Reaction Channels Research Articles

Subnanometric Bismuth Clusters Confined in Pyrochlore-Bi2 Sn2 O7 Enable Remarkable CO2 Photoreduction.

The development of highly efficient photocatalysts for conversion of carbon dioxide (CO2 ) with water (H2 O) into chemical fuels is of great importance for energy sustainability and carbon resource utilization. Herein, we demonstrated a facile hydrothermal method for in situ construction of subnanometric Bi metallic clusters in pyrochlore-Bi2 Sn2 O7 frameworks, leading to the remarkable improvements of photocatalytic performances for CO2 reduction into CO in the absence of sacrificial reagent. More specifically, an outstanding CO evolution activity of 114.1 μmol g-1  h-1 has been achieved, more than 20-fold improvement compared with the pristine Bi2 Sn2 O7 (5.7 μmol g-1  h-1 ). Detailed experiments together with in situ characterizations reveal that the spatially confined Bi clusters could significantly promote charge-separation/electron-enrichment and adsorption/activation of CO2 molecules, which provides highly efficient reaction channels to facilitate the generation of *COOH intermediate as well as the subsequent desorption of *CO towards CO formation. These demonstrations provide an important knowledge for precise design and fabrication of highly efficient photocatalysts for CO2 conversion into solar fuels.

Direct production of molecular oxygen from carbon dioxide and helium ion collisions

The prebiotic mechanism to produce molecular oxygen (O2) in carbon dioxide (CO2)-rich planetary atmospheres is of great importance in understanding astrochemical reactions and is potentially relevant to the origin of life on Earth. Here, we demonstrate that, aside from the direct productions of O2 by photodissociation and dissociative electron attachment, the low-energy ion-molecule reaction between cationic helium in solar winds and molecular CO2 is a noticeable mechanism. Branching ratios of the reaction channels are determined, and their absolute cross-sections are estimated accordingly. The present findings represent a further, indispensable step towards fully understanding the origins of atmospheric O2.

Peristaltic flow of a bioconvective sutterby nanofluid in a flexible microchannel with compliant walls: Application to hemodynamic instability

A theoretical investigation is conducted for bioconvective peristaltic transport of a non-Newtonian nanofluid through a porous symmetric channel with compliant walls. The Sutterby nanofluid model is utilized to characterize the fluid under an applied magnetic field. The use of radiative heat flux along with the heat source and the thermodynamics energizes the flow phenomena. In addition, the novelty of the present study is to analyze the behavior of bioconvective Sutterby nanofluid in a chemically reactive porous channel with heat and mass transfer aspects. To reduce the complexity of the system, we used a long wavelength and low Reynolds number approximation. Furthermore, to tackle the dimensionless equations related to the flow phenomena, numerical computations are performed by utilizing MATLAB's built-in bvp5c function. The consequences of the pertinent parameters on the flow characteristics are presented through tables and graphs. An increase in both the Darcy number and the buoyancy ratio parameters raises the velocity distribution of a Sutterby nanofluid. The magnitude of the thermal field is enhanced in a symmetric channel with a rising Eckert number and the energy generation parameter. The thermophoresis diffusion parameter strengthens the temperature profile but decreases the concentration of the Sutterby nanofluid. We believe that the outcomes of this study have a wide range of implications to targeted drug delivery, the pharmaceutical industry, thermal devices, biosensors, sustainable fuel cell technologies, and solar systems.

A different view on the deactivation process of 3-hydroxy-salicylidene-methylamine system

Schiff bases stand out as a highly significant class of photochromic materials with widespread applications. The exploration of their photochromic mechanisms has garnered substantial interest over the past decades. In this work, we investigated the photochromic mechanism of 3-hydroxy-salicylidene methylamine (3-OH-SMA) by high-level electronic structure calculations and on-the-fly excited state dynamics simulations. Our investigation revealed the identification of three minimum energy conical intersections between S1 and S0 states, while only the one characterized by the central C = N bond twisting motion was involved in the deactivation process. This finding contrasts with previous reports, suggesting that the excited state intramolecular proton transfer (ESIPT) process was the main reaction channel in 3-OH-SMA. The proposed new decay mechanism provides valuable theoretical insights, paving the way for the further enhancement or rational design of photochromic materials.

Analysis of Ca+(2S) + HD (v0 = 0, j0 = 0) → CaH+/CaD+ + D/H reaction dynamics using time-dependent wave packet method

Using the time-dependent wave packet method on a newly reported potential energy surface, the reaction channels of Ca+(2S) + HD (v0 = 0, j0 = 0) → CaH+/CaD+ + D/H were investigated in the collision energy range of 2.3 eV and 4.0 eV. Our analysis commenced with an investigation of the integral and differential scattering cross sections, as well as the reaction probabilities for both reaction channels. The results reveal that the CaH+ + D reaction channel plays a primary role which is consistent with experimental results. The complex forming mechanism and direct-abstraction reaction mechanism exist in this reaction process.

Coupled reaction channel analysis of one- and two-nucleon transfer in $$^{\textbf{28}}$$Si+$$^{\textbf{90,94}}$$Zr

Coupled reaction channel analysis of one- and two-nucleon transfer in $$^{\textbf{28}}$$Si+$$^{\textbf{90,94}}$$Zr

Development of a two-dimensional model to assess carbon dynamics and anthropogenic effects on CO2 emissions in the Tan river, southern China

Tidal rivers are key biochemical reaction channels along the land-ocean aquatic continuum, receiving carbon from wastewater and agricultural drains, which can considerably affect CO2 emissions. We developed a two-dimensional hydrodynamic and ecological model coupled with an inorganic carbon module along the Tan River in southern China. The simulations of and observations regarding discharge, temperature, total organic carbon (TOC), total inorganic carbon (TIC), and other common water quality variables were generally in good agreement. Based on the validated model, we employed statistical and scenario analyses to evaluate the carbon distribution, TOC and TIC budgets, and the imbalances induced by climatic and anthropogenic changes, providing insights into their potential greenhouse effect. The Tan River was consistently supersaturated with CO2 with an annual mean air-water CO2 emission flux (FCO2) of 226.1 ± 84.9 mmol m−2 d−1, and significant temporal and spatial variations of FCO2, TOC, and TIC were observed. Urban small streams tended to emit additional CO2 during wet seasons, and rural tributaries usually had an increase in TOC concentrations during the dry season. FCO2 was significantly positively correlated with air temperature and negatively correlated with total nitrogen, total phosphorus, and TOC. The annual riverine input of carbon to the urban river network was 17.37 Gg C yr−1, with 59.82% of TOC, and carbon output was 15.31 Gg C yr−1, with 66.87% of TOC. The retention rates for TOC and total carbon were 50.7% and 11.8% in the urban branch, respectively. Furthermore, warming and wastewater treatment could prevent urban river networks and downstream rivers from becoming carbon sources. Therefore, our findings suggest that riverine management strategies change the global CO2 release from tidal rivers and estuarine systems under climate change.

Using machine learning to go beyond potential energy surface benchmarking for chemical reactivity.

We train an equivariant machine learning (ML) model to predict energies and forces for hydrogen combustion under conditions of finite temperature and pressure. This challenging case for reactive chemistry illustrates that ML potential energy surfaces are difficult to make complete, due to overreliance on chemical intuition of what data are important for training. Instead, a 'negative design' data acquisition strategy using metadynamics as part of an active learning workflow helps to create a ML model that avoids unforeseen high-energy or unphysical energy configurations. This strategy more rapidly converges the potential energy surfaces such that it is now more efficient to make calls to the external ab initio source when query-by-committee models disagree to further molecular dynamics in time without need for ML retraining. With the hybrid ML-physics model we realize two orders of magnitude reduction in cost, allowing for prediction of the free-energy change in the transition-state mechanism for several hydrogen combustion reaction channels.

Measurement and analysis of leakage neutron spectra from Lead slab samples with D–T neutrons

The leakage neutron spectra from three different sizes of Lead samples were measured by a TOF technique at 60° and 120°. The essential characteristic properties of the experimental measurement spectra can be reproduced well by MCNP code simulations with the ENDF/B-VIII.0, CENDL-3.2, JENDL-5.0, JEFF-3.3 and TENDL-2021 evaluated nuclear data libraries. The calculated results of JENDL-5.0 and JEFF-3.3 libraries agree better with the experimental data in the whole energy range. The results from ENDF/B-VIII.0 and CENDL-3.2 are overestimated in the 4–9 MeV range at 60° and in the 4–12.5 MeV range at 120°. The differences of the leakage neutron spectra by MCNP simulations using five evaluated nuclear data libraries mainly originate from the differences of the spectrum distributions of neutron reaction channels in these libraries. And the secondary neutron energy distribution and angular distribution from the five libraries have been present to explain it.

Gamma -Ray detection with CsI(Tl) scintillators of the FARCOS array

The measurement of the response function of the CsI(Tl) scintillators of the FARCOS array, to standard sources, cosmic rays and environmental background allows the assessment of their performance. Fast–Slow analysis discriminates between gamma -rays and charged particles. The relatively good energy resolution allows the observation of well resolved escape peaks due to the interaction of the 4.44 MeV gamma -ray generated by AmBe source. Furthermore, the small noise enables to discriminate from the background the annihilation 511 keV gamma -rays of the ^{22}Na source. The energy loss of muons generated by cosmic rays has been also measured and the radioactive contaminants as ^{137}Cs, ^{40}K and ^{208}Tl have been identified. The quality of the detectors suggests the possibility to use the array also for the measurement of gamma -ray decay in reactions induced by stable and radioactive beams, once a well-defined reaction channel has been identified. Moreover, a dedicated compact detection module as a portable, high efficiency radiation detector for the control of environmental contamination will be developed.

Optimized anode, cathode and coolant flow designs for enhanced performance of proton exchange membrane fuel cells

This study deals with various flow field designs for anode, cathode and coolant plates for optimizing the performance of proton exchange membrane fuel cell using H2 and air. In particular, the 3D models with various flow field patterns such as single parallel serpentine (anode), multi parallel (anode), multi-parallel serpentine (cathode), multi serpentine (cathode) have been evaluated for enhancing the fuel cell performance at 60 °C, with three different coolant flow designs (mirror serpentine, multi serpentine and parallel serpentine). Both the peak power and limiting current density are considered based on the parameters such as temperature distribution, pressure distribution, reactants/species distribution and the membrane water content on the active area (50 cm2) region. It is interesting to note that the coolant channel also has a significant effect in regulating the fuel cell performance at high current densities, in addition to reactant gas flow channels. The simulated single cell with Nafion (thickness: 18 μm) demonstrates a peak power density of 0.97 W cm−2 with single parallel serpentine (anode), multi parallel serpentine (cathode) and serpentine (coolant) and 0.91 W cm−2 with multi parallel (anode), multi serpentine (cathode), and parallel serpentine (coolant) flow field designs. The simulated fuel cell performance is also experimentally validated at 60 °C using H2 fuel and air as the oxidant.

Significant non-adiabatic effects of the K(4s2S) + H2 reaction

The non-adiabatic dynamical calculations of the K(4s2S) + H2(v 0 = 1, 2, j 0 = 0) reaction are carried out using the time-dependent wave packet method. The non-adiabatic dynamics results, such as reaction probabilities and integral cross sections, are calculated and compared with previous adiabatic values. The adiabatic values are several tens of times larger than those of the non-adiabatic results. The non-adiabatic effect becomes stronger with the increase in the number of excited vibrational states. In addition, the excitation of the vibrational states of H2 can increase the reaction probability of the reaction channel. However, the KH product is still barely formed through the K(4s2S) + H2 reaction, even if the H2 molecule is excited to a high vibrational excited state, which also leads to the opposite conclusion from the adiabatic results. The forward-biased differential cross sections indicate that a direct stripping mechanism plays a dominant role in the reaction.

Theoretical investigation of electron capture processes in slow O7+–H collisions

Aims. The total and n-, l-, and S -resolved single-electron-capture cross sections for the collisions of O7+ with atomic hydrogen are studied in the energy region from 10−3eV u−1−5keV u−1. Methods. These state-selective cross sections were calculated by employing the full quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio multireference single- and double-excitation configuration interaction approach, with optimized atomic basis sets to accurately describe the highly excited states, was used to obtain the adiabatic potentials and the radial and rotational coupling matrix elements that are required in the QMOCC calculation. Results. Our results are compared with other available theoretical and experimental data. The n = 5 manifold is the dominant reaction channel for the chasrge-transfer process for this collision system over the entire energy range, and our results agree better with the experimental data than the other theoretical results in the energy region in which they overlap because we included the necessary highly excited states in the expansion basis set. These charge-exchange cross-section data are useful for understanding and modeling the X-ray emission in astrophysical environments.

Further revealing reaction mechanism on the oxidation behavior of the lignin model molecules

It is urgent to further study the mechanism of the oxidation process of biomass energy. Theoretical investigation on the oxidation of p-hydroxybenzyl alcohol (HOL), vanillyl alcohol (VOL) and syringic alcohol (SOL) at the atomic and molecular levels is completed by density function theory (DFT). The oxidative reaction mechanism was further revealed and the oxidation reaction pathway on phenolic hydroxyl group site was identified in detail. The potential energy surface information of fifteen possible reaction channels at B3LYP/6–311 + G(d,p) level was obtained. The influence of substituent effects on the oxidative reaction energy barrier has been estimated. Theoretical calculation results showed that the reactivity of phenolic hydroxyl group is stronger than methoxyl group and hydroxymethyl group. The oxidative reaction energy barrier decreases with increasing of the methoxyl group number. The elucidation of the oxidation mechanism provides a novel perspective for the study of catalytic oxidation in lignin model materials.

Homoprotocatechuate dioxygenase active site: Imitating the secondary sphere base via computational design.

Oxidative ring cleavage reactions have attracted great interest and various studies on the catechol ring-cleaving enzyme homoprotocatechuate dioxygenase (HPCD) have been reported in the literature. The available data on how the proton transfer takes place led us to design a potential HPCD model structure. A secondary sphere effect of utmost importance, the assistance of His200, which is critical for the catechol proton to migrate to dioxygen, was cautiously included on the first coordination shell. This was done mainly by modifying the axial ligands in the first coordination shell of HPCD such that the dual basic/acidic role in the proton transfer pathway of His200 was reproduced. Model systems with mono-, bi-, and tridentate ligands are reported. Energetically feasible reaction channels on synthetically promising ligand structures are identified. Key structural and electronic principles for obtaining viable proton transfer paths are outlined.

Examining the influence of phonon coupling and nucleon transfer channels in reactions $$^{34,36}$$S + $$^{58}$$Ni, $$^{32,36}$$S + $$^{110}$$Pd and $$^{40,48}$$Ca + $$^{90}$$Zr around Coulomb barrier energies

Examining the influence of phonon coupling and nucleon transfer channels in reactions $$^{34,36}$$S + $$^{58}$$Ni, $$^{32,36}$$S + $$^{110}$$Pd and $$^{40,48}$$Ca + $$^{90}$$Zr around Coulomb barrier energies

On the decomposition mechanism of propanal: rate constants evaluation and kinetic simulations

The reactivity of aldehydes has been the subject of considerable interest in chemical kinetics, with propanal often chosen as the representative species. Despite its relevance, the reactivity of propanal is currently estimated from analogy and fitting of experimental data measured in limited temperature and pressure ranges, while the few literature theoretical studies have focused more on the exploration the potential energy surface (PES) than on the estimation of rate constants. The purpose of this work is to reinvestigate the propanal decomposition kinetics using the ab initio transition state theory based master equation approach with the intent of: (1) Determining accurate rate constants of key reaction channels; (2) Updating and validating an existing kinetic model by simulating available experimental data on propanal pyrolysis. It is found that propanal decomposition at the initial stages of pyrolysis occurs through four unimolecular barrierless reactions to form CHO + C2H5, CH2CHO + CH3, CH3CHCHO + H, and CH3CH2CO + H, and a termolecular pathway leading to the formation of C2H4 + CO + H2. High pressure rate constants were determined for each barrierless reaction channel using Variable Reaction Coordinate Transition State Theory and used to estimate phenomenological temperature and pressure dependent channel specific rate constants integrating the 1 dimensional master equation over the whole PES. The decomposition rate constants so determined are in agreement with the few available experimental data and significantly faster than previous literature estimates. The estimated kinetic parameters were finally implemented into the CRECK kinetic mechanism, leading to an improved agreement with shock tube pyrolysis data from the literature.

Study on fire extinguishing mechanism of allophanate based on Monnex dry powder

Monnex (allophanate) dry powder has a good fire extinguishing effect and is environmentally friendly. However, the reaction processes of allophanate with OH· and H· free radicals, which are of great importance for investigating its fire suppression mechanisms, are still unclear. In this work five reaction pathways related to the pyrolysis of ureyl formates, five pathways to capture OH· radicals and seven pathways to capture H· radicals were studied. It was found that, for the CO2 and NHCONH2 generation pathway possesses the energy barrier much lower than others in pyrolysis of allophanate. The generation of NHCONHCOO + H2O is the most feasible reaction channel for the reaction of allophanate with OH free radical. Moreover allophanate and its derivatives capture H radicals to achieve continuous consumption of free radicals. This study shows, it is worth further studying its applicability in fire extinguishing applications.

Reactions induced by 30 MeV 3He beam on 9Be : cluster transfer reactions* *Supported by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (AP14870958)

An experiment was conducted for studying the cluster structure of Be induced by He ions at an energy of 30 MeV. As results of the nuclear reaction 3He + 9Be, the differential cross sections for the exit channels – elastic, inelastic, α + 8Be, 6He + 6Be, 6Li + 6Li, and 7Be + 5He – were measured. Elastic and inelastic scattering data were treated within both the optical model and coupled channel method. A new set of optical potentials was considered for the elastic scattering. The deformation parameter was established for the transition . Cluster transfer reactions were analyzed via the coupled reaction channel method. The nuclear reactions with the exit channels 6He + 6Be, 6Li + 6Li, and 7Be + 5He were complemented by two-step transfer mechanisms. The contribution of each reaction mechanism were shown and compared with the findings of other authors.

Mxene quantum dots bipolar electrochemiluminescent platform for hepatitis C virus envelope protein E2 detection

A burgeoning diversified closed bipolar electrochemiluminescent (d-BPE-ECL) based on photothermal amplification biosensor via the thermophysical and photochemical properties of niobium carbide Mxene quantum dots (Nb2C MQDs) has been proposed. The device consists of three components: separated intermediate recognition, cathodic catalytic hydrogen evolution reaction (HER) and anodic ECL response channel. Wherein, the recognition compartment was innovatively designed as a temperature-sensitive conductivity modulated interface, and the introduction of photothermal material PDA@Nb2C MQDs through target mediated rolling circle amplification strategy increases the interface temperature under near-infrared light radiation, thereby enhancing the BPE current and leading to the amplification of the anode ECL signal of Nb2C MQDs. In addition, MoS2@Ni–Cu–P features excellent electrocatalytic activity, which can promote HER and thus accelerate electron transfer, further amplifying the ECL signal. Therefore, a highly sensitive d-BPE-ECL biosensor for hepatitis C virus envelope protein E2 detection with a linear range from 10−4 to 10 ng/mL and detection limit of 3.3 × 10−5 ng/mL was obtained. This work is expected to provide a new direction for exploring BPE multiple signal amplification strategy and broaden the application of BPE-ECL in bioassays.