Thermal Stability and Detonation Properties of Potassium 4,4'-Bis(dinitromethyl)-3,3'-azofurazanate, an Environmentally Friendly Energetic Three-Dimensional Metal-Organic Framework

Application and prospects of EMOFs in the fields of explosives and propellants

Energetic Metal-Organic Framework (EMOF) compounds have gained significant attention in recent years as a hot research topic in the fields of explosives and propellants. This article provides an overview of the latest research progress of EMOFs in various areas, including heat-resistant explosives, burning rate catalysts and initiating explosives. It discusses the recent development trends of high-energy EMOFs, such as high-dimensional and solvent-free structural design, simplified and scalable synthesis conditions, environmentally friendly manufacturing processes with tunable structures, high-energy, low-sensitivity and multifunctional target products. The challenges and issues faced by EMOFs in heat-resistant explosives, burning rate catalysts and initiating explosives are presented. Furthermore, the key research directions for future applications of EMOFs in the fields of explosives and propellants are discussed, including solvent-free high-dimensional EMOFs design and synthesis, precise modulation of EMOFs molecular composition and pore structure, improvement of accurate prediction methods for physicochemical properties of high-energy EMOFs, low-cost large-scale production and development of multifunctional composite EMOFs as energetic materials, exploration of influencing factors, and comprehensive study on the application of novel and high-performance multifunctional EMOFs.

Detonation Performance of Insensitive Nitrogen-Rich Nitroenamine Energetic Materials Predicted from First-Principles Reactive Molecular Dynamics Simulations

Because of the excellent combination of high detonation and low sensitivity properties of the 1,1-diamino-2,2-dinitroethylene (FOX-7) energetic material (EM), it is useful to explore new energetic derivatives that start with the FOX-7 structure. However, most such derivatives are highly sensitive, making them unsuitable for EM applications. An exception is the new nitroenamine EM, 1,1-diamino-2-tetrazole-2-nitroethene (FOX-7-T) (synthesized by replacing a nitro group with a tetrazole ring), which exhibits good stability. Unfortunately, FOX-7-T shows an unexpected much lower detonation performance than FOX-7, despite its higher nitrogen content. To achieve an atomistic understanding of the insensitivity and detonation performance of FOX-7 and FOX-7-T, we carried out reactive molecular dynamics (RxMD) using the ReaxFF reactive force field and combined quantum mechanics MD (QM-MD). We found that the functional group plays a significant role in the initial decomposition reaction. For FOX-7, the initial decomposition involves only simple hydrogen transfer reactions at high temperature, whereas for FOX-7-T, the initial reaction begins at much lower temperature with a tetrazole ring breaking to form N2, followed by many subsequent reactions. Our first-principles-based simulations predicted that FOX-7-T has 34% lower CJ pressure, 15% lower detonation velocity, and 45% lower CJ temperature than FOX-7. This is partly because a larger portion of the FOX-7-T mass gets trapped into condensed phase carbon clusters at the CJ point, suppressing generation of gaseous CO2 and N2 final products, leading to reduced energy delivery. Our findings suggest that the oxygen balance is an important factor to be considered in the design of the next generation of high-nitrogen-containing EMs.

Deep Potential Molecular Dynamics Study of Chapman-Jouguet Detonation Events of Energetic Materials

Detonation of energetic materials (EMs) is of great importance for military applications, while the understanding of detailed events and mechanisms for the detonation process is scarce. In this study, the first deep neural network potential NNP_Shock for molecular dynamics (MD) simulation of shock-induced detonation of EMs was generated based on a deep potential model, providing DFT accuracy but 106 times the computational efficiency. On this basis, we employ our deep potential to perform MD simulations of shock-induced detonation of high-performance EM material 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20, C6H6N12O12) and obtain the theoretical Chapman-Jouguet (C-J) detonation velocities and pressures directly by multiscale shock technique (MSST) for the first time, which are in good agreement with experiment. In addition, the Hugoniot curves and initial reaction mechanisms were successfully obtained. Therefore, the NNP_Shock potential is competent in research of the detonation performance and shock sensitivity of CL-20, and the method can also be transplanted to studies of other EMs.

Facile synthesis and superior properties of a nitrogen-rich energetic Zn-MOF with a 2D azide-bridged bilayer structure

Exploring the facile synthesis of Pb-free energetic metal-organic frameworks (EMOFs) with both high nitrogen content and high thermostability is a significant but challenging task in the field of MOF-based green energetic materials. Herein, a new EMOF, [Zn₂(atz)₃(N₃)]_n (atz = 5-amino-1H-tetrazole), has been synthesized by simply using a commercial ligand (atz) under mild conditions. A probable mechanism for the formation of azide groups in the product has been proposed, in which the fraction of C-N and N-N bonds in atz is the key. The X-ray single crystal structure analysis reveals the EMOF's unique graphene-like and azide-group-bridged 2D bilayer structure with gourd-type micropores. More impressively, the EMOF shows a high nitrogen content of 59.33% and superior thermostability of up to 362 °C, both among the best of existing EMOFs. In addition, detonation property calculations and sensitivity tests have been carried out, which demonstrate its high-energy and low-sensitivity features. Moreover, [Zn₂(atz)₃(N₃)]_n shows the ability to accelerate the thermal decomposition of ammonium perchlorate (AP) and hexanitrohexaazaisowurtzitane (CL-20), making it a potential combustion promoter for green and insensitive propellants.

Increasing Oxygen Balance Leads to Enhanced Performance in Environmentally Acceptable High-Energy Density Materials: Predictions from First-Principles Molecular Dynamics Simulations

Environmental concerns have stimulated the development of green alternatives to environmentally pollutive nitramine compounds used for high-energy density materials (HEDMs). The excellent energetic properties of CL20 make it a promising candidate, but its negative oxygen balance limits its efficiency for industrial and military applications. We predict here that CL20-EO formed by introducing ether links into the CC bonds of the original CL20 structure to attain balanced CO₂ and H₂O production leads to improved performance while minimizing the formation of carbonaceous clusters and toxic gases. To test this concept, we predicted the detonation properties at the Chapman-Jouguet (CJ) state using reactive molecular dynamics simulations with the ReaxFF force field combined with quantum mechanics based moleculear dynamics. We predict that CL20-EO enhances energetic performance compared to CL20 with a 6.0% increase in the CJ pressure and a 1.1% increase in the detonation velocity, which we attribute to achieving the correct oxygen balance to produce fully oxidized gaseous products. After expansion to normal conditions from the CJ state, CL20-EO leads only to nontoxic fully oxidized gases instead of forming the carbonaceous clusters and toxic gases found with CL-20. Thus, CL20-EO is predicted to be environmentally green. These results indicate that oxygen balance plays an important role in both energy availability and end-product toxicity and that balanced CO₂ and H₂O production systems provide promising candidates for the next generation of environmentally acceptable alternatives to toxic HEDMs while also enhancing the detonation performance.

Construction of highly energetic metal-organic frameworks with a nitrobenzene derivative

Three metal–organic frameworks [CdL(DMF)]n 1, {[CuL(H2O)(DMF)]•DMF•0.5H2O}n 2 and [Nd(HL)L(DMF)3]n 3 have been synthesized with a nitrobenzene derivative 4-((5-hydroxy-2,4-dinitrophenoxy)methyl)-3-nitrobenzoic acid (H2L). Compound 1 has a dense three-dimensional framework with 1D Cd...

Synthesis and characterization of thermally stable energetic complexes with 3,5-diaminopyrazolone-4-oxime as a nitrogen-rich ligand

Two thermally stable complexes based on DAPO were synthesized. The thermal decomposition temperatures were 287 °C and 344 °C, respectively. The detonation properties of the complexes were excellent with good detonation velocity and detonation pressure superior to that of TNT.

Optimized energetic HNTO/AN co-crystal and its thermal decomposition kinetics in the presence of energetic coordination nanomaterials based on functionalized graphene oxide and cobalt

The present research aims to select the optimal molar ratio of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) and ammonium nitrate (AN) to produce an energetic co-crystal. For a comparison purpose, the heat release, cost, density and hygroscopicity of the different co-crystals were evaluated. The obtained results indicated that HNTO/AN at the 1 : 3 ratio exhibited a higher heat release, better thermal stability, low water content and a reasonable cost, compared to other co-crystals. This new co-crystal was fully characterized through powder X-ray diffraction (XRD), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC), confirming that this latter displayed similar characteristics to those of the co-crystal with a 1 : 1 ratio, which was recently developed. On the other hand, the catalytic activity of two energetic coordination polymers of triaminoguanidine-cobalt (T-Co) complexes, with or without graphene oxide (GO-T-Co-T), on the thermolysis of the developed co-crystal has been also assessed by DSC under non-isothermal conditions. It is revealed that these catalysts have greatly decreased the decomposition temperature of the HNTO/AN cocrystal. Moreover, because of the complete decomposition in the case of the (HNTO/AN)/GO-T-Co-T composite, the heat release has been increased as well. Isoconversional integral kinetic methods were exploited to determine the kinetic parameters of the different systems. According to the obtained results, these catalysts have a strong catalytic action on the decomposition of the co-crystal AN/HNTO for which the activation energy and the pre-exponential factor are considerably lowered. Consequently, the developed co-crystal and the energetic catalysts could be considered as potential ingredients for the next generation of composite solid propellant formulations.

Energetic metal–organic frameworks achieved from furazan and triazole ligands: synthesis, crystal structure, thermal stability and energetic performance

Energetic metal–organic frameworks (EMOFs) have witnessed increasing development and been proved as promising candidates for new high energy density materials (HEDMs).

Facile Fabrication of an AIE-Active Metal-Organic Framework for Sensitive Detection of Explosives in Liquid and Solid Phases

Nowadays, the practical applications of metal-organic framework (MOF)-based fluorescence detectors are severely hindered because of the complex synthesis process of linkers or heavy metal contamination. The development of a simple, inexpensive, and environmentally friendly fluorescence sensing system remains a huge challenge. In this study, we designed and synthesized a TPE@γ-CD-MOF-K complex using the facile in situ encapsulation method. The unique pore structure of γ-CD-MOF allowed it to effectively include TPE and explosives as guests simultaneously. The TPE@γ-CD-MOF-K showed stronger fluorescence emission than TPE and sensitive fluorescence quenching activities in response to nitro-aromatic compounds in the liquid phase with detection limits as low as 3 ppm. Furthermore, TPE@γ-CD-MOF-K can also effectively detect nitro-aromatic compounds in the solid state, which is very convenient for practical detection of explosives. The unique pore structure of γ-CD-MOF-K and the interaction between K⁺ and nitro compounds play important roles in solid-state quenching.

A quantum-based molecular dynamics study of the ICM-102/HNO3 host-guest reaction at high temperatures

The contradiction between energy and safety of explosives is better balanced by the host-guest inclusion strategy. Understanding the reaction mechanism of the host-guest explosive is necessary. To deeply analyze the role of the small guest molecules in the host-guest system, a quantum-based molecular dynamics method was used to calculate the initial decomposition reaction of the new host-guest explosive ICM-102/HNO3 against the pure ICM-102 at several high temperatures. The incorporation of HNO3 had no significant influence on the initial decomposition step of ICM-102. Conversely, the earliest intramolecular hydrogen transfer reaction is delayed partly because the H and O atoms of HNO3 connect with the O and H atoms of ICM-102, respectively. As the reaction proceeds, guest molecules get heavily involved in the reaction and increase the reaction rate. The generation rate and quantity of the small oxidizing molecules in the final product were increased significantly in the ICM-102/HNO3 system. These mechanisms revealed that HNO3 molecules inhibit the early stages of the initial decomposition of ICM-102 to some extent, and play an important role in accelerating the decomposition subsequently.

Constructing Strategies and Applications of Nitrogen-Rich Energetic Metal–Organic Framework Materials

The synthesis of energetic metal–organic frameworks (EMOFs) with one-dimensional, two-dimensional and three-dimensional structures is an effective strategy for developing new-generation high-energy-density and insensitive materials. The basic properties, models, synthetic strategies and applications of EMOF materials with nitrogen-rich energetic groups as ligands are reviewed. In contrast with traditional energetic materials, EMOFs exhibit some interesting characteristics, like tunable structure, diverse pores, high-density, high-detonation heat and so on. The traditional strategies to design EMOF materials with ideal properties are just to change the types and the size of energetic ligands and to select different metal ions. Recently, some new design concepts have come forth to produce more EMOFs materials with excellent properties, by modifying the energetic groups on the ligands and introducing highly energetic anion into skeleton, encapsulating metastable anions, introducing templates and so on. The paper points out that appropriate constructing strategy should be adopted according to the inherent characteristics of different EMOFs, by combining with functional requirements and considering the difficulties and the cost of production. To promote the development and application of EMOF materials, the more accurate and comprehensive synthesis, systematic performance measurement methods, theoretical calculation and structure simulation should be reinforced.

Thermal decomposition and diffusion of methane in clathrate hydrates from quantum mechanics simulations

Clathrate hydrates are ice-like crystalline substances in which small gas molecules are trapped inside the polyhedral cavities of water molecules. They are of great importance in both scientific research and the petroleum industry because of their applications in modern energy and environmental technologies. To achieve an atomistic-level understanding of the diffusion and decomposition of trapped molecules in clathrate hydrate, we used methane hydrates (MHs) as the prototype system and examined the methane diffusion and decomposition mechanism by employing quantum mechanics (QM) and quantum mechanics molecular dynamics (QMD) simulations. Our QMD simulations illustrated that the initial decomposition reaction in MHs initiates from hydrogen transfer among water molecules and attacks by fragments of O and OH on CH₄ molecules are responsible for the destruction of the methane molecules. Next, our QM simulations revealed that the methane molecule prefers to escape from the ice cage through the hexagonal face at low temperature. To suppress the methane diffusion, we demonstrated that the diffusion barrier is significantly enhanced by adding electron or hole carriers. This is because the extra electrons and holes enhance the electrostatic interaction between methane and water molecules, leading to an increased diffusion barrier. Thus, the clathrate hydrates could be stabilized by adding extra free electron or hole carriers.

Methane decomposition initiates from water fragment attack and methane hydrates could be stabilized by adding free electron or hole carriers.

Energetic Metal-Organic Frameworks Incorporating NH3OH+ for New High-Energy-Density Materials

Energetic metal-organic frameworks (E-MOFs) have witnessed increasing development over the past several years. However, as a highly energetic cation, NH₃OH⁺ has never been explored to construct transition-metal-based E-MOFs. Herein, we report the first examples of NH₃OH⁺-containing E-MOFs with bis(tetrazole)methane (H₂btm) as a ligand and copper and manganese as central metal ions, [(NH₃OH)₂(Cu(btm)₂)]_n and [(NH₃OH)₂(Mn(btm)₂)]_n. Crystal structure determinations reveal that both E-MOFs show two-dimensional layered structures. Experimental results suggest that they have high thermal decomposition temperatures (>200 °C). Among them, Cu-based E-MOFs possesses outstanding thermal stability (T_dec = 230.3 °C), which surpasses those of known NH₃OH⁺-containing compounds. They also have high energy density; in particular, the Cu-based E-MOF affords a high heat of combustion (11447 kJ kg^-1) and high heat of detonation (713.8 kJ mol^-1) beyond the most powerful organic explosives in use today. Additionally, the two E-MOFs show completely different sensitivity properties: the Mn-based E-MOF is an insensitive high-energy-density material (IS > 40 J; FS > 360 N; EDS > 20 J), while the Cu-based E-MOF can be classified as a sensitive energetic material (IS = 13 J; FS = 216 N; EDS = 10.25 J), demonstrating their diverse applications in different fields. Our research proposes a unique class of high-energy-density materials.