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Open access Aug 2026

Development of a ReaxFF Reactive Force Field for the Investigation of Thermochemical, Thermophysical and Oxidation Behavior of Titanium Diboride

To predict the thermochemistry and thermophysical properties and oxidation mechanisms of titanium diboride (TiB2), we have developed a ReaxFF reactive force field in which the parameters are trained against a set of quantum mechanics data, including the heats of formation and elastic properties for various titanium boride phases, as well as heats of formation of various titanium oxide and boron oxide phases. The developed ReaxFF accurately reproduces the formation energies, relative stability, and elastic properties of these phases. To demonstrate the applicability of our developed ReaxFF force field, we performed ReaxFF-based molecular dynamics simulations to evaluate thermal expansion and melting behavior and validated the results against published experimental data. The thermal expansion simulations reflected the experimentally observed anisotropic behavior, demonstrating greater expansion along the c-axis compared to the a-axis, and showed good agreement in volume expansion measurements. The predicted bulk melting temperature of 3120.87 K is consistent with experimental values (3063–3498 K), while a lower surface melting point of 3049.20 K was observed due to reduced atomic coordination. Moreover, the oxidation behavior of TiB2 was investigated using molecular dynamics simulations. To accelerate the oxidation process within the accessible MD time scales, we employed elevated oxygen concentrations and high-temperature conditions. Additionally, replica exchange molecular dynamics (REMD) simulations were conducted at a temperature of 1970 K, corresponding to experimental oxidation conditions. The simulations revealed that oxidation was initiated with the formation of titanium oxides, consistent with the lower formation energy of TiO2 compared to B2O3. Notably, the titanium oxide formed during the REMD simulations mostly resembled the TiO2 phase in terms of crystallinity. Smaller boron oxide species were also observed through REMD simulations. These results confirm that the developed ReaxFF potential reliably models both the thermochemical and thermophysical behavior of TiB2, as well as complex oxidation mechanisms, making it an accurate and computationally inexpensive tool for simulating high-temperature ceramic materials.

M. Mirakhory, S. Ness, S. McCormack et al. · 0 citations
Open access Aug 2026

Expanded Group Additivity Framework for Thermochemical Prediction of Fluorocarbons and PFAS from Large-Scale DFT Data

Fluorinated molecules, including per- and polyfluoroalkyl substances (PFAS), present persistent challenges for thermochemical characterization due to limited experimental data, strong carbon–fluorine bonding, and the rapidly expanding size and diversity of fluorinated chemical space. While density functional theory (DFT) calculations can provide useful thermochemical data for individual fluorinated species, their routine application becomes increasingly impractical as molecular size, conformational complexity, and the number of distinct PFAS compounds continue to grow. Existing Benson-type group additivity schemes provide limited resolution for fluorinated environments, restricting their applicability to modern fluorinated and PFAS-relevant systems. Here, we develop a chemically resolved group additivity (GA) framework for fluorinated and PFAS-relevant species by fragmenting DFT-derived thermochemistry for 3070 molecules. This approach expands the available fluorinated Benson-type group library from 14 to 159 local environments and integrates the resulting groups within the Python Group Additivity (pGrAdd) framework. 10-fold cross-validated regression against DFT data yields root-mean-square deviations (RMSDs) of 8.14 kcal·mol–1 for enthalpy and 10.05 cal·mol–1·K–1 for entropy, which are reduced to 2.55 kcal·mol–1 and 6.36 cal·mol–1·K–1, respectively, following application of independently defined nongroup interaction correction terms in pGrAdd. Comparison with available experimental thermochemical data shows improved agreement and reduced bias compared to legacy Benson group libraries. This expanded fluorinated GA framework enables scalable and chemically interpretable thermochemical predictions for fluorinated and PFAS-relevant species, supporting kinetic modeling and mechanistic studies where direct electronic structure calculations are feasible but not scalable.

S. Eccles, Steven Pellizzeri · 0 citations
Open access Aug 2026

Atmospheric Reactions of HFE-7100 with HO2 and NH2 radicals: Kinetics Mechanism and Atmospheric implications

In recent pasts, HFE-7100 finds its industrial applications like cleaning electronic equipment, secondary refrigerant and carrier fluids for lubricant. Detailed theoretical investigations have been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CF3CF2CF2CF2OCH3 (HFE-7100) and HO2 and NH2 radicals using DFT-based M06-2X/6-311++G(d,p) level of theory. Two important H abstraction channels have been identified and one transition state has been located for each reaction channel. The pre-reactive and post-reactive complexes are validated at entrance and exit channels, respectively. The potential energy surface of the HFE-7100 with HO2 and NH2 radicals has been investigated using DFT method. The rate constants of the two reactions are computed over the temperature range of 250–450 K for the first time. Our results suggest that hydrogen abstraction by NH2 radical is likely the dominant route for the atmospheric oxidation of HFE-7100 under reaction conditions. Keywords: Segregated HFE; M06-2X; DFT; Rate constant; Amino radical

Narendra Pramanik, Devaprasad Dev, N. K. Gour et al. · 0 citations
Review Open access Jul 2026

End-of-Life Chemistry of Polytetrafluoroethylene: From Destruction to Fluorine Reuse

Polytetrafluoroethylene (PTFE) is one of the most chemically and thermally resilient synthetic materials. That resilience underpins its value in aggressive service environments, but it also complicates end-of-life treatment. The central challenge is not simply to remove the parent polymer, but to determine where fluorine and carbon go after carbon-fluorine (C-F) bond cleavage and whether those products are benign, controllable or useful. This Review organizes the emerging chemistry of PTFE end-of-life management around five distinct endpoints, namely parent disappearance, bulk defluorination, fluorine mineralization, fluoride recovery and fluorine reuse. It compares high-temperature destruction, molten-hydroxide mineralization, reductive defluorination and mechanochemical conversion through a common set of descriptors spanning fluorine mass balance, sink quality, carbon fate, process intensity and deployment plausibility. A consistent picture emerges in which thermal routes remain the benchmark for feed tolerance and rapid elimination, but their practical value depends on suppressing incomplete-destruction products and coupling bond cleavage to robust fluoride capture. Milder chemical and solid-state routes show that PTFE can also be directed into defined mineral sinks or directly reusable fluorinating reagents, although they are often constrained by interfacial transport, crystallinity and feed heterogeneity. Future progress will depend on treating PTFE not only as a recalcitrant waste, but as a concentrated fluorine reservoir whose end-of-life chemistry must unite selective bond activation with accountable fluorine stewardship.

Zhangmeng Liu, Leyan Liu, Xinghao Qi et al. · 0 citations
Aug 2026

Computational Study of the Gas-Phase Thermal Degradation and the Reaction Rate Coefficients of Chlorinated Perfluoro-Alkyl Carboxylic Acids

Per- and polyfluoroalkyl substances (PFAS) are a class of ubiquitous pollutants that do not appreciatively biodegrade. A ban on the most commonly used PFAS, perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl sulfonic acids, created a gap that was filled by several similarly heavily fluorinated compounds. While chemical and biological studies on several subclasses of PFAS have progressed significantly, testing on the chlorinated PFAS is still lagging. For most PFAS, the main treatment consists of filtration followed by pyrolysis of the laden adsorbents. Herein, the pyrolytic degradation pathways of mono- and polychlorinated PFCA (ClxPFCA) are analyzed. This study showed that the bond dissociation energies (BDEs) are slightly lower in the acid form compared to the carboxylate form. The C–Cl bonds are generally the weakest (∼70 kcal/mol) while the strongest are the C–F bonds (105-110 kcal/mol). After studying their BDEs, the secondary degradation pathways of the radicals formed by the first bond cleavage were analyzed. Five reaction pathways were studied for the chlorinated radicals generated by the first bond cleavage. The activations energies (Ea) and the enthalpies (ΔH) in the cases of a barrierless reaction are similar among the group of radicals. The lowest Ea are those of the Cl-shifts (∼10–25 kcal/mol) while the most energetic pathways are the F-losses (50–65 kcal/mol). Finally, a kinetic study was performed to evaluate the reaction rate coefficients of each pathway. It showed a preference for the β-scission pathways at the highest temperatures analyzed and the F-shift followed by Cl-loss at the lowest temperatures. The lifetimes of the radicals are generally in the ms-min for the perfluorinated alkyl radicals and min-hr for the perfluorocarboxyalkyl radicals.

Unknown authors · 0 citations
Jul 2026

Local polarization-piezoelectric field promotes water dissociation for efficient fluorinated pollutants defluorination.

Active hydrogen radicals (•H) from water dissociation hold great promise for the defluorination of perfluorooctanoic acid (PFOA). However, the mechanism governing •H generation under a local polarization piezoelectric electric field (LPPEF) remains insufficiently explored in borate-based piezocatalysts, which hinders an understanding of the piezocatalysis-driven water dissociation. Herein, we investigated piezocatalyst, Sr2B5O9Cl (SBOC) and its KBH4-impregnated derivative (B-SBOC) in PFOA defluorination. Under ambient conditions, B-SBOC achieves a degradation rate constant of 1.34 × 10-2 min⁻1 for an initial PFOA concentration at 24.2 μM, along with a synchronous defluorination ratio of 78% within 120 min, representing a 2.5-fold enhancement over pristine SBOC. The incorporated electron-deficient boron atoms serve as Lewis acid sites, which not only enhance surface hydrophilicity and reverse the surface charge to facilitate PFOA adsorption but, more critically, intensify the LPPEF. The strengthened LPPEF promotes the preferential adsorption of •OH, thereby effectively suppressing •OH/•H recombination. This accelerates the kinetics of water dissociation and promotes subsequent •H dominated H/F exchange reactions, boosting efficient PFOA defluorination. This work provides fundamental insight into the LPPEF dominated radical separation process and offers a potential strategy for designing highly efficient piezocatalytic systems for recalcitrant fluorinated pollutants remediation.

Yi Liu, Zhikui Zhou, Yuhang Xu et al. · 0 citations

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