Explosive Molecules Research Articles

Surface enhanced Raman scattering-based sensing and ultrafast nonlinear optical properties of silver-hexagonal boron nitride nanocomposites achieved by femtosecond laser ablation

This study investigated the surface-enhanced Raman spectroscopy (SERS) properties and nonlinear optical (NLO) behavior of silver nanoparticles (Ag NPs) decorated hexagonal boron nitride (hBN) nanocomposites. Although Ag NPs are known for their excellent plasmonic properties, their susceptibility to oxidation in ambient conditions significantly reduces SERS activity. To overcome this, a femtosecond laser-assisted single-step novel approach is developed for synthesizing hybrid Ag-hBN nanocomposites via ablating Ag target in a solution of exfoliated hBN nanosheets, forming uniformly embedded Ag NPs on hBN nanosheets. The morphological characteristics and elemental compositions were validated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). TEM analysis revealed that Ag NPs averaged 15 nm in size, while hBN nanosheets had lateral dimensions of approximately 250 nm. The SERS activity of the prepared nanocomposites was investigated using dye and explosive molecules, achieving detection sensitivities of 1 μM and 100 μM, respectively, with high reproducibility. These detection sensitivities are significant as they demonstrate the potential of the Ag-hBN nanocomposites for sensitive and reliable detection of trace amounts of analytes. Notably, the Ag-hBN nanocomposites showed enhanced SERS activity compared to pure Ag NPs, with a 2.5-fold improvement for Nile blue, 3.6-fold for methylene blue, and 2.4-fold for RDX. The current study also demonstrates that hBN prevents Ag NPs’ oxidation and preserves the SERS functionality even at elevated temperatures. Furthermore, the NLO properties of the nanocomposites were investigated using the standard Z-scan technique, revealing two-photon and three-photon absorption coefficients of 3 × 10−4 cm/GW and 6.5 × 10−5 cm3/GW2, respectively. The findings highlight the potential of Ag-hBN nanocomposites to enhance SERS and NLO devices, enabling future applications in sensing and photonics.

Influence of Carbon-Nitride Dot-Emitting Species and Evolution on Fluorescence-Based Sensing and Differentiation.

Carbon dots have attracted widespread interest for sensing applications based on their low cost, ease of synthesis, and robust optical properties. We investigate structure-function evolution on multiemitter fluorescence patterns for model carbon-nitride dots (CNDs) and their implications on trace-level sensing. Hydrothermally synthesized CNDs with different reaction times were used to determine how specific functionalities and their corresponding fluorescence signatures respond upon the addition of trace-level analytes. Archetype explosives molecules were chosen as a testbed due to similarities in substituent groups or inductive properties (i.e., electron withdrawing), and solution-based assays were performed using ratiometric fluorescence excitation-emission mapping (EEM). Analyte-specific quenching and enhancement responses were observed in EEM landscapes that varied with the CND reaction time. We then used self-organizing map models to examine EEM feature clustering with specific analytes. The results reveal that interactions between carbon-nitride frameworks and molecular-like species dictate response characteristics that may be harnessed to tailor sensor development for specific applications.

Simple synthesis of monocyclic pyrimidine-based energetic molecule with “amino–nitro–hydrazino” arrangement

With the constant development of energetic materials, numerous explosive molecules have been synthesized, some of which feature competitive performances. However, energetic materials are directly oriented to application requirements. Therefore, more emphasis is gradually placed on route simplification and cost reduction while designing novel energetic molecules. In this work, monocyclic energetic compound 2,4-diamino-6-hydrazineyl-5-nitropyrimidine (3) was successfully obtained. This compound exhibits an alternating “amino–nitro–hydrazino” arrangement, featuring strong intramolecular hydrogen-bonding interaction. With cheap raw material, the whole reaction comprised only two steps, and exhibited simple post processing, only filtration. This novel energetic molecule possesses excellent mechanical security (IS > 40 J, FS > 360 N), acceptable thermal stability (Td = 225°C), and good detonation parameters (Dv = 8470 m·s‒1, P = 24.9 GPa), indicating that compound 3 may act as a candidate of insensitive explosives.

Spin Polarized Chemiresistive CNT Sensors for Selective Detection of Explosive Molecules

Spin Polarized Chemiresistive CNT Sensors for Selective Detection of Explosive Molecules

Highly emissive pyrrolo[1,2-a]quinoxaline based narrow band fluorescent sensors for detection of nitroaromatics and their application in spot paper test

In the modern day, explosive detection is essential to public safety, and fluorescent small molecules have gained popularity for their quick and accurate detection. Herein, we present the design and synthesis of a series of pyrrolo[1,2-a]quinoxaline-based conjugated small organic fluorophores (PQ-Ph-OH, PQ-Ph-NMe, PQ-Ph-OMe, PQ-Ph-Me, and PQ-Ph-CN) as fluorescence-based sensors for explosive molecules. The sensor molecules were synthesized in good to excellent yields using a dehomologative functionalization strategy. They exhibited excellent photophysical characteristics, which was tunable based on the substituent on the phenyl linker at position 3. DFT studies showed that the pyrroloquinoxaline moiety could act as an on-demand electron donor or acceptor, depending on the phenyl substituent. The molecules also exhibited solid state emission due to twisted geometry around the CC single bond between the heterocyclic scaffold and the phenyl derivative. This resulted in low band intense emission for the synthesized molecules. In the presence of electron-deficient nitroaromatic explosives, all the fluorophores showed excellent fluorescence quenching. Detection limits in the range of 10−4 M were obtained for all the fluorophores. Stern-Volmer plots show high values of binding constants, indicating good interaction between the fluorophores and the explosive molecules. The mechanism of sensing was confirmed by UV-PL spectral overlap and fluorescence lifetime measurements, which suggest a static quenching based on the formation of a ground state complex. Owing to solid state emissions in some of the derivatives, the synthesized molecules were applied to paper strips for spot detection of explosive molecules.

Standoff Deep Ultraviolet Raman Spectrometer for Trace Detection.

We developed a state-of-the-art, high-sensitivity, low-stray-light standoff deep-ultraviolet (DUV) Raman spectrometer for the trace detection of resonance Raman-enhanced chemical species. As an excitation source for Raman measurements, we utilized our recently developed, second-generation, miniaturized, diode-pumped, solid-state neodymium-doped gadolinium orthovanadate (Nd:GdVO4) laser that generates quasi-continuous wave 228 nm light. This 228 nm excitation enhances the Raman intensities of vibrations of NOx groups in explosive molecules, aromatic groups in biological molecules, and various aromatic hydrocarbons. Our DUV Raman spectrograph utilizes a custom DUV f/8 Cassegrain telescope with an ∼200 mm diameter primary mirror, high-efficiency DUV transmission gratings, custom DUV mirrors, and a custom 228 nm Rayleigh rejection filter. We utilized our new standoff DUV Raman spectrometer to measure high signal-to-noise ratio spectra of ∼50 μg/cm2 drop-cast explosives: ammonium nitrate (AN), trinitrotoluene, pentaerythritol tetranitrate as well as aromatic biological molecules: lysozyme, tryptophan, tyrosine, deoxycytidine monophosphate, deoxyadenosine monophosphate at an ∼3 m distance within 10-30 s accumulation times. We roughly estimate the average ultraviolet resonance Raman (UVRR) detection limits for the relatively homogeneous drop-cast films of explosives and biological molecules to be ∼1 μg/cm2 when utilizing a continuous raster scanning that averages Raman signal over ∼1 cm2 sample area to avoid quick analyte depletion due to ultraviolet (UV) photolysis. We determined 3 m standoff UVRR detection limits for drop-cast AN films and identified factors impacting UVRR detection limits such as analyte photochemistry and analyte morphology. We found a detection limit of ∼0.5 μg/cm2 for drop-cast AN films on glass substrates when the Raman signal is averaged over ∼0.5 cm2 of sample surface using a continuous raster scan. For a step raster scan, when the probed sample area is limited to the laser spot size, the detection limit is approximately tenfold higher (∼5 μg/cm2) due to the impact of UV photochemistry.

The {Cu2I2} cluster bearing metal organic frameworks: crystal structures and fluorescence detecting performances towards cysteine and explosive molecules.

Two {Cu2I2} cluster-bearing metal organic frameworks (MOFs) of {[Eu(CuI)2(INA)3DMF]·0.95DMF}n (Eu-CuI-INA) and {K[(CH3)2NH2]Sr4(INA)2(DMF)2{(Cu2I2)2(INA)8}·2H2O}n (Sr-K-CuI-INA, HINA = isonicotinic acid, DMF = N,N-dimethyl formamide) were prepared and characterized in this work. Both materials feature a three-dimensional (3-D) structure, in which the {Cu2I2} clusters and Eu3+ (or Sr2+) metal ions are coordinated by INA- ligands with pyridine and carboxylic groups, respectively. Impressively, Sr-K-CuI-INA exhibits sensitive fluorescence sensing behaviors towards cysteine and nitro-bearing molecules, demonstrating potential FL sensing applications for bio and explosive molecules. This work would provide a good reference for designing fluorescent MOF probes containing CuI molecules.

Robust nanotube-based nanosensor designed for the detection of explosive molecules.

The adequate determination and detection of explosive molecules is key to introducing improvements in areas related to safety, whose progress depends on an adequate and rapid determination of dangerous substances. To detect explosives down to the molecular level and accurately discriminate between different but somehow similar substances, it is necessary to design sensors that can differentiate them uniquely and efficiently. In this study, we present a new generation nanoscale sensor based on carbon nanotubes with an adapted nanopore shape that is capable of effectively discriminating between five types of explosive compounds (TATP, RDX, PENT, HMX and DNT). We show that the interaction of each compound with the walls of the nanotubes induces changes in transmission and current that allows clear differentiation of each type of molecule. Interestingly, the transport properties do not depend on the orientation of the molecules within the nanopore in most cases, making it a robust device with high reproducibility and stability. The results also show that these systems can lead to relatively high thermoelectric performances and, furthermore, the Seebeck coefficient can be used to discriminate between them.

A Soluble Porous Coordination Polymer for Fluorescence Sensing of Explosives and Toxic Anions under Homogeneous Environment.

In the past decades, porous coordination polymers (PCPs) based fluorescent (FL) sensors have received intense attention due to their promising applications. In this work, a soluble Zn-PCP is presented as a sensitive probe towards explosive molecules, chromate, and dichromate ions. In former reports, PCP sensors were usually ground into fine powders and then dispersed in solvents to form FL emulsion for sensing applications. However, their insoluble characters would cause the sensing accuracy which is prone to interference from environmental effects. While in this work, the as-made PCP could be directly soluble in organic solvents to form a clear solution with bright blue emission, representing the first soluble PCP based fluorescence sensor to probe explosive molecules under a homogeneous environment. Moreover, the FL PCP solution also shows sensitive detection behaviors towards the toxic anions of CrO42- and Cr2O72-, which exhibit a good linear relationship between the fluorescence intensity of Zn-PCP and the concentrations of both analytes. This work provides a reference for designing task-specific PCP sensors utilized under a homogeneous environment.

Solubility prediction and intermolecular interaction energies of four explosives in the studied solvents at different temperatures

ABSTRACT Solubility prediction and intermolecular interaction of four explosives (1,3,5-Trinitroperhydro-1,3,5-triazine,ε‑2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaiso-wurtzitane, 3-Nitro-1,2,4-triazolin-5-one，3,4-dinitro-1 H-pyrazole) are researched by the Conductor-like Screening Model – Realistic solvents (COSMO-RS). The results show that the study of σ-surface and σ-profile can qualitatively analyze the potential mechanism of the dissolution behavior of four explosives in the studied solvents. COSMO-RS can accurately predict the solubility of four explosives in the studied solvents, but some of the predicted solubility is different from the experimental solubility, and the deviation between the predicted solubility and the experimental solubility was analyzed. The molecular interaction energy between explosive molecules and solvent partially reveals the internal mechanism of the dissolution of explosives, however, the solvation of the four explosives is a complex process that requires the synthesis of various molecular interactions. This has a great effect on the study of solvation of explosives, and it is of great significance for solvent screening of other explosives molecules.

Synthesis and characterization of energetic molecules based on pyrimidine rings: Selection and verification of computational-assisted synthesis pathways

The current rise in performance prediction techniques for energetic compounds provides the possibility of prejudging the effectiveness of derived patterns. In this work, 2,4-diamino-6-chloropyrimidine was used as the precursor, and the three possible derived pathways were systematically explored (guest oxidant, nitration, and N-oxidation). Theoretical calculations were adopted to predict the energy and stability parameters of possible products. The calculations indicated that constructing bridged-ring energetic molecules with N-oxide and nitro group is an effective way to balance energy and safety. Based on this protocol, we synthesized a series of pyrimidine-based energetic molecules within three steps and tested and analyzed their physicochemical properties, verifying the consistency between experimental results and theoretical predictions. This work provides a research model for determining the feasibility and effectiveness of the derivative pathway based on a specific energetic compound precursor and can offer guidance for the directed and large-scale synthesis of high-energy and low-sensitivity explosive molecules.

Shedding Novel Photophysical Insights Toward Discriminative Detection of Three Toxic Heavy Metal Ions and a hazard class 1 nitro-explosive By Using a Simple AIEE Active Luminogen.

In this work, we introduced a simple aggregation-induced emission enhancement (AIEE) sensor (PHCS) which can selectively detect and discriminate three environmentally and biologically imperative heavy metal ions (Cu2+, Co2+ and Hg2+) and a hazard class 1 categorized nitro-explosive picric acid (PA) in differential media. By virtue of its weak fluorescence attributes in pure organic medium owing to the synergistic operation of multiple photophysical quenching mechanisms, the molecular probe showcased highly selective 'TURN ON' fluorogenic response towards hazardous Hg2+ with a limit of detection (LOD) as low as 97nM. Comprehensive investigation of binding mechanism throws light on the cumulative effect of probe-metal complexation induced chelation enhanced fluorescence (CHEF) effect and subsequent AIEE activation within the formed probe-metal adducts. Noteworthily, the probe (PHCS) can be readily used in real water samples for the quantitative determination of Hg2+ in a wide concentration range. In addition, the probe displayed modest colorimetric recognition performances to selectively detect and discriminate two essential heavy metal ions (Cu2+ and Co2+) with a LOD of 96nM and 65nM for Cu2+ and Co2+ respectively, in semi-aqueous medium. Intriguingly, based on high photoluminescence efficiency, the AIEE active nano-aggregated PHCS displayed a remarkable propensity to be used as a selective and ultra-sensitive 'TURN-OFF' fluorogenic chemosensor towards PA with LOD of 34.4ppb in aqueous medium. Finally, we specifically shed light on the interaction of PHCS hydrosol towards PA using some unprecedented techniques, which helped uncover new photophysical insights of probe-explosive molecule interaction.

Carbon nano-onion as next-generation functional nanomaterial: Synthesis methods and practical applications

Carbon nano-onion (CNO) (also known as onion-like carbon, OLC), exhibiting multiple enclosed fullerene shell structures, as one of the most promising nanoforms, has attracted worldwide attention during the past decades due to its exceptional chemical and physical properties such as non-toxicity, high chemical stability, large sufficient surface area with low density, and superior high electronic and thermal conductivities, visible photoluminescence, etc. Nowadays, functional CNOs have been applied in energy storage devices, supercapacitors, photovoltaics, light-emitting diodes and bio-imaging technology. Since the first observation of CNOs by transmission electron microscopy as a byproduct in the synthesis of carbon black in 1980, numerous experimental and theoretical studies including expressive practical applications of CNOs have been intensively developed in modern chemistry. With respect to synthetic techniques, the high-temperature annealing of nano diamond, detonation of high explosive molecules, arc discharge of graphite, chemical vapor deposition, laser ablation, thermal pyrolysis, hydrothermal carbonization, and microwave pyrolysis have been reported. It has been addressed that the synthesis approach plays a key role in determining the structure of CNOs and resultant properties. This paper reviewed the developments of CNOs through major synthesis methods utilized for a selected wide spectrum of applications, by covering both the past and current progress. The contents outlined in the current review will offer readers comprehensive insights into the design and development of CNO materials.

Rapid Detection of Trace Nitro-Explosives under UV Irradiation by Electronic Nose with Neural Networks.

The development of an electronic nose (E-nose) for rapid explosive trace detection (ETD) has been extensively studied. However, the extremely low saturated vapor pressure of explosives becomes the major obstacle for E-nose to be applied in practical environments. In this work, we innovatively combine the decomposition characteristics of nitro explosives when exposed to ultraviolet light into gas sensors for detecting explosives, and an E-nose consisting of a SnO2/WO3 nanocomposite-based chemiresistive sensor array with an artificial neural network is utilized to identify trace nitro-explosives by detecting their photolysis gas products, rather than the explosive molecules themselves or their saturated vapor. The ultralow detection limits for nitro-explosives can be achieved, and the detection limits toward three representative nitro-explosives of trinitrotoluene, pentaerythritol tetranitrate, and cyclotetramethylene tetranitroamine are as low as 500, 100, and 50 ng, respectively. Moreover, by extracting the features of sensor responses within 15 s, a classification system based on convolutional neural network (CNN) and long short-term memory network (LSTM) is introduced to realize fast and accurate classification. The 5-fold cross-validation results demonstrate that the CNN-LSTM model exhibits the highest classification accuracy of 97.7% compared with those of common classification models. This work realizes the detection of explosives photolysis gases using sensor technology, which provides a unique insight for the classification of trace explosives.

MoS2 nanosheets decorated plasmonic silicon nanowires as SERS substrates for ultra-sensitive multiple analyte detection

We report the fabrication of hybrid SERS-active substrates for ultra-sensitive detection of diverse analyte molecules such as explosives, dyes, and bio-proteins. Vertically aligned (12-µm long, 250-nm diameter) Si nanowires (SiNWs) were prepared by a facile silver-assisted electroless (SAE) etching process. Ag and Au nanoparticles (NPs) were initially decorated on SiNWs using a simple immersion bath method. A hybrid SERS substrate was designed by encapsulating the 2D material (MoS2) on bi-metallic (Ag-Au nanoparticles) functionalized SiNWs. The synergetic effect from MoS2 nano-sheets and bi-metallic NPs produced superior detection of analytes down to ultra-trace levels. The versatility of hybrid substrate was tested extensively by detecting (i) malachite green (MG), (ii) melamine, (iii) naphthalene, (iv) bovine serum albumin (BSA), (v) adenine, (vi) L-Cysteine, (vii) Escherichia coli (E. coli), and (viii) tetryl (an explosive) molecules. We have observed excellent signal reproducibility with very low RSD values (3–5%). The analytic enhancement factors were estimated to be 3.6 × 108 for MG, 1.2 × 107 for melamine, and 6.4 × 105 for BSA, respectively. The estimated ‘limits of detection’ (LOD) for MG, melamine, naphthalene, adenine, and BSA were 216 pM, 42 nM, 78 nM, 5 nM, 7 nM, respectively. Furthermore, the durability of the substrate was studied extensively by evaluating the signal strength of 100 µM melamine for a prolonged duration in an ambient atmosphere. These established novel, robust, versatile, and potentially practical SERS-active hybrid substrates facilitate easy molecular detection in the field in conjunction with a portable or hand-held Raman spectrometer.

A Cerium Organic Framework with {Cu2I2} Cluster and {Cu2I2}n Chain Modules: Structure and Fluorescence Sensing Properties

In this work, a copper iodine module bearing a coordination polymer (CP) with a formula of [(Cu2I2)2Ce2(INA)6(DMF)3]·DMF (1, HINA = isonicotinic acid, DMF = N,N'-dimethyl formamide) is presented. The title compound features a three dimensional (3D) structure, in which the {Cu2I2} cluster and {Cu2I2}n chain modules are coordinated by N atoms from a pyridine ring in INA- ligands, while the Ce3+ ions are bridged by the carboxylic groups of INA- ligands. More importantly, compound 1 exhibits an uncommon red fluorescence (FL) with a single emission band maximized at 650 nm belonging to near infrared (NIR) luminescence. The temperature dependent FL measurement was applied to investigate the FL mechanism. Remarkably, 1 could be used as a FL sensor to cysteine and the nitro-bearing explosive molecule of trinitropheno (TNP) with high sensitivity, demonstrating its potential FL sensing applications for biothiol and explosive molecules.

Over-coupled Helmholtz-like optical resonator for enhanced infrared spectroscopy of molecules

Electromagnetic Helmholtz resonators are able to strongly and homogeneously enhance an electric field in relatively large volumes, making them attractive for applications to surface enhanced infrared absorption spectroscopy of molecules. We show in this study that such a structure, designed in the over-coupling regime can demonstrate strong enhancement of molecular modes of the polymer poly(methyl methacrylate) and the explosive molecule 2,4-dinitrotoluene over a very wide wavelength range between 5 and 10 µm. Reflectivity contrast provides access to the analyte’s absorption and quantitative information. Helmholtz-like resonators therefore offer a new platform for the creation of sensitive and versatile sensors.

Machine learning quantitatively characterizes the deformation and destruction of explosive molecules.

Although explosives have been widely used in mines, road development, old building demolishing, and munition explosions; currently, how chemical bonds between atoms break and recombine, how the molecular structure is deformed and destroyed, how the reaction product molecules are formed, and the details for this rapid change process in explosive reactions are not yet fully understood, which limits the full use of explosive energy and safer use of explosives. This paper presents a quantitative model of molecular structure deformation using machine learning algorithms as well as a qualitative model of its relationship with molecular structure destruction, based on a molecular dynamics simulation and detailed analysis of the shock-loaded ε-CL-20, providing new perspectives for explosive community research. Specifically, the quantitative model of molecular structure deformation establishes the quantitative relationship between the molecular volume change and molecular position change, and between molecular distance change and molecular volume change using the machine learning algorithms such as Delaunay triangulation, clustering, and gradient descent. We find that the molecular spacing in explosives is strongly compressed after being shocked, and the peripheral structure can shrink inward, which is beneficial to keep the cage structure stable. When the peripheral structure is compressed to a certain extent, the cage structure volume begins to expand and is then destroyed. In addition, hydrogen atom transfer occurs within the explosive molecule. This study amplifies the structural changes and the chemical reaction process for explosive molecules after being strongly compressed by a shock wave, which can enrich the knowledge of the real detonation reaction process. The analysis method based on quantitative characterization using machine learning proposed in this study can also be used to analyze the microscopic reaction mechanism in other materials.

The Effects of BTTN, TMETN and DEGDN Molecules on the Explosion Properties of PETN Molecule

Molecular modelling is an appreciated tool that brings valuable data on physical and chemical characteristics of materials that eliminates the necessity of conducting any experiment. This method allows to calculate the performance of energetic molecules to be synthesized. In the work, the detonation parameters of the energetic organic compounds Pentaerythritol tetranitrate(PETN), Butanetriol trinitrate (BTTN), Trimetylolethane trinitrate (TMETN) and Diethyleneglycol dinitrate (DEGDN) has theoretically been calculated and some values compared with the literature values. Moreover, three hypothetical molecules combining PETN with other explosive molecules have been designed. The detonation properties have been calculated using density functional theory (DFT) with B3LYP/6-31G (d,p) basis set. It has been concluded that all molecules have the effect of increasing the explosion parameters of PETN.

Gold nanoparticles coated LIPSS on GaAs for trace detection of RDX and Tetryl

Femtosecond laser-induced periodic surface structures (LIPSS) on GaAs were accomplished using ablation in the air by varying the input pulse energy (5–100 μJ). A single laser scan line was drawn at each energy, and sub-wavelength LIPSS were observed within each line. Their morphology was thoroughly analysed, and their formation mechanisms were discussed with appropriate theoretical support (SIPE-Drude model). These GaAs-LIPSS have good quality over large ablation areas, and the periodicity (663±16 nm) was nearly the same for all energies. Further, a set of GaAs-LIPSS was produced within an area of 2 × 2 mm2 utilizing an optimized energy of 5 μJ. Photoluminescence and Raman studies were performed to understand the laser-induced damage on these structures. Subsequently, these samples were coated with a 25 nm Au layer and annealed at 400 °C in ambience. The resulting plasmonic Au nanoparticles decorated GaAs-LIPSS were used as SERS substrates for detecting dye (MB) and explosive (RDX, Tetryl) molecules. Enhancement factors of ∼105 and ∼104 (lowest detected concentrations of 10−9 M and 10−5 M) were recorded for dye and explosive molecules, respectively. We believe that these results will aid in further developing GaAs-LIPSS with smaller feature sizes for improved sensing and optoelectronic applications.