Chemical Engineering April 2019 - 14

Newsfront
A Bright Future for
Quantum Dots
The novel performance characteristics and tunability of quantum dots make them a promising
nanomaterial in numerous emerging applications
IN BRIEF
FIRST CONTINUOUS
PROCESSING METHOD
QDS FOR
SUSTAINABILITY
ADVANCED IMAGING AND
BEYOND
Q
uantum dots (QDs) represent a
broad group of semiconducting
nanoparticles that feature a unique
combination of optical and electronic
properties. For example, QDs provide
many of the same benefits as organic dyes in
existing applications, but they are more robust
in terms of light-conversion capabilities and can
also withstand harsh chemical solvents, higher
temperatures and corrosion, while generally
providing a broader light-absorption band. Perhaps
QDs are most prominently known for their
ability to emit extremely pure colors for long
durations (Figure 1) - they have been widely
used to improve the display characteristics
of high-end televisions. But QDs' applicability
stretches far beyond consumer electronics
into wide-ranging potential end uses from solar
power to agriculture to water purification.
First continuous processing method
Quantum Materials Corp. LLC (QMC; San
Marcos, Tex.; www.qmcdots.com) has developed
what is said to be the world's first
continuous production process for QD
manufacturing. QMC's technology uses all
fluidized materials and continuous-flow reactors,
whereas the vast majority of QD production
depends on batch production. " We
use microflow reactors, which can achieve
high rates of heat and mass transfer, resulting
in a very uniform product. Therefore, very
little post-processing is required, " explains
Krishna Kowlgi, senior research engineer at
QMC. In addition to product homogeneity,
another benefit of continuous QD processing
over batch is time - the entire continuousflow
process can be automated and requires
much less manual intervention. " From start to
finish, it takes a minimum of 5 s to a maximum
of 19 min, based on the QD material
type, to convert raw materials to functional
QDs. We think this is the fastest QD production
currently on the market. The numbers in
literature for batch QD processes range from
14
2.0 nm
2.5 nm
3.0 nm
3.9 nm
Quantum Materials
4.2 nm
FIGURE 1. Quantum dots are known for their ability to instill
brilliant colors into electronics displays, but their chemistry
and tunability make them ripe for innovation in many
other areas
multiple hours to days or even weeks, " adds
Kowlgi. He emphasizes that QMC's reactors
are flexible enough to produce different QDs
for different end uses. " The light-emission capabilities
of the QD depends on its geometry
and chemical composition. A 4-nm spherical
QD would produce different emissions than
one with a 3-nm diameter, " he adds. Due to
the fluidized flow chemistry of QMC's process,
QDs are produced in solution, so they are either
filtered or undergo some other type of
post-processing separation step.
Currently, QMC has production capabilities
to manufacture around 3 kg/h of QDs at its
site in San Marcos (Figure 2). In late 2018,
the company signed a license agreement to
construct a large-scale QD plant in Assam,
India. QDs produced at the Assam site are expected
to mainly be deployed in solar power
and display and lighting applications. Once
operational, the Assam site will be among the
world's largest manufacturing plants for active
nanoparticles, and the only industrial-scale
site to employ continuous QD production.
Moving forward, QMC is continuing to push
the boundaries of its continuous-flow process.
" Because the flow reactors have a very small
footprint, they are well suited for handling extreme
process conditions, " explains Kowlgi. By
examining different combinations of processing
conditions, more robust QDs can be taiCHEMICAL
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APRIL 2019

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Chemical Engineering April 2019

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