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Chinese Chemical Letters 22 (2011) 993–996

A novel way to synthesize Pb nanotapes in liquid ammonia

Lei Sun *, Meng Lei Zhang, Xiao Jun Tao, Yan Bao Zhao

Key Laboratory for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004, China

Received 25 September 2010

Available online 18 May 2011

Abstract

Lead nanotapes were synthesized in liquid ammonia solvent in the presence of sodium metal at low temperature. The process

was template free. Transmission electron microscopy (TEM) observations and X-ray diffraction (XRD) characterizations revealed

that the as-prepared Pb nanotapes have average diameters in the range of 40–50 nm, and lengths up to several hundred nanometers,

and exhibit cubic crystal structures.

# 2011 Lei Sun. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: Pb; Nanotapes; Chemical synthesis; Liquid ammonia

The synthesis of one-dimensional metal and semiconductor materials has received much attention recently because

of their potential use in fabricating nanoscale electronic, photonic, and sensing devices [1–4]. Up to now, considerable

effort has been focused on the fabricating of these one-dimensional materials and some nanowires such as Ag [5,6], Ni

[7], Cu [8], InP [9], In2O3 [10] and GaN [11]. have been successfully synthesized. Many experimental approaches of

fabricating nanotapes have been reported, utilizing a variety of nanofabrication techniques and crystal growth

methods, including electrodeposition [7], thermal decomposition [12,13], template synthesis [14], vapor–liquid–solid

(VLS) growth [9,11,15], catalytic chemical vapor deposition (CVD) growth [10,16], and so on.

In this paper, we demonstrate a novel method to prepare Pb nanotapes without template. The process was performed

in liquid ammonia in the presence of sodium metal. The ability of liquid ammonia dissolving alkali and alkaline earth

metals to form blue solutions is one of its most remarkable and useful properties. Such solutions contain stable

solvated electrons and have been consequently used in both organic and inorganic chemistry [17,18]. Compared with

conventional reduction in aqueous solvent, this method is carried out at very low temperature (below the boiling point

of ammonia, �33.4 8C). However, the solvent can be recycled, it is expected that the method could be used in

industrial scale as a cheap and convenient way in preparation of chemicals.

Lead(II) iodide and sodium metal were of chemical purity and used as received. Ammonia gas was produced by

dropping ammonia liquor onto sodium hydroxide. The synthesis reaction was processed in a DC-4006 low

temperature thermostat. The temperature can be adjusted in the range of�40 to 90 8C, and absolute ethanol was used

as medium in the bath. The structure of synthesized nanotapes was characterized on a Philips X’per pro X-ray powder

diffractometer (XRD), using Cu Ka radiation (l = 1.5418 A), the operation voltage and current were 40 kV and

40 mA, respectively. The morphology and selective area electron diffraction (SAED) patterns of nanotapes was

* Corresponding author.

E-mail address: sunlei@henu.edu.cn (L. Sun).

1001-8417/$ – see front matter # 2011 Lei Sun. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

doi:10.1016/j.cclet.2011.03.001

L. Sun et al. / Chinese Chemical Letters 22 (2011) 993–996994[()TD$FIG]

Fig. 1. XRD patterns of Pb nanotapes.

observed on a JEOLTEM-2010 transmission electron microscope (TEM); for the observations, samples were prepared

by dropping the product powder ethanol dispersion on carbon-coated Cu grids, and observed under an electric

potential of 200 kV. The surface structure charaction of Pb nanotapes was performed on an AVATAR 360 Fourier

transform infrared spectroscopy (FT-IR) using KBr pellet. The element analysis of nanotapes was measured on an

Oxford Link ISIS energy-dispersive X-ray spectrometer (EDX).

In a typical procedure, a 250 mL three-neck flask was kept in the thermostat bath. The flask was equipped with a

drain sleeve, which was connected with outer-cycle of the thermostat so that the ammonia gases can be condensed to

liquid ammonia. The temperature of thermostat was set to �40 8C. After the temperature was lower than �34 8C,

ammonia gas was produced by dropping ammonia liquor onto a large amount of solid sodium hydroxide, and it was

dried through two solid NaOH columns before led into drain sleeve. Ammonia gas was condensed to liquid ammonia

in the flask, after about 50 mL liquid ammonia was collected, 0.92 g PbI2 (2.0 mmol) was added to the flask, under

violent stirring. After the dispersion of PbI2 in liquid ammonia, the colour of suspension was white. Later, 0.69 g

(30 mmol) of sodium metal was carefully added to the flask and the colour of solution became dark. After 30 min at

�40 8C, 60 mL of absolute ethanol was carefully added to the flask to quench the reaction. The reaction mixture was

kept at ambient temperature over night. The ammonia gas from the flask was absorbed by distilled water. The black

precipitate was filtered and washed six times with 80 mL absolute ethanol, then dried in vacuum at room temperature

for 2 days. The black powder was the expected product, Pb nanotapes.

XRD measurements were made on the bulk samples and to assess the overall crystal structure and phase purity of

the product. Fig. 1 shows the XRD patterns of as-prepared Pb nanotapes. The diffraction peaks at 2u = 31.28, 36.28,52.28, 62.18, 65.28, 76.98, 85.48 and 88.28 correspond to the (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), (4 0 0), (3 3 1) and

(4 2 0) planes, respectively. All the diffraction peaks can be indexed to a cubic structure Pb according to the literature

pattern (JCPDS 04-0686). The strong intensities of the Pb diffraction peaks relative to the background signal exhibit

that the resulting powder had high purity of the cubic Pb Phase. XRD pattern also indicates that there is no impurity in

the product. The results show that PbI2 was reduced to Pb perfectly. It is supposed the reaction mechanism is that

sodium metal dissolved in liquid ammonia, which contains solvate electrons, reduced Pb2+ to Pb0.

Fig. 2 shows TEM images of Pb nanotapes. A typical whole morphology and SAED of Pb nanotapes is shown in

Fig. 2a. It can be seen that the most of nanotapes are straight and uniform along their entire length with an average

diameter of about 40–50 nm and lengths up to several hundred nanometers. The orientations of Pb nanotapes are in

disorder. The spotty diffraction rings in Fig. 2a (inset) show the polycrystalline nature of the Pb nanotapes. Fig. 2b

shows a part of individual Pb nanotapes. It can be seen that the surface of nanotapes is smooth, and the diameter is

uniform along the length. The formation mechanism of Pb nanotapes is not very clear, but we suppose that it may be as

follows: As it is well known that the ammoniate electron is in a cavum surrounded by ammonia molecules, both

reduction and nucleation reactions processed in these cavums. The surface of Pb nanocrystals adsorbed a large amount

of ammonia molecules, which formed chains through hydrogen bond; this is assisting Pb nanocrystals to growth of

nanotapes.

L. Sun et al. / Chinese Chemical Letters 22 (2011) 993–996 995[()TD$FIG]

Fig. 2. TEM images of Pb nanotapes: (a) a whole morphology and the SAED pattern (inset), (b) an individual Pb nanotape.

Fig. 3 shows the FT-IR spectrum of Pb nanotapes. The broad band at 3434 and 1646 cm�1 are assigned to the

stretching and in-plane bending vibration of –NH2, respectively. The band range 900–650 cm�1 is attributed to the

out-of-plane bending vibration of –NH2 [19]. These indicate that the surfaces of Pb nanotapes are adsorbed by

ammonia molecules. The bands at 1453 and 1394 cm�1 are attributed to the asymmetric and symmetric bending

[()TD$FIG]

Fig. 3. FT-IR spectrum of Pb nanotapes.

[()TD$FIG]

Fig. 4. EDX spectrum of Pb nanotapes.

L. Sun et al. / Chinese Chemical Letters 22 (2011) 993–996996

vibrations of –CH3, respectively. The band at 3434 cm�1 is also attributed to the stretching vibration of –OH, which

are caused by the adsorbed alcohol molecules in the quench reaction and rinsed process.

The EDX spectrum of Pb nanotapes shown in Fig. 4 indicates that the nanotapes are not stoichiometric PbO but free

element of Pb as calculated from the quantitative analysis of the data within the experimental error. C and O elements

are found in Fig. 4 which corresponds with the residuum of –CH3 and –OH on the sample surface as indicated by the

FT-IR spectrum.

Lead(II) iodide was reduced to Pb nanotapes by salvation electron in the liquid ammonia solution of sodium metal

at low temperature. This new method to fabricate metal nanotapes is free of template. The structure and morphology of

as parpared Pb nanotapes were characterized by the means of XRD, TEM, SAED, FT-IR and EDX. The results reveal

that the Pb nanotapes have a cubic structure and have an average diameter in the range of 40–50 nm.

Acknowledgments

The authors are grateful for the financial support by the National Natural Science Foundation of China (No.

50701016) and the Foundation of Education Department of Henan Province (Nos. 2007150008, 2008B150003).

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