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One-Step Femtosecond Laser Ablation Synthesis of Sub-5 Nm Gold Nanoparticles Embedded in Silica

preprint
submitted on 12.09.2018 and posted on 13.09.2018 by Mallory John, Katharine Tibbetts

We report the synthesis of silica-gold nanoparticles (silica-Au NPs) using a one-step femtosecond-reactive laser ablation in liquid (fs-RLAL) technique by focusing femtosecond laser pulses onto a silicon wafer immersed in an aqueous KAuCl4 solution. Characterization of the silica-Au NPs revealed two populations of Au NPs: (i) larger, isolated Au NPs with diameter 7.3±2.1 nm, and (ii) smaller Au NPs (3.4±0.8 nm) embedded in an amorphous silica matrix, along with new species of silicon observed from XPS analysis. The catalytic activity of the silica-Au NPs towards the reduction of para-nitrophenol by NaBH4 is significantly higher compared to the control Au NPs synthesized in the absence of a silicon wafer and other Au NPs recently reported in literature. The formation of the two populations of silica-Au NPs is ascribed to reaction dynamics occurring on two distinct timescales. First, the dense electron plasma formed within tens of femtoseconds of the laser pulse initiates reduction of the [AuCl4]– complex, leading to the formation of larger isolated Au NPs. Second, silicon species ejected from the wafer surface hundreds of picoseconds or later after the initial laser pulse reduce the remaining [AuCl4 ]– and encapsulate the growing clusters, forming ultrasmall Au NPs embedded in the silica matrix. The morphologies of the silica-Au NPs generated from fs-RLAL are distinct from those reported in recent RLAL experiments with nanosecond lasers, reflecting distinct mechanisms occurring on the different pulse duration timescales.

Funding

American Chemical Society Petroleum Research Fund (57799-DNI10);

History

Email Address of Submitting Author

johnmg@vcu.edu

Institution

Virginia Commonwealth University

Country

USA

ORCID For Submitting Author

0000-0002-6984-7010

Declaration of Conflict of Interest

No conflict of interest

Version Notes

version one

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