Protein-assisted synthesis of single-crystal nanowires of bismuth compounds

Article abstract of DOI:10.1039/b413584a

Lysozyme, a protein, has been found to be a new morphology-directing agent and a simple and mild bio-molecule assisted method has been proposed for the synthesis of single-crystal bismuth sulfide and oxide nanowires.

Full text of DOI:10.1039/b413584a

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Protein-assisted synthesis of single-crystal nanowires of bismuth
compounds{
Feng Gao, Qingyi Lu and Sridhar Komarneni*
Received (in Cambridge, UK) 3rd September 2004, Accepted 15th October 2004
First published as an Advance Article on the web 2nd December 2004
DOI: 10.1039/b413584a
Lysozyme, a protein, has been found to be a new morphology-
directing agent and a simple and mild bio-molecule assisted
method has been proposed for the synthesis of single-crystal
bismuth sulfide and oxide nanowires.
Lysozyme is a protein with relatively high stability and is
responsible for breaking down the polysaccharide walls of many
25
types of bacteria. Furthermore it has also been confirmed that it
26,27
shows chelating interactions with metal ions.
Thus it is
reasonable to expect the morphology-directing function of protein
lysozyme in the formation of 1D inorganic nanomaterials.
However, it has not so far found application in the synthesis of
nanomaterials. Herein we report a simple lysozyme-assisted
method for the synthesis of single-crystal bismuth sulfide and
oxide nanowires.
One-dimensional (1D) nanomaterials have been touted to be
important for applications of electrical transport, optical phenom-
1–3
ena, and as functional units in nanocircuitry. Pursuit of methods
for the synthesis of semiconducting and metallic nanowires has
4
yielded strategies including vapor liquid solid (VLS) growth,
5
hydrothermal and solvothermal routes, hard template directing
Pure and crystalline bismuth sulfide could be synthesized from
Bi(NO ) ?5H O, thiourea and lysozyme as reactants at 160 uC
6
7
technique and surfactant-assisted approach. Although each
method developed for the production of nanowires has had
success in achieving high-quality materials, developing simple and
effective methods for the fabrication of 1D systems remains a
challenge to materials chemists.
3
3
2
under hydrothermal conditions, as confirmed by its X-ray
diffraction (XRD) pattern (see ESI{ for experimental details and
XRD). Fig. 1(a) and (b) show transmission electron microscope
(TEM) images of the obtained bismuth sulfide sample, which
clearly show that the crystallites have a wire-like morphology. The
diameters are in the range of 10–50 nm and lengths are up to
micrometers (see ESI{ for further TEM images). Its selected area
electron diffraction (SAED) pattern (Fig. 1(a), inset) displays
several diffraction rings, which could be indexed as the
orthorhombic phase of bismuth sulfide in agreement with XRD.
Besides nanowire aggregates, single nanowires have also been
observed. Fig. 1(c) displays the TEM image of one nanowire with
Bismuth sulfide has a complicated structure, arranged by chain-
8
like structure in two different ways. As a semiconductor with wide
applications in various devices, it has attracted much attention
based on its 1D nanostructure and bismuth sulfide nanowires have
9,10
been synthesized by many methods. Bulk bismuth oxide itself is
an excellent opto-electronic material and catalyst and has also been
extensively used as an effective component in third-order nonlinear
11–13
optical glasses, cataphoresis and medical products.
Recently it
has been confirmed that the nonlinear susceptibility of bismuth
oxide nanoparticles is 100 times larger than that of bulk bismuth
1
4
oxide. The availability of bismuth oxide nanowires might be able
to bring new types of applications and/or to enhance the
performance of the currently existing devices. However, so far to
the best of our knowledge, no bismuth oxide nanowires have been
reported.
Biomolecules, such as proteins, peptides and single-stranded
DNA, are some of the most underused, yet powerful and versatile
15–17
building blocks.
Their molecular recognition properties are
18
unmatched by conventional synthetic analogues. So far, many
smart inorganic materials have been prepared, such as virus-based
19
synthesis of magnetic and semiconducting nanowires, bacterial
20
S-layers as template for the synthesis of CdS superlattices, DNA-
21
assisted synthesis of Au particle nanowires, and biotemplate
22
synthesis of metal nanowires. Fully investigating and exploiting
these selective biomolecules might be of great importance in the
development of novel materials, especially in the areas of medicine
23,24
and nanotechnology.
{
Electronic supplementary information (ESI) available: XRD pattern,
TEM images. See http://www.rsc.org/suppdata/cc/b4/b413584a/
komarneni@psu.edu
Fig. 1 TEM images, SAED patterns and HRTEM image of the
*
obtained bismuth sulfide sample.
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its corresponding SAED pattern (inset). The two diffraction spots
perpendicular to each other in the SAED pattern could be indexed
to (002) and (220), respectively, which indicates that the nanowire
is a single crystal and has a preferred growth direction of [001]. The
single-crystal nature of the obtained nanowires is different from
those using bio-molecules as templates for particle assembled
nanowires. A high-resolution transmission electron microscope
(HRTEM) image (Fig. 1(d)) directly confirms that the nanowires
are single crystals with high crystallinity. The crystal planes,
perpendicular and parallel to the wire axis, have spacings of about
0.40 and 0.79 nm, which correspond to those of (001) and (110)
planes, respectively. This result indicates that the nanowires might
have [001] directional preferred growth, in agreement with the
SAED result.
Although the exact mechanism of the 1D growth is unclear, we
believe the formation of single-crystal 1D nanostructures is
relevant to the coordination interaction between inorganic ions
and bio-molecules. Bi(III) could easily react with many inorganic
negative ions and organic compounds. Previous literature has
reported that bismuth ions could react with amino acids with
2
8
amino- and thiol-groups to form complexes. Lysozyme is a
protein formed by amino acids containing nitrogen and sulfur
atoms. Thus it is reasonable to expect that lysozyme could
coordinate with bismuth ions to form an intermediate complex,
which might benefit the 1D growth of the final product. In our
experiments, the reaction to form bismuth sulfide does not occur
initially when the several reagents are mixed. The added lysozyme
could react with Bi(III) to form an intermediate compound and
with the increase of temperature and pressure it could react with
hydrogen sulfide from the decomposition of thiourea to form
bismuth sulfide. Without the addition of lysozyme, the obtained
sample contains irregular shapes with a large range in size
distribution. An appropriate ratio between bismuth ion and
lysozyme is important to the formation of nanowires. At a lower
bismuth ion concentration, the obtained bismuth sulfide grains
have a spherical structure formed by short, film-like rods (rod-like
shape but formed by the rotation of thin films; see ESI for TEM
image{). With the increase of the bismuth ion concentration, these
short film-like rods change to be separated rods and then the
length of these 1D nanostructures increases gradually. This result
means that high lysozyme concentration is not beneficial to the
formation of nanowires. This may be because at a relatively high
bio-molecule concentration, the bio-molecules might have stronger
Fig. 2 TEM images, SAED pattern and HRTEM images of the
obtained bismuth oxide sample.
spacing of 0.28 nm, which is consistent with those of (002) crystal
planes. This means that the nanowire is apparently growing in a
preferred direction of [001].
In summary, we report a simple method for the synthesis of
bismuth sulfide and oxide nanowires with the first use of protein
lysozyme as a morphology controlling agent. The obtained
bismuth sulfide and oxide nanowires have single-crystal nature,
which is different from particle-assembled nanowires using
templates such as DNA. The use of protein lysozyme directs the
1D growth of nanowires of bismuth compounds and this might be
extended to nanowires of other compounds.
This work is supported by the NSF MRSEC under grant
number, DMR-0213623 and Huck Institutes of the Life Sciences.
TEM work was performed in the electron microscopy facility of
the Materials Research Institute at Penn State University.
Feng Gao, Qingyi Lu and Sridhar Komarneni*
Materials Research Institute, The Pennsylvania State University,
University Park, PA 16802, USA. E-mail: komarneni@psu.edu
29
assembly activity rather than morphology directing function. To
further confirm this suggestion, we kept the concentration of
bismuth ion constant, but increased the concentration of lysozyme
and we found that the length of the obtained 1D bismuth sulfide
nanostructures decreases and the formed nanorods have a
tendency to aggregate gradually (see ESI{ for TEM image).
Moreover, the morphology controlling function of lysozyme can
be extended to the synthesis of bismuth oxide nanowires. Fig. 2(a)
and (b) show the TEM images and SAED pattern of the bismuth
oxide sample prepared without the addition of thiourea and with
the addition of 0.1 g lysozyme. It can be seen that the obtained
bismuth oxide also has high crystallinity and wire-like morphology
with an average diameter of y8 nm and lengths up to several
micrometers. Fig. 2(c) and (d) display a HRTEM image and a
selected area magnified HRTEM image of nanowires. The crystal
planes perpendicular to the long axis of the nanowire have a
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