Explosives in the Cage: Metal-Organic Frameworks for High-Energy Materials Sensing and Desensitization

Sensing and Discrimination of Explosives at Variable Concentrations with a Large-Pore MOF as Part of a Luminescent Array

Metal-organic frameworks (MOFs) have shown great promise for sensing of dangerous chemicals, including environmental toxins, nerve agents, and explosives. However, challenges remain, such as the sensing of larger analytes and the discrimination between similar analytes at different concentrations. Herein, we present the synthesis and development of a new, large-pore MOF for explosives sensing and demonstrate its excellent sensitivity against a range of relevant explosive compounds including trinitrotoluene and pentaerythritol tetranitrate. We have developed an improved, thorough methodology to eliminate common sources of error in our sensing protocol. We then combine this new MOF with two others as part of a three-MOF array for luminescent sensing and discrimination of five explosives. This sensor works at part-per-million concentrations and, importantly, can discriminate explosives with high accuracy without reference to their concentration.

Relationship between Energetic Performance and Clustering Effects on Incremental Nitramine Groups: A Theoretical Perspective

Nitramine compounds are typical high-energy-density materials (HEDMs) and are widely used as explosives because of their superior explosive performance over conventional energetic materials. In this work, the thermal properties of 1-nitropiperidine (NPIP), 1,4-dinitropiperazine (DNP), and 1,3,5-trinitro-1,3,5-triazinane (RDX) were investigated from quantum mechanics (QM) and reactive force field (ReaxFF) molecular dynamics simulations. We found that the bond dissociation energy of the N-NO₂ bond, heat of formation, released energy, produced fragments, and oxygen balance are closely related to the incremental nitramine group. The nitramine group has a significant effect on the energetic performance of these nitramine compounds. In addition, the increase of the nitramine group will improve thermal decomposition activity, promote the generation of small molecules, and restrain the formation of carbon clusters. We hope that this work can shed new light on the design of energetic materials.

Multiple Emitting Amphiphilic Conjugated Polythiophenes-Coated CdTe QDs for Picogram Detection of Trinitrophenol Explosive and Application Using Chitosan Film and Paper-Based Sensor Coupled with Smartphone

Novel multiple emitting amphiphilic conjugated polythiophene-coated CdTe quantum dots for picogram level determination of the 2,4,6-trinitrophenol (TNP) explosive are developed. Four biocompatible sensors, cationic polythiophene nanohybrids (CPTQDs), nonionic polythiophene nanohybrids (NPTQDs), anionic polythiophene nanohybrids (APTQDs), and thiophene copolymer nanohybrids (TCPQDs), are designed using an in situ polymerization method, which shows highly enhanced fluorescence intensity and quantum yield (up to 78%). All sensors are investigated for nitroexplosive detection to provide a remarkable fluorescence quenching for TNP and the quenching efficiency reached 96% in the case of TCPQDs. The fluorescence of the sensors are quenched by TNP through inner filter effect, electrostatic, π-π, and hydrogen bonding interactions. Under optimal conditions, the detection limits of CPTQDs, NPTQDs, APTQDs, and TCPQDs are 2.56, 7.23, 4.12, and 0.56 × 10-9 m, respectively, within 60 s. More importantly, portable, cost effective, and simple to use paper strips and chitosan film are successfully applied to visually detect as little as 2.29 pg of TNP. The possibility of utilizing a smartphone with a color-scanning APP in the determination of TNP is also established. Moreover, the practical application of the developed sensors for TNP detection in tap and river water samples is described with satisfactory recoveries of 98.02-107.50%.

A recyclable indole-based polymer for trinitrotoluene adsorption via the synergistic effect of dipole–π and donor–acceptor interactions

A new type of indole-based porous organic polymer with amine units (PAIN) has been constructed, which possesses encouraging and effective adsorption properties for trinitrotoluene by taking advantage of the synergistic effect of dipole–π and donor–acceptor interactions.

Functional construction of a water-stable Tb-coordination polymer luminescent sensor for highly selective detection of picric acid in an aquatic environment

In order to achieve convenient and efficient detection of picric acid in a water environment, based on function-oriented strategy, we combine luminescence performance with recognition performance, taking into account the application conditions.

1-AminoTriazole Transition-Metal Complexes as Laser-Ignitable and Lead-Free Primary Explosives

This unique complex study describes two isomeric aminotriazoles as auspicious nitrogen-rich ligands for energetic coordination compounds (ECCs) to replace the commonly used highly poisonous and environmentally harmful lead-based primary explosives. The triazoles were obtained by easily scalable and convenient synthetic routes starting solely from commercially available starting materials. 1-Amino-1,2,3-triazole (1, 1-ATRI) and, for the first time, 1-amino-1,2,4-triazole (2, 1A-1,2,4-TRI) were employed as ligands to form highly energetic transition-metal(II) complexes. The desired characteristics could be altered successively by using various nonpoisonous metal(II) centers (Cu²⁺ , Mn²⁺ , Fe²⁺ , and Zn²⁺ ) and anions (Cl^- , NO₃ ^- , ClO₃ ^- , ClO₄ ^- , picrate, styphnate, 2,4,6-trinitro-3-hydroxyphenolate, and 2,4,6-trinitro-3,5-dihydroxyphenolate). The 14 synthesized coordination compounds were characterized comprehensively by XRD, IR and UV/Vis spectroscopy, elemental analysis, and differential thermal and thermogravimetric analyses. Ball-drop impact, electrostatic discharge (ESD), and mechanical (impact and friction) sensitivities were determined according to BAM standard methods. In addition to laser ignition experiments, selected ECCs were evaluated in classical secondary explosive initiation tests (detonators filled with pentaerythritol tetranitrate (nitropenta)), which revealed their enormous potential and proved them to be very attractive for future applications in explosives.

A C-C bonded 5,6-fused bicyclic energetic molecule: exploring an advanced energetic compound with improved performance

A C-C bonded amino-nitro pyrazole (7) and its ring-expansion product (9) have been synthesized and characterized. The synthetic route to 9 proceeds in several steps from the commercial substrate diethyl oxalate and acetone. The process was found to be straightforward, practical and easily scalable. Both of these structures were confirmed by single crystal X-ray diffraction. Compound 9 with a high density (1.85 g cm-3) at room temperature, excellent thermal stability (Td: 315 °C), good detonation performance and low sensitivity to impact and friction has potential as a high-temperature energetic material.

Photostable and Low-Toxic Yellow-Green Carbon Dots for Highly Selective Detection of Explosive 2,4,6-Trinitrophenol Based on the Dual Electron Transfer Mechanism

Advances in the development of fluorescent carbon dots (CDs) for detecting nitro-explosives have attracted great interest. However, developing long-wavelength luminescence CDs for highly selective determination of 2,4,6-trinitrophenol (TNP) and getting insight into the detection mechanism remain further to be investigated. Here, excitation-independent yellow-green emission CDs with good photostability and low biotoxicity were introduced for detecting TNP selectively. Then, two types of electron transfer (ET) processes including hydrogen-bond interaction-assisted ET and proton transfer-assisted ET are suggested to be responsible for their photophysical behavior. Finally, the visual detection of TNP has been successfully developed by a CD-based indicator paper. The facile, highly sensitive, and selective detection for TNP in both of a solution and a solid phase makes CDs potentially useful in environmental sensor applications.

Design and synthesis of metal hydroxide three-dimensional inorganic cationic frameworks

Three-dimensional (3D) cationic frameworks are rare but crucial host materials with vast industrial applications. However, the controlled synthesis of 3D inorganic cationic framework (ICF) materials still remains a challenge. Here, we develop a new strategy to construct 3D inorganic cationic frameworks by octahedral metal-hydroxide (M(OH)₆) unit induced reconstruction of layered rare-earth hydroxides. Based on this strategy, a large family (>187 members) of 3D-ICF with a general formula: RE₁₂(OH)₁₈((RE_1-x-y,M_xM'_y)(OH)₆)₄·ACl₆ (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y; M = Al, Cr; M' = Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn; A = Na, K) were achieved. This newly constructed strategy would greatly promote the development of 3D inorganic cationic materials. Furthermore, the discovery of this new family of cationic frameworks would pave the way for the potential application of cationic materials in different sorts of fields.

Construction of Zeolite-Like Cluster Organic Frameworks from 3 d-4 d/3 d-3 d Heterometallic Supertetrahedral Secondary Building Units: Syntheses, Structures, and Properties

Two zeolite-like cluster organic frameworks based on Cd-Cu/Mn-Cu heterometallic supertetrahedral secondary building units have been successfully constructed under solvothermal conditions, namely, Cu[Cd₄ Cu₆ (L)₄ (H₂ O)₁₈ ](Ac)₉ ⋅DMA⋅3 H₂ O (1), and Cu[Mn₄ Cu₆ (L)₄ (Ac)₃ (H₂ O)₁₂ ](Ac)₆ ⋅CH₃ CN⋅13 H₂ O (2), where H₃ L=2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol, Ac=CH₃ COO^- , DMA=N,N'-dimethylacetamide. Single-crystal X-ray structural analysis reveals that both 1 and 2 exhibit 3-dimensional zeolite-like architectures with similar 4-connected components, but possess definitely different topologies of diamondoid (dia) and uncommon lonsdaleite (lon), respectively. 1 and 2 represent the first cases of zeolite-like cluster organic frameworks containing Cd-Cu/Mn-Cu heterometallic supertetrahedral secondary building units. Furthermore, the magnetic properties and porous nature of 1 and 2 were also studied.

Optimizing the oxygen balance by changing the A-site cations in molecular perovskite high-energetic materials

Two new members of molecular perovskite high-energetic materials exhibit optimized oxygen balances by changing the A-site cations.

A two-fold interpenetrated zinc–organic framework: luminescence detection of CrO42−/Cr2O72− and chemical conversion of CO2

A novel two-fold interpenetrated 3D framework can adsorb CO₂ and serve as an efficient and recyclable catalyst for the conversion of CO₂ with epoxides. Furthermore, it can also act as a sensitive and recyclable luminescent probe to detect CrO₄²⁻/Cr₂O₇²⁻ among many anions in aqueous solution.

A highly stable and tightly packed 3D energetic coordination polymer assembled from nitrogen-rich tetrazole derivatives

A tightly packed 3D energetic cadmium(ii) coordination polymer was synthesized with high stability and remarkable energetic performance.

A Heat-Resistant and Energetic Metal-Organic Framework Assembled by Chelating Ligand

Heat-resistant explosives with high performance and insensitivity to external stimulus or thermal are indispensable in both the military and civilian worlds especially when utilized under harsh conditions. We designed and synthesized a new heat-resistant three-dimensional chelating energetic metal-organic framework (CEMOF-1) by employing 4-amino-4H-1,2,4-triazole-3,5-diol (ATDO) as a ligand. Because of its chelating 3D structural feature, good oxygen balance (-29.58%), and high crystal density (2.234 g cm^-3), CEMOF-1 demonstrates high decomposition temperature (445 °C), insensitivity to stimulation, and excellent detonation velocity (10.05 km s^-1) and detonation pressure (49.36 GPa). The advantages of facile synthesis, thermal stability, and powerful explosive performance make CEMOF-1 as a promising candidate for heat-resistant explosives in future applications.