Katsuhiko Ariga

A new family of carbon materials: synthesis of MOF-derived nanoporous carbons and their promising applications

Nanoporous carbons possessing high surface area and narrow pore size distribution are among the most important classes of porous materials that are practically utilized in industries. Recently, several metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have been demonstrated as promising precursors to create functional nanoporous carbons. In this highlight article, we briefly review the recent progress in preparation of these novel MOF-derived nanoporous carbons. Some promising applications in energy and environment-related areas and future outlook are also discussed.

Synthesis of Nanoporous Carbon–Cobalt-Oxide Hybrid Electrocatalysts by Thermal Conversion of Metal–Organic Frameworks

Nanoporous carbon-cobalt-oxide hybrid materials are prepared by a simple, two-step, thermal conversion of a cobalt-based metal-organic framework (zeolitic imidazolate framework-9, ZIF-9). ZIF-9 is carbonized in an inert atmosphere to form nanoporous carbon-metallic-cobalt materials, followed by the subsequent thermal oxidation in air, yielding nanoporous carbon-cobalt-oxide hybrids. The resulting hybrid materials are evaluated as electrocatalysts for the oxygen-reduction reaction (ORR) and the oxygen-evolution reaction (OER) in a KOH electrolyte solution. The hybrid materials exhibit similar catalytic activity in the ORR to the benchmark, commercial, Pt/carbon black catalyst, and show better catalytic activity for the OER than the Pt-based catalyst.

Fullerene Nanoarchitectonics: From Zero to Higher Dimensions

The strategic design of nanostructured materials, the properties of which could be controlled across different length scales and which, at the same time, could be used as building blocks for the construction of devices and functional systems into new technological platforms that are based on sustainable processes, is an important issue in bottom-up nanotechnology.Such strategic design has enabled the fabrication of materials by using convergent bottom-up and top-down strategies. Recent developments in the assembly of functional fullerene (C60) molecules, either in bulk or at interfaces, have allowed the production of shape-controlled nano-to-microsized objects that possess excellent optoelectronic properties, thus enabling the fabrication of optoelectronic devices. Because fullerene molecules can be regarded as an ideal zero-dimensional (0D) building units with attractive functions, the construction of higher-dimensional objects, that is, 1D, 2D, and 3D nanomaterials may realize important aspects of nanoarchitectonics. This Focus Review summarizes the recent developments in the production of nanostructured fullerenes and techniques for the elaboration of fullerene nanomaterials into hierarchic structures.

Low‐Temperature Remediation of NO Catalyzed by Interleaved CuO Nanoplates

A copper(II)-oxide-based exhaust catalyst exhibits better activity than Pt- and Rh-nanoparticle catalysts in NO remediation at 175 °C. Following theoretical design, the CuO catalyst is rationally prepared; CuO nanoplates bearing a maximized amount of the active {001} facet are arranged in interleaved layers. A field test using a commercial gasoline engine demonstrates the ability of the catalyst to remove NO from the exhaust of small vehicles.

Activated interiors of clay nanotubes for agglomeration-tolerant automotive exhaust remediation†

Naturally occurring clay nanotubes, halloysite (Al2Si2O5(OH)4·2H2O), with exterior and interior surfaces, respectively, composed of SiOx and AlOx layers, act as an agglomeration-tolerant exhaust catalyst when copper–nickel alloy nanoparticles (Cu–Ni NPs, 2–3 nm) are immobilized at the AlOx interior. Co-reduction of Cu2+ and Ni2+ (respectively derived from CuCl2 and NiCl2) in the presence of sodium citrate (Na3C6H5O7·2H2O) and halloysite yielded the required nanocomposite, Cu–Ni@halloysite. Cu–Ni@halloysite efficiently catalyzes the purification of simulated motor vehicle exhaust comprising nitrogen monoxide (NO) and carbon monoxide (CO) near the activation temperature of Pt-based exhaust catalysts, ≤400 °C, showing its potential as an alternative to Pt-based catalysts. In contrast, a different halloysite nanocomposite with the SiOx exterior decorated with Cu–Ni NPs, Cu–Ni/halloysite, is poorly active even at >400 °C because of particle agglomeration. The enhanced exhaust-purification activity of Cu–Ni@halloysite can ultimately be attributed to the topology of the material, where the alloy NPs are immobilized at the tubular AlOx interior and protected from particle agglomeration by the tubular form and SiOx exterior.

Mesoporous architectures with highly crystallized frameworks

Porous materials have played an increasingly critical role in materials sciences and chemistry. From the viewpoint of applications, highly crystallized mesoporous architectures are very promising mainly due to their unique properties arising from the crystallized frameworks and many exciting applications in diverse fields. In this Highlight article, we summarize recent innovative researches in the creation of mesoporous architectures possessing crystalline pore walls. In particular, new strategies to synthesize highly crystallized mesoporous metals and metal oxides, metal–organic frameworks with large-sized mesopores, and zeolites with hierarchical mesoporosity are described. These mesoporous architectures show a lot of promise in energy and environment-related areas.

Supramolecular Approaches for Drug Development

Various supramolecular systems can be used as drug carriers to alter physicochemical and pharmacokinetic characteristics of drugs. Representative supramolecular systems that can be used for this purpose include surfactant/polymer micelles, (micro)emulsions, liposomes, layer-by-layer assemblies, and various molecular conjugates. Notably, liposomes are established supramolecular drug carriers, which have already been marketed in formulations including AmBisome(®) (for treatment of fungal infection), Doxil(®) (for Kaposis sarcoma), and Visudyne(®) (for age-related macular degeneration and choroidal neovascularization). Microemulsions have been used oral drug delivery of poorly soluble drugs due to improvements in bioavailability and predictable of absorption behavior. Neoral(®), an immunosuppressant used after transplant operations, is one of the most famous microemulsion-based drugs. Polymer micelles are being increasingly investigated as novel drug carriers and some formulations have already been tested in clinical trials. Supramolecular systems can be functionalized by designing the constituent molecules to achieve efficient delivery of drugs to desired sites in the body. In this review, representative supramolecular drug delivery systems, that may improve usability of candidate drugs or add value to existing drugs, are introduced.

Selective CO2 Capture and High Proton Conductivity of a Functional Star-of-David Catenane Metal–Organic Framework

Network structures based on Star-of-David catenanes with multiple superior functionalities have been so far elusive, although numerous topologically interesting networks are synthesized. Here, a metal-organic framework featuring fused Star-of-David catenanes is reported. Two triangular metallacycles with opposite handedness are triply intertwined forming a Star-of-David catenane. Each catenane fuses with its six neighbors to generate a porous twofold intercatenated gyroid framework. The compound possesses exceptional stability and exhibits multiple functionalities including highly selective CO2 capture, high proton conductivity, and coexistence of slow magnetic relaxation and long-range ordering.

Soft 2D nanoarchitectonics

Nanoarchitectonics is a new paradigm to combine and unify nanotechnology with other sciences and technologies, such as supramolecular chemistry, self-assembly, self-organization, materials technology for manipulation of the size of material objects, and even biotechnology for hybridization with bio-components. The nanoarchitectonic concept leads to the synergistic combination of various methodologies in materials production, including atomic/molecular-level control, self-organization, and field-controlled organization. The focus of this review is on soft 2D nanoarchitectonics. Scientific views on soft 2D nanomaterials are not fully established compared with those on rigid 2D materials. Here, we collect recent examples of 2D nanoarchitectonic constructions of functional materials and systems with soft components. These examples are selected according to the following three categories on the basis of 2D spatial density and motional freedom: (i) well-packed and oriented organic 2D materials with rational design of component molecules and device applications, (ii) well-defined assemblies with 2D porous structures as 2D network materials, and (iii) 2D control of molecular machines and receptors on the basis of certain motional freedom confined in two dimensions.2D materials: Soft systems get organizedThe pursuit of ever smaller functional materials has required nanotechnology to be combined with other fields such as self-assembly, or hybridization with biomolecules—these approaches are now unified in the concept of ‘nanoarchitectonics’. A Japan-based team led by Katsuhiko Ariga at the National Institute for Materials Science in Tsukuba review recent nanoarchitectonic developments with 2D soft materials, traditionally less explored than rigid 2D materials such as graphene. Sheets composed of organic molecules held together by weak forces, typically hydrogen bonding or metal coordination, have been constructed that serve as organic crystalline semiconductors, molecular machines, or receptors. A film of living cells has also been obtained at a liquid–liquid interface. These achievements show that soft 2D nanoarchitectonics holds great promise for a variety of fields ranging from organic electronics to biomaterials.A target of this review is soft 2D nanoarchitectonics because scientific views on soft 2D nanomaterials are not fully established as compared with rigid 2D materials. The presented examples are selected according to the following three categories on the basis of 2D spatial density and motional freedoms: (i) well-packed and oriented organic 2D materials with rational design of component molecules and device applications, (ii) well-defined assemblies with 2D porous structures as 2D network materials, and (iii) 2D controls of molecular machines and receptors on the basis of certain motional freedom with confined nature in 2D plain.

Nanoarchitectonics from Molecular Units to Living‐Creature‐Like Motifs

Important points for the fabrication of functional materials are the creation of nanoscale/molecular-scale units and architecting them into functional materials and systems. Recently, a new conceptual paradigm, nanoarchitectonics, has been proposed to combine nanotechnology and other methodologies including supramolecular chemistry, self-assembly and self-organization to satisfy major features of nanoscience and promote the creation of functional materials and systems. In this account article, our recent research results in materials development based on the nanoarchitectonics concept are summarized in two stories, (i) nanoarchitectonics from fullerenes as the simplest nano-units and (ii) dimension-dependent nanoarchitectonics from various structural units. The former demonstrates creativity of the nanoarchitectonics concept only with simple construction stuffs on materials fabrications, and a wide range of material applicability for the nanoarchitectonics strategy is realized in the latter ones.