Shape-controlled continuous synthesis of metal nanostructures

Abstract

A segmented flow-based microreactor is used for the continuous production of faceted nanocrystals. Flow segmentation is proposed as a versatile tool to manipulate the reduction kinetics and control the growth of faceted nanostructures; tuning the size and shape. Switching the gas from oxygen to carbon monoxide permits the adjustment in nanostructure growth from 1D (nanorods) to 2D (nanosheets). CO is a key factor in the formation of Pd nanosheets and Pt nanocubes; operating as a second phase, a reductant, and a capping agent. This combination confines the growth to specific structures. In addition, the segmented flow microfluidic reactor inherently has the ability to operate in a reproducible manner at elevated temperatures and pressures whilst confining potentially toxic reactants, such as CO, in nanoliter slugs. This continuous system successfully synthesised Pd nanorods with an aspect ratio of 6; thin palladium nanosheets with a thickness of 1.5 nm; and Pt nanocubes with a 5.6 nm edge length, all in a synthesis time as low as 150 s.

Microfluidic Devices in Fabricating Nano or Micromaterials for Biomedical Applications

“…For example, the crystallinities, dimensions, and morphologies of polycaprolactone‐ block ‐poly(ethylene oxide) (PCL‐ b ‐PEO) nanoparticles change with flow rate in a segmented MD, but is not observed in a single phase laminar MD ( Figure a) . In general, segmented flow microfluidics have been used for the synthesis of a variety of monodispersed nanoparticles including semiconducting QDs, metal nanocrystals (Pt, Fe, Au, Ag,) and their composites, polymer nanoparticles, and metal organic frameworks (MOFs) . When performing the synthesis in liquid–liquid segmented microfluidics, Arndt et al accelerated the rate of formation of Ag nanoparticles by a factor of four (30–150 s) compared to batch processing, with diameters ranging from 7 to 120 nm.…”

“…For example, by varying the composition of the gas segments (H 2 , N 2 , O 2 , or CO), the crystalline phase (magnetite, feroxyhite, goethite), size, and shapes (octahedral, nanoflake, platelet, nanosheets, nanobars) of the resulting iron oxide nanoparticles can be accurately tuned . Sebastian et al fabricated Pt nanocubes, Pd nanorods, and Pd trigonal and hexagonal nanosheets, using the same gas–liquid segmented MD, with a change of gas between N 2 , O 2 , CO leading to a change of morphology (Figure b). Even though segmented flow MDs demonstrate better mixing than single phase laminar flow, mixing might still be insufficient for certain reactions, necessitating the use of other mechanical energy such as a ultrasonic bath (Figure d).…”

“…a) Schematic of single phase laminar flow and two phase segmented flow synthesis of PCL‐ b ‐PEO polymeric nanoparticles . b) Schematic of the gas–liquid segmented flow and internal circulation and the summary of nanomaterials obtained under different gas environment . c) Schematic of the segmented continuous flow microwave‐assisted MD for fabricating MOF‐74(Ni) .…”

“…Copyright 2016, American Chemical Society. b) Reproduced under the terms of the CC BY 3.0 license . Copyright 2016, Royal Society of Chemistry.…”

Manipulation and Control of Structure and Size of Inorganic Nanomaterials in Microchemical Systems

“…Correspondingly, novel quantum dots, small-sized nanocubes, nanosheets, and nanorods have been successfully prepared in microchemical systems. Sebastian et al synthesized nanocubes, nanosheets, and nanorods in a silicon-Pyrex microreactor containing a cooled mixing zone and a heated reaction zone, which could withstand higher temperature (the maximum was approximately 350°C) and pressure (nearly 1 MPa) [28,65]. Gas was introduced to form the segmented flow, as indicated in Fig.…”