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The OTA method helps improve the porous properties of activated carbon providing higher surface area and mesopore volume than the conventional activation method.

Monolithic catalysts have attracted attention as a substitute for particulate catalyst beds in gas-liquid-solid three-phase reactions. In this work, carbon gel monoliths with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) were synthesized, and Pt particles with an average particle diameter of 3.0 nm were supported on them in a highly dispersed state through the incipient wetness method. In addition, it was confirmed that the supported Pt shows a high resistance to sintering. Hydrogenation of p-nitrophenol was carried out in order to evaluate the catalytic activity of Pt/CMHs in three-phase reactions. As a result, Pt/CMHs showed a high catalytic activity even at ambient temperature and normal pressure. Furthermore, the hydrogenation reaction significantly proceeded even when hydrogen was provided at the minimum flow rate required to complete the reaction. Since Pt/CMHs showed higher reaction activity than the same catalyst in the form of particles, it was concluded that the efficiency of three-phase reactions can be significantly improved by using monolithic catalysts with a microhoneycomb structure.

Due to their high theoretical energy density, lithium-air batteries (LABs) are expected to become the standard secondary battery system of the next generation. However, for practical usage, their cycle performance needs to be improved. Thus far, few studies have investigated how the structure of carbon cathode materials affects their cycle performance. In this study, meso- to macro-porous carbon gels (CGs) heat-treated at different temperatures were prepared, and were used as model materials to discuss the relationship between carbon structure and cycle performance. Nitrogen adsorption experiments, X-ray diffraction analysis, Raman spectroscopy analysis, and thermal gravimetric analysis were conducted to derive the pore structure, crystal structure, carbon bonding state, and oxidation resistance of CGs, respectively. In addition to standard analysis methods, temperature program desorption measurements were conducted under vacuum to aid the analysis of surface oxygen-containing functional groups. Charge-discharge measurements indicated that cycle performance improves when the carbons were heat-treated at higher temperatures. Functional groups on the carbon surface were found to promote side reactions and reduce reversible capacity. Defects in the carbon are thought to promote uneven deposition of deposits which tend to cause the sudden "death" of LAB.

Microporosity and basic-site density of mixed oxides formed from Mg-Al layered double hydroxides possessing interlayer isethionate (MgAl-Ise) were investigated to seek for a potential application of them to basic catalyst supports for natural gas conversion. The oxide samples were prepared by thermal activation of MgAl-Ise at 500 °C in air, 5% O2 in N2, N2, vacuum, H2 in helium with various concentrations, H2, and NH3 to investigate effects of gas atmosphere. The N2 adsorption data show that Mg-Al mixed oxides obtained by thermal activation of MgAl-Ise in H2, NH3, and N2 possess substantially larger micropore volumes characterized by N2 uptake at the relative pressure

A simple co-grinding treatment with fructose is introduced for the efficient and scalable preparation of g-C3N4 nanoplates. The results revealed that these g-C3N4 nanoplates still preserved the basic framework of carbon nitride and even displayed superior morphological properties and electronic structures. With respect to the pristine carbon nitride, the few-layered g-C3N4 impressively demonstrated an enhanced photocatalytic activity towards hydrogen generation and the degradation of Rhodamine B (RhB) under visible light illumination, emphasizing the vital roles of the morphology and electronic structures on the photocatalytic performance. This study provided sustainable and cost-effective tactics for the delamination of g-C3N4 for efficient energy conversion. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Titanium dioxide is a promising electrode material for lithium-ion capacitors. When using TiO2 as an electrode material, it is necessary to combine it with carbon at the nanometer level to improve its low electrical conductivity and low reactivity with Li+. However, preparation methods of reported TiO2/porous-carbon nanocomposites are generally not cost-effective, and their productivities are low. In this study, the vacuum liquid-pulse chemical vapor deposition (VLP-CVD) technique was developed to easily prepare TiO2/porous-carbon nanocomposites, where TiO2 nanoparticles with a diameter of similar to 4 nm could be homogeneously deposited inside the pores of meso- or macroporous carbons. Because the deposited TiO2 nanoparticles had access to effective electrically conductive paths formed by the porous-carbon substrate, they showed a high discharge capacity of similar to 200 mA h g(-1)-TiO2 (based on TiO2 weight). In particular, the composite prepared from macroporous carbon showed an extremely high rate performance, where 50% of the discharge capacity was retained at a current density of 15 000 mA g(-1) when compared to that measured at 50 mA g(-1). In addition, the composite also showed very high cyclability, where 80% of the discharge capacity was retained at the 10 000(th) cycle. Because the VLP-CVD technique can be performed using simple apparatus and commercially available starting materials, it can be expected to boost industrial production of TiO2/porous-carbon for lithium-ion capacitors.

Intercalation of 2-hydroxyethanesulfonate (2-heS) and 3-hydroxy-1-propanesulfonate (3-hpS) into layered Mg–Al double hydroxides (Mg–Al LDHs) allows delamination of layers in water and enables the synthesis of high-surface-area oxides through non-oxidative thermal decomposition. To investigate the roles of anionic heads and hydroxyl tails in these organic sulfonates, 2-hydroxyethanephosphonate (2-heP) and 1,3-propanedisulfonate (1,3-pDS) were tested as analogs of hydroxyalkylsulfonates, and the thermal characteristics of the resultant LDHs were investigated. Exchange of interlayer CO32− with 2-heP proceeds similarly to 2-heS, causing the same degree of interlayer expansion. However, the resultant LDH resists swelling and delamination in water, demonstrating the distinct property enabled by the –SO3− group. Although LDH possessing 1,3-pDS intercalants seems to resist delamination because of the lack of hydroxyl groups, its thermal characteristics resemble those of its 3-hpS counterpart, demonstrating the crucial role of alkyl sulfonate groups to allow the formation of enhanced microporous structures through non-oxidative thermal treatments. Our results show further that even a partial exchange of CO32− by 3-hpS, corresponding to 0.05 equivalents relative to the exchangeable Al sites, triggers unique thermal characteristics observed for LDH-sulfonates.

Activated carbons for electrodes of non-aqueous electric double layer capacitors were prepared from composites of poly(methymethacrylate) particles and phenolic resins. Their surface areas can be increased up to 3000 m2 g−1 through simple CO2 activation. Through the characterization of pore properties of the resulting carbons, it was found that the activation process appears to be composed of two steps. The pore properties of the activated carbons were optimized to maximize their performances as electrodes for non-aqueous electric double layer capacitor electrodes.

We studied X-ray absorption of multiwall carbon nanotube (MWCNT) produced by the chemical vapor deposition method using ethanol and benzene precursors at 1473 K with X-ray absorption fine structure in order to obtain a new designing direction for X-ray shielding fabrics. Acid oxidation and thermal annealing further treated the MWCNTs. The energy dependence of X-ray absorptivity of MWCNTs was efficiently used to remove the effect of the metallic impurity contribution, to elucidate the relationship between X-ray mass attenuation coefficient and the structure of MWCNT. The thermal annealing treatment at 2773 K was the most effective method to increase the crystallinity and to remove the impurities of MWCNTs. The acid and oxidation treated MWCNT induced not only the surface structure difference between MWCNT and highly oriented pyrolytic graphite (HOPG) but also the addition of surface oxygen related functional groups from those treatments, which influence the mass attenuation coefficient (μ/ρ). The X-ray absorptivity of heat treated E-MWCNT and B-MWCNT at 2773 K was close to that of HOPG indicating that those MWCNTs have a well-ordered crystal structure, quite similar to HOPG. On the other hand, E-MWCNT having a less-crystalline surface structure showed larger X-ray absorptivity than HOPG by about 9%.

Monolithic cesium ion (Cs+) adsorbents were synthesized via the directional freezing of a silica hydrogel containing ammonium molybdophosphate (AMP) particles, followed by freeze-drying. The adsorbents have a honeycomb-like structure with nearly straight microchannels (approximately 21 µm in diameter) running through them and with AMP particles partially embedded intact within the channel walls. Because of its honeycomb-like structure, the adsorbent, denoted as AMP silica microhoneycomb (AMP-SMH), achieves a significantly lower pressure drop than a typical column packed with spherical particles with similar diffusion path lengths for Cs+ when water was passed through it (about 35-times lower). Comparison of breakthrough curves between the AMP-SMH and columns packed with particles by numerical simulation also indicates that AMP-SMH shows shorter length of unused bed values. These results demonstrate that the AMP-SMH shows a high performance in the continuous separation of Cs+ due to their unique microhoneycomb structure.

Adsorption of phenol using carbon adsorbents in the form of a packed bed of particles inherently suffers from the incompatibility between low hydraulic resistance and short diffusion path length. In this work, carbon gel monoliths made from resorcinol–formaldehyde gels with introduced straight microchannels in the range of 60–160 µm were successfully synthesized using polyesters fibers as templates. The advantage of this synthesis method is that both channel size and channel density can be tuned independently. Introduced microchannels were effective in minimizing the pressure drop of a fluid flowing through the sample to less than a hundredth of beds packed with particles having the same diffusion path length. Synthesized monoliths also possess sufficient mechanical strength (more than 12 kg per monolith) to be activated to increase their adsorption capacity. Adsorption experiments of phenol in a continuous flow system show that synthesized monoliths can be used as effective adsorbents for phenol removal. The tunable channel size and channel density of the proposed synthesis method has the potential for the synthesis of monoliths which could be used to fulfill various process demands.

Mg–Al mixed oxides with record-high surface areas and basic site concentrations were synthesized from Mg–Al layered double hydroxides with interlayer isethionate (Ise) or 3-hydroxy-1-propanesulfonate (HPS). Anion exchange of interlayer CO32– in synthetic hydrotalcites with the organic sulfonates induces disorders in layer stacking as characterized by powder X-ray diffraction and enables facile delamination in water. Thermal treatment of materials anion-exchanged by Ise (MgAl–Ise) and HPS (MgAl–HPS) in N2 and H2 resulted in the formation of Mg–Al mixed oxides with marked enhancement in Brunauer–Emmett–Teller (BET) surface area relative to those treated in air. Treatment in a flow of H2 is particularly effective, doubling the surface area of mixed oxides derived from MgAl–Ise relative to those obtained in a flow of N2. A higher degree of disorder in layer stacking in MgAl–HPS than MgAl–Ise resulted in the formation of Mg–Al mixed oxides with higher surface areas than those from MgAl–Ise. As a result, thermal activation of MgAl–HPS in a flow of H2 yielded Mg–Al mixed oxides with the highest BET surface area (410 m2 g–1) and CO2 uptake (1.6 mmol g–1 at 25 °C and 100 kPa) in all samples. These values are significantly higher than those obtained from the initial hydrotalcites as well as those reported in the literature with similar Mg–Al ratios. Investigation of the thermal activation steps by thermogravimetric analysis and mass spectrometry indicates that the key factors to achieve high surface area and CO2 uptake are to weaken interactions between layers by inducing stacking disorders and to facilitate the removal of interlayer sulfonates by preventing the formation of sulfates from them via thermal activation under a reducing environment.

Immobilization of TiO2-based photocatalysts usually suffers from lowered surface area and mass transfer limitation compared with their suspended counterpart. In this work, TiO2–SiO2 monolithic photocatalysts having straight macropores, called microhoneycombs, were synthesized. The obtained samples had straight macropores with a diameter in the range of 15–40 μm formed by walls having a thickness up to 5 μm. The samples also contain micropores and small mesopores inside their walls, which contribute to high surface areas of more than 500 m2 g–1. Synthesized photocatalysts were tested in a continuous flow system using the decolorization of methylene blue as a model reaction. It was found that the unique morphology of the samples can be used to promote the uniform distribution of the target fluid while reducing the pressure drop across the photocatalyst to less than a hundredth compared with a packed bed system. In addition, calcination at 600–800 °C improved the strength and photocatalytic activity of the m...

Controlling the concentration of defects in reduced graphene oxide (rGO) to tailor its electrical and physicochemical properties has remained a significant challenge. We report that extent of microwave (MW)-driven annealing of rGO is influenced significantly by its bulk density, which allows us to vary its defect density and crystallite size over wide ranges by controlling this parameter. Extent of annealing was investigated by multiple techniques including Raman and X-ray photoelectron spectroscopies, and electrical conductivity measurements. Improved corrosion resistance of rGOs upon annealing was examined by cyclic voltammetry in H 2 SO 4 electrolyte and temperature-programmed oxidation of rGO. Our results indicate that a low bulk density of rGO facilitates defect annealing, yielding high-quality carbon with 99.3 wt% purity, oxidative resistance as high as graphite powder, and an electrical conductivity of 36,000 S m –1 in the compressed powder form. These results demonstrate a prospective synthesis route for tailor-made nanocarbons from rGO through MW-driven annealing.

Analysis of literature data on acid-catalyzed esterification reaction of levulinic acid (LA) with ethanol (EtOH) has suggested that some sulfonated carbon catalysts exhibit higher active-site performance than other solid acid catalysts such as macroreticular resins bearing sulfonic acid groups, zeolites, mesoporous silica functionalized with alkyl- and arene-sulfonic acid groups. To elucidate factors that enable the higher performance of sulfonated carbon catalysts, a series of sulfonated carbon catalysts was synthesized by sulfonating various carbon materials whose concentrations of surface oxygen-containing functional groups, porous structure, and swelling ability differ significantly. The catalysts were tested not only in the liquid-phase esterification reaction of LA with EtOH but also in the reaction of acetic acid (AcA) with EtOH because the latter reaction serves as a test reaction to probe the performance of –SO 3 H sites with minimal influence by mass transfer limitation and to provide an insight into a role of γ-keto group of LA in catalysis. The results show that all catalysts exhibit nearly the same turnover frequency per –SO 3 H site in the esterification reaction of AcA with EtOH despite widely different structural properties. In contrast, the data indicate that neighboring functional groups such as –COOH and –OH facilitate the reaction of LA with EtOH presumably through hydrogen-bonding interaction between these surface functional groups and γ-keto group of LA. These results suggest a general design strategy to improve the performance of solid acid catalysts further by precisely tuning the distance between –SO 3 H sites and neighboring functional groups.

Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanoplates (CNNP) have become a hot research topic in photocatalysis due to their small thickness and large specific surface area that favors charge transport and catalytic surface reactions. However, the wide application of 2D g-C3N4 nanoplates prepared by ordinary methods suffers from increased band gaps with a poor solar harvesting capability caused by the strong quantum confinement effect and reduced conjugation distance. In this paper, a facile approach of exfoliation and the following fast thermal treatment of the bulk g-C3N4 is proposed to obtain a porous few-layered g-C3N4 with nitrogen defects. Due to the preferable crystal, textural, optical and electronic structures, the as-obtained porous CNNP demonstrated a significantly improved photocatalytic activity towards water splitting than the bulk g-C3N4 and even the 3 nm-thick CNNP obtained by sugarassisted exfoliation of the bulk g-C3N4. The difference in the enhancement factors between the H2O splitting and organic decomposition has revealed the effect of N defects. This study offers insightful outlooks on the scalable fabrication of a porous few-layered structure with a promoted photocatalytic performance. (C) 2020 Elsevier Inc. All rights reserved.

Mg-Al mixed oxides with highly accessible basic sites were synthesized from Mg-Al layered double hydroxides bearing interlayer isethionates (Ise). Anion-exchange of interlayer carbonates in synthetic hydrotalcites with Ise induces stacking disorders in layered structure, and subsequent delamination in water followed by drying causes further disordering as characterized by X-ray diffraction technique. However, thermal activation of these materials in air formed Mg-Al mixed oxides with low surface area and low CO2 adsorption capacity. In contrast, thermal activation in N2 or N2 followed by air formed materials exhibiting marked increases in CO2 adsorption capacity up to ∼800% relative to those obtained by thermal activation in air. Thermogravimetric and elemental analyses and IR spectroscopy characterization indicate that thermal activation in N2 enables removal of sulfur species formed from Ise at ∼400 °C, and limits the formation of sulfate species that bridge nanosheets and cause irreversible stacking of them. The proper thermal activation procedure in addition to disordered structure of aggregates of Mg-Al double hydroxide nanosheets enabled the formation of Mg-Al mixed oxides with higher surface area and larger micropore volume than those obtained from the initial hydrotalcites. These results highlight the critical importance of thermal activation steps for such materials, and demonstrate a prospective route to synthesize new porous materials based on Mg-Al mixed oxides.

TiO2 has attracted attention as a highly safe anode material for lithium-ion batteries (LIBs). To improve the low electrical conductivity of TiO2, nanostructured TiO2 and/or TiO2/carbon nanocomposites have been prepared, which generally involve costly and labor-intensive methods. In this study, TiO2/C nanocomposites were prepared using the liquid pulse injection technique, whereby a liquid initial source is simply injected as liquid pulses into a heated tubular reactor. Optimizing the preparation temperature and carrier-gas flow rate, anatase-type TiO2 nanoparticles covered with carbon layers were successfully prepared from titanium tetraisopropoxide. The obtained composite had a reversible capacity of 180 mAh/g, which is higher than that of conventional anode materials for safe LIBs, such as lithium titanium oxide. Furthermore, the capacity hardly decreased until the 100th cycle. The composite prepared by the proposed method, which is suitable for industrial production, is thus expected to be a safe anode material alternative to conventional materials.

In the development of lithium-air batteries, to understand how the porous structure of the cathode affects the performance of the battery system is important because the main electrochemical reaction which occurs in this system is the deposition of Li2O2 in the pores of the cathode. To clarify the relationship between the porous structure of the cathode and the performance of the battery system, we used carbon gels with different pore size distributions as model cathodes and investigated how their pores are filled during discharging by analyzing the structure of cathodes discharged to different depths through N-2 adsorption experiments. The dominant deposit formed during discharging was identified to be Li2O2 by X-ray diffraction. Interestingly, the ratio of the volume of the Li2O2 deposited in fully discharged cathodes to the meso-macropore volume of the cathode was in the range of 0.5-0.6 and was fairly constant among the samples. Such ratios are higher than those of microporous carbon cathodes such as activated carbon cathodes. These results suggest that increasing the meso-macro pore volume of the cathode is effective to obtain large capacities in lithium-air batteries.

Ternary Mo–V oxide nanocrystals (Nano-MoVO) were hydrothermally synthesized in the confined space of a mesoporous carbon template and tested in the oxidative dehydrogenation (ODH) of ethane and propane. The synthesized nanocrystals are approximately 60 nm in length, 20 nm in diameter on average, and possess a structure resembling orthorhombic MoVO (Orth-MoVO) as indicated by spectroscopic and microscopy characterization. The Nano-MoVO catalyst has a 5-fold higher mesopore volume and a 4-fold larger external surface area than an Orth-MoVO synthesized by a conventional method (Orth-MoVO) as characterized through N2 adsorption analysis. Nano-MoVO shows similar activation energy in the ODH of ethane compared with other conventional MoVO catalysts. However, Nano-MoVO exhibits significantly higher propane/ethane activation rate ratio and higher propene selectivity even in the absence of elements such as Te and Nb that suppress overoxidation of propane-derived species to COx. The results suggest the benefits of the nanocrystalline morphology to limit overoxidation.

The present work was aimed to evaluate the suitability of resorcinol-formaldehyde carbon gels as adsorbent for water pollutants removal. The carbon gels were characterized using N2 adsorption-desorption isotherm for specific surface area, and Fourier transform infrared (FTIR) for surface functional groups. Methylene blue and cesium were employed as model water pollutants. Results show that the un-oxidized carbon gel, despite its lower specific surface area (333 m2/g) displayed a 118 mg/g removal of methylene blue, that is higher than 35 mg/g by the oxidized carbon gel (418 m2/g). The evaluation of adsorption kinetics revealed a lower pseudo-first order rate constant of 0.088 h-1 for 10 mg/L methylene blue adsorption. A positive effect of surface oxidation was demonstrated for cesium adsorption. On molar basis, however, the oxidized carbon gel exhibits a selective removal towards methylene blue compared to cesium. Carbon gel is a promising candidate for water pollutants removal, and further treatment needs to be sought to boost its performance.

Silica microhoneycombs (SMHs) loaded with an ionic liquid (IL) (IL-SMHs) were successfully synthesized by impregnating SMHs with an IL bearing an amino group, trihexyl(tetradecyl)phosphonium alanate ([P66614][Ala]). SMHs can incorporate at least 50 wt % [P66614][Ala] without its straight channels being clogged as demonstrated by a low pressure drop when He was passed through the material. The IL-SMH containing 50 wt % [P66614][Ala] shows a CO2 capacity of ∼0.26 mmol-CO2·g–1 in a CO2 33%–N2 67% atmosphere at 303 K. IL-SMHs can be readily regenerated by heating them at 393 K and can be reused at least three times without losing the CO2 absorption ability. IL-SMH can also effectively separate CO2 in a flow system. The length of unused bed was very short (only 19 mm). These results demonstrate the high potential of IL-SMHs to be used for effective CO2 separation in flow systems.

For the preparation of physically-activated carbons with ultra-high surface areas that are comparable to those of chemically-activated carbons, we synthesized meso-, macroporous carbons from phenolic resins using poly(methylmethacrylate) particles as a template and activated them using CO2. Our aim was to achieve uniform activation by reducing the practical depth within the carbon which needs to be activated. Our results show that the shorter the practical depth becomes, the higher the achievable BET surface area becomes. Extremely high BET surface areas (~3000 m2 g−1) can be attained by reducing this depth to the order of a few tens of nanometers. We also relate the practical length of the developed nanopores with the practical depth through the results obtained from EDLC measurements. The results reveal that the shortening of the practical activation depth also leads to the shortening of the lengths of the nanopores introduced during activation.

Carbon microhoneycombs (CMHs), which can be prepared from a resorcinol formaldehyde (RF) hydrogel using ice crystals as a template, are attractive materials for industrial applications such as solid catalysts and adsorbents in flow system reactors. For such applications, pores in a material are important for mass transfer, but the mesopore volumes of CMHs are smaller than that of typical RF-derived carbons because ice crystals compress RF gels during freezing, and mesopores partly collapse. The introduction of mesopores into CMHs requires an additional step such as HCl treatment in the preparation process, and this increases the preparation time. In this work, we developed a convenient method for introducing mesopores into CMHs, in which dextran was added to the initial RF solution. This simple step increased the mesopore volume from 0.015 to 0.191 cm(3)/g. We investigated the porous structure of the sample at each step in the preparation, and found that dextran protected the porous structure of the RF hydrogel from growth of ice crystals, enabling mesopore introduction. A combination of dextran addition and HCl treatment further increased the mesopore volume to 0.753 cm3/g; this cannot be achieved using HCl treatment alone. This may be because the HCl solution can diffuse through the mesopores introduced by dextran addition, and this promotes pore formation. (C) 2016 Elsevier Inc. All rights reserved.

To investigate the effects of the porous structure of carbon support for bimetallic PtRu PEFC anode catalysts on their CO tolerance, a series of Resorcinol-formaldehyde carbon gels with different resorcinol to catalyst (R/C) ratios (i.e., 200, 800 and 1000) were synthesized and used to support Pt2Ru3 nanoparticles. Synthesized catalysts were characterized by powder X-ray diffraction, N2 gas adsorption/desorption experiments, and scanning transmission electron microscopy. CO tolerances were evaluated by using a single cell in a H2 feed in the presence of CO ranging from 100 to 2000 ppm. The potential difference of the cell using Pt2Ru3/RC1000ac58 anode catalyst was 0.655 V whereas the cell using a commercial Pt2Ru3/C catalyst showed a voltage of 0.570 V in the presence of 500 ppm CO. The results reveal that high modal size and volume of mesopore enhance diffusivity of CO resulted in effectively oxidization of CO.

Adsorption of phenol from an aqueous solution in batch and continuous flow systems using carbon gels with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) was studied. The obtained monolithic CMHs had fairly straight channels, 25–45 μm in diameter, and the thickness of the walls which form the channels was around 5 μm. The CMHs showed 370 times lower hydraulic resistance when compared with a column packed with particles having the same diffusion path length as it. The obtained CMHs have a hierarchical micro-meso porous structure giving BET surface area in the range of 513–1070 m2·g−1.When used for phenol adsorption from an aqueous solution, the CMHs quickly adsorbed phenol at first, and then, the uptake gradually increased, which indicates that the adsorption mechanism is based on not only simple physisorption. The phenol adsorption capacity increased with the increase in carbonization temperature of the CMH and the decrease in its hydrophilicity. CMHs carbonized at temperatures higher than 1073 K showed the highest phenol adsorption capacity which was around 160 mg·g−1. The CMHs could continuously adsorb phenol from aqueous solutions, and their length of unused bed (LUB) values depended on operation conditions but were in the range of 0.3–0.7 cm. The experimental results indicated that carbon cryogels with a microhoneycomb structure have a high potential to be used for effective separation of phenol.

Pt–Ru/SnO2/C catalysts were prepared by a rapid quenching method. The structure and morphology of Pt–Ru particles in Pt–Ru/SnO2/C are controlled to obtain the same Pt–Ru particle as that in a commercial Pt–Ru catalyst. The Pt–Ru/SnO2/C and commercial Pt–Ru catalysts were characterized by X-ray diffraction and scanning transmission electron microscopy. Electrochemical activities were evaluated by CO stripping voltammetry, single cell tests, in situ infrared reflection–absorption spectroscopy (IRRAS) and surface-enhanced infrared absorption spectroscopy (SEIRAS). The Pt–Ru/SnO2/C catalyst showed the same structure, morphology and catalytic activity for hydrogen oxidation reaction (HOR) in the absence of CO as those of a Pt–Ru/C catalyst. Both the activity for electrochemical CO oxidation and Pt–CO bond strength were quantitatively evaluated. The addition of SnO2 decreased the Pt–CO bond strength with maintained HOR activity to enhance CO tolerance.

Immobilization of TiO2-based photocatalysts usually suffers from lowered surface area and mass transfer limitation compared with their suspended counterpart. In this work, TiO2–SiO2 monolithic photocatalysts having straight macropores, called microhoneycombs, were synthesized. The obtained samples had straight macropores with a diameter in the range of 15–40 μm formed by walls having a thickness up to 5 μm. The samples also contain micropores and small mesopores inside their walls, which contribute to high surface areas of more than 500 m2 g–1. Synthesized photocatalysts were tested in a continuous flow system using the decolorization of methylene blue as a model reaction. It was found that the unique morphology of the samples can be used to promote the uniform distribution of the target fluid while reducing the pressure drop across the photocatalyst to less than a hundredth compared with a packed bed system. In addition, calcination at 600–800 °C improved the strength and photocatalytic activity of the monoliths while preserving the high surface area of the samples.

To improve the performance of carbon paper used for applications such as electrodes for electrochemical devices and air filters, two types of long carbon nanofibers (CNFs) with average diameters of 20 and 49 nm were prepared by the liquid pulse injection (LPI) technique by adjusting reaction conditions. Carbon paper was made from the CNFs through a simple filtration process. The paper prepared from the CNFs with an average diameter of 20 nm (LPI-CNF(20) paper) was firm and flexible even though it was prepared without using any binders. LPI-CNF(20) paper also had a high surface area and showed a high electrical conductivity and a moderate gas permeability according to its void size. These properties are required for cathodes in the latest battery systems such as lithium–air batteries. In electrochemical experiments conducted to evaluate the performance of LPI-CNF(20) paper as a cathode, the paper showed a larger discharge capacity on the basis of the cathode weight than a conventional cathode (a commercially available carbon paper combined with a porous carbon), which indicated that it has a high potential to be used as a cathode in lithium–air batteries.

Flexible film-type catalysts were synthesized by encapsulating urease within a κ-carrageenan gel network supported on a cellulose-acetate membrane filter. Synthesized film-type catalysts are flexible and can be easily formed into a shape that is suitable for a specific process configuration. The filter membrane has macropores about 200 nm, which are formed by interconnected bead-shaped membrane material. Scanning electron microscopy shows that the surface of the membrane material is coated homogeneously with the κ-carrageenan hydrogel. Urease entrapped within the gel network hardly leaches out during urea hydrolysis catalysis conducted at 310 K in a batch reactor and exhibits high catalytic performance. Analysis of the reaction data by the Michaelis–Menten equation shows that the film-type catalyst shows kinetic parameters ( K M and V max ) and apparent activation energy (24 kJ mol − 1 ), which are all similar to those found for free urease. Estimation of the mass transfer rate of urea within the κ-carrageenan network and the urea hydrolysis rate show that the diffusion rate of urea within the thin film is five orders of magnitude higher than the reaction rate. The film catalyst can be recycled at least 7 times with

A series of sulfonic-acid-containing carbon catalysts were synthesized through the pyrolyzation of resorcinol–formaldehyde resins and subsequent sulfonation to investigate the tunability of their pore structure and surface properties. These catalysts were characterized by nitrogen gas adsorption, water vapor adsorption, elemental analysis, Boehm titration, and IR spectroscopy. Catalytic consequences of these properties were examined using two esterification reactions in which reactants of substantially different sizes (oleic acid vs acetic acid) are involved as well as the condensation of furfural with 2-methylfuran. The esterification of acetic acid with ethanol proceeded at nearly the same activity (TOF ∼ 0.02 s–1) for all synthesized catalysts regardless of the variation of their surface and pore properties. Poisoning experiments of acid groups in the synthesized catalysts with NaCl indicate that nearly all −SO3H groups are accessible to the reactants. However, the esterification of oleic acid with met...

Efficacy of a new approach for the synthesis of graphene oxide (GO) nanosheets that has been recently reported (Ogino et al. in Chem Mater 26:3334–3339, 2014) was investigated further using graphite oxides with various degrees of oxidation and average particle sizes. The approach consists of rapid freeze–thaw cycles of water containing graphite oxide, which enables the efficient exfoliation of graphite oxide layers with the minimal fragmentation of GO sheets. The method is effective for the exfoliation of graphite oxides with C/O atomic ratios ≤2.6 as shown by experiments with various degrees of oxidation of graphite oxides. When this method was tested for large particle-size graphite oxide that had been prepared from graphite with the average particle size of 60 μm, it formed approximately tenfold larger GO sheets than those prepared using sonication. Exfoliation experiments conducted at different freezing rates of water demonstrate that a faster freezing rate of water yielded a higher concentration of a dispersed GO solution. Thus, the results support the hypothesis that rapid phase change enables efficient layer exfoliation.

Resorcinol–formaldehyde carbon gels (RFCs) show several advantageous properties as a catalyst support over other carbons, as their pore volume and pore size can be readily tailored, for example, via CO2 activation. In this study, RFCs were synthesized with various activation degrees (burn-off) as 0, 37, 58, and 88% and used as the support for a PtRu anode electrode; a commercial Pt2Ru3/C anode catalyst was used as a reference. The catalysts were characterized by powder X-ray diffraction (PXRD), BET surface area, transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The performance and CO tolerance of the obtained catalysts were tested through single cell performance analysis with CO contaminations ranging from 100 to 2000 ppm. The prepared Pt2Ru3/RFC catalysts showed superior CO tolerance. Especially Pt2Ru3/RFC prepared using an RFC with a burn-off of 58% (RC1000Ac58) showed the highest performance and best CO tolerance. The activation degree could affect the volume...

High-surface-area carbon xerogels were prepared in the form of disks via carbonization of precursor resorcinol–formaldehyde (RF) polymer disks and subsequent activation of the resultant RF carbon xerogels by CO2. RF carbon xerogels allow the preparation of a set of pre-activated carbon disks having different mesopore volumes. Analysis of the relationship between the mesopore volume of the samples and their CO2 activation efficiency showed that the presence of mesopores is crucial for obtaining a high-surface-area carbon with minimal burn-off of carbon atoms. Activation of an RF carbon disk with a mesopore volume of 1.0 cm3 g−1 up to a burn-off of 81% yielded an activated carbon disk with a high BET surface area of ∼3000 m2 g−1. Such disks could be readily used as electrode materials for an electric double layer capacitor without filler or binder addition and exhibited competitive EDLC performance against other electrode materials previously reported.

Dispersed graphene oxide (GO) nanosheets in water were synthesized via a new approach involving sonication-free exfoliation, as promoted by repetitive simple freeze–thaw cycles. These cycles consist of rapid freezing of an aqueous solution containing graphite oxide and subsequent thawing of the resultant solid. This approach is effective for exfoliation of graphite oxide and yields approximately 80% GO after six repetitive freeze–thaw cycles. The GO synthesized by the new method experiences minimal fragmentation during the exfoliation process and has a lateral size at least 3-fold larger than that of GO prepared by using sonication, as evidenced by atomic force microscopy and dynamic light scattering. We also demonstrate use of the resulting exfoliated GO that is synthesized using this approach as a building block for the synthesis of a low-density (≈0.02 g cm–3) macroporous monolithic material, using directional freezing, which forms ice rods within the solution that served as the template to direct the ...

Monolithic carbon cryogels having a honeycomb structure with pore openings a few tens of micrometers in diameter (Carbon Micro Honeycomb, CMH) were synthesized by directional freezing of precursor resorcinol formaldehyde (RF) hydrogels and subsequent carbonization at temperatures >= 674 K. Aging of precursor RF monoliths with 1 N HCl aq. was found to markedly increase the hydrophobicity of the corresponding CMHs as characterized by water vapor adsorption experiments conducted at 298 K. Analysis of the water vapor adsorption data indicates that levels of hydrophobicity of CMHs are similar to those exhibited by other types of highly hydrophobic adsorbents, such as a coal-derived activated carbon and a defect-free pure silica zeolite Beta. HCl aging also drastically changes the porous structure of CMHs from microporous to micro/mesoporous as characterized by nitrogen adsorption/desorption experiments. Because of significantly enhanced hydrophobicity of CMHs as well as hierarchical pore structure (straight macropores connected with micro/mesopores), CMHs can readily separate 1-butanol molecules from a diluted aqueous solution at 310 K and demonstrate high capacities (up to approximate to 3.13 mol kg(-1) at a 1-butanol concentration of 135 mM). The unique morphology of CMHs, consisting of straight macropores coupled with micro/mesopores embedded within honeycomb walls, and the highly hydrophobic surface properties offer future prospects of CMHs in various applications that require fast separation of hydrophobic molecules from a large volume of aqueous solutions.

A carbon-based monolithic acid catalyst with a honeycomb structure (CMHC) was synthesized via carbonization of a resorcinol-formaldehyde resin and subsequent sulfonation using sulfuric acid. The CMHC has nearly straight flow-through macropores (e.g., 47–78 μm) formed by the directional freezing of the resin precursor. These macropores are surrounded by thin carbon walls of approximately 6-μm thickness that are micro- and mesoporous as characterized by nitrogen adsorption experiments. The straight macropores enable a low hydraulic resistance to a liquid flow as demonstrated by >1000-fold less pressure drops of water flowing through the CMHC than those calculated for a packed bed of spherical particles with the same diameter as the approximate wall thickness of the CMHC. The CMHC shows a stable catalytic activity in the liquid-phase esterification of acetic acid with ethanol at 333 K in a flow reaction system for 50 h of operation. These results show prospective features of the CMHC for applications in flow...

A honeycomb-type silica monolith was functionalized with sulfonic acid groups to synthesize a solid acid catalyst for flow reaction systems. The sulfonic acid groups were introduced via anchoring of 3-mercaptopropyltrimethoxysilane (MPTS) on the silica surface and subsequent oxidation using a H2O2 solution. The honeycomb-type monolith used as the substrate was prepared using ice crystals as a template and was found to have a high open frontal area of ≈85% and flow-through macropores (≈27 μm in diameter) that are surrounded by silica walls (≈2 μm in thickness). The catalyst was tested by the liquid phase esterification of ethanol with acetic acid at 333 K in a batch reactor as well as a flow reactor. The catalyst was found to exhibit about 2-fold higher catalytic activity than Amberlyst-15 in a batch reactor. The catalyst also showed a stable catalytic activity for 24 h in a flow reactor.

In this work, the growth behavior of carbon nanofibers synthesized using the liquid pulse injection technique was clarified by analyzing samples collected at different growth stages. It was confirmed that, due to the high catalytic activity of the ultrafine metal catalyst particles generated through this technique, the fibers elongate at an extremely high rate during the initial stage of growth, which leads to the high efficiency of carbon nanofiber production. Owing to this high elongation rate, the elongation process and thickening process can be practically considered as two consecutive processes. This allows the modification of the production sequence, resulting in a significant enhancement in production efficiency.

Magnesium ammonium phosphate (MgNH 4 PO 4 ·6H 2 O:MAP) releases approximately 70% of its ammonia at a mild temperature of 378 K. The resultant material (magnesium hydrogen phosphate (MgHPO 4 :MHP)-like material), which appears to be an amorphous phase, to remove ammonia from wastewater was investigated. Because the original size of MAP crystals was found to critically affect the kinetics of ammonia uptake by the corresponding MHP-like material, MAP with different sizes were synthesized by changing concentration, pH and temperature of the synthesis solution. The variation in the synthesis concentration was found to change the size of MAP as well as the aspect ratio of the long-axis to the short-axis. The rate of ammonia uptake depends primarily on the dimension of the short-axis of the corresponding MAP crystals. Furthermore, analysis of ammonia uptake using a method similar to the shrinking-core model shows approximately 0.5 μm from the surface is effectively used for ammonia uptake over a period of a realistic process time. Thus, the results suggest it is crucial to synthesize small MAP crystals with the size of short-axis less than 1 μm. Our results also show that small MAP crystals can be used at least four times repeatedly for ammonia uptake.