Kinetic Approach Research Articles

Nitrogen‐doped reduced graphene oxide/Fe2O3 hybrid as efficient catalyst for ammonium nitrate

AbstractIn this investigation, we successfully synthesized a hybrid material, N‐rGO@Fe2O3, via a one‐step hydrothermal process, comprising nitrogen‐doped reduced graphene oxide and α‐Fe2O3. Thorough characterization using diverse analytical methods validated its structure. Employing this hybrid composite as a catalyst, we studied its efficacy in the catalytic thermal decomposition of ammonium nitrate (AN). The N‐rGO@Fe2O3/AN composite was prepared using a recurrent spray coating method with 3 % mass of the hybrid material. Thermo‐gravimetric (TG) and differential scanning calorimetric (DSC) analyses were employed to investigate the catalytic effect. Computational assessment of Arrhenius parameters was conducted through isoconversional kinetic approaches. Results from the kinetic analysis allowed the determination of the critical ignition temperature. Furthermore, calorific values for pure AN and N‐rGO@Fe2O3/AN were measured using an oxygen calorimetric bombe, revealing a 41 % reduction in activation energy barrier and a lowering of the critical ignition temperature from 292 °C to 283 °C upon incorporation of the hybrid material. Notably, the surface modification of AN with N‐rGO@Fe2O3 resulted in an increase of 1440 J/g in the observed calorific values. These findings highlight the potential of N‐rGO@Fe2O3 as an effective catalyst, offering promising implications for applications in enhancing ammonium nitrate thermal decomposition.

Investigating the effects of drying on the physical properties of Kombucha Bacterial Cellulose: Kinetic study and modeling approach

Kombucha bacterial cellulose (KBC), obtained as a by-product of tea fermentation, has potential applications in diverse fields. The high water content and presence of post-fermentation residues necessitate the implementation of suitable drying conditions that can significantly affect the final characteristics of this versatile biopolymer. Thus, to study the effect of different drying methods on its properties, KBC was subjected to microwave drying (180–900 W), hot air oven drying (30–70 °C), and shade drying (25 °C). Additionally, the acquired data were fitted into ten different models to study the drying kinetics of KBC. The dried sheets were then analyzed to study the changes in water absorption and holding capacity, rehydration, surface color, and other physicomechanical properties (UTM, XRD, and contact angle analysis). Hence, optimization of the drying conditions will help reduce the time and cost without compromising any of the intrinsic properties that allow it to be processed into various value-added products.

Turbulence spreading by resonant wave-wave interactions: A fractional kinetics approach.

This paper is concerned with the processes of spatial propagation and penetration of turbulence from the regions where it is locally excited into initially laminar regions. The phenomenon has come to be known as "turbulence spreading" and witnessed a renewed attention in the literature recently. Here, we propose a comprehensive theory of turbulence spreading based on fractional kinetics. We argue that the use of fractional-derivative equationspermits a general approach focusing on fundamentals of the spreading process regardless of a specific turbulence model and/or specific instability type. The starting point is the Hamiltonian of resonant wave-wave interactions, from which a family of scaling laws for the asymptotic spreading is derived. Both three- and four-wave interactions are considered. The results span from a subdiffusive spreading in the parameter range of weak chaos to avalanche propagation in regimes with population inversion. Attention is paid to how nonergodicity introduces weak mixing, memory and intermittency into spreading dynamics, and how the properties of non-Markovianity and nonlocality emerge from the presence of islands of regular dynamics in phase space. Also we resolve an existing question concerning turbulence spillover into gap regions, where the instability growth is locally suppressed, and show that the spillover occurs through exponential (Anderson-like) localization in case of four-wave interactions and through an algebraic (weak) localization in case of triad interactions. In the latter case an inverse-cubic behavior of the spillover function is found. Wherever relevant, we contrast our findings against the available observational and numerical evidence, and we also commit ourselves to establish connections with the models of turbulence spreading proposed previously.

Organocatalytic desymmetrization provides access to planar chiral [2.2]paracyclophanes

Planar chiral [2.2]paracyclophanes consist of two functionalized benzene rings connected by two ethylene bridges. These organic compounds have a wide range of applications in asymmetric synthesis, as both ligands and catalysts, and in materials science, as polymers, energy materials and dyes. However, these molecules can only be accessed by enantiomer separation via (a) time-consuming chiral separations and (b) kinetic resolution approaches, often with a limited substrate scope, yielding both enantiomers. Here, we report a simple, efficient, metal-free protocol for organocatalytic desymmetrization of prochiral diformyl[2.2]paracyclophanes. Our detailed experimental mechanistic study highlights differences in the origin of enantiocontrol of pseudo-para and pseudo-gem diformyl derivatives in NHC catalyzed desymmetrizations based on whether a key Breslow intermediate is irreversibly or reversibly formed in this process. This gram-scale reaction enables a wide range of follow-up derivatizations of carbonyl groups, producing various enantiomerically pure planar chiral [2.2]paracyclophane derivatives, thereby underscoring the potential of this method.

Kinetic plasma-wall interaction using immersed boundary conditions

The interaction between a plasma and a solid surface is studied in a (1D-1V) kinetic approach using immersed boundary conditions and penalization to model the wall. Two solutions for the penalized wall region are investigated that either allow currents to flow within the material boundary or not. Essential kinetic aspects of sheath physics are recovered in both cases and their parametric dependencies investigated. Importantly, we show how the two approaches can be reconciled when accounting for relevant kinetic effects. Non-Maxwellian features of the ion and electron distribution functions are essential to capture the value of the potential drop in the sheath. These features lead to a sheath heat transmission factor for ions 60% larger than usually predicted and 35% for electrons. The role of collisions is discussed and means of incorporating minimally-relevant kinetic sheath physics in the gyrokinetic framework are discussed.

Total Synthesis of Keramaphidin B and Ingenamine by Base-Catalyzed Diels-Alder Reaction Using Dynamic Regioselective Crystallization.

The control of the selectivity is a central issue in the total synthesis of complex natural products. In this paper, we report the total synthesis of (±)-keramaphidin B and (±)-ingenamine. The key reaction is a DMAP-catalyzed Diels-Alder reaction in which the regioselectivity is completely controlled by dynamic crystallization. Our synthesis successfully demonstrates that dynamic crystallization can be an alternative when the selectivity is not controlled by either kinetic or thermodynamic approaches in solution.

Exploring bioenergy prospects from malt bagasse: Insights through pyrolysis with multi-component kinetic analysis and thermodynamic parameter estimation

Malt bagasse is a by-product of little commercial value in the brewing industry. Under this scenario, the current study represents the first investigation aiming to determine the kinetic triplet and thermodynamic parameters for malt bagasse pyrolysis using a multi-component kinetic approach to elucidate its bioenergy prospects. The pyrolysis progress profiles of malt bagasse were obtained through slow pyrolysis experiments on a thermogravimetric scale in an inert atmosphere, employing four distinct heating rates (10, 15, 25, and 40 °C min−1). This investigation also used the Frazer-Suzuki deconvolution function to elucidate the relative contributions of hemicellulose, cellulose, and lignin to malt bagasse pyrolysis. Activation energies for devolatilization reactions were determined by the isoconversional methods of Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink, and revealed the lowest and highest mean values for pseudo-hemicelluloses (158.3−215.3 kJ mol−1) and pseudo-lignin (279.5−294.8 kJ mol−1), respectively. Frequency factors in malt bagasse pyrolysis ranging from 8.9 × 1016 and 2.2 × 1023 min−1 offer evidence of a simplified reaction chemistry pathway in the conversion towards bioenergy production. The integral master plot indicates the involvement of order-based and geometrical contraction-based mechanisms in malt bagasse pyrolysis. After defining multiple kinetic triplets, a differential equation encompassing contributions from all pseudo-components was formulated, and the simulated results aligned closely with experimental data, accurately describing pyrolysis progress profiles with at least 92.8% precision. The thermodynamic analysis reveals positive ΔH and ΔG values, indicating the non-spontaneous nature of malt bagasse pyrolysis. Higher disorder in the resultant products is attributed to volatile release and molecular rearrangement and is signified by positive ΔS values compared to the initial reactants. This study provided valuable insights into the valorization of malt bagasse, offering crucial information for optimizing pyrolysis reactors, scaling, and designing malt bagasse conversion into valuable biofuels, constituting an effort towards bio-circular economy principles based on the zero-waste concept.

Optimized coupling of photocatalysis and cavitation for phenol degradation: Use of an extended-kinetic approach

The coupling of hydrodynamic cavitation (HC) and photocatalysis (PC) predominantly exhibits a complementary nature, which is highlighted through a synergistic index. However, this calculation, based on pseudo-first order kinetics, fails to accurately represent the concentration data, often skewed by the formation of reaction intermediates. To address this, an ‘extended’ kinetic approach previously developed with two parameters, which accounts for the formation of intermediates, was adopted. The PC process was optimized for a simulated wastewater containing phenol of concentration (C0) of 100 ppm by applying a UV-A light source of intensity 175 ± 8 W/cm2 on an operating volume (VL) of 200 mL. Catalyst loading, solution pH and initial concentration (C0) were optimized. These optimal parameters were used to operate HC-PC (VL = 3500 mL) at a comparable illumination intensity across the 2 techniques’ reactors. It was observed that phenol conversion was observable only with halved C0 (= 50 ppm) for the HC-PC system, increasing catalyst loading from 0.5 to 1.0 g/L exhibited no increase in phenol conversion. The obtained results from experiments were interpreted with the help of the two-parameter model. For the PC system, the initial rate constant (k0) exhibits a similar trend to the final oxidation extent, however, it did not compare quantitatively. The second parameter – ‘y’ showed a high finite value, denoting the need for dosing external oxidants. The trends of the two-parameters with respect to different relevant parameters presented will help leverage this kinetic approach for AOPs, while optimizing and translating processes to larger scales of operation.

Degradation of Methyl Red Azo Dye by Hexacyanoferrate(III) Ions from Water using Ultrafine Ir–Cu Bimetallic Nanoparticles: a Kinetic Approach

Degradation of Methyl Red Azo Dye by Hexacyanoferrate(III) Ions from Water using Ultrafine Ir–Cu Bimetallic Nanoparticles: a Kinetic Approach

Quantum kinetic approach to the Schwinger production of scalar particles in an expanding universe

Quantum kinetic approach to the Schwinger production of scalar particles in an expanding universe

The Generation of 150 km Echoes Through Nonlinear Wave Mode Coupling

AbstractA fundamental problem in plasma turbulence is understanding how energy cascades across multiple scales. In this paper, a new weak turbulence theory is developed to explain how energy can be transferred from Langmuir and Upper‐Hybrid waves to ion‐acoustic waves. A kinetic approach is used where the Boltzmann equation is Fourier‐Laplace transformed, and the nonlinear term is retained. A unique feature of this approach is the ability to calculate power spectra at low frequencies, for any wavelength or magnetic aspect angle. The results of this theory explain how the predominant type of 150‐km radar echoes are generated in the ionosphere. First, peaks in the suprathermal electron velocity distribution drive a bump‐on‐tail like instability that excites the Upper‐Hybrid mode. This excited wave then couples nonlinearly to the ion‐acoustic mode, generating the ∼10 dB enhancement observed by radars. This theory also explains why higher frequency radars like ALTAIR do not observe these echoes.

Kinetic Model for the Heterogeneous Biocatalytic Reactions Using Tethered Cofactors.

Understanding the mechanism of interfacial enzyme kinetics is critical to the development of synthetic biological systems for the production of value-added chemicals. Here, the interfacial kinetics of the catalysis of β-nicotinamide adenine dinucleotide (NAD+)-dependent enzymes acting on NAD+ tethered to the surface of silica nanoparticles (SiNPs) has been investigated using two complementary and supporting kinetic approaches: enzyme excess and reactant (NAD+) excess. Kinetic models developed for these two approaches characterize several critical reaction steps including reversible enzyme adsorption, complexation, decomplexation, and catalysis of the surface-bound enzyme/NAD+ complex. The analysis reveals a concentrating effect resulting in a very high local concentration of enzyme and cofactor on the particle surface, in which the enzyme is saturated by surface-bound NAD, facilitating a rate enhancement of enzyme/NAD+ complexation and catalysis. This resulted in high enzyme efficiency within the tethered NAD+ system compared to that of the free enzyme/NAD+ system, which increases with decreasing enzyme concentration. The role of enzyme adsorption onto solid substrates with a tethered catalyst (such as NAD+) has potential for creating highly efficient flow biocatalytic systems.

Assessment of captan pesticide stability by thermal and spectroelectrochemical analysis

In this study, thermal analysis and electrochemical methods were used to evaluate the stability of captan pesticide (CPTN). Simultaneous Thermogravimetry (TG), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) were successfully applied to study the stability of CPTN in the temperature range from 20 to 600 °C. The stability evaluation of CPTN by spectroelectrochemical analysis was carried out using cyclic voltammetry (CV) and electrolysis at constant current density in association with UV−Vis spectrophotometry. Thermoanalytical results revealed a relative stability of CPTN up to a temperature of 154 °C, and above this temperature the pesticide molecule undergoes irreversible degradation. The kinetic approach of the electrochemical results on the electrochemical degradation of CPTN showed a rate constant of 0.02 min−1 in the presence of chloride ions and 0.089 min−1 in the presence of bromide ions. Thermal and electrochemical methods are considered effective strategies applied in order to eliminate pesticides from polluted waters, and the choice of optimal parameters can considerably increase the efficiency of decontamination. The study also aims to provide insights into electrode processes to address the mechanism of electrochemical degradation.

Adsorptive removal of Cu(II) ions from aqueous solution using Teff (Eragrostis tef) hay based magnetized biocarbon: RSM-GA, ANN based optimization and kinetics aspects

Abstract Teff (Eragrostis tef) is known as a staple grain crop which grown as edible seeds, remarkably in Ethiopia. However, after removal of its seeds, the hay obtained from this crop, are considered as agro-waste. Such a lignocellulosic agro-waste can be potentially exploited to prepare activated carbon to treat the harmful industrial effluents for detoxification. In this study, Teff hay (TH) was used as a precursor for preparing the activated carbon. The using H2SO4, chemical activation was carried out followed by carbonaceous process was undertaken to prepared activated carbon (AC) by pyrolysis. The prepared AC was modified as magnetized AC and characterized by various characterization methods. Further, as a bio-absorbent, its potency for adsorptive removal of Cu(II) ions was ascertained. Notably, the most studied and important process factors for adsorption, such as, initial concentration of metal ion, adsorbent dosage, pH, and contact time were subjected to optimization using response surface method (RSM). Further, to ensure the statistical optimization of aforementioned factors, the non-statistical techniques, genetic algorithm (GA) and artificial neural network (ANN) tools have been executed. In addition, the use of prepared Teff-hay based magnetized AC for the removal of Cu(II) by adsorption process was evaluated through different isotherms and kinetic approaches.

Microwave catalytic pyrolysis of heavy oil: A lump kinetic study approach

Managing heavy oil (HO) has become a vital issue in terms of environmental considerations. Microwave pyrolysis of HO is one of the efficient methods of upgrading and recycling this complex material. In this work, microwave catalytic pyrolysis (MCP) of HO was explored by investigating the effect of heating time (2–10 minutes) and temperature (460–730ºC) on the product yield and quality. The most critical point of this study was utilizing a unique design of SiC foam@HZSM-5 as a microwave absorber and catalyst simultaneously. This special design could eliminate the main problem of previous studies: the unwanted temperature gradient inside the reactor, which was misleading the prediction of kinetic parameters by recording the wrong temperature. The yield of each product’s category from the MCP process was reconstructed through a biharmonic spline interpolation (BSI) algorithm to visualize the simultaneous effect of the heating time and temperature on the yield. The optimum temperature for the MCP process was about 600ºC and a heating time of 6 minutes, which yielded the most valuable hydrocarbons in liquid and gas products. The produced liquid oil and non-condensable gases were analyzed through GC-MS and the collected results were categorized based on the properties of the detected compounds. An eight-lump kinetic model was then proposed based on that categorization. The calculated pre-exponential factors (k0) were higher than the expected values, while the apparent activation energies (Ea) were considerably lower than the reported data in the literature, which was due to the non-thermal and thermal effects of microwave irradiation on the reaction mechanism. The validation of the proposed model indicated the capability of this model to predict reliable data under these conditions.

The Environmental Oxidation of Acetaminophen in Aqueous Media as an Emerging Pharmaceutical Pollutant Using a Chitosan Waste-Based Magnetite Nanocomposite

Clean water is a precious and limited resource that plays a crucial role in supporting life on our planet. However, the industrial sector, especially the pharmaceutical industry, significantly contributes to water consumption, and this can lead to water body pollution. Fenton’s reagent was introduced in the current investigation to oxidize acetaminophen as an emerging pollutant in such effluents. Therefore, we employed a straightforward co-precipitation method to fabricate chitosan-coated magnetic iron oxide, which is referred to in this study as Chit@Fe3O4. X-ray diffraction spectroscopy (XRD), Fourier transform infrared (FTIR), diffuse reflectance spectra (DRS), scanning electron microscopy (TEM), and transmission electron microscopy (TEM) were utilized to characterize the sample. It is crucial to treat such effluents due to the rapid increase in emerging pollutants. In this study, a photo-Fenton system was introduced as a combination of a Chit@Fe3O4 catalyst augmented with hydrogen peroxide under ultraviolet (UV) illumination conditions. The results reveal that only 1 h of irradiance time is efficient in oxidizing acetaminophen molecules. Doses of 20 and 200 mg/L of Chit@Fe3O4 and H2O2, respectively, and a pH of 2.0 were recorded as the optimal operational conditions that correspondingly oxidize 20 mg/L of acetaminophen to a 95% removal rate. An increase in the reaction temperature results in a decline in the reaction rate, and this, in turn, confirms that the reaction system is exothermic in nature. The sustainability of the catalyst was verified and deemed adequate in treating and oxidizing acetaminophen, even up to the fourth cycle, achieving a 69% removal rate. A kinetic modeling approach is applied to the experimental results, and the kinetic data reveal that the oxidation system conforms to second-order kinetics, with rate constants ranging from 0.0157 to 0.0036 L/mg·min. Furthermore, an analysis of the thermodynamic parameters reveals that the reaction is exothermic and non-spontaneous, predicting an activation energy of 36.35 kJ/mol. Therefore, the proposed system can address the limitations associated with the homogeneous Fenton system.

Adsorption of Methylene Blue Dye and Analysis of Two Clays: A Study of Kinetics, Thermodynamics, and Modeling with DFT, MD, and MC Simulations.

The purpose of this research was to learn more about the primary and secondary properties of Moroccan natural clay in an effort to better investigate innovative adsorbents and gain access to an ideal adsorption system. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis (SEM-EDX) and X-ray fluorescence were employed for identification. SEM revealed clay grains, including tiny particles and unevenly shaped sticks. First- and second-order rate laws, representing two distinct kinetic models, were applied in the kinetic approach. Adsorption of dye MB onto natural clay was studied, and the results agreed with the 2 s order model. The significant correlation coefficients support the inference that the adsorption process was governed by the Langmuir model. Subsequent DFT analyses demonstrated that the methylene blue dye's HOMO and LUMO surfaces are dispersed across most of the dye's components, pointing to a strong interaction with the clay. To determine how the dye might be adsorbed onto the clay, we employed quantum descriptors to locate its most nucleophilic and electrophilic centers. Endothermic reactions are evident during the MB adsorption process on clay, as indicated by the positive values of ΔH0 and ΔS0 (70.49 kJ mol-1of RC and 84.19 kJ mol-1 of OC and 10.45 J mol-1 K-1 of RC and 12.68 mol-1 K-1 of OC, respectively). Additionally dye molecules on the adsorbent exhibit a higher order of distribution than in the solution, indicating that the adsorption process is spontaneous.

Deciphering SO2 poisoning mechanisms for passive NOx adsorption: A kinetic modeling approach and development of a high-resistance catalyst

Passive NOx adsorption (PNA) is a promising technology aimed at reducing NOx emissions from vehicles during the cold start phase of the engine. This work investigated the SO2 poisoning mechanism of PNA through a combination of experimental research and kinetic modeling, leading to the development of a novel PNA sample with high resistance to SO2 poisoning. Pd/SSZ-13 samples were synthesized using different drying conditions, revealing that samples dried at room temperature showed lower degradation (10 %) compared to those dried at 80 °C (26 %). Investigation into the degradation revealed that ion-exchanged Pd sites with a hydroxyl group were more resistant to SO2 poisoning than other Pd sites. It is also found that SO2 aids in NOx storage on Pd sites, enhancing the PNA performance. A kinetic model was developed to describe the SO2 poisoning behavior and its influence on NOx storage. The model, which was verified under various conditions, effectively simulated the PNA behavior and SO2 poisoning of Pd/SSZ-13.

Analysis of Photochemical Characteristics and Sensitivity of Atmospheric Ozone in Nanjing in Summer

Tropospheric ozone (O3) is mainly produced through a series of photochemical reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). The reaction process presents complex non-linear relationships. In this work, datasets of atmospheric ozone and volatile organic compounds (VOCs) observed during the summer of 2018 in Nanjing were used. Combining with the framework for 0-D atmospheric model-master chemical mechanism (F0AM-MCM), the characteristics of photochemical reactions for ozone (O3) formation in Nanjing during the O3 episode days and non-episode days were investigated. The results showed that φ(O3) and φ(TVOCs) in the O3 episode days were 47.8×10-9 and 49.0×10-9, respectively, exceeding those in the non-episode days by factors of 1.8 and 1.6. Furthermore, F0AM, the empirical kinetic modeling approach (EKMA), and relative incremental reactivity (RIR) were utilized for the calculation of ozone chemical sensitivity. It was found that O3 formation in Nanjing was attributed to both VOCs and NOx limitation. In addition, the modeled ·OH and HO2 concentrations in the O3 episode days were 1.3 and 1.8 times higher than those in the non-episode days. The higher formation and loss rates of ·OH and HO2 were also found during O3 episode days. These findings reflected that the enhancements of atmospheric oxidation capacity resulted in increased production rates of O3, providing an explanation for the enhancements of O3 concentrations in Nanjing during the O3 episode days. The findings also improved the understanding of the O3 photochemical characteristics over Nanjing in the summer during the O3 episode days.

Elucidating uptake and metabolic fate of dipeptides in CHO cell cultures using 13C labeling experiments and kinetic modeling

The rapidly growing market of biologics including monoclonal antibodies has stimulated the need to improve biomanufacturing processes including mammalian host systems such as Chinese Hamster Ovary (CHO) cells. Cell culture media formulations continue to be enhanced to enable intensified cell culture processes and optimize cell culture performance. Amino acids, major components of cell culture media, are consumed in large amounts by CHO cells. Due to their low solubility and poor stability, certain amino acids including tyrosine, leucine, and phenylalanine can pose major challenges leading to suboptimal bioprocess performance. Dipeptides have the potential to replace amino acids in culture media. However, very little is known about the cleavage, uptake, and utilization kinetics of dipeptides in CHO cell cultures. In this study, replacing amino acids, including leucine and tyrosine by their respective dipeptides including but not limited to Ala-Leu and Gly-Tyr, supported similar cell growth, antibody production, and lactate profiles. Using 13C labeling techniques and spent media studies, dipeptides were shown to undergo both intracellular and extracellular cleavage in cultures. Extracellular cleavage increased with the culture duration, indicating cleavage by host cell proteins that are likely secreted and accumulate in cell culture over time. A kinetic model was built and for the first time, integrated with 13C labeling experiments to estimate dipeptide utilization rates, in CHO cell cultures. Dipeptides with alanine at the N-terminus had a higher utilization rate than dipeptides with alanine at the C-terminus and dipeptides with glycine instead of alanine at N-terminus. Simultaneous supplementation of more than one dipeptide in culture led to reduction in individual dipeptide utilization rates indicating that dipeptides compete for the same cleavage enzymes, transporters, or both. Dipeptide utilization rates in culture and cleavage rates in cell-free experiments appeared to follow Michaelis-Menten kinetics, reaching a maximum at higher dipeptide concentrations. Dipeptide utilization behavior was found to be similar in cell-free and cell culture environments, paving the way for future testing approaches for dipeptides in cell-free environments prior to use in large-scale bioreactors. Thus, this study provides a deeper understanding of the fate of dipeptides in CHO cell cultures through an integration of cell culture, 13C labeling, and kinetic modeling approaches providing insights in how to best use dipeptides in media formulations for robust and optimal mammalian cell culture performance.