International Journal of Chemical Kinetics最新文献

Colloidal solutions of ionic liquids extend the concepts of surface science. Cationic oligomeric silsesquioxanes formed the silsesquioxane core and cationic organic substituents, namely OSS(C₃N⁺Br⁻)_n and OSS(C₁₀N⁺Br⁻)_n, are amorphous with a glass transition temperature below 0°C and possess prerequisites for the formation of supramolecular aggregates in aqueous solutions. The hydrodynamic size and zeta potential values of colloidal species were determined by dynamic and electrophoretic light scattering. The local surface potential and acidity were estimated by the spectrophotometric study of acid-base equilibria of bound bromophenol blue. The kinetic effect of these colloidal species in the idea of micellar rate effect emphasizes the importance of the “diverting” effect of cationic head groups introduced recently. The nanospecies morphology, size, and charge densities vary with the length of the alkyl substituent of OSS. This modification opens up potentially broader applications of cationic oligomeric silsesquioxanes, which are synthesized as ionic liquids. The behavior in an aqueous solution determines the future environmental fate of the ionic liquids, which are defined as environment-friendly compounds, basically as non-volatile and non-flammable.

Reactivity and nucleophilicity are enlightening aspects of the substituent effect (SE) in most aromatic electrophilic and nucleophilic substitution reactions. Herein, we have quantitatively delved into the reactivity of some monosubstituted benzene derivatives having either an electron donating or withdrawing substituent by exploring the real time progress of their rapid aqueous iodinations at pH 7.4 using iodine solutions devoid of iodide ions chronoamperometrically, employing hydrodynamic voltameter (HV) reinforced with a sensitive Keithley 2450 Digital Source Meter (KDSM). All the reactions are studied in purely aqueous medium using micromolar quantities of reactants, wherein green chemistry principles are adhered, ensuring sustainable development. Voltammograms of the substrates in the reactions were acquired to evince their reduction propensities, these being a quantitative measure of their nucleophilicities. The reactivity of these substrates was evidenced in terms of their specific reaction rates, half-lives, energies of activation, and entropies of activation, while their nucleophilicities were revealed in terms of the half-wave potentials. Unanticipated concomitant kinks in reactivity and nucleophilicity trends have been observed, and a linear mathematical correlation between them has been established in the reactions studied.

Photochemical irradiation of tri-thiocyanuric acid at low temperatures results in the formation of a higher energy isomer, the tri-thiol 1,3,5-triazine-2,4,6-trithiol [Rostkowska Journal of Physical Chemistry A 109 (2005): 2160]. The question arises as to how, and whether, the latter can revert to its parent 1,3,5-triazine-2,4,6-trithione in a reasonable time at temperatures of 10–300 K. Quantum chemical calculations using both density functional and wave function theories attempt to compute the kinetics of the return voyage. We show that reactivity is dominated by hydrogen atom tunneling and conformational changes, calculated from variational transition state theory allied to small-curvature tunneling effects, rather than purely thermal reactions, and that there is no way back during the usual laboratory lifetimes. Both water and methanol are shown to act as catalysts by both accepting and donating hydrogen atoms, reducing the barrier to reaction by more than one-half and enhancing the reaction rate, with methanol being the more effective agent.

The reaction kinetics of hydrogen abstractions from cyclopentanol by hydroperoxyl radical have been comprehensively studied using multistructural canonical variational transition state theory with small curvature tunneling approximation (MS-T-CVT/SCT). The barrier heights and reaction energies have been calculated at the CCSD(T)/cc-pVDZ and CCSD(T)/cc-pVTZ levels of theory with basis set corrections from MP2/cc-pVnZ (where n = D, T, and Q), based on the geometries optimized with the M06-2X/6-311+G(2df,2p) method. The rate coefficients of different hydrogen abstraction sites (α-carbon, β-carbon, γ-carbon, and OH) have been calculated by direct dynamics based on M08-HX/jun-cc-pVTZ electronic structure calculations, as this model chemistry shows the lowest averaged mean unsigned error relative to the benchmark CCSD(T) method. The reaction barrier heights for hydrogen abstraction from various sites follow the order of α-carbon < γ-carbon < β-carbon < OH and follow the order of C─H and O─H bond dissociation energies. Kinetic results suggest that the multistructural torsional anharmonicity, tunneling, and hydrogen bonding interaction are important influential factors for calculating accurate rate coefficients and branching ratios. Hydrogen abstraction reaction from α-carbon site shows the largest contribution to the overall rate coefficients below 1100 K, beyond which hydrogen abstraction reactions from β-carbon and γ-carbon sites become dominant. Hydrogen bonding interaction involved in the transition states significantly reduces the reaction barrier heights and accelerates the single-structural rate coefficients at lower temperatures, but has only a marginal impact on the overall and site-specific MS-T-CVT/SCT rate coefficients, except for the hydrogen abstraction reaction from β-carbon site. However, hydrogen bonding interaction influences the MS-T-CVT/SCT branching ratios. The thermodynamic properties of cyclopentanol and four derived fuel radicals are calculated using the atomization method together with the multistructural partition functions. The simulated auto-ignition reactivity of cyclopentanol/air mixtures is sensitive to the newly calculated rate coefficients and thermodynamic parameters, especially at low temperatures.

The activity and stability of nanoparticles synthesized from plants; green-synthesized nanoparticles are obtaining more consideration from scientists. This work aimed to synthesize the green silver nanoparticles (AgNPs) using the fruit extract of Azadirachta indica A. Juss. The fruit extract acts as both a capping and reducing agent. The physicochemical properties of synthesized nanoparticles were studied through x-ray diffraction (XRD), FT-IR, UV-vis, scanning electron microscopy (SEM), and EDX. Furthermore, antioxidant properties and antibacterial activity of the nanoparticles were also studied. The reaction was preceded under sunlight, and the color of the reaction mixture changed from colorless to dark brown, indicating the production of Ag nanoparticles. A UV-vis analysis revealed an absorption peak of 429 nm, which was measured after 30 min of reaction. The XRD spectroscopy results suggest that the nanoparticles are crystalline with an average diameter of 36.50 µm. SEM images show that the majority of the AgNPs are spherical and fairly distributed. The obtained AgNPs showed efficient antibacterial activity against gram-negative (Escherichia coli) and gram-positive (Staphylococcus) bacterial species. Surprisingly, the synthesized Ag nanoparticles from A. indica fruit by the DPPH assay method show 55% antioxidant activity.

The hydrometallurgy processing of copper from electronic waste (e-waste) by citric and malic acids was studied as a friendly leaching process. Influencing factors, for example, contact time, temperature, pulp density, and acid concentration, were studied. These studies revealed that 98.07% of copper can be dissolved by using 0.5 g e-waste/100 mL of 3% citric acid at 70°C for 15 h. Whereas, 100% can be leached by using 0.5 g/100 mL of 1% malic acid at 80°C for 20 h. Also, the mechanism of leaching by these acids was studied and found that the leaching process is performed by acidification and complexion reactions. Finally, kinetic studies of copper leaching were studied using the modified shrinking core models.

This study focuses on the green synthesis and characterization of silver nanoparticles (Ag-NPs) using Glycyrrhiza glabra root extract as a natural reducing agent. The antimicrobial potential of these nanoparticles was evaluated against a range of pathogens, including both bacteria and fungi. The synthesis process was initiated by adding Glycyrrhiza glabra root extract to a silver nitrate solution, resulting in a distinct color change from colorless to dark yellow, and eventually to black, signaling the formation of Ag-NPs. The formation and properties of the nanoparticles were further confirmed through UV–visible spectroscopy, which revealed a strong surface plasmon resonance peak at 421 nm, characteristic of Ag-NPs. X-ray diffraction (XRD) analysis showed that the nanoparticles possessed a face-centered cubic (FCC) structure, confirmed by the observation of well-defined Bragg reflections. Additionally, Energy Dispersive x-Ray Spectroscopy (EDX) and scanning electron microscopy (SEM) analyses were performed to assess the elemental composition and morphology of the synthesized nanoparticles. EDX results confirmed the presence of silver, while SEM images revealed the presence of nanoparticle aggregates, though no distinct morphology was observed. The antimicrobial activity of the synthesized Ag-NPs was tested against both Gram-positive and Gram-negative bacteria, with results indicating a significantly stronger antimicrobial effect against Gram-negative bacteria. These findings highlight the promising potential of green-synthesized Ag-NPs as effective antimicrobial agents, providing a sustainable and eco-friendly approach to nanoparticle synthesis with significant implications for various biomedical applications.

Although potassium (K) vanadyl phosphate fluoride (KVPO₄F) is considered one of the most promising cathode materials for K-ion batteries, its practical application is hindered by poor electronic conductivity and fluorine (F) loss during the synthesis process. In this work, a novel synthetic route is designed to realize the advanced KVPO₄F cathode material (denoted as KVPO₄F@C) by adopting in situ carbon coating approach initiated by isobutanol molecular intercalation, delivering two distinct characteristics of high F-containing and limited particle growth. On one hand, the as-generated in situ carbon coating layer enhances the electronic conductivity of KVPO₄F material and prevents the particle agglomeration during the calcination process. On the other hand, the as-introduced V–F–C bonds at the KVPO₄F/C interface realizes a high F-containing of KVPO₄F@C cathode material without large-scale F loss. As a result, the KVPO₄F@C cathode retains a high discharge capacity of 63.94 mAh g⁻¹ after 100 cycles at 2C as well as superior rate performance. This study highlights the critical role of the pathway to realize carbon coating approach in enhancing the electrochemical performance of KVPO₄F cathode.