Effect of charge distribution on RDX adsorption in IRMOF-10

Thermal Reactivity of High-Density Hybrid Hexahydro-1,3,5-trinitro-1,3,5-triazine Crystals Prepared by a Microfluidic Crystallization Method

In this paper, the two-dimensional (2D) high nitrogen triaminoguanidine-glyoxal polymer (TAGP) has been used to dope hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) crystals using a microfluidic crystallization method. A series of constraint TAGP-doped RDX crystals using a microfluidic mixer (so-called controlled qy-RDX) with higher bulk density and better thermal stability have been obtained as a result of the granulometric gradation. The crystal structure and thermal reactivity properties of qy-RDX are largely affected by the mixing speed of the solvent and antisolvent. In particular, the bulk density of qy-RDX could be slightly changed in the range from 1.78 to 1.85 g cm^-3 as a result of varied mixing states. The obtained qy-RDX crystals have better thermal stability than pristine RDX, showing a higher exothermic peak temperature and an endothermic peak temperature with a higher heat release. E_a for thermal decomposition of controlled qy-RDX is 105.3 kJ mol^-1, which is 20 kJ mol^-1 lower than that of pure RDX. The controlled qy-RDX samples with lower E_a followed the random 2D nucleation and nucleus growth (A2) model, whereas controlled qy-RDX with higher E_a (122.8 and 122.7 kJ mol^-1) following some complex model between A2 and the random chain scission (L2) model.

Judicious design functionalized 3D-COF to enhance CO2 adsorption and separation

The effects of functional groups (including OH, OCH₃ , NH₂ , CH₂ NH₂ , COOH, SO₃ H, OCO(CH₂ )₂ COOH(E-COOH), and (CH₂ )₄ COOH(c-COOH)) in 3D covalent organic frameworks (3D-COFs) on CO₂ adsorption and separation are investigated by grand canonical Monte Carlo (GCMC) simulations and density functional theory calculations. The results indicate that interaction between CO₂ and the framework is the main factor for determining CO₂ uptakes at low pressure, while pore size becomes the decisive factor at high pressure. The binding energy of CO₂ with functionalized linker is correlated to CO₂ uptake at 0.3 bar and 298 K on 3D-COF-1, suggesting functional groups play a key role in CO₂ capture in microporous 3D-COFs. Moreover, CO₂ selectivity over CH₄ , N₂ , and H₂ can be significantly enhanced by functionalization, where CH₂ NH₂ , COOH, SO₃ H, and E-COOH enhance CO₂ adsorption more effectively at 1 bar. Among them, SO₃ H is the most promising functional group in 3D-COFs for CO₂ separation.

Luminescent sensing of nitroaromatics by crystalline porous materials

Designing strategies for the syntheses of targeted luminescent MOFs, nanoparticle/MOF composites and COFs described and their application in sensing nitroaromatic compounds and explosives discussed.

Theoretical Investigation of the Topology of Spiroborate-Linked Ionic Covalent Organic Frameworks (ICOFs)

A novel type of ionic covalent organic framework (ICOF) with a spiroborate linkage has been recently designed and synthesized by Zhang and co-workers (Ionic Covalent Organic Frameworks with Spiroborate Linkage, Angew. Chem. Int. Ed. 2016, 55, 1737-1741). The spiroborate-linked ICOFs exhibit high Brunauer-Emmett-Teller (BET) surface areas and significant amounts of H₂ and CH₄ uptakes, combined with excellent thermal and chemical stabilities. Inspired by the novel properties of ICOFs, with the aim of gaining better understanding of the structure of such spiroborate-linked ICOFs, a series of potential 3D network configurations of ICOFs connected with tetrahedral [BO₄ ]^- nodes were proposed, assuming the [BO₄ ]^- node in spiroborate segments takes a tetrahedral configuration. These ICOFs, in terms of 2D and 3D topology through torsional energy of the [BO₄ ]^- fragment, pore-size distribution, total energy of the framework, and gas adsorption properties were compared and systematically investigated by density functional theory calculations, molecular mechanics, and well-established Grand canonical Monte Carlo simulations. The results indicate that spiroborate-linked ICOFs are likely a mixture of various topologies. Among these architectures, the five-fold interpenetrating model shows the lowest energy and reasonable gas uptakes, therefore, it is considered to be the most possible structure. More importantly, the five-fold interpenetrating model, showing high CH₄ uptakes compared with several classic porous materials, represents a promising CH₄ storage material.

Luminescent metal–organic frameworks as explosive sensors

A perspective summarizing the recent advancement in explosive sensing by luminescent metal organic framework (LMOF) materials.

Luminescent metal–organic frameworks for chemical sensing and explosive detection

This review provides an update on the photoluminescence properties of LMOFs and their utility in chemical sensing and explosive detection.

Molecular simulations of adsorption of RDX and TATP on IRMOF-1(Be)

The influence of different sorption sites of isoreticular metal-organic frameworks (IRMOFs) on interactions with explosive molecules is investigated. Different connector effects are taken into account by choosing IRMOF-1(Be) (IRMOF-1 with Zn replaced by Be), and two high explosive molecules: 1,3,5-trinitro-s-triazine (RDX) and triacetone triperoxide (TATP). The key interaction features (structural, electronic and energetic) of selected contaminants were analyzed by means of density functional calculations. The interaction of RDX and TATP with different IRMOF-1(Be) fragments is studied. The results show that physisorption is favored and occurs due to hydrogen bonding, which involves the C-H groups of both molecules and the carbonyl oxygen atoms of IRMOF-1(Be). Additional stabilization of RDX and TATP arises from weak electrostatic interactions. Interaction with IRMOF-1(Be) fragments leads to polarization of the target molecules. Of the molecular configurations we have studied, the Be-O-C cluster connected with six benzene linkers (1,4-benzenedicarboxylate, BDC), possesses the highest binding energy for the studied explosives (-16.4 kcal mol(-1) for RDX and -12.9 kcal mol(-1) for TATP). The main difference was discovered to be in the preferable adsorption site for adsorbates (RDX above the small and TATP placed above the big cage). Based on these results, IRMOF-1 can be suggested as an effective material for storage and also for separation of similar explosives. Hydration destabilizes most of the studied adsorption systems by 1-3 kcal mol(-1) but it leads to the same trend in the binding strength as found for the non-hydrated complexes.

Applications of a general random-walk theory for confined diffusion

A general random walk theory for diffusion in the presence of nanoscale confinement is developed and applied. The random-walk theory contains two parameters describing confinement: a cage size and a cage-to-cage hopping probability. The theory captures the correct nonlinear dependence of the mean square displacement (MSD) on observation time for intermediate times. Because of its simplicity, the theory also requires modest computational requirements and is thus able to simulate systems with very low diffusivities for sufficiently long time to reach the infinite-time-limit regime where the Einstein relation can be used to extract the self-diffusivity. The theory is applied to three practical cases in which the degree of order in confinement varies. The three systems include diffusion of (i) polyatomic molecules in metal organic frameworks, (ii) water in proton exchange membranes, and (iii) liquid and glassy iron. For all three cases, the comparison between theory and the results of molecular dynamics (MD) simulations indicates that the theory can describe the observed diffusion behavior with a small fraction of the computational expense. The confined-random-walk theory fit to the MSDs of very short MD simulations is capable of accurately reproducing the MSDs of much longer MD simulations. Furthermore, the values of the parameter for cage size correspond to the physical dimensions of the systems and the cage-to-cage hopping probability corresponds to the activation barrier for diffusion, indicating that the two parameters in the theory are not simply fitted values but correspond to real properties of the physical system.