2 research outputs found
<i>In Situ</i> Xâray Scattering Guides the Synthesis of Uniform PtSn Nanocrystals
Compared to monometallic nanocrystals
(NCs), bimetallic ones often
exhibit superior properties due to their wide tunability in structure
and composition. A detailed understanding of their synthesis at the
atomic scale provides crucial knowledge for their rational design.
Here, exploring the PtâSn bimetallic system as an example,
we study in detail the synthesis of PtSn NCs using <i>in situ</i> synchrotron X-ray scattering. We show that when PtÂ(II) and SnÂ(IV)
precursors are used, in contrast to a typical simultaneous reduction
mechanism, the PtSn NCs are formed through an initial reduction of
PtÂ(II) to form Pt NCs, followed by the chemical transformation from
Pt to PtSn. The kinetics derived from the <i>in situ</i> measurements shows fast diffusion of Sn into the Pt lattice accompanied
by reordering of these atoms into intermetallic PtSn structure within
300 s at the reaction temperature (âŒ280 °C). This crucial
mechanistic understanding enables the synthesis of well-defined PtSn
NCs with controlled structure and composition via a seed-mediated
approach. This type of <i>in situ</i> characterization can
be extended to other multicomponent nanostructures to advance their
rational synthesis for practical applications
Tuning Precursor Reactivity toward Nanometer-Size Control in Palladium Nanoparticles Studied by in Situ Small Angle Xâray Scattering
Synthesis of monodisperse
nanoparticles (NPs) with precisely controlled
size is critical for understanding their size-dependent properties.
Although significant synthetic developments have been achieved, it
is still challenging to synthesize well-defined NPs in a predictive
way due to a lack of in-depth mechanistic understanding of reaction
kinetics. Here we use synchrotron-based small-angle X-ray scattering
(SAXS) to monitor in situ the formation of palladium (Pd) NPs through
thermal decomposition of PdâTOP (TOP: trioctylphosphine) complex
via the âheat-upâ method. We systematically study the
effects of different ligands, including oleylamine, TOP, and oleic
acid, on the formation kinetics of Pd NPs. Through quantitative analysis
of the real-time SAXS data, we are able to obtain a detailed picture
of the size, size distribution, and concentration of Pd NPs during
the syntheses, and these results show that different ligands strongly
affect the precursor reactivity. We find that oleylamine does not
change the reactivity of the PdâTOP complex but promote the
formation of nuclei due to strong ligandâNP binding. On the
other hand, TOP and oleic acid substantially change the precursor
reactivity over more than an order of magnitude, which controls the
nucleation kinetics and determines the final particle size. A theoretical
model is used to demonstrate that the nucleation and growth kinetics
are dependent on both precursor reactivity and ligandâNP binding
affinity, thus providing a framework to explain the synthesis process
and the effect of the reaction conditions. Quantitative understanding
of the impacts of different ligands enables the successful synthesis
of a series of monodisperse Pd NPs in the broad size range from 3
to 11 nm with nanometer-size control, which serve as a model system
to study their size-dependent catalytic properties. The in situ SAXS
probing can be readily extended to other functional NPs to greatly
advance their synthetic design