In Situ PDF Study of the Nucleation and Growth of Intermetallic PtPb Nanocrystals

Abstract

The mechanism of Pt and PtPb nanocrystal formation under supercritical ethanol conditions has been investigated by means of in situ X‐ray total scattering and pair distribution function (PDF) analysis. The metal complex structures of two different platinum precursor solutions, chloroplatinic acid and Pt(acac)2 (acac=acetylacetonate) provide atomic‐scale detail about the nucleation mechanisms after initiation of the reaction with Pb(acac)2 by heating. The stronger Pt−O chemical bonding in the Pt(acac)2 precursor complex compared with the Pt−Cl bonding in the chloroplatinic acid precursor complex leads to a much slower reduction of the Pt center, and this allows more optimal co‐reduction conditions providing a pathway for formation of phase‐pure intermetallic PtPb product. The matching chemistry of the Pt(acac)2 and Pb(acac)2 precursors allow development of a facile continuous flow supercritical ethanol process for obtaining phase‐pure hexagonal PtPb nanocrystals. The study thus highlights the importance of in situ studies in revealing atomic‐scale information about nucleation mechanisms, which can be used in design of specific synthesis pathways, and the new continuous‐flow process to obtain PtPb nanocrystals holds potential for large‐scale production.

Autocatalytic Formation of High‐Entropy Alloy Nanoparticles

“…Similar structural features are observed for all metal precursor solutions with distinct peaks below 3 Å (note enlargement in the Figure) and weak correlations at longer interatomic distances. The peaks below 3 Å correspond to interatomic distances within a metal acetylacetonate complex, [24] and the lack of long‐range features indicates that only monomers are present.…”

Monitoring the assembly–disassembly–organisation–reassembly process of germanosilicate UTL throughin situpair distribution function analysis

“…Other materials can be prepared by controlling the relative orientation of the layers prior to calcination. 8,31,46 The rate of the final two steps are greatly enhanced by an increase in hydrochloric acid concentration, [H + ] (Fig. 1).…”

“…[27][28][29][30] PDF allows for structure changes in both solidsolid transformations and crystallization of solids to be monitored in situ. 21,[31][32][33] Analysis of zeolites and silicates through in situ PDF allow for a more thorough examination of both the nucleation and crystal transformations over time or due to a temperature change. 27,[34][35][36][37][38] The success of recent in situ total scattering experiments can be attributed to dedicated beamlines with large area detectors allowing for high qmeasurements in a short time.…”

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

“…This can be achieved by careful selection of metal precursors with comparable reduction rates suggested by in situ X-ray total scattering, as shown by an example presented in the reductive synthesis of PtPb intermetallic compounds in supercritical ethanol (250-350 °C, 25 MPa). 244 The areas under the peaks in the PDF corresponding to Pt-O in Pt bis(acetylacetonate) and Pb-O in Pb bis(acetylacetonate) started to decrease at an almost identical rate 20 s after starting the reaction, suggesting a simultaneous co-reduction of Pt and Pb resulting in intermetallic compounds. In contrast, when H2PtCl6 was taken as the precursor, Pt was identified in the product.…”

“…Total X-ray scattering, also known as pair distribution function (PDF) analysis, complements the issue and is able to characterize structures that are intrinsically disordered so as to provide valuable information on the process prior to the crystallization. 220,229,230,243,244 For instance, by calculating the atomic pair distance distribution from the in situ X-ray total scattering data, peaks in the temporally evolved distributions assigned to the Pt-Cl and Pt-Pt bonds were used to clarify the transformation process in the primary stage during the synthesis of Pt NPs by reducing H2PtCl6 in supercritical ethanol (250 °C,25 MPa) (Fig. 9e).…”