One-step femtosecond laser ablation synthesis of sub-3 nm gold nanoparticles stabilized by silica

Abstract

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 KAuCl 4 solution. Characterization of the silica-Au NPs revealed two populations of Au NPs: (i) larger, isolated Au NPs with diameter 7.0±2.0 nm, and (ii) smaller Au NPs (1.9±0.7 nm) stabilized by an amorphous silica matrix, along with new species of silicon observed from XPS analysis. The silica-Au NPs were catalytically active towards the model reaction of para-nitrophenol reduction by NaBH 4. 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 [AuCl 4 ]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 [AuCl 4 ]and encapsulate the growing clusters, forming ultrasmall Au NPs stabilized by 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.

Controlling the morphology of copper-silica nanocomposites from laser ablation in liquid

“…The experimental laser setup has been described in detail in Refs. [36,39,40] Fourier Transform Infrared Spectroscopy (FTIR) FTIR analysis was conducted on a Nicolet iS50 FTIR spectrometer equipped with a mid-and far-IR-capable diamond ATR. Spectra were obtained using 32 scans in the range of 4000 to 400 cm 1 with 5 cm 1 resolution.…”

“…All samples have peaks around 1652 cm 1 , which corresponds to the O H bending mode of adsorbed water [11,62]. Experimental details and calculations for determining the catalytic rate constants have been described in detail elsewhere [36,38] and are provided in the…”

“…For instance, mixed-metal Pt-Co and Pt-Co-Cu oxide NPs for fuel cell applications were synthesized by ablating a Co target immersed in Pt and Cu metal salt solutions [28][29][30], and Ni-Fe layered hydroxides doped with Ti and La for electrochemical water splitting were synthesized by ablation of Fe powder in aqueous solutions of Ni, Ti, and La salts [31,32]. Complex metaloxide mineral phases of copper and zinc were synthesized by RLAL of Zn or Cu targets immersed in aqueous Zn or Cu salt solutions [33], and silica-supported Au or Ag nanomaterials have been synthesized by ablating silicon wafers in aqueous gold or silver salt solutions [27,[34][35][36]. Recently, we generated sub-3 nm Au NPs dispersed throughout a silica matrix by ablating a silicon wafer immersed in a [AuCl 4 ]solution using femtosecond laser pulses [36].…”

“…Complex metaloxide mineral phases of copper and zinc were synthesized by RLAL of Zn or Cu targets immersed in aqueous Zn or Cu salt solutions [33], and silica-supported Au or Ag nanomaterials have been synthesized by ablating silicon wafers in aqueous gold or silver salt solutions [27,[34][35][36]. Recently, we generated sub-3 nm Au NPs dispersed throughout a silica matrix by ablating a silicon wafer immersed in a [AuCl 4 ]solution using femtosecond laser pulses [36].…”

Laser-assisted synthesis of gold–graphene oxide nanocomposites: effect of pulse duration

“…This down-shifted value has been observed in some previous reports of Au-GO composites 17,19 and in our previous reports of Au NPs synthesized by laser processing. 47,49,56 The down-shift can be attributed to interaction with the GO support, 17,19 the presence of low-coordinated Au atoms, 47,49,56,57 or both. The peaks at 84.7 eV (fs) and 85.0 eV (ns) are slightly lower than the reported for Au + (85.6 eV) and correspond to partially oxidized Au atoms, denoted as Au d+ .…”