Unexpected compositional and structural modification of CoPt₃ nanoparticles by extensive surface purification

Area of Science:

• Materials Science
• Nanotechnology
• Catalysis

Background:

• Chemically synthesized nanoparticles (NPs) often require purification to optimize performance.
• Ligand removal is a common step in NP processing.
• Understanding structural changes during purification is crucial for catalyst development.

Purpose of the Study:

• To investigate the structural transformations of cobalt-platinum (CoPt3) nanoparticles after ligand removal.
• To correlate structural changes with catalytic activity.
• To elucidate the mechanisms behind NP transformation during purification.

Main Methods:

• Synchrotron X-ray scattering techniques, including small-angle X-ray scattering (SAXS).
• X-ray fluorescence (XRF) spectroscopy for elemental analysis.
• Extended X-ray absorption fine structure (EXAFS) spectroscopy for local atomic structure determination.

Main Results:

• Extensive ligand removal via solvent/nonsolvent methods transforms CoPt3 NPs into CoPt3/Pt core/shell structures.
• A significant platinum (Pt) shell (∼0.5 nm) forms, indicating cobalt (Co) leaching.
• Improved catalytic activity in octyne hydrogenation is attributed to these core/shell structures, not solely a cleaner surface.

Conclusions:

• The transformation into CoPt3/Pt core/shell structures is the primary reason for enhanced catalytic activity after purification.
• Ligand removal, not cobalt leaching in aqueous media, drives the structural changes in water-transferred NPs.
• Findings are relevant for other transition metal-based multicomponent NPs.