International Journal of Chemical Kinetics最新文献

Heavy metals adsorption by adsorbents prepared from natural materials is a low-cost, effective method for their removal from aqueous environments. This study aims to investigate the kinetic studies on the adsorption of hexavalent chromium from its aqueous solution on raw and activated cassava rhizome. The coarse and fine raw cassava rhizome powder was activated by thermal (drying), pyrolysis, 1% (v/v) acetic acid, and 1% (w/v) KOH solutions. The batch adsorption studies were carried out by varying time (0–60 min) with adsorption capacity (meq/g) as a dependent variable. Adsorption capacity increased with an increase in time up to 40 min and then remained constant for all adsorbents with variation in adsorption capacity from 1.5 to 2.1 meq/g in the order of fine pyrolysis > fine thermal > fine acid = coarse pyrolysis > fine alkali = coarse thermal > coarse acid > coarse alkali > raw fine > raw coarse. Then, the effect of time on adsorption capacity data was fit to mechanistic models of pseudo-first, pseudo-second, zeroth, and half-order kinetics. Adsorption of hexavalent chromium on raw coarse and fine cassava rhizome powder followed pseudo-first-order kinetics. Also, the data were fit to empirical models based on regression and neural network, and the goodness of model fit was evaluated using the correlation coefficient (R). Regression analysis indicates the optimal fit with an R value of 0.9948 when the effect of time on adsorption capacity was investigated. Neural network analysis reveals the best fit at an R value of 0.9985. Hence, a higher rate constant for fine particles compared to coarse particles indicates that fine particles have a greater effective surface area and enhanced diffusional properties, facilitating more efficient adsorption, which suggests that the finer particles interact more with the adsorbate, allowing for quicker transport and adsorption processes.

The present study investigates the adsorption performance of SnOFe₂O₃TiO₂ nanocomposite for the removal of Basic Fuchsin (BF) dye from aqueous solution. The nanocomposite was synthesized via the coprecipitation method and characterized using various techniques such as TEM, SAED, and EDAX. TEM images confirmed the nanocomposite's crystalline structure with nanoscale particle sizes, while SAED patterns revealed its polycrystalline nature. EDAX analysis revealed the presence of Ti (54.9%), O (39.5%), Fe (4.8%), and Sn (0.7%), indicating TiO₂ as the dominant phase, with Fe and Sn contributing additional functionalities. Adsorption experiments were conducted to examine the effect of various operational parameters, such as pH, contact time, adsorbent dose, and initial dye concentration. The adsorption capacity increased with pH, reaching a maximum at pH 8.5. The adsorption process followed pseudo-second-order kinetics with a high correlation coefficient (R² = 0.99), indicating chemisorption as the primary mechanism. The Langmuir isotherm model best described the equilibrium data, with a maximum adsorption capacity (Q_max) of 344.42 mg/g at 25°C. Thermodynamic analysis showed that the adsorption process was spontaneous and exothermic, with a slightly negative enthalpy change (ΔH°) of −0.008314 kJ/mol and a negative Gibbs free energy (ΔG°) of −3.150 kJ/mol at 298 K. The SnOFe₂O₃TiO₂ nanocomposite exhibited excellent reusability, retaining over 90.71% of its adsorption capacity after five consecutive cycles of regeneration using a simple desorption process. These results demonstrate the potential of SnOFe₂O₃TiO₂ nanocomposite as a highly efficient and sustainable adsorbent for the removal of BF dye from wastewater.

AMPD (2-Amino-2-methyl-1,3-propanediol) is a candidate hindered amine for CO₂ separation from biogas. In this study, the performance of water-lean mixtures of AMPD with the organic solvents ethylene glycol (EG) and propanol (PrOH) was explored. Hindered amines load more CO₂, while organic solvents desorb CO₂ at low temperature. As a result, the proposed mixtures will be useful for improved CO₂ removal from biogas. Thus, CO₂ solubility in the blends AMPD/H₂O (AMPD = 1 M) and AMPD/EG/PrOH/H₂O (AMPD = 1 M, EG:PrOH = 1:1, H₂O = 15 wt.%) was measured at 303, 313, and 323 K. The equilibrium CO₂ partial pressure varied in the 0.05–240 kPa range. Upon replacing water with the chosen organic solvents, the rate of CO₂ desorption in AMPD doubled, and low-temperature regeneration (T = 363 K) was possible. Besides, the heat of CO₂ absorption was lowered too, as evident from the Gibbs–Helmholtz equation. Since these outcomes were encouraging, absorption kinetics were also studied in the fast pseudo-first order reaction regime using the stirred cell technique and rate constants at 308 K were reported. Such water-lean mixtures were hitherto scarcely studied, and we filled this gap in this work.

The hydrolysis of carboxylate ester, that is, p-nitrophenyl acetate (PNPA) with α-nucleophiles, such as acetohydroxamic acid (AHA) and benzohydroxamic acid (BHA), has been studied in mixed surfactant systems (CTAB + C₁₆-10-C₁₆, 2Br⁻; CTPB + C₁₆-10-C₁₆, 2Br⁻; CTAB + C₁₆-12-C₁₆, 2Br⁻; and CTPB + C₁₆-12-C₁₆, 2Br⁻) at pH 8.0 and 27°C. Each reaction proceeded with pseudo-first-order kinetics. The rate of reactions with a system of mixed gemini surfactants has been shown to accelerate noticeably. The gemini mixed system had a higher rate constant than the single surfactant system. Gemini surfactants' spacer length has been tested in single systems, and their rate data are contrasted with those of monomeric surfactants, such as cetytrimethylammonium bromide (CTAB) and cetytriphenylphosphonium bromide (CTPB).

The kinetics of highly efficient oxidation of cadaverine (CAD) by Ce(IV) in both HClO₄ and H₂SO₄ solutions were examined using UV–Vis absorption spectra at numerous temperatures. The last products of CAD oxidation were recognized as ammonia and 5-aminopentanal, that is, an essential organic compound in both biological and chemical settings. From the obtained data, it's clear that the reactions’ kinetics demonstrated a first-order dependence in [Ce^IV], where they exhibited lower than unit orders with regard to [CAD] over the studied concentration range. In HClO₄ and H₂SO₄, the oxidation reactions showed positive and negative incomplete unit orders in [H⁺], correspondingly. Based on the obtained results, the mechanistic reactions’ pathways were suggested. The reliable rate laws were derived, and the reactions’ rate constants were estimated. In addition, the activation and thermodynamic parameters were calculated and discussed. This study illuminated the role of the oxidant, medium, temperature, and other conditions on the oxidation kinetics and mechanisms of these redox systems.

An investigation of autoignition using molecular dynamics simulations and ReaxFF force fields is presented. The study is motivated by the fact that combustion at rocket engine conditions of high pressures can involve real gas behavior that is not captured by chemical kinetic models and kinetic solvers based on ideal gas assumptions. Also, the mechanistic reaction pathways at these conditions may not be well known. Molecular dynamics simulations based on reactive force fields can be used to gain insight into combustion under these conditions. However, for such molecular dynamics simulations to yield useful and trustworthy results, they must be able to simulate thermodynamic ensembles that are relevant to practical combustion, such as constant volume adiabatic reactors. They must also be able to reproduce known features from combustion simulations using continuum and statistical chemical kinetic models. These aspects can be verified for small molecular fuel systems, such as methane. In this work, the autoignition of methane-oxygen mixtures at pressures of 200 atm is simulated using non-equilibrium molecular dynamics with the ReaxFF force fields and the LAMMPS software package. To account for difficulties associated with maintaining the internal energy constant, a combination of NVT and NVE ensembles is used to capture the rapid temperature rise associated with autoignition. The evolution of key chemical species is examined and a characteristic ignition delay time is defined for each temperature. The results are contextualized by comparing them to the predictions of two continuum and statistical chemical kinetic models and the Chemkin Pro solver. ReaxFF simulations are found to reproduce the chemical structure of autoigniting reactors. The ignition delay times obtained from the ReaxFF are comparable to those obtained from continuum kinetic models, although the ReaxFF results are characterized by a higher global activation energy. With respect to the final products of the ignition process, ReaxFF predicts CO and OH levels that are comparable with continuum kinetic and equilibrium models. Generally, ReaxFF under predicts the formation of triatomic molecules. This study advances the use of molecular dynamics simulation to study standard combustion problems, such as constant-volume autoignition.

Sorption profoundly influences the destiny and behavior of agrochemicals in soil and water. The goal of the current study is to use the batch equilibrium technique to examine the adsorption–desorption behavior of the neonicotinoid pesticide imidacloprid in 10 distinct types of Pakistani soils (Ss1–Ss10). Adsorption coefficients (K_d) and associated parameters were assessed using the batch equilibrium approach. The findings showed that the best fit to the experimental data was given by the Freundlich isotherm. In view of this, the Ss6 depicted the highest adsorption coefficient (K_d) value (13.30 µg/mL), followed by Ss7 and Ss8. The positive correlation between K_d and soil organic matter decided it as a major affecting parameter for high adsorption. Negative Gibbs free energy values exhibited the weaker physio-sorption between soil and imidacloprid molecules. Minimum half-lives recorded in photolytic and biodegradative experiments were 247 and 28 days, respectively showing the persisting nature of imidacloprid. Results indicated that imidacloprid had a moderate to strong binding to the chosen soils, resulting in increased persistence and less breakdown. Work currently being done can be expanded to further optimize these impermissible methods to provide workable solutions for cleaning up the environment using natural means.