Chemical Engineering April 2019 - 16

Quantum Materials
UbiQD
FIGURE 3. An emerging application for QDs is in anti-counterfeit inks, where their unique color signatures
can strengthen security measures
UbiQD believes that the agricultural
market will quickly become another
major application area, with solar energy
not far behind. " Quantum dots
are already making the world a better
place, but there is huge untapped potential, "
emphasizes McDaniel.
Water purification is another area
where QDs can improve sustainability.
A group of researchers from the
University of South Carolina (Columbia;
www.sc.edu) and the SmartState
Center of
Catalysis
Fuels (www.smartstatesc.org)
for Renewable
have
successfully integrated QDs into a
reverse-osmosis (RO) membrane
designed for high-flux desalination
processes. The team used nitrogendoped
graphene-oxide quantum dots
(N-GOQDs) as an additive in the fabrication
of a polyamide membrane.
" The very small size of GOQDs and
their rich functional groups make them
an excellent additive in polymeric
membranes, or even as basic building
blocks for GOQD membranes if
packed and crossed appropriately, "
says Miao Yu, one of the lead researchers
on the project, and currently
a professor of chemical and biological
engineering at Rensselaer Polytechnic
Institute (Troy, N.Y.; www.rpi.edu). According
to Yu, this work is the first to
investigate GOQDs in membrane applications.
" There are many nanoparticles
that have been added to RO
membrane matrices, but much of
this work is still at the lab stage, and
the water flux increase is not as significant
as that seen with the addition
of N-GOQDs, " he adds. The research
showed that adding just 0.02 wt.% of
GOQDs tripled the polyamide membrane's
water permeability, while still
rejecting salts at a comparable rate to
an untreated polyamide membrane.
Yu says that N-GOQDs' functional
groups can be easily crosslinked into
16
an RO membrane matrix without introducing
large cavities, and that their
hydrophilic nature helps to further facilitate
water transport, increasing flux.
Thus far, a membrane with a permeation
area of 10 cm2 has been demonstrated,
but Yu says that the fabrication
process, based on interfacial polymerization,
is compatible with industrial
membrane-preparation processes,
making its scaleup more promising.
The team has applied for a patent and
plans to work with an industry partner
on larger-scale production.
Advanced imaging and beyond
In China, NajingTech (Hangzhou;
www.najingtech.com) is working to
extend the performance of QDs for
both photoluminescent (photonto-photon)
and electroluminescent
(electron-to-photon) uses. Founded in
2002 by QD pioneer and former professor
of chemistry at the University
of Arkansas, Xiaogang Peng, NajingTech's
U.S. subsidiary, NN-Labs LLC
(Fayetteville, Ark.; ww.nn-labs.com)
was among the first commercial providers
of QD nanocrystals. Currently,
NajingTech is focused on the deployment
of QD light-converting devices
(QLCD) and QD light-converting films
(QLCF), as well as commercializing
electroluminescent QD light-emitting
diode (QLED) technologies (Figure 5),
along with emerging work in the fields
of photovoltaics, sensors and detectors,
lasers, bio-imaging and more,
says Wei Huang, senior researcher
at NajingTech. On the biotechnology
front, NajingTech is currently working
to develop QD-based immunochromatography
technologies and QDlinked
immunosorbent assays. The
company is also investigating ways
to minimize or eliminate the Cd content
in QD materials for large-scale
applications and electroluminescent
FIGURE 4. QD films in greenhouses can adjust sunlight
to improve crop yield
devices, since Cd introduces toxicity
and limits materials' ability to be used
in certain commercial end markets.
For example, NN-Labs has developed
copper indium sulfide/zinc sulfide
(CuInS/ZnS) core-shell QD products
for use in biomedical, solar energy and
LED lighting applications. The company
also offers a line of indium phosphide/
zinc sulfide-based (InP/ZnS) QDs as an
alternative to Cd-based formulations.
" We use a solution-based 'green
synthesis' method to make QDs by
using the non-coordinating solvent octadecene
along with stable and safe
precursor materials, " explains Huang.
This synthesis method enables precise
tuning of nanocrystal size and size distribution,
and the use of a non-coordinating
solvent is said to make the process
simpler and more environmentally
friendly than other techniques. Since
being developed by Peng and patented
in 2006, many QD companies
have also adopted this process. In the
future, says Huang, the company plans
to deploy a printing-based technology
to fabricate QLED-based technologies.
MilliporeSigma (Burlington, Mass.;
www.emdmillipore.com) and EMD
Performance Materials, two of the
North American operating companies
of Merck KGaA (Darmstadt, Germany;
www.merckgroup.com), supply QD
materials for researchers working on
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APRIL 2019

http://www.sc.edu http://www.smartstatesc.org http://www.najingtech.com http://ww.nn-labs.com http://www.rpi.edu http://www.emdmillipore.com http://www.merckgroup.com http://WWW.CHEMENGONLINE.COM

Chemical Engineering April 2019

Table of Contents for the Digital Edition of Chemical Engineering April 2019