Search

In this work, we describe an aqueous synthetic strategy for producing bone-shaped Au − Ag2S metal-semiconductor hybrid nanorods. Specifically, Au nanorods were first synthesized and used as seeds to synthesize bone-shaped Au − Ag nanorods by selectively overgrowing Ag shells at both ends of Au nanorods. Through the site-selective sulfidation strategy using Na2S aqueous solution, the Au − Ag bimetallic nanorods were transformed into Au–Ag2S metal–semiconductor hybrid nanorods. When used as photocatalysts for the photooxidative degradation of methylene blue (MB) under sunlight irradiation, the Au–Ag2S hybrid nanorods showed excellent photocatalytic performance due to the synergistic action of metal and semiconductor components. [ABSTRACT FROM AUTHOR]

As an alternative to the graphite-based anode in lithium-ion battery (LIBs), the TiO2-based anode has continuously drawn attention due to its high stability and long operating life, especially in the field of electric vehicles (EVs). Although a spinel structure lithium titanate (LTO, Li4Ti5O12) anode is commercially available, there has been a constant need to improve the anode capacity with TiO2-based materials because they have much higher theoretical capacity compared to LTO. In this regard, nanostructured TiO2-based materials with high surface area are thought to be ideal for LIB anode application. In this study, a lotus-root shaped meso-/macroporous TiO2 (LR-700) material was prepared and employed as an anode material for LIB with expectancy to have large channels for easy Li+ insertion and thus show better electrical property. Coin cell tests were carried out with the anodes prepared from LR-700, LTO, and nano-sized TiO2 powder (known as P25) for comparison by charging and discharging at 0.5 C. Despite the presence of large macroporous channels and mesopores in the walls for LR-700, the capacity of 158 mAh/g for LR-700 anode was found to be slightly lower than the LTO's theoretical discharge capacity of 175mAh/g. We envision that less thicker walls would enhance the performance through effective ion diffusion and electronic conduction. [ABSTRACT FROM AUTHOR]

Understanding charge transport in π‐conjugated polymers is critical for the design of high‐mobility polymers. However, charge transport in donor–acceptor (D–A) type copolymers and the roles of D and A units are still unclear. Herein, the charge transport properties of three cyclopentadithiophene (CDT)‐based D–A type copolymers with CDT as a common donor and benzothiadiazole, fluoro‐2,1,3‐benzothiadiazole, or pyridyl‐2,1,3‐thiadiazole (PTz) as an acceptor are investigated. The best charge transport is found for CDT‐PTz showing 0.79 ± 0.01 cm2 V−1 s−1 hole mobility in field‐effect transistors, with the lowest energetic disorder by temperature‐dependent mobility measurements. Using various structural probes and density functional theory simulations, it is found that CDT‐PTz has the most rigid and planar backbone structure and the strongest intramolecular dipole moment thanks to the noncovalent N–S interactions and the strong electron‐withdrawing PTz acceptor unit. These structural properties lead to strong intermolecular interactions in CDT‐PTz, reducing its π–π stacking distance, producing strong aggregation even in hot dilute solutions. The enhanced mobility in CDT‐PTz is attributed to this high quality π–π stacking, driven by increased backbone rigidity and strong molecular dipoles. This work suggests that rigidifying the copolymer backbone with enhanced push–pull strength of the D–A units is a key requirement for high‐mobility D–A copolymers. [ABSTRACT FROM AUTHOR]

MoO2 was produced by mixing MoS2 and MoO3 via a solid-state reaction in a fluidized bed reactor. The basic fluidization data were acquired by monitoring the minimum fluidization velocity of MoS2 and MoO3. The conversion rate of MoS2 and MoO3 to MoO2 was derived based on the solid-state reactions carried out for 1 h at various stoichiometric ratios. This study confirmed that the optimal stoichiometric ratio of MoS2 and MoO3 was 1.0: 6. The conversion rate at the optimum stoichiometric ratio was studied by varying the reaction temperature. A conversion rate of 99% was achieved when the reaction temperature and superficial gas velocity were 973 K and 0.3 m/s, respectively. Detailed analysis of the final product after the solid-state reaction was by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD), to determine the shape, structure, and diffraction patterns. [ABSTRACT FROM AUTHOR]

Plasmonic superstructures composed of multiple metal nanoparticles (NPs) may represent an elegant example for hot-spot mediated surface-enhanced Raman scattering (SERS) enhancement. For sufficient SERS activity in the superstructures, the gap distance between adjacent NPs has to be engineered to be as small as possible, and often a sub-5 nm gap distance is necessary to create intensive hot spots. However, despite the recent advances in synthesis, the preparation of such plasmonic superstructures still requires laborious assembly, purification, and separation steps. In addition, the resulting plasmonic assemblies often undergo agglomeration and conformational change, which deteriorates the uniformity of the gap distance as well as SERS reproducibility. To overcome these issues, we utilized the self-segregating behavior of block copolymer micelles, and concomitantly functionalized the core and corona of micelles with different kinds of metal NPs. The prepared micellar NP assemblies structurally resembled colloidal core–satellite NP assemblies and exhibited strong SERS activity. However, unlike the initial expectation, the plasmonic coupling between dissimilar NPs was blocked in the micellar structure. Alternatively, we discovered that the local field inside the micellar NP assembly could be enormously amplified by multiple scattering processes, which significantly increased the path length of incident photons for SERS enhancement. [ABSTRACT FROM AUTHOR]

The photocatalytic decomposition characteristics of individual and binary vapors of benzene, toluene, and ethylbenzene by a UV reactor were studied. The reactor was custom-designed to have a synergistic effect of photochemical oxidation by ozone generated by UV254+185 nm lamps and photocatalytic oxidation by TiO2 photocatalyst whose surface area was almost doubled by helically inserted TiO2-coated perforated planes. The removal efficiencies of individual vapors of benzene, toluene, and ethylbenzene generally increased in proportion to the relative humidity and oxygen supply. The photocatalytic decomposition kinetics of individual vapors, as well as binary vapors consisting of benzene-toluene, benzene-ethylbenzene, and toluene-ethylbenzene, followed the Langmuir-Hinshelwood (L-H) equation quite well. Maximum elimination capacities of individual vapors were 560 g/m3∙day, 630 g/m3∙day, and 1,024 g/m3∙day for benzene, toluene, and ethylbenzene, respectively. In view of mutual impact for the photocatalytic decomposition of binary vapors, the reaction rate of the target component was more influenced by the presence of the counter component with lower bond dissociation energy. [ABSTRACT FROM AUTHOR]

A novel heterogeneous one-component catalyst was developed by the covalent post functionalization of zeolitic imidazolate framework-90 (ZIF-90) with a pyridinium based ionic liquid (IL) to generate IL supported ZIF-90 (IL-ZIF-90). The synthesized catalyst has been characterized using a range of analytical, spectroscopic, and electron microscopy techniques followed by successful employment for the solventless cycloaddition of epoxides and CO2 to yield cyclic carbonates under mild reaction conditions. The effects of reaction parameters like catalyst amount, reaction time, reaction temperature, and CO2 pressure have been investigated. A reaction mechanism for the IL-ZIF-90 catalyzed PO–CO2 cycloaddition has been proposed on the basis of density functional theory (DFT) calculations. The catalyst system was separable by centrifugation and reused four consecutive times successfully. In general, it can be suggested that IL supported porous metal organic frameworks (MOFs) may introduce a new class of highly porous catalyst species showing excellent CO2 transforming capability. [ABSTRACT FROM AUTHOR]

The removal of boron is a very important issue in desalination using seawater reverse osmosis (SWRO). A novel approach using polyol compounds to remove boron is introduced in this study. Polyols are compounds possessing multiple hydroxyl groups and they can combine with uncharged boric acid by generating anionic complexes. As a result, a large molecule is formed and it can be easily rejected by SWRO membrane at seawater pH. Lab-scale SWRO tests were performed to investigate the effect of polyol on the boron removal using different types of polyol (xylitol, glycerol, and D-mannitol). The polyol–boron reaction occurs in seawater condition with low boron concentration and various ion compounds, which leads to two important findings that boron-polyol reaction occurs with low boron and polyol concentrations, and there are no significant inhibitors for the reaction in seawater. The boron-polyol reaction rate is so fast that it can be easily applied to full-scale SWRO processes. The boron removal rate increases at higher polyol concentrations and at larger numbers of hydroxyl groups of polyol. [ABSTRACT FROM AUTHOR]

The CO2 sorption capacity of the 3D In-MOF (Et2NH2)[In(2,6-NDC)2] ·2H2O ·DEF ( I) (where 2,6-NDC is 2,6-naphthalenedicarboxylate and DEF is N, N-diethylformamide) was investigated. The solvent-free I contains three distinct types of 1D micropores with different shapes and pore dimensions. The evacuated I sorbed 297.2 cm3 g-1 (13.3 mmol g-1) of CO2 at 196 K, 72.2 cm3 g-1 (3.22 mmol g-1) at 273 K, and 39.8 cm3 g-1 (1.78 mmol g-1) at 298 K. The difference between the uptake at 196 K and those at 273 and 298 K is relatively large. The shapes of the sorption isotherms are also dramatically different. At 196 K, the adsorption-desorption isotherms are S-shaped without significant hysteretic behavior between the adsorption and desorption branches. On the contrary, the adsorption isotherms measured at 273 and 298 K fit well with the Langmuir-Freundlich equation. The low-surface-coverage isosteric heat ( Qst) of CO2 adsorption by I is 19.6 kJ mol-1. Detailed estimations of the adsorption sites for CO2 were then performed by DFT calculations. The calculated binding energies were typically dependent on the dimension of the micropores when nonbonding (van der Waals) interactions were considered; the larger the micropore dimensions, the smaller the calculated binding energy. In addition, not only the framework CH ···OCO contacts for Ch3 but also the counter-cation CH ···OCO contacts for Ch1 and Ch2 were found to be important. [ABSTRACT FROM AUTHOR]

An easily accessible, highly soluble, small-molecule phenanthroimidazole derivative has been synthesized and characterized. The synthesized compound shows strong luminescence in solution and exhibits good thermal stability. Single crystal X-ray crystallography studies were carried out. Correlations between the X-ray structures, photophysical properties and the performance in light-emitting electrochemical cells (LECs) are described. A yellowish green emission was achieved by using the target compound in a LEC device configuration. The constructed prototype device performance was promising with a maximum brightness of 125 cd m−2. The results suggest that the phenanthroimidazole derivative can function as an active material in LEC devices. [ABSTRACT FROM AUTHOR]

Reported is the application of ZIF-90, which is a highly porous zeolitic imidazolate framework, as a novel catalyst for the cycloaddition of propylene oxide (PO) with CO2 in the absence of co-catalysts and solvents under moderate reaction conditions. The effects of various reaction parameters were investigated. The activity of ZIF-90 was compared with that of various metal-organic-framework (MOF)-based catalysts for the cycloaddition of PO with CO2. Density functional theory calculations elucidated the role of ZIF-90 in creating a favorable environment for the PO-CO2 cycloaddition reaction. A reaction mechanism for the ZIF-90-catalyzed PO-CO2 cycloaddition on the basis of DFT calculations is proposed and the regeneration of ZIF-90 is discussed. [ABSTRACT FROM AUTHOR]

Abstract: DFT calculations were employed to investigate transamination during metalorganic chemical vapor deposition (MOCVD) of transition metal nitrides films, such as titanium nitride (TiN) and tantalum nitride (TaN). The calculated energetics and rate constants for the ligand exchange of tert-butylimidotris(dimethylamido) tantalum (TBTDMT) with NH3 demonstrated that NH3 addition to form the ammonia adduct, TBTDMT·NH3, proton transfer and dissociation of dimethylamine to afford net transamination of the dimethylamido ligand are facile even at low temperature (∼300°C). The transamination of the tert-butylimido ligand, however, was relatively slow at those temperatures but became facile at temperatures appropriate for CVD growth (∼600°C). Rapid transamination is consistent with lower temperature for growth of TaN by MOCVD in the presence of NH3, efficient removal of carbon-containing ligands, and incorporation of higher levels of nitrogen in the resulting films. [Copyright &y& Elsevier]