Reaction Kinetics, Mechanisms and Catalysis最新文献

This work reports for the first time the application of copper coatings prepared by cold spray deposition as electrocatalysts for the hydrogen evolution reaction (HER) in alkaline medium. Structural and surface characterizations (SEM, EDX, XRD, Raman spectroscopy, and profilometry) revealed dense and adherent coatings with a highly textured surface, enhanced roughness, and the coexistence of metallic Cu, Cu₂O, and CuO phases. These features were directly correlated with superior electrocatalytic performance. The cold-sprayed Cu electrode exhibited a low onset potential of 0.26 V vs. RHE, a Tafel slope of 94.2 mV dec⁻¹, and an exchange current density of 4.17 mA cm⁻², confirming improved HER kinetics compared with bulk Cu. Electrochemical impedance spectroscopy indicated a reduced charge-transfer resistance, while hydrogen quantification demonstrated a stable production rate of 1330.59 µmol h⁻¹ under continuous operation. The results establish cold spray as a novel and scalable strategy to fabricate efficient Cu-based electrodes, opening new avenues for large-scale hydrogen production.

In this study, we explored the photocatalytic degradation of methyl orange (MO) and Rhodamine B (RhB) via 2.0 wt% I–Bi₂S₃, ZnIn₂S₄, and their composite ZnIn₂S₄/2.0 wt% I–Bi₂S₃ under visible light irradiation. While 2.0 wt% I–Bi₂S₃ revealed insignificant photocatalytic activity, ZnIn₂S₄ showed outstanding efficiency, degrading 94.7% of MO in 150 min and 98.9% of RhB in just 35 min. The composite achieved even better performance, 95% MO degradation (150 min) and 99.7% RhB degradation (35 min), demonstrating a synergistic effect between 2.0 wt% I–Bi₂S₃ and ZnIn₂S₄. TEM, SEM, XRD, XPS, UV–Vis DRS, ESR, photoelectrochemistry, and PL tests were performed to characterize the structure, morphology, and separation efficiency of the products. According to kinetic studies, the photocatalytic degradation kinetics of rhodamine B and methyl orange exhibited various patterns. For Rhodamine B (RhB), a nonlinear exponential decay function was applied to obtain the rate constants, yielding k = 0.17186 ± 0.00147 min⁻¹ for ZnIn₂S₄ and k = 0.25567 ± 0.00405 min⁻¹ for the composite with R² = 0.99. This outcome indicates that RhB degradation follows first order kinetics closely. While the degradation of methyl orange fulfills R² ≈ 0.93, which means it is less consistent with the first order model. The computed rate constants were k = 0.01171 ± 0.00157 min⁻¹ for ZnIn₂S₄ and k = 0.01362 ± 0.00184 min⁻¹ for the composite. MO degradation is characterized by pseudo-first order behavior due to the deviation from linearity of a first order reaction. The boost in photocatalytic degradation was related to the reduction in electron–hole recombination that resulted from the creation of a heterostructure and a doping strategy. This study shows the potential of ZnIn₂S₄-based composites as high-performance photocatalysts for environmental remediation, displaying an exceptional solution for effectively eliminating hazardous organic dyes from wastewater.

Zinc-based layered double hydroxide (Zn–Fe LDH) and its calcined mixed metal oxide (Zn–Fe MMO) were synthesized using a simple co-precipitation method. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and UV–visible diffuse reflectance spectroscopy (UV–vis DRS) to confirm their structural, morphological and optical properties. Both photocatalysts showed high efficiency in the visible-light degradation of crystal violet (CV) dye, achieving removal rates of ~ 95% for Zn–Fe LDH and 89% for Zn–Fe MMO under optimal conditions (10 mg catalyst, 10 mg L⁻¹ dye, neutral pH, room temperature). The photocatalytic mechanism, catalyst dosage effect, and kinetic behavior were systematically investigated. Additionally, both materials demonstrated effective antibacterial activity against Gram-positive and Gram-negative strains. These results highlight the potential of Zn–Fe LDH and Zn–Fe MMO for applications in environmental remediation and antibacterial treatments.

This study aimed to investigate the potential of Algerian biomass Date Palm Spikelet (Phoenix dactylifera) as an efficient adsorbent for the removal of Malachite Green (MG). The valorization of biomass was performed by chemical treatment with sulfuric acid (H₂SO₄). The obtained material (TDPS) was analyzed through adsorption – desorption of N₂, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Boehm titration, and pH of point of zero charge (pH_PZC). The specific surface area of TDPS was S_BET = 0.5 m²/g, and pH_PZC was 3.2. The Box–Behnken design (BBD) was used to analyze the impact of the adsorbent mass (A), initial dye concentration (B), and solution pH (C) on the removal efficiency of MG dye from aqueous solutions. The interaction between factors A and B was statistically significant, with a p-value of AB less than 0.05. The results showed that MG adsorption was best described by the Freundlich isotherm model, indicating multilayer behavior, which was endothermic and followed the pseudo-second order model. The chemical regeneration of TDPS by NaOH indicated that the material exhibited excellent MG adsorption efficiency after four cycles. Density functional theory (DFT) calculations indicated that the adsorption mechanism of MG is governed by electrostatic interactions, hydrogen bonding, and n-π interactions with MG molecules and TDPS.

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The photocatalytic degradation of aqueous solutions of cephalexin (CEP) and rifampicin (RIF) antibiotics using strontium titanate nanoparticles (STO NPs) as a photocatalyst activated by 365-nm UV light was investigated. Experimental results demonstrated that the photocatalytic degradation of both antibiotics was efficient and influenced by operational parameters, including photocatalyst dosage, irradiation time, solution pH, initial antibiotic concentration, and the presence of hydrogen peroxide. The kinetics, rate limiting steps, and thermodynamic parameters of the degradation processes were analyzed by fitting the experimental data to the modified Langmuir–Hinshelwood, Weber–Morris intraparticle diffusion, Arrhenius, and Eyring models. The photocatalytic degradation rate constants were estimated to be 0.049 ± 0.005 and 0.012 ± 0.002 min^‒1 for CEP and 0.301 ± 0.015 and 0.016 ± 0.002 min^‒1 for RIF. The rate limiting steps involved a combination of external mass transfer and intraparticle diffusion onto the surfaces of STO NPs. Thermodynamic analysis indicated that the overall degradation reactions were spontaneous, endothermic, and accompanied by an increase in the surface entropy of the photocatalyst. Radical scavenging experiments confirmed that the degradation process is governed by oxidation reactions involving O₂^·‒ and OH^· radicals generated on the photocatalyst surfaces. Based on the chemical structures of the detected intermediates and degradation products, plausible degradation pathways were proposed, involving fragmentation through ring opening, hydroxylation, deamination, decarboxylation, dealkylation, and demethylation. The environmental safety of the degradation products was preliminarily assessed through antibacterial screening tests, which confirmed a reduction in antibacterial activity compared to the parent antibiotics, suggesting a reduced ecological risk.

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Keggin type tungstovanadophosphoric acid H₄PW₁₁VO₄₀.8 H₂O (PVW) was prepared and impregnated on acid activated bentonite under mild conditions. In acidic solution, PVW was incorporated into a clay interlayer template using the sol–gel process. The catalysts were characterized by XRD, BET and FTIR analysis. The catalytic activity was evaluated in cyclohexene oxidation. Characterization analyses indicated that PVW was distributed more uniformly in the encapsulated sample compared to the impregnated sample. The most intriguing aspect about heterogenizing homogenous catalysts is that they can be recovered. The optimal conditions for cyclohexene oxidation by PVW/AAB and PVW-SC catalysts using H₂O₂ as oxidant. The influence of catalyst weight, method preparation of catalyst, reaction temperature, time and the molar ratio Cyclohexene/H₂O₂ were studied. To relate the process variables to the two responses, central composite design-based two-second order polynomial models were developed. The significant effects of parameters on each response were determined using the statistical analysis of variance. The significant variables influencing each response have been determined by the analysis of variance. According to the fitted models, predicted and actual responses typically are identical. Optimum conditions were estimated as 85.4 mg of catalyst, molar ratio of 2/1 (oxidant/cyclohexene) and impregnated catalyst (PVW/AAB) for preparation method under 72 °C for 10.2 h. The conversion and selectivity calculated by the model are 76% and 100%, they are close to the experimentally measured value 70% and 95% under the operating conditions quoted above.

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Bis (8-hydroxyquinoline) manganese (Mnq₂) material was prepared by the liquid-phase synthesis method. The material was characterized by SEM, FTIR, UV–vis, BET, and PL. The synthesized Mnq₂ was used as a photocatalyst, and methylene blue (MB) was used as the targeted contaminant to study the effect of the addition amount of Mnq₂ on the photocatalytic performance. The findings indicated that the reaction conformed to the Langmuir–Hinshelwood pseudo-first order kinetic model, with the degradation efficiency (D) and the reaction rate constant (k) displaying a consistent variation trend. When the addition amount of Mnq₂ was 40 mg, the degradation effect on the 20 mg/L methylene blue solution was the best. After 210 min of degradation, D = 98.23%, and k = 0.02109 min⁻¹. After three cycles, the degradation rate still remained above 95%. Different addition amounts could achieve a degradation rate of over 95% after 210 min of degradation. This suggests that Mnq₂ holds potential for the remediation of methylene blue-containing wastewater, exhibiting favorable photocatalytic activity and stability in the process.

This study reports a green synthesis of bimetallic gold–palladium nanoparticles (Au–Pd BNPs) using Passiflora edulis fruit peel extract as a sustainable reducing and stabilizing agent. Transmission electron microscopy revealed uniformly dispersed spherical nanoparticles with a core–shell structure, comprising a dense Au core and a thinner Pd shell, and an average diameter of 15.9 ± 2.4 nm. The core–shell architecture was further confirmed by X-ray diffraction (XRD), while Fourier-transform infrared spectroscopy (FTIR) indicated the involvement of hydroxyl and carbonyl-containing phytochemicals in nanoparticle formation. X-ray photoelectron spectroscopy (XPS) verified the presence of elemental Au and Pd in Au–Pd BNPs. The catalytic activity of monometallic (AuNPs, PdNPs) and bimetallic (Au₃Pd₁, Au₁Pd₁, Au₁Pd₃) nanoparticles was assessed in the NaBH₄-assisted reduction of rhodamine B (RhB) and methyl orange (MO). Among all catalysts, Au₁Pd₃ BNPs exhibited superior performance, achieving > 99% reduction of both dyes within 5 min. The reactions followed pseudo-first order kinetics, with apparent rate constants of 14.7 ± 0.6 × 10⁻³ s⁻¹ for RhB and 16.1 ± 0.5 × 10⁻³ s⁻¹ for MO, obtained from the nonlinear exponential fitting. These findings highlight the effectiveness of green-synthesized Au–Pd BNPs as promising catalysts for rapid and efficient dye degradation.

This study investigates the dynamical behavior and control strategies of a modified Brusselator model in the context of sustained chemical reactions. A new dimensionless model incorporating dynamic inflow of reactant species is developed to better capture real world chemical environments. The system of nonlinear differential equations under consideration introduces a coupling with an additional variable z, representing an intermediate species or external influence, thereby extending the classical Brusselator model. We analyze the equilibrium points and explore the local and global bifurcation phenomena that emerge due to variations in key parameters (alpha) and m with bifurcation behavior which shifts for different values of (alpha). Furthermore, we develop and implement an adaptive control mechanism to regulate the system dynamics, ensuring desired behavior even in the presence of nonlinear instabilities. Numerical simulations, using MATLAB’s ode45 solver, demonstrate how varying parameters influence the system’s behavior and validate the effectiveness of the proposed adaptive controller. The results provide insights into managing complex chemical reactions through robust control methods, as the tracking error converges to zero and parameter estimation stabilizes over time.