Chemical Reaction Rate Research Articles

Assembly-Driven Oxidative Degradation of Melarsomine Triggered by Cyanuric Acid.

Molecular self-assembly can trigger or regulate specific chemical reactions that would otherwise be infeasible when molecules exist individually. Supramolecular structures can significantly affect the rate of chemical reactions; therefore, optimizing supramolecular structures by manipulating intermolecular interactions is crucial for achieving the desired reactivity. Melamine is known to form hydrogen bonds with cyanuric acid, resulting in the formation of a supramolecular network. Melarsomine, an effective medication for heartworm treatment in dogs, contains a melamine moiety. It has yet to be studied how the chemical stability of melarsomine is affected by its interaction with other molecules. Herein, we report the formation of a two-dimensional supramolecular network between melarsomine and cyanuric acid via hydrogen bonds. This network structure captures dissolved oxygen in an aqueous solution, accelerating the oxidative degradation of melarsomine.

In English

The paper considers the problem of choosing the composition, structure, and size of spherical catalyst nanoparticles for carrying out plasmon-induced polymerization reactions. The concept of reducing the activation energy of the reaction in the presence of a catalyst and, accordingly, increasing the rate of a chemical reaction during heating due to the excitation of surface plasmon resonance is presented. Using the Drude model for the dielectric function, relationships were obtained for the frequency dependences of such characteristics as the real and imaginary parts of the polarizability, heating and the rate of chemical reactions when monometallic and bimetallic nanoparticles are used as catalysts, as well as the amplification of fields in their vicinity. The concepts developed in this work take into account the classical size dependence of the effective electron relaxation rate in monometallic and bimetallic nanoparticles under the assumption of diffuse scattering of electrons. Changes in the positions of the maxima of the imaginary part of the polarizability, heating, and reaction rate are analyzed with a change in the radii of monometallic and bimetallic nanoparticles. It is shown that the maxima of the dependences under study correspond to dipole surface plasmon resonances, and their number depends on the particle morphology. Changes in the amplification of electric fields in the vicinity of nanoparticles of different morphology have been studied. It has been found that the enhancement of the fields in all considered cases is maximum on the surface of the nanoparticle and decreases with distance from it. Practical recommendations are formulated regarding the size, composition and structure of nanoparticles for plasmon catalysis, which provide the highest rates of chemical reactions. Thus, all obtained frequency dependences have one maximum for monometallic and two maxima for bimetallic nanoparticles.

Effects of Limbs' Spasticity on Spinopelvic Alignment in Post-Stroke Patients: A Cross-Sectional Study.

Objectives: This study aimed to determine the impacts of upper and lower limb (UL and LL) spasticity and impairment on spinal alignment in chronic post-stroke patients. Methods: A total of 45 consecutive chronic post-stroke patients, 18 women and 27 men, from 18 to 70 years old who presented post-stroke hemiparesis were recruited in this cross-sectional study. The clinical assessment included the Modified Ashworth Scale (UL-MAS and LL-MAS spasticity), Upper Limb Motricity Index (UL-MI), FAST-UL, and Five Times Sit-to-Stand Test (5T-STS); the Associated Reaction Rating Scale was used to measure associated reactions in the hemiparetic UL, the plumb line distance from the spinous process of C7 on the sagittal (PL-C7s) and frontal plane (Pl-C7f), the kyphosis apex (PL-AK), and the spinous process of L3 (PL-L3). Angular measures of spinal alignment were measured by a Bunnell scoliometer™ (angle of trunk rotation-ATR) and a gravity-dependent inclinometer (inclination at C7-T1 and T12-L1). Results: In chronic post-stroke patients, there was found to be an association between the 5T-STS and PL-C7f (β = 0.41, p = 0.05) and the angle of inclination at T12-L1 (β = 0.44, p = 0.01). The FAST-UL correlated with PL-C7f (β = -0.41, p = 0.05), while the UL-MI correlated with this last parameter (β = -0.36, p = 0.04) and the ATR (β = -0.31, p = 0.05). The UL-MAS showed correlation with the ATR (β = 0.38, p = 0.01). Conclusions: The results lead to the possibility that, in chronic post-stroke patients, spinal misalignment on the frontal and sagittal plane is associated both with strength impairment and UL spasticity. The improvement or restoration of spinopelvic parameters can take advantage of therapeutic interventions targeted at motor improvement and spasticity reduction of the hemiparetic side.

Effect of catalyst distribution in the combustion catalytic layer on heat and mass transport characteristics of the microchannel reactor

PurposeThe purpose of this study is to investigate the effect of catalyst distribution in the combustion catalytic layer on heat and mass transport characteristics of the auto-thermal methanol steam reforming microchannel reactor.Design/methodology/approachComputational fluid dynamics (CFD) method is used to study four different gradient designs. The corresponding distributions of temperature, species and chemical reaction rate are provided and compared.FindingsThe distributions of species, temperature and chemical reaction rate are significantly affected by the catalyst distribution in the combustion catalytic layer. A more uniform temperature distribution can be observed when the gradient design is used. Meanwhile, the methanol conversion rate is also improved.Practical implicationsThis work reveals the effect of catalyst distribution in the combustion catalytic layer on heat and mass transport characteristics of the auto-thermal methanol steam reforming microchannel reactor and provides guidance for the design of reactors.Originality/valueThe temperature uniformity and hydrogen production performance can be improved by the gradient design in the combustion catalytic layer.

Study on the effects of medium-low pressure and oxygen concentration on positive streamer based on a two-dimensional fluid model

We studied positive streamers with a 5 mm gap under 20–101 kPa pressure and 1%–31% O2 concentrations conditions using a 2D axisymmetric fluid model based on local field approximation. As the pressure decreases from 101 kPa to 20 kPa, the axial reduced electric field, the mean electron energy and the electron diffusion coefficient increase, which leads to the acceleration of the streamer propagation velocity and the increase of the streamer channel radius. The opposite change of ionization cross section and gas molecular density caused by the decrease of pressure leads to the non-monotonic change of the peak of net ionization rate. At medium-low pressure, there is a wider ionization region at the streamer head. As the O2 concentration decreases from 31% to 1% in N2/O2, the streamer propagation velocity decreases. When the O2 concentration drops to 1%, the streamer velocity decreases with a descent gradient of nearly 4 times, compared to 11% O2. Based on the space charge effect and chemical reaction rate, a possible mechanism is proposed to explain the abrupt change in the streamer velocity.

Development of Problem-Based-Learning (PBL)-Oriented Electronic Student Worksheets (e-Worksheet) to Improve Critical Thinking Skills of Class XI Senior High School Students on Factors that Influence Rate of Chemical Reactions Material

Education system changes from time to time, and with these changes, the existing curriculum in Indonesia also continues to undergo several curriculum updates. The Merdeka Curriculum is the answer to the high level of competition that occurs in the 21st century. Factors that influence the rate of chemical reactions are one of the materials in chemistry phase F of the Merdeka curriculum, which has abstract characteristics and requires experimentation. Based on these characteristics, the problem-based-learning (PBL) learning model is suitable for use and can improve students’ critical thinking skills. This research aims to determine the feasibility of developing a PBL-oriented student e-worksheet to improve critical thinking skills on factors that influence reaction rates. The method used in this research is R&D with a 4D model. The results obtained are that the student e-worksheet developed is feasible because the content and construct validity results obtained in mode 5 with a very valid category, then the practicality results obtained a response questionnaire score of 98.44%, which was supported by the results of the student activity sheets, and the effectiveness was obtained. From the data from the pretest and posttest results, which were analyzed using the SPSS Paired Sample t-Test, the results showed that there was an increase in students’ critical thinking skills, namely with a significance value of 0.00.

Effect of mineral dissolution on fault slip behavior during geological carbon storage

Geological carbon dioxide storage is one of the most effective technologies to reduce greenhouse gas emissions to the atmosphere. The mineral dissolution is inevitable during the long-term storage process, while the chemical effect on fault slip behavior remains poorly understood. In this paper, we present a hydro-chemical–mechanical coupled fault reactivation study using the unified pipe-interface element method (UP-IEM). The impact of chemical dissolution on stress redistribution is considered. The accuracy of the numerical method to simulate reactive solute transport and fault frictional slip are confirmed by analytical solution and numerical verification. Two different fault tectonic scenarios, of which fault locating in the caprock and fault crosscutting the reservoir and caprock, are designed to investigate the fault slip behavior induced by mineral dissolution. The effect of dissolved CO2 solute concentration, fault aperture, reservoir permeability and chemical reaction rate are discussed. Results show that fault locating in the caprock is easier to be activated. The chemical reaction has a more significant effect on fault slip behavior than fluid pressure during the long-term low-velocity CO2 leakage. The increase of CO2 solute concentration and reservoir reaction rate cause an obvious growth on fault slip displacement. The decrease of fault initial aperture results in the fault slip velocity slower and the slipping area smaller. The high-permeability reservoir keeps the fault more stable than low-permeability reservoir under the influence of mineral dissolution.

Na-doped Li4SiO4 as an efficient sorbent for low-concentration CO2 capture at high temperature: Superior adsorption and rapid kinetics mechanism

Lithium silicate (Li4SiO4) sorbent has garnered attention in CO2 capture due to its high theoretical adsorption capacity and fast kinetics. However, its adsorption capacity and kinetics were hindered by low CO2 concentration. Improving adsorption performance of Li4SiO4 at low CO2 concentration has become the key to industrial application. In this work, high-activity Na-doped Li4SiO4 with controllable active substance Li3NaSiO4 was achieved. The influences of raw materials ratios on the CO2 adsorption performance were systematically investigated. When RLi/Si=4.05:1 and RNa/Si=0.15:1, the sample exhibited the highest adsorption capacity of 32.28 wt% with an equilibrium time of 29 min, and a superior stable capacity of 31.09 wt% in 15 cycles. Importantly, the double exponential fitting revealed that LiNaCO3 accelerated the ion diffusion rate and real-time adsorption processes showed Li3NaSiO4 expedited surface chemical reaction rate. Based on these, a novel Na2CO3 eutectic doping mechanism was proposed. The active substance Li3NaSiO4, generated through Na doping, along with its product formed from the reaction with CO2, molten LiNaCO3, acted synergistically to improve adsorption performance by accelerating surface chemical reaction rate and ion diffusion rate. Compared with other doped Li4SiO4, the sorbent prepared in this work demonstrated competitive adsorption performance, providing theoretical and technical support for the large-scale production of high-activity Li4SiO4.

Enhancement of Heat and Mass Transfer in 2D-Mixed Convection Nano-Liquid Flow Over a Flexible Riga Plate with Heat Source/Sink and Chemical Reaction

This study delves into the complex dynamics of two-dimensional (2D) hydro-magnetic nano-fluidic flow over an elastic Riga plate, aiming to elucidate the interactions among thermal energy, concentration transfer, pressure gradient, and convective & zero mass flux at the boundary. Notably, the investigation incorporates concentration and temperature buoyancy forces, integrating them into the analysis with a comprehensive energy transfer equation and essential nanofluid properties in the species concentration. Further, the internal heat source/sink and rate of first order chemical reaction are considered. Employing the advanced capabilities of MATHEMATICA12 software, the study applies the Optimal Homotopy Analysis Method (OHAM), reducing the governing equations partially to ordinary ones. Furthermore, the study reveals intriguing patterns, highlighting the significant impact of the modified Hartmann number on velocity and concentration gradients, while displaying contrasting effects on thermal profiles. Moreover, the dual nature of pressure gradient behavior underscores the complexity of the studied phenomenon, offering valuable insights for further research and practical applications in nano-fluidic systems.

Cattaneo-Christov Heat Flux Model for Bio-Convective Radiative Eyring-Powell Nanofluid with Viscous-Ohmic Dissipation and Magnetic Dipole Impacts

In this work we studied the solutions of the bio-convected Eyring-Powell nanofluid involving gyrotactic micro-organisms in the presence of viscous-ohmic dissipation, double diffusion, and magnetic field over a stretched sheet under the impacts of nonlinear radiation and Arrhenius activation energy. The magneto-nanoparticles suspension in microorganisms are beneficial in nanofluid stability. Also, they have number of applications in nanosciences, biotech, pharmaceuticals, and mechanical development. The nonlinear coupled PDEs are transformed into ODEs by taking a suitable set of similarity transformations and then computationally solved with MATLAB’s bvp4c and RK4-Shooting technique. The skin friction coefficient, Nusselt number, and Sherwood number are represented in tabular form. The mass and heat transmission rate improve in the presence of gyrotactic microorganisms. The temperature as well as concentration of Eyring-Powell Nanofluid get decreased by accelerating the significant mass and thermal stratification. The concentration profile Φ(η) depreciate for higher Chemical reaction rate (σ), Schmidt number (Sc), and temperature difference (δ1) parameters but rises upon increasing values of Activation energy (Ea). Also, the microorganism concentration difference parameter (β1), bioconvection Lewis number Lb and Peclet number Pe are opposing the motile microorganism density profile.

Strong coupling-induced frequency shifts of highly detuned photonic modes in multimode cavities.

Strong coupling between light and molecules is a fascinating topic exploring the implications of the hybridization of photonic and molecular states. For example, many recent experiments have explored the possibility that strong coupling of photonic and vibrational modes might modify chemical reaction rates. In these experiments, reactants are introduced into a planar cavity, and the vibrational mode of a chemical bond strongly couples to one of the many photonic modes supported by the cavity. Some experiments quantify reaction rates by tracking the spectral shift of higher-order cavity modes that are highly detuned from the vibrational mode of the reactant. Here, we show that the spectral position of these cavity modes, even though they are highly detuned, can still be influenced by strong coupling. We highlight the need to consider this strong coupling-induced frequency shift of cavity modes if one is to avoid underestimating cavity-induced reaction rate changes. We anticipate that our work will assist in the re-analysis of several high-profile results and has implications for the design of future strong coupling experiments.

Oxygen vacancies promote the activation of O2 in transition metal oxide doped ε-MnO2 for low-temperature CO oxidation

Carbon monoxide (CO), a toxic pollutant usually formed from incomprehensive combustion especially at low temperature, has harmful effects on human health. Therefore, the catalytic oxidation of CO always receives widespread attention. Herein, we reported transition metal (Cu, Co, Ni, Fe) doped ε-MnO2 as CO catalysts using a hydrothermal-deposition method. Physiochemical properties for CO oxidation were meticulously analyzed employing characterization techniques such as SEM, XRD, BET, XPS, EPR, CO-TPR. The doped ε-MnO2 catalyst showed expanded BET surface area, increased oxygen vacancy defects, more active sites, enhanced adsorption, and faster electron transfer. Catalytic activity tests indicated that the ε-MnO2 catalyst doped with transition metals exhibited exceptionally high catalytic activity, with the Cu-doped catalyst showing the fastest chemical reaction rate and the lowest complete conversion reaction temperature (TOF of 9.92 × 10−3 s−1, at 65℃). Density Functional Theory (DFT) calculations indicated that Cu doping more effectively induced oxygen vacancy defects compared to Co, Ni, Fe, and raw ε-MnO2 catalysts. It identifies the CO oxidation reaction and improved the CO adsorption capacity of the catalyst. Furthermore, a novel potential reaction pathway for the M-vK mechanism in transition metal oxides was proposed.

Optimization and Parameter Investigation of the Planar Photocatalytic Microreactor.

The microreactor could break the limitation of mass transfer and photon transmission in photocatalysis. Through a facile assembly method, a planar photocatalytic microreactor was constructed to fit most of the photocatalysts regardless of their strict preparation method. This microreactor exhibits a 2.41-fold efficiency compared to a bulk reactor. Parameters that affect the photocatalytic performance were discussed in detail by experiment and calculation. The diffusion rate is the main bottleneck in a planar microreactor under a laminar flow. The microreactor with lower height shows higher efficiency owing to faster mass transfer, while the length and width affect slightly. Elevating the light power density provides a diminishing benefit. Faster flow speed reduces the apparent degradation percent but increases the chemical reaction rate, in fact. The reaction rate increases to 9.31 times by reducing the height from 500 to 100 μm and grows another 1.76 times by adding the flow speed from 10 to 40 mL/h. This work illustrates the influence of parameters on planar photocatalytic microreactors and offers a promising prospect for large-volume photocatalytic water treatment.

Influence of point bars on nitrogen transport and reaction in riparian zones

Point bars formed by riverbank deposition are an important part of the hyporheic zone, where surface water and groundwater are actively exchanged; they play a key role in the nitrogen biogeochemical processes of river ecosystems. In this study, we aimed to investigate the effects of point bars on nitrogen transport and reactions in riparian zones. A two-dimensional (2D) coupled flow-reactive transport model was developed, and three key chemical reactions, namely, aerobic respiration, nitrification, and denitrification, were considered to study the effects of the curvature and size of a point bar on the nitrogen distribution and chemical reaction rate in the hyporheic zone. The results indicated that the point bar altered the groundwater velocity field, resulting in higher flow velocity and shorter subsurface residence time, which significantly increased the depth of the four key species [dissolved oxygen (DO), nitrate (NO3−), dissolved organic carbon (DOC), and ammonium (NH4+)] that are generally transported to riparian zones. This phenomenon played a significant role in increasing the nitrification and denitrification rates. In the scenario wherein a point bar was formed, the amount of nitrogen removed was 4.29 times higher than that in the scenario wherein no point bar was formed. Furthermore, the transfer depths of DO, NO3−, DOC, and NH4+ and the amount of nitrogen removed increased with the curvature/area of the bar. This study indicates that the presence of a point bar can accelerate the nitrogen cycle and increase the nitrogen removal capacity in riparian zones.

Sodium alginate-based MHD ternary nanofluid flow across a cone and wedge with exothermic/endothermic chemical reactions: A numerical study

The use of magnetohydrodynamic ternary nanofluid flow for heat transfer is essential in various industrial and commercial applications. This work examines heat transfer over cone and wedge shapes with Sodium Alginate-based ternary nanofluid flow, considering the effects of activation energy and exothermic/endothermic processes. Using similarity transformations, the controlling set of partial differential equations is converted into a network of interconnected nonlinear ordinary differential equations. Numerical solutions using the Runge-Kutta Fehlberg 4th 5th order method and shooting approach offer insights into the effects of several dimensionless factors. The outcomes show that the magnetic field parameter is crucial in lowering fluid velocity within a cone more efficiently than a wedge. Due to activation energy considerations, the cone shape notably impacts heat transmission in exothermic reactions, but the wedge geometry is more effective in endothermic reactions. Concentration profiles rise with activation energy and fall with increasing chemical reaction rates. The rate of thermal distribution is 48.68% more in wedge than cone geometry for the exothermic case and 35.57% in the endothermic case while the rate of mass transfer is higher in cone geometry than wedge geometry, about 7.83% in the exothermic case and 19.27% in the endothermic case. The present study has many applications, including optimizing heat transfer processes in sectors such as thermal systems, energy generation, and electronics. Additionally, it may be used to guide the design of magnetically affected systems and provide assistance for uses in chemical engineering.

Suppressed atmospheric chemical aging of cooking organic aerosol particles in wintertime conditions

Abstract. Cooking organic aerosol (COA) is one of the major constituents of particulate matter in urban areas. COA is oxidized by atmospheric oxidants such as ozone, changing its physical, chemical and toxicological properties. However, atmospheric chemical lifetimes of COA and its tracers such as oleic acid are typically longer than those that have been estimated by laboratory studies. We tackled the issue by considering temperature. Namely, we hypothesize that increased viscosity of COA at ambient temperature accounts for its prolonged atmospheric chemical lifetimes in wintertime. Laboratory-generated COA particles from cooking oil were exposed to ozone in an aerosol flow tube reactor for the temperature range of −20 to 35 °C. The pseudo-second-order chemical reaction rate constants (k2) were estimated from the experimental data by assuming a constant ozone concentration in the flow tube. The estimated values of k2 decreased by orders of magnitude for lower temperatures. The temperature dependence in k2 was fit well by considering the diffusion-limited chemical reaction mechanism. The result suggested that increased viscosity was likely the key factor to account for the decrease in chemical reactivity at the reduced temperature range, though the idea will still need to be verified by temperature-dependent viscosity data in the future. In combination with the observed global surface temperature, the atmospheric chemical lifetimes of COA were estimated to be much longer in wintertime (> 1 h) than in summertime (a few minutes) for temperate and boreal regions. Our present study demonstrates that the oxidation lifetimes of COA particles will need to be parameterized as a function of temperature in the future for estimating environmental impacts and fates of this category of particulate matter.

A resonance triggers chemical reactions between the coldest molecules

The rich energy structure of ultracold molecules (at -459 °F or -273 °C), gives rise to collisional dynamics where the state-of-the-art models are inadequate for describing collisional resonances. We have discovered a pronounced magnetically tuned resonance in collisions between two NaLi molecules, which enhances the chemical reaction rate by more than a factor of a hundred.

Experimental study and numerical simulation on porosity dependent direct reducibility of high-grade iron oxide pellets in hydrogen

The transition to more environmentally friendly steel production methods has intensified research into hydrogen-based direct reduction (HyDR) of iron oxide pellets. The aim of this study is to systematically investigate the kinetics of the reduction process, the evolution of porosity and the resulting microstructural changes on the reduction behavior of high-quality pellets during HyDR of iron ore at different temperatures. A modified mathematical model is developed based on the shrinkage kernel model, taking into account both mass and heat transport in a hydrogen atmosphere. The effects of temperature, particle size and time on the reduction behavior of the pellets are investigated. The simulated results are validated and discussed by the results of a batch of iron oxide pellets consisting of ten almost spherical pellets subjected to the direct reduction process with pure hydrogen. The results show that the total energy input to the HyDR process is a complex balance of factors, including chemical reaction rates, diffusion dynamics and entropy generation. The increase in free volume and simultaneous decrease in pore diameter reflect the dynamic nature of the microstructure, which includes additional free volume and defects due to the volume discrepancies and associated stresses between the reactant and product phases. Furthermore, the data show that higher temperatures accelerate the reduction reactions, especially the transformation of wustite into metallic iron. This phase transition is characterized by a significant volume change that cannot be accommodated by elastic deformation alone, leading to the development of lattice defects such as cracks, creep pores and dislocations that serve as stress relief mechanisms. The trends for porosity change at 950 °C and 1000 °C observed in the experimental results are correct and in good agreement with the numerical and simulated results.

Dissipative Non-Slip MHD Nanofluid Flow with Variable Viscousity and Thermal Conductivity in the Presence of Arrhenius Chemical Reaction

This research investigates the intricate dynamics of dissipative non-slip magnetohydrodynamic (MHD) nanofluid flow, characterized by variable viscosity and thermal conductivity, under the influence of an Arrhenius chemical reaction. The inclusion of the Arrhenius chemical reaction adds complexity through heat generation or absorption, impacting temperature and concentration gradients. The study is motivated by the extensive applications of nanofluids in engineering and industrial processes, where precise control of heat and mass transfer is critical. We develop a comprehensive mathematical model that incorporates the variable properties of the nanofluid, the effects of the Lorentz force due to the applied magnetic field, and the temperature-dependent reaction rates dictated by the Arrhenius equation. The formulated governing equations were non-dimensionalised to identify the flow governing parameters. Finite Element Method (FEM), grid generation, solution algorithms, and post-processing to analyse velocity, temperature, and concentration distributions were used to obtain the numerical methods to solve fluid flow problems based on the Navier-Stokes equations, involving concepts of discretization. pdsolve subpackage in Maple 2023 was used to numerically solve PDEs with specific initial and boundary conditions, incorporating the plot and display commands for graphical analysis, and the results are presented and discussed. The findings reveal that the interplay between parameters like Hartmann number, Darcy parameter, and heat generation or absorption profoundly influences flow behaviour and thermal characteristics. The reactivity parameter is crucial, dictating the rate of chemical reactions and affecting system dynamics. This research enhances understanding of the interdependencies among fluid properties, chemical reactions, and external parameters in nanofluid flows.

Leaching kinetics of waste pharmaceutical blister package aluminium in phosphoric acid media

This study investigated the process of treating secondary aluminium recovered from waste pharmaceutical blister packages (WPBs) using phosphoric acid solutions as a potential strategy for recycling this currently non-recycled waste material. The findings indicate that, when recycling via the hydrometallurgical process, the aluminium passivated during leaching can be effectively counteracted by employing moderately concentrated phosphoric acid solutions (1.0 M), elevated temperatures (60–80 °C) and specifically the addition of H2O2 (1.25–2.5 vol.%). Under these conditions, complete extraction of aluminium was achieved within four hours. The estimated activation energy (∼82 kJ/mol) indicates that the leaching reaction is primarily limited by the chemical reaction rate rather than film diffusion. An aluminium phosphate solution could be obtained by leaching WPBs in a way that is suitable for subsequent aluminium phosphate crystallisation. This approach could provide a promising pathway for valorising aluminium from the currently under-utilised waste fraction of pharmaceutical blister packages.