This paper reports a methodology for preparing ordering hydrophilic metal nanoparticles into close-packed 2-dimensional arrays at a hexane-water interface with alkanethiol in the hexane layer. The destabilization of metal nanoparticles by the addition of alcohol caused the nanoparticles to adsorb to an interface where the surface of entrapped Au nanoparticle was in situ coated with the long-chain alkanethiols present in a hexane layer. The adsorption of alkanethiol to the nanoparticle surface caused the conversion of the electrostatic repulsive force to a van der Waals interaction, which is a key feature in forming highly ordered close-packed nanoparticle arrays.
We report a methodology for synthesis of palladium (Pd) nanospring structures using an anodic aluminum oxide (AAO) membrane template and facile electrochemical deposition. The hydroxyl-terminated surfaces of alumina nanochannels and localized hydrogen evolution contribute to the growth of Pd atoms at peripheral positions of the alumina nanochannels in the presence of an effectual electric potential and a plating solution consisting of PdCl(2), CuCl(2), and HCl. Structural characterization including EDS line analysis and element mapping revealed Pd nanodomains curling up on the Cu nanorods. A clear Pd nanospring shape was observed after selectively removing Cu. The lengths of the nanosprings were dictated by the charges transported through electrodeposition, and the diameters of the nanosprings were tunable by altering the diameter of the alumina nanochannels. Screw dislocation is the most probable crystallographic defect responsible for the formation of coiled Pd nanostructures. Pd nanosprings have potential applications in nanomachines, nanosensors, nanoinductors, and metamaterials. We anticipate that our synthesis method will motivate and inform the synthesis of more advanced nanomaterials.
One fundamental goal of modern nanochemistry involves the development of various synthetic pathways to nanoparticles in order to tailor their physical and chemical properties. Special attention has been focused on bimetallic alloys and core/shell nanoparticles because such structures have unusual catalytic, [1,2] electronic, [3] optical, [4][5][6] and magnetic properties. [7,8] Platinum-group metals (especially platinum) constitute interesting catalytic materials that offer efficient electrooxidation characteristics that are of fundamental and industrial interest to hydrogen and fuel-cell communities. Spherical platinum-group nanoparticles are often employed commercially in fuel cells and related applications because they offer high surface-area-to-volume ratios. [9,10] In contrast to spherical nanoparticles, 1D structures such as nanorods exhibit additional advantages associated with their anisotropic architecture and unique structure, which allows for a multicomponent composition.[11] Recently, we [12][13][14] and others [15-18] developed methods for preparing multicomponent nanorods comprising organic and inorganic materials, which give rise to a variety of properties based on the individual constituents. Nanomaterials that display shape-dependent catalytic properties are currently of fundamental interest. [19] Here, we describe a new strategy for synthesizing electrocatalytically active, bimetallic, core/shell nanorod arrays by coating an atomically thin layer of a platinum-group metal over a nanoporous gold nanorod array. In this material, the nanoporous gold nanorod architecture plays the role of the template, and an electrocatalytically active metal such as platinum resides primarily on the surface where its use as a catalyst can be maximized. The use of gold nanorods as the template offers several advantages, including the easy formation of a porous structure by relying on dealloying, which is the selective dissolution of a less-noble-metal component (i.e., silver).[20] The resulting nanoporous gold nanorod array enables the deposition of an ultrathin overlayer through copper underpotential deposition (UPD), followed by spontaneous replacement of the copper ions with the more noble platinum-group metal ions. Previously, we applied a similar approach to the synthesis of smooth, spherical, gold/ platinum core/shell nanoparticles.[21]In a typical experiment, a thin layer of gold (ca. 400 nm) was thermally evaporated on one side of a nanoporous anodic alumina membrane (pore size = 250-350 nm); this material served as the working electrode in a three-electrode electrochemical cell after making physical contact with a glassy carbon electrode. Platinum wire and a Ag/AgCl electrode were employed as the counter and reference electrodes, respectively. Next, gold nanorods were electrodeposited in the interior of an anodic alumina template at a constant potential, -1.0 V versus Ag/AgCl. The length of the gold nanorod can be controlled by monitoring the charge passed during the electrodeposition process. After deposit...
This paper describes a new strategy for synthesizing hollow nanotubes (pore d > 100 nm) with nanoporous walls (pore d < 10 nm) as well as how the nanoporous hollow nanotubes exhibit better intrinsic electrocatalytic activity toward methanol oxidation compared with an analogous nanotube system with smooth walls. Compared with vertical arrays of a nanorod system, the nanotube system is better in terms of increasing the effective surface area because the inner and outer surfaces are both in contact with the reaction medium. Au nanotubes with smooth wall and nanoporous walls were synthesized using AAO and conducting polymer nanorod templates. The surface of Au nanotube walls could be electrochemically coated with ultrathin Pt layers without changing the nanoporous structure. The resulting nanotubes showed different “intrinsic” electrocatalytic activities toward methanol oxidations depending on the wall structure (smooth or nanoporous). We compared its catalytic activity with the commercially available carbon-supported Pt nanoparticles and found that the catalytic activity of nanoporous nanotubes is the best among the investigated samples. The reason for this superior catalytic activity was attributed to the higher CO-poisoning tolerance and shorter effective length for electronic transportation.
This paper reports on a methodology for synthesizing vertical arrays of hollow platinum nanotubes with [111] single-crystalline nanoflakes. Initially, single-component nickel nanorods were fabricated with the aid of AAO templates and electrochemical deposition. When the resulting nickel nanorods were immersed in a Pt-ion-containing aqueous solution, the nickel metal dissolved into Ni2+ ions through spontaneous galvanic replacement with Pt ions. However, the direct replacement between nickel nanorods and Pt ions led to an irregular architecture in the resulting deposition of platinum. Instead, a pitting corrosion pretreatment of the nickel nanorods produced nucleation sites for replacement with the Pt ions. This step was critical for accelerating the interfacial replacement reaction rate and the formation of the regular platinum nanotubes with ultrathin superficial nanoflakes. We found that the Kirkendall effect was operative in the formation of platinum nanotubes.
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