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30
Chemistry Letters Vol.35, No.3 (2006)
Preparation of Single-crystalline Selenium Nanowires in the Presence
of Ethylenediaminetetramethylenephosphonic Acid
ꢀ
Yun Lei, Lide Yao, Yuping He, Shiquan Wang, Richeng Yu, and Bingsuo Zou
Nanoscale Physics and Device Laboratory, Beijing National Laboratory for Condensed Matter Physics,
Institute of Physics, Chinese Academy of Sciences, Beijing 100080, P. R. China
(Received December 16, 2005; CL-051543; E-mail: zoubs@aphy.iphy.ac.cn)
Selenium nanowires have been synthesized by using 2-mer-
for 2 days. A gradual change of color from red to dark-red and
gray indicated that CdSe NPs were transformed into selenium
NWs. The detailed influences of temperature on the diameters
of selenium NWs were examined and given in Supporting Infor-
mation (1).
captoethylamine-depleted CdSe nanoparticles as selenium
source and ethylenediaminetetramethylenephosphonic acid as
chelating agent. The products were characterized by X-ray dif-
fraction, scanning electron microscopy, high-resolution trans-
mission electron microscopy, and UV–vis spectrophotometry.
The result shows that the selenium nanowires are single crystals
grown along the [001] direction of hexagonal lattice. The optical
measurement shows a blue shift relative to the bulk hexagonal
selenium, and the optical bandedge might be attributed to the
interchain interactions within a hexagonal selenium crystal.
It has been demonstrated that excess stabilizers together
with cadmium ions form complex on the surface of the CdSe
particles and the layer of cadmium stabilizer complex can be
9
considered as a shell, preventing NPs from oxidizing. When
the prepared NPs were washed with water and ethanol several
times, the shell of cadmium stabilizer complex was partially
removed, and the bare CdSe particles were exposed to the air.
2
ꢂ
ꢂ
The standard redox potentials for Se /Se and O2/OH are
ꢂ0:924 and 0.401 V, respectively, which makes the oxidation
One-dimensional (1D) nanostructures, such as nanowires,
nanotubes, nanorods, and nanobelts, have attracted growing in-
terests on their synthesis, characterization, and applications be-
cause of their unique optical, electrical, and mechanical proper-
2
ꢂ
of Se thermodynamically possible in the presence of oxygen.
However, the activation energy of molecular precursors releas-
ing from stabilizer-depleted particles is expected to be quite
low, which obviously cannot satisfy the requirement in the trans-
formation from CdSe NPs to selenium NWs. Thus, other driving
forces are needed in this reaction system. The gradually increas-
ing temperature provides energy to promote the dynamic trans-
formation process and facilitates the lateral and longitudinal
growth. Moreover, EDTMP is a strong chelating agent towards
cadmium ions, and as a derivative of ethylenediamine it tends
to form a stable complex with selenium atoms. The resulting
complex intermediate including Cd and Se can promote the
1
ties. Selenium atoms tend to form helical chains through cova-
lent bonding, and helical chains can be readily packed into a
hexagonal lattice through van der Waals interactions. So the
crystallization for generating 1D structure tends to occur along
[
001] direction favoring the stronger covalent bonds over the
relatively weak van der Waals forces. Several synthesis methods
for 1D selenium nanostructures have been reported in the litera-
ture. Notable examples include a solution-phase approach via
2
,3
the reduction of selenious acid with excess hydrazine, a hydro-
4
2ꢂ
thermal process with polycrystalline selenium powders, a phys-
ical vapor deposition process of selenium powders with copper
oxidation of Se and further lead to the anisotropic growth of
1
0
selemium NWs. The proposed mechanism for stimulating the
oxidation can be described as following:
5
,6
plates as substrates or Si powders as catalyst, and a carbother-
mal chemical vapor deposition route via evaporation of an active
CdSe þ H2EDTMP ! CdSe(EDTMP)4ꢂ þ 2Hþ; ð1Þ
2ꢂ
7
carbon and selenium powder mixture. The above-mentioned
4
ꢂ
methods are conventional approaches to fabricate 1D nanostruc-
tures of hexagonal selenium nanowires (NWs), but vapor depo-
sition routes involve high temperature procedure accompanied
with a constant flow of inert gas, and solution-phase approaches
are limited by their tendency to form unstable colloidal particles
owing to the absence of any stabilizing ligands. So it remains a
great challenge to develop mild solution routes to selenium NWs
with an appropriate chelating agent capable of transformation of
atoms or ions from unstable precursors to a stable crystalline
product. In this manuscript a continuous transformation of
selenium NWs from CdSe NPs using ethylenediaminetetra-
methylenephosphonic acid (EDTMP) and 2-mercaptoethyl-
amine (MA) is reported.
2CdSe(EDTMP) þ O þ 2H O !
2
2
2
2ꢂ
ꢂ
Se þ 2Cd(EDTMP) þ 4OH :
ð2Þ
The typical X-ray diffraction (XRD) pattern of the prepared
sample is shown in Figure 1. No impurities such as selenium
oxides or allotropes of selenium can be found in the pattern.
2
-MA-stabilized CdSe NPs were prepared using a synthetic
8
20
30
40
50
/ deg.
60
70
route reported earlier. The prepared CdSe NPs were washed
with water and ethanol several times and redispersed into
2
θ
11.5 mM EDTMP solutions at pH of 9.0. The solutions contain-
ing CdSe NPs and EDTMP were incubated in dark environment
under 40 C for 3 days and then were gradually elevated to 60 C
Figure 1. XRD pattern of the synthesized selenium nanowires
supported on a glass slide. All peaks could be indexed to the
hexagonal selenium.
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Copyright Ó 2006 The Chemical Society of Japan
Lei, Yun
