Reaction Constants Research Articles

Activation volume and quantum tunneling in the hydrogen transfer reaction between methyl radical and methane: A first computational study.

We present a theory of the effect of quantum tunneling on the basic parameter that characterizes the effect of pressure on the rate constant of chemical reactions in a dense phase, the activation volume. This theory results in combining, on the one hand, the extreme pressure polarizable continuum model, a quantum chemical method to describe the effect of pressure on the reaction energy profile in a dense medium, and, on the other hand, the semiclassical version of the transition state theory, which includes the effect of quantum tunneling through a transmission coefficient. The theory has been applied to the study of the activation volume of the model reaction of hydrogen transfer between methyl radical and methane, including the primary isotope substitution of hydrogen with deuterium (H/D). The analysis of the numerical results offers, for the first time, a clear insight into the effect of quantum tunneling on the activation volume for this hydrogen transfer reaction: this effect results from the different influences that pressure has on the competing thermal and tunneling reaction mechanisms. Furthermore, the computed kinetic isotope effect (H/D) on the activation volume for this model hydrogen transfer correlates well with the experimental data for more complex hydrogen transfer reactions.

Theoretical Study on Ethylamine Dissociation Reactions Using VRC-VTST and SS-QRRK Methods.

Barrierless bond dissociation reactions play an important role in fuel combustion. In this work, the pressure-dependent dissociation rate constants of ethylamine (EA) are accurately determined using variable-reaction-coordinate variational transition-state theory combined with the system-specific quantum Rice-Ramsperger-Kassel method. Before the kinetics calculations, the performances of four density functional theory methods in describing the bond dissociation of EA are evaluated against the benchmark method, FIC-MRCISD(T)+Q/cc-pVTZ, and the MN15-L/cc-pVTZ method is the best choice. By comparison of the Gibbs free energies and the rate constants for the bond dissociation reactions of EA, ethanol, and propane, the influence of functional groups on the reaction kinetics is discussed. The kinetics calculations show that the dissociation rate constants of EA are sensitive to pressure at low pressures and high temperatures, and the dominant channel is the reaction that yields C2H5 and NH2 radicals. A literature combustion model of EA is updated with our calculations, and the satisfactory agreement between the model predictions and reported ignition delay times of EA suggests the reliability of our calculations.

Synergistic effects of micronanobubbles and AC/Ag–TiO2 nanocomposites in photocatalytic process

The AC/Ag–TiO2 nanocomposites were prepared by sol-gel method using different concentrations of Ag. Comprehensive characterization of the crystalline structure, surface morphology, elemental composition, and optical properties of the AC/Ag–TiO2 photocatalysts was carried out using XRD, FTIR, SEM, EDX, TEM, and UV–vis DRS techniques. Consequently, a detailed investigation into the photocatalytic degradation of Indigo Carmine (IC) and Reactive Black 5 (RB5) dyes was conducted, thoroughly examining the involved photocatalytic mechanisms. The study revealed promising outcomes, particularly with the hybrid photocatalyst AC/0.5%Ag–TiO2, showcasing enhanced characteristics in both photooxidation and absorption processes, thereby boosting overall efficacy for IC (70.15%) and RB5 (69.9%). Remarkably, the introduction of small air bubbles significantly improved the removal efficiency of IC and RB5 dyes, achieving removal levels of 93.66% and 88.66%, respectively. The utilization of these micro-nanobubble systems (MNBs) resulted in notably higher first-order reaction constants compared to scenarios without MNBs, indicating the pivotal role of the photocatalyst in dye removal processes. Additionally, the photocatalyst showed unmatched efficacy in eliminating the pesticide carbaryl, attaining 100% removal with and without the presence of MNBs. Moreover, the AC/Ag–TiO2 photocatalyst exhibited significant inhibition of both gram-positive and gram-negative pathogenic bacteria, showcasing its capability to curb their growth even without MNB aeration. This underscores its potential for applications in environmental remediation and microbial control.

Fungal cellulolytic enzyme complex immobilized on chitosan-functionalised magnetic nanoparticles for paddy straw saccharification

Utilization of biopolymeric functionalized nanocomposites for enzyme immobilization has been actively explored for their potential role as catalysts in sustainable agro-residue valorization models. In the present study, cellulase immobilization on control and chitosan functionalized magnetic nanoparticles (c-MNP & Ch-MNP, respectively) was investigated. A cellulase binding efficiency of 67.50% on c-MNP and 74.06% on Ch-MNP was achieved. The enzyme immobilization on nano-supports was confirmed using electron microscopic and spectroscopic techniques. The immobilized cellulase (E-Ch-MNP) exhibited carboxymethyl cellulase, cellobiase and avicelase specific activities of 48.68, 25.98 and 33.80 nmol min−1 mg−1 protein. The optimum pH for free and immobilized enzyme were reported to be pH 5 and 6, respectively. An increased thermal stability for E-Ch-MNP was observed over a broader temperature range with a peak relative enzyme activity at 60℃. The binding constant (Km= 5.00 mg ml−1) and maximal rate of reaction (Vmax= 0.12 µmol min−1 ml−1) were also determined for E-Ch-MNP. Molecular docking studies determined the flexibilities of both the receptor cellulase protein and the ligand immobilization support molecules with respect to the binding energy and inhibition constants, reflecting their desired conformation and stability. Maximum reducing sugar content of 242.14 mg g−1 of pre-treated straw was reported at 96 h of incubation for E-Ch-MNP with a saccharification efficiency of 35.78%. The retained relative activity of immobilized cellulase was 82.83, 75.17, 44.61 and 27.95% of initial activity after second, third, fourth and fifth cycle, respectively. Therefore, immobilization of cellulase on chitosan coated magnetic nanoparticles holds promise for further optimization for improved cellulose hydrolysis.

A comprehensive equilibrium model for the phosphonate scale inhibitor-carbonate system including coupled adsorption/precipitation (Γ/Π)

Inorganic scale deposition is one of the main flow assurance issues in hydrocarbon production, and injection systems, leading to significant loss in production and subsequent expense to mitigate. Scale Inhibitors (SI) are chemicals that are commonly used to prevent the inorganic scale from building up in the system. SIs are usually injected into the porous media, where they can react and be retained, and released back into the produced brine as the production commences. This in situ scale prevention method is known as “squeeze treatment”, and the lifetime of this process is determined when the SI concentration in the return fluid falls below the MIC (Minimum Inhibitor Concentration), where the SI is sufficiently effective at preventing or efficiently reducing scale formation. In this study, a general chemical equilibrium model has been developed to simulate the chemical reaction of phosphonate scale inhibitors and their retention in a carbonate system (calcite), in the presence of an aqueous phase containing free divalent cations. The model couples together the following processes (i) the carbonate system, (ii) speciation of the SI, modelled as a weak polyacid, HnA, (iii) the metal (Ca2+, Mg2+) binding – SI chelant interactions, (iv) phosphonate SI acid impurity reactions, (v) adsorption of the free and complex species to the rock surface and (vi) and finally, the precipitation of complex species (SI-Ca-Mg). To find the equilibrium conditions, charge balance and mass balances for key components in the system were considered, and combined utilizing reaction constants, i.e. equilibrium constants, stability constants, and solubility constants. This full equation set can be solved numerically to find the equilibrium concentration of all engaged species to characterize the equilibrium condition. To account for the adsorption and precipitation retention in this system, a coupled adsorption/precipitation (Γ/Π) isotherm has been presented and used for the first time. The coupled Γ/Π isotherm is a mathematical representation of the retention amount in the system that coupled adsorption and precipitation retention mechanisms are in action, which can scale up the retention results to other systems with different mass to volume ratios. To validate the proposed model, experimental results of a DETPMP-Calcite equilibrium system in NSSW were considered. The model and the experimental results were in good agreement demonstrating the reliability of the model. Furthermore, the reliability of the model in stoichiometry prediction of complexes, and distribution of species in different conditions was evaluated which confirmed the validity of the model.

Sorption of U(VI) on MX-80 Bentonite and Granite in Ca-Na-Cl Saline Solutions

Uranium has been identified as an element of interest for the safety assessment of a deep geological repository for used nuclear fuel. This paper examines the sorption behavior of U(VI) onto MX-80 bentonite and granite in Ca-Na-Cl solutions of varying ionic strengths [0.05 to 3 mol/kgw (m)] and across a pH range of 4 to 10. U(VI) sorption on MX-80 showed that U(VI) sorption gradually increased with pHm until pHm = 6, where it reached its maximum, and decreased slightly with pHm until pHm = 8, and then became constant. U(VI) sorption on granite increased along with pHm, reached the maximum around pHm = 7 to 8, and then slightly decreased with pHm. Both MX-80 and granite showed essentially no ionic strength dependence for sorption of U(VI). A nonelectrostatic surface complexation model successfully predicted sorption of U(VI) onto MX-80 and granite using the formation of an inner-sphere surface complex. Optimized values of surface complexation reaction constants (log K0) for the formation reactions of these surface species are proposed.

What Principle Governs the Chemical Dynamic/Kinetic Process (3)?

In this work we discussed the description of the chemical dynamic/kinetic process. It is noticed that the conventional one way description about the chemical dynamic/kinetic process is a mathematically correct but physically incorrect description, because the chemical reaction doesn’t follow the one way mechanism as scientist’ will. Instead, the forward chemical dynamic/kinetic processes are always accompanied by the backward chemical dynamic/kinetic processes. Based on this physical picture for the chemical reaction dynamic/kinetic process, it is concluded: 1.the forward and backward chemical reactions follow the same route, just the time direction is reversed and 2.the exponential factor of the rate constant of the chemical reaction is the same for forward and backward chemical reaction dynamic/kinetic processes.

Deciphering the mechanism of glutaredoxin-catalyzed roGFP2 redox sensing reveals a ternary complex with glutathione for protein disulfide reduction

Glutaredoxins catalyze the reduction of disulfides and are key players in redox metabolism and regulation. While important insights were gained regarding the reduction of glutathione disulfide substrates, the mechanism of non-glutathione disulfide reduction remains highly debated. Here we determined the rate constants for the individual redox reactions between PfGrx, a model glutaredoxin from Plasmodium falciparum, and redox-sensitive green fluorescent protein 2 (roGFP2), a model substrate and versatile tool for intracellular redox measurements. We show that the PfGrx-catalyzed oxidation of roGFP2 occurs via a monothiol mechanism and is up to three orders of magnitude faster when roGFP2 and PfGrx are fused. The oxidation kinetics of roGFP2-PfGrx fusion constructs reflect at physiological GSSG concentrations the glutathionylation kinetics of the glutaredoxin moiety, thus allowing intracellular structure-function analysis. Reduction of the roGFP2 disulfide occurs via a monothiol mechanism and involves a ternary complex with GSH and PfGrx. Our study provides the mechanistic basis for understanding roGFP2 redox sensing and challenges previous mechanisms for protein disulfide reduction.

Changes in Mechanism and Transition State Structure for Solvolysis Reactions of Ring Substituted Benzyl Chlorides in Aqueous Solution.

Rate and product data are reported for the solvolysis reactions of twenty-seven mono, di (3,4) and tri (3,4,5) ring-substituted benzyl chlorides. The first order rate constant for solvolysis in 20% acetonitrile in water decrease from k solv = 2.2 s-1 for 4-methoxybenzyl chloride to 1.1 x 10-8 s-1 for 3,4-dinitrobenzyl chloride. The product rate constant ratios k MeOH/k TFE for solvolysis in 70/27/3 (v/v/v) HOH/TFE/MeOH range from a minimum of k MeOH/k TFE = 8 to a maximum of 110. The rate data were fit to a four-parameter Hammett equation that separates the resonance and polar effects of the aromatic ring substituents on the reaction rate. Increases in the values of the Hammett reaction constants and are observed as the substituent constants or are increased. A sharp decrease in the product selectivity k MeOH/k TFE = 26 for stepwise solvolysis of 4-methoxybenzyl chloride is observed as electron-withdrawing meta-substituents are added to 4-methoxybenzyl ring due to a Hammond-effect on the position of the transition state for solvent addition to the substituted 4-methoxybenzyl carbocation reaction intermediates. Sharp increases in the selectivity k MeOH/k TFE are observed with decreasing reactivity of other 3,4,5-subsituted benzyl chlorides due to anti-Hammond shifts on a two-dimensional More-O'Ferrall reaction coordinate diagram in the position of the transition state for a concerted solvolysis reaction.

Enhanced Photocatalytic Degradation of Methyl Orange Using Nitrogen‐Functionalized MesoporousTiO2 Decorated with Au9 Nanoclusters

A novel catalyst for dye degradation is fabricated through attaching Au9 nanoclusters (Au9 NCs) to N functionalized mesoporous TiO2 (NMTiO2). The NMTiO2 is created through chitosan‐assisted soft templating resulting in an N terminated surface preventing the agglomeration of the Au9 NCs adsorbed surface and enhancing the overall loading with Au9. The calcination atmosphere influenced the surface properties of the NMTiO2 and its capability to adsorb the Au9 NCs. The photocatalytic effectiveness of these materials was probed through methyl orange (MO) dye degradation. The black coloured Au9/NMTiO2 catalyst is highly effective to completely degrade MO dyes within 20 min due to its large reaction constant (0.176 min−1). Parameter interactions for the dye degradation process were explored using response surface methodology (RSM) and the dependency of MO degradation on the affecting parameters was evaluated based on the statistical analysis and 3D plots.

Kinetic study of H-abstraction and preliminary pyrolysis of n-decane in post-injection fuels

The combustion and pyrolysis process of n-decane was investigated via quantum chemical method to enhance the understanding of post-injection fuels. The hydrogen abstraction reactions were the main reactions that initiated combustion and pyrolysis of n-decane via H atoms and CH3/OH/NO2 radicals. The potential energy surface of hydrogen abstraction and preliminary pyrolysis was determined via high precision CBS-QB3 and M06–2X/6–311++G (d,p) methods. RRKM - Master Equation theory had been utilized to calculate the rate constants of isomerization and β-dissociation reactions in the temperature range of 300–2000 K. In this PES, the ε-site was the most advantageous site in contrast with others and the α-site has the highest energy barrier and was the most challenging hydrogen abstraction site. The isomerisation reactions of decyl radicals play a crucial role in the combustion and pyrolysis of n-decane at low temperature, particularly via 1,5-H shift and 2,5-H shift reaction. At high temperatures, the scission of the CC bond becomes the primary mechanism. Additionally, modified information was incorporated into the detailed model of n-decane combustion and pyrolysis. The modified model exhibited good agreement with experimental measurements of the mole fractions of various significant products in Jet-stirred reactor (JSR) experiments. The research provides a foundation for future investigations of n-decane combustion and pyrolysis support.

Photomodulated phase-separation kinetics in block copolymer melts: a DPD simulation study

ABSTRACT We study phase-separation kinetics of symmetric diblock copolymer (BCP) melt in 3 d subjected to sequential light on/off cycles. The incompatible blocks of each BCP chain are connected by a photosensitive bond, which undergoes breakage during photo-illumination (on-cycle) and recombination during the off-cycle. We set a shorter fixed time limit for each on-cycles and focus on analysing how the much longer duration of the light off-cycles affects the segregation kinetics. We explore two scenarios for each off-cycle time variation: one with equal and another with increasing durations. For both cases, we determine the rate constants for bond formation and degradation reactions and assess their influence on the dynamical scaling functions and the growth scale of evolving morphologies. The average domain size typically exhibits diffusive growth ( R ( t ) ∼ t 1 / 3 ) for a couple of cycles in the beginning. However, the domain growth nearly freezes during the rest of the cycles, resulting in bicontinuous and nearly frozen isotropic morphologies.

Photogeneration and quenching of singlet molecular oxygen by bacterial C40 carotenoids with long chain of conjugated double bonds.

Measurement of photosensitized luminescence of singlet oxygen has been applied to studies of singlet oxygen generation and quenching by C40 carotenoids (neurosporene, lycopene, rhodopin, and spirilloxanthin) with long chain of conjugated double bonds (CDB) using hexafluorobenzene as a solvent. It has been found that neurosporene, lycopene, and rhodopin are capable of the low efficient singlet oxygen generation in aerated solutions upon photoexcitation in the spectral region of their main absorption maxima. The quantum yield of this process was estimated to be (1.5-3.0) × 10-2. This value is near the singlet oxygen yields in solutions of ζ-carotene (7 CDB) and phytoene (3 CDB) and many-fold smaller than in solutions of phytofluene (5 CDB) (Ashikhmin et al. Biochemistry (Mosc) 85:773-780, https://doi.org/10.1134/S0006297920070056 , 2020, Biochemistry (Mosc) 87:1169-1178, 2022, https://doi.org/10.1134/S00062979221001082022 ). Photogeneration of singlet oxygen was not observed in spirilloxanthin solutions. A correlation was found between the singlet oxygen yields and the quantum yields and lifetimes of the fluorescence of the carotenoid molecules. All carotenoids were shown to be strong physical quenchers of singlet oxygen. The rate constants of 1O2 quenching by the carotenoids with long chain of CDB (9-13) were close to the rate constant of the diffusion-limited reactions ≈1010M-1s-1, being many-fold greater than the rate constants of 1O2 quenching by the carotenoids with the short chain of CDB (3-7) phytoene, phytofluene, and ζ-carotene studied in prior papers of our group (Ashikhmin et al. 2020, 2022). To our knowledge, the quenching rate constants of rhodopin and spirilloxanthin have been obtained in this paper for the first time. The mechanisms of 1O2 photogeneration by carotenoids in solution and in the LH2 complexes of photosynthetic cells, as well as the efficiencies of their protective action are discussed.

Understanding Nucleophilicity of Pyridine-N-oxides Towards 2,4,6-Trinitrophenylbenzoate Through Simple Absorption Spectroscopic Studies

Aims: Understanding nucleophilicity of poor nucleophiles like pyridine-N-oxides. Background: Nucleophilicity plays a vital role in substitution reactions. It helps to determine the possibility and extent of the substitution reactions. The study of the nucleophilicity of poor nucleophiles is challenging, and it has limited substrate scope. Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative way is important. Objective: Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative way. Selection of appropriate electrophile for the reactions with the poor nucleophiles-pyridine-N-oxides. Development of suitable methodology for kinetic studies of the reaction. Methods: UV-Vis spectroscopic methods for monitoring the reactions. Results: The kinetic studies revealed that the second-order rate constants of the nucleophilic reactions are 1.67× 102 L mol-1 min-1, 29.8 L mol-1 min-1, 29.51 L mol-1 min-1, where the nucleophiles are p-methylpyridine-N-oxide, pyridine-N-oxide, and p-nitropyridine-N-oxide, respectively. The UV-Vis spectroscopic analysis revealed the nucleophilicity of p-methylpyridine-N-oxide > pyri-dine-N-oxide > p-nitropyridine-N-oxide. Conclusion: This comparative study suggests that the strength of nucleophilicity of the p-methylpyridine-N-oxide is 5.6 times and 66.53 times more than that of pyridine-N-oxide and p-nitropyridine-N-oxide, respectively, whereas the strength of nucleophilicity of the pyridine-N-oxide is 11.87 times more than that of p-nitropyridine-N-oxide.

Solar Light Active Graphitic Carbon Nitride/Biochar Nanocomposite for RhB Dye Degradation

AbstractIn this work, nanocomposite graphitic carbon nitride/biochar is successfully prepared by physical mixing method to achieve efficient charge separation and photodegradation of RhB dye under sunlight. The biochar is synthesized by heating biomass in muffle furnace in an inert atmosphere. The graphitic carbon nitride is prepared using melamine as a precursor and heating it in a muffle furnace in air atmosphere. The structural characterizations FTIR and X‐ray diffraction are done to confirm the functional groups and crystallography of prepared samples. The photodegradation of RhB dye by nanocomposite is analyzed using a UV–visible spectrophotometer under solar irradiation. It is found that the RhB dye is completely reduced by the nanocomposite in less than 6 min in the presence of sunlight. The kinetic study confirms the photodegradation of RhB dye is first order reaction and rate constant is found to be 0.31 min−1.

SPH simulation of shock-induced chemical reactions in reactive powder mixtures

Reactive materials (RMs) are a mixture of two or more nonexplosive solid components in which, under extreme conditions, self-sustaining chemical reactions occur with the release of a high amount of energy. Knowing the kinetics of chemical reactions in RMs plays the key role in their efficient applications. In this work, we propose a macroscopic mathematical model of shock-induced chemical reactions based on smoothed particle hydrodynamics (SPH) for particle-scale simulation. The model includes the elastic-plastic deformation of materials, heating due to deformation and chemical reactions, diffusion of components, and heat transfer. The test calculations performed for the zero- and first-order reactions in the Al/S mixture showed a need for a more reliable determination of criteria and constants of chemical reactions. For this purpose, we propose a schematic experimental arrangement for the experimental and theoretical determination of the critical reaction pressure and the rate constant of the reaction. The type and corresponding constants of chemical reactions can be determined, for example, by the maximum likelihood method. We theoretically determined the zones of chemical reaction with different modes and found the influence of the projectile velocity and the intensity of shock waves on the development and completion of chemical reactions.

Enhancing the Selectivity of Trivalent Actinide over Lanthanide Using Asymmetrical Phenanthroline Diamide Ligands.

Phenanthroline diamide ligands have been widely used in the separation of trivalent actinides and lanthanides, but little research has focused on extractants with asymmetrical substitutes. Two novel asymmetrical phenanthroline-based ligands N2,N2,N9-triethyl-N9-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DE-ET-DAPhen) and N2-ethyl-N9,N9-dioctyl-N2-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DO-ET-DAPhen) were first synthesized in this work, whose extraction ability and complexation mechanism to trivalent actinides [An(III)] and lanthanides [Ln(III)] were systematically investigated. The ligands dissolved in n-octanol exhibit good extraction ability and high selectivity toward Am(III) in acidic solutions. The complexation mechanism of the ligands with Ln(III) in solution and solid state was analyzed using slope analysis, 1H NMR spectrometric titration, ESI-MS, and calorimetric titration. It is revealed that the ligands complex with Am(III)/Eu(III) with 1:1 stoichiometry. The stability constant (log β) of the complexation reaction of Eu(III) with DE-ET-DAPhen determined by UV-vis spectrophotometric and calorimetric titration is higher than that of DO-ET-DAPhen, indicating the stronger complexation ability of DE-ET-DAPhen. Meanwhile, the calorimetric titration results show that the complexation process is exothermic with a decreased entropy. The structures of 1:1 complexes of Eu(III) and Nd(III) with DE-ET-DAPhen were analyzed through single-crystal X-ray diffraction. This work proves that ligands containing asymmetrical functional groups are promising for An(III)/Ln(III) separation, which shows great significance in efficient extractants designed for the spent nuclear fuel reprocessing process.

Au9 clusters deposited as co-catalysts on S-modified mesoporous TiO2 for photocatalytic degradation of methyl orange

Au9 nanoclusters (Au9 NCs) were deposited onto S-functionalized mesoporous TiO2 (SMTiO2) to produce efficient photocatalysts for Methyl Orange (MO) dye degradation with UV light. The morphology, the surface composition and the size of the deposited Au9 NCs of the catalyst was analysed. SMTiO2 could adsorb more clusters with lesser Au9 cluster agglomeration than unmodified MTiO2. This finding is attributed to the capability of the thiol groups to form strong bonds with the Au9 clusters. To study Au9 NCs effect on dye degradation activity, the MO degradation reaction constants under UV-light irradiation for SMTiO2 nanoparticles (NPs) and Au9 NCs decorated SMTiO2 photocatalysts were studied, which were 0.07 min−1 and 0.149 min−1, respectively. Hence, it takes almost half the time to completely degrade MO using Au9 NCs decorated SMTiO2 photocatalysts compared to SMTiO2 substrate. Results were analysed using the response surface methodology (RSM) to study the interaction between the reaction parameters.

Removal of tetracycline by ultraviolet/sodium percarbonate (UV/SPC)advanced oxidation process in water

Tetracycline (TC) was widely used and frequently detected in various water bodies, where the presence of TC posed a significant threat to the health of aquatic organisms. Furthermore, antibiotics were hardly degraded by biological treatment. Thus, in order to enhance the removal of TC, we proposed the use of a novel ultraviolet/sodium percarbonate (UV/SPC) advanced oxidation process and initiated an in-depth study. The study investigated the influence of oxidant dosage, initial pH, UV intensity, and TC concentration on the removal of TC. The results demonstrated that the UV/SPC system efficiently removed TC, with removal efficiency increasing as the SPC concentration increased. Within the pH range of 3–11, TC degradation exhibited minimal variation, indicating the UV/SPC system's strong adaptability to pH variations. The research on the impact of the water matrix on TC removal revealed that HCO3− had an inhibitory effect on TC degradation, while NO3− promoted TC degradation. Additionally, the presence of free radical species (·OH, ·CO3−, ·O2−) were detected and rate constants for the secondary reactions (k·OH,TC = 6.3 × 109 L mol−1·s−1, k·CO3-,TC = 3.4 × 108 L mol−1·s−1) were calculated, indicating that ·OH exhibited a stronger oxidative performance compared to ·CO3−. This study did not only present a novel strategy via UV/SPC to remove TC but also uncovered the unique role of ·CO3− for contaminant removal.

High-Pressure Limit and Pressure-Dependent Rate Rules for β-Scission Reaction Class of Hydroperoxyl Alkyl Hydroperoxyl Radicals (•P(OOH)2) in Normal-Alkyl Cyclohexanes Combustion.

Chemical kinetic studies of the β-scission reaction class of hydroperoxyl alkyl hydroperoxyl radicals (•P(OOH)2) from normal-alkyl cyclohexanes are carried out systematically through high-level ab initio calculations. Geometry optimizations and frequency calculations for all species involved in the reactions are performed at the B3LYP/CBSB7 level of theory. Electronic single-point energy calculations are calculated at the CBS-QB3 level of theory. Rate constants for the reactions of β-scission, in the temperature range of 500-1500 K and the pressure range of 0.01-100 atm, are calculated using transition state theory (TST) and Rice-Ramsberger-Kassel-Marcus/Master-Equation (RRKM/ME) theory taking asymmetric Eckart tunneling corrections and the one-dimensional hindered rotor approximation into consideration. The rate rules are obtained by averaging the rate constants of the representative reactions of this class. These rate rules can greatly assist in constructing more accurate low-temperature combustion mechanisms for normal-alkyl cyclohexanes.