi-spherical nanoparticles were obtained [15]. However Fig. 1. shows that Au nanoplates were the main product. The preferential formation of nanoplates under microwave heating is likely due to the rapid and homogeneous dielectric heating, which cannot be achieved under traditional hydrothermal conditions. The presence of the electromagnetic field induces the rotation of the water, a polar solvent, converting electromagnetic energy into thermal energy, increasing the rate of nucleation of Au nanoparticles [16]. This in turn promotes homogeneous distribution of the nuclei favoring the presence of planar defects (stacking faults) in the seeds, which can induce 2D anisotropic growth, resulting in the formation of nanoplates. Fig. 2 shows typical SEM images of Au nanoparticles prepared at different temperatures and ratios of [KAuCl4]/[NaCl], in the presence of Pluronic P-123 (13 wt.%). Although a small quantity of irregularly shaped Au nanoparticles are also present (inset of Fig. 2 e and i), the majority of particles are triangular/hexagonal plates, decahedra and icosahedra (Fig. 1), which are mainly caped by the (111) family of planes. The phase purity and high crystallinity of the nanoparticles are supported by X-Ray diffraction (inset, Fig. 1). The sample shows an intense peak at 2θ = 38.2, which corresponds to the (111) lattice plane of face-centered cubic (FCC) metallic Au. Whereras the peaks at 2θ = 44.4 and 64.7, corresponding to the lattice planes (200) and (220), are very weak. The intensity ratio of (200) and (111) is 0.026,
much lower than the conventional value (0.53) for FCC Au. These data indicate that for the as-synthesized nanoparticles the (111) family of planes is dominant. The peak at 2θ ≈ 70° is assigned to the silicon wafer used to support the Au nanoparticles. Lee et. al. reported that increased dosage of [Cl−], resulted in a greater proportion of triangular and hexagonal nanoplates when using Pluronic P123 as reducing and stabilizing agent following heating at 60 °C for 25 min [15]. The use of microwave heating has significantly extended this approach and showed that greater shape and size selectivity is possible, as a function of both temperature and [Cl-]. The presence of [Cl−] is reported to interact with an Au surface to promote the anisotropic growth of Au crystalst [17]. Under microwave irradiation, as the molecular ratio of [AuCl4] −/[Cl−] increased from 1/2 to 10/1, the quantity of Au nanoplates increased (Fig. 2 i, j, k and l). A similar trend was observed with reaction temperature; increasing the temperature from 80 to 120 °C increased the quantity of Au nanoplates. Typically, at 120 °C and R = 10/1, N 90% of the nanoparticles present were Au nanoplates with edge lengths of ~ 1 μm (Fig. 2l). With a lower dosage of [Cl−], a lower proportion of irregular shaped nanoparticles was observed and more uniform icosahedra and decahedra, ~ 180 nm in size, were detected (Fig. 2a, b and c). Increasing the reaction temperature from 80 to 120 °C was effective at reducing the size of the decahedra and icosahedra (from ~ 200 nm to ~ 160 nm) (Fig. 2 c, g and k). This is likely due to higher temperatures promoting the generation of more Au nuclei; under these conditions, with the same quantity of Au available, the average diameter decreased as a result. The Au nanoparticles produced using this technique are potentially applicable as chemical or biological sensors [17], in therapeutics [18], in photothermal cancer therapies [19], in optical coatings [20] and catalysts [21]. 4. Conclusions Icosahedral Au nanoparticles and nanoplates were obtained through a simple and benign method, with water as a solvent under microwave irradiation. The size and shape of the resultant nanoparticles could be tuned by changing the [Cl−] ion dosage and reaction
Fig. 1. (main) SEM image of Au nanoparticles synthesized by the reduction of 0.5 ml 0.01 M KAuCl4 with 8 ml 13 wt.% Pluronic P123 under microwave irirradiation at 60 °C for 5 min, and (inset) typical TEM image and the XRD pattern of nanoparticles produced under the same reaction conditions.
W. Liang, A.T. Harris / Materials Letters 65 (2011) 2307–2310
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Fig. 2. Two dimentional map of Au nanoparticles synthesized at different temperatures and [KAuCl4]/[NaCl] ratios with SEM images showing the reaction products synthesized at the selected reaction conditions: (a) 80 °C and R = 1/2, (b) 80 °C, and R = 1/1, (c) 80 °C and R = 5/1, (d) 80 °C and R = 10/1, (e) 100 °C and R = 1/2, (f) 100 °C and R = 1/1, (g) 100 °C and R = 5/1, (h) 100 °C and R = 10/1, (i) 120 °C and R = 1/2, (j) 120 °C and R = 1/1, (k) 120 °C and R = 5/1, (l) 120 °C and R = 10/1. The insets in (a)-(l) show high magnification images of particles from each experiment. The scale bars in these inset images indicate a length of 200 nm.
temperature. Typically, when the reaction proceeded at 120 °C with [AuCl4] −/[Cl−] = 10, N90% of the product were nanoplatelets. Acknowledgements The authors are grateful to S. Bulcock, P. Trimby and A. Sikorski for assistance with electron microscopy and XRD measurements, respectively. References [1] Xia Y, Xiong Y, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals: simple chemistry meets complex physics? Angew Chem Int Ed 2009;48(1):60–103. [2] Burda C, Chen X, Narayanan R, El-Sayed MA. Chemistry and properties of nanocrystals of different shapes. Chem Rev 2005;105(4):1025–102. [3] Lewinski N, Colvin V, Drezek R. Cytotoxicity of nanopartides. Small 2008;4(1): 26–49. [4] Raveendran P, Fu J, Wallen SL. Completely “green” synthesis and stabilization of metal nanoparticles. J Am Chem Soc 2003;125(46):13940–1. [5] Paterson IF, Chowdhry BZ, Leharne SA. Investigations of naphthalene solubilization in aqueous solutions of ethylene oxide-b-propylene oxide-b-ethylene oxide copolymers. Langmuir 1999;15(19):6187–94.
[6] Kozlov MY, Melik-Nubarov NS, Batrakova EV, Kabanov AV. Relationship between pluronic block copolymer structure, critical micellization concentration and partitioning coefficients of low molecular mass solutes. Macromolecules 2000;33(9):3305–13. [7] Alexandridis P, Yang L. Micellization of polyoxyalkylene block copolymers in formamide. Macromolecules 2000;33(9):3382–91. [8] Sakai T, Alexandridis P. Single-step synthesis and stabilization of metal nanoparticles in aqueous pluronic block copolymer solutions at ambient temperature. Langmuir 2004;20(20):8426–30. [9] Zhang C, Zhang J, Han B, Zhao Y, Li W. Synthesis of icosahedral gold particles by a simple and mild route. Green Chem 2008;10(10):1094–8. [10] Kim JU, Cha SH, Shin K, Jho JY, Lee JC. Preparation of gold nanowires and nanosheets in bulk block copolymer phases under mild conditions. Adv Mater 2004;16(5):459–64. [11] Tsuji M, Hashimoto M, Nishizawa Y, Kubokawa M, Tsuji T. Microwave-assisted synthesis of metallic nanostructures in solution. Chemistry European J 2005;11(2): 440–52. [12] Kundu S, Peng L, Liang H. A new route to obtain high-yield multiple-shaped gold nanoparticles in aqueous solution using microwave irradiation. Inorg Chem 2008;47(14):6344–52. [13] Kundu S, Liang H. Polyelectrolyte-mediated non-micellar synthesis of monodispersed ‘aggregates’ of gold nanoparticles using a microwave approach. Colloids Surf A 2008;330(2–3):143–50. [14] Kundu S, Wang K, Liang H. Size-controlled synthesis and self-assembly of silver nanoparticles within a minute using microwave irradiation. J Phys Chem C 2009;113(1):134–41.
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W. Liang, A.T. Harris / Materials Letters 65 (2011) 2307–2310
[15] Lee WK, Cha SH, Kim KH, Kim BW, Lee JC. Shape-controlled synthesis of gold icosahedra and nanoplates using Pluronic P123 block copolymer and sodium chloride. J Solid State Chem 2009;182(12):3243–8. [16] Tompsett GA, Conner WC, Yngvesson KS. Microwave synthesis of nanoporous materials. Chemphyschem 2006;7(2):296–319. [17] Rai A, Singh A, Ahmad A, Sastry M. Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles. Langmuir 2006;22(2): 736–41. [18] Sassaroli E, Li KCP, O'Neill BE. Numerical investigation of heating of a gold nanoparticle and the surrounding microenvironment by nanosecond laser pulses for nanomedicine applications. Phys Med Biol 2009;54(18):5541–60.
[19] Abdulla-Al-Mamun M, Kusumoto Y, Mihata A, Islam MS, Ahmmad B. Plasmoninduced photothermal cell-killing effect of gold colloidal nanoparticles on epithelial carcinoma cells. Photochem Photobiol Sci 2009;8(8):1125–9. [20] Xu X, Stevens M, Cortie MB. In situ precipitation of gold nanoparticles onto glass for potential architectural applications. Chemistry Materials 2004;16(11): 2259–66. [21] Bi Y, Lu G. Morphological controlled synthesis and catalytic activities of gold nanocrystals. Mater Lett 2008;62(17–18):2696–9.