Particle formation mechanisms supported by in situ synchrotron XAFS and SAXS studies: a review of metal, metal-oxide, semiconductor and selected other nanoparticle formation reactions

Abstract

Following the definition of and four primary criteria for obtaining reliable, disproof-based mechanisms of particle formation, 74 literature papers utilizing synchrotron XASF and SAXS are analyzed with an emphasis on 8 case studies.

Chemical Considerations for Colloidal Nanocrystal Synthesis

“…The advancement of analytical methods has provided the scientific community with the necessary tools to investigated nucleation in greater detail than was possible in 1950 . Small angle X-ray scattering (SAXS), for example, has been instrumental in disproving the concept of burst nucleation. , In the cases of Pd, CdSe, InP, and PbS­(e) nanocrystals, researchers clearly observe a steady increase of the particle number throughout a large portion of the reaction time; ,− see Figure for an example on Pd nanocrystals.…”

“…When studying the chemistry of nucleation, we should thus not reduce the problem to an abstract monomer, but one needs to take into account the specific chemical nature of the species. This requires detailed investigation of the coordination chemistry of precursors and their exact decomposition mechanism. ,,,,− Such studies benefit greatly from X-ray based (synchrotron) techniques, e.g., small-angle X-ray scattering (SAXS), extended X-ray absorption fine structure (EXAFS) spectroscopy, and pair distribution function (PDF) analysis. ,, …”

“…29,38,43,79,109−111 Such studies benefit greatly from X-ray based (synchrotron) techniques, e.g., small-angle X-ray scattering (SAXS), extended X-ray absorption fine structure (EXAFS) spectroscopy, and pair distribution function (PDF) analysis. 89,106,112 We are still very far from a retro-synthetic analysis of nanocrystals, but we have made important progress in recent years. We dismissed burst nucleation, introduced superfocusing, and are starting to look into the fine chemical details of nanocrystal synthesis.…”

Dispersive XAFS Study on the Laser-Induced Reduction of a Rh3+Ion Complex: Presence of a Rh+Intermediate in Direct Photoreduction

“…Finke's model has been applied not only for the photoinduced preparation of PM nanoparticles but also for wet chemical synthesis and has been used to explain in situ X-ray absorption fine structure (XAFS) spectroscopy and small-/ wide-angle X-ray scattering data. 23 According to experimental photocatalytic reduction results, the photoreduction rates of PM n+ ions decrease in the order of Ag > Pd > Au > Pt ≫ Rh. 24,25 Owing to a slow reduction rate, there have been few reports on the photoreduction of Rh 3+ ion complexes in aqueous solutions.…”

“…Finke’s model has been applied not only for the photoinduced preparation of PM nanoparticles but also for wet chemical synthesis and has been used to explain in situ X-ray absorption fine structure (XAFS) spectroscopy and small-/wide-angle X-ray scattering data …”