18 research outputs found
Gold Nanoparticle Synthesis Using Spatially and Temporally Shaped Femtosecond Laser Pulses: Post-Irradiation Auto-Reduction of Aqueous [AuCl<sub>4</sub>]<sup>−</sup>
Simultaneous
spatiotemporal focusing (SSTF) of femtosecond laser
radiation is used to produce gold nanoparticles from aqueous [AuCl<sub>4</sub>]<sup>−</sup> solutions. Multiphoton ionization and
dissociation of water produces electrons and hydrogen atoms for the
reduction of [AuCl<sub>4</sub>]<sup>−</sup> to Au(0) during
irradiation with the temporally chirped (36 ps) pulse and produces
hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) as a long-lived reducing
agent which persists after irradiation is terminated. Aqueous H<sub>2</sub>O<sub>2</sub> is found to reduce [AuCl<sub>4</sub>]<sup>−</sup>, remaining in solution after the laser irradiation is terminated,
leading to growth and transformation of the existing Au(0) species.
The highly efficient postirradiation reduction of [AuCl<sub>4</sub>]<sup>−</sup> to Au(0) by H<sub>2</sub>O<sub>2</sub> is ascribed
to reactions occurring on gold nanoparticle surfaces. In the absence
of added surfactant, the negatively charged gold particles formed
during irradiation are a complex mixture of irregularly shaped and
spherical morphologies that are only metastable as aqueous dispersions.
These particles become transformed into more perfectly shaped gold
crystals, as the remaining [AuCl<sub>4</sub>]<sup>−</sup> is
reduced in the postirradiation period. The addition of polyethylene
glycol (PEG<sub>45</sub>) accelerates the rate of the [AuCl<sub>4</sub>]<sup>−</sup> reduction during laser irradiation and directs
the exclusive formation of spherical nanoparticles. Varying the concentration
of PEG<sub>45</sub> tunes the diameter and size distribution of the
Au nanoparticles formed by laser processing from 3.9 ± 0.7 to
11 ± 2.4 nm
Gold Nanotriangle Formation through Strong-Field Laser Processing of Aqueous KAuCl<sub>4</sub> and Postirradiation Reduction by Hydrogen Peroxide
Femtosecond
laser irradiation of aqueous KAuCl<sub>4</sub> followed
by postirradiation reduction with hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) is investigated as a new approach for the synthesis
of gold nanotriangles (AuNTs) without any added surfactant molecules.
Laser irradiation was applied for times ranging from 5 to 240 s, and
postirradiation reduction of the solutions was monitored by UV–vis
spectroscopy. Laser processing of aqueous KAuCl<sub>4</sub> for 240
s, where the full reduction of Au(III) occurred during irradiation,
produced spherical gold nanoparticles (AuNPs) with an average size
of 11.4 ± 3.4 nm. Irradiation for shorter times (i.e., 15 s)
resulted in the formation of laser-generated AuNP seeds (5.7 ±
1.8 nm) in equilibrium with unreacted KAuCl<sub>4</sub> after termination
of laser irradiation. The postirradiation reduction of these solutions
by H<sub>2</sub>O<sub>2</sub> produced a mixture of spherical and
triangular AuNPs. Decreasing the laser irradiation time from 45 to
5 s significantly reduced the number of laser-generated Au seeds,
the amount of H<sub>2</sub>O<sub>2</sub> produced, and the rate of
postirradiation reduction, resulting in the formation of a large number
of AuNTs with sizes increasing from 29.5 ± 10.2 to 125 ±
43.2 nm. Postirradiation reduction is kinetically inhibited in the
absence of laser-generated AuNP seeds
Triangular Gold Nanoplate Growth by Oriented Attachment of Au Seeds Generated by Strong Field Laser Reduction
The synthesis of surfactant-free
Au nanoplates is desirable for the development of biocompatible therapeutics/diagnostics.
Rapid Δ-function energy deposition by irradiation of aqueous
KAuCl<sub>4</sub> solution with a 5 s burst of intense shaped laser
pulses, followed by slow addition of H<sub>2</sub>O<sub>2</sub>, results
in selective formation of nanoplates with no additional reagents.
The primary mechanism of nanoplate formation is found to be oriented
attachment of the spherical seeds, which self-recrystallize to form
crystalline Au nanoplates
Mechanism of Improved Au Nanoparticle Size Distributions Using Simultaneous Spatial and Temporal Focusing for Femtosecond Laser Irradiation of Aqueous KAuCl<sub>4</sub>
The production of gold nanoparticles
(AuNPs) by irradiation of aqueous [AuCl<sub>4</sub>]<sup>−</sup> with femtosecond laser pulses is investigated using simultaneous
spatial and temporal focusing (SSTF) and compared to the results of
conventional geometric focusing (GF). The effects of capping agent,
laser power, reaction conditions in the cuvette, and laser chirp are
studied, and we find that SSTF produces smaller particles with fewer
irregular structures and fewer outlying large particles than GF in
all cases except for one, in which the particle size distributions
are the same. The difference is primarily ascribed to the intrinsic
plasma properties of the two geometries: SSTF produces a plasma that
is more homogeneous and spatially symmetric than that of GF, promoting
efficient intrinsic mixing of the solution
Gold nanorings synthesized via a stress-driven collapse and etching mechanism
10.1038/am.2016.163NPG Asia Materials811e32