WO2022051219A1 - Capteurs à base de nanotubes de titane fonctionnalisés pour la détection d'engins explosifs improvisés (eei) - Google Patents

Capteurs à base de nanotubes de titane fonctionnalisés pour la détection d'engins explosifs improvisés (eei) Download PDF

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WO2022051219A1
WO2022051219A1 PCT/US2021/048210 US2021048210W WO2022051219A1 WO 2022051219 A1 WO2022051219 A1 WO 2022051219A1 US 2021048210 W US2021048210 W US 2021048210W WO 2022051219 A1 WO2022051219 A1 WO 2022051219A1
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tatp
sensor
detection device
device defined
metal
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PCT/US2021/048210
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Vaidyanathan Subramanian
Manoranjan Misra
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Nevada Research & Innovation Corporation
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
    • G01N27/127—Composition of the body, e.g. the composition of its sensitive layer comprising nanoparticles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0057—Warfare agents or explosives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites

Definitions

  • This invention relates to the detection of explosive devices by sensing the presence of one or more airborne chemical constituents of explosive materials.
  • the invention more particularly relates to a portable device for detecting the proximate presence of explosive devices.
  • Improvised Explosive Devices are the ammunition of choice for terrorism in different parts of the world including the United States.
  • peroxide based explosives such as triacetone triperoxide (TATP) are the most potent and dangerous.
  • TATP triacetone triperoxide
  • Peroxide based explosive, such as TATP pose a significant risk to the US military owing to its ease of fabrication and difficulty in direct detection.
  • HMTD hexamethylene triperoxide diamine
  • FTIR Fourier transform infrared
  • the present invention aims to provide a device for sensing airborne chemical components of explosive devices. More specifically, the present invention aims to provide such a device that is highly selective or sensitive, compact, robust, and simple to operate. Preferably, the device is manually portable and cost competitive (inexpensive).
  • the present invention contemplates a device that detects peroxide-based explosives such as triacetone triperoxide (TATP) and its surrogates.
  • peroxide-based explosives such as triacetone triperoxide (TATP) and its surrogates.
  • the device senses airborne chemical components of explosive devices, particularly TATP, that is efficient, rapid, reliable, and robust with a detection capability of less than 5 ppb.
  • a device in accordance with the present invention for detecting airborne chemical components of explosive devices includes a sensor incorporating a functionalized metal oxide nanotubular array.
  • the present invention recognizes that solid state sensors with metal oxide arrays or coated quartz sensors represents an opportunity for detection of peroxide-based explosives onsite.
  • the invention contemplates a portable detection device with a sensor of based on a metal oxide substrate having a coating or layer that selectively and specifically binds to the peroxide molecules. The binding generates or induces a positive response of the sensor by changing the physical and/or chemical behavior of the metal oxide array.
  • the present invention realizes that one dimensional metal oxide materials are ideal platform materials for sensing systems owing to their semiconducting nature, corrosion resistant property, ease of preparation and handling by electrochemical anodization method.
  • Metal oxide materials for use in the present invention include TiO2, SnO2, ZnO, AI2O3, WO3, Fe2O3 and Ga2O3, with TiO2 often being used.
  • a sensor module of an explosives detection device has a nanotubular architecture.
  • the highly ordered structure of nanotubular architecture enhances field-effect carrier mobility, provides increased electrical conductivity and reduces activation energy for electrical conduction.
  • the device is configured for detection of vapors of peroxide based explosives (POE).
  • Metal ions such as cobalt ions, Co 2+
  • TiO 2 nanotube (NT) arrays of the device sensor component bind with airborne POE (peroxide moiety).
  • the Co 2+ ion is effective as a TATP binding agent on titania (TiO 2 ).
  • TiO 2 NTs and POE bonding is the metal ion exchanged on the surface of the TiO 2 NTs.
  • a sensing device in accordance with the invention is cost-competitive to manufacture and exhibits a fast response time, a high sensitivity and selectivity, and a small footprint.
  • the sensor core of the device can be easily integrated into remote surveillance devices.
  • the presently preferred embodiment detects triacetone triperoxide (TATP) as well as its precursor H 2 O 2 and is reusable.
  • TATP triacetone triperoxide
  • the present sensor detects explosive-origin compounds in the gas phase (air sampling).
  • the detection capability of different techniques are compared in Table 1. It can be seen that the titania (TIO 2 ) nanotube based sensor technique of the present invention has advantages such as universal detection capability (able to detect both nitro based and peroxide based explosive), ease of operation and point of use detection capability.
  • the response time of the present device is less than 5 second.
  • the sensor is re-useable and low cost in fabrication
  • FIG. 1 is a diagram depicting concepts underlying the present invention, specifically, point-of-use sensor technology for screening of Hydrogen peroxide and/or TATP using metal functionalized titania nanotubular sensing platform.
  • FIG. 2 is a diagram of operative components of a detection device pursuant to the present invention.
  • FIG. 3 is a diagram of a detection device in accordance with the present invention, showing wireless connectively thereof with a portable device such as a laptop or a cellular phone.
  • FIG. 4 is a block diagram explaining the detection device with additional functionality pursuant to the present invention.
  • FIGS. 5a-e are chemical models showing DFT (B3LYP/SDD-631 G+(2d) optimized structures of (a) TATP, (b) metal-TATP complex Cu , (c) metal-TATP complex Co , (d) metal-TATP complex Sb
  • FIGS. 6a, 6b are chemical models showing a) Mulliken charge distribution on different atoms of 2+ 2+ 2+
  • Co -TATP complex (b) molecular orbital of Co -TATP (HOMO), showing Co binding with a TATP molecule.
  • HOMO molecular orbital of Co -TATP
  • FIG. 7 is a graph showing sensor response for TATP and other VOCs detected using a Co-TiG 2 substrate.
  • the Co functionalized sensor is specific to TATP and not specific for common VOCS found in the environment. Level of VOCs at 20 ppm.
  • FIG. 8 is a graphical representation of a chemical model showing unrelaxed (101) anatase (b) surfaces with different types of sites labelled.
  • the (101) crystallographic plane is represented by an arrow b.
  • Notation such as “Ti 5c ” refers to a 5-fold-coordinated Ti site.
  • Small blue spheres are Ti and large red spheres are O and are scaled according to the relative ionic radii. Structure contains four Ti and 12 atomic layers.
  • FIG. 9 is a diagram showing electron transfer in a sensor device pursuant to the present invention.
  • FIG. 10 is a diagram of a TiO 2 sensor integrated into a microdevice for portable sensing, pursuant to the present invention.
  • a point-of-use (POU) device for sensing Improvised Explosive Devices (IED) as disclosed herein uses the specific molecular interactions between embedded metal ions in a titania (TiO 2 ) nanotube array substrate and triacetone triperoxide (TATP) vapors.
  • Triacetone triperoxide (TATP) is of particular interest as it has a very high vapor pressure and most potent explosive compound that can be synthesized using commercially available starting materials. The use of this compound has grown significantly among terrorist groups recently. In last 10 years, use of TATP in explosives killed more than 235 people and injured about 1350 others across the globe.
  • a point-of-use device 20 for screening of TATP includes a housing 22 that defines an internal chamber 24 having a forced (suction preferred) or a natural draft air inlet or passageway 26 on one side and an outlet 28 on another side.
  • a metal functionalized titania nanotubular sensing platform 30 is disposed inside chamber 24 between inlet 26 and outlet 28.
  • a fan or impeller 32 is disposed inside chamber 24, for instance, proximate outlet 28, for drawing a stream of ambient air into the chamber and past sensing platform 30.
  • Sensing platform 30, and particularly nanotubes 34 thereof, is connected to a voltage source 36 and to a current sensor 38. As the concentration of TATP in the ambient air increases and results in a greater degree of binding of the TATP or peroxide molecules to the nanotubes, the current measured by sensor 38 increases proportionately.
  • a sensing device 40 for rapid detection of TATP includes a sensing platform 42 of functionalized TiO 2 nanotubules 44 connected to a miniature potentiostat 46 (EmStat) or an equivalent that measures changes in current conducted through the nanotubes.
  • the current changes in accordance with a concentration of TATP in ambient air owing to exudation or volatilization of TATP and associated peroxide compounds from explosive devices (lEDs).
  • Sensing device 40 communicates wirelessly with a portable device such as a smartphone 48 that may be provided with an app for automated analysis and informing the user of nearby explosive devices.
  • Nanotubes 34, 44 preferably consist of titania (TiO 2 ) packed arrays and have diameters between 80 nm and 250 nm and lengths of 2-5 pm.
  • the present invention contemplates the use of nanotubular sensing platforms for detecting peroxide based explosives such as hydrogen peroxide, triacetone triperoxide (TATP) or hexamethylene triperoxide diamine (HMTD) and explosives based on other compounds such as tri-nitro toluene (TNT) and cyclotrimethylenetrinitramine (RDX).
  • peroxide based explosives such as hydrogen peroxide, triacetone triperoxide (TATP) or hexamethylene triperoxide diamine (HMTD)
  • TNT tri-nitro toluene
  • RDX cyclotrimethylenetrinitramine
  • Devices 20, 40 may utilize metal ions other than or in addition to the cobalt divalent ion to bind to TATP, TNT or RDX.
  • metal ions of different valences include monovalent Li 1+ and Cu 1+ , divalent Fe 2+ , Ni 2+ , Cr 2+ , Co 2+ , Pb 2+ , and Zn 2+ , trivalent ln 3+ , Co 3+ , Cr 3+ , and Sb 3+ , and tetravalent Pd 4+ and Pt 4+ selected on the basis of the Hard-Soft-Acid-Base principle.
  • a binary or ternary combination of these metal ions can also be helpful in the detection process.
  • the effectiveness and suitability of other metal ions or combinations of metal ions for detecting of TATP, TNT, RDX and other explosive agents may be determined using density functional theory (DFT) modeling methods. This identifies metals with a high affinity for TATP that may be used as active binding elements for detecting molecules of TATP. The same modeling can be used to determine metal ions that not only bind to explosively unstable compounds but also do not bind to background chemical compounds, that is, non-explosive chemical compounds that may typically be found in a target area.
  • DFT density functional theory
  • a point-of-use device 50 for screening of TATP or other airborne explosive chemical includes a nanotube array 52 functionalized, as disclosed above, with a metal ion layer or coating on nanotube substrate material, preferably metal oxide, and with a voltage source (not shown).
  • a current sensor 54 is connected to nanotube array 52 for detecting changes in current owing to binding of explosive molecules or other chemically related compounds drawn from the ambient air past the nanotube array by a fan or suction source 56.
  • Sensor 54 is connected to a digital comparator 58 via an analog-to-digital converter 60 and a random access memory (RAM) 62.
  • Comparator 58 which may be realized as a stand alone unit or part of a microprocessor 64, receives digitized current values from RAM 62 and reference values from a readonly memory or reference store 66.
  • Microprocessor 64 also includes a concentration gradient calculator 68 that may use results from comparator 58, and data from RAM 62 to determine not only that detected molecular concentrations are increasing but a real-time rate at which the concentration change happens.
  • concentration gradient calculator 68 calculates the rate of concentration increase and optionally decrease.
  • concentration gradient calculator 68 is connected to an audio generator 72 and/or a display 74 for providing an operator or user with an acoustic or visual alert signal and further information as desired.
  • DFT non-periodic density functional theory
  • TATP ligand
  • C, O, H The ligand (TATP) atoms i.e. C, O, H are described by the 6-31 G+(2d) basis set.
  • Geometry optimizations may be performed for different metal- TATP complexes without any symmetry restrictions and for each structure.
  • One may implement a normal mode analysis in the gas phase to confirm their character as local minimum.
  • Geometry optimizations may be done until forces are less than 10' 5 au and energy convergence by 10' 8 heartree.
  • TATP is a nine-member cyclic molecule (FIG. 5a).
  • the calculated lowest energy structures of metal-TATP complexes, as calculated are shown in FIGS. 5b-5e.
  • the stable structures (FIG. 5b-e) of metal cations in the center of the TATP ring and binding of metal cation to three alternate oxygen atoms from adjacent peroxide linkage can be observed.
  • An isomer of the metal-TATP system where nonalternate-oxygen atoms are bound to the central metal ion is considered initially. Energetically, the former isomer is deemed more favorable. The latter one is less stable by about -10 Kcal/mol considering Zn 2+ as metal candidate. Hence, it is not considered further.
  • the bonding of oxygen atoms to the metal center is through the donation of lone pair of electrons available on oxygen to the vacant orbitals of the metal ions.
  • This can be rationalized by increase in electronic population in metal valance orbitals and decrease in the same for bound oxygen atoms of TATP.
  • the population in Co 2+ valence orbitals (3d, 4s, 4p) is slightly increased, by about 10% as calculated from natural bond analysis.
  • cleavage of peroxide bonds joining adjacent acetone units is observable (FIGS.
  • the stable products in such cases contain three individual units of acetone peroxide with one oxygen atom bound to the metal center.
  • the cyclic structure of TATP is preserved for monovalent and divalent metal cation complexes with TATP, except for Pd 2+ and Ni 2+ .
  • the electronic charge distribution in the metal-TATP complex as obtained from Mulliken (FIG. 4a) and Natural Bond Order (NBO) population analysis shows that the negative charge on the O b atoms in the metal ion-TATP complex is somewhat larger (30%) than that in the TATP molecule. Also, one can detect a decreased charge by 10% on O u following the ion- TATP complex formation.
  • TATP complexation and the amount of charge transfer in the complex exhibits a positive correlation, namely, larger charge transfer corresponding to a stronger binding energy.
  • This correlation suggests that bond formation in the ion-TATP complex includes a large contribution from Coulomb interactions.
  • the binding interaction of metal ion and TATP molecule is described with a molecular orbital picture (FIG. 6b).
  • NBO analysis provides details of electronic distribution in various molecular orbitals of metal-TATP complexes. It is to be noted that the vacant valence orbitals are of s, p, d nature.
  • the population on Sb 3+ ion is 5S (1 .79) 5p(1 .01), where there is a large increase in population in the p orbital by 1 1 %. This is hypothesized as the reason for the cleavage of TATP cyclic structure.
  • the free energy of binding computed for different metal-TATP complexes shows an increase from monovalent to tetravalent metal ions complexing with TATP: the range in AG B is from 100 Kcal. mol -1 to -1210 Kcal. mol’ 1 .
  • the AG B is calculated as positive for monovalent metal cations such as Li 1+ and Cu 1+ , which shows less probability in complexing TATP.
  • the AG B is around - 100 Kcal. mol -1 or below that except for Pd 2+ and Ni 2+ ions, opening of TATP ring structure leads to a different geometry.
  • the trend in stability of the divalent metal ions is as follows: Co 2+ >Fe 2+ >Zn 2+ >Cr 2+ .
  • the free energy of complexation for trivalent metal ions is spread over a range from -371 to -664 Kcal. mol’ 1 .
  • the trivalent metal-TATP complexes are calculated with cleaved TATP ring structure (FIG. 3d).
  • the trend in stability of these metal-TATP complexes is Co > Cr >ln >Sb .
  • the sensor gives a positive response through change in conductivity, once the metal coating on to the TiO 2 nanotubes bonds to the peroxide molecules.
  • This increase in conductivity is measured by applying an external bias (-0.5V) and taking simple current readings.
  • the increase in current is proportional to the concentration of the explosive molecule adsorbed on the surface of the nanotube.
  • FIG. 2 shows such a sensor.
  • the sensor array is constructed on a planar TiO 2 substrate. Two copper electrical leads are connected to each side of the sensor using a standard silver epoxy.
  • the leads are connected to a potentiostat that provides a bias voltage to the sensor and measures the current.
  • the sensor and particularly the effectiveness of the Co 2+ -TiG 2 material, may be tested inside a glove box under nitrogen atmosphere.
  • the bias voltage for sensing measurement is determined to be -0.5V from the current- voltage curve for Co 2+ -TiG 2 system.
  • Electric current measurements are taken with and without passing TATP vapors through the sensor material at -0.5V.
  • the current measured at -0.5V bias without exposure to TATP is considered as the background current.
  • the sensor is exposed to TATP vapor by placing 5 mg of TATP in a 1000 ml round bottomed flask and passing the vapor generated from the TATP through a 1 mm diameter glass nozzle with an air flow rate of about 30 seem.
  • FIG. 7 shows preliminary data for the functionalized TiO 2 sensor when compared to several volatile organic compounds (VOCs) found in the environment (ethanol, methanol, acetone benzene, and phenol all at 20 ppm concentrations).
  • VOCs volatile organic compounds
  • Sensor response is calculated as the ratio of difference in maximum current when the sensor is exposed to the TATP vapor and when the sensor is exposed to air (baseline current) (/.e. sensor response is (l d - l b )/l b , where l d is the current measured when the sensor is exposed to a volatile compound and l b is the baseline current before detection).
  • the sensor response to ethanol, methanol, acetone, benzene, and phenol ranges from 0.02 to 1 .38 indicating these compounds have little effect on the sensor.
  • a large change in sensor response (7x) is observable. This indicates that the sensor is specific for TATP and has the potential to detect the molecule in the presence of other chemical compounds that are found commonly in the environment.
  • the present disclosure contemplates the use, in an explosives detector, of metal ions with high affinity towards TATP and other explosive molecules such TNT and HMTD, but not towards predominant VOCs in the environment (selectivity) such as formaldehyde, methylene chloride, ethylene glycol, and toluene among others.
  • Metal ions such as Fe 2+ ,Zn 2+ ,Cr 2+ ,Cu 1+ ,Li 1+ are considered candidates depending on detailed comparison of relative strength of their interaction for different Metal-TATP complexes. The binding free energy of metal ions and the higher binding strength determine the selective nature of metal ions towards the TATP.
  • Binding strength of metal ions to other peroxide explosive molecules such as H 2 O 2 , HMTD can be calculated as to their selectivity properties. A higher binding to TATP compared to these molecules provides for selectivity criteria. The binding process to other explosive molecules such as RDX and TNT verifies the application of the present sensor device for a wide range of explosive molecules.
  • Atomistic modeling calculations and analysis can be accomplished using non-periodic DFT methods as implemented in the Gaussian 09 program package. The parameters used in preliminary studies are used for this work.
  • anatase polymorph For the modeling of TiO 2 nanotube structures, one may consider anatase polymorph, as it is observed to be the predominant phase of annealed TiO 2 with a temperature at 500°C. Furthermore, (101) surface of anatase is chosen for adsorption study (FIG. 8), because it is the most stable surface of anatase titania. Both adsorption sites of oxygen, O 2c and O 3c are considered on anatase (101) surface.
  • TiO 2 nanotubes may be modeled using the periodic DFT suite of codes Quantum ESPRESSO (QE).
  • QE Quantum ESPRESSO
  • the generalized-gradient approximation with Perdew-Burke-Ernzerhof (PBE) exchange-correlation functionals is used to handle many-body interactions and a width of 0.02 Ry for Marzari-Vanderbilt smearing functions due to the metallic nature of the systems and/or elements involved.
  • Self-consistent field calculations over the Brillouin zone can use an 8 x 8 x 8 Monkhorst-Pack grid for k-points with energy and electron density cut-offs of 80 Ry and 960 Ry, respectively.
  • the bond lengths are predicted with an error of less than 0.01 A.
  • the TATP interaction with M-TiO 2 prompts a change in the electrical resistivity of the device, which basically underlines the process for the sensing mechanism.
  • the ET mediated via TATPs interaction with M-TiO 2 is an ultrafast process originating from TATPs molecule, subsequently transferred to the semiconducting band edge resulting in a current variation.
  • the hypothesis behind the charge transduction in the sensor device is that the electron transfer occurs from highest occupied molecular orbital (HOMO) of the TATP molecule to the conduction band (CB) of the semi-conducting material TiO 2 via the lowest unoccupied molecular orbital (LUMO) of TATP molecule (FIG. 9).
  • Modeling ET in real time scale is very challenging.
  • Non-adiabatic molecular dynamics (NAMD) provides a direct strategy for modeling ET process in real time at the atomistic level.
  • the sensor of the present invention comprises three parts, a left-hand side electrode, a right-hand side electrode and a device region, where the regions interact in pairs.
  • the electrodes are silver and titanium, and the device region will be titania nanotube with varying length (40-80 A).
  • the electrode can be defined in two different ways; one with the 5 layers of silver/titanium at a distance of 1.5-2 A from the device region; two, another with the central region sandwiched between two semi-infinite titanium dioxide electrodes of the same structure as the nanotube in the center.
  • the system’s Green’s function in the linear regime (including the effects of the electrodes via self-energies) reduces to the Landauer Buttiker formalism and one can calculate the transmission coefficients.
  • the NAMD may be performed for TATP-M-TiO 2 system with DFT using the Quantum ESPRESSO suite of codes.
  • the adiabatic trajectory can be generated using a micro canonical ensemble approach for 1fs time scale. Adiabatic energy and NA coupling parameters can be computed subsequently.
  • single walled TiO 2 nanotube of varying length 40-80 A may be considered.
  • the optimized geometries as obtained from MD simulation for (i) the probe and linkage molecule attached to the nanotube, (ii) the described molecules in the previous state and the target stand attached to the probe stand are transferred to the transport calculations, performed using DFT/NEGF.
  • the electrical transport calculations are performed within DFT framework using the SIESTA code and the transport properties are calculated using the non-equilibrium Green's functions (NEGF) formalism implemented in the SMEAGOL code and Atomistix simulator at zerobias voltage in the linear response limit. Transmission coefficients and density of states as a function of energy are calculated from these simulations. Also, the conductance depending on bias can be analyzed from the electric current-voltage curve. The change in current in TiO 2 -Metal-TATP system with respect to the current for TiO 2 .Metal system, gives the response for sensor. The computational work is verifiable by comparing with the experimental data for the corresponding system and related properties.
  • NEGF non-equilibrium Green's functions
  • the present methodology contemplates synthesizing self-ordered and vertically oriented nanotubes by a simple electrochemical anodization method.
  • the TiO 2 nanotube array format creates a sensor with extremely high surface area within a small amount of space.
  • the tubular morphology allows more potential areas to be functionalized with elements that can bind TATP, thus increasing its sensitivity.
  • the TiO 2 nanotubes have excellent charge transport properties after annealing which makes them suitable for detecting binding events that occur on the nanotube surface.
  • electrochemical anodization is considered simple, inexpensive, and easily scalable to large area synthesis.
  • the present methodology fabricates self-ordered and vertically oriented TiO 2 nanotubular templates using an ultrasound assisted anodization process. The ultrasonication results in better ordering of the nanotubes.
  • Templates of TiO 2 nanotubular oxide arrays are formed by anodization of the Ti foils (0.1 mm thick) in an electrolytic solution consisting of 0.5 wt% NH 4 F+ 5 vol% H 2 O in ethylene glycol under an ultrasonically agitated condition using an ultrasonic bath (100 W, 42 KHZ, Branson 2510R-MT). A two-electrode configuration is used for anodization.
  • a flag shaped platinum (Pt) electrode serves as a cathode.
  • the anodization is carried out by varying the applied potential from 20 to 60 V using a rectifier (Agilent, E3640A). Varying the anodization potential can control the diameter of the tubes, and changing the anodization time can vary the length of the tubes.
  • the as-anodized TiO 2 templates are annealed in oxygen at 500 °C for 6 h to increase their electrical resistance. TiO 2 nanotubes tend to have very high electrical resistance so that when the nanotubes are biased appropriately and binding events occur between the functionalized nanotube and TATP, a current change is detected.
  • Ordered arrays of vertically oriented and free standing TiO 2 oxide nanotubes with diameters in the range of 100-200 nm, length in the range of 1-3 pm can be generated using the above-described processes.
  • IE ion exchange
  • PED pulsed electrodeposition
  • This method results in functionalization of the metal on the TiO 2 nanotubes and is successful when using Zn.
  • This method can be used with other metals identified as binders for TATP.
  • This technique leads to a uniform deposition of Ni ions on the TiO 2 nanotubes.
  • This method can be used to functionalized TiO 2 nanotubes with other metals as binders for VOCs.
  • Metal sensitized crystalline NTs are investigated using a variety of characterization techniques.
  • the following characterization method can be employed to establish the material properties and successful sensitization of the metal oxide NTs; (1) Glancing angle X-ray diffraction (GXRD) - for phase identification;
  • FESEM Field emission scanning electron microscopy
  • XPS X-ray photoelectron spectroscopy
  • the operating conditions of the sensor In order to achieve rapid detection of TATP, the operating conditions of the sensor must be optimized in to achieve rapid and clear detection. Under optimal conditions, the sensor response is on the order of seconds.
  • each substrate functionalized with a different metal In order to determine the appropriate biasing conditions for detection of TATP, each substrate functionalized with a different metal must be characterized for TATP to determine at what point the sensor is most sensitive. To achieve this, a voltage sweep from -5V to 5V (using a Gamry Potentiostat) is conducted on each sensor with associated TATP to see where the maximum change in current occurs when the TATP is introduced to the nanotube sensor array. Once this has been achieved, the sensor may be tested to quantify its performance at different concentrations of the TATP. These concentrations are from 100ppm down to 1 ppb. The goal is to optimize the sensor for detection of levels at the 1 pbb or lower, likely sufficient to detect low levels of TATP and other types of explosives.
  • TATP is synthesized in the laboratory in 5 mg quantities by following laboratory safety rules, for instance, in a quantity restricted to 5 mg at a time and stored in recommended low temperature. Tests may be conducted in controlled environment (glove box) with strict control of air composition using gas flow controllers. A known quantity of TATP is loaded onto a plastic cell. The closed ends of the cell have ports for inlet and outlet of purging gas. Known quantity of high purity nitrogen are purged through the container. The TiO 2 sensor array is placed in front of the outlet of the cell. Since vapor pressure of peroxide based explosives is high, the purging gas carries the vapor of the peroxide explosive to the TiO 2 sensor assembly.
  • the concentration of the explosive molecules to be detected by the sensor By varying the total mass of the peroxide explosive in the cell and varying the flow rate of purging gas, one can vary the concentration of the explosive molecules to be detected by the sensor.
  • An equilibrium concentration is established by recirculating the explosive molecule laden gas.
  • a calibration curve is generated to determine the concentration of the explosive molecules at different mass levels, different flow rates of purging gas, and different accumulation times.
  • the exact concentration of the explosive in the gas stream is determined from the master calibration curves.
  • the output signal for detecting explosive molecule is change in the current.
  • the potential scanning provides simultaneous reading of potential and current as a function of time.
  • the time vs. current plots at preset bias voltages during exposure and non-exposing conditions provides data on the sensing characteristics of the TiO 2 nanotube sensor. The same tests may be repeated for nitrate based explosives.
  • sensor performance is preferably satisfactory in various environmental conditions.
  • selectivity and sensitivity of the sensor are adaptable to ambient air which contains many chemical compounds.
  • the present sensor may be affected by changes in humidity and temperature and these changes may be accounted for in data analysis. It is also well known that ambient air is full of chemical compounds that come from various sources including vehicle emissions, pollution from industrial plants, and chemicals. Examples of such compounds are methane, ethane, isobutene, propene, acetone and others.
  • the effect of moisture on the operative of the present sensor is minimal when compared to signals from TATP.
  • An environmental chamber (Vacuum Atmosphere Corporation) with precise control over these parameters may be used to compensate effects of humidity, temperature, and gas flow.
  • the sensor is placed in the chamber and exposed to the explosive molecule. During each experiment, the temperature is changed from -10°C to 50° (just beyond the range of temperatures the sensor is expected to operate in). A similar experiment may be done for humidity going from 0-100% in increments of 5%.
  • Potential effects of the rate of gas flow over the sensor can be anticipated by changing the volumetric flow rate from 1 cubic foot/min (CFM) to 200 CFM in increments of 10.
  • CFM cubic foot/min
  • the average noise value of the sensor is measured in air. Then a calibration curve is generated with known concentrations (starting at 100ppm) reducing the concentration until the sensor response is three times the height of the noise. This yields the absolute limit of detection. Quantification limit is determined by adjusting the concentration to 10 times the noise which gives the lowest concentration at which we can state the concentration of the explosive molecule.
  • the TATP vapor can be separated by utilizing low cost MEMS based gas chromatography micro-channels using at front end to the sensor and delivered to the sensor. Since the TATP vapor is known, the elution time can be predicted and the sensor can be switched on only at the expected time the TATP vapor of interest exits (or is expected to exit) the micro-channels. This portable preprocessing step would help insure only the chemical of interest is delivered to the nanosensor and minimize the effect of confounding gases in TATP sample. Ideally this method minimizes false negatives and false positives.
  • the present disclosure aims at a sensor with a small footprint having an integrated air sampling system for bringing explosive vapor phase to the sensor material, a battery based power system and a signal processing system.
  • the air sampling system is integrated with the optimized sensor material and required electronics.
  • the TiO 2 sensor array is integrated into a microchannel network to create a small convenient package for use in the field.
  • the small dimensions of the microchannel have the advantage of reducing the diffusion distance the TATP molecules travel to reach the sensor array, thus speeding the detection time.
  • Channel heights range from 10 microns -100 microns.
  • the active air sampling component is integrated into the channel network to draw samples into the microchannel network.
  • FIG. 10 shows a conceptual design for a TiO 2 sensor integrated into a microchannel.
  • a sensor as described herein may have a single air intake or include a recirculation air intake. Total size of the packaged sensor array is about 6 by 6 cm.
  • the microchannel network may be made of PDMS (polydimethylsiloxane) attached to a base sensor substrate, for instance, titanium.
  • the electronic hardware needed for operation of the sensor consists of potentiostat that provides the bias voltage and measures the current under different sensing conditions.
  • potentiostats are available off the shelf (EmStat) with a footprint size 6 x 5 x 1 .5 cm. These units may be integrated with the packaged sensor array.

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Abstract

L'invention concerne un dispositif de détection d'explosifs comprenant un boîtier définissant une chambre interne, au moins un orifice d'entrée et au moins un orifice de sortie communiquant avec ladite chambre. Un capteur disposé à l'intérieur de ladite chambre comprend un réseau de nanotubes fonctionnalisés avec un ou plusieurs ions métalliques afin de détecter au moins un type de composé moléculaire trouvé dans des engins explosifs ou lié chimiquement à un tel composé moléculaire.
PCT/US2021/048210 2020-09-01 2021-08-30 Capteurs à base de nanotubes de titane fonctionnalisés pour la détection d'engins explosifs improvisés (eei) WO2022051219A1 (fr)

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Citations (6)

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Publication number Priority date Publication date Assignee Title
WO2011154939A1 (fr) * 2010-06-08 2011-12-15 Ramot At Tel-Aviv University Ltd. Nanostructures fonctionnalisées servant à détecter des composés azotés
RU127466U1 (ru) * 2012-12-05 2013-04-27 Федеральное государственное автономное образовательное учреждение высшего профессионального образования "Уральский федеральный университет имени первого Президента России Б.Н. Ельцина" Модуль обнаружения взрывчатых веществ в воздухе с наноструктурированным сенсорным элементом
US8542024B2 (en) * 2010-12-23 2013-09-24 General Electric Company Temperature-independent chemical and biological sensors
US8673219B2 (en) * 2010-11-10 2014-03-18 Invention Science Fund I Nasal passage insertion device for treatment of ruminant exhalations
US9964528B2 (en) * 2011-09-29 2018-05-08 Commissariat A L'energie Atomique Et Aux Energies Alternatives Use of transition-metal oxide nanoparticles as sensitive materials in chemical sensors for detecting or assaying vapors of target molecules
US10705047B2 (en) * 2012-10-29 2020-07-07 University Of Utah Research Foundation Functionalized nanotube sensors and related methods

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011154939A1 (fr) * 2010-06-08 2011-12-15 Ramot At Tel-Aviv University Ltd. Nanostructures fonctionnalisées servant à détecter des composés azotés
US8673219B2 (en) * 2010-11-10 2014-03-18 Invention Science Fund I Nasal passage insertion device for treatment of ruminant exhalations
US8542024B2 (en) * 2010-12-23 2013-09-24 General Electric Company Temperature-independent chemical and biological sensors
US9964528B2 (en) * 2011-09-29 2018-05-08 Commissariat A L'energie Atomique Et Aux Energies Alternatives Use of transition-metal oxide nanoparticles as sensitive materials in chemical sensors for detecting or assaying vapors of target molecules
US10705047B2 (en) * 2012-10-29 2020-07-07 University Of Utah Research Foundation Functionalized nanotube sensors and related methods
RU127466U1 (ru) * 2012-12-05 2013-04-27 Федеральное государственное автономное образовательное учреждение высшего профессионального образования "Уральский федеральный университет имени первого Президента России Б.Н. Ельцина" Модуль обнаружения взрывчатых веществ в воздухе с наноструктурированным сенсорным элементом

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