Microsegmented Flow-Through Synthesis of Silver Nanoprisms with Exact Tunable Optical Properties

Abstract

In this work, a multistep microcontinuous flow-through synthesis procedure for the generation of homogeneous, high-quality silver nanoprisms is presented. The particle synthesis is based on the wet chemical reduction of silver nitrate in the presence of the polyanionic polymer poly(sodium styrenesulphonate). To obtain a high yield of homogeneous prism-shaped Ag nanoparticles with a triangular base, two main experimental steps are necessary. The first step is the synthesis of seed particles. To match the quality criteria for small, homogeneous seed particles, the synthesis was carried out in a microcontinuous flow-through system. Constant residence times and an effective mixing of the reactants were realized by the application of the microsegmented flow technique. The advantage of good reactant mixing was also adapted in the second experimental step. The growth of silver nanoprisms by reduction of silver nitrate on the noncapped surfaces of the seed particles was again carried out within microfluid segments during a continuous flow-through synthesis. The obtained colloidal solutions of both, Ag seeds and Ag nanoprisms, were analyzed using differential centrifugal sedimentation, UV–vis spectrophotometry, and scanning electron microscopy. The size distributions of the product particles of the individual process steps were extremely narrow. For the Ag seed particles, an average particle diameter of 3.8 nm with a distribution half-width of 2.3 nm was found. The edge length of the Ag nanoprisms could be varied between 35 and 180 nm, while the size distribution remained narrow and the yield of particles of the desired shape high. Because of the strong sensitivity of the optical properties of the nanoprisms from the geometrical aspects, Ag nanoprisms promise a high potential for sensor applications. Constraints on nanoparticles presented by these applications, such as uniformity and narrow size distributions, can be met by microreaction technology. In particular, by applying a microsegmented flow, an improvement of the product quality can be achieved because of the enhanced segment-internal mixing and the suppression of a residence time distribution.

Synthesis of silver nanoparticles in a microfluidic coaxial flow reactor

“…There are various studies which implemented different strategies to avoid fouling, such as the segmented-ow approach and the reduction of wall interactions through pH alteration and surface silanization of the channel walls. [21][22][23] One type of design that alleviates the occurrence of fouling is the coaxial ow reactor (CFR) which allows an inner stream of reagent to be surrounded by an outer stream, creating a reaction interface between the streams. 15,16,[24][25][26][27][28] The CFR is less susceptible to fouling because the reduction of precursor ions and nucleation of metal NPs occur at the interface between the inner and outer streams, rather than near the channel walls.…”

The Mixed-Electrode Concept for Understanding Growth and Aggregation Behavior of Metal Nanoparticles in Colloidal Solution

“…Alternatively, a stepwise growth from the reduction of the first metal ion over the chemical formation and attachment of the second metal atom and a first stable Figure 1. Examples of metal nano and polymer composite particles synthesized by use of microfluidic preparation steps: (a) example of a chip device for generation of microfluid segment sequences for systematic variation of reactant concentration ratios in micro flow syntheses [23], (b) gold nanocubes [20], (c) gold nanorods, (d) gold polyeders [20], (e) flat triangular silver nanoprisms [21], (f) polyacrylamid submillimeter composite particle [24], (g) submicrometer composite particle with two incorporated types of metal nanoparticles [25], (f) submicrometer composite particle with gold nanoparticles [24].…”

“…These experiments supplied particle populations of high homogeneity and high yield [16][17][18], which supported a rational interpretation of underlying mechanisms. As well as composed spherical metal nanoparticles [19], metal rods, cubes, polyeders [20] as well as flat nanotriangles had been prepared to a high quality using microfluidic techniques [21]. The control of electrical surface charges also allowed the preparation of different types of polymer/polymer and polymer/metal composite particles [22].…”

Synthesis of Silver Nanoparticles Using a Microfluidic Impinging Jet Reactor

“…IJR is a particularly useful device to use in the synthesis of NPs since it does not clog because of absence of channel walls. Fouling is particularly problematic in microfluidic devices since their small dimensions make them potentially vulnerable to blockage, and various strategies in the literature have been used to avoid fouling such as segmented flow [24], coaxial flow [20,25], and surface silanization [26].…”