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Detection and Characterisation of Sub-Critical Nuclei during Reactive Pd Metal Nucleation by X-ray Absorption Spectroscopy

DOI: 10.1039/C5CE01883H DOI Help

Authors: S.-y Chang (University of Manchester) , Y. Grunder (University of Manchester) , S. G. Booth (University of Manchester) , L. B. Molleta (University of Manchester) , A. Uehara (University of Manchester) , J. F. W. Mosselmans (Diamond Light Source) , G. Cibin (Diamond Light Source) , V.-t. Pham (Synchrotron SOLEIL) , L. Nataf (Synchrotron SOLEIL) , R. A. Dryfe (University of Manchester) , S. L. M Schroeder (The University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Crystengcomm

State: Published (Approved)
Published: December 2015
Diamond Proposal Number(s): 8405

Open Access Open Access

Abstract: The interfacial reduction of aqueous [PdCl4]2− at the interface with an organic solution of ferrocene has been characterised by X-ray absorption fine structure (XAFS) spectroscopy. Use of a liquid–liquid interface as a model for homogeneous nucleation permits control of the thermodynamic driving force for nucleation, through variation of the [PdCl4]2− and ferrocene concentrations in the bulk of the adjacent phases. We demonstrate that this approach permits characterisation of the system under conditions of (i) no particle nucleation, (ii) fast spontaneous nucleation of stable nanoparticles and (iii) an intermediate state, in which formation of metastable Pd sub-critical nuclei takes place. Analysis of the XAFS spectra in the metastable state revealed a stochastically fluctuating equilibrium in which Pd nuclei are constantly formed and re-dissolved, as evident from oxidation state fluctuations detected by the Pd XAFS. Supersaturation was evidently sufficient to induce nanoparticle formation but insufficient for nuclei to grow beyond the critical cluster size. We were able to maintain a system in this metastable state for several hours. Such sub-critical clusters are predicted by classical nucleation theory, but have not been detected except in liquid-cell TEM imaging and scanning electrochemical microscopy studies.

Subject Areas: Chemistry


Instruments: B18-Core EXAFS

Other Facilities: SOLEIL