| dc.description.abstract | One of the key challenges in nanoparticle synthesis is the quality control on scaling up
the operation from bench to plant scale, which is constrained by conventionally adopted
batch operation. Translation from batch operation to continuous green synthesis (metal,
bi-metallic core-shell, and alloy nanoparticles (NPs)) with low polydispersity index
(PDI) could unlock potential applications of metallic nanostructures with a projected
market of $40.6 Billion and more by 20271. However, the continuous large-scale
production suffers from high polydispersity due to lack of process optimization. We
attempt to address such scale-up challenges while using the green synthesis of metallic
nanoparticles in this work. The objective of this thesis is to optimize continuous
processing of metal nanoparticle synthesis and demonstrate application of metallic
nanostructure printed of flexible substrate using inkjet printing technology.
The first part of the thesis is motivated by the desire to translate the batch protocol for
NPs synthesis (developed in our group earlier)2,3 to a continuous process, and hence
increase the affordability of NPs for end users. In this work, nanoparticle colloids are
synthesized using different designs of CFRs and steady-state synthesis of nanoparticles
is achieved with insignificant variation in particle size. Our results further showed that
a balance between engineering and chemical parameters are required to obtain desired
particle size distribution (PSD) and morphology during green synthesis of NPs. We
improved our reactor design from channel to pool-based to address poor reagent mixing
and our results show that the pool reactors could produce uniform particles of sizeii
7.2±1.0 nm with the production rate of 7.1 mg/h. We later moved to a CSTR-based
reactor to address variations in the particles’ morphology while changing the flow rate
of precursor salt. We found that the CSTR-based reactor can synthesise colloids (Gold,
Silver, bimetallic gold-silver core-shell, and gold-silver alloy) at higher (10 times) flow
rates and offers a better and affordable route for continuous nanoparticles synthesis
within numerous applications in the healthcare and energy sectors. For the first time, to
the best of my knowledge, the steady-state synthesis of metal nanoparticles is
demonstrated here. After attaining steady state, the particle size distribution does not
vary significantly. Investigations are performed to find out the effect of engineering
parameters as well as chemical parameters. Particle size distribution is more sensitive
to chemical parameters in comparison to engineering parameters. Although,
engineering parameters like reactor design, mixing, temperature are important
parameters to tailor nanoparticle size in a controlled fashion. Hence, there must be a
balance between both to get desired particle size and morphology.
In the second part of the thesis, we demonstrated the application of in-situ fabricated
silver nanowires on copier paper for non-enzymatic glucose, using a form of inkjet
printing technology. The inkjet printing technique is another avenue of fabrication of
nanostructure-based flexible substrates that can be scaled using roll to roll printing
techniques. Using this technique, we could fabricate, and customize electroadhesive
pads based on interdigitated electrode designs with an interelectrode distance of 1 mm
on paper. It was observed that, if left as a residue, lateral silver ion migration on
applying high voltage leads to lowering of the gaps between electrodes, which resultsiii
in increased load capacity. Further electromigration can be controlled by chemical
fixing of the sample, i.e., by immersing printed samples in 0.5 M Sodium thiosulphate.
The advantage of this process is that different designs of electrodes can be easily
fabricated depending upon the required application. The in-situ fabricated silver
nanowires incorporated with CuO/Cu2O nanoparticles are used for non-enzymatic
glucose detection. Non-enzymatic sensors (4th generation) can replace the enzymatic
detectors (3rd generation)4, but major challenge associated with 4th generation detectors
is that it requires alkaline pH for reaction to be initiated. Paper based standard electrode
(Ag/AgCl); silver nanowire incorporated with CuO/Cu2O nanoparticles (synthesised by
wet chemical method) are used as working electrode. Ag nanowires modified with CuO
nanoparticles show a linear increment in current with increase in glucose concentration.
Glucose detection is performed in the concentration range of normal sugar level in
human body in the range from 2.2 – 6.6 mM.iv
References:
1 Metal Nanoparticles - Global Market Trajectory & Analytics 2021,
<https://www.researchandmarkets.com/reports/5030157/metal-nanoparticlesglobal-market-trajectory> (19/09/2021).
2 Sivaraman, S. K., Kumar, S. Santhanam, V. Room-temperature synthesis of
gold nanoparticles; Size-control by slow addition. Gold Bulletin 43, 275-286
(2010).
3 Sivaraman, S. K., Kumar, S. Santhanam, V. Monodisperse sub-10nm gold
nanoparticles by reversing the order of addition in Turkevich method – The role
of chloroauric acid. Journal of Colloid and Interface Science 361, 543-547
(2011).
4 Toghill, K. E. & Compton, R. G. Electrochemical non-enzymatic glucose
sensors: a perspective and an evaluation. Int. J. Electrochem. Sci 5, 1246-1301
(2010). | en_US |
