Morphology-dependent catalytic activity of Fe2O3 and its graphene-based nanocomposites on the thermal decomposition of AP

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.

The thermal decomposition mechanism of RDX/AP composites: ab initio neural network MD simulations

A neural network potential (NNP) is developed to investigate the decomposition mechanism of RDX, AP, and their composites. Utilizing an ab initio dataset, the NNP is evaluated in terms of atomic energy and forces, demonstrating strong agreement with ab initio calculations. Numerical stability tests across a range of timesteps reveal excellent stability compared to the state-of-the-art ReaxFF models. Then the thermal decomposition of pure RDX, AP, and RDX/AP composites is performed using NNP to explore the coupling effect between RDX and AP. The results highlight a dual interaction between RDX and AP, i.e., AP accelerates RDX decomposition, particularly at low temperatures, and RDX promotes AP decomposition. Analyzing RDX trajectories at the RDX/AP interface unveils a three-part decomposition mechanism involving N-N bond cleavage, H transfer with AP to form Cl-containing acid, and chain-breaking reactions generating small molecules such as N2, CO, and CO2. The presence of AP enhances H transfer reactions, contributing to its role in promoting RDX decomposition. This work studies the reaction kinetics of RDX/AP composites from the atomic point of view, and can be widely used in the establishment of reaction kinetics models of composite systems with energetic materials.

Synthesis of Covalently Modified Energetic Graphene Oxide/CuO Composites with Enhanced Catalytic Performance for Thermal Decomposition of Ammonium Perchlorate

In this study, a new covalently modified energetic graphene oxide (CMGO) was synthesized by introducing the energetic component 4-amino-1,2,4-triazole on GO sheets through valence bond bonding. The morphology and structure of CMGO were studied by scanning electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy, and the results showed that CMGO was successfully synthesized. Then, CMGO/CuO was prepared by loading nano-CuO onto CMGO sheets using an ultrasonic dispersion method. Furthermore, the catalytic effect of CMGO/CuO on the thermal decomposition of ammonium perchlorate (AP) was investigated using differential scanning calorimetric technique and thermogravimetric analysis. The results revealed that the high decomposition temperature T_H and Gibbs free energy ΔG^⧧ of the CMGO/CuO/AP composite decreased by 93.9 °C and 15.3 kJ/mol compared with those of raw AP, respectively. The CMGO/CuO composite exhibited more significant catalytic effect on the thermal decomposition of AP than GO/CuO, and the heat release Q of CMGO/CuO/AP was greatly increased from 132.9 to 1428.5 J/g with 5 wt % CMGO/CuO. The above results demonstrated that CMGO/CuO is an excellent composite energetic combustion catalyst, which is expected to be widely used in composite propellants.

Preparation of SiO2@Ag@molecular imprinted polymers hybrid for sensitive and selective detection of amoxicillin using surface-enhanced Raman scattering

In this work, we fabricated a 300 nm-sized silver-coated silica (SiO₂@Ag) SERS substrate. Based on SiO₂@Ag, we designed SiO₂@Ag@molecular imprinted polymers (SiO₂@Ag@MIPs) to realize selectively detection of amoxicillin by coating a molecular imprinted layer averagely thinner than 10 nm on SiO₂@Ag. The as-prepared SERS-active substrate demonstrates excellent enhancement for amoxicillin as well as the enhancement factors were 1.63 × 10⁶ of SiO₂@Ag@MIPs and 2.97 × 10⁵ of SiO₂@Ag, respectively. The SiO₂@Ag@MIPs core-shell hybrids as SERS substrates and the minimum detectable concentration of amoxicillin was as low as 2.7 × 10^-9 M, and the detection limit of SiO₂@Ag was 2.7 × 10^-7 M. The linear relationship between intensities of characteristic peaks and concentrations of amoxicillin was established. Both SiO₂@Ag and SiO₂@Ag@MIPs substrates were highly sensitive and could achieve qualitative and semi-quantitative analysis of amoxicillin in aqueous media with good linear correlations. Based on the above, SiO₂@Ag@MIPs will be conducive to detecting actual samples and expanding the practical application.

3D Electron-Rich ZIF-67 Coordination Compounds Based on 2-Methylimidazole: Synthesis, Characterization and Effect on Thermal Decomposition of RDX, HMX, CL-20, DAP-4 and AP

ZIF-67 is a three-dimensional zeolite imidazole ester framework material with a porous rhombic dodecahedral structure, a large specific surface area and excellent thermal stability. In this paper, the catalytic effect of ZIF-67 on five kinds of energetic materials, including RDX, HMX, CL-20, AP and the new heat-resistant energetic compound DAP-4, was investigated. It was found that when the mass fraction of ZIF-67 was 2%, it showed excellent performance in catalyzing the said compounds. Specifically, ZIF-67 reduced the thermal decomposition peak temperatures of RDX, HMX, CL-20 and DAP-4 by 22.3 °C, 18.8 °C, 4.7 °C and 10.5 °C, respectively. In addition, ZIF-67 lowered the low-temperature and high-temperature thermal decomposition peak temperatures of AP by 27.1 °C and 82.3 °C, respectively. Excitingly, after the addition of ZIF-67, the thermal decomposition temperature of the new heat-resistant high explosive DAP-4 declined by approximately 10.5 °C. In addition, the kinetic parameters of the RDX+ZIF-67, HMX+ZIF-67, CL-20+ZIF-67 and DAP-4+ZIF-67 compounds were analyzed. After the addition of the ZIF-67 catalyst, the activation energy of the four energetic materials decreased, especially HMX+ZIF-67, whose activation energy was approximately 190 kJ·mol^-1 lower than that reported previously for HMX. Finally, the catalytic mechanism of ZIF-67 was summarized. ZIF-67 is a potential lead-free, green, insensitive and universal EMOFs-based energetic burning rate catalyst with a bright prospect for application in solid propellants in the future.

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 Investigation of Graphene and Fe2O3 Catalytic Activity for Decomposition of Ammonium Perchlorate

The employment of catalysts is an effective way to improve ammonium perchlorate (AP) decomposition performance during the combustion of composite solid propellants. Understanding the micromechanism of catalysts at the atomic level, which is hard to be observed by experiments, can help attain more excellent decomposition properties of AP. In this study, first-principles simulations based on density functional theory were used to explore the effect of the graphene catalyst and iron oxide (Fe₂O₃) catalyst on AP decomposition. Considering the transfer of a H atom during AP decomposition, the most stable adsorption sites for aforementioned catalysts were found: the top of the C atom of the graphene surface with the adsorption energy of -0.378 eV and the top of the Fe atom of the Fe₂O₃ surface with the adsorption energy of -1.596 eV. On the basis of adsorption results, our transition state calculations indicate that, in comparison to control groups, graphene and Fe₂O₃ can reduce the activation energy barrier by ∼19 and ∼37%, respectively, to promote AP decomposition with a transfer process of a H atom on the catalyst surface. Our calculations provide a way for explaining the micromechanism of the catalytic activity of graphene and Fe₂O₃ nanocomposites in AP decomposition and guide experimental applications of graphene and Fe₂O₃ for catalytic reactions.

Enhanced thermal and energetic properties of NC-based nanocomposites with silane functionalized GO

The surface functionalization of graphene oxide (GO) is always attractive in improving certain properties of the polymer. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyl-trimethoxysilane (SPTES) have been used to make silane functionalized graphene oxides (SiGOs). The APTES-grafted GO (NH-SiGO), SPTES-grafted GO (SH-SiGO) and pure GO have been separately introduced into the nitrocellulose (NC) matrix. The morphology, thermal properties and energetic properties of the prepared nanocomposites (NH-SiGO and SH-SiGO) were investigated comprehensively. It is shown that the presence of GO and SiGOs have different influences on the thermal reactivity of NC with various contents, and NH-SiGO with 0.5 wt% content showed better catalytic performance on the thermal decomposition of NC than others and showed prominently higher efficiency in improving its heat of combustion. Adding 0.5 wt% of NH-SiGO to NC may decrease its decomposition temperature from 202.1 °C to 196.6 °C, and the residue was decreased from 10.61 wt% to 3.95 wt%, respectively. One isoconversional kinetic method was exploited to determine the kinetic parameters of NC and its nanocomposites. It was found that NH-SiGO had a strong catalytic action on the thermal decomposition of NC-based nanocomposites for which the activation energy and the pre-exponential factor were considerably lowered, while SH-SiGO exhibited an inverse effect. The heat of combustion from NC/GO/0.5, NC/NH-SiGO/0.5 and NC/SH-SiGO/0.5 were determined as 11 249.5, 11 675.1 and 11 491.5 J g^-1, respectively, which are higher than that of the pure NC (10 908.4 J g^-1). From the combustion process of NC/NH-SiGO/0.5, it was shown that the nanocomposite was combusted completely.

Ferrocene functionalized graphene: preparation, characterization and application as an efficient catalyst for the thermal decomposition of TKX-50

Novel ferrocene functionalized graphene with different molecular structures were designed, fabricated and characterized via SEM, EDS, FTIR, XPS and RAMAN methods. SEM results show the two-dimensional structure of the as-prepared catalysts, and the active metal Fe is uniformly distributed on the surface of graphene. The FTIR, XPS and RAMAN results confirmed the successful preparation of ferrocene functionalized graphene. The catalytic effects of the as-synthesized catalysts for the thermal decomposition of energetic TKX-50 were monitored by DSC, and the corresponding kinetic parameters were calculated using multi kinetic methods including traditional and nonlinear models. The results showed that the as-prepared ferrocene functionalized graphene can effectively promote the thermal decomposition of TKX-50 with the reduced decomposition peak temperatures and activation energies. In addition, the effects of ferrocene functionalized graphene for TKX-50 decomposition are reflected in both high and low temperature stages, and the effect on the high temperature stage is more significant. The outstanding catalytic activity of ferrocene functionalized graphene is related not only to the good dispersion of active Fe, but also to the enhanced interaction of small molecule products on two-dimensional graphene. Among the ferrocene functionalized graphene studied, G-792-Fe and G-902-Fe exhibit better catalytic effects on the thermal decomposition of TKX-50, which can be used as candidate catalysts for TKX-50-based solid propellants.