The fluid flow dynamics under reactive regimes are visualized by the use of particle tracking. Our numerical simulations elucidate the role of pH variations and additional ionic species counterions toward flow reversal. The combination of these techniques highlights the interplay between electrocatalytic and electrokinetic phenomena on the occurrence of flow reversal. Copper colloids typically demonstrate excellent catalytic and electric properties, but their synthetic approaches lag behind their more expensive cousins.
In this manuscript we investigate the synthesis of Cu colloids using a polyol-based method. We employ phthalonitrile as an additive, leading to competing reactions during the nucleation step and finally resulting in distinct sizes and properties of the copper particles. Even though during the polyol synthesis, the copper particles are partially protected from the high tendency of copper to oxidize, further treatment leads to the formation of a thin passivating and semiconducting CuxO layer.
CuxO is known to be a visible light photocatalyst. We therefore investigate the size-dependent photo catalytic activity of these colloids using rhodamine B RhB as a model organic pollutant. Following asymmetrization via deposition of a thin Au layer on one hemisphere, we also demonstrate the applicability as a photocatalytic micromotor.
Understanding the reactivity of boron and nitrogen codoped graphene BNG under the charged environment is essential in developing Pt-free counter electrode materials in the dye-sensitized solar cells DSSCs. It was found experimentally that a reduced ZnCr2O4 spinel performs well in syngas conversion to ketene CH2CO , which is a key intermediate for ethylene production.
In this work, we have systematically investigated the stability of several ZnCr2O4 spinel surfaces by using first-principles calculations. It was identified via microkinetic modeling that the partially reduced ZnCr2O4 surface is preferable to produce ketene.
Finally, we propose a global optimization algorithm for ranking the importance of elementary reactions and pathways, which can be considered as a useful tool for simplifying the reaction network and rational design of catalysts in the future.
The study of self-assemblies of a series of Pd II meso-tetraphenylporphyrin PdTPP derivatives with different substitutions indicates the cofacial dimer is only observed for molecules with carboxyl substituents. The Rh K-edge extended X-ray absorption fine structure revealed that the supported Rh nanoparticles formed an interfacial Rh—O—P bond via the interaction with the surface-terminated [P2O7] unit with a corner-shared bitetrahedral structure.
The electronic state of the Rh was therefore affected by the M—O—P bond. According to the X-ray photoelectron spectroscopy analysis, the Rh exhibited an electron deficiency due to an electron-withdrawing effect from the [P2O7] unit, which had a Lewis acid character.
The extent of electron deficiency was significantly larger when the Rh nanoparticles were supported on SiP2O7, which has a more covalent bonding character compared with ZrP2O7 and TiP2O7, thus leading to the lack of chemisorption capacity for CO.
Metal-free boron-based catalytic systems are growing to be promising choices in the oxidative dehydrogenation ODH of light alkanes to olefins. However, the ambiguity in the understanding of the mechanism has impeded the improvement of novel catalytic systems. Herein, by using density functional theory DFT , we mapped a complex reaction network for the B2O3-catalyzed ODH of propane, which displayed a typical feature of interplay between the on-surface and off-surface channels through the whole reaction from the initiation stage to the termination stage.
The results showed that the interplay between the channels in the two regimes was necessary in two aspects: On one hand, to guarantee high selectivity for olefin products, the gaseous channels need the intervention of the surface sites to eliminate the oxygenated intermediates, for example, alkoxyl radicals, that would otherwise evolve into deep oxidation products.
The mechanism also well explained the catalytic role of trace water and addressed the surface dynamical restructuring, thus constituting a plausible comprehensive understanding of the ODH of propane catalyzed by an oxygenated boron system. Gas-phase infrared spectroscopy on the reactant exhaust gases and optical emission spectroscopy OES on the plasma region are used to identify the species that are involved in the ALD process.
Furthermore, the infrared analysis of the precursor exhaust gas indicated the release of CO2 during precursor adsorption. Besides providing insights into the chemistry of atmospheric-pressure PE-s-ALD of SiO2, our results demonstrate that infrared spectroscopy performed on exhaust gases is a valuable approach to quantify relevant process parameters, which can ultimately help evaluate and improve process performance.
A variety of semilocal and nonlocal density functionals DFs have been used to predict preferred adsorption sites, energies, and geometries of the adsorbates. Although their binding energies are similarly small, we find that the nature of the adsorbate—substrate interaction in each system can be different, and so is the performance of each DF.
Rare gases N2 and SF6 mainly physisorb on Au , whose binding energies correlate well with their corresponding polarizabilities. NO and C2H2 appear to deviate from the correlation between polarizability and binding energy, reflecting some contributions of weak chemical bonding to their adsorption. These results not only lay the foundations for accurately describing the scattering dynamics of these species on Au , but also provide useful benchmark data for further development of electronic structure methodologies.
Our study shows that when the metal is exposed to the surface, CO2 will convert to HCOOH with a high selectivity with the limiting potential of 0.
Bipolar membranes BPMs possess the potential to optimize pH environments for electrochemical synthesis applications when employed in reverse bias. Unfortunately, the performance of BPMs in reverse bias has long been limited by the rate of water dissociation WD occurring at the interface of the BPM.
Herein, we develop a continuum model of the BPM that agrees with experiment to understand and enhance WD catalyst performance by considering multiple kinetic pathways for WD in the BPM junction catalyst layer. The model reveals that WD catalysts with a more highly alkaline or acidic pH at the point of zero charge pHPZC exhibit accelerated WD kinetics because the more acidic or alkaline pHPZC catalysts possess greater surface charge, enhancing the local electric field and rate of WD.
Finally, the model is used to simulate the operation of bimetallic WD catalysts, demonstrating that an optimal bimetallic catalyst has an acidic pHPZC catalyst matched with the cation-exchange layer and an alkaline pHPZC catalyst matched with the anion-exchange layer.
The study provides insight into the operation of BPM WD catalysts and gives direction toward the development of next-generation WD catalysts for optimal BPM performance under water-splitting and related conditions. Iron and nitrogen codoped carbons Fe-Nx-C are potential nonprecious metal catalysts to substitute Pt for oxygen reduction reaction ORR.
The essential goal for Fe-Nx-C catalysts is to obtain high-density and well-dispersed Fe-Nx active sites. Herein, we demonstrate that this can be realized by a NaCl crystallites-templated copyrolysis of iron phthalocyanine FePc and zinc phthalocyanine ZnPc , in which Zn vitally induces rich micropores and stabilizes the edge-doped N atoms, thus providing effective footholds for the formation of well-dispersed high-density Fe-Nx coordination sites.
Furthermore, a minimal ca. Excited-state absorption ESA , particularly multiple-photon absorption, was observed regardless of the shape and size of the cluster. The strong plasmon-like state in Ag20 Td drastically decayed into a weak state near twice the resonant energy, as confirmed by a comparison of the time-dependent difference density and the transition densities calculated from linear-response time-dependent density functional theory LR-TDDFT. The multiple-photon absorption that results in a rapid decay of the dipolar plasmon offers fundamental insights about dynamical light—matter interactions in silver materials not only in the direction of plasmon conversion but also in enhancing nonlinear optical properties.
UFH is therefore clearly a chemical species of environmental concern, as anhydrous UF4 is an intermediate uranium form in the nuclear fuel cycle. We use inelastic neutron scattering INS to probe the full vibrational spectra of UFH and its deuterated analogue in an effort to improve the fundamental understanding of its vibrational spectra.
Coupled with density functional theory DFT calculations, the first for this compound, and full spectral modeling, we generate the complete vibrational spectra of UFH and compare them to prior optical spectroscopic results.
In particular, the combination of DFT with INS allows us to identify multiple distinct chemical environments in the water bending and OH stretching regions. Whereas the water molecules directly bound to the U atoms execute OH stretching around cm—1, a second class of H-bonded waters vibrate below cm—1, an indicator of strong H bonding.
In addition, a class of librational water modes are observed between and cm—1, which themselves can be separated in energy according to their chemical environments. Measurements presented herein directly assist in the assignment of certain spectral features in the infrared spectrum and will inform future investigations of UFH for environmental or forensics purposes.
Semiconducting single-walled carbon nanotubes SWCNTs often exhibit distinctive spectral features due to a complex dark exciton manifold. One of those features, the K-momentum dark exciton KDE state, has been of significant recent interest because of the unique photophysics required to brighten the nominally optically forbidden state.
Although the energy of the KDE state relative to the bright singlet excitonic state E11 is currently understood, how the KDE state is efficiently populated, and its resulting dynamics, is not. Time-correlated single photon counting TCSPC and kinetic modeling were used to study the dynamics of the KDE state as temperature and lattice defect concentration varied.
Photoluminescence PL time decays corresponding to the KDE state exhibited biexponential character with average lifetime values roughly 6 times longer than those of the typical E11 state. This trend strongly suggested that the dark singlet excitonic state D11 situated a few millielectronvolts below the bright plays a significant role in KDE dynamics. Transition times between the E11 and D11 states, as well as dark-to-bright excitonic conversion efficiencies, were extracted by using a kinetic analysis of the experimentally determined KDE state time decays.
Together, the experimental results and kinetic modeling strongly suggest that mixing between the bright and dark singlet excitonic states is the driving force that dictates KDE state dynamics. We report on high-dimensional quantum dynamical simulations of electron—hole separation in self-assembled mesomorphic nanostructures composed of donor—acceptor conjugated co-oligomers. The latter are based on perylene diimide PDI acceptor units combined with fluorene-thiophene-benzothiadiazole donor units, which form highly ordered, stacked structural motifs upon self-assembly.
Simulations are shown for a first-principles parametrized model lattice of 25 stacked PDI units under the effects of an applied external field and temperature. The simulations are carried out with the multilayer multiconfiguration time-dependent Hartree ML-MCTDH method with nearly vibrational degrees of freedom and 25 electronic states. Temperature effects are included using the thermofield dynamics approach. A transition between a short-time coherent dynamics and a kinetic regime is highlighted.
From a flux-over-population analysis, electron—hole dissociation rates are obtained in the range of 5—20 ns—1 in the absence of static disorder, exhibiting a moderate field and temperature dependence.
These results for electron—hole separation rates can be employed as a benchmark to calibrate the parametrization of kinetic Monte Carlo simulations applied to much larger lattice sizes. Inorganic halide perovskite nanocrystals NCs exhibit many excellent optical and semiconductor properties. The CsPbBr3 HNCs exhibit apparent linear and two-photon fluorescence properties, and their two-photon absorption cross section is Our results provide comprehensive insights into the photophysical properties of inorganic halide perovskite nanomaterials and examine their potential in the optoelectronic field.
Atomically thin porous membranes display high selectivity for gas transport and separation. To create such systems, defect engineering of two-dimensional 2D materials, e. Our study advances the understanding of the mechanisms behind gas permeability and selectivity through sub-nanometer pores in WS2 and potentially other inorganic 2D materials.
Our results showed that the CFs were dominantly formed around grain boundaries, while some grain interior regions showed very low conductivity. These studies on the CF formation mechanism provide a better understanding of RS memory characteristics in multication perovskite materials. Interfacial charge-transfer transitions ICTTs between organic compounds and inorganic semiconductors have recently attracted increasing interest for their potential applications in photoenergy conversions and chemical sensing because of the unique features of visible-light absorption with colorless organic molecules and direct photoinduced charge separation.
TiO2 nanoparticles chemically linked to aromatic carboxylic acids are one of the most important photoinduced electron-transfer systems in the above applications. Here, we systematically examine the electronic and optical properties of surface coordination complexes of TiO2 nanoparticles with benzoic acid BA and its derivatives experimentally and computationally. Our research unambiguously reveals that ICTT generally takes place between TiO2 nanoparticles and BA derivatives possessing electron-donating groups, and the absorption wavelength range can be controlled by adjusting the electron-donating ability and the number of substituent groups.
Our research widely expands the scope and utility of ICTT and provides a new guiding principle for material development of interfacial light absorbers featuring direct photoinduced charge separation for photoenergy conversions. Optoplasmonic bio-detection assays commonly probe the response of plasmonic nanostructures to changes in their dielectric environment. The accurate detection of nanoscale entities such as virus particles, micelles and proteins requires optimization of multiple experimental parameters.
Performing such optimization directly via analyte recognition is often not desirable or feasible, especially if the nanostructures exhibit limited numbers of analyte binding sites and if binding is irreversible.
Here we introduce photothermal spectro-microscopy as a benchmarking tool for the characterization and optimization of optoplasmonic detection assays. Supported transition metal materials have been identified as ideal candidates for decades to catalyze various reactions of interest in the fields of hydrocarbon refining, energy, and environmental catalysis.
As the resources in transition metals on Earth are known to be limited, it appears to be of utmost interest to improve the efficiency of the catalytic materials in achieving the best use of these transition metals, in other words, the highest metal accessibility when supported on oxide carriers.
The present study demonstrates that the deposition of oxotungstates with a W surface density of 1. Oxotungstates are found to decrease the number of nucleation sites of CeO2 and, therefore, to act as spacers leading to the isolation of the nucleation sites. Oxotungstates may also act as a physical barrier preventing the sintering of the Rh metallic phase in the course of the reduction step at high temperature.
Various morphologies of sub-nanometric Rh clusters exhibiting a limited atomicity 4—13 Rh atoms were considered, and most were found to be consistent with the very low coordination numbers of 4. The coordination numbers and the H2 chemisorption data led the conclusion that the Rh sub-nanometric clusters must be at the maximum two to three Rh layers thick and not larger than five Rh atoms.
Antimony halide hybrids have been recently revealed to show reversible solvent-induced phase transformation along with solvatochromic photoluminescence PL. However, the effects of guest molecules on such phase transformation are not yet well understood due to metastable solvent-induced phases. Due to more compact and rigid structures that suppress octahedral distortion, smaller Stokes shifts are observed for both PhPi 2SbCl7-V 1. Our findings highlight the role of guest molecules in tuning [SbCl6] octahedral distortion to enhance the luminescence efficiency of Sb-based halides.
The early stages of silica deposition on vitreophobic citrate-capped gold nanoparticles AuNPs are studied using in situ optical spectroscopy supported by electron microscopy and hydrodynamic size measurements. Through extinction spectra fitting, the time dependence of the surface plasmon resonance, which acts as a sensitive probe of the local environment, reveals three distinct stages of uniform silica shell formation on AuNPs.
The first stage, which has not previously been reported, is characterized by an increase in plasmon damping by adsorption of silica precursors. The initial silica growth is shown by electron microscopy to be highly anisotropic, proceeding radially from the vertices of the faceted AuNPs before forming conformal shells.
However, probing their lattice dynamics with vibrational spectroscopy remains challenging. The influence of the fundamental octahedral building block in the perovskite lattice can be better resolved in zero-dimensional 0D vacancy-ordered double perovskites of form A2BX6.
The isolated [TeX6]2— octahedral units serve as the vibrational, absorbing, and emitting centers within the crystal. Serving as the vibrational centers, the isolated octahedra inform the likelihood of a random distribution of 10 octahedral symmetries within the mixed-halide spaces, as well as the presence of strong exciton—phonon coupling and anharmonic lattice dynamics.
Serving as the absorbing and emitting centers, the isolated octahedra exhibit compositionally tunable absorption 1. The use of Pt—Rh catalysts is central in a number of industrial processes, and to explain their performance it is essential to have a solid understanding of their nanoscopic surface structure. Here we use scanning tunneling microscopy to investigate the growth, elemental nanostructuring, and reconstruction behavior of various Pt—Rh near-surface alloys NSA on fcc Rh and Pt Metallic nanostructures can source, detect, and control light through surface plasmons with applications ranging from photocatalysis and biochemical sensors to light trapping in thin-film solar cells.
Although the commonly used plasmonic materials such as gold and silver have shown great optical properties, they experience significant ohmic losses that severely limit the device performances.
Sodium is predicted to be an ideal plasmonic material with much lower loss than gold and silver across the whole ultraviolet to near-infrared wavelength regime.
This paper describes how sodium nanoparticles can exhibit high-quality plasmonic resonances through the excitation of surface lattice plasmons. We investigate both the sodium nanoparticles size, array period, unit structure and the excitation light polarization, angle of incidence to manipulate how light interacts with sodium nanoparticles. Specifically, by exciting in-plane and out-of-plane surface lattice plasmons, we obtain resonances with extremely narrow line widths and localized electromagnetic field with amplified intensities for sodium nanoparticles.
Sodium, as a low-cost and low-loss plasmonic material, provides an affordable alternative in a range of plasmon-enhanced applications such as chemical sensing, thin-film solar cells, and photonic circuits. The interactions of molecules such as surfactants with solid interfaces are not sufficiently understood since their study is challenging with standard spectroscopic methods.
In this work, octanol-d17 as a model system confined in the mesopores of SBA is studied by variable temperature deuterium solid-state NMR, and the findings are compared to those of bulk octanol-d Learn more. Search now. All the circuit-breakers, both three-pole and four-pole, are available in the fixed version; sizes T4 and T5 in the plug-in version and T4, T5, T6, and T7 also in the withdrawable one. High breaking capacity in compact dimensions High values of short circuit breaking capacity are guaranteed at different voltage levels, without compromising overall dimensions.
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