Highly Efficient Separation of Anionic Organic Pollutants from Water via Construction of Functional Cationic Metal-Organic Frameworks and Mechanistic Study

Thinking Outside the Energetic Box: Stabilizing and Greening High-Energy Materials with Reticular Chemistry

ConspectusReticular chemistry has provided intriguing opportunities for systematically designing porous materials with different pores by adjusting the building blocks. Among them, framework materials have demonstrated outstanding performance for the design of new functional materials used in a broad range of fields, including energetic materials. Energetic materials are widely used for rockets, satellites, mining, and tunneling. In terms of energetic materials, explosophores and nitrogen-rich heterocycles are fundamental building blocks for high-energy compounds. However, the traditional strategy of synthesizing HEDMs (high energy density materials) at the molecular level has faced the long-term challenge of balancing energy and stability. Inspired by reticular chemistry, nitrogen-rich heterocycles offer diverse nitrogen sites for designing diversified coordination interactions. Ionic bond interactions exist in a wide range of energetic salts. Furthermore, most metastable explosophores, e.g., nitro, nitramino, and amino groups, can form strong hydrogen-bonding networks. Based on these noncovalent interactions (such as coordination, ionic, and/or hydrogen bonds (HBs)) and/or covalent interactions can determine intermolecular packing/linkage of the energetic fuel and oxidizer components, reticular chemistry provides a new platform evolving from single-molecular design to various energetic frameworks (E of the energetic frameworks with superior comprehensive properties. For example, to achieve coordination with metals or introduce sufficient hydrogen bond donor/acceptor structural units, the host structure of energetic framework materials usually contains less oxygen-rich substituents such as nitro, so the host molecules of the framework, F) at the crystal level, which can enhance the integrated stabilities of EFs.Along with growing concerns about the environment and safety issues, considerable effort has been devoted to pursuing environmentally friendly and insensitive energetic materials. The newly emerging EFs are conducive to introducing explosophores into a green chemical pathway. Benefiting from these cross-disciplinary achievements, taming metastable energetic molecules in specific porous frameworks is a green strategy to desensitize energetic materials while concomitantly retaining excellent energetic properties, which has become one of the most forward and promising investigations. In the past decade, EFs have achieved further results in stabilizing and greening energetic materials using HBs, covalent bonds, and alkaline earth metal-involving coordination bonds to avoid heavy metal toxicity and to employ halogen-free oxidizers. Because this field is still expanding rapidly, it is of great value for researchers and possible users of the work to be able to view all the progress.Through this Account, we intend that more readers will become knowledgeable about EFs, including their definition, history, synthesis, properties, and possible applications. The aim of this Account is to present the latest advances in EFs in recent years and to offer a perspective on the future direction of this field.

Construction of Adaptive Deformation Block: Rational Molecular Editing of the N-Rich Host Molecule to Remove Water from the Energetic Hydrogen-Bonded Organic Frameworks

Energetic hydrogen-bonded organic frameworks (E-HOFs), as a type of energetic material, spark fresh vitality to the creation of high energy density materials (HEDMs). However, E-HOFs containing cations and anions face challenges such as reduced energy density due to the inclusion of crystal water. In this work, the modification of amino groups in N-rich organic units could form a smart building block of hydrogen-bonded frameworks capable of changing the volume of the void space in the molecule through adaptive deformation of E-MOF blocks, thus enabling the replacement of water. Based on the above strategy, we report an interesting example of a series of hydrogen-bonded organic frameworks (E-HOF 2a and 3a) synthesized using a facile method. The crystal structure data of all of the compounds were also obtained in this work. Anhydrous 2a and 3a exhibit higher density, good thermal stability, and low mechanical sensitivity. The strategy of covalent bond modification for the host molecules of energetic frameworks shows enormous potential in eliminating the crystalline H2O of hydration and exploring high energy density materials.

Development of p-n Heterostructures Using Phosphorene and SnO2: Its Efficacy toward the Adsorption Study of CO2 and Rose Bengal Dye

Adsorption-mediated methods for environmental pollution control are suitable as they are cost-effective and easy to use. Porous materials can play an important role in adsorption studies. Herein, we synthesized a p-n heterostructure of phosphorene and metal oxide using a simple hydrothermal approach. The synthesized material is porous in nature, with a surface area of 127.44 m2/g and pore volume of about 1.73 nm with appreciable thermal stability. As the material is microporous, we used it for the adsorption of CO2 gas and dye. For CO2 adsorption, we determined the CO2 gas uptake according to the mass balance principle of the ideal gas equation, and it was found to be about 21.478 mol/kg. We have also studied different isotherm models to check the adsorption phenomena. Moreover, for dye adsorption, we have chosen the xanthene-derived rose bengal (RB) dye, which shows a removal percentage of about 92.02%. In the case of dye adsorption, the material shows good reusability and significant adsorption up to five cycles.

Size-matched hydrogen bonded hydroxylammonium frameworks for regulation of energetic materials

Size matching molecular design utilizing host-guest chemistry is a general, promising strategy for seeking new functional materials. With the growing trend of multidisciplinary investigations, taming the metastable high-energy guest moiety in well-matched frameworks is a new pathway leading to innovative energetic materials. Presented is a selective encapsulation in hydrogen-bonded hydroxylammonium frameworks (HHF) by screening different sized nitrogen-rich azoles. The size-match between a sensitive high-energy guest and an HHF not only gives rise to higher energetic performance by dense packing, but also reinforces the layer-by-layer structure which can stabilize the resulting materials towards external mechanic stimuli. Preliminary assessment based on calculated detonation properties and mechanical sensitivity indicates that HHF competed well with the energetic performance and molecular stability (detonation velocity = 9286 m s-1, impact sensitivity = 50 J). This work highlights the size-matched phenomenon of HHF and may serve as an alternative strategy for exploring next generation advanced energetic materials.

Energetic bimetallic complexes as catalysts affect the thermal decomposition of ammonium perchlorate

Two bimetallic complexes of 4-hydroxy-3,5-dinitropyrazole, [K₂Mn(DNPO)₂(H₂O)₄]_n·2H₂O (BMEP-1) and [K₂Zn(DNPO)₂(H₂O)₆]_n (BMEP-2), were synthesized and characterized by IR spectroscopy and elemental analysis. The crystal structures of BMEP-1 and BMEP-2 were determined by single-crystal X-ray diffraction. It is noteworthy that these complexes presented different metal-organic frameworks. The thermal behaviors of BMEP-1 and BMEP-2 were investigated by differential scanning calorimetry and thermogravimetric analysis measurements. These bimetallic complexes exhibited high thermal stability (348.0 °C and 331.0 °C) due to their large coordination bonds and three-dimensional interconnected structure. The catalytic performances of BMEP-1 and BMEP-2 on the thermal decomposition of ammonium perchlorate were investigated by TGA-DSC, TGA-FTIR, and non-isothermal kinetic analyses. The results showed that BMEP-1 and BMEP-2 exhibited excellent catalytic performance in the thermal decomposition of ammonium perchlorate. Notably, there was only a single exothermic peak at 302.6 °C and 318.6 °C, and the activation energy values of ammonium perchlorate decreased to 123.88 kJ mol^-1 and 128.43 kJ mol^-1, respectively. TGA-FTIR results showed that BMEP-1 and BMEP-2, as effective components of catalysis, will promote the production of H₂O, N₂O, NO₂, and HCl in advance, during the thermal decomposition of ammonium perchlorate. BMEP-1 and BMEP-2 are expected to be two candidate additives for the catalytic decomposition of ammonium perchlorate in composite solid propellants.

Construction of Coplanar Bicyclic Backbones for 1,2,4-Triazole-1,2,4-Oxadiazole-Derived Energetic Materials

Combining different nitrogen-rich heterocycles into a molecule can fine-tune its energetic performance and physical properties as well as its safety for use in energetic materials. Here, 1,2,4-oxadiazole was incorporated into 1,2,4-triazole to construct new energetic backbones. 3-(5-Amino-1H-1,2,4-triazol-3-yl)-1,2,4-oxadiazol-5-amine (5) was designed and synthesized. Nitramino-functionalized N-(5-(5-amino-1,2,4-oxadiazol-3-yl)-3H-1,2,4-triazol-3-yl)nitramide (6) and N-(5-(5-(nitramino)-1,2,4-oxadiazol-3-yl)-3H-1,2,4-triazol-3-yl)nitramide (7) were also obtained, and two series of corresponding nitrogen-rich salts were prepared, leading to the creation of new energetic compounds. All derivatives were fully characterized, and five of them were further confirmed by X-ray diffraction. The theoretical calculations, energetic performance, safety, and the main decomposition gaseous products of 1,2,4-triazole-1,2,4-oxadiazole-derived energetic materials were studied. Compound 7 and its dihydroxylammonium salt (7 c) exhibited prominent detonation performance comparable to that of RDX while possessing satisfying thermal stabilities and mechanical sensitivities.

Highly Selective Separation Intermediate-Size Anionic Pollutants from Smaller and Larger Analogs via Thermodynamically and Kinetically Cooperative-Controlled Crystallization

Selective separation of organic species, particularly that of intermediate-size ones from their analogs, remains challenging because of their similar structures and properties. Here, a novel strategy is presented, cooperatively (thermodynamically and kinetically) controlled crystallization for the highly selective separation of intermediate-size anionic pollutants from their analogs in water through one-pot construction of cationic metal-organic frameworks (CMOFs) with higher stabilities and faster crystallization, which are based on the target anions as charge-balancing anions. 4,4'-azo-triazole and Cu2+ are chosen as suitable ligand and metal ion for CMOF construction because they can form stronger intermolecular interaction with p-toluenesulfonate anion (Ts-) compared to its analogs. For this combination, a condition is established, under which the crystallization rate of a Ts--based CMOF is remarkably high while those of analog-based CMOFs are almost zero. As a result, the faster crystallization and higher stability cooperatively endow the cationic framework with a close-to-100% selectivity for Ts- over its analogs in two-component mixtures, and this preference is retained in a practical mixture containing more than seven competing (analogs and inorganic) anions. The nature of the free Ts- anion in the cationic framework also allows the resultant CMOF to be recyclable via anion exchange.

A 2-Fold Interpenetrated Nitrogen-Rich Metal-Organic Framework: Dye Adsorption and CO2 Capture and Conversion

A bifunctional ligand strategy for modification of the functional pores is of great significance in the structural design of metal-organic frameworks (MOFs). Herein, a new 2-fold interpenetrated "pillared-layer" 3D Co-MOF, {[Co(HL)(4,4'-bipy)]·DMF·2H₂O}_n (1), was successfully synthesized by using two kinds of ligands, imidazolecarboxylic acid and pyridine. The metal-carboxylic layers are pillared by the 4,4'-bipy ligand, displaying a 3D framework with rectangular 3D channels (high BET surface of 190.9 m² g^-1 and maximum aperture of 3.9 Å) that are decorated with abundant uncoordinated N and O atoms. 1 shows good water stability and thermal stability (320 °C). The proper pores and active sites endowed 1 with a selective adsorption of Congo red in aqueous solution. In addition, a high CO₂ adsorption capacity and an excellent CO₂ chemical conversion were observed.