Understanding the intrinsic nature of materials requires ultrahigh-purity materials because impurities affect various properties. Ion-exchange separation is one of the most promising purification technologies; however, the thermodynamic details of the ion-exchange reaction have not been made clear. The condition of metal species in the solution phase is fundamental to investigating the ion-exchange reaction. In this paper, the distribution of ferric chloro complexes in hydrochloric acid solutions was investigated by factor analysis of UV-Vis absorption spectra, followed by fitting analysis of a theoretical model to individual molar attenuation coefficients obtained by mathematical decomposition of UV-Vis absorption spectra. Five ferric species were detected by principal component analysis using a novel index proposed in this paper. In the results of factor analysis followed by fitting analysis, [FeIII]3+, [FeIIICl]2+, [FeIIICl2]+, [FeIIICl3]0, and [FeIIICl4]− were identified. The activity coefficients of charged species in concentrated aqueous solutions were estimated by using a modified Debye-Hückel equation. The thermodynamic parameters of the four cumulative formation constants and a Setchénow coefficient for neutral species of [FeIIICl3]0 were determined. The adsorbability of ferric, cupric, and cobalt species to an anion exchanger from hydrochloric acid solutions was qualitatively discussed using the results obtained in this paper.
The formation of Cu active sites for nitric oxide (NO) direct decomposition on ZSM-5, mordenite, and low Si/Al beta zeolites under similar Cu ion-exchange conditions was investigated. On all the Cu-zeolites applied in this work, it was observed that with an increase in the Cu ion-exchange level, catalytic activity for NO direct decomposition increased with an S-shaped curve. However, it was demonstrated that the efficiency of Cu active site formation for NO direct decomposition on the zeolites is affected by the zeolite topology. For the zeolites applied in this work, the efficiency of Cu active site formation follows the order: ZSM-5 ∼ mordenite > beta. It was revealed by NO probe IR measurements that Cu ion on different zeolites possesses different oxidation state distribution (Cu+/Cu2+ ratio) and coordination environment, suggesting that they are the origin of the different efficiencies for Cu active site formation for NO direct decomposition. The interpretation of our results combined with previous discussion on the structure of Cu active sites on the ZSM-5 zeolite suggests that the distribution of ion-exchange sites in the zeolite frameworks can affect the oxidation state distribution and coordination environment of Cu sites on the zeolites.
We accomplished zinc catalyzed hydrosilylation of carbon dioxide (CO2) to silyl formate (C+II), bis(silyl)acetal (C0), methoxysilane (C−II), and finally methane (C−IV). Among several zinc salts, we found that Zn(OAc)2 with ligand 1,10-phenanthroline was the best. A turnover number of 815000 was achieved using the zinc catalyst to yield C+II. Unexpectedly, we observed the generation of CO from CO2 and hydrosilane for the first time. In addition to Zn, other first-row transition metals (Mn, Fe, Co, Ni, and Cu) also served as Lewis acid catalysts for CO2 hydrosilylation, regardless of the nature of the metal.
The stable structure of the spinels MgCo2O4 and MgCo1.5Mn0.5O4, as Mg secondary battery cathode materials, was investigated by first-principles calculations. The calculated stable structures were compared with the crystal structures obtained by quantum beam measurements. The effect on the electronic structure of the substitution of Mn in MgCo2O4 was examined. Pair distribution function fitting of the normal spinel of MgCo1.5Mn0.5O4 gave a better agreement with experiments than that of MgCo2O4. It was found that Mg/Co cation mixing decreased by the substitution of Mn, as found for the Rietveld analysis of the synchrotron X-ray diffraction. From electron density analysis, it was expected that the Mn-O6 octahedra were more stable than the Co-O6 octahedra because Mn is more attracted to an O atom than a Co atom, that is, the Mn-O bond was stronger than the Co-O bond. The Mg in MgCo1.5Mn0.5O4 was more easily inserted and moved than in MgCo2O4 because the Mg-O bonds near Mn became weak. This fact is consistent with the fact that the first discharge capacity and cycling performance of MgCo1.5Mn0.5O4 were improved over those of MgCo2O4 in charge and discharge tests.
In search for a qualitative understanding of the effects of molecular packing on singlet fission (SF) rate, a simplified version of the frontier orbital model is described and illustrated on a pair of tetracene molecules. To identify all favorable physically accessible pair geometries, all significant local maxima of the square of the electronic matrix element for SF have been located within the six-dimensional space of possible arrangements of two rigid bodies, using a grid of over 4.7 × 108 pair geometries. Those at which the molecules interpenetrate were excluded using a hard-sphere model. The effects of intermolecular interaction on the SF energy balance and thus its rate constant kSF were approximated using Marcus theory at each of the maxima using the same simplified version of the frontier orbital model. Starting at these local maxima, the pair geometries were optimized for maximum kSF and the 21 best are reported along with their computed Davydov splitting and triplet biexciton binding energies. The optimal pair structures at the resulting maxima follow qualitative rules published previously and further elaborated here.
CH3NH3PbI3 (MAPbI3) perovskite layers can be obtained by thermal annealing thin films of the intermediate dimethyl sulfoxide (DMSO) intercalated complex, MA2Pb3I8·2DMSO. In the present work, the formation, structure, and thermal transformation of the intermediate complex in both bulk and thin film form is examined in detail. The grain size and orientation of the intermediate crystallites in the solvent-intercalated thin film material is shown to directly influence the flatness of the annealed perovskite layer. Flat-lying orientation of the small needle-like intermediate crystallites is found to yield dense and flat perovskite layers. Optimized spin coating and annealing processes are developed for the formation and thermal conversion, respectively, of the intermediate film. Based on these methods, MAPbI3 perovskite solar cells with high power conversion efficiency (maximum ∼20.3%) were obtained with high reproducibility.
We found that cobalt nanoparticle catalysts supported on nitrogen-doped carbon could facilitate oxygenation of styrenes in a heterogeneous manner. Both the nitrogen dopant and cobalt species were essential to promote the reactions. Based on several mechanistic studies, the formation of radical intermediates on cobalt nanoparticles is proposed.
We successfully developed a novel time-resolved synchrotron-radiation X-ray diffraction (t-SXRD) measurement system with high temporal resolution (minimum time: 50 ms) at the BL02B2 facility at SPring-8 for the in situ observation of the crystal structure changes of inorganic compounds in aqueous solution during chemical reactions. For evaluating the performance of this novel system, we applied it to observe the crystal structure change of a layered double hydroxide consisting of Mg and Al (Mg/Al = 2) with chloride as the exchangeable anion species (Cl−-MgAl(1/3)LDH) during the anion-exchange reaction from Cl− and NO3− in aqueous solution under various [NO3−] conditions. The t-SXRD patterns from the MgAl(1/3)LDH crystal particles dispersed in aqueous solution were recorded every 0.2 s using our measurement system; that is, we obtained t-SXRD data for kinetic analysis. Thus, we identified the features for the anion-exchange reaction of Cl−-MgAl(1/3)LDH from Cl− and NO3− in aqueous solution under various [NO3−] conditions. All the present results revealed that the novel t-SXRD measurement system developed herein is very useful and effective for monitoring the in situ structural changes of crystalline compounds dispersed in solution during chemical reactions with a fast time constant.
The anharmonic vibrational wavenumbers of dihalogeno-methanes CH2X2 and 1,2-dihalogenoethanes CH2XCH2X (X: F, Cl, and Br) were calculated by using hybrid and double-hybrid density-functional methods. For comparison of the methods of calculation, the molecular-orbital method at the CCSD(T) level was also tested for CH2F2 and CH2Cl2. It was found that the hybrid-type B3LYP functional method was not satisfactory for calculating anharmonic vibrational wavenumbers. It was possible to improve the B3LYP functional method by altering the coefficients of the energy formula for CH2F2, but the set of obtained coefficients was not transferrable to CH2Cl2. The double-hybrid-type B2PLYP functional method with carefully chosen sets of basis functions gave molecular structures and anharmonic vibrational wavenumbers in good agreement with the published experimental values. The molecular-orbital method at the CCSD(T) level gave calculated results comparable with (or even better than) those by the B2PLYP functional method. However, the cost of computation by the B2PLYP functional method is far lower than that by the molecular-orbital method at the CCSD(T) level. The B2PLYP functional method, which has the advantage of giving satisfactory results with relatively low costs of computation, may become a realistic approach for anharmonic vibrational analyses of relatively large molecules in general.
In order to precisely design the active sites in two-dimensional (2D) gold-based catalysts, we have developed a convenient and versatile plasma-assisted droplet evaporation-rigid crosslinking method for the fabrication of gold nanoparticle (Au NP) array film. Four kinds of Au NP arrays have been decorated respectively with rigid sulfurated crosslinkers i.e. thieno[3,2-b]thiophene, 2,2′-bithiophene, 1,4-benzenedithiol and 4,4′-thiodibenzenethiol, and the density of crosslinkers can be adjusted under plasma treatment. Particularly, the utilization of 4,4′-thiodibenzenethiol gave uniform particle sizes to form a periodical 2D structure, which provides multiple exposed active sites of gold nanoparticles rather than enwinding by the alkyl chains. Meanwhile, the weaker electron-donating effect and steric hindrance of rigid groups in the crosslinkers could also enhance the catalytic activity. In addition, the Au NP array film can be transferred from the glass substrate and further composited with polymers and metal organic framework (MOF) into self-standing composite membrane. Therefore, this rigid crosslinked array film can serve as an environmentally friendly catalyst for CO2 cycloaddition under atmospheric CO2 pressure, which offers a novel application of Au NPs array film, and opens up a new way for the design and fabrication of 2D hybrid materials.
Two of the biggest limitations for titanium dioxide (TiO2) as a photocatalysis are the lack of visible light response and the need for higher surface areas in order to maximize sites where reactions can take place. In this work, a Metal-Organic Framework (MOF), specifically MIL-125, is employed as a template to produce TiO2 particles with high specific surface area and well-controlled porosity. When annealed under a hydrogen atmosphere to create an oxygen deficient TiO2−δ, which is black in appearance, enhanced photocatalytic properties are observed, importantly including a significant visible light response in the degradation of model pollutant Rhodamine B.
Polycyclic aromatic hydrocarbons (PAHs) containing 4–7 benzene rings were synthesized via a methylarene-based protocol. Trimethyl[2-(trifluoromethyl)allyl]silane was electrophilically benzylated with Ar1CH2Br (prepared from Ar1CH3) to afford 2-trifluoromethyl-1-alkenes that were in turn nucleophilically benzylated with Ar2CH2Li (prepared from Ar2CH3) through an SN2′-type reaction to produce 1,1-difluoroethylenes, which are cyclization precursors bearing two 2-arylethyl groups. Magic acid efficiently promoted the domino Friedel–Crafts-type cyclization of these precursors, followed by dehydrogenation that enabled the connection among two aryl groups (Ar1 and Ar2) by forming two benzene rings between them, facilitating the synthesis of the desired higher-order PAHs. With the proposed protocol, the combination of even a limited number of methylarenes can yield a variety of PAHs in diverse configurations.
Substantial research interests have been focused on cyclic π-conjugated molecules owing to their unique chemical and physical properties. By constructing hybrid aromatic arrays within these cyclic systems, new series of composite macrocycles would be provided. Our group has been studying the construction of such hybrids by adopting the palladium-catalyzed direct coupling of heteroaromatics. We herein report the synthesis and characterization of thiophene-thiazole composite macrocycles. X-ray diffraction analyses revealed that some of these coupling products exhibit characteristic helical assemblies in the solid state. Additionally, we synthesized a heteroarene-fused cyclooctatetraene composed of four different heteroaryl fragments.
Improvement of the utilization efficiency of Pt by improving the mass diffusion is key especially for carbon nanotube (CNT)-based electrocatalyst layers (CL) of polymer electrolyte membrane fuel cells (PEMFC). Here, we introduced hydrophobic spherical polytetrafluoroethylene (PTFE) particles into the CNT-based CL for the first time to improve the diffusion of oxygen and water. Catalyst-coated gas diffusion layers (CCG) were prepared by vacuum filtration method and membrane electrode assembles were prepared by hot pressing of CCGs with Nafion membrane. By incorporating PTFE particles specifically into the cathode CL, a large increase of power density was obtained mainly due to the improvement of hydrophobicity. Addition of the PTFE was effective especially during low humidity operations. Since the filtration process is simple and useful especially for CNT-based electrocatalysts, our findings are quite beneficial to realize CNT-based PEMFC, which is promising especially for the next generation PEMFCs operated under high-temperature and low humidity.
When biomaterials come into contact with biological fluids, water molecules immediately adsorb onto the surface of the materials. To understand the origin of the crucial roles of water molecules in biological interfaces, it is necessary to relate particular states of hydration water to various physicochemical properties of hydrated polymers. Here, advances in the intermediate water concept are reviewed. This account provides an overview of the progress made in the design of multi-functional biomedical polymers by controlling the bio-interfacial water states. Using principles of intermediate water, which is common in hydrated biopolymers and only biocompatible synthetic polymers, we found the synthetic methodology to create novel biocompatible polymers moves toward a more high-throughput way.