Determination of hazardous vapors from the thermal decomposition of organochlorinated silica xerogels with adsorptive properties.

The incorporation of organic groups into sol-gel silica materials is known to have a noticeable impact on the properties and structure of the resulting xerogels due to the combination of the properties inherent to the organic fragments (functionality and flexibility) with the mechanical and structural stability of the inorganic matrix. However, the reduction of the inorganic content in the materials could be detrimental to their thermal stability properties, limiting the range of their potential applications. Therefore, this work aims to evaluate the thermal stability of hybrid inorganic-organic silica xerogels prepared from mixtures of tetraethoxysilane and organochlorinated triethoxysilane precursors. To this end, a series of four materials with a molar percentage of organochlorinated precursor fixed at 10%, but differing in the type of organic group (chloroalkyls varying in the alkyl-chain length and chlorophenyl), has been selected as model case study. The gases and vapors released during the thermal decomposition of the samples under N2 atmosphere have been analyzed and their components determined and quantified using a thermogravimetric analyzer coupled to a Fourier-transform infrared spectrophotometer and to a gas chromatography-mass spectrometry unit. These analyses have allowed to identify up to three different thermal events for the pyrolysis of the organochlorinated xerogel materials and to elucidate the reaction pathways associated with such processes. These mechanisms have been found to be strongly dependent on the specific nature of the organic group.

Control of Explosive Chemical Reactions by Optical Excitations: Defect-Induced Decomposition of Trinitrotoluene at Metal Oxide Surfaces.

Interfaces formed by high energy density materials and metal oxides present intriguing new opportunities for a large set of novel applications that depend on the control of the energy release and initiation of explosive chemical reactions. We studied the role of structural defects at a MgO surface in the modification of electronic and optical properties of the energetic material TNT (2-methyl-1,3,5-trinitrobenzene, also known as trinitrotoluene, C7H5N3O6) deposited at the surface. Using density functional theory (DFT)-based solid-state periodic calculations with hybrid density functionals, we show how the control of chemical explosive reactions can be achieved by tuning the electronic structure of energetic compound at an interface with oxides. The presence of defects at the oxide surface, such as steps, kinks, corners, and oxygen vacancies, significantly affects interfacial properties and modifies electronic spectra and charge transfer dynamics between the oxide surface and adsorbed energetic material. As a result, the electronic and optical properties of trinitrotoluene, mixed with an inorganic material (thus forming a composite), can be manipulated with high precision by interactions between TNT and the inorganic material at composite interfaces, namely, by charge transfer and band alignment. Also, the electron charge transfer between TNT and MgO surface reduces the decomposition barriers of the energetic material. In particular, it is shown that surface structural defects are critically important in the photodecomposition processes. These results open new possibilities for the rather precise control over the decomposition initiation mechanisms in energetic materials by optical excitations.

Effects of Nanoparticle Size on the Thermal Decomposition Mechanisms of 3,5-Diamino-6-hydroxy-2-oxide-4-nitropyrimidone through ReaxFF Large-Scale Molecular Dynamics Simulations.

ReaxFF-lg molecular dynamics method was employed to simulate the decomposition processes of IHEM-1 nanoparticles at high temperatures. The findings indicate that the initial decomposition paths of the nanoparticles with different sizes at varying temperatures are similar, where the bimolecular polymerization reaction occurred first. Particle size has little effect on the initial decomposition pathway, whereas there are differences in the numbers of the species during the decomposition and their evolution trends. The formation of the hydroxyl radicals is the dominant decomposition mechanism with the highest reaction frequency. The degradation rate of the IHEM-1 molecules gradually increases with the increasing temperature. The IHEM-1 nanoparticles with smaller sizes exhibit greater decomposition rate constants. The activation energies for the decomposition are lower than the reported experimental values of bulk explosives, which suggests a higher sensitivity.

Comparative Thermal Research on Energetic Molecular Perovskite Structures.

Molecular perovskites are promising practicable energetic materials with easy access and outstanding performances. Herein, we reported the first comparative thermal research on energetic molecular perovskite structures of (C6H14N2)[NH4(ClO4)3], (C6H14N2)[Na(ClO4)3], and (C6H14ON2)[NH4(ClO4)3] through both calculation and experimental methods with different heating rates such as 2, 5, 10, and 20 °C/min. The peak temperature of thermal decompositions of (C6H14ON2)[NH4(ClO4)3] and (C6H14N2) [Na(ClO4)3] were 384 and 354 °C at the heating rate of 10 °C/min, which are lower than that of (C6H14N2)[NH4(ClO4)3] (401 °C). The choice of organic component with larger molecular volume, as well as the replacement of ammonium cation by alkali cation weakened the cubic cage skeletons; meanwhile, corresponding kinetic parameters were calculated with thermokinetics software. The synergistic catalysis thermal decomposition mechanisms of the molecular perovskites were also investigated based on condensed-phase thermolysis/Fourier-transform infrared spectroscopy method and DSC-TG-FTIR-MS quadruple technology at different temperatures.

Thermal Decomposition of Anionic, Zwitterionic, and Cationic Polyfluoroalkyl Substances in Aqueous Film-Forming Foams.

In this study, we investigated thermal decomposition mechanisms of cationic, zwitterionic, and anionic polyfluoroalkyl substances, including those present in aqueous film-forming foam (AFFF) samples. We present novel evidence that polyfluoroalkyl substances gave quantitative yields of perfluoroalkyl substances of different chain lengths during thermal treatment. The results support a radical-mediated transformation mechanism involving random-chain scission and end-chain scission, leading to the formation of perfluoroalkyl carboxylic acids such as perfluorooctanoic acid (PFOA) from certain polyfluoroalkyl amides and sulfonamides. Our results also support a direct thermal decomposition mechanism (chain stripping) on the nonfluorinated moiety of polyfluoroalkyl sulfonamides, resulting in the formation of perfluorooctanesulfonic acid (PFOS) and other structurally related polyfluoroalkyl compounds. Thermal decomposition of 8:2 fluorotelomer sulfonate occurred through end-chain scission and recombination reactions, successively yielding PFOS. All of the studied polyfluoroalkyl substances began to degrade at 200-300 °C, exhibiting near-complete decomposition at ≥400 °C. Using a high-resolution parent ion search method, we demonstrated for the first time that low-temperature thermal treatments of AFFF samples led to the generation of anionic fluoroalkyl substances, including perfluoroheptanesulfonamide, 8:2 fluorotelomer sulfonic acid, N-methyl perfluorooctane sulfonamide, and a previously unreported compound N-2-propenyl-perfluorohexylsulfonamide. This study provides key insights into the fate of polyfluoroalkyl substances in thermal processes.

Computational Design of High Energy RDX-Based Derivatives: Property Prediction, Intermolecular Interactions, and Decomposition Mechanisms.

A series of new high-energy insensitive compounds were designed based on 1,3,5-trinitro-1,3,5-triazinane (RDX) skeleton through incorporating -N(NO2)-CH2-N(NO2)-, -N(NH2)-, -N(NO2)-, and -O- linkages. Then, their electronic structures, heats of formation, detonation properties, and impact sensitivities were analyzed and predicted using DFT. The types of intermolecular interactions between their bimolecular assemble were analyzed. The thermal decomposition of one compound with excellent performance was studied through ab initio molecular dynamics simulations. All the designed compounds exhibit excellent detonation properties superior to 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), and lower impact sensitivity than CL-20. Thus, they may be viewed as promising candidates for high energy density compounds. Overall, our design strategy that the construction of bicyclic or cage compounds based on the RDX framework through incorporating the intermolecular linkages is very beneficial for developing novel energetic compounds with excellent detonation performance and low sensitivity.

Initial Decomposition Mechanism of 3-Nitro-1,2,4-triazol-5-one (NTO) under Shock Loading: ReaxFF Parameterization and Molecular Dynamic Study.

We report a reactive molecular dynamic (ReaxFF-MD) study using the newly parameterized ReaxFF-lg reactive force field to explore the initial decomposition mechanism of 3-Nitro-1,2,4-triazol-5-one (NTO) under shock loading (shock velocity >6 km/s). The new ReaxFF-lg parameters were trained from massive quantum mechanics data and experimental values, especially including the bond dissociation curves, valence angle bending curves, dihedral angle torsion curves, and unimolecular decomposition paths of 3-Nitro-1,2,4-triazol-5-one (NTO), 1,3,5-Trinitro-1,3,5-triazine (RDX), and 1,1-Diamino-2,2-dinitroethylene (FOX-7). The simulation results were obtained by analyzing the ReaxFF dynamic trajectories, which predicted the most frequent chain reactions that occurred before NTO decomposition was the unimolecular NTO merged into clusters ((C2H2O3N4)n). Then, the NTO dissociated from (C2H2O3N4)n and started to decompose. In addition, the paths of NO2 elimination and skeleton heterocycle cleavage were considered as the dominant initial decomposition mechanisms of NTO. A small amount of NTO dissociation was triggered by the intermolecular hydrogen transfer, instead of the intramolecular one. For α-NTO, the calculated equation of state was in excellent agreement with the experimental data. Moreover, the discontinuity slope of the shock-particle velocity equation was presented at a shock velocity of 4 km/s. However, the slope of the shock-particle velocity equation for ß-NTO showed no discontinuity in the shock wave velocity range of 3-11 km/s. These studies showed that MD by using a suitable ReaxFF-lg parameter set, could provided detailed atomistic information to explain the shock-induced complex reaction mechanisms of energetic materials. With the ReaxFF-MD coupling MSST method and a cheap computational cost, one could also obtain the deformation behaviors and equation of states for energetic materials under conditions of extreme pressure.

Predicting Trigger Bonds in Explosive Materials through Wiberg Bond Index Analysis.

Understanding the explosive decomposition pathways of high-energy-density materials (HEDMs) is important for developing compounds with improved properties. Rapid reaction rates make the detonation mechanisms of HEDMs difficult to understand, so computational tools are used to predict trigger bonds-weak bonds that break, leading to detonation. Wiberg bond indices (WBIs) have been used to compare bond densities in HEDMs to reference molecules to provide a relative scale for the bond strength to predict the activated bonds most likely to break to trigger an explosion. This analysis confirms that X-NO2 (X=N,C,O) bonds are trigger linkages in common HEDMs such as TNT, RDX and PETN, consistent with previous experimental and theoretical studies. Calculations on a small test set of substituted tetrazoles show that the assignment of the trigger bond depends upon the functionality of the material and that the relative weakening of the bond correlates with experimental impact sensitivities.

Effects and mechanism of metal ions on the stability of glucosinolates in aqueous solution.

Glucosinolates (GLs) are important precursors of anticancer isothiocyanates in cruciferous plants. However, GLs in aqueous solution have been found to decompose under certain conditions, and the effect of metal ions remains unclear. In this study, high-purity glucoraphanin and glucoraphenin were used to explore the effects of metal ions with thermal treatment. The degree of GLs decomposition was affected by the type and concentration of metal ions, temperature, and duration of heating. Fe3+ (1 mM) was found to cause the decomposition of 78.1 % of glucoraphanin and 94.7 % of glucoraphenin in 12 h at 100 °C, while Cu2+ completely decomposed both GLs. The decomposition products were all the corresponding nitriles, and decomposition dynamic curves were first-order. In addition to accelerating hydrolysis, metal ions may promote the generation of nitriles as catalysts. The exploration of GLs decomposition could help to adopt more effective methods to avoid the formation of toxic compounds.

Research on the decomposition mechanisms of lithium silicate ores with different crystal structures by autotrophic and heterotrophic bacteria.

Ores serve as energy and nutrient sources for microorganisms. Through complex biochemical processes, microorganisms disrupt the surface structure of ores and release metal elements. However, there is limited research on the mechanisms by which bacteria with different nutritional modes act during the leaching process of different crystal structure ores. This study evaluated the leaching efficiency of two types of bacteria with different nutritional modes, heterotrophic bacterium Bacillus mucilaginosus (BM) and autotrophic bacterium Acidithiobacillus ferrooxidans (AF), on different crystal structure lithium silicate ores (chain spodumene, layered lepidolite and ring elbaite). The aim was to understand the behavioral differences and decomposition mechanisms of bacteria with different nutritional modes in the process of breaking down distorted crystal lattices of ores. The results revealed that heterotrophic bacterium BM primarily relied on passive processes such as bacterial adsorption, organic acid corrosion, and the complexation of small organic acids and large molecular polymers with metal ions. Autotrophic bacterium AF, in addition to exhibiting stronger passive processes such as organic acid corrosion and complexation, also utilized an active transfer process on the cell surface to oxidize Fe2+ in the ores for energy maintenance and intensified the destruction of ore lattices. As a result, strain AF exhibited a greater leaching effect on the ores compared to strain BM. Regarding the three crystal structure ores, their different stacking modes and proportions of elements led to significant differences in structural stability, with the leaching effect being highest for layered structure, followed by chain structure, and then ring structure. These findings indicate that bacteria with different nutritional modes exhibit distinct physiological behaviors related to their nutritional and energy requirements, ultimately resulting in different sequences and mechanisms of metal ion release from ores after lattice damage.

Temperature and pressure effects on the decomposition mechanisms of 2,6-diamino-3,5-dinitropyrazine-1-oxide crystal: ab initio molecular dynamics study.

CONTEXT: The decomposition process of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) crystal at high temperatures (2500 and 3390 K) and detonation pressure of 33.4 GPa coupled with temperatures were studied by ab initio molecular dynamics simulations. The results show that the initial decomposition mechanism of LLM-105 is the same under different conditions. The product analysis indicates that high temperature is conducive to the formation of N2 and CO2, but inhibited the formation of H2O. It is found that the formation mechanism of H2O is the same under different conditions, which involves the reaction between OH radical and H radical. Although the detailed processes of the formation of N2 are different, they all involve the reaction between nitrogen-containing fragments, and its core is the formation of intermediates with R1-NN-R2 structure. The core of the formation of CO2 under different conditions is to form the intermediate R1-CO-R2 with carbonyl structure, and then generate the fragment with -OCO- structure, and finally generate CO2. This research may provide new insights into the initiation and subsequent decomposition mechanisms of energetic materials under extreme conditions. METHODS: The LLM-105 supercell was constructed using the Materials Studio 7.0 package. AIMD simulations were performed in the CASTEP package. AIMD simulations adopted NVT and NPT ensemble, and the temperature was controlled by Nosé thermostat, while the pressure was controlled by Andersen barostat. Besides, DFT calculations were carried out at the B3LYP/6-311 + G(d,p) level using the Gaussian 09 package.

Unraveling the Interphasial Chemistry for Highly Reversible Aqueous Zn Ion Batteries.

A robust solid electrolyte interface (SEI) is crucial to widen the electrochemical stability window of the electrolyte and enable sustainably stable electrode reactions in aqueous Zn ion batteries. Different from the SEI in nonaqueous electrolytes, it is of great importance to form a functional and stable SEI due to parasitic reactions with water in aqueous Zn ion batteries. However, the concrete SEI formation in aqueous electrolytes has been elusive so far. Here, we regulate and unravel the decomposition mechanisms of organic Zn salts at the Zn anode-electrolyte interface in the widely studied zinc triflate-based aqueous electrolytes. By introducing a buffering adsorption layer with an optimal concentration of acetate anions, the uncontrollable decomposition of organic zinc triflate salt is greatly inhibited on Zn anodes, resulting in a stable interface. The average Coulombic efficiency of the Zn anode thus can reach as high as 99.95% and stable cycling for 4200 h. With the cooperation of buffering adsorption layers, the tetraethyl ammonium trifluoromethanesulfonate additive as the decomposition promoter could further regulate the decomposition of triflate anions for the formation of robust SEI layers for Zn anodes in electrolytes with a dilute salt concentration. Zn-polyaniline (PANI) full cells demonstrate stable cycling with controlled N/P ratios in such electrolytes. This work proposes an insightful perspective on rational regulation of the decomposition pathway of electrolyte components by forming a stable electrode-electrolyte interface for improved electrochemical performance of aqueous Zn ion batteries.

Investigation of kerogen thermal decomposition mechanisms and kinetics via ReaxFF molecular dynamics simulations.

This study investigates the mechanisms and kinetics of kerogen thermal decomposition using molecular dynamics simulations with the ReaxFF force field. The cook-off simulation at the constant heating rate shows that the decomposition of kerogen begins with the cracking at terminals and weaker linkages of kerogen molecule, and the final products are formed by radicals recombination, dehydrogenation, and other reactions. The Flynn-Wall-Ozawa kinetic analysis based on the thermal decomposition simulations at various heating rates shows that the activation energy increases with the conversion of decomposition. These results reveal the thermal decomposition mechanisms and the thermal stability of kerogen in different stages during the process of thermal decomposition.

Recruiting Perovskites to Degrade Toxic Trinitrotoluene.

Everybody knows TNT, the most widely used explosive material and a universal measure of the destructiveness of explosions. A long history of use and extensive manufacture of toxic TNT leads to the accumulation of these materials in soil and groundwater, which is a significant concern for environmental safety and sustainability. Reliable and cost-efficient technologies for removing or detoxifying TNT from the environment are lacking. Despite the extreme urgency, this remains an outstanding challenge that often goes unnoticed. We report here that highly controlled energy release from explosive molecules can be accomplished rather easily by preparing TNT-perovskite mixtures with a tailored perovskite surface morphology at ambient conditions. These results offer new insight into understanding the sensitivity of high explosives to detonation initiation and enable many novel applications, such as new concepts in harvesting and converting chemical energy, the design of new, improved energetics with tunable characteristics, the development of powerful fuels and miniaturized detonators, and new ways for eliminating toxins from land and water.

Gaseous Products Evolution Analyses for Catalytic Decomposition of AP by Graphene-Based Additives.

A quantitative evaluation method has been developed to study the effects of nanoadditives on thermal decomposition mechanisms of energetic compounds using the conventional thermogravimetry coupled with mass spectrometry (TG/MS) technique. The decomposition of ammonium perchlorate (AP) under the effect of several energetic catalysts has been investigated as a demonstration. In particular, these catalysts are transition metal (Cu2+, Co2+ and Ni2+) complexes of triaminoguanidine (TAG), using graphene oxide (GO) as dopant. They have been well-compared in terms of their catalytic effects on the concentration of the released gaseous products of AP. These detailed quantitative analyses of the gaseous products of AP provide a proof that the proton transfer between O and O2 determines the catalytic decomposition pathways, which largely depend on the type of reactive centers of the catalysts. This quantitative method could be applied to evaluate the catalytic effects of any other additives on the thermal decomposition of various energetic compounds.

Spectral, thermal studies and biological activity of pyrazinamide complexes.

Synthesis and spectrothermal characterization of new fabricated pyrazinamide complexes with metal [Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)] salts are reported. The structural chemistry of these complexes is achieved via elemental analysis, spectral (UV, visible, and IR), thermal (DTA and TGA) as well as magnetic susceptibility. In these new octahedral complexes (Zn complex is tetrahedral), pyrazinamide acts as a bidentate ligand. Pyrazinamide complexes show higher activity than pyrazinamide for some strains. The geometry of the complexes is converted from Oh to Td during their thermal decomposition. The decomposition mechanisms are suggested and the thermodynamic parameters for the thermal decomposition steps are evaluated.

Thermal decomposition mechanisms of poly(vinyl chloride): A computational study.

The studies on the pyrolysis mechanisms of waste PVC contribute to development and application of pyrolysis technology for mixed waste plastics. In the article, the thermal decomposition mechanisms of model compound of poly(vinyl chloride) (PVC) have been investigated by employing density functional theory methods at M06-2X/6-31++G(d,p) level in order to illuminate the elimination of HCl and the formation of hydrocarbons. Various possible pyrolysis paths for the formation of main products were proposed, and the thermodynamic and kinetic parameters in every path were calculated. The calculation results show that the HCl elimination can occur through the concerted reaction and the energy barrier of HCl elimination changes from 167.4 to 243.3 kJ/mol; allyl group can obviously reduce the activation energy of HCl elimination, and the branched-chain can lower the energy barrier of HCl elimination at the carbon sites near the branch chain; a free radical is more easily converted into aromatic compound through a series of isomerizations, cyclization and dehydrogenation; the conjugated polyene could be decomposed in parallel reaction channels: one is the evolution of aromatics, another is the formation of small molecule products. The above analysis is consistent with previous experimental results and analysis.

Synergistic effects between hydroxyl radicals and hydrated electrons on strengthening decomposition of an s-triazine compound: A combined experimental and theoretical study.

The decomposition of an environmentally recalcitrant s-triazine compound, prometry (PMT), was carried out by experimental and theoretical approaches to study the combined effects of hydroxyl radicals (OH) and hydrated electrons (eaq-). With the participation of strongly oxidative radicals OH and reductive radicals eaq- induced by electron beam (EB), PMT obtained a good decomposition performance, which was obviously better than those methods simply using OH as the single active species. The evolution of cyanuric acid (CA) during the EB and UV irradiation processes elucidate that former method could efficiently decompose such chemically stable intermediate. The experiments of radical scavengers further suggest that OH was the predominant radical during PMT degradation, while eaq- was beneficial to further decomposition and mineralization. Combined with the results of density functional theory (DFT) calculations, the strengthened synergistic effects between OH and eaq- were proven. The calculations illustrated OH could attack the carbon-branch-chains of s-trazine ring and form OH-adducts rather than nitrogen oxides. Moreover, the presence of eaq- could not only greatly change the geometry of the s-triazine ring, but also help cleaving alkyl chain on ring, thus facilitate the complete mineralization.

Dominant Decomposition Pathways for Ethereal Solvents in Li-O2 Batteries.

The promise of high specific energies for Li-O2 batteries has driven research toward the development of new compatible materials for this emerging technology. Obtained energies, however, fall short of the theoretical values partly due to parasitic chemistries arising from organic solvent decomposition during battery cycling. Electrolyte solvent and salt decomposition have also been identified as limiting factors for rechargeability of the battery. Although lithium trifluorosulfonamide (LiTFSI) dissolved in 1,2-dimethoxyethane (DME) has been shown to be a promising solvent/electrolyte candidate for Li-O2 batteries, significant challenges remain, namely minimizing decomposition of both the solvent and electrolyte salt during battery cycling. Herein, we provide spectroscopic labeling studies to identify the source of H2 at high potentials during charge and propose a decomposition pathway for DME to lithium formate and acetate products at low potentials. NMR studies were preformed to show that DME decomposes to lithium formate and acetate in aqueous Li2O2, products which are also observed after D2O workups on cathodes after discharge. Finally, we use density functional theory (DFT) to elucidate a mechanistic pathway for DME decomposition that is based on known organic oxidation processes.