Effects of Temperature on Novel Molecular Perovskite Energetic Material (C6H14N2)[NH4(ClO4)3]: A Molecular Dynamics Simulation

Molecular dynamics (MD) simulations were performed on the energetic molecular perovskite (C6H14N2)[NH4(ClO4)3], with excellent detonation properties, thermal stability, and high specific impulse, which is a potential replacement for AP as the next generation propellants. The cohesive energy density, binding energy, pair correlation function, maximum bond length (Lmax) of the N-H trigger bond, and mechanical properties of the (C6H14N2)[NH4(ClO4)3] were reported. The calculated cohesive energy density and binding energy decrease with increasing temperature, indicating a gradual decrease in the thermal stability with temperature. In addition, H···O hydrogen bonding interactions have been found based on the results of pairwise correlation functions. The maximum length (Lmax) of the N-H trigger bond was calculated and used as a criterion to theoretically judge the impact sensitivity. The maximum bond length of the N-H trigger bond grows gradually with temperature; however, it does very slightly yet gradually above 373 K. This suggests that an increase in temperature leads to a higher impact sensitivity and lower thermal stability. However, this effect becomes less pronounced when the temperature surpasses 373 K. Moreover, the calculated mechanical data indicate that as the temperature rises, the material's stiffness, hardness, yield strength, and fracture strength all decrease. The material's ductility shows an upward trend with increasing temperature, reaching its peak at 373 K and subsequently declining as the temperature continues to rise.

A promising perovskite primary explosive

A primary explosive is an ideal chemical substance for performing ignition in military and commercial applications. For over 150 years, nearly all of the developed primary explosives have suffered from various issues, such as troublesome syntheses, high toxicity, poor stability or/and weak ignition performance. Now we report an interesting example of a primary explosive with double perovskite framework, {(C6H14N2)2[Na(NH4)(IO4)6]}n (DPPE-1), which was synthesized using a simple green one-pot method in an aqueous solution at room temperature. DPPE-1 is free of heavy metals, toxic organic components, and doesn't involve any explosive precursors. It exhibits good stability towards air, moisture, sunlight, and heat and has acceptable mechanical sensitivities. It affords ignition performance on par with the most powerful primary explosives reported to date. DPPE-1 promises to meet the challenges existing with current primary explosives, and this work could trigger more extensive applications of perovskite.

Periodate-based molecular perovskites as promising energetic biocidal agents

Epidemics caused by pathogens in recent years have created an urgent need for energetic biocidal agents with the capacity of detonation and releasing bactericides. Herein we present a new type of energetic biocidal agents based on a series of iodine-rich molecular perovskites, (H₂dabco)M(IO₄)₃ (dabco = 1,4-diazabicyclo[2.2.2]octane, M = Na⁺/K⁺/Rb⁺/NH₄ ⁺ for DAI-1/2/3/4) and (H₂dabco)Na(H₄IO₆)₃ (DAI-X1). These compounds possess a cubic perovskite structure, and notably have not only high iodine contents (49-54 wt%), but also high performance in detonation velocity (6.331-6.558 km s^-1) and detonation pressure (30.69-30.88 GPa). In particular, DAI-4 has a very high iodine content of 54.0 wt% and simultaneously an exceptional detonation velocity up to 6.558 km s^-1. As disclosed by laser scanning confocal microscopy observation and a standard micro-broth dilution method, the detonation products of DAI-4 exhibit a broad-spectrum bactericidal effect against bacteria (E. coli, S. aureus, and P. aeruginosa). The advantages of easy scale-up synthesis, low cost, high detonation performance, and high iodine contents enable these periodate-based molecular perovskites to be highly promising candidates for energetic biocidal agents.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available in the online version of this article at 10.1007/s40843-022-2257-6.

Research progress of EMOFs-based burning rate catalysts for solid propellants

Energetic Metal Organic Frameworks (EMOFs) have been a hotspot of research on solid propellants in recent years. In this paper, research on the application of EMOFs-based burning rate catalysts in solid propellants was reviewed and the development trend of these catalysts was explored. The catalysts analyzed included monometallic organic frameworks-based energetic burning rate catalysts, bimetallic multifunctional energetic burning rate catalysts, carbon-supported EMOFs burning rate catalysts, and catalysts that can be used in conjunction with EMOFs. The review suggest that monometallic organic frameworks-based burning rate catalysts have relatively simple catalytic effects, and adding metal salts can improve their catalytic effect. Bimetallic multifunctional energetic burning rate catalysts have excellent catalytic performance and the potential for broad application. The investigation of carbon-supported EMOFs burning rate catalysts is still at a preliminary stage, but their preparation and application have become a research focus in the burning rate catalyst field. The application of catalysts that can be compounded with EMOFs should be promoted. Finally, environmental protection, high energy and low sensitivity, nanometerization, multifunctional compounding and solvent-free are proposed as key directions of future research. This study aims to provide a reference for the application of energetic organic burning rate catalysts in solid propellants.

First-principles study on the mechanical and electronic properties of energetic molecular perovskites AM(ClO4)3 (A = C6H14N2 2+, C4H12N2 2+, C6H14N2O2+; M = Na+, K+)

Density functional theory (DFT) simulations were conducted to study the crystal structures, and mechanical and electronic properties of a series of new energetic molecular perovskites, including (C6H14N2)[Na(ClO4)3], (C6H14N2)[K(ClO4)3], (C4H12N2)[Na(ClO4)3] and (C6H14N2O)[K(ClO4)3], abbreviated as DAP-1, DAP-2, PAP-1, and DAP-O2, respectively. By calculating the elastic constants, moduli (Young's modulus E, bulk modulus B, and shear modulus G), Poisson ratio ν and Pugh's ratio B/G, we found that the four energetic molecular perovskites not only possessed good mechanical stability but excellent mechanical flexibility and ductility. In addition, DFT calculations were used to investigate the electronic properties of all of the perovskite compounds. The band gaps of DAP-1 and DAP-2 were comparable, and the band gap of PAP-1 was the smallest and that of DAP-O2 was the largest. A comprehensive analysis of the density of states and the M-O bonding characteristics provided a good explanation for the band gap characteristics. Besides, we found that the modulus properties of these molecular perovskite energetic compounds are also tightly bound to the strength of M-O bonding.

Anisotropic Impact Sensitivity of Metal-Free Molecular Perovskite High-Energetic Material (C6H14N2)(NH2NH3)(ClO4)3 by First-Principles Study

Density functional theory simulations were carried out to investigate energetic molecular perovskite (C₆H₁₄N₂)(NH₂NH₃)(ClO₄)₃ which was a new type energetic material promising for future application. The electronic properties, surface energy, and hydrogen bonding of (100), (010), (011), (101), (111) surfaces were studied, and the anisotropic impact sensitivity of these surfaces were reported. By comparing the values of the band gaps for different surface structures, we found that the (100) surface has the lowest sensitivity, while the (101) surface was considered to be much more sensitive than the others. The results for the total density of states further validated the previous conclusion obtained from the band gap. Additionally, the calculated surface energy indicated that surface energy was positively correlated with impact sensitivity. Hydrogen bond content of the surface structures showed distinct variability according to the two-dimensional fingerprint plots. In particular, the hydrogen bond content of (100) surface was higher than that of other surfaces, indicating that the impact sensitivity of (100) surface is the lowest.

Thermal kinetics, thermodynamics, decomposition mechanism, and thermal safety performance of typical ammonium perchlorate-based molecular perovskite energetic materials

In this work, we report the thermal kinetics, thermodynamics, and decomposition mechanism of AP-based molecular perovskite energetic materials and estimate their thermal safety performance. Typical AP-based molecular perovskite energetic materials, (H2dabco)[NH4(ClO4)3] (DAP-4), (H2pz)[NH4(ClO4)3](PAP-4), (H2mpz)[NH4(ClO4)3](PAP-M4), and (H2hpz)[NH4(ClO4)3] (PAP-H4), were synthesized and characterized. These were studied using differential scanning calorimetry (DSC). The results show that all of the obtained AP-based molecular perovskite energetic materials have higher thermal decomposition temperatures, and the peak temperatures are more than 360 °C. All follow random nucleation and growth models. Other thermodynamic parameters, such as the reaction enthalpy (ΔH), entropy change (ΔS), and Gibbs free energy (ΔG), show that they are generally thermodynamically stable. Moreover, their adiabatic induced temperatures were obtained; TD24 of DAP-4, PAP-4, PAP-M4, and PAP-H4 were 246.6, 201.2, 194.5, and 217.5 °C, respectively. This study offers an important and in-depth understanding of the thermal decomposition characteristics of AP-based molecular perovskite energetic materials and their potential applications.

Silver(I)-Based Molecular Perovskite Energetic Compounds with Exceptional Thermal Stability and Energetic Performance

In recent years, molecular perovskite energetic materials have attracted more attention because of their simple synthesis processes, high thermal stabilities, excellent performances, and great significance as a design platform for energetic materials. To explore the possibility of the application of molecular perovskite energetic materials in heat-resistant explosives, four silver(I)-based molecular perovskite energetic compounds, (H₂A)[Ag(ClO₄)₃], where H₂A = piperazine-1,4-diium (H₂pz²⁺) for PAP-5, 1-methyl-piperazine-1,4-diium (H₂mpz²⁺) for PAP-M5, homopiperazine-1,4-diium (H₂hpz²⁺) for PAP-H5, and 1,4-diazabicyclo[2.2.2]octane-1,4-diium (H₂dabco²⁺) for DAP-5, were synthesized by a one-pot self-assembly strategy and structurally characterized. The single-crystal structures indicated that PAP-5, PAP-M5, and DAP-5 possess cubic perovskite structures while PAP-H5 possesses a hexagonal perovskite structure. Differential thermal analyses showed that their onset decomposition temperatures are >308.3 °C. For PAP-5 and DAP-5, they have not only exceptional calculated detonation parameters (D values of 8.961 and 8.534 km s^-1 and P values of 42.4 and 37.9 GPa, respectively) but also the proper mechanical sensitivity (impact sensitivities of ≤10 J for PAP-5 and 3 J for DAP-5 and friction sensitivities of ≤5N for both PAP-5 and DAP-5) and thus are of interest as potential heat-resistant primary explosive components.

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.

Molecular solid solutions for advanced materials – homeomorphic or heteromorphic

Crystalline molecular solid solutions are discussed on the basis of homeomorphism and heteromorphism of blended molecules.

Fast synthesis of MoO3-x and its catalytic effect on the thermal decomposition of ammonium perchlorate based molecular perovskite (DAP-4)

In this work, it is shown that MoO3-x has a positive effect on the thermal decomposition of ammonium perchlorate based molecular perovskite (H2DABCO)[NH4(ClO4)3] (DAP-4). MoO3-x was prepared by heat treatment, and the morphology, structure, and thermal decomposition performance were characterized. The morphology and structure characterization results showed that MoO3-x was an irregular layered structure material and the Mo element was mainly in the +6 chemical valence state, with a small amount of Mo5+. Thermal analysis results showed that the thermal decomposition peak temperature of DAP-4 was effectively reduced from 394.4 °C to 353.7 °C, 321.4 °C, and 312.5 °C in the presence of 1%, 5%, and 10% MoO3-x, respectively. It is particularly worth noting that the maximum heat release rate of the DAP-4/10% MoO3-x mixture was increased by 4.9 times compared with pure DAP-4. Through the two classic thermal decomposition kinetic methods, Kissinger and Starink, the reliable kinetic parameters of DAP-4/MoO3-x were obtained. The increase of the reaction rate constant k indicated that the maximum thermal decomposition reaction rate of DAP-4 was effectively improved. This work provided a feasible technology for using MoO3-x as an effective catalyst to improve the thermal performance of DAP-4.

Optimizing degradation conditions of treatment of TATB explosive wastewater by γ-Fe2O3 nanoparticles and UV synergistic degradation

In this work, the effect of superparamagnetic γ-Fe2O3 nanoparticles and ultraviolet light (UV) synergistic degradation on the treatment of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) explosive wastewater was studied. γ-Fe2O3 nanoparticles were prepared by hydrolysis method and the degradation performance of TATB explosive wastewater was systematically studied with UV light assisted. The results showed that γ-Fe2O3 magnetic nanoparticles have a low size distribution that ranged from 5 to 10 nm and possesses superparamagnetic properties. The optimized degradation condition was investigated and best degradation performance was obtained with the optimized conditions: the initial of pH = 3, UV illumination intensity (5 w/cm2), reaction temperature (25 °C), initial total organic carbon concentration (4.025 mg/L) as well as reaction time (60 min). This work can offer a new idea to degrade the explosive wastewater.