Self-Supported ZIF-Derived Co3 O4 Nanoparticles-Decorated Porous N-Doped Carbon Fibers as Oxygen Reduction Catalyst.

Oxygen reduction is a significant cathodic reaction in the state-of-art clean energy devices such as fuel cell and metal-oxygen battery. Here, ZIF-incorporated hybrid polymeric fibres have been fabricated by using a dual-phase electrospinning method. These are then transformed into Co3 O4 -nanoparticle-decorated porous N-doped carbon fibres (ZIF-Co3 O4 /NCF) through multi-step annealing treatment. The resultant ZIF-Co3 O4 /NCF is interweaved into a self-supported film and can be used as a bi-functional catalyst for catalysing oxygen reduction in both aqueous and non-aqueous electrolytes. Electrochemical tests demonstrate that ZIF-Co3 O4 /NCF displays a high catalytic activity for oxygen reduction with a half-wave potential (E1/2 ) of 0.813 V (vs. RHE) and an almost favourable four-electron reduction pathway in alkaline medium. ZIF-Co3 O4 /NCF catalyst only shows 4 mV negative shift of E1/2 after 5000 continuous CV cycles. In addition, the ZIF-Co3 O4 /NCF can be applied as the cathode catalyst of non-aqueous Li-O2 battery, exhibiting a remarkable ORR activity in LiPF6 contained 1,2-dimethoxyethane electrolyte. The excellent electrocatalytic performance of ZIF-Co3 O4 /NCF is probably due to the abundance of active sites of graphitic carbon-wrapped Co3 O4 nanoparticles, as well as the cross-linked fibrous nitrogen-doped carbon texture.

Development of Sulfonic-Acid-Functionalized Mesoporous Materials: Synthesis and Catalytic Applications.

Sulfonic acid based mesostructures (SAMs) have been developed in recent years and have important catalytic applications. The primary applications of these materials are in various organic synthesis reactions, such as multicomponent reactions, carbon-carbon bond couplings, protection reactions, and Fries and Beckman rearrangements. This review aims to provide an overview of the recent developments in the field of SAMs with a particular emphasis on the reaction scope and advantages of heterogeneous solid acid catalysts.

Conversion of a 2D Lepidocrocite-Type Layered Titanate into Its 1D Nanowire Form with Enhancement of Cation Exchange and Photocatalytic Performance.

Layered titanates with one-dimensional (1D) shapes have been an important class of nanomaterials due to their combination of 1D and 2D fascinating properties. Among many layered titanates, lepidocrocite-type layered titanates have significant advantages such as superior intercalation and exfoliation properties, while the synthesis of the 1D-shape forms is still challenging. Here, we report on a facile one-pot hydrothermal conversion of a lepidocrocite-type layered titanate into the corresponding nanowire-shape form. The reaction mechanism involves the decomposition of the starting layered titanate into 1D small segments which assemble into the nanowire. This new nanowire shows properties resulting from the combination of 1D and 2D nanostructural features, excellent cation exchange ability, and high photoinduced charge separation and photocatalytic efficiency. As a demonstration, we evaluate the nanowire as a sequestrating material capable of collecting toxic cations, like Cd2+, from water and photoreducing them (immobilizing them tightly). We find that the nanowire shows an efficient and ultrafast photoimmobilization activity, whereas the starting layered titanate and a benchmark TiO2 photocatalyst (P25) show no activity under the identical conditions. The photoimmobilization rate (within 1 min) is considerably faster than the cation exchange rates reported for state-of-the-art cation exchangers (with no photoimmobilization ability). The nanowire used for photoimmobilization reactions is easily recovered from water by decantation, showing the possible practical use for safe disposal of toxic cations in the environment.

Materials Nanoarchitectonics Using 2D Layered Materials: Recent Developments in the Intercalation Process.

Layered inorganic solids as an attractive classification of 2D materials offer material diversity and a wide range of interesting properties. Layered inorganic solids provide an expandable 2D nanospace between each individual layer, the so called interlayer space, to accommodate/arrange guest species such as molecules, nanoparticles, and polymer chains and design unique nanoarchitectures, resulting in the production of intercalation compounds showing different properties in comparison to those of virgin layered materials and guest species. Layered inorganic solids can also be exfoliated to result in nanosheet production. Further ordering of exfoliated nanosheets is also possible via different methods and normally leads to creating soft materials presenting properties and applications different from that of relatively rigid intercalation compounds. Here, the latest studies and up-to-date developments on the possible techniques of designing novel types of materials using layered inorganic solids are specifically highlighted.

Significant Effect of Pore Sizes on Energy Storage in Nanoporous Carbon Supercapacitors.

Mesoporous carbon can be synthesized with good control of surface area, pore-size distribution, and porous architecture. Although the relationship between porosity and supercapacitor performance is well known, there are no thorough reports that compare the performance of numerous types of carbon samples side by side. In this manuscript, we describe the performance of 13 porous carbon samples in supercapacitor devices. We suggest that there is a "critical pore size" at which guest molecules can pass through the pores effectively. In this context, the specific surface area (SSA) and pore-size distribution (PSD) are used to show the point at which the pore size crosses the threshold of critical size. These measurements provide a guide for the development of new kinds of carbon materials for supercapacitor devices.

Solid-State 31P Nuclear Magnetic Resonance Study of Interlayer Hydroxide Surfaces of Kaolinite Probed with an Interlayer Triethylphosphine Oxide Monolayer.

The solid acidity of the interlayer aluminol surfaces of kaolinite was explored by solid-state 31P nuclear magnetic resonance with magic angle spinning (MAS) using triethylphosphine oxide (TEPO), which formed a monolayer with a uniform orientation between the layers of kaolinite as a probe molecule. Intercalation of TEPO between the layers of kaolinite was achieved using methoxy-modified kaolinite as an intermediate. The presence of TEPO in the reaction products was revealed by the two signals at 21 and 7 ppm, which were assignable to ethyl groups in TEPO, in the solid-state 13C nuclear magnetic resonance with cross polarization and magic angle spinning techniques (13C CP/MAS NMR). The presence of TEPO between the layers of kaolinite was demonstrated by the expansion of basal spacing from 0.86 nm, the interlayer distance of methoxy-modified kaolinite to 1.16 nm, as shown by the X-ray diffraction patterns, suggesting the formation of a TEPO monolayer between the layers of kaolinite. The formation of hydrogen bonds between the P═O groups of TEPO and the aluminol groups on the interlayer surfaces of kaolinite was also revealed by the appearance of an additional OH stretching band at 3598 cm-1 in the Fourier-transform infrared spectrum and narrow solid-state 31P MAS NMR signals observed at 55-53 ppm which were shifted from the position of the physisorbed TEPO (50 ppm). These results clearly indicate that the solid acidity of interlayer aluminol groups of methoxy-modified kaolinite was probed using an interacted TEPO monolayer.

Merging Cation Exchange and Photocatalytic Charge Separation Efficiency in an Anatase/K2Ti4O9 Nanobelt Heterostructure for Metal Ions Fixation.

Efficient collection and safe disposal of toxic metals ions from aqueous solutions is critical for applications in environmental remediation. Although extensive efforts have been devoted to the synthesis of functional TiO2 materials, photocatalytic reduction (photoreduction) of aqueous metal ions into solid metals remains a challenge. We designed a TiO2 nanoparticle-decorated layered titanate (K2Ti4O9) material that retained the cation exchange ability of K2Ti4O9 but also possessed the enhanced charge separation efficiency of K2Ti4O9. Combining cation exchange with enhanced charge separation efficiency results in a heterostructured material with remarkably high activity for the photoreduction of metal ions. Initially we demonstrated how the photocatalyst can efficiently reduce aqueous Ni2+ cations, whereas the benchmark TiO2-based P25 catalyst showed little to no activity. The resulting Ni-deposited heterostructure can then be used as a catalyst for visible light-induced photocatalytic H2 evolution in water.

Photoexcited charge carrier dynamics of interconnected TiO2 nanoparticles: evidence of enhancement of charge separation at anatase-rutile particle interfaces.

The charge carrier kinetics of hydrothermally treated TiO2 nanoparticles, consisting of interconnected anatase and rutile crystallographic forms, was investigated using a heterodyne transient grating technique to obtain direct evidence of the enhancement of charge separation efficiency. We found that surface recombination arising from trapped electrons was retarded, compared with that of P25 TiO2 nanoparticles, with the aid of an increase of particle interfaces. This means that the charge separation efficiency of hydrothermally treated TiO2 nanoparticles is higher than that of P25 TiO2 nanoparticles, to which the enhanced photocatalytic performance of the hydrothermally treated TiO2 nanoparticles could be attributed.

Highly Ordered Mesostructured Vanadium Phosphonate toward Electrode Materials for Lithium-Ion Batteries.

Highly ordered mesostructured vanadium phosphonates (VP) have been synthesized in the presence of cetyltrimethylammonium bromide (CTAB) as a structure-directing agent. Nitrilotris(methylene)triphosphonic acid (NMPA) and (ammonium/sodium) metavanadate (NH4 VO3 /NaVO3 ) have been used for the construction of pore walls. The CTAB templates are removed from the materials by an extraction process without destroying the parent mesostructure. The formation mechanism for the ordered mesoporous structure and its impact on electrochemical application in lithium ion batteries (LIBs) are explained by considering the structural and electrochemical stability of the framework. The results demonstrate that the counter cations (NH4+ /Na+ ) of the metavanadate precursors have a crucial role in stabilizing the mesoporous structure of the mesoporous VP materials. Mesoporous VP materials with highly ordered structure have great applicability as high-performance electrode materials in LIBs due to the advantages of their large contact area with electrolyte and short transport paths for lithium ions. Mesoporous VP electrodes exhibit high reversible specific capacity with superb cycling stability (100 cycles) and excellent retention of capacity (92 %).

Hydrothermal Conversion of Layered Niobate K4Nb6O17·3H2O to Rare Microporous Niobate K6Nb10.8O30.

We report a new facile route to synthesizing K6Nb10.8O30, a rare microporous niobate. When hydrothermally treated under alkali conditions, a layered niobate, K4Nb6O17·3H2O, was converted to K6Nb10.8O30. This product had a much smaller particle size than K6Nb10.8O30, prepared by a conventional solid-state reaction, and showed enhanced adsorption properties.

Facile synthesis of nanoporous Li1+xV1-xO2@C composites as promising anode materials for lithium-ion batteries.

Recently, a layered material with composition Li1+xV1-xO2 has been discovered as a promising alternative anode material to graphite due to its high volumetric capacity and low operation potential. Herein, we demonstrate a mild and cost-effective synthetic methodology to construct a novel nanoporous anode material (P-LVO@C), comprising Li1+xV1-xO2 nanocrystals embedded in a porous carbon matrix. The thermal decomposition of organic materials, including a triblock copolymer (P123) and citric acid, in a N2 atmosphere is the source of the nanoporous carbon in the porous composite material, while citric acid also plays a crucial role in maintaining the reductive environment of the synthetic medium. Due to the novel composition of Li1+xV1-xO2 (x ≥ 0.03), as well as its porous structure and well-integrated conductive framework, our P-LVO@C has great applicability as a high performance anode material for lithium-ion batteries. Our P-LVO@C composite electrode shows high reversible capacity with an excellent cycling performance (100 cycles) and good capacity retention (82%) at a higher rate (0.48C).

Cyano-Bridged Trimetallic Coordination Polymer Nanoparticles and Their Thermal Decomposition into Nanoporous Spinel Ferromagnetic Oxides.

The synthesis of a novel family of cyano-bridged trimetallic coordination polymers (CPs) with various compositions and shapes has been reported by changing the compositional ratios of Fe, Co, and Ni species in the reaction system. In order to efficiently control the nucleation rate and the crystal growth, trisodium citrate dihydrate plays an important role as a chelating agent. After the obtained cyano-bridged trimetallic CPs undergo thermal treatment in air at three different temperatures (250, 350, and 450 °C), nanoporous spinel metal oxides are successfully obtained. Interestingly, the obtained nanoporous metal oxides are composed of small crstalline grains, and the grains are oriented in the same direction, realizing pseudo-single crystals with nanopores. The resultant nanoporous spinel oxides feature interesting magnetic properties. Cyano-bridged multimetallic CPs with various sizes and shapes can provide a pathway toward functional nanoporous metal oxides that are not attainable from simple cyano-bridged CPs containing single metal ions.

Unprecedentedly enhanced solar photocatalytic activity of a layered titanate simply integrated with TiO2 nanoparticles.

We report a simple, low-cost methodology for unprecedentedly enhancing the photocatalytic activity of layered inorganic semiconductors. A layered titanate with a lepidocrocite-type structure scarcely showed photocatalytic activity for a test reaction, the oxidative decomposition of formic acid in water into CO2, under simulated solar light, but it showed highly enhanced photocatalytic activity upon mixing with a much smaller amount (approximately 10 wt%) of commercially available TiO2 nanoparticles (P25) in water. The photocatalytic activity of the mixture was approximately 5 times that of P25, a benchmark photocatalyst. From various analyses, the enhancement resulted from the transfer of photoexcited electrons from the layered titanate to P25 at their particle interfaces and retardation of charge recombination. When applied to a photocatalyst for H2 production from water containing methanol under simulated solar light, the layered titanate/P25 mixture showed considerably enhanced activity and the apparent quantum yield was 23% (at 320 nm). By replacing P25 with Pt co-catalyst-loaded P25, the apparent quantum yield of the mixture increased from 23 to 73%, although an extremely small amount (below 0.06%) of Pt was used in the system.

Self-Construction from 2D to 3D: One-Pot Layer-by-Layer Assembly of Graphene Oxide Sheets Held Together by Coordination Polymers.

Deposition of Ni-based cyanide bridged coordination polymer (NiCNNi) flakes onto the surfaces of graphene oxide (GO) sheets, which allows precise control of the resulting lamellar nanoarchitecture by in situ crystallization, is reported. GO sheets are utilized as nucleation sites that promote the optimized crystal growth of NiCNNi flakes. The NiCNNi-coated GO sheets then self-assemble and are stabilized as ordered lamellar nanomaterials. Regulated thermal treatment under nitrogen results in a Ni3 C-GO composite with a similar morphology to the starting material, and the Ni3 C-GO composite exhibits outstanding electrocatalytic activity and excellent durability for the oxygen reduction reaction.

Tunable-Sized Polymeric Micelles and Their Assembly for the Preparation of Large Mesoporous Platinum Nanoparticles.

Platinum nanoparticles with continuously tunable mesoporous structures were prepared by a simple, one-step polymeric approach. By virtue of their large pore size, these structures have a high surface area that is accessible to reagents. In the synthetic method, variation of the solvent composition plays an essential role in the systematic control of pore size and particle shape. The mesoporous Pt catalyst exhibited superior electrocatalytic activity for the methanol oxidation reaction compared to commercially available Pt catalysts. This polymeric-micelle approach provides an additional design concept for the creation of next generation of metallic catalysts.

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

Temperature-dependent photocatalytic hydrogen evolution activity from water on a dye-sensitized layered titanate.

Visible light-induced hydrogen evolution activity from water on a ruthenium complex-sensitized layered titanate was modified when the reaction was conducted at higher temperature.

Functionalization of layered titanates.

This review article describes the synthesis, modification, and function of lepidocrocite-type layered titanate (A(x)Ti(2-y)M(y)O4, A: A, interlayer cation; M, metal or vacancy). Due to the compositional variation, which affects cation exchange, semiconducting and swelling properties, lepidocrocite-type layered titanates have attracted increasing attention in solid-state materials chemistry. The immobilization of functional units has been done to improve the properties as well as to impart additional functions. Here, we highlight recent developments of hybrid materials derived from the intercalation of inorganic and organic cations, organic functional groups, and nanoparticles into lepidocrocite-type layered titanates.

Layered Silicates Exhibiting MOF-Like Gate-Opening Behaviors in Liquid-Phase Adsorptions: Experimental and Theoretical Investigations.

Layered silicates, including clay minerals, can be used as liquid-phase adsorbents in many important applications. However, because their two-dimensional interlayer space is narrow and not entirely opened due to the presence of interlayer species, guest species are forced to penetrate while expanding the interlayer space, which limits their adsorption performances compared with microporous materials such as MOFs and zeolites. Herein, as reported for the adsorption of gaseous species on flexible MOFs, we report a layered silicate that exhibits gate-opening adsorption in liquid phases. This layered silicate, synthesized via dilute acid treatment of the parent sodium-type, exhibits an abrupt increase in the basal spacing (layer thickness + interlayer space) to reach a plateau even at an earlier stage of benzoic acid adsorption from acetonitrile, whereas a typical layered silicate, magadiite, exhibits a gradual increase in the basal spacing as adsorption progress under identical conditions. The layered silicate shows an excellent adsorption capacity and rate for benzoic acid uptake from acetonitrile, which is considerably higher than that of magadiite. With comprehensive adsorption tests using different adsorbates and solvents, we propose that the layered silicate has zeolite-like but distorted, flexible open microchannels within each layer, and the intralayer microchannels can effectively and rapidly accommodate the solvent (acetonitrile) molecules, which are capable of expanding the framework to initiate the adsorption of aromatic compounds. The density function theory calculation revealed the adsorption mechanism, where the layered silicate accommodates acetonitrile in the intralayer microchannel followed by the interlayer space, and the former selectively plays a role as the adsorption site of aromatic compounds via exchange with acetonitrile.