Reaction Kinetics, Mechanisms and Catalysis最新文献

This work portrays a sustainable utilization of fruits and vegetable waste (FVW) and aims in extraction of valuables. The waste chosen for the study are papaya peel, pea pod, mustard oil cake, banana peel, orange peel, pomegranate peel, pineapple peel, used coffee bean, onion peel, and apple peel. The extraction of bioactive components was done with methanol by percolation method at room temperature. The extraction was also done using microwave extractor and bath ultrasonicator. The extracts were analyzed for total phenolic content (TPC) using Folin-Ciocalteu method in terms of mg/ml of gallic acid equivalents (GAE). Total phenolic content was found to be highest in apple peels (0.171 mg/ml), papaya peels (0.166 mg/ml), onion peel (0.146 mg/ml), and pomegranate (0.126 mg/ml). The extracts were analyzed for their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and cupric reducing antioxidant capacity (CUPRAC) assays. Pomegranate peel showed 51.05% degradation in comparison to pure ascorbic acid which is a super antioxidant showing 90% degradation of DPPH (0.2 mM). Total protein content was determined by Biuret method. Anthrone reagent was used to determine the amount of carbohydrate in each sample quantitatively. The results underscore the immense potential for sustainability and innovation within the domain of food waste utilization for extraction of valuables.

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The present work shed light on the investigation of the textural and compositional properties of Activated Carbons derived from palm Date Seeds (DSAC). Initially, DS were pyrolyzed and chemically activated using H₃PO₄ activating agent at different ratio/temperatures. In that sense, various techniques were performed, particularly, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry–differential thermal analysis (TGA/DTG), Brunauer–Emmett–Teller (BET) surface area analysis and energy dispersive spectroscopy (EDS) coupled to scanning electron microscopy (SEM). Our outcomes showed that the activation with H₃PO₄ at lower and higher ratio produced activated carbons with higher pore volume (0.507 and 0.680 cm³/g), narrower average pore diameter (1.10 and 1.49 nm) and higher surface areas (917.082 and 828.60 m²/g). DSAC were used for the adsorption of methylene blue (MB) dye from an aqueous solution. The adsorption efficiency of the studied samples was investigated varying the amount of activated carbon, contact time, temperature and initial dye concentration. Acid-activated samples showed improved adsorption capacity for MB compared to pyrolyzed ones: up to 302 mg/g. This was mainly attributed to a more adequate texture as confirmed by the presence of a pronounced porosity in the SEM analyses. The adsorption equilibria were analyzed; the Langmuir isotherm revealed the best correlation with the experimental data, and the pseudo-second-order kinetic model was the most suitable for the adsorption of MB dye. The thermodynamic parameters revealed the spontaneity and endothermicity nature of the MB adsorption process. According to the obtained results our synthesized added-value product can be used to remove dyes contained in industrial effluent.

An analytic solution is presented for the simultaneous substrate elimination problem that combines Michaelis-Menten (MM) consumption with an irreversible homo-dimerization process. The implicit solution involves logarithm and inverse tangent functions and perfectly agrees with the numerical solution of the differential equation. A solution is also presented for the generalized dynamical problem that simultaneously combines MM kinetics with first and second-order processes. The exact expressions for the half-life and the area under the curve are also presented for these problems.

The kinetics of the reaction between tungstate ion and hydrogen peroxide in aqueous medium containing phosphate ions has been followed spectrophotometrically at 225 nm. This wavelength led to two different kinds of absorbance-time plots, showing either an increasing-maximum-decreasing temporal pattern or a continuously decreasing one, depending on the medium pH. This allowed to carry out two independent kinetic studies, one at high pH (first reaction stage) concerning the formation of a long-lived intermediate, thought to be W(V), and the other at low pH (second reaction stage) concerning its decay. The kinetic tool chosen to obtain the quantitative information was that of the initial rate method. The results indicated that, whereas both reaction stages were of first order in hydrogen peroxide, the rate dependence on the concentration of tungstate ion differed for the two stages: an apparent kinetic order intermediary between 1 and 2 for the first stage, and a well-defined order 1 for the second stage. There was also a difference between the dependences of the initial rates of the two stages on the concentrations of phosphate ions (the rate of the first stage independent and that of the second decreasing) and of the background electrolyte KCl (for the first stage an increasing effect and for the second a decreasing one). Both stages showed catalysis by hydrogen, copper(II), zinc and manganese(II) ions, the latter three probably acting as superoxide radical scavengers. Although the activation energy of the first stage was unusually close to zero (1.0 ± 1.2 kJ mol⁻¹), that of the second stage was considerably higher (28 ± 3 kJ mol⁻¹). Finally, a mechanism coherent with the available experimental information, and where the solvent cage effect plays an important role, has been proposed for each reaction stage.

Graphical abstract

In this study, the photocatalytic degradation of Congo red dye was investigated using aluminum-doped nickel cadmium manganese prepared from a sol–gel auto-combustion process and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) for morphological and chemical studies. UV–Vis spectroscopic investigations were performed to explore the optical properties of the synthesised spinel ferrite. The results show that the particle size decreases, the surface area increases, and the band gap energy of ferrite nanoparticles decreases with aluminum doping, which is responsible for their enhanced photocatalytic activity under visible light irradiation. The photodegradation efficiency of the aluminum-doped catalyst was found to be remarkable, up to 99.54% for Congo red after 60 min as compared to undoped 56.78% in 60 min under normal conditions. At optimized conditions Congo red dye (10 ppm) was degraded by 100% in 30 min under pH 3, 40 °C, 100 mg/100 mL catalyst dosage, 200 W light intensity conditions. Superoxide radicals, together with hydroxyl radicals and holes, appear to be key species in the degradation mechanisms, as determined in previous studies. Therefore, the recycled catalyst showed excellent stability and reusability over five cycles of photocatalytic performance.