In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

Abstract

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N 2 gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5-100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10 5 particles/cm 3) corresponding to a volume fraction below 3 × 10-10 , which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

Distinguishing Gas-Phase and Nanoparticle Contributions to Small-Angle X-ray Scattering in Reacting Aerosol Flows

“…Pyrolytic and flame-synthesis techniques have become a popular means for producing a wide range of carbonaceous, metallic, and metal oxide nanoparticles. − However, the inherently high and variable temperatures and chemical reactivity of the synthesis conditions present a challenge for operando monitoring and optimization of the synthesis process. Small-angle X-ray scattering (SAXS) is potentially extremely useful as an operando diagnostic; ,− measurements can be performed in situ without perturbing the reaction conditions, and the wavelength regime associated with tender to hard X-ray-scattering can provide nanometer-scale spatial resolution for probing particle formation and fine-structure evolution. Such photon energies are also able to penetrate and probe high-pressure systems.…”

In situsmall-angle X-ray scattering investigation of X-ray-induced gold nanoparticle synthesis without stabilizer

“…Small-angle X-ray scattering (SAXS) plays a major role in the study of submicroscopic structures and morphological characteristics of nanomaterials, and many groups have used in situ SAXS to study the nucleation and growth of AuNPs (McKibbin et al, 2019;Polte, Erler et al, 2010;Abe ´cassis et al, 2007).…”

Predicting the deposition spot radius and the nanoparticle concentration distribution in an electrostatic precipitator

“…In order to perform detailed characterization of engineered aerosol nanoparticles, or to investigate the ultra-fine particles that surround us in the atmosphere, it is preferable to first collect such particles onto a substrate for ex situ characterization. Even though in situ and in-flight characterization techniques of aerosols have improved greatly in the last years (McKibbin et al 2019;Ouf et al 2016), ex situ characterization, using electron microscopy or x-ray methods on already collected particles are still the standard way to characterize aerosol nanoparticles. The deposition and collection of aerosol nanoparticles can be achieved in several different ways.…”