Chemphyschem最新文献

Water is widely recognized as critical to the tunability and electrochemical stability of nonaqueous solvents such as deep eutectic solvents (DESs) and ionic liquids (ILs). Traditionally, the water content of these solvents has been controlled by either drying or adding small amounts of water to control their bulk properties to meet specific application requirements. The total water content by itself, does not provide sufficient information about the chemical reactivity and molecular interactions within DES- and IL-water mixtures. In this concept article, water activity is highlighted as a thermodynamically more rigorous descriptor to quantify the influence of the co-solvent water on DES- and IL-water mixtures. Water activity relates measurable physical properties, such as vapor pressure, density, viscosity, electrochemical stability, and conductivity of DESs and ILs to the underlying molecular interactions between their components. Furthermore, water activity of DESs and ILs correlates with changes in local solvent structures and thermodynamic excess properties, including excess molar volume, enthalpy, and Gibbs energy.

Hydrofluorocarbons (HFCs), a class of polyfluorocarbon (PFC), represent a key group of chemicals exploited extensively in refrigeration and innovative future technological cooling applications. To separate, purify, and reuse HFCs, spectroscopic properties of these compounds must be available. To quantify these materials under cryogenic conditions, a condensed-phase spectroscopic investigation of their physical parameters is required. Herein, the optical and spectroscopic properties of HFCs used as refrigerant at low temperature (10 K) are investigated. Refractive indices of 1,1,1,2-tetrafluoroethane (CF₃CH₂F; HFC134a), 2,3,3,3-tetrafluoropropene (CF₃CF=CH₂; R1234yf), and 3,3,3-trifluoropropene (CF₃CH=CH₂; R1243zf) are found to be 1.24 ± 0.02, 1.34 ± 0.02, and 1.30 ± 0.02, respectively. Infrared band strengths of the abovementioned HFC ices on a cold silver substrate are measured utilizing absorption reflection infrared spectroscopy. The fundamental vibrational modes are analyzed using quantum chemical calculations in tandem with vibrational spectroscopic analysis. The strongest infrared absorption corresponds to combined CF vibrational modes originating from CF₃ group and olefinic CF bonds, which has band strengths ranging 2 × 10^-18 to 3 × 10^-18 cm molecule^-1. Comparisons of solid and vapor-phase spectra show vibrational shifts, aiding understanding of solid-state interactions and ice formation. These findings enhance knowledge of low-temperature HFC chemistry, focusing on optical and spectroscopic changes during ice development.

Surface plasmon-driven chemical reactions have attracted considerable attention as a means of developing specific chemical processes. To integrate plasmonic effects with heterogeneous catalytic reactions, it is desirable to use chemically active metals such as Pt, rather than inert materials like Au. In this study, we fabricated Pt nanoantennas and investigated surface plasmon responses with infrared transmission absorption measurements. Observed transmission absorption bands are attributed to surface plasmon excitations in the Pt nanoantennas. As the longitudinal length of the Pt nanoantennas increased, the resonance energy decreased and the linewidth narrowed, exhibiting similar behavior to that observed in Au nanoantennas. The present observations suggest that the Pt nanoantennas exhibited electric field enhancement due to infrared surface plasmon excitations. Furthermore, by adsorbing benzene molecules on the Si substrate with Pt nanoantennas at 100 K, surface-enhanced infrared absorption spectra were obtained. The enhancement factor for the C-C stretching vibrational mode was evaluated to be ∼900. The present work is an important step toward catalytic technologies that employ infrared surface plasmons to selectively and strongly excite specific vibrational modes.

Benzazole derivatives exhibit distinctive photophysical behavior due to excited-state intramolecular proton transfer (ESIPT), making them promising candidates for optoelectronic applications such as organic light-emitting diodes (OLEDs) and fluorescent sensors. Understanding their sublimation energetics, phase behavior, and emissive properties is essential for both fundamental studies and materials design. This article reports an investigation on two benzazole derivatives-2-(2-hydroxyphenyl)benzothiazole and 2-(2-hydroxyphenyl)benzoxazole (HBO)-through studies of thermal analysis, vapor pressure measurements, and fluorescence spectroscopy to establish structure-property relationships. Thermal stability and phase transitions are characterized using simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) and heat-flux DSC. Vapor pressures are determined using both Knudsen effusion mass loss and mass spectrometry. The derived standard molar enthalpies of sublimation, vaporization, and fusion highlight the presence of heteroatom (S versus O) on intermolecular interactions. Solid-state fluorescence measurements reveal strong emission in both compounds, with a large Stokes shift-consistent with ESIPT-and complex spectra attributed to solid-state molecular packing. This comprehensive experimental strategy delivers benchmark thermodynamic and photophysical data, offering new insights into the interplay between molecular structure, thermal behavior, and fluorescence of benzazole derivatives. Such understanding is relevant for the development of advanced optoelectronic materials.

Herein, a density functional theory based mechanistic and kinetics study of experimentally reported pincer metal complex catalyzed homogenous dehydrogenation of methanol and diamine into diamide is explored. The reaction proceeds through dehydrogenation and hydrogenation reactions for the reversible interconversion between methanol and diamine. The mechanism proceeds via a step-by-step formation of aldehyde, amide, and diamide complexes. The generated formaldehyde reacts with ethylenediamine in the second cycle to make monoamide, which reacts with formaldehyde from the first cycle to produce diamide. The complete diamide formation reaction follows a cross-multicarrousel type mechanism. The turnover-determining transition state is the formation of the first amide bond, where the addition of amine and metal aldehyde takes place. The alternative reaction of metal aldehyde and alcohol via an ester formation reaction is a minor path. The rate equation is derived from the most feasible path. From the dissociation dynamics simulations, the dehydrogenation reaction of metal hydride is found to be favorable, and a strong Mn and H₂ interaction is present during the H₂ release, which may facilitate the hydrogenation reaction. Diamide dissociation is more challenging than amide dissociation, and a high temperature is required for diamide dissociation dynamics.

Germanium (Ge) is a crucial semiconductor material. Germanium powder is typically manufactured through hydrogen reduction of germanium dioxide (GeO₂). However, the traditional reduction method frequently results in suboptimal hydrogen utilization, larger-than-desired granular sizes, and nonuniform granular distribution. In this article, a novel vertical gas-flow field reduction process is proposed for addressing the above challenges, and the effects of reduction temperature and hydrogen flow rate are investigated. The results show that the novel process promotes the contact between GeO₂ and hydrogen, reducing H₂O partial pressure at the reduction interface. Accordingly, conversion efficiency (the ratio of weight loss ratio W_t to the theoretical maximum weight loss ratio W_max) is much higher than the traditional method by 20%-30%, and the obtained Ge powder conforms to the desired dimensions and uniformity. This article provides a novel process for manufacturing high-quality germanium powder with a short production cycle, less hydrogen consumption, and low energy consumption.

Noncovalent interactions (NCIs) between lignin and polysaccharides are increasingly being recognized as contributors to the structural integrity and recalcitrance of lignocellulosic biomass (LCB). In this work, density functional theory (M06-2X/6-311++G**) in combination with quantum theory of atoms in molecules (QTAIM) analyses at the MP2/6-311++G** level were employed to systematically analyze 189 physically bound complexes formed between the monolignols p-coumaryl (H), coniferyl (G), and sinapyl (S) alcohols and representative hemicellulose monosaccharides: mannopyranose, xylopyranose, glucuronic acid, and arabinofuranose. Calculated binding energies of these complexes range from -15.8 to -98.5 kJ/mol, with stability increasing with methoxy substitution on the lignin moiety and with the presence of a carboxylate functionality on the sugars. These results are consistent with experimental studies showing that LCB from genetically modified plants, with reduced methoxy in lignin and reduced acidic groups in sugars, are easier to break down when compared to the corresponding wild-type plants. The observations presented in this work, in combination with experimental evidence, suggest that reducing the methoxy content in lignin and the number of carboxylate groups in hemicellulose may be promising strategies for improving LCB valorization efficiency. Furthermore, charge transfer values extracted from QTAIM qualitatively correlate with the stabilization of the complexes, revealing that electron-deficient aromatic rings in lignin, such as those methoxy-substituted aromatic moieties in G- and S-lignin, and electron-rich sugars, such as glucuronic acid in side chains of hemicellulose, lead to the formation of strong hydrogen bonds and $\pi$ -lone-pair interactions. Solvent screening computations also demonstrate that selective association of toluene, $\gamma$ -valerolactone, and tetrahydrofuran with lignin attenuates lignin-sugar NCIs, lowering the delocalization index (a QTAIM descriptor of electron sharing between species that correlates with the strength of interactions) between interacting monolignols and monosaccharides. These findings provide a detailed molecular-level description of the structural features that modulate NCIs in LCB. This study provides a rational basis for tuning lignin composition or for screening/designing solvent environments to mitigate biomass recalcitrance and advance cost-effective and efficient deconstruction of LCB.

The construction of efficient Z-scheme heterojunctions is considered as a promising approach to improve the transfer and separation of photogenerated carries in the field of photocatalytic hydrogen evolution from water splitting. Herein, a novel CdS/UiO-66(Ce) with Z-scheme heterostructure is successfully fabricated from metal sulfide CdS and cerium-based UiO-66 metal-organic framework via a hydrothermal method. The Z-scheme CdS/UiO-66(Ce) heterojunctions can provide abundant active centers, broaden the response range to visible-light region, accelerate the transfer of interfacial charges, and suppress the recombination rate of photogenerated electron-hole pairs. As a result, CdS/UiO-66(Ce) (ω(CdS) = 30%) exhibits a hydrogen production rate of 1.975 mmol g^-1 h^-1, which is 19.1 times higher than that of UiO-66(Ce). Overall, this article may provide a new pathway for the rational design of efficient Z-scheme heterojunctions with photocatalytic hydrogen evolution.

To claim the real-world applications of electrocatalysts in water electrolysis, evaluating their performance at elevated temperatures is imperative. Variations in the operational temperature of water electrolyzers directly impact the reaction kinetics, electrolyte conductivity, and thermodynamic aspects of surface adsorption. This governs the efficiency of hydrogen and oxygen production. In this work, compared to room temperature, the overpotential of the trimetallic layered double hydroxide (LDHs) based nanocatalysts for the oxygen evolution reaction and hydrogen evolution reaction is significantly reduced by 20% and 10%, respectively, at 55°C. The reasons for performance loss beyond this temperature are also elucidated. In-depth density functional theory calculations establish the role of Cu-doping on formation energy, charge density, and density of states of pristine NiCo-LDH. The values of these electronic and thermodynamic parameters play an important role in deciding the applications of an electrocatalyst in advanced electrolyzers.

The spread of per- and polyfluoroalkyl substances (PFAS) in global waterways has become a subject of significant concern. Modeling the interaction of PFAS with the major constituents of natural and artificial waterways will advance our understanding of the spread of PFAS and aid in the development of adsorption and remediation methods. In this work, it considers the adsorption of linear perfluoroalkyl acids on two model clay hydrophobic surfaces: montmorillonite and kaolinite. This investigates the absorption affinities and preferential adsorption of acidic linear PFAS on model clay surfaces with varying fluorocarbon tail lengths. It also consideres the binding affinity when these PFAS are hydrated. Both carboxylic and sulfonic acid head groups are considered. The computed results indicate that there is an increased binding energy of the target PFAS on the clay surfaces with increasing chain length, and that perfluoroalkyl sulfonic acids have greater binding energy than perfluorocarboxylic acids with the same tail length.