Photochemical Synthesis of Water-Soluble Gold Nanorods: The Role of Silver in Assisting Anisotropic Growth

Abstract

The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by statistical analysis of the relevant TEM data. EXAFS measurements at the Ag K-edge have unambiguously disclosed the presence of Ag species in the final product, identifying their chemical state as well as the most probable lattice environment around them with a reasonably high level of confidence. The extensive sample knowledge gained by the combination of spectroscopic, structural, and morphological measurements has provided reliable information regarding the most relevant processes underlying the Ag+-assisted formation of Au NRs by the photochemical route. An induction period prior to occurrence of fast nanoparticle nucleation has been identified, which has been correlated to the slow accumulation of a critical concentration of Au(I)−surfactant species from reduction of their Au(III) parent precursors. The role played by Ag in directing Au growth toward the formation of NRs has been clarified through demonstration of preferential adsorption of zerovalent Ag species on {110} facets of the growing Au nanoparticles, which can be therefore responsible for restricting crystal development along the relevant crystallographic directions

Visible-Light-Active TiO2-Based Hybrid Nanocatalysts for Environmental Applications

“…The frequency of this resonance depends on the nanoparticle size, shape, chemical composition and proximity to other nanoparticles. Therefore, control of such parameters allows us to tune the position of the plasmon absorbance band in the whole Vis-NIR (Near-Infrared) range [48][49][50][51][52]. In particular, in an anisotropic nanoparticle, such as a nanorod (NR), the oscillation of electrons could occur along the transverse and longitudinal axis, thus splitting the typical plasmon band in two signals.…”

Direct growth of shape controlled TiO2 nanocrystals onto SWCNTs for highly active photocatalytic materials in the visible

“…Rod formation is typically based on anisotropic crystal growth which can occur when surface free energy of the various crystallographic planes differs significantly, thus favouring growth along one specific direction, or, alternatively, when the growth of certain crystallographic planes is somehow prevented [38,39]. In a monosurfactant system, like the investigated reaction mixture, the potential for unidirectional growth of TiO 2 particles could arise from the intrinsic anisotropic reactivity of the titania precursor and from the adsorbing-chelating ligand (i.e.…”

Photo-thermal effects in gold nanorods/DNA complexes

“…In second step, 500 mL of water dispersed CTAB-stabilized GNRs (5. [19,20]. At this point, 0.8 mL of seed solution were added to the growth solution and the resulting mixture was stirred.…”