Chemical sensors containing carbon nanotubes, method for making same, and uses therof

Abstract

A device is disclosed for detecting at least one chemical compound comprising at least one carbon nanotube with several graphene layers, on which is grafted at least one molecule bearing group G1 capable of reacting with the chemical compound or a precursor of such a group G1. The uses and the method of making such a device is also disclosed.

Claims

1. A device for detecting at least one chemical compound, the device comprising at least one carbon nanotube with several graphene layers, wherein at least one molecule bearing a group G.sub.1 capable of reacting with the chemical compound or a precursor of the group G.sub.1 is grafted on the carbon nanotube with several graphene layers, wherein the carbon nanotube with several graphene layers is annealed under an inert atmosphere in a temperature above 1500? C. after being prepared, and before being grafted.

2. The device according to claim 1, wherein the carbon nanotube has a length of between about 1 ?m and about 1 mm.

3. The device according to claim 1, wherein the molecule to be grafted is a cleavable aryl salt selected from the group consisting of aryl diazonium salts, aryl ammonium salts, aryl phosphonium salts and aryl sulfonium salts, the aryl group bearing a group G.sub.1 capable of reacting with the chemical compound or a precursor of the group G.sub.1.

4. The device according to claim 1, wherein the molecule to be grafted is a cleavable aryl salt of the following formula (I):
RN.sub.2.sup.+,A.sup.?(I) wherein: A represents a monovalent anion and R represents an aryl group R bearing a group G.sub.1 capable of reacting with the chemical compound or a precursor of the group G.sub.1.

5. The device according to claim 3, wherein the aryl group is selected from the group consisting of aromatic or heteroaromatic carbon structures, consisting of one or more aromatic or heteroaromatic rings each including 3 to 8 atoms, the heteroatom(s) including N, O, P or S.

6. The device according to claim 4, wherein A is selected from the group consisting of halides, haloborates, perchlorates, sulfonates, alcohoholates and carboxylates.

7. The device according to claim 1, wherein the molecule grafted on the carbon nanotube is a polymer or copolymer mainly derived from several identical and/or different monomer units, said polymer or copolymer bearing at least one group G.sub.1 capable of reacting with said chemical compound or a precursor of the group G.sub.1.

8. The device according to claim 7, wherein the monomer units are monomers which are polymerizable via a radical route.

9. The device according to claim 8, wherein the monomers are selected from monomers of the following formula (II): ##STR00002## and wherein the groups R.sub.1 to R.sub.4, either identical or different, represent a non-metal monovalent atom selected from the group consisting of a halogen atom, a hydrogen atom, a saturated or unsaturated chemical group such as an alkyl, aryl group, a nitrile, a carbonyl, an amine, an amide or a COOR.sub.5 group wherein R.sub.5 represents a hydrogen atom or a C.sub.1-C.sub.12, or a C.sub.1-C.sub.6 alkyl group.

10. The device according to claim 1, wherein the group G.sub.1 capable of reacting with the chemical compound is selected from the group consisting of hydroxyl, thiol, azide, epoxide, azyridine, amine, nitrile, isocyanate, thiocyanate, nitro, amide, halide notably alkyl halide, carboxylic acid and ester functions.

11. The device according to claim 1, further comprising a support; and two electrodes positioned on the support, wherein the carbon nanotube is configured to ensure electric contact between the two electrodes.

12. The device according to claim 11, wherein the electrodes have an interdigitated comb configuration.

13. The device according to claim 1, wherein the nanotube has an orientation substantially perpendicular with respect to the two electrodes.

14. A system comprising at least two devices according to claim 1.

15. A method of using at least one device according to claim 1 for detecting and optionally quantifying one or more gaseous chemical compounds.

16. The method according to claim 15, wherein the gaseous chemical compound is selected from the group consisting of volatile organic compounds, hydrogen, carbon monoxide, carbon dioxide, chlorine and chlorinated compounds, ammonia, organo-phosphorus gases, hydrocyanic acid, thionyl chloride, phosphene, tetrahydrofurane, methane and dimethyl methyphosphonate.

17. A method for preparing a device for detecting at least one chemical compound according to claim 1, wherein the method comprises depositing on two electrodes, at least one carbon nanotube with several graphene layers, wherein at least one molecule bearing a group G.sub.1 capable of reacting with the chemical compound or a precursor of the group G.sub.1 is grafted on the carbon nanotube with several graphene layers, and wherein the carbon nanotube ensures electric contact between the electrodes, wherein the carbon nanotube with several graphene layers is annealed in a temperature above 1500? C. in an inert atmosphere after being prepared, and before being grafted.

18. The method according to claim 17, wherein deposition is carried out by dielectrophoresis.

19. The method according to claim 17, wherein the method comprises grafting on the carbon nanotube the molecule bearing a group G.sub.1 capable of reacting with the chemical compound or a precursor of the group G.sub.1.

20. The method according to claim 17, wherein the method comprises: annealing the carbon nanotube with several graphene layers, placing the annealed nanotube in contact with a solution S.sub.2 containing at least one molecule bearing a group G.sub.1 capable of reacting with the chemical compound or a precursor of the group G.sub.1 or at least one precursor of the latter to form a mixture; submitting the mixture to non-electrochemical conditions so as to graft on the nanotube, the molecule or the precursor; recovering the grafted nanotube obtained and depositing the grafted nanotube on two electrodes, notably by dielectrophoresis.

21. The device according to claim 5, wherein the aryl group is mono-substituted or poly-substituted, and wherein the substituent(s) contain one or more hetero-atoms or C.sub.1-C.sub.6 alkyl groups.

22. The device according to claim 8, wherein the monomer units comprise molecules of the ethylene type.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of the principle of a device according to the present invention.

(2) FIG. 2 shows the initial resistance of the sensor versus the number of drops (8 ?L per drop) deposited on the electrodes with and without dielectrophoresis.

(3) FIG. 3 shows optical microscopy images of multi-walled carbon nanotubes deposited on interdigitated electrodes by dielectrophoresis after deposition of a suspension drop (FIG. 3A) and without dielectrophoresis after depositing sixteen suspension drops (FIG. 3B).

(4) FIG. 4 shows optical microscopy images of multi-walled carbon nanotubes deposited on the interdigitated electrodes by dielectrophoresis after depositing a suspension drop (5 mg/L), the carbon nanotubes being either crude (FIG. 4A), or annealed (FIG. 4B).

(5) FIG. 5 shows the curves for detecting chlorine at a content of a 100 ppb (diluted in nitrogen) of sensors based on ?crude? and ?annealed? nanotubes. The normalized resistance, i.e. the measured resistance divided by the initial resistance, is plotted in ordinates versus the time expressed in minutes.

(6) FIG. 6 shows the curve for detecting chlorine at a content of 27 ppb (diluted in nitrogen) by means of a sensor according to the invention based on annealed nanotubes. The normalized resistance, i.e. the measured resistance divided by the initial resistance, is plotted in ordinates versus the time expressed in minutes.

(7) FIG. 7 shows scanning electron microscopy images of ?crude? nanotubes (FIG. 7A where the arrows indicate the presence of iron-based particles in the core of the nanotubes), of functionalized ?crude? nanotubes (FIG. 7B), of annealed nanotubes (removal of iron) (FIG. 7C) and of functionalized annealed nanotubes (FIG. 7D).

(8) FIG. 8 shows optical microscopy images of crude multi-sheet carbon nanotubes functionalized by groups -Ph-CH.sub.2NH.sub.2 (FIG. 8A) or of multi-sheet carbon nanotubes annealed and functionalized with groups -Ph-CH.sub.2NH.sub.2 (FIG. 8B).

(9) FIG. 9 shows the comparison of the curves for detecting chlorine at a content of 100 ppb (diluted in nitrogen) between the sensors based on ?crude? nanotubes and sensors according to the invention based on functionalized nanotubes.

(10) FIG. 10 shows the comparison of the curves for detecting chlorine at a content of 100 ppb (diluted in nitrogen) between the sensors based on annealed nanotubes and the sensors according to the invention based on annealed and functionalized nanotubes.

(11) FIG. 11 shows the comparison of the curves for detecting chlorine at a content of 100 ppb (diluted in nitrogen) between the sensors according to the invention either based on functionalized nanotubes, annealed or not.

DETAILED DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

Example 1: Preparation of Suspensions of Long Multi-Sheet Carbon Nanotubes

(12) The suspensions of different concentrations (1?100 mg/L) of long multi-sheet carbon nanotubes (400 ?m) in isopropanol are prepared with an ultrasonic probe. In this example, the suspensions are subject to ultrasounds for 8 minutes with a power of 250 W. Up to 10 mg/L, the suspensions are (visibly) stable for several hours.

(13) For more concentrated suspensions, flocculation or sedimentation of the nanotubes appears after a few tens of minutes. The suspensions having a nanotube concentration of 5 to 10 mg/L are used for making sensors based on the use of non-functionalized nanotubes.

(14) The suspensions of functionalized nanotubes, as for them, are stable in isopropanol for a few hours or even a few days at concentrations of less than 100 mg/L. The suspensions having a nanotube concentration in the range from 20 to 100 mg/L are used for preparing sensors based on functionalized nanotubes.

Example 2: Effect of Dielectrophoresis During the Preparation of Sensors According to the Invention

(15) The applied dielectrophoresis conditions are a 5 MHz sinusoidal 20 V peak-to-peak voltage.

(16) The initial resistance of a sensor depending on the number of drops (8 ?L per drop) deposited on the electrodes with and without dielectrophoresis was investigated (FIG. 2). The nanotube concentration for the suspension used for both sensors is 5 mg/L.

(17) In this example, with dielectrophoresis, it is possible to reduce by a factor of 16 the number of deposited drops in order to attain the proper initial resistance value.

(18) Further, the optical microscopy image of multi-walled carbon nanotubes deposited on the interdigitated electrodes by dielectrophoresis, after depositing a suspension drop, reveals that the nanotubes are quasi individual and have a preferential orientation perpendicular to the electrodes (FIG. 3A). The nanotubes are, on the contrary, organized as a cluster as viewed on the optical microscopy image of the multi-walled carbon nanotubes deposited on the interdigitated electrodes without any dielectrophoresis, after depositing sixteen drops of the suspension (FIG. 3B).

Example 3: Effect of Annealing on Carbon Nanotubes

(19) This example aims at comparing a device based on ?crude? carbon nanotubes and a device based on carbon nanotubes annealed at 2,000? C. for one hour under argon.

(20) FIGS. 4A and 4B are optical microscopy images obtained for respectively ?crude? or ?annealed? multi-walled carbon nanotubes, deposited on the interdigitated electrodes by dielectrophoresis after depositing one drop of suspension (5 mg/L).

(21) The sensitivity of such sensors based on ?crude? and ?annealed? nanotubes towards chlorine diluted in nitrogen at a content of 100 ppb was also compared. The results shown in FIG. 5 show that the sensitivity (S?(RR.sub.0)/R.sub.0)*100) at 50 mins of the sensor based on ?annealed? nanotubes is twice greater, as compared with that of the sensor based on ?crude? nanotubes (26 versus 12.5).

(22) Further, the sensitivity (S?(RR.sub.0)/R.sub.0)*100) towards chlorine diluted in nitrogen at a content of 27 ppb of a sensor based on ?annealed? nanotubes and measured at 50 minutes is 7% (FIG. 6).

Example 4: Elaboration of Sensors Based on Multi-Sheet Carbon Nanotubes Functionalized by -Ph-CH2NH2 Groups

(23) The functionalization of the nanotubes is carried out by following the procedure described hereafter.

(24) Fifteen mg of nanotubes are subject to an ultrasound treatment for 8 mins at 250 W in 30 mL of 0.5 M HCl with 3.10.sup.?3 mol of 4-aminobenzyl amine. To this mixture, is then added 3.10.sup.?3 mol of sodium nitrite dissolved in 30 mL of distilled water. Four g of iron powder are added to the whole which is transferred into an ultrasound pan.

(25) After 90 minutes of reaction, the iron powder is removed by means of a magnetic bar and the mixture is filtered and then thoroughly washed with ethanol, acetone and distilled water. The nanotubes are then dried in the oven at 120? C. The functionalized nanotubes are subject to a treatment with ultrasound again with isopropanol for 8 mins at 250 W in an amount from 20 to 100 mg/L. The suspensions are stable for several hours or even one day.

(26) The crude or ?annealed? nanotubes, either functionalized or not, are observed by transmission electron microscopy. Iron-based particles are present in the core of non-functionalized ?crude? nanotubes (FIG. 7A) and a thin polymer layer (<10 nm) covers the surface of the functionalized ?crude? nanotubes (FIG. 7B). The iron was removed from the ?annealed? nanotubes (FIG. 7C) and a thin polymer layer (<20 nm) covers the surface of the functionalized ?annealed? nanotubes.

(27) The crude or ?annealed? functionalized (-Ph-CH.sub.2NH.sub.2) multi-sheet nanotubes are deposited on the interdigitated electrodes by dielectrophoresis with three drops (8 ?L) with respectively a 20 mg/L and a 40 mg/L suspension (FIGS. 8A and 8B).

(28) The functionalization leads to a 120% sensitivity gain (at 200 mins) (S?(RR.sub.0)/R.sub.0)*100), toward chlorine diluted in nitrogen at a content of 100 ppb, in sensors compared with sensors based on crude nanotubes without any functionalization (FIG. 9).

(29) The functionalization leads to a 35% sensitivity gain (at 200 mins) (S?(RR.sub.0)/R.sub.0)*100), toward chlorine diluted in nitrogen at a content of 100 ppb, in sensors based on ?annealed? and functionalized nanotubes compared with sensors based on ?annealed? nanotubes without any functionalization (FIG. 10).

(30) The sensors based on ?annealed? and functionalized nanotubes have a 40% sensitivity gain (S?(RR.sub.0)/R.sub.0)*100) (at 200 mins) toward chlorine diluted in nitrogen at a content of 100 ppb, as compared with sensors based on functionalized nanotubes but not annealed beforehand (FIG. 11).

REFERENCES

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