Platinum nanostructured networks

Platinum nanostructured networks (PNNs) were prepared via chemical reduction of H2PtCl6 by benzyl alcohol imder microwave irradiation. The networks were micrometer long and consisted of connected secondary nanoparticles, which were actually formed by aggregation of aroimd 3 nm Pt nanocrystals. The formation of the PNN structure was attributed to the collision-induced fusion of Pt nanocrystals due to the cooperative functions of microwave irradiation and benzyl alcohol [150]. Kessler and coworkers reported a one-step synthesis of hydrophilic spherical palladium nanoparticles of imiform size and shape by solvothermal decomposition of Pd(II) acetylacetonate in acetophenone [151]. 

Figure 17.7 (A) Cyclic voltammogram of catechol on a platinum electrode. (B) Effect of poly(aniline-co-o-aminophenol) fiber diameter on the electrochemical oxidation of catechol, at a scan rate of 60 mV Average fiber diameter ( ) 70 nm, (2) 90 nm, (3) 100 nm, (4) 107 nm, in a solution consisting of 5 mM catechol and 0.3 M Na2S04 with pH 5.0. (Reprinted with permission from Electrochimica Acta, Poly(aniline-co-o-aminophenol) nanostructured network Electrochemical controllable synthesis and electrocatalysis byShaolin Mu, 51, 17, 3434-3440. Copyright (2006) Elsevier Ltd)...

A templating approach can be important for preparing low-dimensional platinum nanostructures, as the platinum metal has a fee cubic symmetry. In template-free solution-phase synthesis, the introduction of defects can serve as a useful strategy. Some examples of nanorods, nanowires and nanotubes of platinum prepared using different methods, with and without templates, are shown in Figure 10.8. Notably, when the diameter of nanowires becomes very small, they can exhibit excellent flexibUity and form interconnected networks. 

CNTs offer an exciting possibility for developing ultrasensitive electrochemical biosensors because of their unique electrical properties and biocompatible nanostructures. Luong et al. have fabricated a glucose biosensor based on the immobilization of GOx on CNTs solubilized in 3-aminopropyltriethoxysilane (APTES). The as-prepared CNT-based biosensor using a carbon fiber has achieved a picoamperometric response current with the response time of less than 5 s and a detection limit of 5-10 pM [109], When Nation is used to solubilize CNTs and combine with platinum nanoparticles, it displays strong interactions with Pt nanoparticles to form a network that connects Pt nanoparticles to the electrode surface. The Pt-CNT nanohybrid-based glucose biosensor... 

Both, templating and self-assembly approaches have been explored in order to create extended networks of 3-D nanostructures. In an initial templating method, ordered mesoporous structures such as MCM41, MCM-48 and their derivatized forms were popular templates [119, 181]. For this method it was first necessary to introduce Pt precursors into the channels of the templates through surface adsorption. The 3-D network of platinum could then be generated after reduction by hydrogen gas. 

A second method was based on the direct assembly of platinum building blocks, where hyperbranched multipods with high aspect ratios could serve as the nanostructured precursors. A network of platinum nanowires directly assembled from a solution phase is shown in Figure 10.15. Unlike the networks made from templates, these assembled networks could either be disassembled into individual multipods in dispersion form, or sintered into connected networks. 

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