Kinetic Aspects Research Articles

Theoretical study of the mechanism of the hydrogen evolution reaction on the V2C MXene: Thermodynamic and kinetic aspects

Both experimentally and theoretically, the MXene family has shown promising hydrogen evolution reaction (HER) capabilities. However, so far, the theoretical approach has been relying on the well-known thermodynamic descriptor, ΔGH, whereas experimental studies report Tafel plots, containing kinetic rather than thermodynamic information. Aiming to link theory to experiments, the present study explores five different HER pathways over the exemplary V2C (0001) MXene by density functional theory calculations. While the surface coverage under HER conditions (with either H* or OH* adsorbates) is extracted from a Pourbaix diagram, we determine the energetics of the reaction intermediates and transition states for both surface species as active sites. This enables the construction of free-energy diagrams for the Volmer-Heyrovsky and Volmer-Tafel mechanisms and allows for the simulation of Tafel plots by a rigorous microkinetic framework. While the active-site motif V2C-OH seems to be less relevant for the HER under typical reaction conditions, we demonstrate that the HER is kinetically facile on the V2C-H surface. For this surface termination, we report a potential-depending switching of the preferred mechanism from the Volmer-Heyrovsky to the Volmer-Tafel description with increasing overpotential while encountering similarities to the HER over Pt.

Thermodynamic, kinetic and dynamic aspects of biogas upgrading using nano-engineered grazynes

Different nano-engineered grazynes have been studied as possible membranes to separate methane (CH4) from carbon dioxide (CO2) by density functional theory (DFT) and molecular dynamics (MD) computational simulations. The study tackles the process thermodynamics, kinetics, and dynamical aspects associated to the diffusion rates and selectivities in the context of biogas upgrading while comparing to other materials available in the literature. Small adsorption energy values have been obtained for three semi-permeable grazynes, with low diffusion energy barriers which severely reduce as long as the grazyne pore increases. Selectivities towards CO2 permeation as large as 39 are found at high pressures for [1],[2]{2}-grazyne, closely followed by [1],[2]{(00),2}-grazyne, posing grazynes as excellent membranes for biogas upgrading with clear advantages compared to scrubbing materials in terms of much improved selectivity, continuous workflow and an order of magnitude larger quantity of separated CO2 per material gram. Present computational simulations reveal that grazynes could be able to upgrade biogas beyond 97 % (v/v) in methane, accomplishing standard worldwide government requirements.

Kinetic Aspects of Benzene Degradation over TiO2-N and Composite Fe/Bi2WO6/TiO2-N Photocatalysts under Irradiation with Visible Light

In this study, composite materials based on nanocrystalline anatase TiO2 doped with nitrogen and bismuth tungstate are synthesized using a hydrothermal method. All samples are tested in the oxidation of volatile organic compounds under visible light to find the correlations between their physicochemical characteristics and photocatalytic activity. The kinetic aspects are studied both in batch and continuous-flow reactors, using ethanol and benzene as test compounds. The Bi2WO6/TiO2-N heterostructure enhanced with Fe species efficiently utilizes visible light in the blue region and exhibits much higher activity in the degradation of ethanol vapor than pristine TiO2-N. However, an increased activity of Fe/Bi2WO6/TiO2-N can have an adverse effect in the degradation of benzene vapor. A temporary deactivation of the photocatalyst can occur at a high concentration of benzene due to the fast accumulation of non-volatile intermediates on its surface. The formed intermediates suppress the adsorption of the initial benzene and substantially increase the time required for its complete removal from the gas phase. An increase in temperature up to 140 °C makes it possible to increase the rate of the overall oxidation process, and the use of the Fe/Bi2WO6/TiO2-N composite improves the selectivity of oxidation compared to pristine TiO2-N.

Handrim Wheelchair Propulsion Technique in Individuals With Spinal Cord Injury With and Without Shoulder Pain: A Cross-sectional Comparison.

The aim of this study was to compare handrim wheelchair propulsion technique between individuals with spinal cord injury with and without shoulder pain. A cross-sectional study including 38 experienced handrim wheelchair users with spinal cord injury was conducted. Participants were divided into the "shoulder pain" ( n = 15) and "no-shoulder pain" ( n = 23) groups using the Local Musculoskeletal Discomfort scale. Kinetic and spatiotemporal aspects of handrim wheelchair propulsion during submaximal exercise on a motor-driven treadmill were analyzed. Data were collected using a measurement wheel instrumented with three-dimensional force sensors. After correction for confounders (time since injury and body height), linear regression analyses showed that the pain group had a 0.30-sec (95% confidence interval, -0.5 to -0.1) shorter cycle time, 0.22-sec (95% confidence interval, -0.4 to -0.1) shorter recovery time, 15.6 degrees (95% confidence interval, -27.4 to -3.8) smaller contact angle, and 8% (95% confidence interval, -15 to 0) lower variability in work per push compared with the no-pain group. Other parameters did not differ between groups. This study indicates that individuals with spinal cord injury who experience shoulder pain propel their handrim wheelchair kinematically differently from individuals with spinal cord injury without shoulder pain. This difference in propulsion technique might be a pain-avoiding mechanism aimed at decreasing shoulder range of motion.

CO Oxidation Reaction by Platinum Clusters on the Surface of Multiwalled Carbon Nanotubes: Experimental and Theoretical Study of Kinetics in a Wide Range of O2/CO Ratios

This work presents a systematic study of the kinetic aspects of CO oxidation reaction catalyzed by platinum nanoparticles (NPs) supported on the surface of multiwalled carbon nanotubes (MWCNTs). The investigation presented is closely related to the actual practical task of air purification in enclosed spaces. Therefore, the catalytic reaction was carried out in the presence of an excess of oxygen (5 vol.%) and over a wide range of CO concentrations from 50 ppm to 1600 ppm. For the catalyst characterization, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were applied. Kinetic modelling based on the Langmuir–Hinshelwood and Mars-van Krevelen mechanisms was taken as a basis, using the results obtained on Pt foil. Simulation of CO oxidation reaction on platinum NPs at temperatures above 90 °C was carried out using a kinetic model describing the reaction mechanism on bulk platinum. The description of the kinetics of CO oxidation reaction on Pt NPs over the entire temperature range, including the low temperatures down to −40 °C, required the introduction of the steps characterizing an additional concerted mechanism related to CO-assisted O2 dissociation. Using the presented model, some predictions of the kinetic behaviour of the system were made.

An introduction to one- and two-dimensional lineshape analysis of chemically exchanging systems

Molecules are dynamic entities, and understanding intra- and inter-molecular reactions and changes in conformation is one of the most fascinating, important and complex subjects in NMR. Conformational changes and chemical reactions result in observed spins exchanging between different magnetic environments, and the sensitivity of NMR spectra to such dynamic processes has been recognised since the earliest days of the field. Careful analysis of such spectra, acquired using one- or two-dimensional experiments, can provide insight into structural, thermodynamic, kinetic and mechanistic aspects of the underlying exchange process. The theoretical principles of these lineshape analysis methods will be introduced in this article, alongside a practical discussion of calculation methods, data acquisition and analysis software.

Theoretical study of formation mechanism for 4-methyl-3-phenylbenzonitrile in the course of the Hiyama and Suzuki–Miyaura reactions

A theoretical study on the mechanism of conversion of 3-bromo-4-methylbenzonitrile into 4-methyl-3-phenylbenzo-nitrile in the course of the Suzuki–Miyaura and Hiyama−Denmark cross-coupling reactions has been performed at Cam-B3LYP-D3 level of theory. With the use of Pd–NHC type complex as the catalyst, the Hiyama−Denmark cross-coupling is best suited for this process from both thermodynamic and kinetic aspects.

Research on aspects of the extraction kinetics of metabolites of Сarlina acaulis while mixing

This study reports the features of the mass transfer kinetics during the extraction of phenolic compounds and flavonoids from the Carlina acaulis roots. The extraction process of target compounds was optimized and the mathematical model was selected, which implies that the mass transfer of target compounds occurs during the extraction of the solid phase (plant cells) into the liquid phase (extractant). The most effective hydrodynamic conditions for the production of phenolic compounds and flavonoids were determined. An experimental verification of the kinetic equation was carried out by extracting the target compounds from the studied object of various sizes in a vessel with a stirrer using 40% and 70% ethanol as an extractant. The results of the experiment indicated that the target compounds extraction process, namely phenolic compounds and flavonoids from the Carlina acaulis roots, proceeds more efficiently under stirring conditions when using particles with a diameter of 2 mm and 70% ethanol as an extractant. The experimental data are in good agreement with the theoretically calculated results, which confirms the appropriateness of using the selected mathematical model. Studies of the kinetics of Carlina acaulis roots extraction process will allow minimizing the losses of target compounds, and improving the extraction process and the quality of final product.

Organic Inhibitors of Metal Corrosion in Acid Solutions. I. Mechanism of Protective Action

The review summarizes and analyzes the current state of research in the field of corrosion of metals in acid solutions and their inhibitory protection. The most important concepts about the metal corrosion mechanism in acidic media were considered. The existing experimental approaches to the study of metal corrosion in acid solutions and the effect of organic corrosion inhibitors on this process were discussed. It was shown that electrochemical and physicochemical methods play an important role in studies of the state of the metal surface. The mechanisms of metal corrosion inhibition in acid media were analyzed. The thermodynamic and kinetic aspects of adsorption of inhibitors on metals were considered. The maximum efficiency in metal protection is shown by organic compounds whose molecules are capable of chemisorption interaction with the metal surface, forming polymolecular protective layers of molecules chemically bonded with one another.

A Thermodynamic and Kinetic Study on Electrochemical Esterification in Aroma-Enhanced Distilled Liquor (Baijiu)

The development of low-alcohol Baijiu is consistent with demand for the industry’s sustainable development. However, the ester aroma of low-alcohol Baijiu is insipid and unstable—mainly due to the hydrolysis of esters during shelf life—thus reducing the industry scale of low-alcohol Baijiu to a significantly small range. An electrochemical method for improving low-alcohol Baijiu’s ester concentration and stability was investigated from the aspects of thermodynamics and kinetics. The key finding is that the new Baijiu’s ester content obtained through distillation is relatively high, exceeding its content in the thermodynamic equilibrium state. Thus, the ester will be hydrolyzed during shelf life. The idea of applying electrochemical catalytic esterification technology to the production of low-alcohol Baijiu in this study is directly derived from the production practice of Baijiu factories; it provides a direction for the further optimization of low-alcohol Baijiu to facilitate the production of an alternative product that will contribute to public health.

Key element course-tracked copyrolysis of sewage sludge and biomass for resource recovery and pollution control through kinetic and thermodynamic insights

Ameliorating sewage sludge (SS) pyrolysis process with biomass increasingly becomes an effective strategy to utilize SS-entraining resources and depress pollutant evolution, while real-time track of SS and biomass copyrolysis as well associating thermochemical reactions in aspects of kinetics and thermodynamics is yet to be unveiled. Here a combinative thermogravimetry combined with Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry (TG-FTIR-GC/MS) pyrolysis system, lab-scale furnace and theoretical calculation were adopted to develop a key element course-tracked copyrolysis of SS and corn stalk (CS) for simultaneous accommodation of profitable products and derived pollutants. The formation of alkanes and alkene with small carbon number (below 4) was promoted during copyrolysis, while those with heavy carbons (over 5) were contributed by the inherent organic fraction of SS. The release of those nitrogen (N)-/sulfur-/chlorine-involving inorganic pollutants was depressed with the increase in the CS addition. The increased release of CO2 and H2O as well carboxylic volatiles with a high CS addition evidenced the promoted dehydroxylation and decarboxylation. Consequently, the speciation of N and phosphorus (P) and the bioavailability of toxic metals (TMs) were regulated with the increasing CS addition, that is, enhancements of proteins and protein-like N transformation to the other nitrogen species, P within orthophosphate diesters to orthophosphate monoesters, and TM reactivity-dependent bioavailability depression. A low addition (below 20 %) was prone to maintain a congruent mechanism, while the total Gibbs energy tended to decrease with an increasing addition and pyrolysis temperature, leading to a converged pressure-constant heat capacity (∼1430 J/K) at 700 °C. Those thermochemical reactions occurring over sewage sludge ash matrix were pivoted with biomass addition, which can be adopted as a useful strategy for an efficient, cleaner and sustainable mining of waste resources.

Reversible Ultrathin PtOx Formation at the Buried Pt/YSZ(111) Interface Studied In Situ under Electrochemical Polarization.

Three different platinum oxides are observed by in situ X-ray diffraction during electrochemical potential cycles of platinum thin film model electrodes on yttria-stabilized zirconia (YSZ) at a temperature of 702 K in air. Scanning electron microscopy and atomic force microscopy performed before and after the in situ electrochemical X-ray experiments indicate that approximately 20% of the platinum electrode has locally delaminated from the substrate by forming pyramidlike blisters. The oxides and their locations are identified as (1) an ultrathin PtOx at the buried Pt/YSZ interface, which forms reversibly upon anodic polarization; (2) polycrystalline β-PtO2, which forms irreversibly upon anodic polarization on the inside of the blisters; and (3) an ultrathin α-PtO2 at the Pt/air interface, which forms by thermal oxidation and which does not depend on the electrochemical polarization. Thermodynamic and kinetic aspects are discussed to explain the coexistence of multiple phases at the same electrochemical conditions.

Kinetic aspects of malachite deposition on marble from copper lactate solutions

Experiments were conducted to study the formation of copper minerals on carbonate material (marble) from lactate solutions. Main kinetic parameters were estimated from the curves of copper ions deposition. The reaction rate constant is 4.19×10 -6 s -1 and the effective diffusion coefficient is 1.39×10 -12 m 2 /s at room temperature (25 °C). IR spectra of sediments show good agreement with natural samples of malachite and azurite (Spassk deposit, Central Kazakhstan). The results show the possibility of using organic complexing agents for intensifying the processes of secondary mineral formation of copper carbonate minerals (malachite and azurite) to prevent the dissipation of heavy metal ions in soluble forms from poor deposits and dumps during their remediation.

Adsorption kinetics studies of ciprofloxacin in soils derived from volcanic materials by electrochemical approaches and assessment of socio-economic impact on human health.

The use of antibiotics in the livestock sector has resulted in the entry of these drugs into the soil matrix through the disposal of manure as an organic amendment. To define the fate of these drugs, it is necessary to evaluate kinetic aspects regarding transport in the soil-solution. The aim of this paper is to evaluate the adsorption kinetic parameters of Ciprofloxacin (CIPRO) in Ultisol and Andisol soil which allows obtaining main kinetic parameters (pseudo-first and pseudo-second order models) and to establish the solute transport mechanism by applying kinetic models such as the Elovich equation, Intraparticle diffusion (IPD) and, the Two-site non-equilibrium models (TSNE). The adsorption kinetics of this fluoroquinolone (FQ), on both soils derived from volcanic ashes, is developed using electrochemical techniques for their determination. The experimental amount of CIPRO adsorbed over time (Qt) data best fit with the pseudo-second order kinetic models; R2 = 0.9855, Ɛ = 10.17% and R2 = 0.9959, Ɛ = 10.77% for Ultisol and Andisol, respectively; and where CIPRO adsorption was considered time dependent for both soils but the lower adsorption capacity in Ultisol; with 17.6 ± 2.8 μmol g−1; which could mean a greater risk in environmental. Subsequently, applying models to describe solute transport mechanisms showed differences in the CIPRO adsorption extent for the fast and slow phases. Adsorption isotherms were evaluated, where Ultisol occurs on heterogenous sites as multilayers and Andisol by monolayer with similar Qmax. Finally, the socio-economic impact of antibiotic usage is presented, giving the importance of antibiotics in the livestock sector and their effects on human health.

Experimental and Computational Exploration of Chitin, Pectin, and Amylopectin Polymers as Efficient Eco-Friendly Corrosion Inhibitors for Mild Steel in an Acidic Environment: Kinetic, Thermodynamic, and Mechanistic Aspects.

Herein, the inhibition impacts of chitin, pectin, and amylopectin as carbohydrate polymers on the corrosion of mild steel in 0.5 M HCl were researched utilizing various experimental and theoretical tools. The acquired outcomes showed that the inhibition efficiencies (% IEs) of the tested carbohydrate polymers were increased by raising their concentrations and these biopolymers acting as mixed-kind inhibitors with major anodic ones. The acquired % IEs values were reduced with rising temperature. The higher % IEs of the tested polymers were inferred via powerful adsorption of the polymeric molecules on the steel surface and such adsorption obeyed the Langmuir isotherm. The computed thermodynamic and kinetic quantities confirmed the mechanism of physical adsorption. The kinetics and mechanisms of corrosion and its protection by polymeric compounds were illuminated. The results obtained from all the techniques used confirmed that there was good agreement with each other, and that the % of IEs followed the sequence: chitin > amylopectin > pectin.

Biosorbent Based on Poly(vinyl alcohol)-Tricarboxi-Cellulose Designed to Retain Organic Dyes from Aqueous Media.

Methylene Blue, a cationic dye, was retained from aqueous solutions using a novel biosorbent made of poly(vinyl alcohol) reticulated with tricarboxi-cellulose produced via TEMPO oxidation (OxC25). The study of the Methylene Blue biosorption process was performed with an emphasis on operational parameters that may have an impact on it (such as biosorbent concentration, pH of the aqueous media, and temperature). The current study focused on three areas: (i) the physic-chemical characterization of the biosorbent (scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX)); (ii) biosorption data modeling to determine the quantitative characteristic parameters employing three equilibrium isotherms (Langmuir, Freundlich, and Dubinin-Radushkevich-DR); and (iii) the study of temperature influence. The results of the study showed that the Langmuir model provided a good fit for the experimental data of biosorption, realizing a maximum capacity of 806.45 mg/g at 20 °C. The free energy of biosorption (E) evaluated by the DR equation was in the range of 6.48-10.86 KJ/mol. The values of the thermodynamic parameters indicated an endothermic process because the free Gibbs energy ranged from -9.286 KJ/mol to -2.208 KJ/mol and the enthalpy was approximately -71.686 KJ/mol. The results obtained encourage and motivate the further study of this biosorption process by focusing on its kinetic aspects, establishing the biosorption's controlled steps, identifying the mechanism responsible for the retention of textile dyes presented in moderate concentration in aqueous media, and studying the biosorption process in a dynamic regime with a view to applying it to real systems.

Batchwise Leaching of Calcium from Demolition Concrete Fines in an Aqueous Ammonium Nitrate Solution: Part 2 Modeling

This article addresses the application of the indirect mineral carbonation process to recycled concrete aggregates (RCA). In such a process, calcium is first leached from the RCA feedstock into an aqueous ammonium nitrate solution and then it is carbonated to precipitate calcium carbonate. The calcium leaching step is modeled in this contribution, whereas it was investigated experimentally in part 1 of this series, where the focus was more on thermodynamic aspects than on kinetics. In this part 2 paper, kinetics aspects are also included by modeling them using two different approaches. In the first approach, the reaction–diffusion model is implemented, accounting for the congruent dissolution of the calcium hydroxide phase and the incongruent dissolution of the calcium silicate hydrate components of concrete fines. In the second approach, a double-shrinking-core model is used, which for the sake of simplicity assumes congruent dissolution of calcium silicate hydrates as well, infinitely fast reaction/dissolution kinetics, and pseudo-steady-state diffusion. The model parameters have been either determined through targeted experiments or estimated by fitting measurements obtained in experiments with two different materials, both in the size range of up to a diameter of 4 mm. Both models exhibit satisfactory accuracy in describing the experimental data; particularly for particles larger than about 0.1 mm in diameter, the two models calculate a nearly identical evolution of the calcium concentration in solution. The simplifications of the double-shrinking-core model lead to a loss of resolution in characterizing the evolution of leaching inside the particles, whereas they enable faster computations. The latter feature makes such a model a convenient tool for studying process performance, namely, productivity, calcium recovery, and solvent efficiency, through parametric analysis; this has been demonstrated as reported in the last part of the article.

Ability of Azathiacyclen Ligands To Stop Cu(Aβ)-Induced Production of Reactive Oxygen Species: [3N1S] Is the Right Donor Set.

Alzheimer's disease (AD) is an incurable neurodegenerative disease that leads to the progressive and irreversible loss of mental functions. The amyloid beta (Aβ) peptide involved in the disease is responsible for the production of damaging reactive oxygen species (ROS) when bound to Cu ions. A therapeutic approach that consists of removing Cu ions from Aβ to alter this deleterious interaction is currently being developed. In this context, we report the ability of five different 12-membered thiaazacyclen ligands to capture Cu from Aβ and to redox silence it. We propose that the presence of a sole sulfur atom in the ligand increases the rate of Cu capture and removal from Aβ, while the kinetic aspect of the chelation was an issue encountered with the 4N parent ligand. The best ligand for removing Cu from Aβ and inhibiting the associated ROS production is the 1-thia-4,7,10-triazacyclododecane [3N1S]. Indeed the replacement of more N by S atoms makes the corresponding Cu complexes easier to reduce and thus able to produce ROS on their own. In addition, the ligand with three sulfur atoms has a weaker affinity for CuII than Aβ, and is thus unable to remove Cu from CuAβ.

Chlorination mechanism and kinetics of cathode materials for spent LiCoO2 batteries in the presence of graphite

In the face of the rapid growth of lithium industry's demand for energy metals, recycling spent lithium-ion batteries (LIBs) has become the key to the sustainable development of related industries. The chlorination roasting process is effective at recycling spent LIBs. Factories usually recycle the black mass as raw material instead of only the cathode material in actual production. The black mass is mainly composed of cathode material and graphite. However, studies on the effect of graphite on the chlorination process of cathode materials are lacking. In this study, the effect of graphite on the chlorination process of cathode materials is investigated, focusing on the reaction mechanism and kinetics aspects. The results show that the presence of graphite can accelerate the destruction of the LiCoO2 structure, thereby reducing the pyrolysis temperature of LiCoO2. The cobalt in the roasted product exists in the form of metallic cobalt rather than cobalt oxide or cobalt chloride. The reaction model of the LiCoO2 chlorination stage conforms to the random nucleation and nuclear growth modes. The mechanism function is g(α) = [-ln(1-α)]3/4. Ea and A are 196.107 kJ/mol and 3.575 × 106, respectively. Furthermore, thermodynamic activation parameters are calculated and equations are established.

Accurate computational simulations of perturbed Chen–Lee–Liu equation

This research aims to look into alternative unique solitary wave solutions to the perturbed Chen–Lee–Liu (CLL) equation to explain the kinetic and physical aspects of an optical fiber pulse. The perturbed CLL equation is one of the most well-known icon models derived from the well-known Schrödinger equation. Two different analytical methodologies are used to develop novel solitary wave solutions. These responses are then thoroughly evaluated using a well-known numerical approach to establish their underlying veracity. Various graphics are used to show the pulse wave analysis process and outcomes in an optical cable. We show how scientifically unique the study is by explaining the comparison figure that was made from our data and has been used in many recent research studies