One-pot aqueous synthesis of cysteine-capped CdTe/CdS core-shell nanowires

TLDR: In this article, high fluorescent cysteine-capped CdTe/CdS core-shell nanowires were successfully synthesized by reacting CdCl2 with NaHTe in aqueous solution under refluxing at 100°C for 140min.

Abstract: Highly fluorescent cysteine-capped CdTe/CdS core–shell nanowires were successfully synthesized by reacting CdCl2 with NaHTe in aqueous solution under refluxing at 100 °C for 140 min. On increasing the reaction time from 10 to 140 min, CdTe/CdS nanocrystals gradually grew into nanorods and eventually completely evolved into nanowires. The nanowires have amino and carboxyl functional groups on their surfaces and can be well dispersed in aqueous solution. The as-prepared CdTe/CdS nanowires show a fluorescence quantum yield (QY) of 7.25 % due to the unique nature of cysteine and the formation of a CdS shell on the surface of the CdTe core, they have a narrower diameter distribution (d = ~5 nm) and a length in the range of 175–275 nm, and their aspect ratio is between 1/35 and 1/55.

Figures

Figure 1. TEM and high-resolution TEM images of Cys-capped CdTe/CdS nanocrystals prepared in aqueous solution: (a-b) reaction 10 min, (c-d) reaction 30 min, and (e-f) reaction 140 min (d = ~5 nm, length in the range of 175 to 275 nm).

Figure 4. EDS spectrum of Cys-capped CdTe/CdS nanowires.

Figure 2. Photograph of Cys-capped CdTe/CdS nanocrystal solutions under excitation of 365 nm UV lamp (top) and their corresponding UV-vis absorption (a) and PL spectra (b) after refluxing at 100℃ for different times.

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1
One-pot Aqueous Synthesis of
Cysteine-Capped CdTe/CdS Core-shell
Nanowires
Yukai Shan
a
, Zhen Xiao
a
, Yongming Chuan
a
, Hongli Li
a
，Minglong Yuan
a
*, Zhen
Li
b
*, and Shixue Dou
b
a
Engineering Research Center of Biopolymer Functional Materials of Yunnan,
Yunnan University of Nationalities, Kunming 650500, China
b
Institute for Superconducting & Electronic Materials, University of Wollongong,
Innovation Campus, Squires Way, North Wollongong, NSW 2500, Australia
* Corresponding author：Minglong Yuan. Tel.: +86-18987188989.
E-mail address: yml@188.com；Zhen Li：Email: zhenl@uow.edu.au.

2
ABSTRACT
Highly fluorescent cysteine-capped CdTe/CdS core-shell nanowires were successfully
synthesized by reacting CdCl
2
with NaHTe in aqueous solution under refluxing at
100 ℃ for 140 min. On increasing the reaction time from 10 to 140 min, CdTe/CdS
nanocrystals gradually grew into nanorods and eventually completely evolved into
nanowires. The nanowires have amino and carboxyl functional groups on their
surfaces and can be well dispersed in aqueous solution. The as-prepared CdTe/CdS
nanowires show a fluorescence quantum yield (QY) of 7.25% due to the unique
nature of cysteine and the formation of a CdS shell on the surface of the CdTe core,
they have a narrower diameter distribution (d = ~5 nm) and a length in the range of
175 to 275 nm, and their aspect ratio is between 1/35 and 1/55.
KEYWORDS. CdTe/CdS, core-shell nanowires, aqueous preparation, cysteine.
1. INTRODUCTION
In recent years, one-dimensional (1D) semiconductor nanostructures such as
nanorods, nanowires, and nanotubes have attracted considerable attention because of
their special structures, unique electrical and optical properties, and diverse
applications (Tang et al. 2002;Yong et al. 2010). Due to their unique physical and
chemical properties with high dimensional anisotropy, semiconductor nanowires are
of particular importance for fabricating nanoscale biosensors (Fernando et al. 2007;

3
Jay et al. 2009), drug carriers (Lee et al. 2009), solar cells (Jiang et al. 2010;Yu et al.
2010),
and cell imaging devices (Hwa et al. 2009). For example, II – VI CdTe
nanowires (Luo et al. 2012) have an extremely high absorption coefficient, broad
absorption range, and excellent carrier transport properties, so that they are ideal
candidates for the above-mentioned applications (Jiang et al. 2012).
Different techniques have been developed to synthesize nanowires, which can be
generally classified into top-down and bottom-up routes. A conventional bottom-up
method is vapor-liquid-solid (VLS) growth (Simon et al. 2010; Wu et al. 2012; Wang
et al. 2008; Yang et al. 2013), in which nanowire diameters are controlled by the size
of the Au or Bi nanocatalysts. The obtained nanowires have diameters of about 20-60
nm, and are usually not within the quantum confinement region. They also have poor
hydrophilicity, and the preparation process requires high temperature, usually higher
than 500
o
C. In addition,the nanocatalysts that need to be used remain at the ends of
the nanowires, which could influence nanowire properties and performance. Another
common approach is the chemical vapor deposition (CVD) method (Hou et al. 2011;
Park et al. 2008; Carey et al. 2009; Utama et al. 2011), which can produce nanowires
several micrometers in length at high temperature (more than 500 ℃). Similar to
VLS growth, the prepared nanowires are usually larger than 50 nm in diameter.
Compared with above mentioned non-wet chemical methods, preparation of
nanowires by wet-chemical approaches has a few distinct advantages. First, the
resultant semiconductor nanowires have smaller diameters and a narrower diameter

Frequently asked questions

Q1. What are the contributions in "One-pot aqueous synthesis of cysteine-capped cdte/cds core-shell nanowires" ?

Li et al. this paper used Bi nanoparticles as catalysts to prepare colloidal semiconductor nanowires through solution-liquid-solid ( SLS ) growth at relatively low temperature ( 300 ℃ ). 

Q2. How can the authors tune the diameter of colloidal nanowires?

The diameter of these colloidal nanowires can be tuned from a few nanometers to tens of nanometers, so that they exhibit strong quantum confinement effects. 

Q3. What is the main reason for the introduction of the core-shell structure?

In order to reduce the surface defects, the core-shell structure has been introduced and has proven to be a powerful approach to improve the overall physical and chemical properties of the nanowires. 

Q4. What are the advantages of wet-chemical preparation of colloidal nanowires?

the resultant semiconductor nanowires have smaller diameters and a narrower diameterdistribution, and they can exhibit quantum confinement effects like their nanocrystal and nanorod analogues. 

Q5. What is the effect of CdTe/CdS nanowires on cell vi?

On increasing the reaction time from 10-140 min., CdTe/CdS nanocrystals gradually changed from QDs to nanorods, and eventually completely evolved into nanowires. 

Q6. What is the main reason for the nanowires to be used?

In addition,the nanocatalysts that need to be used remain at the ends of the nanowires, which could influence nanowire properties and performance. 

Q7. What is the important reason why nanowires are of particular importance?

In recent years, one-dimensional (1D) semiconductor nanostructures such as nanorods, nanowires, and nanotubes have attracted considerable attention because of their special structures, unique electrical and optical properties, and diverse applications (Tang et al. 2002;Yong et al. 2010). 

Q8. Why are there only a few reports on the preparation of CdTe/Cd?

There are only a few reports, however, on preparation of functional CdTe/CdS core-shell nanowires in aqueous phase, which may be due to thelarge lattice mismatch between CdTe and CdS, as well as additional difficulties associated with the morphological anisotropy of CdTe core nanowires (Wang et al. 2008). 

Q9. What was the relative absorbance on each sample compared to that of a blank control?

Cell viability, defined as the relative absorbance on each sample compared to that of a blank control, was calculated and expressed as a percentage. 

Q10. How long did the reaction time take to change from spherical nanoparticles?

It clearly shows that by increasing the reaction time from 10 min to140 min, samples gradually changed from spherical nanoparticles to nanorods, and eventually completely turned into nanowires. 

Q11. What is the cytotoxicity of the three types of nanocrystals?

Figure 6(A) shows that at the same concentration (50 μg/mL), the cytotoxicity of the three type of nanocrystals is in the order of QDs > nanorods > nanowires, i.e. nanowires have the lowest toxicity, and cell viability is up to 78% after incubation for 16 h.