ARTIC

LECopyright © 2013 by American Scientific Publishers

All rights reserved.

Printed in the United States of America

Advanced Science,Engineering and Medicine

Vol. 5, pp. 1–8, 2013(www.aspbs.com/asem)

Green-Chemical Synthesis of MonodisperseAu, Pd and Bimetallic (Core–Shell) Au–Pd,Pd–Au NanoparticlesEduardo A. Larios-Rodríguez1, F. F. Castillón-Barraza2, Dora J. Borbón-González3,Ronaldo Herrera-Urbina1, and Alvaro Posada-Amarillas4�∗

1Departamento de Ingeniería Química y Metalurgia, Universidad de Sonora, Hermosillo, Sonora, 83000, México2Centro de Nanociencias y Nanotecnología, UNAM, Carretera Tijuana-Ensenada, Ensenada, B.C., México3Departamento de Matemáticas, Universidad de Sonora, 83000 Hermosillo, Sonora, México4Departamento de Investigación en Física, Universidad de Sonora,Apdo. Postal 5-088, 83190 Hermosillo, Sonora, México

Gold and palladium nanoparticles as well as bimetallic AucorePdshell and PdcoreAushell nanoparticles were synthe-sized at 25 �C from aqueous solutions of Au(III) and Pd(II) species using ascorbic acid as reducing agent. Theoptical properties of these nanoparticles were assessed by UV-Vis absorption spectroscopy. Gold nanoparti-cles in aqueous solution exhibit a well defined absorption band whose maximum and position depends on theinitial concentration of ascorbic acid. UV-Visible spectra of bimetallic Au–Pd nanoparticles suggest a core–shellstructure. A surface plasmon band around 520 nm indicates the formation of a gold layer on the surface ofpre-formed palladium nanoparticles, while the absence of this band when Au(III) and Pd(II) species are co-reduced indicates the formation of a palladium layer on a core of gold. Particle shape and size distributionwere assessed from transmission electron micrographs, whereas the average particle size was calculated fromimage analysis of these micrographs. For a fixed concentration of Au(III) species, the size distribution and aver-age size of gold nanoparticles depends on the ascorbic acid concentration. The synthesized Pd nanoparticlesexhibit flower-like shape.

KEYWORDS: Nanostructures, Chemical Synthesis, Nanoflowers, Bimetallic Nanoparticles.

1. INTRODUCTION

Nanoscience and nanotechnology have promoted an intenseresearch activity on the synthesis of nanoscale systemsmainly due to the promising applications that nanoparticleshave in fields such as medicine, biology, renewable energyconversion and electronics.1–6 Such applications are indeedimportant and can be commercialized, but prior to that thephysical and chemical properties must be assessed bothexperimentally and theoretically and the synthesis methodmust be controlled in order to obtain tailor-made nanopar-ticles. A number of techniques have been implemented tosynthesize nanomateriales with specific properties follow-ing chemical, physical or biological approaches.7–13 Spe-cial attention has been given to the synthesis of bimetallictransition and noble metal nanoparticles, in particularthose with a core–shell structure, because they occupy an

∗Author to whom correspondence should be addressed.Email: posada@cifus.uson.mxReceived: 3 August 2012Revised/Accepted: 15 December 2012

exceptional place in current research being important fora variety of potential applications from catalysts to hydro-gen storage devices2�5 to medical diagnostics due to thehigh sensitivity to detect very low concentration of cancerassociated carbohydrate antigens.3�14

Many chemical methods have been used in the synthesisof core–shell nanoparticles such as colloidal solutions andvapor deposition,3�5�15�16 usually starting from the reduc-tion of metal ions to metal atoms. In order to fabricatecore–shell nanoparticles many routes have been investi-gated, one of them is the polyol-mediated synthesis.17–21

Initially the polyol method was described for the prepa-ration of elemental metals and alloys,22–24 subsequently,transition and noble metal such as Au, Pt, Pd and Cu, werestudied on the nanoscale.1�8�12�14�16 Although polyol syn-thesis is a common method to prepare nanoparticles, it hasbeen reported5�15�25 that in most cases the degree of surfacecoverage obtained by these methods (polyol, vapor depo-sition) is low and the metallic coating is nonuniform. As aconsequence, new methods have been explored to preparenanomaterials. Accordingly, striking ecologically friendly

Adv. Sci. Eng. Med. 2013, Vol. 5, No. xx 2164-6627/2013/5/001/008 doi:10.1166/asem.2013.1354 1

Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles Rodríguez et al.

ARTIC

LEmethods have been invented, and recently, transition metalcore/noble metal shell nanoparticles were prepared byNadagouda and Varma25–27 fabricating metal nanocrystalsusing vitamin B2 and aqueous (vitamin C) ascorbic aciddue to its high water solubility, biodegradability, and lowtoxicity compared with other reducing agents, looking fora method that generates composite particles with a uni-form and complete coverage of metallic nanoshell. How-ever, the studies reported using ascorbic acid as reducingagent show no control over the size or polydispersity ofthe particles obtained.The aim of this research work was to synthesize and

control the chemical ordering as well as size distribu-tion, average size and morphology of gold and palladiumnanoparticles, and bimetallic gold-palladium nanoparticleswith a core–shell structure, from aqueous solutions ofAu(III) and Pd(II) species through a soft-chemistry greenmethod using ascorbic acid as a reducing agent. The syn-thesis route followed in this research also allows obtainingnanoparticles of peculiar structural characteristics, such asthe flower-like structures which are obtained for palladiumnanoparticles.

2. EXPERIMENTAL DETAILS

2.1. Materials

The sources of metal species were tetrachloroauric acidtrihydrate (HAuCl4 · 3H2O, 99%) and palladium chloride(PdCl2, 99%), both purchased from Aldrich. Ascorbic acid,purchased from Fischer Chemicals, was used as reduc-ing agent. These chemicals were reagent grade materialsand used as received. All aqueous solutions were preparedwith de-ionized water whose conductivity was 18.2 M�-cm after being treated in a Millipore system (Mili-Q).

2.2. Synthesis of Gold and Palladium Nanoparticles

In a typical synthesis, depending on the concentrationof ascorbic acid, 2 or 3 �L of an aqueous solution ofHAuCl4 · 3H2O or PdCl2 was added to 3 mL water ina glass vial, and the resulting solution was stirred witha vortex blender for about 5 seconds. Then, an aque-ous ascorbic acid solution was added and the system wasagain stirred with the vortex blender for about 15 seconds.At this time, samples for UV-Vis and transmission electronmicroscopy characterization were taken. All dispersions ofmetal nanoparticles were prepared open to the atmosphereand at 25 �C.

2.3. Synthesis of Gold-Palladium Nanoparticles

Gold-palladium nanoparticles were synthesized accordingto two different methods. One involved adding aqueoussolutions of HAuCl4 · 3H2O and PdCl2 to 3 mL waterand stirring this solution with a vortex blender for about

5 seconds. Then, aqueous ascorbic acid was added to thissolution and the system was again stirred with the vor-tex blender for about 15 seconds. In this synthesis, gold-palladium nanoparticles are formed upon co-reductionof Au(III) and Pd(II) species. Another synthesis methodinvolved successive reduction of the two metal precursorsas follows: after the aqueous solution of one metal pre-cursor was added to 3 mL water, this solution was stirredwith a vortex blender for about 5 seconds. Aqueous ascor-bic acid was then added and the system was again stirredduring 15 seconds, resulting in the formation of the corre-sponding metal nanoparticles. The second aqueous metal-lic precursor was added to this nanoparticles dispersionfollowed by another stirring period of 15 seconds.

2.4. Characterization

UV-Vis absorption spectra of aqueous dispersions ofmetallic nanoparticles were obtained with a Lambda 20Perkin-Elmer spectrophotometer using 1-cm path lengthquartz cuvettes and water as blank. Samples for obser-vation under transmission electron microscopy (TEM)were prepared over carbon-coated copper grids as follows.A drop of nanoparticles suspension was deposited onto thecopper grid and dried at room temperature. A JEOL JEM-2010F electron microscope operating at 200 kV was usedfor microscopy characterization. The size of ∼ 250 par-ticles was measured on enlarged micrographs, and thesedata were used to construct the corresponding histogramsand to obtain the average particle size.

3. RESULTS AND DISCUSSION

3.1. Gold Nanoparticles

Aqueous dispersions of gold nanoparticles exhibit signifi-cant differences in color (visible to the bare eye) depending

Fig. 1. UV-Vis absorption spectra of gold nanoparticles synthesizedfrom 0.06 mM HAuCl4 · 3H2O with four different initial concentrationsof ascorbic acid. (a) 0.5, (b) 3.3, (c) 16.6, and (d) 33.3 mM.

2 Adv. Sci. Eng. Med., 5, 1–8, 2013

Rodríguez et al. Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles

ARTIC

LE

on the concentration of ascorbic acid used to reduceAu(III) ions, whose solutions are pale yellow. With a highconcentration of the reducing agent the gold dispersion hasa ruby color, while for low concentrations the system hasa purple color.Figure 1 shows the UV-Vis absorption spectra of the

aqueous dispersions of gold nanoparticles synthesized

(c)

(b)

(a)

Fig. 2. Continue.

from 0.06 mM HAuCl4 ·3H2O and (a) 0.5, (b) 3.3, (c) 16.6,and (d) 33.3 mM of ascorbic acid, respectively. Thesespectra show the characteristic surface plasmon resonance(SPR) band of colloidal gold, but centered at differ-ent wavelengths depending on the amount of ascorbicacid used. For the lowest concentration of ascorbic acid(0.5 mM), the SPR band maximum is centered at around

Adv. Sci. Eng. Med., 5, 1–8, 2013 3

Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles Rodríguez et al.

ARTIC

LE

(d)

(e)

Fig. 2. Transmission electron micrographs of gold nanoparticles synthesized from two concentrations of aqueous tetrachloroauric acid with fourdifferent initial concentrations of ascorbic acid (AA). (a) 0.06 mM HAuCl4 + 0.5 mM AA, (b) 0.06 mM HAuCl4 + 3.3 mM AA, (c) 0.06 mMHAuCl4+16.6 mM AA, (d) 0.06 mM HAuCl4+33.3 mM AA, and (e) 0.06 mM HAuCl4+33.3 mM AA, and their corresponding histograms.

546 nm while for a concentration of 3.3 mM ascorbic acidthe maximum of the SPR band blue-shifts with respectto the previous one, and is centered at about 526 nm. Forthe highest concentration of ascorbic acid used (33.3 mM)the SPR band maximum is centered at 520 nm. The blueshift of the SPR band maximum has been related to adecrease in the average size of gold nanoparticles.28 Thesespectra also show that the bandwidth at half-maximumtends to decrease as the concentration of ascorbic acid usedincreases, indirectly indicating an increase in the monodis-persity of the gold nanoparticles population.The transmission electron micrographs presented in

Figures 2(a)–(d) correspond to gold nanoparticles synthe-sized from 0.06 mM HAuCl4 · 3H2O with four differentascorbic acid concentrations. They show that the shape ofgold nanoparticles prepared with high concentrations ofascorbic acid is more spherical and the nanoparticles arebetter dispersed than those prepared with low concentra-tions. The average size of these gold nanoparticles, cal-culated from the corresponding histograms also shown inFigure 2, was found to decrease as the concentration of

ascorbic acid increased: it is 7�5± 1�9 nm, 8�2± 1�8 nm,9�4± 2�5 nm and 17�5± 5�1 nm for 33.3 mM, 16.6 mM,3.3 mM, and 0.5 mM ascorbic acid, respectively. Theabsorption spectrum of gold nanoparticles with an aver-age size of 7.5 nm, presented in Figure 1(d) shows thatthe SPR band is centered at 520 nm. The histograms ofgold nanoparticles synthesized with a high concentrationof ascorbic acid show a narrow size distribution.Figure 2(e) presents the TEM image of Au nanoparticles

synthesized from 0.04 mM HAuCl4 ·3H2O using 33.3 mMascorbic acid concentration, and their corresponding his-togram. The shape of these nanoparticles is more sphericalthan that of the particles obtained from 0.06 mM HAuCl4 ·3H2O, and they are well dispersed. Their average particlesize is smaller (6�2±0�45 nm) and they present a narrowersize distribution.The initial concentration of tetrachloroauric acid and

ascorbic acid has been found to control the shape, aver-age size, and size distribution of gold nanoparticlessynthesized with this green method. For a fixed concentra-tion of 0.06 mM tetrachloroauric acid, large particles with

4 Adv. Sci. Eng. Med., 5, 1–8, 2013

Rodríguez et al. Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles

ARTIC

LE

Fig. 3. UV-Vis absorption spectrum of (a) aqueous Pd(II) ions and(b) Pd nanoparticles synthesized from 0.04 mM aqueous PdCl2 with0.33 mM ascorbic acid.

irregular shapes and high polydispersity are obtained withlow ascorbic acid concentrations while significantly smallernanoparticles with narrow size distribution and a tendencytowards spherical shapes are produced with high ascorbicacid concentrations. An excess of ascorbic acid moleculesin solution seems to speed up the reduction and nucleationprocesses resulting in more nuclei that consume all goldatoms. As a consequence, the growth period is reducedand this in turn produces smaller and more monodis-perse particles. Also, more ascorbic acid molecules pro-vide greater protection for preventing nanoparticles togrow by sintering.

3.2. Palladium Nanoparticles

Figure 3 shows the UV-Vis absorption spectra of (a) aque-ous Pd(II) ions and (b) Pd nanoparticles synthesized from

Fig. 4. Transmission electron micrograph of Pd nanoparticles synthesized from 0.04 mM aqueous PdCl2 with 33.3 mM initial ascorbic acid, andtheir corresponding histogram.

0.04 mM aqueous PdCl2 with 33.3 mM ascorbic acidadded. An increase in the background of spectrum (b)indicates the presence of palladium nanoparticles,29 whosecolloidal dispersion exhibits a slightly pale brown-greycolor. Because the optical response of palladium nanopar-ticles only shows a small band in the UV region, around280 nm,30 which is hidden by the intense signal of ascorbicacid in this region of the spectrum, colloidal dispersionsof palladium nanoparticles synthesized with ascorbic aciddo not exhibit a well-defined absorption band.Figure 4 presents the TEM image and the corresponding

histogram for Pd nanoparticles synthesized from 0.04 mMaqueous PdCl2 with 33.3 mM ascorbic acid added. Thismicrograph clearly shows that these Pd nanoparticlesaggregate in flower-like clusters of about 20 to 40 nm,but they do not coalescence and remain as monodisperseindividual entities with an average diameter of 4�75±1�09 nm. In other works it has been obtained flower-likePd clusters,31�32 in some cases exhibiting 1-D necklace-type structures as a result of their synthesis method, con-trasting with ours were individual nanoflower structures arepresent. It is worth mentioning that flower-like Pd nanopar-ticles can be used as substrates for surface enhanced Ramanscattering.33 It is important to notice that this flower-likepattern has been observed in studies of nanoparticles pre-pared with other chemical elements, such as cobalt,34

which make our methodology attractive to be used in thesynthesis of a number of new nanomaterials with potentialtechnological applications, for example in pharmaceuticalindustry.

3.3. AucorePdshell Nanoparticles

Figure 5(b) presents the absorption spectrum of bimetal-lic gold-palladium nanoparticles synthesized when ascor-bic acid is added to a solution of tetrachloroauric acid andpalladium chloride. Because this spectrum shows no bands

Adv. Sci. Eng. Med., 5, 1–8, 2013 5

Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles Rodríguez et al.

ARTIC

LE

Fig. 5. UV-Vis absorption spectra of (a) palladium nanoparticles, (b)Aucore–Pdshell nanoparticles, (c) Pdcore–Aushell nanoparticles, and (d) goldnanoparticles.

in the visible region and is similar to the spectrum ofPd nanoparticles, it suggests that gold atoms are confinedin the interior (core) of the formed nanoparticles whereaspalladium atoms are on the surface (shell). The synthe-sis of these bimetallic nanoparticles was achieved uponco-reduction of aqueous Au(III) and Pd(II) species withascorbic acid. The initial pale-yellow color of the aqueousAu(III)–Pd(II) solution turns to brown-grey upon the addi-tion of ascorbic acid indicating the reduction of these ionsand the formation of metallic nanoparticles.The formation of this AucorePdshell nanostructure may

be explained if one considers that the standard reductionpotential for the reaction [AuCl4]

−/Au0 (0.994 V) is morepositive than the standard reduction potential for the cou-ple Pd2+/Pd0 (0.83 V). This means that the reduction of[AuCl4]

− is more favorable than that of Pd(II) ions. There-fore, Au(III) species are reduced first by ascorbic acid,

Fig. 6. Transmission electron micrograph of Au@Pd bimetallic nanoparticles synthesized from the co-reduction of aqueous 0.04 mM tetrachloroauricacid and 0.04 mM PdCl2 with 33.3 mM initial ascorbic acid, and their corresponding histogram.

Au atoms nucleate and form Au nuclei, and then Pd2+

ions are reduced by ascorbic acid and Pd atoms nucleateon the already formed Au nuclei to form the Pd shell.Because the absorption spectrum of this type of bimetallicnanoparticles clearly and undoubtedly shows no Au SPRband, co-reduction of Au(III) and Pd(II) species by ascor-bic acid does not lead to the formation of a mixture ofmonometallic Pd and Au nanoparticles.Figure 6 presents a TEM image of AucorePdshell nanopar-

ticles synthesized by co-reduction of aqueous Au(III) andPd(II) species upon the addition of ascorbic acid, and theircorresponding histogram. This micrograph clearly showswell dispersed nanoparticles with a tendency towards aspherical shape. The average diameter of these nanoparti-cles was calculated to be 7�9±1�6 nm.

3.4. PdcoreAushell Nanoparticles

The absorption spectrum of bimetallic gold-palladiumnanoparticles synthesized by reduction of aqueous Pd(II)species with ascorbic acid, which results in the formationof palladium nanoparticles, and then adding an aqueoussolution of tetrachloroauric acid is shown in Figure 5(c).This spectrum clearly shows an absorption band in the vis-ible region whose maximum is centered at 525 nm verysimilar to the absorption spectrum of gold nanoparticlesalso shown in Figure 5 (spectrum d). These results sug-gest that in this green-synthesis the reduction of aque-ous Au(III) ions and nucleation of gold atoms on thealready formed palladium nanoparticles results in the for-mation of nanoparticles with a palladium core and a goldshell structure. In this system, the pale-yellow color ofthe Pd ions aqueous solution turns to brown-grey afterthe addition of ascorbic acid, indicating the reduction ofPd ions and formation of Pd nanoparticles. After addingthe solution of tetrachloroauric ions to the dispersion ofpalladium nanoparticles, it immediately became reddish

6 Adv. Sci. Eng. Med., 5, 1–8, 2013

Rodríguez et al. Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles

ARTIC

LE

Fig. 7. Transmission electron micrograph of Pd@Au bimetallic nanoparticles synthesized from 0.04 mM aqueous tetrachloroauric acid added intoalready formed palladium nanoparticles using 33.3 mM initial ascorbic acid, and their corresponding histogram.

Table I. The concentration of metal precursor and reducing agent (AA),position of the absorption band maximum, average diameter (Dm�, andstandard deviation (�� of the Au, Pd and Au–Pd bimetallic nanoparticlessynthesized in this research work.

AA HAuCl4 PdCl2 SPR Dm �

Sample [mM] [mM] [mM] (nm) (nm) (nm)

a 0�5 0�06 – 546 17�50 5�10b 3�3 0�06 – 526 9�40 2�50c 16�6 0�06 – 522 8�20 1�80d 33�3 0�06 – 520 7�50 1�90e 33�3 0�04 – 520 6�20 0�45f 33�3 – 0�04 – 4�70 1�09g 33�3 0�04 0�04 – 7�90 1�60h 33�3 0�04 0�04 525 7�20 1�50

indicating the reduction of gold ions and formation ofgold atoms. Figure 7 presents a TEM image of thesePdcoreAushell nanoparticles and their corresponding his-togram. This image shows a population of nanoparticlesmore spherical than the AucorePdshell type, and also welldispersed. The calculated average size of these PdcoreAushellnanoparticles is 7�2±1�5 nm. Table I presents the concen-tration of metal precursor and ascorbic acid, the positionof the surface Plasmon band, the average particle size andthe standard deviation of gold and palladium nanoparticlesas well as bimetallic gold-palladium nanoparticles.

4. CONCLUSIONS

Ascorbic acid functions as a good reducing agent foraqueous Au(III) and Pd(II) species, which leads to theformation of metallic nanoparticles at 25 �C. This green-chemical method allows the synthesis of gold, palladiumand bimetallic gold-palladium nanoparticles. Co-reductionof Au(III) and Pd(II) species as well as reduction ofAu(III) species on already formed palladium nanoparticlesresults in the formation of bimetallic Au–Pd nanoparticles

with a core–shell structure. This nanostructure was indi-rectly deduced from the absorption spectra of gold-palladium nanoparticles. Gold and palladium nanoparticleswith a narrow size distribution of ∼6- and 5 nm, respec-tively, were obtained after finding an optimum additionof ascorbic acid. A judicious methodology also allowedsynthesizing AucorePdshell and PdcoreAushell nanoparticlesexhibiting spherical symmetry with a diameter in the sizerange of 7–8 nm. These results indicate that monodis-perse and discrete gold and palladium nanoparticles aswell as bimetallic gold-palladium nanoparticles are pro-duced with high ascorbic acid concentrations, which pro-vides nanoparticles with a protective molecular overlayerthat prevents sintering during particle growth. Some ofthe factors governing nanoparticles growth under the low-cost, simple, green chemistry method described here havebeen determined, information invaluable to control synthe-sis of gold, palladium and gold-palladium nanoparticlesof well-defined size and shape, significant characteristicsin technological applications of nanomaterials. Advancedfunctional nanomaterials, such as hybrid architectures withoutstanding photocatalytic properties,35 might be producedfollowing a scheme similar to the presented here.

Acknowledgments: Alvaro Posada-Amarillas is grate-ful to CONACYT for financial support through project24060.

References and Notes

1. G. Menagen, J. E. Macdonald, Y. Shemesh, I. Popov, and U. Banin,J. Am. Chem. Soc. 131, 17406 (2009).

2. G. A. Somorjai, H. Frei, and J. Y. Park, J. Am. Chem. Soc.131, 16589 (2009).

3. N. Sounderya and Y. Zhang, Recent Patents on Biomedical Engi-neering 1, 34 (2008).

4. C. Y. Huang and Y. D. Lee, Int. J. Pharm. 325, 132 (2006).5. C. Burda, X. Chen, R. Narayanan, and M. A. El-Sayed, Chem. Rev.

105, 1025 (2005).

Adv. Sci. Eng. Med., 5, 1–8, 2013 7

Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles Rodríguez et al.

ARTIC

LE6. A. P. Alivisatos, Science 271, 933 (1996).7. Z. Yang, Z. H. Lin, C. Y. Tang, and H. T. Chang, Nanotechnology

18, 255606 (2007).8. T. Ming, W. Feng, Q. Tang, F. Wang, L. Sun, J. Wang, and C. Yan,

J. Am. Chem. Soc. 131, 16350 (2009).9. Y. Xu, N. Al-Salim, C. W. Bumby, and R. D. Tilley, J. Am. Chem.

Soc. 131, 15990 (2009).10. S. Wang, L. A. Tang, Q. Bao, M. Lin, S. Deng, B. M. Goh, and

K. P. Loh, J. Am. Chem. Soc. 131, 16832 (2009).11. K. J. Rao, K. Mahesh, and S. Kumar, Bull. Mater. Sci. 28, 19 (2005).12. Z. H. Lin and H. T. Chang, Langmuir 24, 365 (2008).13. C. Chen, L. Wang, G. Jiang, and H. Yu, Rev. Adv. Mater. Sci. 11, 1

(2006).14. C. H. Liang, C. C. Wang, Y. C. Lin, C. H. Chen, C. H. Wong, and

C. Y. Wu, Anal. Chem. 81, 7750 (2009).15. S.D. Perrault andW.C.W.Chan, J. Am.Chem. Soc. 131, 17042 (2009).16. Y. W. Lee, M. Kim, Z. H. Kim, and S. W. Han, J. Am. Chem. Soc.

131, 17036 (2009).17. K. Nagaveni, A. Gayen, G. N. Subbanna, and M. S. Hegde, J. Mater.

Chem. 12, 3147 (2002).18. V. Tzitzios, D. Niarchos, G. Margariti, J. Fidler, and D. Petridis,

Nanotechnology 16, 287 (2005).19. J. Bregado-Gutiérrez, A. J. Saldívar-García, and H. F. López, J. Appl.

Polym. Sci. 107, 45 (2008).20. P. Ragupathy, S. Shivakumara, H. N. Vasan, and N. Munichandraiah,

J. Phys. Chem. C 112, 16700 (2008).

21. O. Palchik, R. Kerner, A. Gedanken, A. M. Weiss, M. A. Slifkin,and V. Palchik, J. Mater. Chem. 11, 874 (2001).

22. L. K. Kurihara, G. M. Chow, and P. E. Schoen, Nanostruct. Mater.5, 607 (1995).

23. P. Y. Silvert, R. Herrera-Urbina, and K. T. Elhsisssen, J. Mater.Chem. 7, 293 (1997).

24. C. Feldmann, Scripta Mater. 44, 2193 (2001).25. M. N. Nadagouda and R. S. Varma, Green Chem. 8, 516

(2006).26. M. N. Nadagouda and R. S. Varma, Cryst. Growth Des. 7, 2582

(2007).27. M. N. Nadagouda and R. S. Varma, J. Nanomater. 8 (2008).28. P. Mulvaney, Langmuir 12, 788 (1996).29. C. Kan, W. Cai, C. Li, L. Zhang, and H. Hofmmeister, J. Phys. D

36, 1609 (2003).30. E. Larios, L. Calderón, K. Guerrero, E. Pinedo, A. Maldonado, and

J. Tánori, J. Disp. Sci. Technol. 33, 719 (2012).31. M. S. Bakshi, J. Phys. Chem. C 113, 10921 (2009).32. T. Redjala, G. Apostolecu, P. Beaunier, M. Mostafavi, A. Etcheberry,

D. Uzio, C. Thomazeau, and H. Remita, New J. Chem. 32, 1403(2008).

33. Y. Li, G. Lu, X. Wu, and G. Shi, J. Phys. Chem. B 110, 24585(2006).

34. S. Senapati, S. K. Srivastava, and S. B. Singh, J. Nanosci. Nano-technol. 12, 3048 (2012).

35. S. Yang and H. Zeng, Adv. Sci. Mat. 4, 449 (2012).

8 Adv. Sci. Eng. Med., 5, 1–8, 2013