Paper 1

This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012 New J. Chem., 2012, 36, 155–160 155

Cite this: New J. Chem., 2012, 36, 155–160

Synthesis of metal–carbon core–shell nanoparticles by RAPET

(Reaction under Autogenic Pressure at Elevated Temperatures)w

Evgeny Butovsky, Alexander Irzh, Boris Markovsky and Aharon Gedanken*

Received (in Montpellier, France) 18th July 2011, Accepted 25th October 2011

DOI: 10.1039/c1nj20627c

We present herein a method to produce metal–carbon core–shell nanoparticles by dissociating

the corresponding metal acetates under their autogenic pressure at elevated temperatures.

The reaction is a one-stage, solvent-free, catalyst-free, competent, and a very cheap way

for the synthesis of metal@carbon nanoparticles with a core–shell structure. The morphology,

air-stability, structure, and other properties of the as-prepared Ag@C, Cu@C and Pb@C

nanoparticles are demonstrated in this paper. We also provide a criterion for those metals whose

acetates would yield metal@carbon structures, as opposed to those metals whose acetates would

yield MO@C as the final product.

Introduction

Nanoparticles have found widespread applications in various

fields of engineering. The synthesis of nanomaterials is the

subject of the current research due to their variety of structures,

interesting properties, as well as technological applications in

electronics, catalysis, chemical engineering, pharmaceutics, biology,

magnetic recording, etc.1,2

Core/shell nanoparticles are nanostructures that have a core

made of a material coated with another material. Materials are

coated for a number of reasons: coatings can make a substance

biocompatible, increase a material’s thermal, mechanical or

chemical stability, increase its durability, lifetime, decrease

friction or inhibit corrosion, avoid aggregation, prevent the

spreading of the nanoparticles to the environment, and they

may change the overall physicochemical properties of the

material. The applications of encapsulated metallic nano-

and micro-structures range from catalysis, purification of

water wells, food additives,3–5 fuel amplifiers,6 electronic

devices, as well as the field of energy storage and conversion.

One of the main challenges in coating substrates is to achieve a

homogeneous layer of the organic/inorganic material without

the formation of excess nanoparticles in the nanocomposite.

The interest in nanocoatings relies mostly on the combination

of the properties of the two (or more) materials involved. An

important feature here is that one of the materials (the shell)

will determine the surface properties of the particles, while the

other (the core) is completely encapsulated by the shell so that

it does not contribute to surface properties at all, but can be

mainly responsible for other (optical, catalytic, magnetic, etc.)

properties of the system. Apart from this extremely important

feature, it is also essential to take into account the possible

interactions between the core and the shell, which may in

certain cases determine the potential applications of the

material. Specifically in energy devices, carbon-based materials

have been added with the active materials in order to improve the

electrical, electrochemical and electrocatalytic properties. Taking

into account the unique combination of properties achieved by

core–shell geometry, we have demonstrated the important role of

in situ-formed amorphous carbon shells in the properties of

various metals.

There are various methods for the formation of nanoparticles

with core–shell structures; sonochemistry,7,8 electrochemistry,9

ammonia catalysis,10 and laser-induced fusion,11 amongst others.

Several reports on the formation of core–shell nanostructures of

transition metals have already been published.12–16 For example,

Tang et al.14 used a MW-assisted method17 to prepare Ag–C

core–shell particles. The size distribution of particles obtained by

this method is wide, namely, ranging from 200 to 800 nm. The

typical diameter is 660 nm. In the work of L. S. Wang et al.15

Ag-core/C-shell nanocables were synthesized via a hydrogen arc

method.15,18 This structure was formed under H2 pressure, a

current of 100 A, and a voltage of 25 V. The method of L.-B.

Luo et al.16 allows the achievement of a silver@carbon-rich

composite by a preparation method that took several days. The

RAPET method is a novel, one-step, solvent-free and very simple

technique for the fabrication of spherical core–shell nano-

particles.17,18 The chemical dissociation and transformation

reaction takes place under the autogenic pressure of the precursor

at a certain temperature, followed by the gradual cooling of the

reactor to room temperature. Herein we report on obtaining

Ag@C, Cu@C, and Pb@C from the corresponding acetates

Department of Chemistry and Kanbar Laboratory for Nanomaterials,the Bar-Ilan University Center for Advanced Materials andNanotechnology, Bar-Ilan University, Ramat-Gan 52900, Israel.E-mail: [email protected]; Fax: +972-3-738-4053w Electronic supplementary information (ESI) available. See DOI:10.1039/c1nj20627c

NJC Dynamic Article Links

www.rsc.org/njc PAPER

Dow

nloa

ded

on 2

6 Ju

ly 2

012

Publ

ishe

d on

17

Nov

embe

r 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C1N

J206

27C

View Online / Journal Homepage / Table of Contents for this issue

156 New J. Chem., 2012, 36, 155–160 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012

using the RAPET method. The current results are compared with

previousmetal@carbon products resulting from the decomposition

of various metal–organic compounds yielding also metal

cores coated by carbon.17–22 The RAPET was conducted at

high temperatures (700–1000 1C); however, the decomposition

mechanism involves several stages. The decomposition of silver,

copper and lead acetates occurs at 150–250 1C.17,18,21 All three

acetates decompose into their corresponding oxides, which are

further reduced by carbon monoxide to the metallic state, as

proposed elsewhere.23–26 Ag@C and Cu@C were found to remain

stable over a long time, whereas Pb tends to oxidize after one day

under ambient conditions. Unlike the acetates of the noble metals,

the acetates of the stronger metals (e.g., Zn and Mg) yield a metal

oxide/carbon core/shell structure. We therefore propose a

‘‘RAPET Rule’’ that relates the standard reduction potential of

the metal in the acetate salt to the nature of the final product

(metal or metal oxide).

Experimental setup

Synthesis

All the precursors, silver acetate (99% purity), copper(II)

acetate (98% purity), and lead (IV) acetate (95% purity) were

purchased from Sigma Aldrich and used as received, without

further purification. Each material was inserted into a cell

assembled from stainless steel Swagelok parts. A ‘‘1/2’’ union

part was capped from both sides by standard plugs (Fig. 1).

The volume of the cell was 4.3 ml. For these reactions, 0.3 g

(1.80 � 10�3 mol) of silver acetate, 3.41 g (18.77 � 10�3 mol)

of copper acetate and 4.3 g (9.70 � 10�3 mol) of lead acetate

were inserted separately into the cell at room temperature

under nitrogen in a glove box. In addition, experiments were

carried out with a large amount of precursors (1.5 g of silver

acetate, 7.8 g of copper acetate and 8.5 g of lead acetate) for

checking the influence of material quantity on the morphology.

The results are shown below.

The filled cell was closed and placed inside an iron pipe in

the middle of the furnace. The temperature of the furnace was

raised to 850 1C at a rate of 10 1C min�1. The cell was kept at

850 1C for three hours. At the end of the reaction, the

Swagelok was cooled to room temperature, opened, and the

black powders of Ag@C (0.205 g, 68.1% yield), Cu@C (1.173 g,

34.4% yield) and Pb@C (1.989 g, 45.6% yield) were obtained.

The yields of the obtained materials are very close to the

weight percentage of metal atoms in the metal-acetate salts

(64.7% Ag in silver acetate, 34.9% Cu in copper(II) acetate

and 46.7% Pb in lead(IV) acetate). This indicates that the main

component remaining at the end of the RAPET reaction is the

metallic core, and most of the C, H, and O in the acetates are

released as hydrocarbon gases, CO, and CO2. This result is

further substantiated by the C, H, N, O and TGA analysis

shown below. The weight percentage of carbon in all obtained

M@C materials is less than 13%, and therefore the good

correlation between the yields and the weight percentage

of metals in the M@C structures is very reasonable. The

morphological and crystal structure characteristics, elemental

content, stability at high temperature and other properties of

the above materials are presented in the Results and Discussion

section.

Characterization

To probe the nature of the product and the purity of its crystal

structure, the X-ray diffraction patterns were measured with a

Bruker AXS D* Advance powder X-Ray diffractometer, Cu–Karadiation, wavelength: 1.5406 A was used. To determine the

content of the C, H, and O in all the products, elemental analysis

was carried out employing an Eager 200 C, H, N analyzer and an

EA1110 Oxygen analyzer. The morphologies and nanostructures

of the as-prepared products were characterized with a Scanning

Electron Microscope (SEM) Model JSM-840, a Transmission

Electron Microscope (TEM) Model JEM-1200EX and a High

Resolution TEM Model JEOL-2010, working at acceleration

voltages of 80 (TEM) and 200 KeV (HRTEM). Samples for

TEM and HRTEM were prepared by ultrasonically dispersing

the products in isopropanol, by placing a drop of this suspension

onto a copper grid (for Ag and Pb) and a gold grid (for Cu)

coated with an amorphous carbon film, and then drying under

air. The study of thermal decomposition of these three precursors

(Ag, Pb and Cu acetates) and products was performed with a

TGAQ500 instrument (TA Instruments, USA) with the following

parameters: heating rate 10 1Cmin�1, nitrogen flow 120mlmin�1,

sample mass about 4–10 mg. Raman spectroscopy was used to

define the nature of the carbon that forms the shell in the

metal@carbon composite for all three metals. An Olympus

BX41 (Jobin Yvon Horiba) Raman spectrometer was employed,

using the 514.5-nm line of an Ar laser as the excitation source. The

impedance of the core–shell Ag@C material was measured at a

frequency range of 50 kHz–500 Hz using a frequency response

analyzer model-1255 from Solartron, Inc. driven by ZPlot soft-

ware (Scribner Associates, Inc.). The results obtained at 301 and

60 1C are presented in the form of Z0, (-Z0 0)-plots (Z0 and -Z0 0 are

real and imaginary parts of the complex impedance). For these

measurements, a pellet made from the Ag@Cmaterial (B1 cm in

diameter, the density of pellet is 4.75 gr cm�3, the pressure applied

for pelletizing was 5 tsi) was placed between two polished stainless

steel discs and mounted in the parts of the 2325 coin-type cell

(from NRC, Canada). For comparison, similar impedance

measurements were performed with silver nano-sized particles of

around 50 nm, at 30 1C. These silver nanoparticles were synthe-

sized in our lab. All the measurements were carried out in a

thermostat. Fig. 1S (in ESIw) shows the SEM micrographs of the

pellet. The broken pellet was also analyzed by SEM, and the

picture was taken at 90 degrees. Particles’ size ranges from tens of

nanometres to few microns.Fig. 1 An overview of Swagelok used for the RAPET reaction.

Dow

nloa

ded

on 2

6 Ju

ly 2

012

Publ

ishe

d on

17

Nov

embe

r 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C1N

J206

27C

View Online

This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012 New J. Chem., 2012, 36, 155–160 157

Results and discussion

In this section we present results related to the different metal

acetates that produce particles with a core–shell structure of

the metal coated with carbon.

Morphology (SEM and HR-TEM analysis)

The transmission electron micrographs at high resolution of

all the products are shown in Fig. 2.

Fig. 2 presents a part of spherical metallic particles (dark

areas) of Ag, Cu and Pb coated by the carbon shell (brighter

areas). Moreover, Fig. 2a and b depict the perfect arrangement

of atomic layers of Ag and Cu that can also prove their

crystallinity that is covered by an amorphous or graphitic

carbon layer. Fig. 2c shows Pb@C nanostructures with a

lower magnification than that of Ag@C and Cu@C because

the electron beam of TEM can melt Pb particles due to their

low melting point (327 1C). The diameter of the Ag@C (a)

particles is in the 50–150 nm range (the thickness of the carbon

shell is in the range of 5–15 nm), while the range for the Cu@C

(b) particles is 50–200 nm (the thickness of the shells is in the

range of 10–20 nm). The size of the Pb@C (c) particles is

50–400 nm (the shells are in the range of 0–50 nm).

Fig. 2S(a)–(c) (ESIw) show aggregates that are obtained in

experiments with a large quantity of the precursor. In this case

the autogenic pressure that was created in the cell is higher and

aggregated particles were obtained.

Fig. 3 shows the SEM image of the obtained particles and

illustrates that most of the products have a spherical shape.

Their sizes vary between 10 nm and 500 nm, similar to the

results obtained from TEM measurements. The picture shows

the mode of aggregation. While the spherical contour of the

particles is well observed for the silver and lead agglomerates,

flat surfaces, and even hexagonal shapes are observed for the

Cu@C products. A transparent shell surrounds the lead cores

in Fig. 3c, emphasizing the core–shell nature of the product.

XRD

Fig. 4 shows the XRD patterns of the as-prepared powders of

Ag@C, Cu@C, Pb@C (measured immediately after the reac-

tion), as well as the XRD pattern of Pb@C obtained after the

sample was kept under ambient conditions for one day. The

last pattern reveals that PbO is obtained after one day under

ambient conditions, while the Ag@C, Cu@C are unchanged,

even after longer exposure to ambient conditions. All the

diffraction peaks can be assigned to metallic silver, metallic

copper, metallic lead or lead oxide, and no diffraction peaks

due to impurities can be detected. The XRD pattern of the

as-prepared Ag@C core–shell particles is presented in Fig. 4a.

The diffraction peaks observed at 2y = 38.121, 44.311, 64.461

and 77.411 are assigned as (111), (200), (220) and (311) crystal

planes of the face-centered cubic phase of Ag (space group:

Fm%3m). The peak positions match the PDF file for Ag

Fig. 2 Transmission electron micrographs of (a) Ag@C, (b) Cu@C and (c) Pb@C core–shell nanoparticles at high resolution.

Fig. 3 Scanning electron micrographs of (a) Ag@C, (b) Cu@C and (c) Pb@C core–shell nanoparticles.

Dow

nloa

ded

on 2

6 Ju

ly 2

012

Publ

ishe

d on

17

Nov

embe

r 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C1N

J206

27C

View Online

158 New J. Chem., 2012, 36, 155–160 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012

(PDF: 01-089-3722). The XRD pattern of the as-prepared

Cu@C core–shell particles is presented in Fig. 4b. The diffrac-

tion peaks observed at 2y = 43.321, 50.451 and 74.131 are

assigned as (111), (200) and (220) crystal planes of the face-

centered cubic phase of Cu (space group: Fm%3m). The peak

position matches the PDF file for Cu (PDF: 01-085-1326). The

XRD pattern of the as-prepared Pb@C core–shell particles is

presented in Fig. 4c. The diffraction peaks observed at 2y =

31.281, 36.271, 52.231, 62.161 and 65.251 are assigned as (111),

(200), (220), (311) and (222) crystal planes of the face-centered

cubic phase of Pb (space group: Fm%3m). The peak position

matches the PDF file for Pb (PDF: 03-065-2873). All the

products were checked again by XRD after aging under an

ambient atmosphere for a certain time period (from one day to

a week). Some lead particles were oxidized, and Fig. 4d shows

the reflections of both lead and lead oxide. The diffraction

peaks of lead oxide observed at 2y = 28.631, 31.831, 35.741,

48.601 and 54.761 are assigned as (101), (110), (002), (112) and

(211) crystal planes of the tetragonal phase of PbO (space

group: P%4nmm). These values are in good agreement with the

diffraction peaks, peak intensities and cell parameters of

crystalline PbO (PDF: 00-005-0561). Relative to the crystal-

linity of the metals the carbon material is amorphous as

revealed in the XRD patterns. But when the y-axis is magnified

and viewed, in the range of 0–500 a.u. we can see a broad peak in

the 2y range of 24–321 which is typical of amorphous carbon.

This peak is detected as shown in Fig. 4a0–c04.

C, H, N, O and TGA analysis

The carbon, hydrogen, nitrogen and oxygen contents in the

products are determined by elemental analysis measurements

(Table 1). The weight percentages of carbon in Ag@C, Pb@C

and Cu@C core–shell nanoparticles are 4.16, 7.48 and 12.63,

of hydrogen 0.02, 0.09 and 0.15, and of oxygen 1.74, 4.93 and

0.30, respectively. The results of the TGA measurements

conducted under air of all the products allow us to probe

their stability at high temperatures.

The results are shown in Fig. 5.

A weight loss of B4% was detected for the Ag@C

core–shell structure at a temperature range of 25–350 1C. This

percentage is approximately the amount of carbon in the

product, and the weight loss is due to carbon combustion.

The constant mass of the Ag@C at 350 1C to 800 1C indicates

that perhaps a thin layer of silver oxide is preventing further

oxidation which would have increased the weight. This layer

also prevents the combustion of the carbon, which would have

resulted in a weight loss. The remaining metal weight at 800 1C

fits well the number in Table 1. TGA analysis of Cu@C

particles shows a weight increase of 10% in air. The maximum

weight increase is reached at 500 1C and remains constant at

higher temperatures. The increase in weight is apparently due

to the formation of CuO. If all the copper would have been

Fig. 4 XRD patterns of (a) Ag, (b) Cu, (c) Pb nanoparticles measured immediately after annealing at 850 1C for 3 hours, and (d) Pb sample

presented in 4c left to age for one day under ambient conditions. a0, b0 and c0 represent the presence of amorphous carbon.

Table 1 The weight percentages of metal, carbon, hydrogen andoxygen in Ag@C, Pb@C and Cu@C samples obtained from theelemental analysis

Sample name %C %H %O %Metal

Ag@C 4.16 0.02 1.74 94.08Pb@C 7.48 0.09 4.93 87.50Cu@C 12.63 0.15 0.30 86.92

Fig. 5 Thermal decomposition curves of Ag@C, Pb@Cand Cu@C in air.

Dow

nloa

ded

on 2

6 Ju

ly 2

012

Publ

ishe

d on

17

Nov

embe

r 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C1N

J206

27C

View Online

This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012 New J. Chem., 2012, 36, 155–160 159

oxidized, an increase of about 9% is expected, which is close to

the detected weight gain. Combustion of carbon leading to the

formation of CO2 occurs as well, as indicated by the TGA

measurement coupled to mass-spectrometry (see picture 3S in

ESIw). Pb@C was also measured by TGA a few days after the

material was prepared and stored under ambient environment.

During this storage period, the composite was oxidized, and

therefore the examined sample by TGA analysis was PbO@C

rather than Pb@C. PbO@C particles showed a weight

decrease at 25–400 1C due to carbon combustion. The weight

percentage of the material at 400–800 1C was B92% of the

starting weight of the PbO@C particles and is in good

agreement with total PbO percentages at C, H, N and O

measurements (B92%, see Table 1).

Raman measurement

Fig. 6 presents the Raman spectrum and shows two peaks

related to carbon at 1332 cm�1 and 1597 cm�1 (D and G

bands, respectively). The G band is related to graphitic carbon

and the D band to disordered carbon.

Impedance measurements

In Fig. 7a, we present Z0, (-Z0 0)-plots obtained from the Ag@C

material at 301 and 60 1C. The results of three measurements

at each temperature during several hours demonstrate a

sufficient reproducibility. We can conclude that the impedance

of the material is slightly dependent on the frequency. As

expected, the impedance of the core–shell Ag@C material at

the elevated temperature (60 1C) is lower than at 30 1C

(B0.18 Ohm vs. B0.28 Ohm, respectively, in the frequency

range of 2.5 kHz–500 Hz). Fig. 7b is a Z0, (-Z0 0)-plot measured

for silver nanoparticles at 30 1C (from the as-prepared pellet)

after 3 and 72 hours. The impedance of the Ag nanoparticles

does not depend upon the frequency, but increases substan-

tially with aging time, indicating some possible reactions of the

nanoparticles and the formation of the surface species due to

adsorbed water and oxygen.27 From the results obtained we

conclude that the Ag@C core–shell material synthesized in

this work possesses low impedance comparable with that of

the nano-Ag particles (around 0.2–0.23 Ohm, Fig. 7b). We

also suggest that the stable impedance of the Ag@C particles

at both temperatures is related, to some extent, to the protective

properties of the carbon shell that may prevent reactions of the

metal core in air.

RAPET rule

All the transition metal acetates in the current study under-

went thermal decomposition in the RAPET system. As a

result, carbon-coated Ag, Cu and Pb nanoparticles are

obtained. For all three acetates their thermal decomposition

takes place at temperatures of 150–300 1C.17,18,21 As explained

above, the metal oxides are intermediates that are further

reduced by CO to form the zero valent metals. Later on the

metals form the core because of their higher solidification rate

than carbon, and carbon forms the shell layer.17 This mechanism

was published in previous studies17,27,28 based on TGA and MS

analysis and is as follows:

M(CH3COO)2 - MCO3 + CH3COCH3 (1)

MCO3 - MO + CO2 (2)

CH3COCH3 - CO + C2H6 (3)

MO + CO - M + CO2 (40)

2CO - CO2 + C (40 0)

where M = Ag, Cu or Pb. Stoichiometric relationships vary

according to the metal. Reactions (1)–(3) occur at 250–350 1C.

Reaction (40) takes place at all the temperature ranges but

becomes more kinetically and thermodynamically favorable

with an increase in temperature. The value of the Gibbs free

energy of reaction (40 0) is negative at temperatures below

700 1C. Therefore, at temperatures higher than 700 1C, theFig. 6 Raman spectrum of all the three materials.

Fig. 7 (a) Resistance plots of the core–shell Ag@Cmaterial measured at 30 1C and 60 1C. (b) Resistance plots of the nano-Ag particles measured

at 30 1C initially and after 3 and 72 hours.

Dow

nloa

ded

on 2

6 Ju

ly 2

012

Publ

ishe

d on

17

Nov

embe

r 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C1N

J206

27C

View Online

160 New J. Chem., 2012, 36, 155–160 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012

only occurring reaction is 40. When the reaction system is

cooled (in the end of the reaction), the carbon shell is formed

around the metallic particles (core) at temperatures below

700 1C. The cooling reduced the solubility of the carbon in

the metal and the carbon phase is separated from the metal

forming a ring around the core. In previous17 and current

works of our research group, the following results were

recorded: metals with a reduction potential lower than

�0.4 V generated their corresponding oxides as core, and

metals with a reduction potential higher than �0.4 V reached

their metallic form. The values of free energy DG0 for each

metal are calculated to form the respective metals from the

corresponding oxide in the presence of carbon monoxide. The

results are shown in Table 2.

The positive values of free energy for Fe and Zn support our

assumption that thermodynamically, the reduction to the

corresponding metallic state is not favorable for these metals;

therefore the results of the RAPET reactions for these metals

(Fe and Zn) are the corresponding oxides. We called this

regularity the ‘‘RAPET Rule’’—stating that the acetates of

strong metals like the alkali, alkaline earth, rare earth metals

with a reduction potential lower than �0.4 V would form a

core–shell structure composed of a metal oxide core. The

acetates of the noble metals, as well as metals with a standard

reduction potential larger than �0.4 V, will yield a product

having a metal as a core.

Conclusions

RAPET is a method developed in our research group. It has

many outstanding advantages; this non-aqueous, template-,

surfactant-, catalyst- and solvent-free method allows us to

synthesize metal–carbon core–shell nanoparticles. In the study

of the RAPET of metal acetates, we have demonstrated a

direct relation between the reduction potential of the metal

and the product obtained from the reaction. The ‘‘RAPET

rule’’ enables us to predict accurately which product will be

obtained—metal or metal oxide coated by carbon.

Notes and references

1 N. Sounderya and Y. Zhang, Recent Pat. Biomed. Eng., 2008, 1,34–42.

2 R. C. Merkle, ‘‘Nanotechnology is coming’’, Frankfurter AllgemeineZeitung, 2000, 55.

3 E. Pena, A. Sanchez, Z. Portillo and L. Solano, Arch. Latinoam.Nutr., 2003, 53, 133–140.

4 D. Ragland, J. L. Schneider, S. F. Amass and M. A. Hill, J. SwineHealth Prod., 2006, 14, 82–88.

5 M. Saric, N. Filipovic, N. Hladni and O. Grujic, Acta Aliment.,1998, 27, 21–27.

6 Y. V. Frolov, P. Pokhil and V. S. Logachev, Combust., Explos.Shock Waves, 1972, 8, 168–187.

7 V. G. Pol, H. Grisaru and A. Gedanken, Langmuir, 2005, 21,3635–3640.

8 Y. Koltypin, N. Perkas and A. Gedanken, J. Mater. Chem., 2004,14, 2975–2977.

9 X. Li, et al., Chem. J. Chin. Univ., 2005, 26, 1869–1872.10 P. Wang, D. Chen and F. Tang, Langmuir, 2006, 22, 4832–4835.11 V. Prashant, J. Phys. Chem. B, 2002, 106, 7729–7744.12 S. V. Pol, V. G. Pol and A. Gedanken, Chem.–Eur. J., 2004,

10, 4467.13 V. G. Pol, G. Seisenbaeva, V. G. Kessler and A. Gedanken, Chem.

Mater., 2004, 16, 1793.14 S. Tang, S. Vongehr, Z. Zheng, H. Liu and X. Meng, J. Phys.

Chem. C, 2010, 114, 18338–18346.15 L. S. Wang, D. B. Buchholz, Y. Li, J. Li, C. Y. Lee, H. T. Chiu and

R. P. H. Chang, Appl. Phys. A: Mater. Sci. Process., 2007, 87, 1–6.16 L.-B. Luo, S.-H. Yu, H.-S. Qian and J.-Y. Gong, Chem. Commun.,

2006, 793–795.17 S. C. Tang, S. Vongehr and X. K. Meng, J. Phys. Chem. C, 2010,

114, 977.18 X. K. Wang, X. W. Lin, M. Mesleh, M. F. Jarrold, V. P. Dravid,

J. B. Ketterson and R. P. H. Chang, J. Mater. Res., 1995, 10, 1.19 S. V. Pol, V. G. Pol and A. Gedanken, Chem.–Eur. J., 2004, 10,

1–8.20 V. G. Pol, S. V. Pol and A. Gedanken, Properties of Nano-

structured Metal Oxides Synthesized by the RAPET Approach,Metal Oxide Nanostructures and Their Applications, AmericanScientific Publishers, 2008.

21 A. Gedanken and E. Luvchik, Eur. J. Inorg. Chem., 2008, 15,2471–2475.

22 S. V. Pol, V. G. Pol and A. Gedanken, J. Phys. Chem. C, 2007, 111,13309–13314.

23 V. Logvinenko, O. Polunina, Yu. Mikhailov, K. Mikhailov andB. Bokhonov, J. Therm. Anal. Calorim., 2007, 90(3), 813–816.

24 A. Y. Obaid, A. O. Alyoubi, A. A. Samarkandy, S. A. Al-Thabaiti,S. S. Al-Juaid, A. A. El-Bellihi and El-H. M. Deifallah, J. Therm.Anal. Calorim., 2000, 61, 985–994.

25 M. A. Mohamed, S. A. Halawy and M. M. Ebrahim, Thermochim.Acta, 1994, 236, 249–262.

26 S. Pol, V. Pol, I. Felner and A. Gedanken, Eur. J. Inorg. Chem.,2007, 14, 2089–2096.

27 R. Janardhanan, M. Karuppaiah, N. Hebalkar and T. N. Rao,Elsevier, 2009, 28, 2522–2530.

28 E. Holodelshikov, I. Perelshtein and A. Gedanken, Inorg. Chem.,2011, 50, 1288–1294.

Table 2 Reduction potentials and calculated thermodynamic data for all the metals

Element Co Ni Fe Ag Cu Pb Zu Bi

Reduction potential/V �0.28 �0.25 �0.44 0.8 0.34 1.57 �0.79 0.32Gibbs free energy of reaction (40)/kJ mol�1 �41 �49 14 �238 �130 �73 55 �282Result Metal Metal Oxide Metal Metal Metal Oxide Metal

Dow

nloa

ded

on 2

6 Ju

ly 2

012

Publ

ishe

d on

17

Nov

embe

r 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C1N

J206

27C

View Online