A straightforward one-step chemical method to in situ synthesis of Ag nanoparticles (Ag NPs) on single-layer graphene oxide (GO) and reduced graphene oxide (r-GO) surfaces is proposed. After simply heating the single-layer GO or r-GO adsorbed on 3-aminopropyltriethoxysilane (APTES)-modified Si/SiOx substrates in a silver nitrate aqueous solution at 75 °C, Ag NPs are synthesized and grow on the GO or r-GO surface. The obtained Ag NPs are investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Our method is unique and important since no reducing agent is required in the reaction. Au NPs on a GO surface are obtained by simply immersing the obtained Ag NPs on the GO surface in HAuCl4 solution.

We have developed a probe of the electromagnetic mechanism of surface-enhanced Raman scattering via Au nanodisk arrays generated by using on-wire lithography. In this approach, disk thickness and interparticle gap are precisely controlled from 5 nm to many micrometers. Confocal Raman microscopy demonstrates that disk thickness and gap play a crucial role in determining surfaceenhanced Raman scattering intensities. Theoretical calculations also demonstrate that these results are consistent with the electromagnetic mechanism, including the surprising result that the largest enhancement does not occur for the smallest gaps.electromagnetic mechanism ͉ nanofabrication ͉ surface-enhanced Raman scattering ͉ templated synthesis ͉ discrete dipole approximation O n-wire lithography (OWL) allows one to fabricate unique one-dimensional structures that cannot be prepared via any other lithographic method (1-3). In particular, it allows one to make nanodisk arrays coated on one side with a thin silica sheath where the disk composition, thickness, and separation along the long axis can be controlled with nanometer precision. This ability enables the exploration of a variety of chemical and physical phenomena, including plasmon coupling and electromagnetic field enhancement in a very unique manner. Electromagnetic field enhancement is, in part, the basis behind surface-enhanced Raman scattering (SERS), a spectroscopic phenomenon discovered over 30 years ago but still perplexing to the scientific community both in terms of its potential and scientific origins (4-27). Two mechanisms are often mentioned in the literature, (6) the electromagnetic mechanism and the chemical mechanism. The latter involves charge transfer excitation (7, 9) between analyte molecules and the metal particles, whereas the former is dominated by plasmon excitation leading to hot spots around nano-sized metal particles (10,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). A challenge in characterizing the electromagnetic mechanism is the difficulty associated with making nanoparticle structures with controllable interparticle gaps and doing so in a way that does not significantly change chemical composition. Because of this problem, it would be particularly useful to be able to make a series of nearly identical nanostructures with controllable gap size that can be probed simultaneously under one set of conditions in a SERS experiment. By designing the experiment in this manner, differences in chemical enhancement are minimized, and one can focus on the relationship between nanostructure and electromagnetic enhancement. Here, we show how OWL can be used to systematically prepare rows of Au disks with precisely controlled thicknesses and gaps, enabling a combinatorial format for identifying structures that provide maximum SERS enhancement.Nanodisk arrays fabricated by OWL are particularly useful for preparing SERS-active nanostructures for the following reasons. (i) Multiple features can be synthesized within a single nanowire, and, once functionalized wi...

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.

Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition-metal dichalcogenides (TMDs) showed outstanding performance as co-catalysts for the hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one-pot wet-chemical method is developed to prepare MS2-CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4-10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2-CdS nanohybrids possess a large number of edge sites in the MS2 layers, which are active sites for the HER. The photocatalytic performances of WS2-CdS and MoS2-CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS2-CdS nanohybrids showed enhanced stability after a long-time test (16 h), and 70% of catalytic activity still remained.

The recent developments of hetero-nanostructures for photocatalytic H2production and CO2reduction are reviewed in detail, based on material compositions that form heterojunctions.