Reaction Kinetics, Mechanisms and Catalysis最新文献

Theoretical two-compartment model of an amperometric biosensor with non-Michaelis-Menten kinetics is analyzed. The biosensor is composed of the enzyme membrane and external diffusion layers. The mathematical model is composed of the non-linear diffusion equations related to non-Michaelis-Menten kinetics. The semi-analytical expressions of the substrate and product concentrations in the membrane layer and diffusion layer are derived using the homotopy perturbation method. The numerical simulations are also presented and the obtained semi-analytical expression correlates well with the numerical simulation for all the parametric values of the model. The semi-analytical expressions for biosensor current, sensitivity and resistance are also presented. The obtained semi-analytical expressions are utilized to analyze the effect of the diffusion, reaction and kinetic parameters. These expressions can be helpful in monitoring the working of the two-layer amperometric biosensor.

Zinc sulfide (ZnS) nanoparticles (NPs) were synthesized via a controlled chemical precipitation method and calcined at 150, 250, and 350 °C to optimize their structural and catalytic properties for piezocatalytic Cr(VI) reduction. X-ray diffraction confirmed phase-pure cubic ZnS with enhanced crystallinity and particle size at higher calcination temperatures, while SEM–EDX verified uniform Zn–S distribution and morphology changes. Under optimized conditions (pH 5–7, 250 rpm, 60 min), the sample calcined at 150 °C achieved the highest Cr(VI) reduction efficiency of 90.0%, compared to 66.8 and 20.0% for the 250 and 350 °C samples. Kinetic analysis indicated that the reduction process followed a pseudo-second order model (R² = 0.961–0.978), suggesting chemisorption as the rate-limiting step. Thermodynamic parameters confirmed an endothermic and spontaneous reaction, with ΔH values of 41.19–74.30 kJ mol⁻¹, ΔS values of 0.151–0.266 kJ mol⁻¹ K⁻¹, and negative ΔG values. Response surface methodology identified reaction time as the most significant factor influencing reduction efficiency. The ZnS NPs retained over 78% of their activity after four reuse cycles, demonstrating excellent stability and reusability. These results highlight the potential of low-temperature–calcined ZnS NPs as efficient, stable, and energy-saving piezocatalysts for Cr(VI) remediation.

Activated carbon (AC) fabricated using Strychnos pungens fruit shells (biowaste) and encapsulated in a chitosan biopolymer (CHO) was applied for the removal of picloram from aqueous solutions. The synthesized activated carbon-chitosan beads (ACCHO) were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Infrared spectroscopy (IR) and Emmett Teller (BET) surface area analysis. The findings demonstrated the successful encapsulation of AC to produce ACCHO with both crystalline and amorphous properties. The application of ACCHO for picloram removal was affected by solution pH, adsorbent dosage, and initial picloram concentration. The efficiency increased with adsorbent dosage, reaching an optimum at 40 g/L. Similarly, efficiency increased as pH increased from 2 to 6, but declined at pH 8. Optimal conditions of pH 6, 40 g/L ACCHO dosage and  50 mg/L picloram produced 88% removal efficiency. The picloram adsorption kinetics best fitted the pseudo-first order (PFO) model. Langmuir and Freundlich adsorption isotherms provide a good description of the picloram adsorption process. The adsorption mechanism on ACCHO was postulated to involve multiple interactions caused by electrostatic and weak forces of attraction. The results of the current study suggest that ACCHO can be used as a potential adsorbent for removing picloram and similar chemicals from contaminated water.

The co-pyrolysis of rice husk (RH) and date palm seeds (DS) was conducted with a focus on their physicochemical properties, thermal decomposition behavior, and thermo-kinetic analysis. During co-pyrolysis, synergistic interactions at various blending ratios were also analyzed. Thermal degradation behavior was investigated using a thermogravimetric analyzer, with kinetic analysis performed via the Friedman method and master plot technique. The blended samples exhibited improved fuel properties. As the DS proportion increased, the TG curves exhibited greater mass loss. A pronounced synergistic effect was observed in the 75%DS + 25%RH blend, where a consistently negative deviation in ΔW indicated stronger interactions between the components. The 75%DS + 25%RH blend exhibited consistent negative deviation in activation energy (ΔE_a) values when α exceeded 0.55, signifying a consistently positive synergy during co-pyrolysis. A significant reduction in average activation energy (E_a) was also observed when the DS proportion was 75%, confirming positive synergy. The average pre-exponential factor (A) values for the blends decreased with increasing DS proportion, indicating a reduction in the frequency of molecular collisions. The pyrolysis of all samples generally followed diffusion and order-based mechanisms. Thermodynamic analysis revealed positive change in enthalpy and gibbs free energy values, confirming that additional energy is required for the co-pyrolysis process.

This study includes the removal of crystal violet dye from its aqueous solution using activated carbon synthesized from the impregnation of fig leaves in zinc chloride solution. Before starting the practical experiments, different proportions of zinc chloride to fig leaves were tested, and then it was found that the mass ratio of 3:2 (FL-ZnCl₂) was the best in terms of removal % and adsorption capacity. The carbonization temperature was also tested on fig leaves at different values (250, 350, and 450 °C), and 250 °C exhibited excellent results compared to other temperatures. The initial concentrations of the dye, the time required for adsorption, the acidic effect of the solution, the temperature, the volume of the solution, and the amount of the substance that performs the adsorption were the most important factors in the present study. Two widely used non-linear models—the Langmuir and Freundlich isotherms—were employed in this study to analyze the experimental data following the adsorption of crystal violet dye. The maximum adsorption capacity was 51.35 mg/g. The non-linear pseudo-first order and pseudo-second order models proved to be more suitable for describing the adsorption process, showing an excellent coefficient of determination (R² > 0.99). The standard enthalpy change (∆H° = 26.95 kJ/mol), calculated using the Van’t Hoff equation, indicated that the adsorption process was endothermic. The adsorption of crystal violet dye onto FLAC-ZnCl₂ was found to be spontaneous, as shown by negative values of standard Gibbs free energy (∆G°), which ranged from –7.31 to –4.13 kJ/mol. It could be concluded that the novel adsorbent has great efficiency in removing dyes from aqueous solution. Reusability studies were conducted using the column-bed method with 0.2 g of FLAC, dilute acetic acid, and a 20 mg/L CV solution. The results demonstrated that FLAC could be used for up to five cycles for CV dye removal.

A semi-analytical study is presented on the nonlinear reaction–diffusion behavior of Langmuir–Hinshelwood (LH) kinetics under strong adsorption in heterogeneous catalytic systems. The governing model is a nonlinear reaction–diffusion equation, where nonlinearity stems from surface adsorption and intrinsic nth order kinetics. Closed-form analytical solutions for concentration profiles are developed using three distinct semi-analytical methods and verified against numerical simulations, showing excellent agreement. Limiting cases are examined to provide mechanistic insights, while parametric analysis highlights the effects of adsorption strength and kinetic parameters on concentration distribution and effectiveness factor. The proposed framework provides an efficient and accurate tool for understanding and optimizing nonlinear reaction–diffusion phenomena in heterogeneous catalysis.

This study investigates a chromium(III)-integrated silica gel (SG-Cr) synthesized using the sol–gel method with tetraethoxysilane (TEOS) and chromium(III) chloride hexahydrate. X-ray diffraction (XRD) analysis has indicated an amorphous nature of the composite. Scanning electron microscopy (SEM) analysis revealed a rough surface texture. Fourier-transform infrared spectroscopy (FTIR) results have confirmed the formation of a siloxane network and demonstrated the successful incorporation of chromium through interactions with silanol (Si–OH) groups. The SG-Cr composite was used as an adsorbent material for methylene blue (MB) and methyl orange (MO). It has shown the good performance in removing methyl orange (MO) dye from water. At 10 mg/L (MB) and 30 mg/L (MO), the removal efficiencies have reached 24.2% and 96.51% respectively. The adsorption performance was observed to be pH-dependent with the acidic conditions (pH 2) for the MO (anionic dye) removal due to electrostatic attraction between the protonated surface, whereas alkaline conditions (pH 11) has enhanced MB (cationic dye) uptake via interactions with deprotonated silanol groups. These results have shown the potential of SG-Cr suitable in the wastewater treatment, particularly for anionic contaminants in the acidic environments.

In this study, we present a simple and efficient microwave-assisted solid-phase synthesis of nitrogen-doped carbon dots (NCDs) using citric acid and 2-aminobenzimidazole as precursors. The synthesis conditions were systematically optimized, and the resulting NCDs were extensively characterized for their physicochemical and optical properties. Transmission electron microscopy revealed that the NCDs are spherical in shape with an average diameter of 5 ± 1 nm. X-ray photoelectron spectroscopy confirmed successful nitrogen incorporation into the carbon framework. The NCDs exhibited bright blue fluorescence under 320 nm UV Light, a high quantum yield of 12.6%, excellent water dispersibility, and strong photostability under varying environmental conditions. The catalytic performance of the NCDs was evaluated through NaBH₄-assisted reduction of malachite green (MG) and crystal violet (CV) dyes. In both cases, over 90% degradation was achieved within 12 min. The reaction kinetics followed a pseudo-first order model, with rate constants of 0.070 ± 0.01 min⁻¹ for MG and 0.139 ± 0.02 min⁻¹ for CV. These results highlight the potential of the synthesized NCDs as effective and eco-friendly catalysts for the rapid removal of dye pollutants in wastewater treatment applications.

The Langmuir–Hinshelwood (LH) equation was derived from separation of time scales and singular perturbation arguments based on singular value decomposition analysis. The quasi-steady state assumption (QSSA) commonly considered for the traditional LH equation was mathematically justified in terms of a sufficient separation of time scales, rather than relying on specific reaction steps. The analysis was extended to second order reaction rate on the active surface, and to open reacting systems. The mathematical analysis provided back up for the broad applicability of the QSSA for LH kinetics in practical cases. Some implications for the analysis of experimental data with LH kinetics were discussed. The need to verify the compliance with the QSSA was highlighted.