Microfluidic nanoparticle synthesis via continuous-wave laser heating

Mohammad, Laheji (2021) Microfluidic nanoparticle synthesis via continuous-wave laser heating. PhD thesis, University of Nottingham.

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Abstract

Microfluidic nanoparticle synthesis has attracted significant attention in recent years, with several advantages over conventional batch synthesis: smaller concentration and temperature gradients, well-controlled and rapidly changeable reaction conditions, and easier scalability. Laser synthesis is a route that offers rapid formation of nanoparticles. Most works in the literature focus on laser ablation in liquids or thermal decomposition of gaseous precursors, but relatively little work has been reported on the decomposition of liquid precursors, most of which have no flow control. The possibility of combining these two synthesis methods is investigated in this thesis. This work presents a novel approach for nanocrystal synthesis within microfluidic chips, wherein thermal decomposition of metal organic precursors was achieved by localised laser heating using a continuous wave laser to produce iron oxide and cadmium selenide particles. As only the precursor solution was being heated, the chips could be made using inexpensive, commercially obtained acrylic.

Laser synthesis of iron oxide nanoparticles carried out in microwells with no flow resulted in polydisperse particles between ~5-500 nm in size, and in many cases had extremely low yields. To overcome these issues, a microfluidic chip was designed with a vertical flow section where the laser was aimed. The greater control over the residence period offered by this design resulted in major improvements in the yield and size distribution. When synthesising iron oxide nanoparticles, the best results were particles with an average size of 84.7 nm and a standard deviation of 46.8 nm (55.3%).

The highly localised heating makes temperature measurement difficult. Hence a basic fluid flow and heat transfer simulation was conducted to gain a better understanding of the temperature distribution within the chip, which illustrated the limitations of the chip design and provided valuable insight for future work. The model was also used to determine suitable parameters for the microfluidic synthesis of cadmium selenide nanocrystals. Quantum dot samples with peak emission wavelengths between 457-500 nm were also synthesised in the chip, with the best result emitting at 500 nm with a FWHM of 39 nm. CdSe clusters and quantum dots could be differentiated by analysing the PL and PLE spectra of the samples.

The work presented in this thesis illustrates some of the possibilities of laser heating for nanoparticle synthesis, in combination with microfluidic chips for controlled irradiation of the reaction mixture. The experimental setup is easy to implement using inexpensive tools and materials.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Lau, Phei Li
Tan, Michelle
Chin, Jit Kai
Keywords: iron oxide; cadmium selenide; nanoparticles; quantum dots; thermal decomposition; synthesis; microfluidic; laser; continuous wave
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Chemical and Environmental Engineering
Item ID: 64888
Depositing User: LAHEJI, MOHAMMAD
Date Deposited: 04 Aug 2021 04:41
Last Modified: 04 Aug 2021 04:41
URI: http://eprints.nottingham.ac.uk/id/eprint/64888

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