TEM photographs were obtained on a JEOL 2010 microscope operated at 200 kV. XRD patterns were obtained on a Bruker D4 X-ray diffractometer using Cu Ka radiation. Nitrogen adsorption±desorption isotherms were acquired using a Micromeritics Tristar 3000 system at 77 K. Metal or semiconductor nanoparticles are of great interest with respect to their applications as catalysts, [1] as well as in sensors and optical [2] and electronic [2] devices. Their properties depend on the size of the nanoparticles. Thus, the accurate control of the particle size is very important for these applications. Nanoparticles have been synthesized by the oxidation or reduction of precursors.[3] Micelles [4] and stabilizing polymers [5] have also been used to restrict particle aggregation. Porous materials have been used as hosts for the synthesis of nanoparticles.[6±10] The synthesis of nanoparticles using porous materials with uniform pore sizes and high surface area as hosts has attracted interest because the sizes of the nanoparticles can be easily controlled in well-defined matrices. Mesoporous (pore size 2±50 nm) silica, FSM-16, [6] MCM-41, [7] SBA-15 [8] have been used for the synthesis of nanoparticles of Pt, Pd, Rh, Au, and Ag. A microporous (pore size < 2 nm) host, zeolite, can also be used for the synthesis of metal carbonyl clusters, [9] which takes a few days for the synthesis in a liquid-phase solvent, [9] and the reduction process generates larger particles on the external surface. These are due to the limitation of mass transfer in the liquid solvent and difficulty in controlling the growth rate of the nanoparticles from salt-type precursors, even though they are smaller than other types of precursors such as organometallic molecules. A filtration process using the vapor phase, such as chemical vapor deposition (CVD), is a very effective method for preparing particles or thin films on a nanometer scale. However, the precursors are limited in terms of high volatility and thermal stability. Conventional methods of preparing nanoparticles in porous matrices often yield nanoparticles of various sizes in the internal pores and on the external surface of the porous matrices. [8,10] Accurate size control of nanoparticles using porous materials as hosts with a wide range of uniform pore sizes, including micropores, and the investigation of the relationship between particle size and their properties still remain challenging. Supercritical fluids [11] (SCFs) have excellent properties of non-cohesivity, high diffusivity, and controllable solubility. Thus, SCFs are expected to overcome the previously men-

Porous silica fibers were synthesized by templating activated carbon fibers using supercritical fluid as a solvent. A precursor of silica, tetraethyl orthosilicate was dissolved in supercritical CO2 and attached to the base-activated carbon. The base-activated carbon in the sample coated with SiO2 was removed by calcination or O2-plasma treatment. Not only the fibrous macro shape, but also the meso structure of the base-activated carbon fiber were faithfully replicated in the silica products. These results suggested the great advantage of supercritical fluid for fabricating ceramic replicates of templates with complex structure, such as activated carbon. We have demonstrated that activated carbon with micropores acts not only as a mold for macroscopic shape control but also as a template for nanoscale structure control, when a supercritical fluid was used as a solvent. The advantage of the supercritical fluid as a medium for replication is attributed to the inability of the supercritical fluid to produce a condensed phase.

Nanoporous metal oxides (TiO 2 , Al 2 O 3 ) have been synthesized using activated carbon templates with supercritical fluid solvents by using the nanoscale casting (NC) process. The precursors were dissolved in supercritical CO 2 and attached to activated carbon fibers or powders as templates. After removal of the activated carbon templates by calcination in air at 873 K or by treatment in oxygen plasma, the nanoporous TiO 2 or Al 2 O 3 replicating the macroscopic shapes of the activated carbon templates was obtained. The surface area of the titania sample was 387 m 2 /g. The titania sample crystallized in the anatase form. The alumina samples have mesopores corresponding to the graphene crystallite size of the activated carbon. The alumina samples crystallized in the γ-alumina form.

The preparation of useful products based on the integration of carbon dioxide fixation and biomass utilization is important for the future development of environmentally harmonized materials technologies. Here we report the use of supercritical carbon dioxide and spin-coated cellulose/chitosan matrices to produce biopolymer films infiltrated with densely packed calcium carbonate (vaterite) particles. Composite films of high uniformity are prepared specifically in the presence of low concentrations of polyacrylic acid.

Safe secondary batteries with high energy densities and high power densities will be necessary if pure-electric and hybrid vehicles are to become more widespread, and all-solid-state lithium-ion batteries (LiBs) are among the most promising options. Much research has focused on the development of cathode materials with solid Li electrolytes, including composites fabricated from calcined microparticles, laser-deposited film systems, and materials with three-dimensional structures. However, because utilization of a high percentage of the active cathode material requires an electrode with a high electrolyte content, achieving high active-material-utilization rates in electrodes with high active-material contents (and thus relatively low electrolyte contents) has been challenging. Herein, we describe the self-assembled block copolymer-templated synthesis of a threedimensional bicontinuous nanocomposite electrode material consisting of LiCoO 2 as the active cathode material and Li 7 La 3 Zr 2 O 12 as the solid Li electrolyte for use in all-solid-state LiBs. In this nanocomposite, 98% of the active material was utilized even though the active-material content was high (89.4%). These percentages are substantially larger than those reported for other cathodes in all-solid-state. The excellent electrochemical properties of the nanocomposite can be ascribed to its unique bicontinuous nanostructure consisting of the active cathode material and the Li electrolyte interspersed on a scale of several tens of nanometers, which is 2 orders of magnitude smaller than the scale reported in previous studies. The process we used to prepare the nanocomposite is expected to be versatile for producing other highly functional devices, such as quantum dot solar cells, thermoelectric devices, and solid oxide fuel cells.