Chemistry Reference
In-Depth Information
obvious bene
ts in the preparation of nanomaterials and is potentially
applicable to other systems. Similarly, a combinatorial approach using
several microreactors and an online detector has been developed to allow the
optimised synthesis of CdSe QDs, examining reaction time, temperature, and
concentration of amine and yielding outcomes on emission quantum yields,
particle size, diameter and product yield.
253
One of the drawbacks of micro
d
n
1
y
4
n
g
|
1
uidic synthesis is the use of relatively low
temperature because of the polymeric substrates, therefore missing the
higher range of temperatures normally associated with the synthesis of high-
quality crystalline particles. To avoid this, Chan
et al.
have developed
a segmented
ow droplet-based glass microreactor that is stable at high
temperatures, and developed a synthesis chemistry based on per
uorinated
polyethers as carrier solvents, using standard reagents such as cadmium
carboxylates, TOPSe and ODE as nanoparticle precursors and solvents.
254
Using this set-up, temperatures as high as 300
C have been used and the
reaction carried out in nanolitre-sized droplets of ODE in the per
d
n
4
.
uorinated
polyether, yielding materials spectroscopically identical to particles prepared
by the standard synthetic route. Related to this is the development of
chemical aerosol
ow synthesis, where precursors and solvent are nebulised
into a mist, which was then carried under inert gas
ow into a reaction
furnace where the QDs formed in sub-micron droplets.
255
There are numerous problems associated with the typical
ask synthesis
of semiconductor nanoparticles, such as side reactions, experimental
conditions that inadvertently e
ect reaction kinetics, and less reproducible
variables such as stirring rate and precursor injection rate. To overcome
this, the synthesis and analysis of CdSe, CdTe and even NaYF
4
has been
automated using combinatorial chemistry and high-throughput analytical
techniques using a combinatorial rig specially designed for high-tempera-
ture synthesis required for semiconductor nanomaterials.
256
The set-up
included low thermal mass reactor elements that allowed controlled heat-
ing, cooling and stirring under an inert atmosphere, and 96-well quartz
microplates or XRD microwell plates that allowed particle analysis. Using
simple green chemical routes described earlier in this chapter, a range of
experimental parameters were explored, allowing the optimisation of
particle growth. This degree of control resulted in extremely high repro-
ducibility with a 0.2% coe
cient of variation over numerous batch runs,
while allowing the tuning of the synthesised particles. One notable discovery
using the combinatorial approach was that the use of inhomogeneous
reactants produced reproducible results; it was suggested that these insol-
uble materials acted as precursor reservoirs. This advance in the repro-
ducible
synthesis of nanomaterials,
if
combined with intelligent
optimisation as described above, o
ers great potential for the future of
synthetic nanomaterial chemistry.
Here, we hope to have shown that the chemistry of II
VI nanomaterials is
varied and can be tuned across a wide spectral range, using a variety of
techniques, structures and synthetic methodologies.
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