Thermal Decomposition Pathways Research Articles

Understanding the stability of a plastic-degrading Rieske iron oxidoreductase system.

Rieske oxygenases (ROs) are a diverse metalloenzyme class with growing potential in bioconversion and synthetic applications. We postulated that ROs are nonetheless underutilized because they are unstable. Terephthalate dioxygenase (TPADO PDB ID 7Q05)is a structurally characterized heterohexameric α3β3 RO that, with its cognate reductase (TPARED), catalyzes the first intracellular step of bacterial polyethylene terephthalate plastic bioconversion. Here, we showed that the heterologously expressed TPADO/TPARED system exhibits only ~300 total turnovers at its optimal pH and temperature. We investigated the thermal stability of the system and the unfolding pathway of TPADO through a combination of biochemical and biophysical approaches. The system's activity is thermally limited by a melting temperature (Tm) of 39.9°C for the monomeric TPARED, while the independent Tm of TPADO is 50.8°C. Differential scanning calorimetry revealed a two-step thermal decomposition pathway for TPADO with Tm values of 47.6 and 58.0°C (ΔH = 210 and 509 kcal mol-1, respectively) for each step. Temperature-dependent small-angle x-ray scattering and dynamic light scattering both detected heat-induced dissociation of TPADO subunits at 53.8°C, followed by higher-temperature loss of tertiary structure that coincided with protein aggregation. The computed enthalpies of dissociation for the monomer interfaces were most congruent with a decomposition pathway initiated by β-β interface dissociation, a pattern predicted to be widespread in ROs. As a strategy for enhancing TPADO stability, we propose prioritizing the re-engineering of the β subunit interfaces, with subsequent targeted improvements of the subunits.

Mechanistic exploration of polytetrafluoroethylene thermal plasma gasification through multiscale simulation coupled with experimental validation

The ever-growing quantities of persistent Polytetrafluoroethylene (PTFE) wastes, along with consequential ecological and human health concerns, stimulate the need for alternative PTFE disposal method. The central research challenge lies in elucidating the decomposition mechanism of PTFE during high-temperature waste treatment. Here, we propose the PTFE microscopic thermal decomposition pathways by integrating plasma gasification experiments with multi-scale simulations strategies. Molecular dynamic simulations reveal a pyrolysis—oxidation & chain-shortening—deep defluorination (POCD) degradation pathway in an oxygen atmosphere, and an F abstraction—hydrolysis—deep defluorination (FHD) pathway in a steam atmosphere. Density functional theory computations demonstrate the vital roles of 1O2 and ·H radicals in the scission of PTFE carbon skeleton, validating the proposed pathways. Experimental results confirm the simulation results and show that up to 80.12% of gaseous fluorine can be recovered through plasma gasification within 5 min, under the optimized operating conditions determined through response surface methodology.

Formaldehyde-free and durable phosphorus-containing cotton flame retardant with -N=P-(N)3- and reactive ammonium phosphoric acid groups

A flame retardant (FR) hexachlorocyclotriphosphazene diethylenetriamine ammonium phosphoric acid (HDAPA) was synthesized. Vertical flammability test and limiting oxygen index (LOI) results showed that cotton samples finished with HDAPA solutions (15 % and 20 %) could pass vertical flame retardancy test, and LOIs reached 30.1 % and 35.4 % even after 50 laundering cycles according to AATCC 61-2013 3A washing standard (3A), performing flame retardancy and washing durability. Meanwhile, Fourier transform infrared and X-ray photoelectron spectroscopy analyses suggested that HDAPA was grafted on cotton fibers through -P(=O)-O-C covalent bond. Total heat release (1.98 MJ/m2) and char residue (16.2 %) of HDAPA treated cotton were much lower than those (4.26 MJ/m2, 3.2 %) of untreated cotton. Thermogravimetry results showed HDAPA changed thermal decomposition pathway of cotton fabric, which was further supported by thermogravimetric-Fourier infrared spectrometer results, revealing HDAPA performed a condensed phase flame retardancy mechanism. Scanning electron microscopy implied HDAPA entered amorphous region of cotton fibers to react with cellulose. Mechanical properties of HDAPA treated cotton decreased a little. Although the synthesis process used formaldehyde but no free formaldehyde released. In consequence, the aforementioned results indicated that the introduction of -N=P-(N)3- and -P(=O)(O−NH4+)2 groups to FR was an viable method to improve flame retardancy and durability.

Sooting tendency of substituted aromatic oxygenates: The role of functional groups and positional isomerism in vanillin isomers

Substituted aromatics are commonly observed in lignin-based biofuel; however, their high sooting tendency prevents direct utilization in commercial combustors. Recent studies have revealed that oxygenated functional group substitution could effectively suppress the soot emission from aromatic biofuels. This study aims to enhance the understanding of sooting tendencies in aromatic oxygenates with mono-, di-, and tri-substitutions, focusing on various functional groups and their positional isomerism. We established a yield sooting index (YSI) database of 42 single-ring aromatic compounds, including 30 new measurements from the present study. The constructed database was utilized to develop a multivariate linear regression (MLR) model to predict the YSI of substituted aromatic oxygenates based on their structural features. The fitted coefficients of the MLR model indicate vastly different impacts of hydroxyl, formyl, and methoxy functional group, as well as the importance of positional isomerism. To understand the role of oxygenated functional groups, we used substituted vanillin isomers containing hydroxyl, methoxy, and formyl groups as a model system. Comparing the sooting tendencies of these compounds revealed a high sensitivity of YSI to positional isomerism. A further mechanistic study using quantum-mechanical calculations showed that subtle interactions between three oxygenated functional groups in vanillin isomers can alter their thermal decomposition pathway, affecting the sooting tendencies of these aromatic fuels. The present study provides a novel statistical and theoretical explanation of how oxygenated substitution and its positional isomerism influence sooting behaviors, facilitating the rational design of lignin-based biofuels with minimal soot emission.

Aerosol-Assisted Chemical Vapor Deposition of 2H-WS2 From Single-Source Tungsten Dithiolene Precursors.

The tungsten carbonyl dimethyldithiolene (dmdt) complexes W(CO)4(dmdt), W(CO)2(dmdt)2, and W(dmdt)3 were evaluated as potential single-source precursors for the chemical vapor deposition of WS2. The results of TGA-MS, DIP-MS, and pyrolysis with NMR analysis were consistent with a thermal decomposition pathway in which loss of 2-butyne through a retro[3+2]cycloaddition of the dithiolene ligand generated terminal sulfido ligands. Aerosol-assisted chemical vapor deposition onto silicon substrates was performed using all three complexes, yielding 2H-WS2 thin films as characterized by Raman spectroscopy and GI-XRD. Film morphology and elemental composition of the films were determined using SEM, EDS, and XPS. Four-point probe measurements afforded a film resistivity of 8.37 Ωcm for a sample deposited from W(dmdt)3 in toluene at 600 °C.

Research progress on the catalytic and thermal decomposition of ammonium dinitramide (ADN).

Ammonium dinitramide (NH4N(NO3)2, ADN) is regarded as a promising oxidizer due to its low signature and high specific impulse. Generally, ADN undergoes exothermic decomposition above 140 °C accompanied by the byproduct of ammonium nitrate (AN). The inevitable endothermic decomposition of AN decreases the overall heat release, and so there is a need to develop efficient catalysts to guide ADN decomposition along desired pathways with a lower decomposition temperature and higher heat release. A suitable catalyst should be able to withstand the harsh conditions in a thruster to achieve a stable thrust force, which poses a huge obstacle for manufacturing a stable and active catalyst. This review gives a comprehensive summary of the thermal and catalytic decomposition pathways of ADN for the first time, which is expected to deepen the understanding of its reaction mechanism and provide useful guidance for designing prospective catalysts toward efficient ADN decomposition.

Using Artificial Solid-Electrolyte Interphase Coatings for Enhancing Safety of High-Energy Li-Ion Batteries from Material Level

The development of high-energy-density Li-ion batteries (LIBs) to meet the demand for electric vehicles and sustainable energy storage applications simultaneously brings about more safety issues. On the anode side, graphite has been a major anode material for high-energy LIBs and is anticipated to continuously play an important role even for the high-capacity Si-graphite (Si-Gr) composite anodes in the near future. The low lithiation electrochemical potential of graphite enables a lower anode potential allowing higher energy for a full cell but is vulnerable to the plating of metallic Li dendrite, which could easily arise from either over-lithiation, due to heterogeneity in the negative electrode, or fast charging. Li dendritic deposits could penetrate through the separator to trigger cell short-circuit and eventually thermal runaway. On the cathode side, the high surface reactivity and low oxygen lattice stability of the Ni-rich layered oxide cathodes lower the thermal stability. This study focuses on enhancing the safety of LIB full-cells by modifying the properties and stability of the solid-electrolyte interphases (SEIs) respectively on the anode and cathode electrodes. A polymeric artificial SEI for the anode is developed not only to improve the electrode performance but also effectively suppress SEI and Li dendrite formation. Meanwhile, a composite coating for the cathode is derived to simultaneously enhance the cycle stability and thermal stability, due to the altered thermal decomposition pathway, of an NCM811 cathode. The overall enhanced safety of the full cells is illustrated with the nail penetration test, and the safety-enhancing mechanisms are revealed by conducting post-mortem and synchrotron-based operando studies.

Investigation of the decomposition mechanism of MTNP melt-cast explosive at different temperatures and pressures through ReaxFF/lg molecular dynamics simulations.

Thermal decomposition of 1-methyl-3,4,5-trinitropyrazole (MTNP), a melt-cast explosive, was investigated at different temperatures (2500, 2750, 3000, 3250, and 3500 K) and pressures (3000 K/0.5 GPa, 3000 K/1 GPa) using the ReaxFF/lg force field. The study aimed to analyze the changes in reactant quantities, initial reaction pathways, and final product yields. The results demonstrated that complete decomposition of MTNP molecules occurred within a timeframe of 200 ps, with shorter decomposition times observed as the temperature increased. The high-temperature thermal decomposition of MTNP was found to follow two primary reaction pathways. Reaction 1 involved denitration, while reaction 2 proceeded with nitro group isomerization. DFT calculations indicated that nitro group isomerization was the most favorable reaction. During the initial stages, higher quantities of NO2, NO, and N2 were observed compared to other species. This can be attributed to the relatively higher nitrogen and oxygen content in the MTNP structure. Among the five reaction temperatures, it was observed that the quantities of small molecules followed the order of NO2 > NO > N2 > CO. Moreover, with increasing temperature, the quantities of all four small molecules increased, indicating that higher temperatures promoted the progression of the reactions. However, as the pressure increased, there was a trend of initially increasing and then decreasing to zero for the quantities of NO2 and NO. This suggests that high temperature accelerated the high-temperature thermal decomposition of NO2 and NO, leading to a significant increase in the content of N2. A 3 × 5 × 5 supercell model of MTNP was constructed in Materials Studio, consisting of 75 unit cells and 300 MTNP molecules. The model was then subjected to a 20 ps geometric optimization using the Polak-Ribiere version of the conjugate gradient (CG) algorithm in the large-scale atomic/molecular massively parallel simulator (LAMMPS) under the isothermal-isobaric (NPT) ensemble at 1 atm pressure and 300 K temperature. Following the optimization, molecular dynamics simulations were performed on the model at five temperatures (2500, 2750, 3000, 3200, and 3500 K) under 1 atm using the NPT ensemble for a total duration of 1 ns. During the simulations, atomic trajectories, as well as information on atomic and molecular species, were output every 500 steps. Subsequently, a custom script was utilized to analyze the thermal decomposition pathways and products. A time step of 0.1 fs was employed for the calculations, and periodic boundary conditions were applied to eliminate boundary effects.

Machine learning approach for ion imprinted (IIP) and non-imprinted (NIP) polymer discrimination based on pyrolysis kinetic data

The improper disposal of effluents containing toxic elements, such as nickel and mercury, can result in the gradual deterioration of surface water quality, impacting aquatic ecosystems and human health. Ionically imprinted polymers (IIPs) are promising candidates for remediating toxic areas due to their high removal rates and selectivity. In this study, multifunctional IIPs were developed using Ni2+ and Hg2+ as template ions and dithizone, methacrylic acid, and ethylene glycol dimethacrylate as complexing agent, monomer, and cross-linking agent, respectively, to remove Ni (II) and Hg (II) from effluents. The thermal decomposition behavior and degradation mechanism of ion imprinted polymers were investigated to address the issue of limited lifespan. The kinetic study revealed that the samples showed significant thermal stability, and the IIP-Duo sample exhibited higher activation energy compared to the non-imprinted polymer (NIP) and the mono-imprinted polymer (IIP), indicating that double impression alters the structure of the polymer and consequently its thermal degradation. Three machine learning models were applied to classify the samples according to imprinting, successfully predicting 95% or more of the classes correctly without overfitting or overmodelling. The master plot method showed that imprinting did not affect the thermal decomposition pathway, with the IIP, IIP-Duo, and NIP samples presenting the same mechanism geometrical contraction model (R3) at a conversion rate between 0.4 and 0.9. These findings suggest that multifunctional IIPs are promising materials for remediating areas impacted by toxic elements.

Synthesis and performance study of sulfur-containing amino acid ammonium phosphate type flame retardants for cotton fabric

In order to obtain cotton fabrics with high efficiency flame retardance, a new ammonium phosphate type active flame retardant N, N -bis (ammonium phosphate) cysteine (NP-BG), which is nonleaching, covalent attached, durable, functional flame retardants, was synthesized by Mannich reaction and applied to the flame-retardant modification of cotton fabrics. Test results such as FTIR and XPS showed that cotton fabrics had been successfully grafted with NP-BG. The LOI of cotton fabrics treated with 30 % flame retardant was as high as 40.2 %, and after 50 washes, the LOI of cotton fabric was still as high as 28.8 %; demonstrating the durability of flame retardance. The thermogravimetric-infrared coupling (TG-FTIR) test results showed that the flame retardant could change the thermal decomposition pathway of cotton fabric and produce a large amount of residual carbon, thus reducing the decomposition of cotton fiber and the release of flammable gas. In addition, cone calorimetry (CONE) experiments showed that the total heat release (THR) and heat release rate (HRR) of cotton fabrics were significantly reduced after the flame-retardant treatment. These findings indicate that NP-BG is a new flame-retardant material with good application prospects.

Investigation of the thermal hazard and decomposition mechanism of 1,1-di(tert-butylperoxy) cyclohexane by experiment and DFT simulation

1,1-Di (tert-butylperoxy) cyclohexane (1, 1-DTBCH), as an important organic peroxide, is commonly used as initiator, curing agent and crosslinking agent in the chemical industry. Due to the presence of peroxy bonds, the thermal instability of 1, 1-DTBCH may incur a decomposition reaction and cause further thermal runaway. The thermal decomposition characteristics and runaway reaction characteristics of 1, 1-DTBCH were investigated by differential scanning calorimetry (DSC) and accelerated rate calorimetry (ARC). The kinetic triplet and thermal safety parameters were calculated by using non-isothermal method. The gaseous products and pyrolysis products of 1, 1-DTBCH was investigated by thermogravimetric and infrared spectroscopy (TG-FTIR) and gas chromatography/mass spectrometry (GC/MS). The thermal decomposition pathway of 1, 1-DTBCH was explored with density functional theory (DFT). The exothermic dominant reaction in the thermal decomposition process of 1, 1-DTBCH was explored by combining experiment and theoretical calculation. The corresponding safety control measures were provided to reduce the thermal runaway hazard of 1, 1-DTBCH.

The Effect of Biochar Addition on Thermal Stability and Decomposition Mechanism of Poly(butylene succinate) Bionanocomposites.

In the present study, poly(butylene succinate) (PBSu) and its bionanocomposites containing 1, 2.5, and 5 wt.% biochar (MSP700) were prepared via in situ melt polycondensation in order to investigate the thermal stability and decomposition mechanism of the materials. X-ray photoelectron spectroscopy (XPS) measurements were carried out to analyze the surface area of a biochar sample and PBSu/biochar nanocomposites. From XPS, it was found that only physical interactions were taking place between PBSu matrix and biochar nanoadditive. Thermal stability, decomposition kinetics, and the decomposition mechanism of the pristine PBSu and PBSu/biochar nanocomposites were thoroughly studied by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TGA thermograms depicted that all materials had high thermal stability, since their decomposition started at around 300 °C. However, results indicated a slight reduction in the thermal stability of the PBSu biochar nanocomposites because of the potential catalytic impact of biochar. Py-GC/MS analysis was employed to examine, in more detail, the thermal degradation mechanism of PBSu nanocomposites filled with biochar. From the decomposition products identified by Py-GC/MS after pyrolysis at 450 °C, it was found that the decomposition pathway of the PBSu/biochar nanocomposites took place mainly via β-hydrogen bond scission, which is similar to that which took place for neat PBSu. However, at higher biochar content (5 wt.%), some localized differences in the intensity of the peaks of some specific thermal degradation products could be recognized, indicating that α-hydrogen bond scission was also taking place. A study of the thermal stability and decomposition pathway of PBSu/biochar bionanocomposites is crucial to examine if the new materials fulfill the requirements for further investigation for mulch films in agriculture or in electronics as possible applications.

Thermal Behavior and Decomposition Pathway for Nitrophenols and Sodium Nitrophenolates

Nitrophenols and corresponding sodium nitrophenolates are the main side products in the production of mononitrobenzene (MNB). These side products are hazardous due to their thermal instability nature. In this article, the thermal decomposition behaviors of nitrophenols and sodium nitrophenolates were first characterized by differential scanning calorimeter and accelerating rate calorimetry techniques. Then, the influence of phenol and sodium phenolate on the thermal decomposition of MNB was studied to clarify the effect of phenolic hydroxyl groups on the thermal stability of nitrophenols. It was found that compared to nitrophenols, the exothermic peaks of sodium nitrophenolates were more intense and presented strongly autocatalytic features. Sodium phenolate could significantly decrease the decomposition temperature of MNB. Aniline was detected as the unique product in the decomposition processes of pure MNB and MNB/sodium phenolate mixtures, and the nitrosobenzene was verified as the intermediate product. It was experimentally proven that sodium phenolate could catalyze the decomposition of nitrosobenzene (the decomposition intermediate of MNB). The violent decomposition of sodium nitrophenols was caused by the intermolecular catalysis effect of phenoxy groups.

Structural and Antimicrobial Investigation of Some New Nanoparticles Mixed Ligands Metal Complexes of Ethyl 6-Amino-4-(4-chlorophenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate in Presence of 1,10-Phenanthroline

A new series of some biologically active Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) complexes was synthesized from the reaction of Ethyl 6-amino-4-(4-chlorophenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate (L) with the previous biological metals in the presence of 1,10-phenanthroline monohydrate (Phen). The structures of the obtained L along with their complexes were authenticated by different analytical and spectral techniques. The data prove that L chelates with all metal ions as bidentate through the nitrogen of the amino group and the nitrogen of the cyano group. Furthermore, Phen chelated with metal ions via two nitrogen atoms. The molar conductance values reflect that all complexes are electrolyte, confirming the 1:3 electrolytic natures for trivalent metal ions and 1:2 electrolytic for bivalent metal ions. The thermal stability and the general thermal decomposition pathways of metal complexes, L, and Phen were evaluating according to the thermogravimetric technique. The activation thermodynamic parameters were estimated from TG curves by utilizing Horowitz–Metzger (HM) and Coats–Redfern (CR) techniques. Powder X-ray diffraction (XRD) analysis proved that L, Cu(II), and Zn(II) compounds have a crystalline nature, whereas, Cr(III), Fe(III), Co(II), and Ni(II) complexes are semicrystalline. The investigated compounds were examined in vitro for their antimicrobial activity towards G(+ve) Staphylococcus aureus and Bacillus subtilis and G(−ve) Escherichia coli and Pseudomonas aeruginosa bacteria, and two fungi: Candida albicans and Aspergillus flavus. According to the findings, the Co(II) complex has a significant efficiency toward bacteria, additionally, Cr(III) complex is highly significant towards fungal strains.

Study on pyrolysis mechanism of 1,7-diacetoxy-2,4,6-trinitro-2,4,6-triazaheptane (BSX)

The thermal decomposition process of 1,7-diacetoxy-2,4,6-trinitro-2,4,6-triazaheptane (BSX) was studied by TG-DSC, TG-MS, TG-FTIR technology and ReaxFF molecular dynamics (ReaxFF MD) simulation. The decomposition activation energy of BSX was calculated according to the test results of TG-DSC. The main thermal decomposition products of BSX were determined by combining experiments and simulations, and the possible thermal decomposition pathways were analyzed. The results showed that the decomposition activation energy of BSX is 161 ± 2.6 kJ·mol−1; The thermal decomposition of BSX may generate the main intermediate products C8H14N5O8, C4H7NO2, C2H3O2, HNO2, NO2 and NO, etc., and the intermediate products continued to decompose to generate the final products CH2O, CO2, CO, H2O and N2; The reaction rate constants of each stage of BSX were calculated, and the possible thermal decomposition pathways of BSX were obtained: BSX → C8H14N5O8 + NO2 → C5H9N3O4 + C4H7N4O6 + C4H7NO2 + C3H5N2O4 → C2H3O2 + C2H3O + CH2O + CO2 + CO + H2O + HNO2 + N2O2 + NO2 + NO + H + OH + … → CH2O + CO2 + CO + H2O + N2 + … This study contributes to a deeper understanding of the decomposition process of BSX after heating and has specific significance for reducing the thermal hazard of the BSX pyrolysis process.

Numerical simulation of nitrogen oxides and carbon monoxide emissions of biodiesel diffusion flame

Biodiesel is one of the most promising fossil fuel replacements for automotive engines, furnaces, and turbines due to its sustainability, energy savings, and reduced carbon emissions. While commonly reported in engine studies, nitrogen oxides (NOx) and carbon monoxide (CO) released from combustion of biodiesel have not been studied in laminar diffusion flames. This numerical study examines the concentrations of NOx and CO emissions of the laminar biodiesel diffusion flames at different carbon flow rates and then compares its emissions with those of two liquid hydrocarbon fuel surrogates, n-heptane and iso-octane. A consistent carbon flow rate of 17.2 g/h is applied at the fuel inlet to compare the NOx and CO emissions of the three liquid fuels. The results show that biodiesel diffusion flame produces greater NOx and CO emissions with increasing carbon flow rate. At the same flow rate, n-heptane produces the greatest NO with 2.1% greater than biodiesel and 4.2% greater than iso-octane. The primary pathway for generating NO in biodiesel flame is the prompt pathway, with significant contributions from the thermal and NO2 decomposition pathways. While the NO productions in n-heptane and iso-octane flames are predominantly through the thermal pathway. It is also observed that biodiesel produces the greatest CO emission with 3.2% more than those of n-heptane and iso-octane. The oxidisation reaction of CO, CO + OH = CO2 + H primarily controls the CO mass fraction in the product for all fuels.

A Physical Organic Approach towards Statistical Modeling of Tetrazole and Azide Decomposition.

Nitrogen atom-rich heterocycles and organic azides have found extensive use in many sectors of modern chemistry from drug discovery to energetic materials. The prediction and understanding of their energetic properties are thus key to the safe and effective application of these compounds. In this work, we disclose the use of multivariate linear regression modeling for the prediction of the decomposition temperature and impact sensitivity of structurally diverse tetrazoles and organic azides. We report a data-driven approach for property prediction featuring a collection of quantum mechanical parameters and computational workflows. The statistical models reported herein carry predictive accuracy as well as chemical interpretability. Model validation was successfully accomplished via tetrazole test sets with parameters generated exclusively in silico. Mechanistic analysis of the statistical models indicated distinct divergent pathways of thermal and impact-initiated decomposition.

TG-DSC and TG-FTIR Studies of Annelated Triazinylacetic Acid Ethyl Esters-Potential Anticancer Agents.

To avoid problems associated with the storage and processing of newly developed potential medicines, there is a need to carry out thermal studies in the preclinical phase of drug development. The thermal behaviour and decomposition pathway of a whole novel class of patented potential molecular pharmaceutics, i.e., ethyl 2-[4-oxo-8-(R-phenyl)-4,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl]acetates (1-6) were reported for the first time in inert and oxidative atmospheres. The experiments were conducted with the use of simultaneous thermogravimetry/differential scanning calorimetry (TG-DSC) and simultaneous thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR). The decomposition pathways of compounds 1-6 were found to be different under oxidative and inert conditions. It was proven that the investigated molecules reveal higher thermal stability under a synthetic air atmosphere than under a nitrogen atmosphere, and their decomposition is preceded by the melting process. Among all the investigated compounds, only the meta-chloro derivative (4) was found to exhibit interesting polymorphic behaviour at a low heating rate (10 °C min-1). It was proven that the oxidative decomposition process of the studied molecules proceeds in three overlapping stages accompanied by strong exothermic effects. Additionally, it was concluded that the title compounds were stable up to a temperature of 195-216 °C in an atmosphere of synthetic air, and their thermal stability decreased in the order of R at the benzene ring: 4-CH3 > 3,4-Cl2 > 4-Cl > H > 2-OCH3 > 3-Cl.

Enthalpy of formation of sodium bis(oxalato)cuprate(II) dihydrate

The thermal decomposition pathways of the mineral wheatleyite (sodium bis(oxalato)cuprate(II) dihydrate, Na2Cu(C2O4)2⋅2H2O) have not been established with certainty and the enthalpy of formation of wheatleyite has not been reported. Thermogravimetric analysis (TG), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) and powder X-ray diffraction (PXRD) were used to establish the chemical reactions that occur during the thermal decomposition of sodium bis(oxalato)cuprate(II) dihydrate under atmospheres of static air and flowing nitrogen. The decomposition occurred in three steps in either atmosphere, but the decomposition temperature and products produced depended on the atmosphere. The initial step was the loss of water to form Na2Cu(C2O4)2 in either atmosphere. The Na2Cu(C2O4)2 decomposed in the second step to form Na2C2O4 and a copper compound that depended on the carrier gas. Cu was the decomposition product formed in nitrogen while CuO was produced in air. During the final decomposition, Na2C2O4 decomposed to form Na2CO3. Once the decomposition reactions were established, differential scanning calorimetry (DSC) was used to measure the enthalpy of formation for Na2Cu(C2O4)2 and Na2Cu(C2O4)2⋅2H2O in an atmosphere of static air. The values determined for the enthalpies of formation were -2095 kJ mol−1 and -2670 kJ mol−1 for Na2Cu(C2O4)2 and Na2Cu(C2O4)2⋅2H2O respectively with a measured standard deviation of ±5 kJ mol−1 and estimated total uncertainty of ±10 kJ mol−1.

Predicting pyrolysis decomposition of PFOA using computational nanoreactors: a thermodynamic study.

Per- and polyfluoroalkyl substances (PFAS) are a large, complex, environmentally persistent, and ever-expanding group of manufactured chemicals. Disposal of these compounds could produce potentially dangerous products necessitating the need to quickly predict their decomposition products. This study focuses on the thermal decomposition of perfluorooctanoic acid (PFOA) using nanoreactor simulations to find the decomposition products and their respective energies. Applying the nanoreactor method, which is novel for this system, allows for rapid prediction of thermal decomposition pathways with minimal researcher bias and it predicted PFOA to decompose at ∼650 °C, consistent with previously reported experimental studies.