Reaction Kinetics, Mechanisms and Catalysis最新文献

Bismuth chromate nanostructures were fabricated via hydrolysis technique using curcuma longa for enhancing the photocatalytic activity. The analytes have been labelled as Bi₂CrO₆-C, when prepared without using curcuma longa and Bi₂CrO₆-G, prepared using curcuma longa extract (Bi₂CrO₆/Curcuma longa). The as-fabricated catalysts have been confirmed via characterization techniques including X-ray diffraction, Transmission electron microscopy (TEM), and Field emission scanning electron microscopy (FESEM), UV–Vis. DRS. The as-synthesised analytes have been evaluated their photocatalytic efficiency via photodegradation of an organic pollutant, Methyl Orange (MO). The current research findings imposed the effect of inculcation of a green extract “curcuma longa” reduces particle size and increases surface area of the material and moreover makes heterostructure with Bismuth chromate and inhibits recombination of photogenerated charges for efficient degradation of the organic pollutant. Bi₂CrO₆-G demonstrates here enhanced photocatalytic activity as compared to Bi₂CrO₆-C.

This study explores oxidative coupling of para-aniline derivatives, including (p-methylthio aniline, p-methyl aniline, p-methoxy aniline, p-hydroxy aniline and p-amino aniline). The study investigates the influence of substituents on the kinetics, thermodynamics and stability constants of the resulting compounds. A number of hybrid exchange–correlation functionals, namely, B3LYP, PBE0, BMK, CAM-B3LYP, M06-2X, HSE06 and BH&HLYP with a number of basis sets, namely, STO-3G, 3-21G, 6-31G, 6-31G*, DGDZVP, 6-311G, LanL2MB, LanL2DZ and SDD have been employed to calculate the electronic spectra of all the products. The results are compared with available experimental data. In most cases studied, the density functional theory results based on the B3LYP functionals with the DGDZVP basis set indicate a better agreement with the experimental absorption bands in the UV–Visible and IR spectra. The study reveals a first order reaction model with rate constants (0.06433–0.09053 min⁻¹) across temperatures for the product of aniline and p-amino aniline. Characterization of the compounds involves experimental and computational techniques such as FTIR and UV–Visible spectrophotometries. Activation energy (E_a) and pre-exponential factor (A) ranging (6.679–9.337 kJ mol⁻¹) and (1.2839–2.809 min⁻¹), with the highest values observed for the product of p-hydroxy aniline. Stability constants increase with temperature indicating an endothermic reaction. Thermodynamic analysis unveiled values for activation parameters: entropy (ΔS* = −0.2513 to −0.2447 kJ mol⁻¹ K⁻¹), enthalpy (ΔH* = 4.168–6.826 kJ mol⁻¹) for the product of p-hydroxy aniline and aniline; and Gibbs free energy (ΔG* = 80.1856–81.0466 kJ mol⁻¹) for the product of p-amino aniline and aniline. ΔG* values indicate a non-spontaneous and endothermic processes. Computational investigations using density functional theory (DFT) with the B3LYP/DGDZVP basis set, authorize reliability and accuracy of the experimental results.

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In the present work, an eco-friendly approach is used to synthesize ZnO nanoparticles (ZnO-NPs) for the removal of propyl paraben in the pharmaceutical industry. ZnO-NPs were prepared from aqueous lemon extract and characterized by different techniques such as XRD, FTIR and UV–Vis DRS spectroscopies, BET, SEM/EDS, and TGA. The crystallites exhibited a mean size of 49.5 nm measured via XRD and were highly pure, while SEM analyses confirmed their spherical or elliptical shape. The functional groups responsible for stabilizing and capping of ZnO-NPs were confirmed using FTIR analysis. UV–Vis DRS revealed that the optical bandgap of ZnO-NPs for direct and indirect transition was 3.17 and 3.04 eV, respectively. Synthesized ZnO-NPs were used to evaluate their possible reactivity through the parabens degradation employed for the fabrication of magnesium pidolate. ZnO-NPs photocatalyst was found to be highly active against propylparaben degradation with reaction efficiency ~ 80% after 120 min of reaction. Owing to the eco-friendly synthesis, and non-toxicity, ZnO-NPs synthesized from lemon extract can be exploited as potential candidates for environmental applications.

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This study effectively synthesized monoclinic bismuth oxide nano-photocatalyst (α-Bi₂O₃) using both template-assisted and template-free methods, employing the hydrothermal process. Xanthan gum, a type of soft biopolymeric material, was used as a sacrificial template to promote the regulated growth of nano-photocatalysts. The structure, morphology, surface features, optical properties, and catalytic activity of both templated and non-templated Bi₂O₃ were analyzed using XRD, FESEM-EDX, IR, and UV–Vis (DRS) spectral analysis techniques. Additionally, the chemical oxygen (COD) analyzer methodology was used to assess the catalytic activity. The combination of synthetic technique and template has successfully produced Bi₂O₃ nano-photocatalyst with a consistent and granular shape. Specifically, the template-assisted processes have produced nanostructures of bismuth oxide that are highly crystalline and low band gap (2.76–2.71 eV). The use of template-assisted metal oxide nanostructures has shown potential as very effective photocatalysts for breaking down developing pollutants, such as 2,4-dichlorophenol (2,4-DCP), which is found in paper and pulp mills, when exposed to sunlight. The xanthan gum templated α-Bi₂O₃ nano-photocatalyst almost completely photodegraded 2,4-DCP within 90 min under sunlight. The remarkable catalytic capability of bismuth oxide (Bi₂O₃) templated by xanthan gum has been confirmed by their high-rate constants of 0.01–0.05 min⁻¹. As the treatment duration increased to 90 min, the degradation of 2,4-DCP resulted in a maximum elimination rate of 97.5% for COD. As a result, the template-assisted approaches have successfully produced nanostructures with customized features, which makes them very efficient in photocatalysis for quickly breaking down certain emergent organic pollutants present in paper and pulp mill wastewater. These eco-friendly synthetic photocatalysts can be efficiently used for treating wastewater that is contaminated with emerging organic contaminants.

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The corrosion of mild steel alloy in 1 M HCl in the absence and presence of sodium iodide as a corrosion inhibitor is investigated. The mathematical and statistical studies for the mild steel mass loss as a function of inhibitor concentration, temperature, and time are performed using the least-squares regression method. Furthermore, morphological studies via atomic force microscopy (AFM) and X-ray diffraction (XRD) are achieved for the polished, corroded, and inhibited mild steel samples. In addition, kinetic studies are employed to determine the reaction order and other kinetic parameters. Three mathematical models were proposed: the exponential model, exponential growth, and the polynomial model. Nonlinear estimation based on Levenberg–Marquardt as the estimation method showed that the best fit was obtained using exponential growth with a 0.988 correlation coefficient. AFM and XRD outcomes showed an improvement in the surface properties in the presence of NaI. The average roughness (R_a) for the polished, corroded, and inhibited steel samples is 131.35, 1343.4, and 219.65 nm. Kinetic experiments showed a zeroth order response with a significant correlation coefficient.

Gold nanoparticles (AuNPs) were synthesized using dragon fruit peel extract (DFE) as a reducing agent and stabilizer. Confirmation of AuNP formation included the distinct red coloration of the solution and the appearance of surface plasmon resonance (SPR) peak at approximately 530 nm in the UV–visible spectrum. Synthesis conditions, such as solution pH, HAuCl₄ concentration, and DFE concentration, were varied to observe their influence on the AuNPs. Characterization using TEM revealed well-dispersed, nearly spherical particles with diameters ranging from 6 to 20 nm and a mean diameter of 12 ± 3 nm. XRD and SAED patterns confirmed the face-centered cubic (FCC) crystal structure. FTIR analysis highlighted the role of DFE functionalities in reducing and stabilizing the AuNPs. Zeta potential analysis indicated a negative surface charge on DFE@AuNPs, ensuring colloidal stability. The antioxidant activity of DFE@AuNPs was assessed using the ABTS assay, demonstrating comparable efficacy to ascorbic acid as a standard. Furthermore, the catalytic activity of the nanoparticles was evaluated through the NaBH₄-assisted reduction of malachite green (MG) dye, with over 90% reduction observed within 24 min, following pseudo-first order kinetics with the rate constant of 0.069 ± 0.011 min⁻¹ obtained from exponential fit.

In order to promote the application of carbon dots as carriers in oxygen reduction reaction, CD with uniform size distribution was prepared by microwave heating using citric acid and urea as raw materials through a bottom-up synthesis method. Due to the presence of a large number of hydroxyl groups on the surface of CD. We found that the prepared CD can be used as a reducing agent and stabilizer to directly reduce PdCl₂ to obtain Pd nanoparticles under oil bath conditions. The obtained Pd/CD system has excellent catalytic effect on the electrocatalytic oxygen reduction. The results show that the half-wave potential of Pd/CD-0.1 catalyst reaches 0.83 V, which is comparable to that of commercial Pd/C, and the corresponding limiting diffusion current density is even larger than that of commercial Pd/C catalyst. After a 5000 cycles stability test, the LSV exhibits a left shift of only 19 mV.

This study reports the synthesis and characterization of Polyvinylidene Fluoride (PVDF)/TiO₂ composite nanofibers for photocatalytic CO₂ conversion. The nanofibers were fabricated via electrospinning, with TiO₂ supported in a PVDF matrix. The electrospinning parameters were optimized, with the speed of drum collector, voltage, flow rate, and temperature set at 321 rpm, 20 kV, 1 ml h⁻¹, and 24 °C. SEM and XRD analyses revealed a nanofiber width of approximately 250 nm and the presence of anatase phase TiO₂, with primary diffraction peaks at 2θ values of 38.24° and 48.62°. The PVDF/TiO₂–NFs sample exhibited a BET surface area of 17.2689 ± 1.1154 m² g⁻¹, a BJH adsorption pore volume of 0.025 cm³ g⁻¹, and a BJH pore diameter of 7.26 nm. The photocatalytic performance of PVDF/TiO₂ nanofibers was evaluated through CO₂ conversion experiments, measuring the production of solar fuels (methanol and ethanol) and the efficiency of carbon utilization. The obtained yield of methanol is at 15.66 μg L⁻¹, while ethanol is recovered at 19.15 μg L⁻¹. The results demonstrated significant CO₂ reduction capabilities, highlighting the potential of PVDF/TiO₂ nanofibers as a sustainable solution for environmental remediation and renewable energy generation.

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In the present work, bifunctional immobilized catalysts, incorporating Lewis acid and nucleophilic reagent, were prepared by supporting Zn–Br with ZSM-5 for the synthesis of propylene carbonate from CO₂ and propylene oxide. When the total loading of Zn–Br, ω, is 7.5wt%, and the molar ratio, n(Br)/n(Zn), is 3.0, ZnO-KBr-7.5-3.0@ZSM-5 exhibits the highest activity with the solvent N, N-dimethylformamide (DMF). The conversion of propylene oxide and the selectivity of propylene carbonate are up to 97.73% and 98.83%, respectively. Gas chromatography results reveal the presence of by-products, specifically acetone and propylene glycol, in addition to propylene carbonate. Characterizations identify the active components in ZnO-KBr-7.5-3.0@ZSM-5 as ZnO and KBr. Meanwhile, the experimental results prove that DMF serves as a co-catalyst. The catalytic mechanism of DMF and ZnO-KBr-7.5-3.0@ZSM-5 on the cycloaddition is proposed, and the reaction process is simulated. DMF contains a tertiary nitrogen structure, able to function as a Lewis base, thereby activating CO₂. ZnO and KBr in ZnO-KBr-7.5–3.0@ZSM-5 work synergistically to boost epoxide ring opening. Subsequently, the activated CO₂ integrates into the ring-opened epoxide, resulting in the formation of propylene carbonate. Additionally, four cycles of replicate experiments show that the catalyst ZnO-KBr-7.5-3.0@ZSM-5 possessed good stability.

In this study, the genetic algorithm, a stochastic global optimization method, was used to investigate complex reaction kinetics. The genetic algorithm’s effectiveness and efficiency were validated through investigating a conventional optimization problem and a theoretically simulated chemical reaction process. The combustion kinetics of biochar derived pinewood sawdust pyrolysis was experimentally investigated, and a distributed activation energy model (DAEM) with a double distribution was utilized to analyze the kinetic behaviors of biochar combustion, and the genetic algorithm was employed to optimize the model parameters. For biochar combustion, two overlapping sub-processes with different activation energy distributions were revealed by the double DAEM: 160–200 kJ mol⁻¹ (peaked at 182.47 kJ mol⁻¹) for the first sub-process and 165–235 kJ mol⁻¹ (peaked at 199.96 kJ mol⁻¹) for the second sub-process. The DAEM with the genetic algorithm for the estimation of model parameters provides a powerful tool for analyzing the thermal decomposition kinetics of complex solid materials.