Controllable Synthesis of Gold Nanoparticles in Aqueous Solution by Microwave Assisted Flow Chemistry

Abstract

The development of energy efficient, reproducible and high throughput approaches to gold nanoparticles (Au-NPs) synthesis have gained increasing attention over the past decades due to their application in biomedicine, sensor and catalysis. In this work, single mode microwave irradiation is for the first time combined with microflow chemistry to fabricate Au-NPs continuously and reproducibly with controllable size in an aqueous solution. The major experimental parameters including microwave power, citrate-to-gold molar ratio ([Cit]/[Au]) and reaction residence time have been investigated systematically. As indicated by TEM, the mean particle width of the synthesised Au-NPs is between 4 and 15 nm with mean aspect ratio between ~1.4 and 2.2 after only 90 s microwave irradiation. Furthermore the Au particle morphology can be manipulated from nanowires to nanoparticles by adjusting the [Cit]/[Au] ratio. HRTEM analysis of the produced Au-NPs and UV-vis spectroscopy suggest a correlation between the red-shifted surface plasmon resonance peak and the particle aspect ratio that is probably dependent on the creation of particle-particle junctions, which alter both the size and the aspect ratio of the Au-NPs. The synthesis further demonstrated high reproducibility.

Microwave Flow Chemistry as a Methodology in Organic Syntheses, Enzymatic Reactions, and Nanoparticle Syntheses

“…A continuous-flow reactor system has been proposed by many researchers. For example, Bayazit and coworkers [39] reported that the development of energy efficient, reproducible, and high throughput approaches to synthesize gold nanoparticles (Au-NPs) has gained increasing attention over the past decades owing to applications in biomedicine, sensors, and catalysis ( Figure 20). In their study, a single-mode microwave irradiation apparatus was combined for the first time with micro-flow chemistry to fabricate Au-NPs continuously and reproducibly with controllable size in an aqueous solution.…”

Microwave Intensified Synthesis: Batch and Flow Chemistry

“…Variations of reaction conditions such as concentration, temperature and reaction time are likely to have a significant effect on both nucleation and particle growth, and a better control over these variables may improve the monodispersity, particle size and its distribution, shape and morphology, crystallinity and purity of the nanoparticles manufactured. [62,63] MI is believed to have more homogeneous heating throughout the solution, resulting in more accurate control on nucleation stage. The extra molecular level mixing force generated by microwave is further expected to help mass and energy transfer dramatically, achieving homogeneity throughout the bulk solution.…”

“…The extra molecular level mixing force generated by microwave is further expected to help mass and energy transfer dramatically, achieving homogeneity throughout the bulk solution. [14,[62][63][64] However, there are some concerns about the use of MI in the large reactors involving microwave penetration depth, requiring strong microwave intensity, long irradiation time and high-pressure resistant reactors. In principle, a capillary reactor (< 1 mm diameter) promoted by MI can make use of all advantages of MI but exclude the drawbacks listed for large reactors.…”

“…(Figure 11). [62,63] Briefly, our in-house developed microwave-assisted flow system ( Figure 12) is composed of a flow reactor (6 mL) made of Teflon tubing having 1/8 in. o.d.…”

“…c) A picture of the flow reactor in microwave holder. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 temperature above 120 8C, while the gold nanoparticles [63] were prepared at 120 8C. We selected to use the Teflon and polyethylene bases for hematite and gold nanoparticles synthesis, respectively.…”