PHOTOCATALYTICALLY ACTIVE SUPPORT WITH TIO2 BASED MATERIALS

Abstract

The present invention relates to a method for producing a support at least micrometric in size, photocatalytically active and at least in the visible range, containing nanocrystals each composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of at least one other metal or semi-metallic oxide, comprising the following steps, from an acidic aqueous reaction medium, at a heating temperature of between 20 and 60° C.: a step of adding the titanium oxide precursor, or a mixture of the titanium oxide precursor and the precursor of the other oxide, in the acidic aqueous reaction medium, and a condensation step on or inside the support, by spraying onto the support or immersing the support in the aqueous reaction medium, for a specific period of condensation, a heating step, the support allowing the nanocrystals to be crystallized, without using surfactant, in the aqueous reaction medium, a step of rinsing with water and a recovery step on the one hand of the support on which the crystallization took place, these nanocrystals being attached by covalent bonds to the support, and on the other hand of a residual solution.

Claims

1. A method for producing a photocatalyst support at least micrometric in size and photocatalytically active at least in the visible range, containing nanocrystals each composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of at least one other metal or semi-metallic oxide, comprising the following steps, without using surfactant: a1) preparing and heating an acidic aqueous solution to a given pH between 0 and 6, and at a temperature between 20° C. and 60° C., with no surfactant, by adding hydrochloric acid, a2) adding a titanium oxide precursor, or a mixture of a titanium oxide precursor and of at least one other precursor of another oxide, to the acidic aqueous solution, a precipitate forming in the acidic aqueous reaction medium composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of another oxide, from the titanium oxide precursor, which is a titanium alkoxide, or a mixture of this titanium oxide precursor with at least one other precursor of another metal or semi-metallic oxide, a3) agitating the acidic aqueous reaction medium so as to dissolve the precipitate formed in step a2), a4) reaction between the precursors obtained in step a3) and the support, to condense the precursors which are attached by covalent bonds to the surface of the support, by: spraying onto the support or immersing the support in the aqueous reaction medium for a specific time period, a5) heating, the heating temperature being between 40° C. and 95° C., the support, at least micrometric in size, making it possible to crystallize the titanium oxide precursors, or a mixture of a titanium oxide precursor and of at least one other precursor of another nanocrystal oxide, on the surface thereof, without using surfactant, in the acidic aqueous reaction medium the precursors crystallizing, once attached to the surface of the support, a6) rinsing in water and recovering: on the one hand, the support on which the crystallization took place, the nanocrystals obtained being composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of at least one other metal or semi-metallic oxide, these nanocrystals being attached to the support by covalent bonds, and on the other hand, a residual solution.

2. The method of producing a support according to claim 1, wherein the method is carried out in open air.

3. The method for producing a support as claimed in one of claim 1, wherein the acidic aqueous reaction medium is produced without cosolvent.

4. The method for producing a support as claimed in claim 3, wherein the acidic aqueous reaction medium is produced without alcohol.

5. The method of producing a support according to claim 1, wherein step a5) has: a first sub-step of heating from 30° to 60° C. for a given first period of time; a second sub-step of heating from 50° to 90° C. for a second period of time.

6. The method of producing a support according to claim 5, wherein: for the first heating sub-step of step a5), the first heating time is several hours; for the second heating sub-step of step a5), the second heating time is several hours.

7. The method of producing a support according to claim 6, wherein: for the first heating sub-step of step a5), the first heating time is at least 24 hours; for the second heating sub-step of step a5), the second heating time is at least 24 hours.

8. The method of producing a support according to claim 1, wherein in step a1): the pH is chosen equal to 5 so as to obtain nanocrystals on the support having a stable Brookite crystalline form, or the pH is between 0 and 2 so as to obtain nanocrystals having a Rutile crystalline form.

9. The method for producing a support as claimed in claim 1, wherein the metal or semi-metallic oxide is chosen from SiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, CeO.sub.2, MgO, ZnO, CuO, NiO.

10. The method for producing a support as claimed in claim 1, wherein the other metal oxide is WO.sub.3, and in step a1), the pH is between 0 and 1, so as to obtain nanocrystals having an Anatase crystalline form of at least 90%.

11. The method of producing a support according to claim 1, wherein in step a6), the support is: (a) immersed in a nitric acid bath, rinsed with water and then dried, or (b) immersed in a metal solution among Ag.sup.+, Cu.sup.2+, Zn.sup.2+, Al.sup.3+, Mg.sup.+, rinsed with water, dried at ambient temperature, then immersed in a nitric acid bath and rinsed.

12. A photocatalyst support, photocatalytically active at least in the visible range and at least micrometric in size, produced by the method according to claim 1, having nanocrystals on the surface thereof attached by covalent bonds, these nanocrystals being composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of another metallic or semi-metallic oxide.

13. The photocatalytically active support as claimed in claim 12, characterized in that the active support comprises from 80 to 95 mol % of TiO.sub.2 and from 5 to 20 mol % of another metal or semi-metallic oxide.

14. The photocatalytically active support as claimed in claim 12, with nanocrystals having a stable Brookite crystalline form.

15. The photocatalytically active support as claimed in claim 12, with nanocrystals having a Rutile crystalline form.

16. The photocatalytically active support as claimed in claim 12, wherein the metal or semi-metallic oxide is chosen from the following list: SiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, CeO.sub.2, MgO, ZnO, CuO, NiO.

17. The photocatalytically active support as claimed in claim 12, with nanocrystals having an Anatase crystalline form of at least 90%, the other metal oxide being WO.sub.3.

18. The photocatalytically active support as claimed in claim 12, wherein the support consists of the following material: polymers; carbon felt/graphite or activated charcoal; glass; textile; micrometric silicates; cement.

19. The photocatalytically active support as claimed in claim 12, wherein the support is micrometric, millimetric, centimetric or metric in size.

Description

DESCRIPTION OF THE DRAWINGS

[0033] This study was conducted with a TiO.sub.2-based material (composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of another oxide) on basalt textile fabric, on carbon felt, on polymers such as polystyrene, on a cotton/polyester support (chemist lab coat), on silica supports of variable macrometric and micrometric size (filtration silica and sand).

[0034] The organic pollutants used are methyl orange (concentration 10 mg/L (or ppm)) and blue bromophenol (concentration 20 mg/L (or ppm)), glyphosate and toluene (concentration 1 mg/L (or ppm)); and they were subjected to 3 hours of radiation (for example, with a Xenon 300 W lamp with UV filter).

[0035] This study shows that with the TiO.sub.2 of the present invention, photocatalysis is possible with radiation in the visible range (which uses little energy to achieve it) and is greater than with a less active commercial TiO.sub.2 alone. Most studies show that the state-of-the-art TiO.sub.2s in particular enable photocatalysis with UV radiation, which uses more energy to achieve it than radiation in the visible range.

[0036] The features and advantages of the invention will emerge from the following detailed description, with reference to drawings which are nonlimiting and given by way of illustration, among which:

[0037] FIG. 1 shows an application diagram of the TiO.sub.2-based materials on support;

[0038] FIG. 2 represents the three TiO.sub.2-based crystalline structures obtained by virtue of the invention;

[0039] FIG. 3 shows a graph illustrating the breakdown of the dyes (methyl orange—MO, bromophenol blue—BBP) on basalt textile fabric; FIG. 3 shows the adsorption of the dye molecules on the untreated textile but greater efficacy in the presence of nanocrystals; the nanocrystals are securely attached in the fibers, and there is no TiO.sub.2 in the solution;

[0040] FIG. 4 shows a graph illustrating the breakdown of bromophenol blue (BBP) concentrated on previously used basalt textile fabric (recycling); FIG. 4 shows that the reuse of textiles is possible without loss of activity, as well as the long lifespan of the textiles;

[0041] FIG. 5 shows a graph illustrating the breakdown of bromophenol blue (BBP) on carbon felt; FIG. 5 shows the adsorption of BBP molecules on carbon felt, but even more reactivity (total disappearance of organic molecules in solution) in the presence of TiO.sub.2; the nanocrystals are securely attached in the felt, and there is no TiO.sub.2 in the solution;

[0042] FIG. 6 shows a graph illustrating the breakdown of methyl orange (MO) on polystyrene and on a polyester/cotton mixture (65%/35%); FIG. 6 shows a polystyrene and polyester/cotton mixture made reactive with the addition of TiO.sub.2; the nanocrystals are securely attached on these two supports, and there is no TiO.sub.2 in the solution;

[0043] FIG. 7 shows a graph illustrating the breakdown of methyl orange (MO) on Fontainebleau sand and sieve pellets (mixture of Al.sub.2O.sub.3 and Fe.sub.2O3); the sand and granules are made reactive with the addition of TiO.sub.2; TiO.sub.2 adheres to SiO.sub.2-based supports but also containing Al.sub.2O.sub.3, Fe.sub.2O.sub.3 on the micrometric scale; the nanocrystals are securely attached to these two supports, and there is no TiO.sub.2 in the solution;

[0044] FIG. 8 represents a graph illustrating the breakdown of methyl orange (MO) on filtration silica (micrometric); micrometric silica is made reactive with the addition of TiO.sub.2; TiO.sub.2 adheres to SiO.sub.2-based supports on the micrometric scale; the silica was treated with Cull grafting before treatment with TiO.sub.2 to improve the amount of silanol groups on the surface, the reaction occurring with no increase in silanol groups;

[0045] FIG. 9 represents polystyrene beads alone with methyl orange (left) at t=0, and polystyrene/Ti beads with methyl orange after radiation;

[0046] FIG. 10 represents photos taken after radiation and drying of the textile: textile without Ti with bromophenol blue (top), textile/Ti immersion with bromophenol blue (middle), textile/Ti by spray with bromophenol blue (bottom);

[0047] FIG. 11 represents an image in transmission electron microscopy—Activated carbon/Ti;

[0048] FIGS. 12a and 12b represent scanning electron microscopy images—sand/Ti. FIG. 12a corresponds to an image of a sand grain/Ti with an image width of 413 μm and FIG. 12b corresponds to an image of the sand grain/Ti with an image width of 16.99 μm and shows TiO.sub.2 crystals attached to the surface.

DETAILED DESCRIPTION OF THE INVENTION

[0049] The present invention relates to a method for preparing an aqueous reaction medium composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of another oxide, from a titanium oxide precursor which is a titanium alkoxide, or from a mixture of this titanium oxide precursor with at least one other precursor of another metal or semi-metallic oxide.

[0050] In an alternative not described here, the titanium oxide precursor could be chosen from Na.sub.2Ti.sub.3O.sub.7 or a derivative.

[0051] The preparation is carried out in an acidic aqueous medium at a given pH, without using surfactants, and comprises the following steps:

[0052] a1) preparing and heating an acidic aqueous solution to a given pH of between 0 and 6, and at a temperature of between 20° C. and 60° C., with no surfactant, by adding hydrochloric acid,

[0053] a2) adding a titanium oxide precursor, or a mixture of a titanium oxide precursor and at least one other precursor of another oxide to the acidic aqueous solution, a precipitate then forming,

[0054] a3) vigorous agitation of the aqueous reaction medium so as to dissolve the precipitate formed in step a2).

[0055] Advantageously, hydrochloric acid is added, for example between 30% and 37% by weight/volume.

[0056] In a first embodiment of the method, in step a1) the pH of the reaction medium is chosen around 5 so as to obtain nanocrystals on the support having a stable Brookite crystalline form, and photocatalytically reactive at least in the visible range.

[0057] In a second embodiment of the method, in step a1), the pH of the reaction medium is chosen around 0-2 so as to obtain nanocrystals having a Rutile crystalline form, and which are photocatalytically reactive at least in the visible range.

[0058] The metal or semi-metallic oxide may be chosen from SiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, CeO.sub.2, MgO, ZnO, CuO, NiO.

[0059] In a third embodiment of the method, the other metal oxide being WO.sub.3, and in step a1), the pH of the reaction medium is between 0 and 1 so as to obtain nanocrystals having an Anatase crystalline form of at least 90%, photocatalytically reactive at least in the visible range.

[0060] The present invention also relates to a method for producing a support that is at least micrometric in size and photocatalytically active at least in the visible range (and even more so in the UV range), containing nanocrystals each composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of at least one other metal or semi-metallic oxide.

[0061] This method for producing the support comprises the following additional steps, starting from the acidic aqueous reaction medium obtained above at a heating temperature of between 20° C. and 60° C.:

[0062] a4) a step of reaction between the precursors (titanium oxide precursor, or a mixture of a titanium oxide precursor and a precursor of the other oxide) obtained in step a3) and the support, in order to condense the precursors that attach thereto by covalent bonds on its surface, on or inside the support, by: [0063] spraying onto the support or [0064] immersing the support in the aqueous reaction medium for the specific duration of the synthesis,

[0065] a5) a step of heating,

[0066] the support allowing the nanocrystals to crystallize, without using surfactant, in the aqueous reaction medium,

[0067] a6) a step of rinsing in water and recovery:

[0068] on the one hand, of the support on which the crystallization took place, the nanocrystals obtained being composed of from 80 to 100 mol % of TiO.sub.2 and from 0 to 20 mol % of at least one other metal or semi-metallic oxide, these nanocrystals being attached to the support by covalent bonds,

[0069] and on the other hand, of a residual solution.

[0070] Thus, the invention makes it possible to produce photocatalytically active supports by incorporating materials based on titanium oxide under mild conditions (no surfactant, aqueous medium, requiring little energy, without excessive temperatures),

[0071] This residual solution could be re-implanted in the reaction medium for a new synthesis depending on whether or not the stoichiometry of the reaction with titanium alkoxide and the surface was complete.

[0072] For silica, the surface was prepared upstream of step a4) in order to increase the attachment points (O—) (Cull grafting).

[0073] All the steps of the method can be carried out in open air, i.e., in contact with ambient air. Advantageously, in a non-limiting manner, the acidic aqueous solution is produced without cosolvent, such as alcohol.

[0074] The agitation of the acidic aqueous reaction medium can be carried out until the disappearance of the precipitate.

[0075] The agitation of the acidic aqueous reaction medium can be carried out between 800 and 1200 rpm.

[0076] Advantageously, the technique used is not dip coating.

[0077] When a support is added, the condensation reaction of the surfactant-free precursors in step a4) is very fast and is performed between 30 and 90 minutes. TiO.sub.2 precursors will make covalent bonds that attach to the surface on or inside the support in order to subsequently grow crystals.

[0078] In the present invention, the TiO.sub.2 precursors are formed after a first formation of precipitate, which is vigorously agitated in order to dissolve it in the medium. Then, in this medium, the TiO.sub.2 precursors attach to the support on the surface thereof, on or inside, and crystallize only on the surface of the support in a single step. In other words, in the present invention, TiO.sub.2 precursors crystallize and grow only after attaching to the support.

[0079] Furthermore, the nanocrystals obtained on the support are generally more heterogeneous in shape and size than the nanocrystals obtained with no support and no surfactant, with only the acidic aqueous reaction medium.

[0080] Step a5) may have: [0081] a first sub-step of heating from 30° to 60° C. for a given first period of time; [0082] a second sub-step of heating from 50° to 90° C. for a second period of time.

[0083] For example, [0084] for the first heating sub-step of step a5), the first heating time may be several hours; [0085] for the second heating sub-step of step a5), the second heating time may be several hours.

[0086] In step a5), the specific heating time can be at least 24 hours to make the material active and crystalline. It should be noted that crystallization can be performed at room temperature or at a higher temperature, below a temperature for which the crystal morphology would change.

[0087] Furthermore, in step a6), the support/materials provided with TiO2-based nanocrystals can be immersed in a HNO.sub.3 bath (optional step), then rinsed in water (to remove the unattached particles).

[0088] Thus, during steps a4) and a5), there are condensation reactions, then crystallization, and finally growth in the size of the crystals and homogenization.

[0089] The TiO.sub.2 obtained very early may be composed, for example, of very small crystals approximately 5 nm squared, while that of 24 hrs at 50° C. and 24 hrs at 90° C. has homogeneous rod-shaped crystals 5 nm by 25 nm.

[0090] Advantageously, the duration of the condensation reaction (polymerization) of step a4) is less than 90 minutes, and the heating temperature is between 40° C. and 95° C., for a heating time of at least 24 hours during the heating step a5).

[0091] Advantageously, the support is millimetric, centimetric or metric in size.

[0092] The support may consist of the following material: polymers (polystyrene, polyester); carbon felt/graphite or active charcoal; glass; textile (cotton, basalt); micrometric silicates (filtration silica, sand); cement.

[0093] To create the support, in step a1): [0094] the pH is chosen around or equal to 5 so as to obtain nanocrystals on the support having a stable Brookite crystalline form, [0095] or the pH is between 0 and 2 so as to obtain nanocrystals having a Rutile crystalline form.

[0096] The support at least micrometric in size may comprise, like the metal or semi-metallic oxide associated with the TiO.sub.2, the following metal oxides from the list: SiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, CeO.sub.2, MgO, ZnO, CuO, NiO.

[0097] In another embodiment, the other metal oxide associated with the TiO.sub.2 is WO.sub.3, and in step a1), the pH is between 0 and 2 so as to obtain nanocrystals having an Anatase crystalline form of at least 90%, photocatalytically reactive at least in the visible range.

[0098] When the nanocrystals are produced on the support by immersion of the support in the aqueous reaction medium, the steps of the method can be defined more precisely as follows: [0099] the support is placed in an oven at 50° C. in a hermetically-sealed container (to avoid any evaporation), under static conditions, for at least 24 hours, then 90° C. for at least 24 hours, [0100] the support is then thoroughly rinsed with water.

[0101] The support can then be dried in an oven at 50° C.

[0102] Advantageously, depending on the nature of the support and the type of oxides present, in order to increase the reactivity and if the support allows it, but not required and non-limiting, the support may then be either:

(a) immersed in a 64% nitric acid bath for 10 minutes, thoroughly rinsed with water and then dried, or
(b) immersed in an ammonia metal solution, from among Ag.sup.+, Cu.sup.2+, Ni.sup.2+, Zn.sup.2+, Al.sup.3+, Mg.sup.+, for 10 minutes, rinsed with water, dried at room temperature, then immersed in a nitric acid bath, for example at 64% and for 10 minutes, thoroughly rinsed with water.

[0103] When the nanocrystals are produced on the support by immersion of the support in the acidic aqueous reaction medium, the steps of the method may be defined more precisely as follows: [0104] the support is immersed in the reaction medium; [0105] depending on its nature and composition, the support is either:
1) placed in the oven under static conditions, or
2) kept in the reaction medium with moderate agitation (400 rpm); in both cases, the temperature of the medium is kept at 50° C. for at least 24 hours and then at 90° C. for at least 24 hours; [0106] the support is then thoroughly rinsed with water.

[0107] The support can then be dried in an oven at 50° C.

[0108] Then, advantageously, but not required and non-limiting, in order to increase the reactivity and if the support allows it, the support may then be either:

a) immersed in a 64% nitric acid bath for 10 minutes, thoroughly rinsed with water and then dried at room temperature,
b) immersed in a metal solution with a pH between 10.5 and 11.5, from among Ag.sup.+, Cu.sup.2+, Ni.sup.2+, Zn.sup.2+, Au.sup.2+, Al.sup.3+, Mg.sup.+, for 10 minutes, rinsed with water, dried at room temperature, then immersed in a 64% nitric acid bath for 10 minutes, rinsed thoroughly with water, then finally dried again at room temperature.

[0109] The present invention also relates to the use of the photocatalytically active support with crystallized nanocrystals on the surface thereof, for the photocatalytic breakdown of compounds.

[0110] The compounds may be chosen from dyes, pharmaceutical active ingredients, herbicides, pesticides, fungicides, hormones, hydrocarbons and volatile organic compounds such as formaldehyde, and BTEX.

[0111] Thus, the breakdown of glyphosate and toluene from TiO.sub.2 according to the present invention is illustrated.

[0112] Breakdown of glyphosate on a basalt-based textile tissue, for example, in 3 hours:

TABLE-US-00001 Efficacy (ppm/mg or Types CO (ppm) C (ppm) Efficacy (%) ppm/cm.sup.2) Textile 1 1 0 0 without Ti Textile/Ti 1 0.49 51% 0.17 Glyphosate 1 1 — —

[0113] The presence of TiO.sub.2 on the textile is essential for eliminating glyphosate molecules.

[0114] The nanocrystals are securely attached to the support, and there is no TiO.sub.2 in the solution.

[0115] Breakdown of toluene on basalt-based textile:

TABLE-US-00002 Types CO (ppm) C (ppm) Efficacy (%) Efficacy (ppm/cm.sup.2) Textile 1 0.49 51 0.17 without Ti Textile/Ti 1 0.36 64 0.21 Toluene 1 1 — —

[0116] The TiO.sub.2 supply improves the elimination of the toluene.

[0117] The nanocrystals are securely attached to the textile, and there is no TiO.sub.2 in the solution.

[0118] Several applications are possible, for example: [0119] 1) air quality, particularly indoor (breakdown of VOCs), with the development of paints or air filters, [0120] 2) water pollution control (breakdown of molecules such as BTEX, pesticides, dyes, etc.), [0121] 3) anti-fouling or anti-stain paint, with the development of paints, antibacterial treatment with the development of air filters, self-cleaning coatings (glass, cement, sand, etc.).