title: Gaining Control over Radiolytic Synthesis of Uniform Sub-3-nanometer Palladium Nanoparticles: Use of Aromatic Liquids in the Electron Microscope.
abstract: Synthesizing nanomaterials of uniform shape and size is of critical importance to access and manipulate the novel structure-property relationships arising at the nanoscale, such as catalytic activity. In this work, we synthesize Pd nanoparticles with well-controlled size in the sub-3 nm range using scanning transmission electron microscopy (STEM) in combination with an in situ liquid stage. We use an aromatic hydrocarbon (toluene) as a solvent that is very resistant to high-energy electron irradiation, which creates a net reducing environment without the need for additives to scavenge oxidizing radicals. The primary reducing species is molecular hydrogen, which is a widely used reductant in the synthesis of supported metal catalysts. We propose a mechanism of particle formation based on the effect of tri-n-octylphosphine (TOP) on size stabilization, relatively low production of radicals, and autocatalytic reduction of Pd(II) compounds. We combine in situ STEM results with insights from in situ small-angle X-ray scattering (SAXS) from alcohol-based synthesis, having similar reduction potential, in a customized microfluidic device as well as ex situ bulk experiments. This has allowed us to develop a fundamental growth model for the synthesis of size-stabilized Pd nanoparticles and demonstrate the utility of correlating different in situ and ex situ characterization techniques to understand, and ultimately control, metal nanostructure synthesis.
authors.affiliation: SuperSTEM Laboratory, SciTech Daresbury Campus , Keckwick Lane, Daresbury WA4 4AD, United Kingdom.
authors.forename: Patricia
authors.initials: P
authors.lastname: Abellan
authors.affiliation: Department of Chemistry & Biochemistry, University of California, San Diego , La Jolla, California 92093, United States.
authors.forename: Lucas R
authors.initials: LR
authors.lastname: Parent
authors.forename: Naila
authors.initials: N
authors.lastname: Al Hasan
authors.affiliation: Department of Industrial and Manufacturing Engineering, Florida State University , Tallahassee, Florida 32306, United States.
authors.forename: Chiwoo
authors.initials: C
authors.lastname: Park
authors.forename: Ilke
authors.initials: I
authors.lastname: Arslan
authors.affiliation: Department of Chemical Engineering, Virginia Polytechnic Institute and State University , Blacksburg, Virginia 24061, United States.
authors.forename: Ayman M
authors.initials: AM
authors.lastname: Karim
authors.forename: James E
authors.initials: JE
authors.lastname: Evans
authors.forename: Nigel D
authors.initials: ND
authors.lastname: Browning