Journal
NANO LETTERS
Volume 17, Issue 3, Pages 1336-1343Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.6b03440
Keywords
Colloidal nanoparticles; droplet microreactors; segmented flow; plasmas; solvated electron
Categories
Funding
- Engineering and Physical Sciences Research Council [EP/K006088/1, EP/K006142/1, EP/K022237/1, EP/M024938/1, EP/M015211/1]
- Royal Society International Exchange Scheme [IE120884]
- Leverhulme International Network [IN-2012-136]
- Invest N. Ireland [RD0714186]
- Engineering and Physical Sciences Research Council [EP/K022237/1, EP/K006088/1, EP/K006142/1, EP/M015211/1, EP/M024938/1] Funding Source: researchfish
- EPSRC [EP/K006088/1, EP/M015211/1, EP/K006142/1, EP/M024938/1, EP/K022237/1] Funding Source: UKRI
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We demonstrate an entirely new method of nanoparticle chemical synthesis based on liquid droplet irradiation with ultralow (<0.1 eV) energy electrons. While nanoparticle formation via high energy radiolysis or transmission electron microscopy-based electron bombardment is well-understood, we have developed a source of electrons with energies close to thermal which leads to a number of important and unique benefits. The charged species, including the growing nanoparticles, are held in an ultrathin surface reaction zone which enables extremely rapid precursor reduction. In a proof-of-principle demonstration, we obtain small-diameter Au nanoparticles (similar to 4 nm) with tight control of polydispersity, in under 150 mu s. The precursor was almost completely reduced in this period, and the resultant nanoparticles were water-soluble and free of surfactant or additional ligand chemistry. Nanoparticle synthesis rates within the droplets were many orders of magnitude greater than equivalent rates reported for radiolysis, electron beam irradiation, or colloidal chemical synthesis where reaction times vary from seconds to hours. In our device, a stream of precursor loaded microdroplets, similar to 15 mu m in diameter, were transported rapidly through a cold atmospheric pressure plasma with a high charge concentration. A high electron flux, electron and nanoparticle confinement at the surface of the droplet, and the picoliter reactor volume are thought to be responsible for the remarkable enhancement in nanoparticle synthesis rates. While this approach exhibits considerable potential for scale-up of synthesis rates, it also offers the more immediate prospect of continuous on-demand delivery of high-quality nanomaterials directly to their point of use by avoiding the necessity of collection, recovery, and purification. A range of new applications can be envisaged, from theranostics and biomedical imaging in tissue to inline catalyst production for pollution remediation in automobiles.
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