An engineering approach to synthesis of gold and silver nanoparticles by controlling hydrodynamics and mixing based on a coaxial flow reactor

Abstract

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 to 3 ml min resulted initially in a constant Au NP size, and beyond 1 ml min 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 °C and a minimum Au NP size of 17.9 ± 2.1 nm was observed at 80 °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.

Designable nanoplasmonic biomarkers for direct microscopy cytopathology diagnostics

“…Then alloy NPs, with 32 ± 2 nm diameter, were synthesized, which can be used as seeds for the next growth stage. NaCit was added before metal salts in order to adjust the pH to slow down the chemical reduction velocity, thus facilitating homogeneous growth of NPs . For following growth stage(s), NPs synthesized in the last stage were used as seeds, and a similar process was performed to obtain the designed bioimaging labels.…”

In-Flow Flash Nanoprecipitation of Size-Controlled D-Leucine Nanoparticles for Spray-Drying Formulations

“…Total flow rate (mL min -1 ) and τ (min) The effect of the total flow rate was firstly investigated in view of its proved effects on the fluidodynamics of the nanoprecipitation. 13,27 Indeed, at low flow rates the regime is almost laminar (low Reynolds number) while it becomes turbulent at higher flow rates. A compromise between nucleation, which is facilitated by laminar mixing and low flow rates, and growth that occurs mainly at longer residence time (τ) is needed for an efficient FNP process.…”

“…A compromise between nucleation, which is facilitated by laminar mixing and low flow rates, and growth that occurs mainly at longer residence time (τ) is needed for an efficient FNP process. 13,27 The effect of the flow rate was investigated by using a 0.5% (w/v) aqueous solution of D-leucine, a 10 mL mesoreactor coil with 1 mm of internal diameter (ID) and a three-way mixer with Y-geometry, according to the flow set-up depicted in Fig. 1.…”

“…10 In this regard, seminal reports have demonstrated the benefits of using flow-assisted nanoprecipitation approaches as they allow to better regulate particle size and distribution, morphology and reproducibility. [10][11][12][13][14][15] Indeed, flow devices ensure a precise control over the mass transfer, the residence time and the timing of reagent addition/mixing, as well as the spatiotemporal separation between nucleation and growth of NPs. 16 In this paper, we describe the development of a novel flowbased method for the preparation of size-controlled D-leucine NPs to be employed as glidants in dry powders for inhalation.…”

Understanding the Influence of Rheological Properties of Shear‐Thinning Liquids on Segmented Flow in Microchannel using CLSVOF Based CFD Model

“…For gold and silver nanoparticles synthesis, Baber et al demonstrated the potential of using microfluidic reactor with a coaxial flow in controlling nanoparticle size and dispersity. Experimental studies on segmented flow have shown that it was highly influential in the synthesis of nanoparticles due to its flexibility in manipulation of mass transfer and hydrodynamics characteristics .…”