Explosive Molecules Research Articles

Study of graphite optode for characterization of solid heterocyclic nitrogen-rich imidazole, 1, 2, 4-triazole, tetrazole molecules using visible –NIR laser based time domain photoacoustic spectroscopy

The paper reports the role of graphite as an optode for recording of time domain photoacoustic (PA) spectra of some new solid heterocyclic groups nitrogen-rich imidazole, 1,2,4-triazole and tetrazole molecules using 532 nm and 1064 nm wavelengths. The fundamental and second harmonic of 30 ps pulse duration are obtained from Q-switched Nd: YAG laser at 10 Hz repetition rate. The used solid HEMs have very weak absorption in the visible and NIR region. Therefore, these compounds are physically mixed with graphite powder in equal proportion for enhancing the PA signal. The optode works as a receptor of incident visible-NIR radiation and releases thermal signal which is communicated to reporter explosive molecules in terms of phonon waves and helps to generate acoustic signature. The study also carried out to understand the behavior of acoustic waves with respect to data acquisition time and incident laser energy. These compounds have different non-radiative decay times and quality factors “Q” of PA cavity, which reveals the change in the structure and conjugate bonds of the molecules in the graphite matrix. The finding is also supported by the Raman spectra due to direct coupling of phonon wave’s momentum between graphite and HEMs in terms of shift in the G and D bands of graphite.

Adsorption behavior of explosive molecules on g-C[formula omitted]N[formula omitted] nanostructure: A novel approach for sensing energetic materials

Inspired by the latest achievements of two-dimensional (2D) materials as gas sensors, we have performed ab-initio calculations to simulate the interactions between the explosive molecules (RDX, TEX, FOX-7 and TATB) and g-C3N4 surfaces in order to exploit the potential applicability of g-C3N4 as explosive sensor. The adsorption energies and measured distances of g-C3N4/explosive configurations indicate that the TATB molecule interacts strongly with g-C3N4 and produces more number of extra peaks within the Fermi level region. The calculated sensitivity (S) test also demonstrates the superior sensitivity of g-C3N4 towards TATB molecule. Keeping other semiconducting materials like graphene and boron nitride in perspective, our calculations show higher binding energies when explosive molecules are adsorbed on g-C3N4 with appropriate charge transfer, representing better sensitivity for the latter. An increased work function is obtained when planar TATB and FOX-7 molecules are placed on the g-C3N4 surface. Further, the sensitivity of g-C3N4 for these explosive molecules is interpreted in terms of electronic and optical properties, where the density of states and absorption spectra show marked variations when explosive molecules are adsorbed on g-C3N4 surface. The significant overlap between the interacting atoms of adsorbate and adsorbent in PDOS spectra represents the formation of chemical bonds at the interface region. Our calculations demonstrate the adsorption and reactivity processes that occur at the interface region, being useful to develop and design devices with extreme sensitivity for explosive detection.

Smartdust 3D-Printed Graphene-Based Al/Ga Robots for Photocatalytic Degradation of Explosives.

Milli/micro/nanorobots are considered smart devices able to convert energy taken from different sources into mechanical movement and accomplish the appointed tasks. Future advances and realization of these tiny devices are mostly limited by the narrow window of material choices, the fuel requirement, multistep surface functionalization, rational structural design, and propulsion ability in complex environments. All these aspects call for intensive improvements that may speed up the real application of such miniaturized robots. 3D-printed graphene-based smartdust robots provided with a magnetic response and filled with aluminum/gallium molten alloy (Al/Ga) for autonomous motion are presented. These robots can swim by reacting with the surrounding environment without adding any fuel. Because their outer surface is coated with a hydrogel/photocatalyst (chitosan/carbon nitride, C3 N4 ) layer, these robots are used for the photocatalytic degradation of the picric acid as an explosive model molecule under visible light. The results show a fast and efficient degradation of picric acid that is attributed to a synergistic effect between the adsorption capability of the chitosan and the photocatalytic activity of C3 N4 particles. This work provides added insight into the large-scale fabrication, easy functionalization, and propulsion of tiny robots for environmental applications.

Prospects of black phosphorus nanoribbon for explosive sensing: A computational approach

We have explored the possibility of using a low-dimensional black phosphorus-based nanoscale device for the detection of nitroaromatic-based explosives. In this work, we have investigated the structural, electronic, adsorption, and quantum transport properties of phosphorene nanoribbon (APNR) in the presence of different nitroaromatic compounds (NACs) using the state-of-the-art first-principle density functional theory (DFT) calculations. Our results reveal that the explosive molecules are interacting with the APNR surface, which neither affects the structure of the explosive molecule nor the APNR surface. However, it changes the electronic energy-gap due to the charge transfer between the APNR and explosive molecule. Furthermore, we have examined the transmission function and the current-voltage (I-V) characteristic curves for the APNR + explosive systems with the APNR device as a reference employing the non-equilibrium Green’s function (NEGFs) combined with DFT approach. The different current-voltage characteristics (compared to pristine APNR device) of the system in the presence of explosive molecules indicate that such APNR based device can be very much sensitive and selective towards certain explosive molecules. Hence, our study demonstrates that APNR material may be an attractive nanodevice for the detection of explosives.

On the Possibility of Obtaining Nitrogen-Free Detonation Nanodiamonds: Effect of Covalently Bound Nitrogen in Explosive Molecules on the Yield of Nanodiamonds

The possibility of obtaining nitrogen-free detonation nanodiamonds from industrial-produced explosives is studied, and the low probability of their production is demonstrated. The dependence of the yield of detonation nanodiamonds on the content of covalently bound nitrogen (C–N) in the molecules of explosives is found, and the optimal range of the nitrogen content (23–28 wt %) is determined.

Colorimetric screening of nitramine explosives by molecularly imprinted photonic crystal array

Colorimetric, selective and sensitive screening of explosives is important not only to military action but also to public security. Normal explosives detection is mainly targeted for nitroaromatic compounds, however, ntiramine explosive is used more widely due to its outstanding performance. Herein, molecularly imprinted photonic crystal (MIPC) sensors were made to detect typical nitramine explosives: 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), cyclotetramethylenete-tranitramine (HMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20). And 2,4,6-trinitrotoluene (TNT) templated MIPC was also made to discriminate not only nitramines but also nitrobenzene explosives. With explosives concentration increase, the diffraction peak and structure color of MIPC sensors both red shifted within 5 min. By adding alkaline solution, the MIPC sensors were softened, and the mass transfer and the sensitivity were improved. The MIPC sensors could respond to lower than 0.05 mM explosives with the limit of detection of 0.01 mM. A MIPC sensor array with the above MIPCs was constructed to achieve a semi-quantitative detection, and Pattern Recognition with a 48 × 4 multivariate data matrix was using to discriminate different explosive molecules. According to principal component analysis, the response of RDX, HMX, CL-20 and TNT scattered in separate areas, and the sensor array could discriminate with a LOD of 1 mM.

Tfbar Sensors for Detection of Explosives Substances

Tfbar Sensors for Detection of Explosives Substances

Leveraging Preconcentration and Partial Separations with Silicon Nanowire Arrays to Improve the Detection of Low Volatility Trace Explosive Vapors

Trace detection of explosive vapors in real world environments is hindered by strict sensitivity and selectivity requirements that need to be met in order for these techniques to be effective. The physical properties of most explosive molecules limit environmentally relevant vapor concentrations to the part per billion (ppbv) – part per trillion (pptv) range due to their saturated vapor pressures under real world conditions. Additionally, trace explosive vapor detectors must be able to discriminate against a number of potential chemical and biological interferents present in complex real world environments. In this work, we present silicon nanowire arrays (SiNW) as a novel tunable material aimed at providing trace explosive vapor detectors with the sensitivity and selectivity necessary for operational use.Dense, highly ordered silicon nanowires are fabricated through a nanosphere lithography process and topped with a porous gold electrode resulting in a high surface area adsorptive substrate intrinsically capable of rapid, precise temperature control via Joule heating. Explosive vapors are selectively preconcentrated onto the SiNW array by exploiting their affinities for the SiO2 surface of the nanowires. Chromatographic like partial separations of preconcentrated material on the array can be achieved through careful selection of desorption parameters. Using a multichannel detector such as an IMS or MS we demonstrate the preconcentration of a number of explosive vapors including 2,6-DNT, TNT, and RDX above and below their saturated vapor concentrations at room temperature, in addition to exploring the effects of desorption flow rates and temperatures on the partial separation of 2,6-DNT, 2,4-DNT, and TNT vapors. Figure 1

Synthesis of Erythritol Tetranitrate Derivatives: Functional Group Tuning of Explosive Sensitivity.

Understanding the factors that affect explosive sensitivity is paramount to the safe handling and development of new explosives molecules. Erythritol tetranitrate (ETN) is an explosive that recently has attracted significant attention in the explosives community because of its ease of synthesis and physical properties. Herein, we report the synthesis of ETN derivatives using azide, nitramine, and nitrate ester functional groups. Impact, spark, and friction sensitivity measurements, computationally calculated explosive properties, and the crystal structure analysis of the ETN derivatives are reported. Mixing explosive functional groups led to changes in the explosive sensitivity, explosive performance as well as physical properties including melting point and physical state at room temperature. Overall, we have demonstrated that combining functional groups can enable the tuning of explosive and physical properties of a molecule. This tunability can potentially aid in the development of new explosives in which characteristics are varied to meet certain specifications.

Gold-nanoparticle- and nanostar-loaded paper-based SERS substrates for sensing nanogram-level Picric acid with a portable Raman spectrometer

Nanoparticle (NP)-loaded filter paper (FP)-based surface-enhanced Raman scattering (SERS) substrates have been prepared using differently shaped gold (Au) NPs. The shape of Au NPs plays a significant role in the amplification of SERS signal. Here, two differently shaped Au NPs were synthesized using two different techniques: (a) femtosecond (fs) laser ablation in liquid and (b) chemical method. Spherical shaped Au NPs were obtained using fs ablation of a bulk Au target in distilled water and Au nanostars (NSs) were achieved through chemical process utilizing N-vinyl-2-pyrrolidone as a reducing/capping agent. The size and shapes of these synthesized NPs and NSs were investigated meticulously using different characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy and X-ray diffraction. Both the NPs and NSs were subsequently loaded onto commercially available FP by simple drop casting method. To achieve higher number of hot spots, the aggregated spherical NPs were obtained by addition of NaCl. The non-aggregated spherical, aggregated spherical, and star Au NPs loaded on FP were used for the detection of a dye (Nile blue) and an explosive molecule (Picric acid).

A bioinspired peptide matrix for the detection of 2,4,6-trinitrotoluene (TNT)

A novel peptide-based three-dimensional probe called “peptide matrix,” inspired by the antibody paratope region, was fabricated on a surface plasmon resonance (SPR) sensor chip to enhance the sensitivity of detecting the explosive 2,4,6-trinitrotoluene (TNT). Although peptide aptamer is an attractive candidate for a molecular recognition probe because of its ease of synthesis and chemical stability, it still has difficulty in applying to highly sensitive (i.e. parts-per-billion (ppb) or sub-ppb level) detections. Thus, we developed the concept of peptide matrix structure, which is constructed by consecutive disulfide bond formation between a large number of peptide fragments. This robust three-dimensional structure displays multiple binding sites which can efficiently associate with each TNT molecule. The peptide matrix lowered the dissociation constant (KD) by two orders of magnitude compared to the linear peptide aptamer, estimating KD as 10.1 nM, which is the lowest concentration reported by using peptide-based TNT probe. Furthermore, the concentration limit of detection of peptide matrix modified SPR sensor was 0.62 ppb, and hence comparable to single-chain variable fragment (scFv)-based TNT sensors. To our knowledge, this is the first report demonstrating peptide matrix fabrication and its application for small explosive molecule detection. This peptide matrix-based approach, which has the advantage of simple synthesis and high sensitivity, will be applicable to many other small-molecule label-free detections.

A relationship between membrane permeation and partitioning of nitroaromatic explosives and their functional groups. A computational study.

Nitroaromatic explosives, such as 2,4,6-trinitrotoluene, are representative aromatic compounds, which are generally highly toxic. For their toxic mechanisms, little is known about their interaction with cell membranes, although this is essential for their absorption, distribution, metabolism, excretion and toxicity profiling. Here, we investigated the membrane permeation and partitioning of 12 nitroaromatic explosives with typical functional groups (e.g., -NO2, -NH2, -OCH3 and -OH) by all-atom molecular dynamics simulations. Based on free-energy curves, we obtained three key parameters that describe the behavior of permeation and partitioning, namely liposome-water partition coefficient (KLW), permeability coefficient (P) and translocation time (τ). Functional groups contribute little to KLW, indicating that the membrane absorption of nitroaromatic explosives is primarily controlled by the hydrophobic effect of the benzene ring. P shows an obvious decline with increasing polar group number (Np), and therefore τ exhibits a continuous increase. In addition, the preferred location (zmin) of explosive molecules in membranes is closer to the head group of lipids when they have more polar groups. Further analysis shows that the hydrogen bond (H-bond) interaction of explosives with water and lipids plays a crucial role in the dependence of permeation and partitioning on polar groups. The molecules with larger Np can form more H-bonds with water in the aqueous phase, which limits their motion into the deeper hydrophobic region of membranes. Moreover, the desolvation/loss of H-bonds leave zmin controls the membrane permeation properties, which is also correlated with Np. The work reveals the physical essence of the relationship between the membrane permeation and partitioning of nitroaromatic explosives and their functional groups. These results may be also applicable to other (e.g., polycyclic) nitroaromatic compounds.

Degradation of High Energy Materials Using Biological Reduction: A Rational Way to Reach Bioremediation.

Explosives molecules have been widely used since World War II, leading to considerable contamination of soil and groundwater. Recently, bioremediation has emerged as an environmentally friendly approach to solve such contamination issues. However, the 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) explosive, which has very low solubility in water, does not provide satisfying results with this approach. In this study, we used a rational design strategy for improving the specificity of the nitroreductase from E. Cloacae (PDB ID 5J8G) toward HMX. We used the Coupled Moves algorithm from Rosetta to redesign the active site around HMX. Molecular Dynamics (MD) simulations and affinity calculations allowed us to study the newly designed protein. Five mutations were performed. The designed nitroreductase has a better fit with HMX. We observed more H-bonds, which productively stabilized the HMX molecule for the mutant than for the wild type enzyme. Thus, HMX’s nitro groups are close enough to the reductive cofactor to enable a hydride transfer. Also, the HMX affinity for the designed enzyme is better than for the wild type. These results are encouraging. However, the total reduction reaction implies numerous HMX derivatives, and each of them has to be tested to check how far the reaction can’ go.

Reaction Mechanism of Embedding Oxidizing Small Molecules in Energetic Materials to Improve the Energy by Reactive Molecular Dynamics Simulations

Novel host–guest/multicomponent energetic materials can be obtained by embedding hydrogen- or nitrogen-containing oxidizing small molecules between the molecules of high-energy explosives, which can improve their explosive energy. To better understand the mechanism of oxidizing small molecules in the reaction and improve the energy, ReaxFF-lg reactive molecular dynamics simulations were performed to investigate the thermal decomposition reaction at different temperatures of the CL-20/H2O2 solvate formed by embedding H2O2 in the cavity of CL-20. We propose an analytical method to investigate the mechanism of H2O2 in the CL-20 reaction by tracing the interactions between the H and O atoms of H2O2 and the C, H, N, and O atoms of CL-20. During thermal decomposition of CL-20/H2O2, CL-20 and H2O2 first separately decompose, and then, the decomposition products react. The H atoms, O atoms, and hydroxyl (HO) groups generated by H2O2 decomposition connect with the O atoms of nitro groups, leading to N–O bond cleav...

Sensors Using the Molecular Dynamics of Explosives in Carbon Nanotubes Under External Uniform Electric Fields.

Possessing a simulated sensor device to identify explosives is of extreme interest to the area of public security to fight against terrorism. In light of this, a carbon armchair nanotube was modeled under the action of an external, longitudinal and uniform electric field at an initial temperature of 1 mK simulation, causing the explosive molecules under analysis to rotate through the carbon nanotube, due to an evanescent effect generated from the action of an electric current and magnetic field induced in this system, and thus behaving as a selective temperature sensor and spinning radius for the molecules. For this, molecular dynamics was used to study the physicochemical properties of the molecules' interactions with a carbon nanotube. The following physical properties, as well as the kinetic, potential, and total energy were calculated for the 2,4,6-trinitrotoluene (TNT), triacetone triperoxide (TATP), hexogen (RDX), hexamethylene triperoxide diamine (HMTD), octogen (HMX) and pentaerythritol tetranitrate (PETN) explosives: thermodynamic conditions such as temperature; entropy variation; and distance between the molecules' center of mass from an armchair type carbon nanotube.

Gas Releasing Mechanism of LLM‐105 Using Two‐Dimensional Correlation Infrared Spectroscopy

AbstractIn this paper, a sealed in‐situ reaction system and infrared spectroscopy (IR) were used to study the gas releasing mechanism of 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) at different temperatures. Three characteristic stages of LLM‐105 during the heating process to 400 °C were detected by the moving‐window two‐dimensional correlation spectroscopy (MW2D). Two‐dimensional correlation infrared spectroscopy (2DCOS) was employed to examine changes of gas concentration in the sealed system at each stage. We found that in the first stage, LLM‐105 first released H2O and NH3. In the second stage, the decomposition is intensified, the explosive molecule first undergoes the decomposition reaction of releasing H2O, and CO2, subsequently chemical reaction producing several nitrogen gases, such as NO, N2O, HCN, NO2 and NH3. In the third stage, the decomposition process mainly releases CO2 and NH3, and the concentrations of HCN and NO2 decreased gradually. 2DCOS proven to be a very sensitive method for detecting thermal decomposition mechanisms and monitoring gas changes in sealed system.

Optofluidic laser explosive sensor with ultralow detection limit and large dynamic range using donor-acceptor-donor organic dye

Due to the significance of explosive detection for homeland security and environmental protection, the research of new materials and new methodologies for sensing electron-deficient explosive nitryl aromatics is urgently imperative. In this paper we demonstrate an optofluidic laser sensor for explosive detection by using a highly electron-rich dye (dye-1) with donor-acceptor-donor conjugated structure. The design and facile synthesis process of dye-1 are described. Theoretical calculations, UV–vis absorption and fluorescence spectra are investigated to understand the structure-property relations. Exceptionally high quantum yield of emission in solution is achieved. As a proof of concept, electron-deficient explosive molecule 2, 4-dinitrotoluene (DNT) is used as a model analyte to evaluate the performance of the optofluidic laser sensor. Experimental results indicate that the optofluidic dye laser sensor achieves a large dynamic range with 4 orders of magnitude and an ultralow limit of detection (10 nM), much better than fluorescent sensor. This work provides a route to expand the applications of optofluidic laser for sensitive biochemical detection through specific luminescent materials.

Trace Detection of Explosives Using Metal Oxide Catalysts

There is a growing need for a continuous monitoring system that can detect explosives at trace levels in the vapor phase. Triacetone triperoxide (TATP) is a common explosive used by terrorists in improvised explosive devices (IED’s) that still goes largely undetected in many densely-populated venues. No electronic trace detection system currently exists, which is capable of continuously monitoring TATP or its precursors. However, we have demonstrated that a thermodynamic sensor employing low mass microheaters and metal oxide catalysts can detect TATP and 2, 4-DNT at the ppb level. The improved selectivity and sensitivity of these low-mass sensors enabled us to investigate the mechanism and pathway responsible for the detection of explosives. We now believe that the sensor response relies on specific oxidation-reduction reactions taking place on the surface of the metal oxide catalyst. These surface reactions are specific to the explosive molecule of interest, catalyst (metal oxide), and the oxidation states of the catalyst. Experiments employing SnO, Cu2O, and ZnO as catalysts were performed to establish a mechanism responsible for the detection of various explosives at trace levels using our thermodynamic sensor. The responses of our trace detection system to TATP and 2, 4-DNT at trace levels will be presented as well as the proposed detection mechanism.

Surface‐enhanced Raman scattering studies of gold‐coated ripple‐like nanostructures on iron substrate achieved by femtosecond laser irradiation in water

AbstractDuring the past several years, numerous efforts have been accomplished on designing efficient surface‐enhanced Raman scattering (SERS) substrates with high sensitivity, good reproducibility, and recyclable nature. However, it still remains a significant challenge to realize all these qualities in a single substrate. We have fabricated ripple‐like nanostructures (NSs) on Iron (Fe) substrate using femtosecond (fs) laser irradiation of Fe target in distilled water. These ripple‐like structures had periodicities in the range of ~90–190 nm, which was confirmed from the analysis of field emission scanning electron microscope (FESEM) data. We subsequently deposited a thin layer of gold on these ripple‐like Fe NSs using thermal evaporation. Later, these coated NSs were effectively utilized as SERS substrates for methylene blue (MB) detection and were found to be sensitive evident from the data obtained at a very low concentration of 500pM. Furthermore, we observed that the SERS signal variations on the substrate were <11.2% indicating the reproducible nature of these substrates. Additionally, we demonstrate that these substrates can be reused (we establish this for three times consecutively) by detecting malachite green (MG) and an explosive molecule (picric acid, PA) followed by the mixture compound (Rhodamine 6G+MB) through employment of simple cleaning procedures. The detected molecular concentrations in terms of masses were found to be 3.2 pg, 36.5 pg, and 23 ng for MB (for a concentration of 500pM), MG (for a concentration of 5nM), and PA (for a concentration of 5μM), respectively. Furthermore, these Fe NSs exhibited superior batch‐to‐batch reproducibility with a relative standard deviation (RSD) value of ~l4%. The proposed method of fabricating ripple structures as SERS platforms are highly feasible, reliable, and have great potential for on‐site detection of several analyte molecules with an easily transportable Raman spectrometer.

Standoff discrimination and trace detection of explosive molecules using femtosecond filament induced breakdown spectroscopy combined with silver nanoparticles

The potential of femtosecond filament induced breakdown spectroscopy technique (fs FIBS) towards the detection of explosive/energetic molecules (EMs) at a standoff (ST) distance of ∼6.5 m is demonstrated. A set of six energetic nitroimidazoles were investigated and discriminated with the fs FIBS technique in tandem with principal component analysis (PCA). The fs ST-FIBS spectra of these EMs were dominated with CN emissions with weak C2 emission and devoid of other atomic peaks (H, N, and O). In addition, an enhancement in LIBS/ST FIBS signal of EMs is achieved in the presence of Ag nanoparticles (NPs) using the nanoparticle enhanced LIBS (NELIBS) technique. Furthermore, the potential of fs filaments for detecting explosive traces is also demonstrated by detecting the residue of an explosive molecule CL-20 on a brass target using the fs NEFIBS technique.