Azusa Takai

Mesoporous platinum with giant mesocages templated from lyotropic liquid crystals consisting of diblock copolymers

Templated synthesis of nanostructured metals with tunable composition, structure, and morphology allows us to finely control the metals properties, which is a typical example of materials nanoarchitectonics that emphasizes the importance of novel sizeand shape-dependent properties. Traditionally, various nanostructured metals (for example, nanowire arrays, bicontinuous nanowire networks, nanoparticle arrays) have been prepared by utilizing hard templates including mesoporous silica. Currently, lyotropic liquid crystals (LLCs), formed by assembling Cn(EO)m-type surfactants (EO = ethylene oxide), have been utilized as soft templates to directly prepare mesoporous metals with hexagonally packed cylindrical mesospace. In such LLCs, metal nanoparticles with almost uniform size are continuously deposited to form unique frameworks consisting of connected nanoparticles, which contribute to the development of novel metal-based nanomaterials that are not achievable by hard templating. Surprisingly, all the mesoporous metals prepared by the soft templating technique have been limited to 2D hexagonal mesostructures with mesopores less than 4 nm in diameter. Both the limits of mesostructures and pore size seriously devalue the advantages of mesoporous metals, because a small mesospace suppresses effective movement of guest species within the mesopores. Giant mesopores can incorporate large biological molecules, and also volume changes caused by incorporation of guest species into host matrices are effectively relaxed. Cage-type mesostructures should enhance the accessibility of various species. Therefore, to further explore the potential properties of nanoarchitectured metals, the versatile control of mesostructures and pore size is vital. Herein, we report the preparation of a new type of mesoporous Pt particle with giant mesocages connected closely in three dimensions, templated from LLCs consisting of diblock copolymers. The size of the mesocages is the largest (about 15 nm) reported in mesoporous metals. The advantage of diblock copolymers is that their high molecular weight and composition are well designed. By utilizing LLCs made of such designed block copolymers, new nanoarchitectured metals with various mesostructures and pore sizes should be realized. First, a precursor solution was prepared by mixing distilled water (0.75 g), hydrogen hexachloroplatinate(IV) hexahydrate (H2PtCl6·6H2O; 0.75 g), poly(styrene-b-ethylene oxide) block copolymer (PS3800-b-PEO4800, polydispersity index: 1.05; 0.25 g), and tetrahydrofuran (THF; 12.5 g) as volatile solvent (Figure 1a). Then, the precursor solution was drop-coated onto an indium tin oxide (ITO; surface resistivity 10 Wcm ) substrate. After the preferential evaporation of THF, a yellow LLC film was formed over the entire area of the substrate (Figure 1b). This LLC mesostructure before Pt deposition was proved by XRD measurement in the lowangle range (see the Supporting Information, Figure S2). An intense single peak (d 16 nm) was observable, which indicates that at least a periodic mesostructure was formed, although the dimensionality was not identified. For the

Pt Fibers with Stacked Donut-Like Mesospace by Assembling Pt Nanoparticles: Guided Deposition in Physically Confined Self-Assembly of Surfactants

A stacked donut-like mesospace is successfully introduced into Pt fibers by assembling Pt nanoparticles with uniform particle size, by utilizing the guided deposition of Pt nanoparticles in preferentially oriented liquid crystals. We clearly demonstrate that the collaboration of both LLC templating by electrochemical processes and hard templating utilizing a confined effect can lead to the genesis of new nanostructured metals. Such a unique metal-based nanoarchitecture enhances the surface area and enables the high-mass transportation of guest species. Preferentially oriented mesochannels should contribute significantly to the fine control and transport of electronic carriers through metal fibers.

Tailored synthesis of mesoporous platinum replicas using double gyroid mesoporous silica (KIT-6) with different pore diameters via vapor infiltration of a reducing agent

We demonstrate facile synthesis of mesoporous Pt replicas using double gyroid mesoporous silica (KIT-6) with different pore diameters via vapor infiltration of a reducing agent. Through controlling the complementary pore size, it becomes possible to selectively deposit Pt into one side pore of the Ia3d bicontinuous structure, thereby forming a mesoporous Pt replica with relatively large mesopores (over 10 nm).

Tailored electrochemical synthesis of 2D-hexagonal, lamellar, and cage-type mesostructured Pt thin films with extralarge periodicity

We report the synthesis of mesostructured Pt films with extralarge periodicity from lyotropic liquid crystals consisting of block copolymers (polystyrene-b-polyethylene oxide, PS-b-PEO) on Au substrates by electrochemical deposition. The Pt films with three types of (two-dimensional (2D)-hexagonal, lamellar, and cage-type) mesostructures are successfully synthesized by controlling the compositional ratio between block copolymers and Pt species in precursor solutions. The mesostructured Pt films have high electrochemically active surface areas. The bumpy mesopore surfaces, which reflect the mesopore walls consisting of connected nanoparticles, greatly contribute to the enhancement of the surface areas. The mesopore walls have single crystal domains over 400 nm(2) region proved by the lattice fringes of Pt extending over several nanoparticles.

Fabrication of mesoporous Pt nanotubes utilizing dual templates under a reduced pressure condition

Pt nanotubes with mesoporous walls have been successfully prepared for the first time by the combination of hard templates (porous anodic alumina membranes, PAAM) and soft templates (lyotropic liquid crystals, LLC).

Platinum Nanopeapods: Spatial Control of Mesopore Arrangements by Utilizing a Physically Confined Space

Spherical mesopores: Mesoporous Pt rods containing cage-type mesopores were prepared with porous anodic alumina membranes (PAAMs). It is noteworthy that spherical mesopores are aligned in the rods due to physical confinement by the PAAM channels. Both the mesopore alignment and the morphological control are realized simultaneously, which could be important for bottom-up approaches to nanometals with desirable structural features (see figure).

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

A repeating template method is presented for the synthesis of mesoporous metals with 2D hexagonal mesostructures. First, a silica replica (i.e., silica nanorods arranged periodically) is prepared by using 2D hexagonally ordered mesoporous carbon as the template. After that, the obtained silica replica is used as the second template for the preparation of mesoporous ruthenium. After the ruthenium species are introduced into the silica replica, the ruthenium species are then reduced by a vapor-infiltration method by using the reducing agent dimethylamine borane. After the ruthenium deposition, the silica is chemically removed. Analysis by transmission and scanning electron microscopies, a nitrogen-adsorption-desorption isotherm, and small-angle X-ray scattering revealed that the mesoporous ruthenium had a 2D hexagonal mesostructure, although the mesostructural ordering is decreased compared to that of the original mesoporous carbon template. This method is widely applicable to other metal systems. By changing the metal species introduced into the silica replica, several mesoporous metals (palladium and platinum) can be synthesized. Ordered mesoporous ruthenium and palladium, which are not easily attainable by the soft-templating methods, can be prepared. This study has overcome the composition variation limitations of the soft-templating method.

Preparation of Mesoporous Bimetallic Au-Pt with a Phase-Segregated Heterostructure Using Mesoporous Silica.

Mesoporous bimetallic Au-Pt with a phase-segregated heterostructure has been prepared by using mesoporous silica SBA-15 as a template. Au nanoparticles were prepared as a seed metal within the mesopores, and subsequently Pt was deposited, sandwiching the Au seeds. Energy-dispersive X-ray (EDX) spectral mapping showed that the framework of mesoporous bimetallic Au-Pt, prepared by removing the silica template with HF, was composed of Au nanoparticles joined with Pt nanowires. The Au/Pt ratio of the mesoporous bimetallic Au-Pt could be varied by controlling the number of Au deposition cycles. Pre-adsorbed CO (COad) stripping voltammetry of the mesoporous bimetallic Au-Pt showed that the surfaces of the joined bimetallic structure were electrochemically active. This could be attributed to the open framework structure having a high ratio of exposed bimetallic mesopore surfaces. The described preparative approach, involving a mesoporous silica template and stepwise deposition within the mesopores, enables control of the nanostructure of the bimetallic material, which is greatly promising for the further development of synthetic methodologies for bimetallic structures.