Enriching Silver Nanocrystals with a Second Noble Metal

Area of Science:

• Nanotechnology and Materials Science
• Surface Chemistry
• Catalysis and Plasmonics

Background:

• Noble-metal nanocrystals are crucial for plasmonics, catalysis, sensing, imaging, and medicine.
• Bimetallic nanocrystal systems offer enhanced properties and expanded applications compared to monometallic ones.
• Seeded growth is a common method for bimetallic nanocrystal fabrication but is limited by galvanic replacement.

Purpose of the Study:

• To develop a controlled seeded growth method for fabricating bimetallic nanocrystals with minimal galvanic replacement.
• To demonstrate the synthesis of silver-bimetallic (Ag@M, Ag@Ag-M where M = Au, Pd, Pt) nanocubes with core-frame and core-shell structures.
• To explore the catalytic and plasmonic properties of the synthesized bimetallic nanocrystals.

Main Methods:

• Utilized silver (Ag) nanocubes as seeds for the deposition of a second metal (M).
• Employed two distinct approaches to control metal deposition: high pH (pH 11.9) using ascorbate monoanion as a strong reductant, and low pH (pH 3.2) with co-precipitation of Ag+ and M^n+ ions.
• Controlled the reaction conditions, including pH and precursor ratios, to suppress galvanic replacement and self-nucleation.

Main Results:

• Successfully synthesized Ag@M and Ag@Ag-M nanocubes with tunable core-frame and core-shell architectures.
• Demonstrated that high pH conditions favor sequential deposition leading to core-shell structures, while low pH with high Ag+/M^n+ ratio promotes core-frame formation.
• Showcased Ag@Ag-Pd core-frame nanocubes as dual catalysts for nitroaromatic transformations and Ag@Au core-shell nanocubes with enhanced stability and surface-enhanced Raman scattering (SERS) activity.

Conclusions:

• The developed seeded growth method effectively overcomes the limitations of galvanic replacement, enabling precise control over bimetallic nanocrystal synthesis.
• The synthesized Ag@M and Ag@Ag-M nanocubes exhibit tailored structures and enhanced functionalities for catalytic and plasmonic applications.
• Selective removal of Ag cores provides a route to novel nanostructures like nanoframes and nanoboxes.