Reaction Kinetics, Mechanisms and Catalysis最新文献

The electrochemical degradation of reactive blue 21 (RB21) was investigated using anodic oxidation on a platinum (Pt) electrode in a basic medium (0.1 M NaOH). Cyclic voltammetry revealed the influence of dye concentration and potential scan rate on RB21’s electrochemical behavior over a potential range of -1 to 0.8 V/SCE. Electrolysis experiments performed by chronopotentiometry showed that increasing current density and electrolysis time significantly enhanced decolorization. Under optimal conditions, a current density of 100 mA cm⁻² and an electrolysis time of 180 min at 25 °C resulted in 99.6% dye removal efficiency. Mass spectrometry analysis identified intermediate degradation products, allowing the proposal of a possible degradation pathway. These results demonstrate the effectiveness of anodic oxidation in alkaline media for efficient dye decolorization and the breakdown of complex dye structures.

Graphical abstract

In the present study we investigated fructose, glucose, and mannose in sodium hydroxide solution. Saccharides in an alkaline solution establish a highly reactive enediolate anion of low concentration. We propose that an internal geometric rearrangement of the sugar required to establish the enediolate is responsible for different concentrations of the reactive anion depending on the sugar. We determined the free energy for the rearrangement and the concentration of the enediolate. We find that for the sugars studied there is a correlation between the magnitude of internal rotation required for hydrogen abstraction and the value of the free energy.

In this study, CuO–ZnO nanocomposites were synthesized using wood apple shell extract as a green, non-toxic reducing and stabilizing agent. The nanocomposites were comprehensively characterized using XRD, FT-IR, UV-DRS, PL, SEM, and EDAX to investigate their structural, optical, and morphological properties. UV-DRS analysis revealed a bandgap energy reduction to 2.86 eV, favoring enhanced visible-light absorption. The photocatalytic performance of the CuO–ZnO nanocomposite was evaluated for the degradation of methylene blue (MB) and rhodamine B (RhB) under sunlight irradiation. The catalyst exhibited exceptional degradation efficiencies, achieving 98.11 ± 1.91% MB removal and 98.57 ± 1.87% RhB removal within 180 min, with corresponding rate constants of 11.3 ± 0.8 × 10⁻³ min⁻¹ and 14.5 ± 1.5 × 10⁻³ min⁻¹,. This significantly outperformed pristine CuO and ZnO nanoparticles, which showed MB degradation of 56.82 ± 2.14% and 69.20 ± 1.86% and RhB degradation of 58.34 ± 2.27% and 69.04 ± 1.98% under identical conditions. The enhanced activity is attributed to the formation of a p-n heterojunction, which improved charge separation efficiency, minimized electron–hole recombination, and broadened the light absorption range. Furthermore, the catalyst demonstrated excellent stability and reusability, retaining 80% of its initial efficiency even after five consecutive cycles. Radical scavenging experiments confirmed that superoxide radicals (^•O₂⁻) played the dominant role in the degradation process, while hydroxyl radicals (^•OH) also contributed significantly.

The efficient catalytic system for the oxidation of alcohols using the wetness impregnation and hydrazine reduction method under mild reaction conditions has been investigated in detail. This method resulted in uniform Cu nanoparticle dispersion in the 4–6 nm range. The hydrazine reduction method prepares a catalyst with excellent stability and enhanced low-temperature activity, suitable for gas-phase oxidation of non-activated primary and secondary aliphatic and activated benzyl alcohol. Detailed characterization of the Cu-SBA-15 catalyst was performed using XRD, XPS, TG–DTA, and TPR analytical techniques. These techniques reveal that this method effectively makes Cu particles tiny and highly dispersed into channels of SBA-15 and on the external surface of SBA-15. The results indicated that CuO was the primary active component on the supported catalysts before calcination. The Cu₂O grain has excellent dispersion on the nanoscale. This catalytic system resulted in complete conversion and high selectivity at 220 °C and aerobic oxidizing reaction conditions.

This study focuses on the optimization of the synthesis tetrazoles using the heterogeneous Fe/SBA catalyst. By immobilizing the catalyst on a solid support, this approach facilitates catalyst recovery, reduces the use of organic solvents, and allows for milder reaction conditions, enhancing both the environmental and economic sustainability of the process. The optimization is based on adjusting key parameters, including temperature (90 °C), catalyst mass (0.05 g), H₂SO₄ concentration (0.24 g), pH (6), and reaction time (120 min), achieving a maximum yield of 98%. Additionally, neural networks were employed to model the complex interactions between these variables and provide accurate predictions, with a coefficient of determination (R²) of 0.94. The performance evaluation also relies on several metrics: Root Mean Square Error (RMSE) of 3.05, Mean Absolute Error (MAE) of 2.35, and Mean Squared Error (MSE) of 9.31. These findings demonstrate that combining artificial intelligence with rigorous experimental methods significantly enhances the efficiency of catalytic processes, paving the way for sustainable and optimized industrial applications.

To study the crystallization process of Na₂O–B₂O₃–SiO₂ based materials, sodium borosilicate-based glass materials used as the ground coating material of steel enamel were prepared by melting and quenching. The powder, fully milled for a certain time, was subjected to differential scanning calorimetry (DSC) at different cooling rates with the starting sample and the non-isothermal crystallization process was observed. The non-isothermal kinetic analysis of the DSC measurements was carried out by the Jeziorny, Ozawa and Mo methods of the modified Avrami equation. The results of the study showed that the Jeziorny and Mo methods well explained the non-isothermal crystallization kinetics of the sodium borosilicate-based glass materials, but the Ozawa method was not suitable. From the Avrami index n obtained, the crystal growth pattern of the corresponding glass material was confirmed by 2D surface growth. As the cooling rate increased, the non-isothermal crystallization kinetics factor Z_c increased and F(T) reflecting the effect of cooling rate on crystallization increased with increasing relative crystallinity. The dependence of the effective activation energy on the relative crystallinity during non-isothermal crystallization was evaluated by the iso-conversional method of Friedman analysis. The effective activation energy of glass materials ranges from − 1330 to − 369 kJ/mol.

This study reports a novel, eco-friendly green synthesis of nickel oxide nanoparticles (NiO NPs) utilizing the red algae Corallina elongata as a biotemplating and reducing agent, followed by calcination. The synthesized NiO NPs were extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), thermogravimetric/differential thermal analysis (TGA/DTA), UV–Visible spectroscopy, photoluminescence (PL) spectroscopy, and electrochemical impedance spectroscopy (EIS). XRD analysis confirmed the formation of cubic phase NiO with an average crystallite size of approximately 12.32 nm. UV–Vis spectroscopy revealed an optical band gap of 2.41 eV, indicating potential for UV/visible light photocatalysis, which was further supported by PL studies identifying defect-mediated emission pathways. The photocatalytic activity of the NiO NPs was evaluated for the degradation of methylene blue (MB) dye under solar irradiation. The effects of catalyst loading, initial dye concentration, and solution pH on the degradation efficiency were systematically investigated. The synthesized NiO NPs exhibited promising photocatalytic activity, achieving a maximum MB degradation efficiency of 93% under optimized conditions (10 mg/L MB concentration, pH 12). Kinetic studies demonstrated that MB degradation followed pseudo-first-order kinetics with a rate constant of 0.01835 min^–1. Furthermore, the NiO NPs exhibited good reusability over three consecutive cycles. This work highlights a sustainable and cost-effective route for synthesizing highly efficient NiO photocatalysts, demonstrating their significant potential for the remediation of dye-polluted wastewater.

In this study, a series of CdS/CdIn₂S₄ heterojunctions were successfully synthesized via a simple one-step hydrothermal synthesis method by regulating the adding amount of thioacetamide (TAA) in stoichiometric Cd²⁺ and In³⁺ solutions. The prepared CdS/CdIn₂S₄ heterojunction exhibits much higher photocatalytic hydrogen evolution reaction (HER) activity than single CdS and CdIn₂S₄. The maximum apparent quantum yield (AQY) reaches 14.2% at 420 nm and shows good stability. The heterostructure facilitates the separation and migration of photo-induced charge carriers, thereby improving the photocatalytic HER performance.

The novel catalyst PEN[MIM]₄[OH]₄ was designed and successfully synthesized, exhibiting outstanding catalytic efficiency in the synthesis of tetrahydrobenzo[b]pyrans, achieving a high yield of 96% under optimized conditions. Its remarkable thermal stability allowed it to endure elevated temperatures without degradation, ensuring consistent performance across multiple cycles. As a heterogeneous catalyst, it was easily separated and reused, significantly minimizing waste and lowering overall costs. The presence of four catalytic units contributed to enhanced reaction kinetics compared to monodentate counterparts, facilitating faster conversions and improved selectivity. Mechanistic investigations revealed a dual activation pathway: the hydroxide anion promoted deprotonation of malonitrile. At the same time, hydrogen bonding between the imidazolium cation and the aldehyde’s carbonyl group stabilized the transition state, effectively reducing activation energy. Computational studies utilizing Density Functional Theory provided critical insights into the catalyst’s electronic properties, with molecular electrostatic potential mapping, reactivity indices (electronegativity, electrophilic index, softness, and hardness), and frontier molecular orbital (HOMO–LUMO) analysis confirming its superior reactivity compared to [DMIM][OH]. These findings establish PEN[MIM]₄[OH]₄ as a highly efficient and reusable catalyst with promising applications in diverse organic syntheses.

This study employed iron-impregnated Kenyan clinoptilolite zeolite for the adsorptive elimination of chloramphenicol, an antibiotic and emerging water contaminant, from aqueous solution. The iron-impregnated zeolite achieved 89% removal compared to 32% achieved by the un-impregnated zeolite. The iron-impregnated zeolite recorded a higher equilibrium adsorption capacity of 22.49 mg/g compared to 8.09 mg/g for the un-impregnated. Impregnating zeolite with iron enhance its adsorption capacity by generating additional active sites through the introduction of iron species and by shifting the point of zero charge toward a neutral pH, thus broadening the pH range conducive for electrostatic attraction. Kinetics, isotherms and thermodynamics of the adsorptive elimination of chloramphenicol were investigated. The adsorptive removal of chloramphenicol by the iron-impregnated zeolite fitted best to the pseudo-first order kinetic model. It was also established that the adsorption rate is not solely controlled by Intra-particle diffusion. The Freundlich isothermal model fitted the experimental data better while a Q_max of 39.34 mg/g was attained by ImZe. The percent removal of chloramphenicol by the iron-impregnated zeolite decreased as the reaction temperature was varied from 25 to 40 °C. The adsorption process attained a ∆H of − 55 kJ/mol and a ∆S of − 148 J/mol/K. Adsorption of chloramphenicol onto the adsorbent was practically feasible, exothermic and spontaneous as shown by the negative values of ∆H and ∆G. Furthermore, the adsorption was characterized by increased orderliness at the sorbent/bulk solution interface as indicated by negative ∆S value. The adsorption mechanism was predominantly characterized by electrostatic attraction. This work is novel because it demonstrates the potential of iron-impregnated Kenyan clinoptilolite zeolite in removal of chloramphenicol from water, which will impact to improve water purification technologies.