TNT Vapor Research Articles

TNT Vapor Detection Based on a Lab-on-a-Fiber: Achieving a Millimeter-Scale Sensing Element on Fiber

In this paper, we discuss in detail the lab-on-a-flber (LOF) concept that we proposed earlier (Ma et ah, Proc. 4th Eur. Workshop Opt. Fiber Sens., 2010, vol. 7653, PP. 76531E-76531E-4), and present a specific example of this platform intended for trace vapor TNT detection. We show how we arrive at the current LOF design by examining the performance, technical difficulties, and complexities of various possible architectures. In the design solution adopted in our example, the sensing section occupies a space measuring only 1.6 × 1.6 × 0.8 mm, but contains several optical and chemical components/functions including a transmission/reflection mirror and TNT sensory film coated on a segment of the side wall of the fiber core. The fiber itself thus serves as the film substrate and when coated with the film becomes an evanescent-wave form fluorescent emission power collector. Its tiny dimensions notwithstanding, the LOF performs several simultaneous functions, including power density tuning and stray excitation light blocking. In addition, this LOF platform features ease of system construction and polymer film application. We demonstrate its fast response to TNT vapor, in the form of a 29% signal drop after 10 s of exposure.

Solid-state sensory properties of CALIX-poly(phenylene ethynylene)s toward nitroaromatic explosives

This study is primarily focused in establishing the solid-state sensory abilities of several luminescent polymeric calix[4]arene-based materials toward selected nitroaromatic compounds (NACs), creating the foundations for their future application as high performance materials for detection of high explosives. The phenylene ethynylene-type polymers possessing bis-calix[4]arene scaffolds in their core were designed to take advantage of the known recognition abilities of calixarene compounds toward neutral guests, particularly in solid-state, therefore providing enhanced sensitivity and selectivity in the sensing of a given analyte. It was found that all the calix[4]arene-poly( para-phenylene ethynylene)s here reported displayed high sensitivities toward the detection of nitrobenzene, 2,4-dinitrotoluene and 2,4,6-trinitrotoluene (TNT). Particularly effective and significant was the response of the films (25–60 nm of thickness) upon exposure to TNT vapor (10 ppb): over 50% of fluorescence quenching was achieved in only 10 s. In contrast, a model polymer lacking the calixarene units showed only reduced quenching activity for the same set of analytes, clearly highlighting the relevance of the macrocyclics in promoting the signaling of the transduction event. The films exhibited high photostability (less than 0.5% loss of fluorescence intensity up to 15 min of continuous irradiation) and the fluorescence quenching sensitivity could be fully recovered after exposure of the quenched films to saturated vapors of hydrazine (the initial fluorescence intensities were usually recovered within 2–5 min of exposure to hydrazine).

Thermo-optical determination of vapor pressures of TNT and RDX nanofilms

Accurate thermodynamic parameters of thin films of explosives are important for understanding their behavior in the nanometer scale as well as in standoff detection. Using UV-absorbance spectroscopy technique, accurate thermodynamic parameters such as activation energies of sublimation, sublimation rates, and vapor pressures of the explosives cyclotrimethylenetrinitramine (RDX) and 2,4,6-trinitrotoluene (TNT) were determined. The values of these parameters are in excellent agreement with those reported using traditional experiments based on gravimetry. In terms of the Clapeyron equation, the dependence of RDX and TNT vapor pressures on temperature can be described by the relations LnP (Pa)=39.6−15459/T (K) and LnP (Pa)=34.9−12058/T (K), respectively. Heats of sublimation of RDX and TNT were also determined to be 128kJ/mol and 100.2kJ/mol, respectively.

Substituted p-phenylene ethynylene trimers as fluorescent sensors for nitroaromatic explosives

New sensory materials based on p-phenylene ethynylene trimers integrating calix[4]arene receptors ( CALIX-PET) and tert-butylphenol ( TBP-PET) moieties have been synthesized and their sensitivity and selectivity for the detection of nitroaromatic compounds (NACs) such as nitrobenzene (NB), 2,4-dinitrotoluene (2,4-DNT), 2,4,6-trinitrotoluene (TNT) and picric acid (PA) investigated in fluid phase and solid-state. It was found that both fluorophores displayed high sensitivities toward NACs detection in solution as evaluated by the Stern–Volmer formalism. For all the tested explosives, the ratio of fluorescence intensities ( F 0/ F) is a linear function of the quencher concentration only after appropriate correction of fluorescence quenching data for inner-filter effects. The quenching efficiencies for CALIX-PET and TBP-PET follow the order PA ≫ TNT > DNT > NB, which correlate well with the quenchers electron affinities as evaluated from their LUMOs energies thereby suggesting a photoinduced electron transfer as the dominant mechanism of fluorescence quenching. The selectivity of these sensors was checked against exemplar interferents possessing differentiated electronic properties (benzoic acid, 2,4-dichlorophenol and benzoquinone) and reduced quenching activity was detected. The quenching efficiencies and response times of the two fluorophores in the solid-state toward NB, 2,4-DNT and TNT vapors were evaluated through steady-state fluorescence quenching experiments with the materials dispersed in polymeric matrices or as neat films. The most significant fluorescence quenching responses were achieved for drop-casted films of TBP-PET upon exposure to nitroaromatics.

PHOTOPLASTIC MICROCANTILEVER SENSOR PLATFORM FOR EXPLOSIVE DETECTION

We present an ultrasensitive and cost effective polymeric microcantilever sensor platform for explosive vapor detection. These sensors were fabricated using SU-8 polymer composite materials with two transduction approaches namely (i) optical and (ii) electrical detection. The cantilevers have been characterized for their electrical and mechanical properties. The functionalization of these microcantilevers has been carried out using selective chemicals for most popular explosives such as TNT and RDX. Optical and electrical responses of respective microcantilevers to TNT and RDX vapors are also presented here.

Amplifying fluorescence sensing based on inverse opal photonic crystal toward trace TNT detection

A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300 s. The results suggest that the fluorescence-amplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

Detection of Explosive Vapors by Surface Acoustic Wave Sensors Containing Novel Siloxane Based Coatings

Surface acoustic wave (SAW) sensor was coated with a new chemoselective polymer to detect nitroaromatic explosives. Adsorption of the analyte influences the propagation of SAW and thus causes a shift in the resonant frequency of the SAW device. A novel azobenzene functionalized siloxane polymer was developed and applied to a surface acoustic wave (SAW) sensing device for the detection of explosive vapors such as 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT). The experimental setup used for evaluating the response of this polymers-coatings is described in the paper. Experimental results indicate that the viscoelastic properties of the polymer coating is fairly insensitive to the temperature changes occurring in our experiments, which is ideal for SAW sensing device. The PDMS coating is able to detect DNT and TNT vapors.

Performance of stacked, flow-through micropreconcentrators for portable trace detection

Improving techniques for portable trace analyte collection and pretreatment is of critical concern for security, medical, food and environmental applications. The trend has been to employ MEMS technologies to meet this need as these microfabricated devices offer advantages such as small dead volumes, low power consumption, capacity for large scale manufacture and a commensurate savings with economies of scale. In this work a prototype trace sampling system intended for use with ion mobility spectrometers is presented. The system utilizes a stack of microfabricated preconcentrator plates capable of collecting samples in a sorbent polymer at flow rates up to 30 LPM. The plates are thermally desorbed after an integration period to produce a concentrated vapor plug that is transferred to the detector for analysis. A real-time controller, FPGA and custom electronics are used to manage independent heating of up to 4 of these devices in either constant voltage or temperature modes. The preconcentrators were tested with a commercial Vapor Tracer II IMS against TNT and RDX vapors ranging in concentration from 2.6 PPT to 620 PPT under a variety of conditions. Results are presented on performance of single preconcentrators with RDX, multiple cascaded devices vs. TNT and RDX, with and without a PDMS detector inlet membrane, and to compare sorbent coated and bare devices. The system demonstrated preconcentration factors of 38 with 2.6 PPT RDX and 30 with 13 PPT TNT.

Template-Free Synthesis of Organically Modified Silica Mesoporous Thin Films for TNT Sensing

In this paper, we present a facile, template-free sol−gel method to produce fluorescent and highly mesoporous organically modified silica (ORMOSIL) thin films for vapor phase sensing of TNT. An alkyltrifunctional, methyltrimethoxysilane MTMS precursor was used to impart hydrophobic behavior to gel network in order to form the spring back effect. In this way, porous films (up to 74% porosity) are obtained at ambient conditions. Fluorescent molecules are physically encapsulated in the ORMOSIL network during gelation. Fluorescence of the films was found to be stable even after 3 months, proving the successful fixing of the dye into the ORMOSIL network. The functional ORMOSIL thin films exhibited high fluorescence quenching upon exposition to TNT and DNT vapor. Fluorescence quenching responses of the films are thickness-dependent and higher fluorescence quenching efficiency was observed for the thinnest film (8.6% in 10 s). The prepared mesoporous ORMOSIL thin films have great potential in new sensor and cata...

Tunable Generation and Adsorption of Energetic Compounds in the Vapor Phase at Trace Levels: A Tool for Testing and Developing Sensitive and Selective Substrates for Explosive Detection

Among various methods for landmine detection, as well as soil and water pollution monitoring, the detection of explosive compounds in air is becoming an important and inevitable challenge for homeland security applications, due to the threatening increase in terrorist explosive bombs used against civil populations. However, in the last case, there is a crucial need for the detection of vapor phase traces or subtraces (in the ppt range or even lower). A novel and innovative generator for explosive trace vapors was designed and developed. It allowed the generation of theoretical concentrations as low as 0.24 ppq for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in air according to Clapeyron equations. The accurate generation of explosive concentrations at subppt levels was verified for RDX and 2,4,6-trinitrotoluene (TNT) using a gas chromatograph coupled to an electron capture detector (GC-ECD). First, sensing material experiments were conducted on a nanostructured tungsten oxide. The sensing efficiency of this material determined as its adsorption capacity toward 54 ppb RDX was calculated to be five times higher than the sensing efficiency of a 54 ppb TNT vapor. The material sensing efficiency showed no dependence on the mass of material used. The results showed that the device allowed the calibration and discrimination between materials for highly sensitive and accurate sensing detection in air of low vapor pressure explosives such as TNT or RDX at subppb levels. The designed device and method showed promising features for nanosensing applications in the field of ultratrace explosive detection. The current perspectives are to decrease the testing scale and the detection levels to ppt or subppt concentration of explosives in air.

Inverted Opal Fluorescent Film Chemosensor for the Detection of Explosive Nitroaromatic Vapors through Fluorescence Resonance Energy Transfer

This paper reports an inverted opal fluorescence chemosensor for the ultrasensitive detection of explosive nitroaromatic vapors through resonance-energy-transfer-amplified fluorescence quenching. The inverted opal silica film with amino ligands was first fabricated by the acid-base interaction between 3-aminopropyltriethoxysilane and surface sulfonic groups on polystyrene microsphere templates. The fluorescent dye was then chemically anchored onto the interconnected porous surface to form a hybrid monolayer of amino ligands and dye molecules. The amino ligands can efficiently capture vapor molecules of nitroaromatics such as 2,4,6-trinitrotoluene (TNT) through the charge-transfer complexing interaction between electron-rich amino ligands and electron-deficient aromatic rings. Meanwhile, the resultant TNT-amine complexes can strongly suppress the fluorescence emission of the chosen dye by the fluorescent resonance energy transfer (FRET) from the dye donor to the irradiative TNT-amino acceptor through intermolecular polar-polar resonance at spatial proximity. The quenching response of the highly ordered porous films with TNT is greatly amplified by at least 10-fold that of the amorphous silica films, due to the interconnected porous structure and large surface-to-volume ratio. The inverted opal film with a stable fluorescence brightness and strong analyte affinity has lead to an ultrasensitive detection of several ppb of TNT vapor in air.

Poly(phenylene ethynylene)-coated aligned ZnO nanorod arrays for 2,4,6-trinitrotoluene detection

The structure of ZnO nanorods coated with fluorescent polymer poly(phenylene ethynylene) (PPE) have been fabricated for 2,4,6-trinitrotoluene (TNT) detection. In this structure, hydrothermally synthesized crystalline ZnO nanorod arrays were used as waveguides and supporting materials for the TNT sensitive polymer, PPE. The evanescent-wave guiding property of the ZnO nanorod waveguide considerably increased fluorescence intensity. The space between the adjacent nanorods and the larger surface-to-volume ratio of the nanorods enhanced the fluorescence response (quenching) to TNT vapor. This work will contribute to design of combining ZnO nanorod arrays with a functional polymer for sensor applications.

Explosive vapor sensor using poly (3-hexylthiophene) and CuII tetraphenylporphyrin composite based organic field effect transistors

Organic field effect transistors based on poly(3-hexylthiophene) and CuII tetraphenylporphyrin composite were investigated as sensors for detection of vapors of nitrobased explosive compounds, viz., 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 2,4,6-trinitrotoluene (TNT), and dinitrobenzene, which are also strong oxidizing agents. Significant changes, suitable for sensor response, were observed in transistor “on” current (Ion) and conductance (S) after exposure. A similar device response was, however, not observed for oxidizing agents such as benzoquinone and benzophenone. The Fourier transform infrared spectrometry experiments supported the results, where exposure to RDX and TNT vapors resulted in a significant shift in IR peaks.

Amine-Capped ZnS−Mn2+ Nanocrystals for Fluorescence Detection of Trace TNT Explosive

Mn2+-doped ZnS nanocrystals with an amine-capping layer have been synthesized and used for the fluorescence detection of ultratrace 2,4,6-trinitrotoluene (TNT) by quenching the strong orange Mn2+ photoluminescence. The organic amine-capped nanocrystals can bind TNT species from solution and atmosphere by the acid-base pairing interaction between electron-rich amino ligands and electron-deficient aromatic rings. The resultant TNT anions bound onto the amino monolayer can efficiently quench the Mn2+ photoluminescence through the electron transfer from the conductive band of ZnS to the lowest unoccupied molecular orbital (LUMO) of TNT anions. The amino ligands provide an amplified response to the binding events of nitroaromatic compounds by the 2- to approximately 5-fold increase in quenching constants. Moreover, a large difference in quenching efficiency was observed for different types of nitroaromatic analytes, dependent on the affinity of nitro analytes to the amino monolayer and their electron-accepting abilities. The amine-capped nanocrystals can sensitively detect down to 1 nM TNT in solution or several parts-per-billion of TNT vapor in atmosphere. The ion-doped nanocrystal sensors reported here show a remarkable air/solution stability, high quantum yield, and strong analyte affinity and, therefore, are well-suited for detecting the ultratrace TNT and distinguishing different nitro compounds.

Porphyrin-doped mesoporous silica films for rapid TNT detection

Two kinds of porphyrin-doped silica films with mesoporous structures were fabricated using evaporation-introduced self-assembly approach and examined for chemosensor applications to detect explosive compounds such as 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), and nitrobenzene (NB). All synthesized silica films showed high fluorescence quenching sensitivity toward the vapors of TNT, DNT, and NB but is strongly dependent on pore structure. The silica film with three dimensional pore structure exhibits the highest quenching efficiency close to the quenching efficiency reported for emissive conjugated polymers, indicating these kinds of mesostructured composites are potentially useful chemosensory materials for rapidly detecting trace explosives. The preparation conditions, the structures of the resulting films, their sensing performances, and the fluorescence quenching mechanism were discussed in this paper.

Fluorescent nanofibrous membranes for trace detection of TNT vapor

Electrospinning is a simple and cost-effective approach for the production of nanofibers and assemblies with controllable structures. In this work, based on sol–gel chemistry and the electrospinning technique, porphyrin-doped nanocomposite fibers with a form of nanofibrous membrane were successfully fabricated without the addition or help of polymers, and were demonstrated as novel fluorescence-based chemosensors for the rapid detection of trace vapor (10 ppb) of explosive. Due to a larger surface area and good gas permeability, these fluorescent nanofibrous membranes exhibit remarkable sensitivity to trace TNT vapor compared to tightly cross-linked silica films, but their sensitivity is strongly dependent upon the morphology and phase aggregation of the used nanofibers. Reducing the diameter and introducing a pore structure into nanofibers can considerably enhance the sensitivity of the resulting materials. The performed experiments suggest that the hierarchically structured, porphyrin-doped nanofibrous membranes are potentially very useful chemosensory materials for detecting trace explosives.

Hierarchically Structured Nanocomposite Films as Highly Sensitive Chemosensory Materials for TNT Detection

Sensitive to TNT vapor: Porphyrin-doped silica films with bimodal porous structures, fabricated using a dual template approach, exhibit remarkable sensitivity towards traces of TNT vapour. These hierarchically structured nanocomposites serve as useful chemosensory materials for rapid detection of explosives (see picture).

Metalloporphyrins as sensing elements for the rapid detection of trace TNT vapor

Download options Please wait... Supplementary files Fluorescence quenching experiments on various metalloporphyrin-doped silica films. PDF (1297K) Article information DOI https://doi.org/10.1039/B606061G Article type Paper Submitted 28 Apr 2006 Accepted 04 Sep 2006 First published 04 Oct 2006 Download Citation J. Mater. Chem., 2006,16, 4521-4528 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Metalloporphyrins as sensing elements for the rapid detection of trace TNT vapor S. Tao, G. Li and H. Zhu, J. Mater. Chem., 2006, 16, 4521 DOI: 10.1039/B606061G To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Shengyang Tao Guangtao Li Hesun Zhu

Determination of the Vapor Density of Triacetone Triperoxide (TATP) Using a Gas Chromatography Headspace Technique

AbstractUsing a GC headspace measurement technique, the vapor pressure of TATP was determined over the temperature range 12 to 60 °C. As a check on the experimental method, TNT vapor pressure was likewise computed. Values for TNT are in excellent agreement with previous published ones. For TATP the vapor pressure was found to be ~ 7 Pa at ambient conditions. This value translates to a factor of 104 more molecules of TATP in air than TNT at room temperature. The dependence of TATP vapor pressure on temperature can be described by the equation log10P(Pa)=19.791−5708/T(K). Its heat of sublimation has been calculated as 109 kJ/mol.

Adsorption–desorption characteristics of explosive vapors investigated with microcantilevers

Understanding the kinetics of adsorption and desorption of explosive vapors such as TNT from surfaces is important in the design of sensors. We report for the first time, the adsorption–desorption characteristics of TNT from a Si-microcantilever exposed to vapors of TNT. It was observed that TNT readily sticks to the exposed Si surface with the adsorption kinetics showing an initial exponential behavior followed by roughly linear kinetics. It was also observed that for cantilever temperatures close to room temperature, TNT desorbs spontaneously from the surface with decaying exponential kinetics. Based on the known equilibrium partial vapor pressures of TNT, the “effective” sticking coefficient for the silicon oxide surface at room temperature under the experimental conditions was calculated to be about 0.02. This information can be very useful in the design of sensors and that of vapor-delivery systems.