Up to now, green synthesis of "naked" nanoobjects with clean surfaces is still a great challenge since structure-directing agents such as surfactants are usually used to induce the anisotropic particle growth for interesting nanostructures in solution. Here, a green synthesis approach for preparing "naked" Pt nanoparticles (NPs) in acetic acid solution was reported. Interestingly, Pt NPs with different morphologies (well-defined polyhedrons, irregular polyhedron-constructed chain networks and nanoflower-constructed chain networks) could be successfully synthesized at different concentrations of acetic acid without adding additional structure-directing agents and reducing agents. The acetic acid itself works both as structure-directing agent and reducing agent for the formation of these interesting Pt NPs. Specifically; the synthesized NPs are "naked" with clean surfaces since the acetic acid is a weakly-capping agent which can be easily removed after the washing process. The versatility of this method is further demonstrated by preparation of "naked" PtPd alloy NPs. In particular, the as-prepared "naked" Pt _5.20 and Pt 3 Pd 1_5.20 NPs are demonstrated to be excellent catalysts with much higher electroactivity and better durability than the commercial Pt black catalyst (Hispec™ 1000) for the methanol oxidation reaction. The method reported in this work may pave the way for simple, low-cost, green and eco-friendly synthesis of "naked" metal catalysts for advanced electrocatalytic applications.
Ag2S/CdS/TiO2 hybrid nanotube array films (Ag2S/CdS/TNTs) were prepared by selectively depositing a narrow-gap semiconductor—Ag2S (0.9 eV) quantum dots (QDs)—in the local domain of the CdS/TiO2 nanotube array films by spotting sample method (SSM). The improvement of sunlight absorption ability and photocurrent density of titanium dioxide (TiO2) nanotube array films (TNTs) which were obtained by anodic oxidation method was realized because of modifying semiconductor QDs. The CdS/TNTs, Ag2S/TNTs, and Ag2S/CdS/TNTs fabricated by uniformly depositing the QDs into the TNTs via the successive ionic layer adsorption and reaction (SILAR) method were synthesized, respectively. The X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS) results demonstrated that the Ag2S/CdS/TNTs prepared by SSM and other films were successfully prepared. In comparison with the four films of TNTs, CdS/TNTs, Ag2S/TNTs, and Ag2S/CdS/TNTs by SILAR, the Ag2S/CdS/TNTs prepared by SSM showed much better absorption capability and the highest photocurrent density in UV-vis range (320~800 nm). The cycles of local deposition have great influence on their photoelectric properties. The photocurrent density of Ag2S/CdS/TNTs by SSM with optimum deposition cycles of 6 was about 37 times that of TNTs without modification, demonstrating their great prospective applications in solar energy utilization fields.
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