Quantum dots and Nanofiber: Definition, synthesizing techniques: traditional and emerging and their application in various fields.

1. Quantum dots and nanofibers
Presented by –
Pooja
Roll no. – 201642
MSc Biotechnology
Central University of Haryana

2. Quantum Dots
 A quantum dot is a nanometer-sized semiconductor particle traditionally with a
core-shell structure. Quantum dots are widely used for their unique optical
properties, as they emit light of specific wavelengths if energy is applied to them
 There are various methods of producing quantum dots. The most typical is via a
colloidal synthesis, which is the process of heating a solution, causing the
precursors to decompose to form monomers, which then produce nanocrystals.
 Plasma synthesis is another popular technique for the production of quantum
dots. This process enables the control of the composition, surface, size, and
shape of the quantum dot, and it also reduces the challenges associated with
doping.
Working principle- Within a quantum dot, there are confined valence band holes,
conduction band electrons, or excitons. These are the particles that carry the
electricity, and because of this confinement, the quantum dot has a distinct energy
level.
 The longest wavelengths of light (red light) are produced by the biggest
quantum dots, and the shortest wavelengths of light (blue light) are generated
by the smallest quantum dots. https://pubs.acs.org/doi/10.1021/acsanm.0c
01386

3. Applications in various fields
QD applications are mostly based on their exquisite optical properties and their role in light emission, conversion, and
detection.
QDS FOR LIGHT-EMITTING DIODES (LEDS) AND DISPLAY APPLICATIONS-
 Among III−V compounds, solution-processed colloidal InP QDs have been explored in LED and display applications
due to their tunable, bright, and narrow PL.
 Different materials are used to obtain QDs emitting in specific spectral ranges. Silicene QDs confined in few-layer
siloxane nanosheets are suggested for potential applications as emitters in blue-light-emitting diodes.
 Thin-film-type LEDs can be based on CsPbX3 QDs fabricated using a new solid-state ligand-exchange method.
Photovoltaics –
 Devices for photovoltaics have long incorporated nanomaterials in order to boost the energy conversion efficiency
E.g., CdS QDs and CdSe and CdSe/CdS core−shell QDs.
PHOTOCONDUCTORS AND PHOTODETECTORS-
 In the IR spectral region, enhanced responsivity in PbS QD photodetectors can be obtained using a two-step ligand
exchange method. Photoconductors were also fabricated from highly packed PbS QD films, synthesized using a
rapid microwave-polyol technique.

4. BIOMEDICAL AND ENVIRONMENTAL APPLICATIONS-
o The high luminescence, narrow emission, and low toxicity and biocompatibility of QDs make them a
perfect candidate for bioimaging, diagnostics, and biosensing applications, mostly related to biomedical
and environmental sciences.
o fibrous phosphorus QDs were demonstrated as fluorescent labels for human adenocarcinoma
bioimaging.
o Bioimaging and biosensing were also demonstrated for QD complexes comprised of zinc chalcogenide
QDs.
o As a different type of diagnostic tool, the luminescence of CuInS2 QDs was used as a thermometer over a
large, biologically relevant temperature interval
CATALYSIS AND OTHER APPLICATIONS-
Semiconductor photocatalysis technology converts light to chemical energy; QDs have also been explored to
improve existing or create new catalytic routes
As for different applications, fluorescent CdTe QDs were assembled with maghemite nanoparticles and
suggested for magnetic particle inspection in ferromagnetic materials.

5. Nanofibers
 Nanofibers are fibers with diameters in
the nanometer range.
 Nanofibers can be generated from
different polymers and hence have
different physical properties and
application potentials.
 One of the most striking features of
nanofibers is their exceptionally high
surface area-to-volume ratio and high
porosity, making them a robust and
attractive candidate for many advanced
applications.
https://www.sciencedirect.com/science/article/pii/S0079670017300692

6. Current strategies for nanofiber fabrication
 Of all the current strategies available for synthesizing one dimensional nanofibers, electrospinning is
one of the most established and widely adopted techniques .
 In general, the electrospinning set-up consists of a syringe with a nozzle, an electric field source, a
counter electrode or grounded target, and a pump.
 The electrospinning process is based on the principle of electrostatics
 For example, more recently, multifunctional colloidal polymer nanofibers have been prepared by
electrospinning the aqueous blends of poly(vinyl alcohol-co-vinyl acetate)/octadecyl amine-
montmorillonite (PVA/ODA-MMT) matrix nanocomposite and poly(maleic acid-alt-acrylic acid)
(poly(Mac-alt-AA) copolymers
 Besides the conventional electrospinning technique, several variations of this method have been
developed lately. These include the multineedle, needleless, and co-electrospinning or co-axial
electrospinning
 Using the self-assembly technique, the preparation of natural or synthetic nanofibers may be achieved
through the spontaneous organization of individual macromolecules into ordered and stable nanoscale
supramolecular structures or patterns

7. Emerging strategies for nanofiber fabrication
1. Solution blow spinning-
It requires only a simple commercial airbrush, concentrated polymer solution, and a compressed gas
source, the technique may potentially be utilized for in situ deposition of nanofiber mats and scaffolds
for conformable coverage of non-conducting targets as well as for numerous tissue engineering and
surgical applications
https://www.sciencedirect.com/science/article/pii/S0079670017300692

8. 2. Plasma-induced synthesis
 Using the plasma-induced synthesis method, nanofibers are prepared based on
five distinct steps:
(1) rapid and energetic bombardment of radicals onto the electrode surface,
(2) atomic vapor deposition,
(3) expansion of plasma,
(4) condensation of solution medium, and
(5) in situ reaction of oxygen and growth of nanofibers.
3.Centrifugal jet spinning-
 The versatile centrifugal jet spinning has been developed for the synthesis of
micro- or nanofibers in a highly efficient, low cost, and high-throughput fashion
.
 In principle, the thinning of solution filament into nanofibers using centrifugal
jet spinning is achieved through the controlled manipulation of centrifugal
force, viscoelasticity, and mass transfer characteristics of the spinning
solutions.
https://www.sciencedirect.com/science/article/pi
/S0079670017300692

9. 4.Electrohydrodynamic direct writing
 Highly versatile and cost-effective MES technique combines both electrical and mechanical
forces to drive the viscous ink for the large scale direct writing of solution-based materials.
https://www.sciencedirect.com/science/article/pii/S0079670017300692

10. Emerging applications in energy generation and storage
1.Batteries and fuel cells-
• Nanofibers are potential electrode materials for energy generation devices, due to
their large specific surface area and high porosity which may be utilized for storing
electrolytes and supporting rapid and long term electron/ion transport.
• Apart from LiBs, the capability of nanofibers to form 3D interconnected networks
with uniform micropores distribution has also been utilized for Li-S battery
applications
2. Supercapacitors-
 Composite nanomaterials based on cellulose nanofibers, have been used as the
building block of flexible supercapacitors.
 For example, solid-state CNFs-graphene hybrid aerogel-based flexible
supercapacitors exhibit high capacitance, power, and energy density
 CNFs have been integrated with single walled carbon nanotubes (CNF/SWCNT) for
the preparation of a novel hybrid non-woven macro fiber mat-based wearable
supercapacitor
https://www.sciencedirect.com/science/article/pii/
S0079670017300692

11. 3. Solar cells –
 Dyesensitized solar cells (DSSCs) have been seen as potential replacements to the conventional single-
crystalline Si solar cells owing to their higher efficiency, simpler production process, lower material cost, and
environmental-friendliness
4. Hydrogen storage and generation-
 nanofibers shorten the diffusion path lengths of hydrogen and active species as well as reduce the thickness of
reactive interfaces during hydrogen absorption and desorption
5. Piezoelectricity-
 piezoelectric polymers may serve as a promising building block owing to their structural flexibility and
toughness, excellent chemical resistance, simple device design and integration, and associated low cost.
 Of all piezoelectric polymers, poly(vinylidenefluoride) (PVDF) and its copolymers are generating tremendous
interests due to their outstanding mechanical-to-electrical energy conversion performance and overall
piezoelectric properties, and high mechanical flexibility and stability

12. Emerging applications in water treatment and environmental
remediation:
1.Water treatment and ultrafiltration-
 catalysts-functionalized nanofibrous materials have been actively
prepared for removing or separating sub-micrometer pollutants
and contaminants from liquid and gas environments based on
various physical and chemical techniques, adsorption and
ultrafiltration.
2. Photocatalysis-
 nanofiber-based photocatalysis has been intensively investigated
for the degradation of pollutants and various toxic environmental
chemicals
3. Chemical and gas sensing-
 These nanofibers are capable of detecting various reducing and oxidizing gases in real-time reliably with excellent
selectivity, sensitivity, and stability.
 In addition to the metal oxide semiconductor-based nanofibers, wide band-gap semiconductors and polymers are
also used for the synthesis of nanofibers for chemical and gas sensing applications
https://www.sciencedirect.com/science/article/pii
/S0079670017300692

13. Emerging applications in healthcare and biomedical engineering
1.Tissue engineering and regenerative
medicine-
• nanofiber-based scaffold emerges as a versatile
alternative for tissue engineering and regenerative
medicine applications.
• biodegradable and biocompatible natural or
synthetic polymers are typically used as the nanofiber
material
2. Wound heal dressing-
• advances in nanotechnology have enabled the
synthesis of nanomaterials possessing architectural
features and morphologies mimicking those of in
vivo ECMs, notably the nanofibrous structures
prepared through electrospinning.
https://www.sciencedirect.com/science/article/pii/S0079670017300692

14. 3.Drug and therapeutic agent delivery-
 The large surface area and the microporous structure of nanofiber networks are advantageous for the
encapsulation and direct incorporation of active biomolecules, including drugs and growth factors, into nanofibers
for cellular function modulation.
 This renders nanofibers suitable as a carrier for drug and therapeutic agent delivery
4.Biological sensing-
 nanofibers have also found application in biological sensing due to the abundant immobilization sites for
biomolecules and active species brought about by their large specific surface area.
 In addition, nanofibers possess excellent electrocatalytic activity and rapid electron transfer characteristic,
resulting in higher redox species diffusion.

15. References-
 www.avantama.com/quantumdots
 https://pubs.acs.org/doi/10.1021/acsanm.0c01386
 https://www.sciencedirect.com/science/article/pii/S0079670017300692