Journal
NANOSCALE
Volume 9, Issue 37, Pages 14149-14161Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7nr04962e
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Funding
- EPSRC
- University College London
- Royal Society
- Engineering and Physical Sciences Research Council [1062993] Funding Source: researchfish
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In this work we present a detailed study of flow technology approaches that could open up new possibilities for nanoparticle synthesis. The synthesis of gold and silver nanoparticles (NPs) in a flow device based on a coaxial flow reactor (CFR) was investigated. The CFR comprised of an outer glass tube of 2 mm inner diameter (I.D.) and an inner glass tube whose I.D. varied between 0.142 and 0.798 mm. A split and recombine (SAR) mixer and coiled flow inverter (CFI) were further employed to alter the mixing conditions after the CFR. The 'Turkevich' method was used to synthesize gold NPs, with a CFR followed by a CFI. This assembly allows control over nucleation and growth through variation of residence time. Increasing the total flow rate from 0.25 ml min(-1) to 3 ml min-1 resulted initially in a constant Au NP size, and beyond 1 ml min-1 to a size increase of Au NPs from 17.9 +/- 2.1 nm to 23.9 +/- 4.7 nm. The temperature was varied between 60-100 degrees C and a minimum Au NP size of 17.9 +/- 2.1 nm was observed at 80 degrees C. Silver NPs were synthesized in a CFR followed by a SAR mixer, using sodium borohydride to reduce silver nitrate in the presence of trisodium citrate. The SAR mixer provided an enhancement of the well-controlled laminar mixing in the CFR. Increasing silver nitrate concentration resulted in a decrease in Ag NP size from 5.5 +/- 2.4 nm to 3.4 +/- 1.4 nm. Different hydrodynamic conditions were studied in the CFR operated in isolation for silver NP synthesis. Increasing the Reynolds number from 132 to 530 in the inner tube created a vortex flow resulting in Ag NPs in the size range between 5.9 +/- 1.5 nm to 7.7 +/- 3.4 nm. Decreasing the inner tube I. D. from 0.798 mm to 0.142 mm resulted in a decrease in Ag NP size from 10.5 +/- 4.0 nm to 4.7 +/- 1.4 nm. Thus, changing the thickness of the inner stream enabled control over size of the Ag NPs.
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