Article pubs.acs.org/Langmuir
Gold Nanotriangle Formation through Strong-Field Laser Processing of Aqueous KAuCl4 and Postirradiation Reduction by Hydrogen Peroxide Behzad Tangeysh,† Katharine Moore Tibbetts,‡ Johanan H. Odhner,† Bradford B. Wayland,† and Robert J. Levis*,† †
Department of Chemistry and the Center for Advanced Photonics Research, Temple University, Philadelphia, Pennsylvania 19122, United States ‡ Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, United States S Supporting Information *
ABSTRACT: Femtosecond laser irradiation of aqueous KAuCl4 followed by postirradiation reduction with hydrogen peroxide (H2O2) 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 KAuCl4 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 KAuCl4 after termination of laser irradiation. The postirradiation reduction of these solutions by H2O2 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 H2O2 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.
■
INTRODUCTION Developing convenient methods for synthesizing gold nanoparticles (AuNPs) is an area of fundamental interest due to the expanding applications of these materials in fields ranging from catalysis to medicine.1−5 Gold nanomaterials exhibit unique optical properties since their surface plasmon resonance (SPR) frequency can be tuned throughout the visible and near-infrared (NIR) regions by varying the size and morphology of the particles.6 Anisotropic AuNPs such as rods, triangles, and cages are desirable for biomedical applications, since their associated SPR band can be extended into the NIR region where tissue absorbance is minimized.7−11 Gold nanotriangles (AuNTs) have the ability to confine an electric field at the sharp tips for applications such as surface-enhanced Raman spectroscopy (SERS).12−14 Since the ratio of surface to bulk atoms in platelike nanostructures, i.e., triangles and disks, is higher than that of any other nanoparticle morphologies, the SPR frequency of these materials is very sensitive to the dielectric constant of the medium, which is an important feature for developing highly efficient chemical and biological sensors.15 Synthesis of nanotriangles is usually performed using chemical-based methods, either by manipulating the experimental parameters (kinetic control) or by selective surface © XXXX American Chemical Society
passivation using additives or capping molecules that act as surface blocking reagents.16,17 Seed-mediated growth is one of the most widely used chemical routes for synthesis of Au and AgNTs.17−20 Seed-mediated growth involves the use of preformed spherical nanoparticle seeds (
