Highly Ordered Platinum Nanodot Arrays with Cubic Symmetry in Mesoporous Thin Films

Abstract

The synthesis of nanometer-sized materials has attracted much attention because of the unique catalytic, magnetic, optical, and electronic properties of such materials. Since the physicochemical properties of nanomaterials are highly dependent on their size, shape, and arrangement, techniques for controlling the nanostructure and organization of materials are highly desirable. Ordered mesoporous materials are potential candidates for fabricating nanomaterials because of their uniform nanopores of various sizes (1.5-30 nm), shapes (cylindrical and cagelike), and arrangements (2D and 3D hexagonal, cubic Pm3 n, cubic Ia3 d, etc). [1][2][3] To date, nanoparticles or nanowires of Pt, [4] Ag, [4d,5] Pd, [4e,6] and Au, [4d,e] using mesoporous powders or thin films. In most cases, the pores were partially filled with materials, and nanoparticles or rods were randomly distributed in mesoporous-silica matrices. Recently, the syntheses of ordered nanoparticle arrays of CdS, [9] Au, [10] and Pt [10] in mesoporous silica films have been reported by independent groups. Fan et al. reported the synthesis of gold nanocrystal/silica mesostructured thin films with a cubic symmetry (Fm3m) via self-assembly of water-soluble nanocrystal micelles with soluble silica.[11] These periodic nanodot arrays in silica thin films could be applied to singleelectron devices mediated by coupling interactions with neighboring nanodots. The ordered lattice and the perfect packing of dots are very important for the 3D array of multitunnel junctions, and it should be possible to control the properties of single-electron devices by changing the pore size and arrangement of the mesoporous silica thin film.Here we present the synthesis of a highly ordered Pt nanodot array of cubic symmetry simply by immersing a mesoporous silica thin film into a Pt-precursor solution followed by photoreduction. Two types of cages of mesoporous thin films have been fully filled with Pt nanoparticles of approximately 4 nm diameter, and an exceptionally ordered cubic-lattice array of nanodots has been obtained.The mesoporous thin films and the Pt-filled mesoporous thin films on silicon wafers were scratched off and placed on Cu grids for high-resolution transmission electron microscopy (HRTEM) measurements. The HRTEM images of both the mesoporous thin films and the Pt-filled thin films are displayed in Figure 1. (Large-area HRTEM images are shown in the Figs. S1 and 2 in the Supporting Information).

Linear and nonlinear optical properties of gold nanocrystal-incorporated mesoporous silica thin films

“…To date, many papers have reported the synthesis of different metals and metal compounds (Au, Ag, Pt, Pd, CdS and TiN) with controlled sizes and morphologies using ordered mesoporous materials as templates. 1,[16][17][18][19][20][21][22][23][24] Well-ordered mesoporous silica thin films (MSTF), incorporating gold nanocrystals (GNCs), are one kind of nanocomposite film. In this paper, we study the optical properties of the GNC/MSTF nanocomposite.…”

“…The neutralization reaction lasted for a period of time, whilst under vacuum at room temperature. Then, the samples were rinsed with deionized water to flush away free HAuCl 4 on the AF-MSTF surfaces and dried in a clean, ambient atmosphere for 24 h. Next, the composite films were calcined at 400 uC (heating rate of 1 uC min 21 ) for 2 h under a hydrogen atmosphere and cooled to room temperature.…”

A Rational Repeating Template Method for Synthesis of 2 D Hexagonally Ordered Mesoporous Precious Metals

“…Currently, mesoporous metals with high electroconductivity have attracted increasing interest for many applications, such as battery electrodes, fuel cells, electronic devices, and catalysts. [6][7][8][9][10][11][12] Mesoporous metals have previously been synthesized by a soft-templating method utilizing lyotropic liquid crystals (LLCs), which consist of self-assembled amphiphilic surfactants, and a metal species. In 1997, Attard et al reported the first mesoporous platinum [6a] with high performance as a glucose sensor and as a direct methanol fuel cell (DMFC) electrode.…”

“…In this method, the resultant metal replicas possess periodically arranged nanostructures reflected in the original mesostructures. [10][11][12] For example, if a 2D hexagonally ordered mesoporous silica with microporosity in the framework (e.g., SBA-15) was used as a hard template, metal nanowires with a uniform width (e.g., Pt, Au, Pd, Ag, and Pt-Au) were prepared and connected to each other by small bridges. [10] Such a periodical arrangement of the nanowires is well-retained even after silica removal, thus providing uniform interspaces among the nanowires.…”

“…As another example, nanoparticle arrays were also synthesized by using cage-type mesoporous structures (e.g., . [11] Thus, the hard-templating method is widely applicable to many metals and alloys that are difficult to prepare by the soft-templating method described above, because the mesoporous silica used as a template has high mechanical and thermal stabilities.…”