Nanoporous Matrix and Use Thereof

Abstract

The invention relates to a nanoporous polyalkoxysilane sol-gel matrix and to a process for producing such a nanoporous polyalkoxysilane sol-gel matrix containing indigo carmine, wherein said process comprises the following steps: a) synthesizing a gel from tetramethoxysilane or from a mixture of tetramethoxysilane and another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, a fluoroalkyltrimethoxysilane, a fluoroalkyltriethoxysilane, a chloroalkylmethoxysilane, a chloroalkylethoxysilane, an aminopropyltriethoxysilane and mixtures thereof, the synthesis being carried out in an aqueous medium in the presence of a polar organic solvent and of the indigo carmine at a temperature ranging from 20 to 70 C., b) drying the gel obtained in step a) so as to obtain a nanoporous polyalkoxysilane sol-gel matrix containing indigo carmine.

Claims

1. A process for preparing a nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo, said process comprising the following steps: a) synthesis of a gel from tetramethoxysilane or from a mixture of tetramethoxysilane and of another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, a fluoroalkyltrimethoxysilane, a fluoroalkyltriethoxysilane, a chloroalkylmethoxysilane, a chloroalkylethoxysilane, an aminopropyltriethoxysilane, and mixtures thereof, the synthesis being performed in aqueous medium in the presence of a polar organic solvent and of carmine indigo at a temperature ranging from 20 to 70 C., b) drying of the gel obtained in step a) so as to obtain a nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo.

2. The process as claimed in claim 1, wherein the synthesis of the gel in step a) is a one-pot synthesis.

3. The process as claimed in claim 1, wherein the synthesis of the gel in step a) is performed using tetramethoxysilane or a mixture of tetramethoxysilane and of another organosilicon precursor chosen from phenyltrimethoxysilane (PhTMOS), phenyltriethoxysilane (PhTEOS), a fluoropropyltrimethoxysilane, a fluoropropyltriethoxysilane, a chloropropylmethoxysilane, a chloropropylethoxysilane, an aminopropyltriethoxysilane, and mixtures thereof.

4. The process as claimed in claim 3, wherein the synthesis of the gel in step a) is performed using tetramethoxysilane.

5. The process as claimed in claim 3, wherein the synthesis of the gel in step a) is performed using a mixture of tetramethoxysilane and of another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, a fluoropropyltrimethoxysilane, a chloropropylmethoxysilane, an aminopropyltriethoxysilane, and mixtures thereof.

6. The process as claimed in claim 5, wherein the synthesis of the gel in step a) is performed using a mixture of tetramethoxysilane and of another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, trimethoxy(3,3,3-trifluoropropyl)silane, (3-chloropropyl)trimethoxysilane and (3-aminopropyl)triethoxysilane.

7. The process as claimed in claim 5, wherein the synthesis of the gel in step a) is performed using a mixture of tetramethoxysilane and of phenyltrimethoxysilane or of phenyltriethoxysilane.

8. The process as claimed in claim 3, wherein the synthesis of the gel in step a) is performed using a mixture of tetramethoxysilane and of another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, a fluoroalkyltrimethoxysilane, a chloroalkyltrimethoxysilane, and mixtures thereof.

9. The process as claimed in claim 3, wherein the molar proportions of tetramethoxysilane/other organosilicon precursor are between 0.97/0.03 and 0.6/0.4.

10. The process as claimed in claim 1, wherein the polar organic solvent is methanol.

11. The process as claimed in claim 1, wherein the molar proportions of polar organic solvent and of water are, respectively, between 4 and 10.

12. A nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo, obtained from tetramethoxysilane or from a mixture of tetramethoxysilane and of another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, a fluoroalkyltrimethoxysilane, a fluoroalkyltriethoxysilane, a chloroalkylmethoxysilane, a chloroalkylethoxysilane, an aminopropyltriethoxysilane, and mixtures thereof, wherein it has a specific surface area of from 55060 m.sup.2.Math.g.sup.1 to 89080 m.sup.2.Math.g.sup.1 and a proportion of micropores of greater than 30%.

13-15. (canceled)

16. An ozone abatement filter comprising the nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo as claimed in claim 12.

17. An ozone sensor comprising the nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo as claimed in claim 12.

18. A method of selectively trapping ozone present in the air comprising contacting the air with the nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo as claimed in claim 12.

19. The method of claim 18, wherein the air is filtered through the nanoporous polyalkoxysilane sol-gel matrix present in an air filter.

20. The method of claim 18, wherein ozone collected in the nanoporous polyalkoxysilane sol-gel matrix containing carmine indigo is detected to measure the presence of ozone.

Description

FIGURES

[0058] FIG. 1: Perspective view of an exposure cell for performing spectrophotometry measurements on rays transmitted by a nanoporous matrix when subjected to radiation from a lamp in the UV-visible range, the cell having a fluidic circuit allowing the matrix to be exposed to a controlled flow rate of air.

[0059] FIG. 2: View in cross section of the exposure cell according to FIG. 3, illustrating in detail the internal fluid circuit, and also the optical assembly.

[0060] FIG. 3: A: Spectral evolution of the indigo-doped sensor of example 1 as a function of the time of exposure to a gaseous mixture containing 50 ppb of O.sub.3 (stream=200 mL.Math.min.sup.1, RH=5%, T=22 C.), B: calibration curve for the sensor established using the monoexponential kinetics of decline of the absorbance at 617 nm as a function of time.

[0061] FIG. 4: A: Spectral variation of the indigo-doped sensor of example 1 as a function of time during exposure to gaseous mixtures of ozone (200 ppb) at 50% RH and 22 C. (stream=260 mL.Math.min.sup.1). B: kinetics of decline of the absorbance of the sensor at 617 nm as a function of time. The rate of disappearance of the band is given by the slope at the origin of the curve.

EXAMPLES

[0062] I. Preparation and Analysis of Nanoporous Sol-Gel Matrices

[0063] Analysis of the liquid nitrogen adsorption-desorption isotherm (77 K) with the DFT (density functional theory) model used for determining the specific surface area and the pore diameter was performed with the Autosorb 1 machine from Quantachrome.

Example 1: TMOS Matrix Doped with Carmine Indigo

[0064] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g/mol), TMOS (CAS number: 681-84-5, molar mass=152.2 g/mol and density d=1.023 mg/L), methanol (CH.sub.3OH, molar mass=32.04 g/mol, purity 98%). Plastic mold 12*12 cm in size and multi-wells 16*10*4 mm in size.

[0065] Procedure for 100 mL of sol: 38.89 mL of TMOS and 42.29 mL of methanol are poured into a round-bottomed flask and mixed with magnetic stirring for 1 minute. 18.82 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 1 hour at room temperature in the tightly sealed flask. The solution is poured into a plastic mold placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0066] After drying, sol-gel blocks in the form of dark blue parallelepipeds close to 6*5*2 mm in size are obtained. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

[0067] The specific surface area for adsorption of the material obtained by analysis of the liquid nitrogen adsorption-desorption isotherm with the DFT (density functional theory) model is 89080 m.sup.2.Math.g.sup.1. The proportion of micropores is 84% and the diameter is centered around 1.0 nm. With these pore sizes, the carmine indigo molecules cannot leave the matrix. Ozone can readily diffuse into the porous network, unlike large-sized molecules such as monocyclic aromatic compounds.

Example 2: TMOS/PhTMOS Matrix Doped with Carmine Indigo

[0068] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g.Math.mol.sup.1), TMOS (CAS number: 681-84-5, molar mass=152.2 g.Math.mol.sup.1 and density d=1.023 mg.Math.cm.sup.3), PhTMOS (CAS number: 2996-92-1, molar mass=198.29 g.Math.mol.sup.1 and density d=1.062 g.Math.cm.sup.3), methanol (CH.sub.3OH, molar mass=32.04 g.Math.mol.sup.1, density=0.792 g.Math.cm.sup.3, purity 98%). Plastic multi-well mold (16*10*4 mm).

[0069] Procedure for 100 mL of sol: 34.623 mL of TMOS and 4.926 mL of PhTMOS are placed in 41.837 mL of methanol in a round-bottomed flask and mixed with magnetic stirring for 1 minute. 18.615 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 1 hour at room temperature in the tightly sealed flask. The solution is poured into a plastic mold placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0070] In the present example, the molar proportions of the reagents are TMOS/PhTMOS/MeOH/H.sub.2O: 0.9/0.1/4/4. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

[0071] The specific surface area for adsorption of the material obtained by analysis of the liquid nitrogen adsorption-desorption isotherm with the DFT (density functional theory) model is 80050 m.sup.2.Math.g.sup.1. The proportion of micropores is 40% and the diameter is centered around 11 nm. The diameter of the mesopores is centered around 25 . With these pore sizes and the tortuosity of the porous network, the carmine indigo molecules cannot leave the matrix. Ozone can readily diffuse into the porous network, unlike large-sized molecules such as monocyclic aromatic compounds.

Example 3: TMOS/PhTEOS Matrix Doped with Carmine Indigo

[0072] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g.Math.mol.sup.1), TMOS (CAS number: 681-84-5, molar mass=152.2 g.Math.mol.sup.1 and density d=1.023 mg.Math.cm.sup.3), PhTEOS (CAS number: 780-69-8, molar mass=240.37 g.Math.mol.sup.1 and density=0.996 g.Math.cm.sup.3), methanol (CH.sub.3OH, molar mass=32.04 g.Math.mol.sup.1, density=0.792 g.Math.cm.sup.3, purity 98%). Plastic multi-well mold (16*10*4 mm).

[0073] Procedure for 100 mL of sol: 26.365 mL of TMOS and 14.252 mL of PhTEOS are placed in 41.097 mL of methanol in a round-bottomed flask and mixed with magnetic stirring for 1 minute. 18.285 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 1 hour at room temperature in the tightly sealed flask. The solution is poured into a plastic mold placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0074] In the present example, the molar proportions of the reagents are TMOS/PhTEOS/MeOH/H.sub.2O: 0.75/0.25/4.3/4.3. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

[0075] The specific surface area for adsorption of the material obtained by analysis of the liquid nitrogen adsorption-desorption isotherm with the DFT (density functional theory) model is 63050 m.sup.2.Math.g.sup.1. The proportion of micropores is 70% and the diameter is centered around 1.1 nm. The diameter of the mesopores is centered around 22 . With these pore sizes and the tortuosity of the porous network, the carmine indigo molecules cannot leave the matrix. Ozone can readily diffuse into the porous network, unlike large-sized molecules such as monocyclic aromatic compounds.

Example 4: TMOS/PhTEOS Matrix Doped with Carmine Indigo

[0076] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g.Math.mol.sup.1), TMOS (CAS number: 681-84-5, molar mass=152.2 g.Math.mol.sup.1 and density d=1.023 mg.Math.cm.sup.3), PhTEOS (CAS number: 780-69-8, molar mass=240.37 g.Math.mol.sup.1 and density=0.996 g.Math.cm.sup.3), methanol (CH.sub.3OH, molar mass=32.04 g.Math.mol.sup.1, density=0.792 g.Math.cm.sup.3, purity 98%). Plastic multi-well mold (16*10*4 mm).

[0077] Procedure for 100 mL of sol: 31.90 mL of TMOS and 9.13 mL of PhTEOS are placed in 40.81 mL of methanol in a round-bottomed flask and mixed with magnetic stirring for 1 minute. 18.16 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 1 hour at room temperature in the tightly sealed flask. The solution is poured into a plastic mold placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0078] In the present example, the molar proportions of the reagents are TMOS/PhTEOS/MeOH/H.sub.2O: 0.85/0.15/4/4. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

[0079] The specific surface area for adsorption of the material obtained by analysis of the liquid nitrogen adsorption-desorption isotherm with the DFT (density functional theory) model is 56050 m.sup.2.Math.g.sup.1. The proportion of micropores is 40% and the diameter is centered around 1.1 nm. The diameter of the mesopores is centered around 24 . With these pore sizes and the tortuosity of the porous network, the carmine indigo molecules cannot leave the matrix. Ozone can readily diffuse into the porous network, unlike large-sized molecules such as monocyclic aromatic compounds.

Example 5: TMOS/3CITMOS Matrix Doped with Carmine Indigo

[0080] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g.Math.mol.sup.1), TMOS (CAS number: 681-84-5, molar mass=152.2 g.Math.mol.sup.1 and density d=1.023 mg.Math.cm.sup.3), 3ClTMOS (CAS number: 2530-87-2, purity 97%, molar mass=198.72 g.Math.mol.sup.1 and density=1.09 g.Math.cm.sup.3), methanol (CH.sub.3OH, molar mass=32.04 g.Math.mol.sup.1, density=0.792 g.Math.cm.sup.3, purity 98%). Plastic multi-well mold (16*10*4 mm).

[0081] Procedure for 100 mL of sol: 30.488 mL of TMOS and 9.627 mL of 3ClTMOS are placed in 41.445 mL of methanol in a round-bottomed flask and mixed with magnetic stirring for 1 minute. 18.44 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 1 hour at room temperature in the tightly sealed flask. The solution is poured into a plastic mold placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0082] In the present example, the molar proportions of the reagents are TMOS/3ClTMOS/MeOH/H.sub.2O: 0.8/0.2/4/4. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

Example 6: TMOS/3FTMOS Matrix Doped with Carmine Indigo

[0083] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g.Math.mol.sup.1), TMOS (CAS number: 681-84-5, purity 97%, molar mass=152.2 g.Math.mol.sup.1 and density d=1.142 mg.Math.cm.sup.3), 3FTMOS (CAS number: 429-60-7, molar mass=218.25 g.Math.mol.sup.1 and density=0.996 g.Math.cm.sup.3), methanol (CH.sub.3OH, molar mass=32.04 g.Math.mol.sup.1, density=0.792 g.Math.cm.sup.3, purity 98%). Plastic multi-well mold (16*10*4 mm).

[0084] Procedure for 100 mL of sol: 25.854 mL of TMOS and 16.108 mL of 3FTMOS are placed in 40.167 mL of methanol in a round-bottomed flask and mixed with magnetic stirring for 1 minute. 17.872 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 1 hour at room temperature in the tightly sealed flask. The solution is poured into a plastic mold placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0085] In the present example, the molar proportions of the reagents are TMOS/3FTMOS/MeOH/H.sub.2O: 0.7/0.3/4/4. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

[0086] The specific surface area for adsorption of the material obtained by analysis of the liquid nitrogen adsorption-desorption isotherm with the DFT (density functional theory) model is 46060 m.sup.2.Math.g.sup.1. The proportion of micropores is 40% and the diameter is centered around 1.6 nm. With these pore sizes, the carmine indigo molecules cannot leave the matrix. Ozone can readily diffuse into the porous network, unlike large-sized molecules such as monocyclic aromatic compounds.

Example 7: TMOS/APTES Matrix Doped with Carmine Indigo

[0087] Reagents: carmine indigo (Sigma-Aldrich, CAS number 860-22-0, molar mass=466.35 g.Math.mol.sup.1), TMOS (CAS number: 681-84-5, purity 97%, molar mass=152.2 g.Math.mol.sup.1 and density d=1.142 mg.Math.cm.sup.3), APTES (CAS number: 919-30-2, molar mass=208.33 g.Math.mol.sup.1 and density=0.933 g.Math.cm.sup.3), methanol (CH.sub.3OH, molar mass=32.04 g.Math.mol.sup.1, density=0.792 g.Math.cm.sup.3, purity 98%). Plastic multi-well mold (16*10*4 mm).

[0088] Procedure for 100 mL of sol: 33.91 mL of TMOS and 1.574 mL of APTES are placed in 45.582 mL of methanol maintained at low temperature (25 C.) in a round-bottomed flask and mixed with magnetic stirring for 2 minutes. 16.934 mL of an aqueous carmine indigo solution at 0.15 mol.Math.L.sup.1 are added to the mixture. The mixture is stirred for 2 minutes and the solution is poured into a plastic mold and then placed in a desiccator, which is covered hermetically with an aluminum membrane. When gelation takes place, the aluminum membrane is replaced with a porous film. Drying is continued in the same desiccator until the solvents have completely evaporated off and the monolith has shrunken to stable final dimensions.

[0089] In the present example, the molar proportions of the reagents are TMOS/APTES/MeOH/H.sub.2O: 0.97/0.03/5/4. The indigo content in the nanoporous matrix is 0.28 mol.Math.dm.sup.3.

[0090] The specific surface area for adsorption of the material obtained by analysis of the liquid nitrogen adsorption-desorption isotherm with the DFT (density functional theory) model is 82070 m.sup.2.Math.g.sup.1. The proportion of micropores is 20% and the diameter is centered around 17 . The proportion of mesopores is 80% and the diameter is centered around 27 .

[0091] II. Ozone Trapping Tests

[0092] The trapping tests of the indigo-doped matrices exposed to O.sub.3 were performed to quantify the trapping efficiency and thus to demonstrate their utility as ozone abatement filters. The matrices in parallepipedal form obtained in Examples 1 to 6 were ground coarsely and screened (passed through two screens) to obtain millimeter-sized granules.

[0093] The filters were prepared in the form of plastic syringes (6 mL volume) equipped with two end pieces, one of which is connected via a tube to the gaseous mixture generator. The outlet end piece of the syringe is connected to a tube which goes into a fume cupboard. These syringes were filled with the various granules and exposed to a mixture of air containing ozone.

[0094] The analysis bench includes mass flowmeters and a humidity injection system to allow exposure of the filters as a function of the flow rate of the gaseous mixture at various humidities. Ozone is generated with an O.sub.3 generator and its concentration is measured upstream and downstream of the filter by means of an O.sub.3 analyzer.

[0095] The flow rate of the stream upstream of the cartridge is 2 L/min and the flow rate downstream was measured for each cartridge so as to check that the pressure loss is approximately the same for all the cartridges. The degree of trapping, , is measured for each type of filter as a function of the exposure parameters. It is defined according to:

[00001]$=\frac{\left[O.Math..Math.3_{\mathrm{upstream}}\right]-\left[O.Math..Math.3_{\mathrm{downstream}}\right]}{\left[O.Math..Math.3_{\mathrm{upstream}}\right]}.Math.100.Math.\%$

[0096] The ozone concentration ([O3.sub.upstream]) chosen, 40 ppb, corresponds to a mean value of the ozone content in the exterior air. The effect of the humidity of the stream of gaseous mixture (% RH=50 and 72) was also studied. The trapping performance qualities were compared for exposure times ranging from 1 minute to 480 hours and up to 20 days for certain tests. Moreover, a comparison of the trapping performance was performed with a commercial ozone trap based on KI and a trap based on active charcoal.

[0097] The data obtained are collated in the tables below.

TABLE-US-00001 TABLE 1 Compared performances of trapping of O.sub.3 at low concentration for various materials Upstream stream = 2 L/min, [O.sub.3].sub.upstream = 42 3 ppb, RH = 50% Degree of trapping Mat 1 Mat 2 Commercial Time (h) (1.79 g) (1.73 g) KI (1.5 g) 1 100% 100% 80% 24 94% 100% 61% 48 82% 100% 48% 72 72% 100% 168 59% 94% 384 30% 64% 480 22% 55% Downstream flow rate 1.32 1.22 1.44 (L/min)

[0098] The materials Mat 1 (Example 1) and Mat 2 (Example 2) both have small pores, but Mat 2 is more hydrophobic, which explains its better performance and service life. Comparison with the commercial product containing KI shows the superiority of the sol-gel materials which simultaneously combines a large specific surface area for adsorption suitable for trapping O.sub.3.

[0099] Tests at high relative humidity, RH=72%, were also performed to compare the efficiency of O.sub.3 trapping under conditions in which the water vapor concentration is very high and might contribute toward clogging the pores of the filter and reducing its efficiency.

TABLE-US-00002 TABLE 2 Compared performances of trapping of O.sub.3 at high humidity of an indigo-doped nanoporous filter with an active charcoal filter Upstream stream = 2 L/min, RH = 72% Degree of trapping Mat 2 CA RBAA3 Exposure time (h) [O.sub.3] (ppb) (1.79 g) (1.75 g) 24 43 5 100% 100% 48 43 5 100% 90% 72 43 5 98% 89% 96 43 5 92% 79% Downstream flow rate 1.27 1.16 (L/min)

[0100] The active charcoal chosen (Norit RBAA-3 rods, Fluka) has very small pores (pore diameter <11 ) and a specific surface area for adsorption of 960 m.sup.2.Math.g.sup.1. The data collated in table 2 show that Mat 2 traps ozone better than active charcoal at high humidity.

[0101] Tests were also performed at a very high concentration of ozone.

TABLE-US-00003 TABLE 3 Compared performances of trapping of O.sub.3 at a high concentration of O.sub.3 for various indigo-doped materials Upstream stream = 2 L/min, [O.sub.3].sub.upstream = 475 10 ppb, RH = 50% Degree of trapping Mat 1 Mat 2 Mat 3 Mat 6 Mat 7 Time (min) (1.79 g) (1.79 g) (1.79 g) (1.79 g) (1.79 g) 10 99.5% 100% 100% 90.8% 100% 20 99.5% 97.3% 99.4% 89.2% 97.3% 180 74.0% 57.6% 55.0% 50.0% 300 51.0% 71.2% 52.0% 39.0% 20.0% 1440 22.0% 26.0% 31.0% 2.0% Downstream flow rate 1.32 1.22 1.22 1.30 1.42 (L/min)

[0102] The materials Mat 1, Mat 2 and Mat 3, which have a high proportion of micropores, have the best O.sub.3 trapping efficiencies at high concentration of the pollutant. Mat 7 is the material which has a high percentage of mesopores and is the least efficient.

[0103] Moreover, one of the advantages of the filter based on carmine indigo is the color change that is visible to the naked eye, which makes it possible to assess its state of saturation. Specifically, the color of the filter changes gradually as ozone is trapped, from blue via green to yellow. For material 2, the filter was still not saturated after 20 days of exposure to a stream of 2 L/min with an O.sub.3 content of 423 ppb, at a relative humidity of 50%.

[0104] III. Measurement of Ozone with the Matrix of Example 1

[0105] The matrix (sensor) is positioned in an exposure cell including a fluidic circuit through which passes the gas stream mixture containing ozone. The exposure cell is equipped with two optical windows through which passes the analysis light conveyed by optical fibers and originating from a UV-visible lamp. After passing through the sensor, the transmitted light is collected by an Ocean-Optics miniature spectrophotometer and the collected data are transmitted to the computer.

[0106] This exposure cell 1 is illustrated in FIGS. 1 and 2 and comprises a body 1 which is composed of two parts 2,3, an upper part and a lower part, respectively. The nanoporous matrix M is positioned by an operator in a cavity 30 formed on the lower part 3, when the two parts 2,3 are dismantled. This cavity 30 is then closed in a gas tight manner by assembling the upper part 2 on the lower part 3.

[0107] The optical assembly comprises a first optical window, materialized by a traversing machined channel 20 from the upper part 2, emerging in the cavity 30, and through which passes the light conveyed by the optical fibers 4 and originating from the UV-visible lamp. A second optical window, materialized by a traversing machined channel 33 from the lower part 3 allows the collection of the rays transmitted by the nanoporous matrix. The collection is performed by optical fibers 5 which convey the collected rays to the Ocean-Optics miniature spectrophotometer.

[0108] The fluidic circuit is materialized on the lower part 3 and comprises a first connection 6 connected to an air feed pipe, which emerges in a traversing machined channel 31 of the lower part 3 conveying the air originating from the pipe to the cavity 30. Another traversing machined channel 32 of the lower part 3 allows the evacuation of the gas from the cavity 30 to a second connection 7, connected to an evacuation pipe.

[0109] A spectrum is collected before exposure. During exposure, the spectra are collected every 10 minutes for 48 hours.

[0110] The gas stream containing ozone at various concentrations originates from a model 165 Megatec ozone generator. The concentration was varied from 3 to 1000 ppb. The ozone concentration was controlled beforehand with a model 49C Megatec ozone analyzer. The exposure flow rate was set at 260 mL.Math.min.sup.1, and is controlled with a mass flowmeter. The humidity of the mixture is provided with a second stream of nitrogen humidified to 100% (by sparging in a bottle of water) with which is mixed the ozone stream.

[0111] An example of spectra collected during the exposure of the matrix of Example 1 to a gaseous mixture containing 50 ppb of ozone (stream=200 mL.Math.min.sup.1, RH=5%, T=22 C.) is shown in FIG. 3.

[0112] The decline kinetics were established from curves of variation of absorbance at 617 nm as a function of time for various ozone concentrations. The reaction rates were deduced from the monoexponential decline kinetics and reported as a function of the ozone concentration. The calibration curve thus established shows a linear variation of the rate of loss of color with the ozone concentration with a coefficient of 7.1510.sup.5 min.sup.1.Math.ppb.sup.1. The detection limit is 3 ppb for an exposure of 60 minutes to a flow rate of 260 mL.Math.min.sup.1. The sensitivity of such a sensor could be further improved by increasing the exposure flow rate of the sensor.

[0113] The color variation of the ozone sensor is also visible to the naked eye. The sensor, which is initially blue (carmine indigo alone), becomes green in the presence of yellow-colored isatin resulting from the reaction of the carmine indigo with ozone (blue+yellow=green), and then yellow at the end of exposure when all of the carmine indigo has disappeared in favor of the isatin.

[0114] IV. Measurement of Ozone with the Matrix of Example 1 in the Presence of 50% Humidity

[0115] The process was performed as in point III, but the relative humidity level of the exposure stream was 50%. The results obtained are collated in FIG. 4. It is observed that the response of the sensor is indeed sensitive and reproducible even with this high humidity level of the order of 50%.

[0116] The calibration curve established for a relative humidity of 50% shows that the response of the sensor is slower with a rate of 2.610.sup.5 ppb.sup.1.Math.min.sup.1, i.e. 2.8 times slower than that obtained at 5% RH. Water interferes by decreasing the trapping of ozone in the nanoporous sensor.

REFERENCES

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