Reaction Kinetics, Mechanisms and Catalysis最新文献

This study introduces a novel thermochemical conversion process to synthesize lignin-derived activated carbons (LEGHs) from sawdust, utilizing ethylene glycol (EG) as a liquefaction agent and phosphoric acid as an activating agent. The process was conducted at a 1:1 impregnation ratio, with temperatures ranging from 300 °C to 500 °C. The obtained materials were characterized using Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy (SEM–EDX), Fourier Transform Infrared Spectroscopy (FTIR), and nitrogen adsorption at 77 K. Optimal activation at 350 °C produced an activated carbon with a high surface area of 1230 m²/g and a micropore volume of 0.348 cm³/g. Adsorption tests for the removal of Basic Blue azo dye (BB9) were conducted in batch experiments mode to assess the influence of various parameters including pH, adsorbent dose, contact time, initial dye concentration, and temperature. The highest adsorption efficiency was obtained at pH 4, dose of 1 g/L and a contact time of 5 h, resulting in an adsorption capacity of 668 mg/g. The Langmuir isotherm model best described the adsorption equilibrium data (R² = 0.99), indicating adsorption on a homogeneous surface. The adsorption kinetics study well fitted by the pseudo-second-order model (R² = 0.99). Thermodynamic studies showed a spontaneous (ΔG°: −45.73 to −50.34 kJ/mol) and endothermic (ΔH° = 196 kJ/mol) adsorption process These findings underscore the potential of LEGHs as an effective and sustainable adsorbent for industrial wastewater dye removal, leveraging lignin, a byproduct of the paper and pulp industry, to enhance sustainability.

In this article we present and discuss the work and scientific legacy of Julian Hirniak, the Ukrainian chemist and physicist who published two articles in 1908 and 1911 about periodic chemical reactions. Over the last 110+ years, his theoretical work has often been cited favorably in connection with Alfred Lotka’s theoretical model of an oscillating reaction system. Other authors have pointed out thermodynamic problems in Hirniak’s reaction scheme. Based on English translations of his 1908 Ukrainian and 1911 German articles, we show that Hirniak’s claim (that a cycle of inter-conversions of three chemical isomers in a closed reaction vessel can show damped periodic behavior) violates the Principle of Detailed Balance (i.e., the Second Law of Thermodynamics), and that Hirniak was aware of this Principle. We also discuss his results in relation to Lotka’s first model of damped oscillations in an open system of chemical reactions involving an auto-catalytic reaction operating far from equilibrium. Taking hints from both Hirniak and Lotka, we show that the mundane case of a kinase enzyme catalyzing the phosphorylation of a sugar can satisfy Hirniak’s conditions for damped oscillations to its steady state flux (i.e., the Michaelis–Menten rate law), but that the oscillations are so highly damped as to be unobservable. Finally, we examine historical and factual misunderstandings related to Julian Hirniak and his publications.

The aim of this study is the degradation of paracetamol (PAM) which is widely used as an analgesic and an anti-inflammatory drug in the pharmaceutical sector by advanced oxidation processes as photocatalysis, photolysis and Like photo-Fenton processes. The ZrWC (Zr–WO₃@ charcoal) material was elaborated to be characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) theory, Fourier Transform Infrared Spectroscopy (FTIR) and UV–vis diffuse reflectance spectra before its application as photocatalyst in the Paracetamol (PAM) removal. The photodegradation efficiency of PAM was studied by varying the ZrWC amount, the pH value and the PAM concentration. The evolution of PAM concentration was measured by UV–visible spectrophotometer and hight performance liquid chromatography, while the mineralization percentage was monitored by the determination of chemical oxygen demand. The characterization results show that the material has meso-porous structure with the specific surface area of 18.3877 m²/g, and an indirect band gap of 3.9 eV. The efficiency Paracetamol removal increased to 73% whereas 60% of COD is removed after 120 min of irradiation. The optimum conditions determined at room temperature were [PAM] = 20 mg/L, [photocatalyst] = 1 g/L and pH 6.

Graphical Abstract

We have studied a method to lower a price and to enhance an electric contact of proton exchange membrane (PEM) water electrolyzer by using hydrophilic carbon paper as anodic porous transport layer (PTL). Hydrophobized carbon papers owing to an anti-oxidation process were turned hydrophilic by facile plasma treatment-1% Nafion solution impregnation in order to use a carbon paper as an excellent anodic PTL. We introduced two step hot-pressing process to strengthening the adhesion between catalyst layer and Nafion membrane when we manufactured membrane electrode assembly (MEA) by hot-pressing carbon papers as anodic and cathodic PTLs on catalyst coated membrane. A total charge transfer resistance of electrolyzer with hydrophilic carbon paper was 0.182Ω cm², and that was 0.035Ω cm² smaller than one with hydrophobic carbon paper. The cell voltages of PEM water electrolyzers with hydrophobic and hydrophilic carbon paper as an anodic PTL at the current density of 1 A cm⁻² were 1.755 V and 1.716 V. The water flow rate played an important role in the performance of PEM water electrolyzer in case of hydrophobic carbon paper, but water was sufficiently supplied even at a low flow rate (20 mL/min) to stabilize the cell voltage which was changed within the range of ± 0.025 V in case of hydrophilic one. Prepared PEM water electrolyzer with the hydrophilic anodic PTL displayed desirable performance; initial voltage at 1.2 A cm⁻² of current density, at 80 °C was 1.76 ± 0.02 V, and finally measured voltage 1.84 ± 0.02 V after 6270 h of testing.

The perovskite powder La_0.75Gd_0.25FeO₃, abbreviated as LGFO, has been successfully synthesized via a solid–solid process and thoroughly investigated using various laboratory techniques. X-ray diffraction (XRD) analysis revealed that the studied powder exhibits an orthorhombic crystal system with the space group Pbnm, accompanied by the formation of nanometric crystallites measuring approximately 41 nm at a synthesis temperature of 1200 °C. The scanning electron microscope (SEM) image exhibits a uniform distribution of grains across the sample surface. Notably, the band gap value of LGFO was estimated using Tauc plot to be 2.40 eV, this value is lower than that of the pure LaFeO₃ phase, and discrepancy attributed to variations in crystallite size and the presence of substituted dopant ions. In a photocatalytic evaluation, LGFO demonstrated remarkable activity in degrading methylene blue (MB) under sunlight irradiation, surpassing the performance of pure LaFeO₃. The decomposition yield reached up to 61% after 120 min of solar exposure, exhibiting a first-order reaction kinetics behavior with an estimated rate constant of 0.00838 min⁻¹.

We have successfully synthesized cadmium ferrite spinel CdFe₂O₄ powder via the sol–gel route and meticulously evaluated its efficacy as a photocatalyst for the eradication of Green Malachite (MG) and Neutral Red (NR) dyes from wastewater. Our synthesized samples underwent comprehensive characterization employing a suite of analytical techniques including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, and UV–Visible measurements. The XRD analysis unequivocally confirmed the formation of CdFe₂O₄ at 700 °C, showcasing a distinct cubic phase structure. Moreover, FTIR spectroscopy unveiled two typical bands at 412 cm⁻¹ and 603 cm⁻¹ for the studied spinel. SEM imaging revealed a unique microstructure characterized by aggregated pseudo-spherical grains of varying sizes and a plethora of pores. BET analysis demonstrated that the prepared CdFe₂O4 powder boasted a substantial specific surface area of 9.58 m²/g along with a notable pore volume. Our optical and photocatalytic assessments elucidated CdFe₂O₄ spinel powder as a semiconductor material featuring a band gap of 2.37 eV, showcasing commendable photocatalytic activity against the targeted dyes. Noteworthy is the attainment of a remarkable removal efficiency of 79.07% for MG and 92.34% for NR following a mere 180 min of exposure to visible light irradiation.

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.

Graphical Abstract

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.

A number of Ce_1-xMn_x catalysts with different Mn contents were prepared by resol-assisted cationic coordinative co-assembly approach and used for the synthesis of dimethyl carbonate (DMC) from CO₂ and methanol. Multiple characterizations of XRD, FT-IR, TEM, BET, CO₂-TPD, NH₃-TPD, H₂-TPR, XPS analyses were applied to investigate the surface properties of the Ce_1-xMn_x catalysts. It turned out that adjusting the proper concentration of Mn ions not only increased the pore volumes, but also improved the content of medium acidic and medium basic sites. When a small amount of Mn was added, the presence of Mn²⁺ on the catalyst surface enhanced, facilitating the conversion of Ce⁴⁺ to Ce³⁺, and leading to higher oxygen vacancy concentration. Consequently, the adsorption and activation of CO₂ and methanol were promoted, and the catalytic efficiency of the reaction was improved. It was found that Ce_0.95Mn_0.05 catalyst exhibited the best catalytic activity, achieving a high DMC yield of 6.44 mmol/g (120 °C, 6.5 MPa, 4 h).

Graphical Abstract

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.