Search

A one-step photoreduction method was applied to the synthesis of platinum colloids of 15 nm in aqueous solution without the need for organic solvents and templates. The formation process of these Pt nanostructures was studied by means of scanning electron microscopy and UV-visible absorption spectroscopy, and the morphology of the Pt nanoparticles (NPs) was illustrated by transmission electron microscopy. The Pt nanostructures were electrochemically characterized by determining the polarization curve and Tafel plot of the hydrogen evolution reaction. The active and easily accessible surface was demonstrated by the self-assembly of these Pt NPs into perfect dendritic structures on the surface of an indium-tin-oxide thin film after the appropriate addition and evaporation of water, which can be explained by diffusion-limited aggregation theory. Further evidence of the easily accessible surface of Pt NPs, is the coordination interaction between the Pt NPs as prepared and the amine ligand of metalloporphyrin resulting in the appearance of nanospheres. In contrast, the two phenomena were not found in citrate ions-stabilized Pt NPs under the same condition, indicating the Pt NPs synthesized with the photoreduction method have great potential in the fields of nanoelectronics, sensors and catalysis, as the “clean” and active surface might improve electrochemical and catalytic performance. Self-assembly and coordination of the Pt nanoparticles due to the easily accessible surface were verified by the formation of Pt dendrites and metalloporphyrin/Pt nanospheres, which might offer perspective to the design of functional materials.

Ultrathin metal nanowires are ultimately analytical tools that can be used to survey the interfacial properties of the functional groups of organic molecules immobilized on nanoelectrodes. The high ratio of surface to bulk atoms makes such ultrathin nanowires extremely electrically sensitive to adsorbates and their charge and/or polarity, although little is known about the nature of surface chemistry interactions on metallic ultrathin nanowires. Here we report the first studies about the effect of functional groups of short-chain alkanethiol molecules on the electrical resistance of ultrathin gold nanowires. We fabricated ultrathin nanowire electrical sensors based on chemiresistors using conventional microfabrication techniques, so that the contact areas were passivated to leave only the surface of the nanowires exposed to the environment. By immobilizing alkanethiol molecules with head groups such as -CH3, -NH2 and -COOH on gold nanowires, we examined how the charge proximity due to protonation/deprotonation of the functional groups affects the resistance of the sensors. Electrical measurements in air and in water only indicate that beyond the gold-sulfur moiety interactions, the interfacial charge due to the acid-base chemistry of the functional groups of the molecules has a significant impact on the electrical resistance of the wires. Our data demonstrate that the degree of dissociation of the corresponding functional groups plays a major role in enhancing the surface-sensitive resistivity of the nanowires. These results stress the importance of recognizing the effect of protonation/deprotonation of the surface chemistry on the resulting electrical sensitivity of ultrathin metal nanowires and the applicability of such sensors for studying interfacial properties using electrodes of comparable size to the electrochemical double layer.