Adsorbent and photocatalytic decontamination gel, and method for decontaminating surfaces using said gel

Abstract

An adsorbent and photocatalytic decontamination gel consisting of a colloidal solution comprising, preferably consisting of: 8% to 30% by weight, preferably 10% to 30% by weight, more preferably 15% to 20% by weight, better still 15% to 20% by weight, the value 15% being excluded, even better still 16% to 20% by weight, for example 20% by weight of TiO.sub.2, optionally doped, relative to the weight of the gel; optionally 0.01% to 10% by weight, preferably 0.1% to 5% by weight, relative to the weight of the gel, of at least one dye and/or of at least one pigment; optionally 0.1% to 2% by weight, relative to the weight of the gel, of at least one surfactant; optionally 0.05% to 5% by weight, preferably 0.05% to 2% by weight, relative to the weight of the gel, of at least one superabsorbent polymer; and the balance of solvent.

Claims

1. Adsorbent and photocatalytic decontamination gel consisting of a colloidal solution comprising: 15% to 20% by weight of TiO2, optionally doped, relative to the weight of the gel; optionally, 0.01% to 10% by weight relative to the weight of the gel of at least one dye and/or at least one pigment; optionally, 0.1% to 2% by weight relative to the weight of the gel, of at least one surfactant; optionally, 0.05% to 5% by weight relative to the weight of the gel, of at least one super-absorbent polymer; and the balance solvent, said solvent being selected from among mixtures of water in a proportion of 40% to 56% by weight, and of ethanol, in a proportion of 24% to 42.5% by weight relative to the weight of gel; and said gel having a pH of 4 or higher.

2. The gel according to claim 1 having a weak acidic pH of 4 to less than 7; or a neutral pH of 7; or a weak basic pH of more than 7 to less than 9; or a very basic pH of 9 or higher.

3. The gel according to claim 1, wherein the pH of the gel is adjusted by the addition of a mineral base.

4. The gel according to claim 1, wherein the TiO2 is in the form of particles of a mean size of 2 to 200 nm.

5. The gel according to claim 1 having a storage time of at least one year.

6. The method for decontaminating at least one surface of a substrate made of a solid material, said surface being contaminated by at least one contaminating species on said surface, wherein at least one cycle is performed comprising the following successive steps: a) applying the gel according to claim 1 on said surface; b) maintaining the gel on the surface at least for a sufficient time for the gel to absorb the contaminating species, for the contaminating species then to be adsorbed on the surface of the TiO2 particles, and for the gel to dry and form a dry and solid residue containing said contaminating species adsorbed on the surface of the TiO2 particles; c) removing the dry and solid residue containing said contaminating species adsorbed in the gel on the surface of the TiO2 particles.

7. The method according to claim 6, wherein the substrate is made of at least one solid material selected from among metals and metal alloys; polymers; glasses; cements and cement materials; mortars and concretes; plasters; bricks; natural or artificial stone; and ceramics.

8. The method according to claim 6, wherein the contaminating species is selected from among ionic, chemical, biological, nuclear or radioactive contaminating species.

9. The method according to claim 8, wherein the contaminating species is an ionic contaminating species selected from among monovalent and multivalent metal ions.

10. The method according to claim 8, wherein the contaminating species is a biological contaminating species selected from among biotoxic species, bacteria, fungi, yeasts, viruses, toxins, pathogenic spores, prions, and protozoa.

11. The method according to claim 8, wherein the contaminating species is selected from among toxic gaseous chemical species.

12. The method according to claim 6, wherein the gel is applied to the surface to be decontaminated in a proportion of 100 g to 2000 g of gel per m2 of surface area, which generally corresponds to a gel thickness deposited on the surface of 0.1 mm to 2 mm.

13. The method according to claim 6, wherein the gel is applied to the solid surface by spraying, with a brush or with a float.

14. The method according to claim 6, wherein during all or part of step a), and/or during all or part of step b), the gel maintained on the surface is exposed to a visible radiation or to a A, B or C Ultraviolet radiation (UVA, UVB or UVC), or to another radiation, to inactivate, and/or degrade, and/or reduce, and/or destroy the contaminating species by photocatalysis.

15. The method according to claim 6, wherein (during step b), drying is carried out at a temperature of 1° C. to 50° C., and under a relative humidity of 20% to 80%.

16. The method according to claim 6, wherein the gel is maintained on the surface for a time of 2 to 72 hours.

17. The method according to claim 6, wherein the dry, and solid residue is in the form of particles of a size of 1 to 10 mm.

18. The method according to claim 6, wherein the dry solid residue is removed from the solid surface by brushing and/or vacuuming, suction.

19. The method according to claim 6, wherein the cycle is repeated 1 to 10 times using the same gel for each cycle, or using different gels for one or more cycle(s).

20. The method according to claim 6 wherein during step b) the gel, before complete drying, is rewetted with a solvent, preferably with the solvent of the gel applied during step a).

21. Adsorbent and photocatalytic decontamination gel consisting of a colloidal solution consisting of: 15% to 20% by weight of TiO2, optionally doped, relative to the weight of the gel; optionally, 0.01% to 10% by weight relative to the weight of the gel of at least one dye and/or at least one pigment; optionally, 0.1% to 2% by weight relative to the weight of the gel, of at least one surfactant; optionally, 0.05% to 5% by weight relative to the weight of the gel, of at least one super-absorbent polymer; and the balance solvent, said solvent being selected from among mixtures of water in a proportion of 40% to 56% by weight, and of ethanol, in a proportion of 24% to 42.5% by weight relative to the weight of gel; and said gel having a pH of 4 or higher.

22. The gel according to claim 3, wherein the mineral base is selected from among sodium hydroxide, potassium hydroxide, and mixtures thereof.

23. The method according to claim 6, wherein said surface is further contaminated by at least one contaminating species below said surface, in the depth of the substrate.

24. The method according to claim 7, wherein the substrate is made of at least one metals or metal alloy selected from the group consisting of stainless steel, painted steels, aluminium and lead.

25. The method according to claim 7, wherein the substrate is made of at least one polymer wherein the polymer is a plastic material or a rubber.

26. The method according to claim 25, wherein the plastic material or rubber is selected from the group consisting of poly(vinyl chloride)s, polypropylenes, polyethylenes, high density polyethylenes, poly(methyl methacrylate)s, poly(vinylidene fluoride)s, and polycarbonates.

27. The method according to claim 9, wherein the monovalent and multivalent metal ions are selected from the group consisting of chromium (VI), nickel (II), silver (I), cadmium (II), mercury (II), arsenic (III) and lead (II) ions.

28. The method according to claim 10, wherein the contaminating species is pathogenic spores.

29. The method according to claim 28, wherein the pathogenic spores is spores of Bacillus anthracis.

30. The method according to claim 10, wherein the biological contaminating species is a toxin selected from the group consisting of botulinum toxin or ricin.

31. The method according to claim 10, wherein the biological contaminating species is a Yersinia pestis bacteria.

32. The method according to claim 10, wherein the biological contaminating species is a vaccine virus.

33. The method according to claim 10, wherein the biological contaminating species is a viruses of haemorrhagic fevers.

34. The method according to claim 11, wherein the toxic gaseous chemical species is selected from the group consisting of neurotoxic or blistering gases.

35. The method according to claim 34, wherein the neurotoxic or blistering gases are selected from the group consisting of Sarin or agent GB, VX, Tabun or agent GA, Soman, Cyclosarin, diisopropyl fluorophosphonate (DFP), Amiton or agent VG, Parathion, mustard gas or agent H or agent HD, Lewisite or agent L, and agent T.

36. The method according to claim 17, wherein the particles are flakes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph illustrating the UV-Visible spectrum of the solution obtained in Example 3 after leaching of the flakes of a TiO.sub.2-based gel, namely the gel prepared in Example 1 in which the solvent is water and which was applied and dried in the dark.

(2) This graph is called «TiO.sub.2—H.sub.2O gel in the dark».

(3) The wavelength is given along the X-axis (in nm), and the absorbance along the Y-axis.

(4) FIG. 2 is a graph illustrating the UV-Visible spectrum of the solution obtained in Example 3 after leaching of the flakes of a comparative gel not conforming to the invention, containing SiO.sub.2, namely the gel prepared in Example 3 for which the solvent is water and which was applied and dried in the dark.

(5) This graph is called «SiO.sub.2—H.sub.2O gel in the dark».

(6) The wavelength is given along the X-axis (in nm), and the absorbance along the Y-axis.

(7) FIG. 3 is a graph illustrating the UV-Visible spectrum of the solutions obtained after leaching of the flakes of the gel («H.sub.2O-40 EtOH gel») according to the invention described in Example 5.

(8) These flakes were obtained either by drying under the radiation of an UV lamp (Curve A) or by drying under visible light (Curve B).

(9) For comparison, this graph also shows the UV-Visible spectrum (curve C) of the solution obtained after leaching of the flakes of a TiO.sub.2 gel, namely the gel prepared in Example 1 the solvent of which is water and which was applied and dried in the dark.

(10) The wavelength is given along the X-axis (in nm), and the absorbance along the Y-axis.

(11) FIG. 4 is a graph illustrating the UV-Visible spectrum of the solutions obtained after leaching of flakes of the gel («H.sub.2O gel» (Curve A), «H.sub.2O-24 EtOH gel» (Curve B), and «H.sub.2O-40 EtOH gel» (Curve C)) described in Example 7 (see Table 7).

(12) These flakes were obtained by drying under an UV lamp.

(13) For comparison, this graph also shows the UV-Visible spectrum (Curve D) of the solution obtained after leaching of the flakes of a TiO.sub.2 based gel of the invention, namely the gel prepared in Example 1, for which the solvent is water and which was applied and dried in the dark.

(14) The wavelength is given along the X-axis (in nm), and the absorbance along the Y-axis.

(15) FIG. 5 is a graph illustrating the change in viscosity as a function of shear rate of the «H.sub.2O gel» (Curve A) and of the «H.sub.2O-40EtOH gel» (Curve B) (see Example 8).

(16) The shear rate is given along the X-axis (in s−1) and the viscosity is given along the Y-axis (in Pa.Math.s).

(17) FIG. 6 is a graph giving the change in shear stress as a function of strain of the «H.sub.2O gel» (Curve A) and of the «H.sub.2O-40EtOH gel» (Curve B) (see Example 8).

(18) Strain (no unit) is given along the X-axis and shear stress (in Pa) along the Y-axis.

(19) FIG. 7 is a graph illustrating the change in loss of weight as a function of time for the «H.sub.2O gel» (Curve A), and of the «H.sub.2O-24EtOH gel» (Curve B) at 25° C. and 50% relative humidity (see Example 11).

(20) FIG. 8 is a photograph of the flakes obtained after drying the «H.sub.2O-24EtOH gel» in a boat of 2 mm depth (see Example 11).

(21) FIG. 9 is a graph illustrating the change in viscosity as a function of shear rate for the gels studied in Example 9.

(22) The shear rate (in s.sup.−1) is given along the X-axis and the viscosity (in Pa.Math.s) is given along the Y-axis.

(23) FIG. 10 is a graph illustrating the change in shear stress as a function of strain for the gels studied in Example 10.

(24) Strain (no unit) is given along the X-axis and shear stress (in Pa) is given along the Y-axis.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(25) The gel of the invention can easily be prepared at ambient temperature.

(26) For example, the gel of the invention can be prepared by dispersing, preferably gradually, the desired quantity of inorganic viscosifying agent(s), namely TiO.sub.2, in the form of particles e.g. of mean diameter 2 to 200 nm in the solvent of the gel.

(27) This dispersion can be obtained via mechanical agitation e.g. with a mechanical agitator equipped with a three-blade impeller. The rotation speed is 200 rpm for example and agitation time 3 to 5 minutes for example.

(28) After dispersion, an opaque white liquid suspension is obtained generally having a pH of about 3.5.

(29) The pH is then gradually increased, under continued agitation, using a base e.g. sodium hydroxide 0.1 M NaOH, until the pH reaches 5 for example which will allow an opaque white viscous gel to form.

(30) When adding the base e.g. sodium hydroxide, the speed of agitation is gradually increased as and when the viscosity increases to arrive at about 400 to 600 rpm without any splashing. The gel is left under agitation for 2 to 5 minutes for example to obtain a fully homogeneous gel.

(31) It is noted here that the amount of base added e.g. sodium hydroxide can be considered to be negligible relative to the initial amount of solvent, and it can therefore be considered that the initial weight composition of TiO.sub.2 and of solvent remains valid once pH=5.

(32) The pH of the gel thus prepared is therefore weak acidic since it is 5.

(33) By continuing to increase the pH up to a pH of 7, it is possible to obtain a neutral gel conforming to the invention which therefore prevents chemical attack of the treated surfaces, and even a weak basic gel conforming to the invention at a slightly basic pH of above 7 to less than 9, or even a very basic gel conforming to the invention at a very basic pH of 9 or higher which therefore has degreasing properties, power, but does not attack the treated surfaces.

(34) In the neutral gel and weak basic gel, but also in the very basic gel, the amount of sodium hydroxide can generally always be considered to be negligible.

(35) In general, the gel of the invention must have a viscosity of less than 200 mPa.Math.s under shear of 1000 s.sup.−1 to allow spraying onto the surface to be decontaminated, at a distance (e.g. at a distance of 1 to 5 m) or close thereto (e.g. at a distance of less than 1 m, preferably 50 to 80 cm).

(36) The viscosity reset time is generally less than one second, and viscosity under low shear is higher than 10 Pa.Math.s so as not to run off on a vertical wall.

(37) The gel of the invention thus prepared is applied to the solid surface to be decontaminated of a substrate or solid material, in other words onto the surface having been exposed to contamination e.g. to a biological contamination.

(38) This contamination has already been described above. In particular, biological contamination may consist of one or more biological species already defined above.

(39) As already indicated above, in the gel of the invention TiO.sub.2—in addition to the role of inorganic viscosifying agent—acts as active decontamination agent e.g. active biological decontamination agent, allowing the removal, destruction or inactivation of a polluting, contaminating species e.g. a biological contaminating species.

(40) There is no limitation as to the constituent material of the surface to be decontaminated, the gel of the invention allowing the treatment of all kinds of materials even fragile materials without any damage.

(41) Even surfaces in materials such as alloys of light metals of aluminium type which could not be treated without being deteriorated by prior art gels, can be successfully treated with the gels of the invention.

(42) The gel of the invention does not generate any deterioration, erosion, chemical mechanical or physical attack of the treated material. The gel of the invention is therefore not in any manner detrimental to the integrity of the treated materials and even allows reuse thereof. For example, sensitive equipment such as military equipment is preserved and can be reused after decontamination, whilst monuments treated with the gel of the invention are absolutely not degraded and have their visual and structural integrity preserved.

(43) This material of the substrate can therefore be selected for example from among metals and alloys such as stainless steel, aluminium and lead; polymers such as plastic materials or rubbers among which mention can be made of PVC, PP, PE in particular HDPE, PMMA, PVDF, PC; glass; cements and cement materials; mortars and concretes; plaster; bricks; natural or artificial stone; ceramics.

(44) In all cases, irrespective of the material, the decontaminating efficacy by the gel of the invention is complete.

(45) The treated surface can be painted or non-painted.

(46) The gel of the invention is just as effective on porous materials such as cementitious matrices e.g. pastes, mortars and concretes, bricks, plaster or natural or artificial stone.

(47) The efficacy of treatment with the gel of the invention is generally total including on materials contaminated to a depth of several microns (see above).

(48) There is also no limitation as to the shape, geometry and size of the surface to be decontaminated, the gel of the invention and the method implementing the gel allowing the treatment of surfaces of large size, complex geometry for example having hollows, corners, recesses.

(49) The gel of the invention ensures efficient treatment not only of horizontal surface such as floors but also of vertical surfaces such as walls, partitions or inclined or overhanging surfaces such as ceilings.

(50) Compared with existing decontamination methods e.g. biological decontamination methods using liquids such as solutions, the decontamination method of the invention which uses a gel is particularly advantageous to treat materials of large surface area that cannot be transported or are installed outside. Since the method the invention uses a gel it allows in situ decontamination, preventing the spilling of chemical solutions into the environment and the dispersion of contaminating species.

(51) The gel of the invention may be applied to the surface to be treated using all applications methods known to the man skilled in the art.

(52) Conventional methods are spraying e.g. with a gun or application with a brush or float.

(53) For application by spraying the gel of the invention onto the surface to be treated, the colloidal solution can be conveyed for example via a low pressure pump e.g. a pump which applies a pressure of 7 bars or less i.e. about 7.Math.10.sup.5 Pascals.

(54) The jetting of the gel on the surface can be obtained using flat jet or round jet nozzle for example.

(55) There may be any distance between the pump and the nozzle e.g. it can be 1 to 50 m, in particular 1 to 25 m.

(56) The sufficiently short reset time of the viscosity of the gel of the invention allows the sprayed gels to adhere to all surfaces e.g. to walls.

(57) The quantity of gel deposited on the surface to be treated is generally 100 to 2000 g/m.sup.2, preferably 500 to 1500 g/m.sup.2, more preferably 600 a 1000 g/m.sup.2.

(58) The quantity of gel deposited per unit surface area and hence the thickness of the deposited gel has an impact on the drying rate.

(59) Therefore, when a film, a layer of gel is sprayed of thickness 0.5 mm to 2 mm onto the surface to be treated, the efficient contact time between the gel and the surface is then equivalent to its drying time, the period during which the active ingredient contained in the gel, here TiO.sub.2, will interact with the contamination.

(60) In the case of porous substrates e.g. cementitious matrices the action time of the decontamination solution, e.g. of the biocidal solution having penetrated into the core of the material, can be longer than the gel drying time in which case it is generally necessary either to carry out rewetting with the decontamination solution or to repeat gel spraying.

(61) In addition, it has surprisingly been shown that the quantity of deposited gel when it lies within the above-mentioned ranges and in particular when it is 500 g/m.sup.2 and higher and particularly within the range of 500 to 1500 g/m.sup.2, which corresponds to a minimum thickness of deposited gel e.g. 500 μm or thicker for a quantity of deposited gel of 500 g/m.sup.2 or higher, allows fractionating of the gel after drying into the form of vacuumable millimetre flakes e.g. of size 1 to 10 mm, preferably 2 to 5 mm.

(62) The quantity of deposited gel, and hence the thickness of deposited gel, preferably of 500 g/m.sup.2 or higher i.e. 500 μm, more preferably 1000 g/m.sup.2 or higher i.e. 1000 μm (1 mm) is the fundamental parameter which impacts the size of the dry residues formed after drying of the gel, and which therefore ensures dry residues of millimetric size to be formed and not powdery residues, the former being easily removed via mechanical means and preferably by vacuuming, suction.

(63) The gel is then maintained on the surface to be treated for the entire period of time that is required for drying. Throughout this drying step, which can be considered as forming the active phase of the method of the invention, the solvent contained in the gel, e.g. the water contained in the gel is evaporated until a dry solid residue is obtained.

(64) Drying time is dependent on the composition of the gel within the concentration ranges of the constituents thereof given above, but also as already specified on the quantity of gel deposited per unit surface area i.e. on the thickness of the deposited gel.

(65) Drying time is also dependent on weather conditions, namely temperature and relative humidity of the atmosphere surrounding the solid surface.

(66) The method of the invention can be implemented under extremely wide weather conditions namely at a temperature T of 1° C. to 50° C. and relative humidity RH of 20% to 80%.

(67) The drying time of the gel of the invention is therefore generally 1 hour to 24 hours at a temperature T of 1° C. to 50° C. and relative humidity HR of 20% to 80%. The gel applied to the contaminated surface may be exposed to a light radiation during the drying time.

(68) Light radiation can be visible radiation or A, B or C ultraviolet radiation produced by a UV lamp for example. For example, the gel applied to the surface can be exposed to UV radiation at a wavelength of 365 nm.

(69) The exposure time to radiation which corresponds to the drying time is generally 1 to 24 h. Drying may be accelerated by this UV exposure.

(70) The contaminating species present on the surface is first absorbed within the gel by solubilisation, diffusion and adsorption on the surface of the TiO.sub.2 particles.

(71) It is then the photocatalytic property of TiO.sub.2 which will allow the destruction and/or inactivation and/or degradation of the contaminating species e.g. the reduction of a multivalent element (changeover from hexavalent chromium to trivalent chromium for example), the degradation of a chemical contaminating species (organic molecule), or activation of the biocidal property of TiO.sub.2, throughout drying.

(72) At the end of drying, the contaminating species is destroyed and/or inactivated and/or degraded and/or absorbed and/or adsorbed.

(73) In particular, the toxicity of the contaminating species is drastically, even fully annihilated.

(74) After drying of the gel, the contamination e.g. the inactivated biological contamination is removed upon recovering the dry gel residue as described below.

(75) After drying of the gel, the gel fractionates homogeneously to give millimetric dry solid residues e.g. of size 1 to 10 mm, preferably 2 to 5 mm that are non-powdery and generally in the form of solid flakes.

(76) The dry residues may contain the one or more inactivated contaminating species.

(77) The dry residues such as flakes obtained after drying have scarce adherence to the surface of the decontaminated material. On this account, the dry residues obtained after drying of the gel may easily be recovered by simple brushing and/or vacuuming, suction. However, the dry residues can also be evacuated by a jet of gas e.g. a jet of compressed air.

(78) Therefore, no rinsing with a liquid is generally necessary and the method of the invention does not generate any secondary effluent.

(79) It is possible however, although not preferred, and if desired, to remove the dry residues by means of a jet of liquid.

(80) The method of the invention therefore first achieves major savings in chemical reagents compared with a decontamination method entailing washing with a solution. Also, since a waste is obtained in the form of a directly vacuumable dry residue, a rinsing operation with water or liquid which is generally needed to remove traces of chemical agents from the part, is generally avoided. The result is evidently a reduction in the amount of effluent produced but also notable simplification in terms of the waste treatment and disposal outlet chain.

(81) On account of the mainly mineral composition of the gel of the invention and low quantity of waste produced, the dry waste can be stored or directed towards an evacuation channel (disposal outlet) without prior treatment.

(82) On completion of the method of the invention, a solid waste is recovered in the form of flakes that can be packaged as such, directly packable; the result, as indicated above, is a signification reduction in the amount of effluent produced and notable simplification in terms of the waste treatment and disposal chain.

(83) In addition, in the nuclear sector, the fact that the flakes do not need to be retreated before packaging of the waste amounts to a considerable advantage; this permits the use of high-performing active agents prohibited up until now in decontamination liquids on account of the operating restrictions for liquid effluent treatment plants (LETPs)

(84) For example, in the routine case in which 1000 grams of gel are applied per m2 of surface area, the weight of dry waste produced is less than 200 grams per m.sup.2.

(85) The invention will now be described with reference to the following examples that are non-limiting and given for illustration purposes.

EXAMPLES

Example 1

(86) In this example, weak acidic, neutral or basic gels are described based on TiO.sub.2, (TiO.sub.2 gel) used in Examples 2, 3, 4, 6 and 7.

(87) The weak acidic based on TiO.sub.2 gel was a gel having the following composition in weight percent: 20% TiO.sub.2; 80% distilled water.

(88) The TiO.sub.2 was TiO.sub.2 marketed by Aerosil® under the trade name Degussa P25®.

(89) This gel was prepared in the following manner:

(90) First, the TiO.sub.2 particles were dispersed in water using a mechanical stirrer equipped with a three-blade impeller at a speed of 200 rpm.

(91) An opaque white liquid suspension was obtained having a pH of about 3.5.

(92) The pH was gradually increased with 0.1. M NaOH, under continued agitation, until the pH reached 5 which allowed an opaque white viscous gel to be formed.

(93) When adding the sodium hydroxide, agitation was gradually increased as and when viscosity increased, to reach about 400 to 600 rpm without splashing. The gel was then left under agitation for 5 minutes.

(94) It is noted here that the amount of sodium hydroxide added is systematically negligible compared with the initial amount of water, and it can be considered that the weight composition of 20% TiO.sub.2 and 80% H.sub.2O remains valid once the pH=5.

(95) The pH of the gel thus prepared is therefore weak acidic since it is 5.

(96) By continuing to increase pH up to a pH of 7, it is possible to obtain a neutral gel which therefore prevents chemical attack of the treated surfaces, and even a very basic gel with a pH of 9 or higher conforming to the invention which therefore has degreasing properties, power.

(97) In the neutral gel and very basic gel, the amount of sodium hydroxide can always be considered to be negligible.

Example 2

(98) In this example, the efficacy of the decontamination of smooth surfaces is shown using a gel prepared in Example 1 containing TiO.sub.2.

(99) The decontamination test was conducted on smooth surfaces polluted with Cr(VI), using a TiO.sub.2 gel prepared in Example 1.

(100) The smooth surfaces were a ceramic surface, an aluminium surface and a high density polyethylene surface (HDPE).

(101) The test on the smooth surface in ceramic used a ceramic tile and 0.25 ml of 10.sup.−2M K.sub.2Cr.sub.2O.sub.7 solution (from Sigma-Aldrich® having 99.0% purity, dissolved in H.sub.2O), equivalent to a 2.Math.10.sup.−2M concentrated solution of Cr(VI), were deposited on the ceramic tile.

(102) The drop was left to dry overnight. A yellow spot was obtained on which the acid gel (pH=5) prepared in Example 1 was deposited, the application being performed in the dark to a thickness of 1.25 mm.

(103) The gel was left to dry in the dark to halt any reduction via photocatalysis of Cr(VI) by TiO.sub.2, so that only the phenomenon of sorption in the gel could be observed. After a drying time of 4 h30, the dry gel flakes were recovered by brushing. The yellow spot had fully disappeared from the substrate and the gel flakes had become a yellow colour (the characteristic colour of hexavalent chromium), proof that the chromium had indeed been absorbed within the flakes.

(104) The flakes were then dissolved in pure hydrofluoric acid under mechanical agitation at 80° C., for several hours. The solution obtained was analysed by Inductively Coupled Plasma—Optical Emission Spectroscopy» (ICP-OES) using ThermoFisher Scientific apparatus, iCAP 6000 Series®.

(105) The results obtained are given in Table 1 below.

(106) It is noted here that the initial weight of hexavalent chromium deposited on the substrate was 0.26 mg.

(107) TABLE-US-00001 TABLE 1 ICP-OES results obtained after dissolution of the gel flakes in Example 2. Weight of HF total Chromium weight % flakes volume determined by ICP decontamination 567 mg 105 mL 0.26 mg 100%

(108) It is observed that the TiO.sub.2 gel fully decontaminates the ceramic tile contaminated with Cr(VI).

(109) The same decontamination test as on a smooth ceramic surface was performed but this time on an aluminium surface and on a smooth surface made of high density polyethylene (HDPE) contaminated with Cr(VI).

(110) The experimental protocol was the same as described above for decontamination of the smooth ceramic surface.

(111) In each case, all the chromium was captured by the gel flakes, leading to 100% decontamination efficacy.

(112) The TiO.sub.2 gel therefore indeed allows full decontamination of hexavalent chromium on a smooth surface, irrespective of the material constituting of this surface.

Example 3

(113) In this example, the retaining (confining) properties of ionic pollution are shown after decontaminating a surface with a gel based on TiO.sub.2.

(114) More exactly, the purpose in this example was to show the capability of an acid gel (pH=5) based on TiO.sub.2, such as described in Example 1, to confine hexavalent chromium in the flakes of dried gel.

(115) These properties, this confining, retaining capability of the TiO.sub.2 gel were compared with those of a comparative gel based on SiO.sub.2.

(116) The comparative gel based on SiO.sub.2 (SiO.sub.2 gel) was a gel having the following composition in weight percent: 12% silica; 88% distilled water.

(117) The silica was commercial silica from EVONIK® under the trade name Aerosil®.

(118) The comparative SiO.sub.2 gel was prepared in the following manner:

(119) The silica was gradually added to the distilled water under mechanical agitation using a mechanical agitator equipped with a three-blade impeller, at a speed of 200 rpm. When adding the silica, agitation was gradually increased as and when viscosity increased to reach about 400 rpm without any splashing. The gel was left under agitation for 5 minutes.

(120) The pH of this gel was 4.5.

(121) A decontamination test was then performed with the TiO.sub.2 gel. Initially the operating protocol of this test was the same as in Example 2, namely: 0.25 mL of 10.sup.−2M K.sub.2Cr.sub.2O.sub.7 solution (from Sigma-Aldrich, having 99.0% purity, dissolved in H.sub.2O), equivalent to a 2.Math.10.sup.−2M concentrated solution of Cr(VI), were deposited on a ceramic tile.

(122) The drop was left to dry overnight.

(123) A yellow spot was obtained on which the TiO.sub.2 gel prepared in Example 1 was deposited and applied in the dark (to prevent reduction of the chromium via photocatalysis) to a thickness of 1.25 mm.

(124) The gel was left to dry in the dark to halt any reduction via photocatalysis of Cr(VI) by TiO.sub.2 and so that only the phenomenon of sorption within the gel is observed.

(125) After a drying time of 4 h30 the following protocol was applied: all the flakes were collected and re-dispersed in 20 mL of H.sub.2O under mechanical stirring using a magnetic stir bar 2 h. The flakes were thus leached in H.sub.2O. In theory, if the entirety of the chromium contained in the flakes was released, this will give a solution of [Cr(VI)].sub.0=2.5×10.sup.−4M.

(126) This value of [Cr(VI)].sub.0=2.5×10.sup.−4M is obtained as follows: 0.25 mL of dried 2.Math.10.sup.−2M solution of Cr(VI) that is finally found in 20 mL i.e. (0.25×2.Math.10.sup.−2)/20=2.5×10.sup.−4. the suspension obtained was then centrifuged for 30 minutes at 4400 rpm and finally filtered through a 0.22 μm filter.

(127) These steps allowed complete separation of the TiO.sub.2 particles and gave a leachate containing the species weakly bonded to the gel flakes. the leachate was analysed with a UV-Visible UV-1800 spectrometer by Shimadzu®, previously calibrated. Calibration was performed using different solutions of K.sub.2Cr.sub.2O.sub.7 of known concentrations, and the baseline was obtained on ultrapure water. The absorption spectrum of hexavalent chromium, in an acid medium, showed peaks at the wavelengths 260 nm and 352 nm. the spectrum for the leachate obtained from TiO.sub.2 gel flakes is given in FIG. 1.

(128) Beer-Lambert's law gives access to the concentration of Cr(VI) contained in the analysed solution.

(129) In this example, the test (i.e. application of the gel followed by drying of the gel and re-dispersion) having been performed in the dark, all the Cr was necessarily in the form of Cr(VI). The chromium released by the flakes was therefore present in the leachate, and the content of Cr(VI) in the leachate ([Cr(VI)] (leachate)) was compared with the initial Cr(VI) content ([Cr(VI)].sub.0) used for contamination.

(130) Since it was shown that the flakes initially contained all the contamination in this case (see Example 2), these measurements gave the quantity of chromium still present in the flakes after leaching. The results obtained are given in Table 2 below.

(131) TABLE-US-00002 TABLE 2 Results obtained after leaching of TiO.sub.2 gel flakes. Absorbance at 352 nm [Cr(VI)] (leachate) [Cr(VI)] (leachate)/[Cr(VI)].sub.0 0.147 8.76 × 10.sup.−5M 0.350

(132) These results show that even after leaching of the TiO.sub.2 gel flakes in H.sub.2O for 2 h, under mechanical agitation, only 35% of the chromium was released into the solution.

(133) The same decontamination test as performed with the TiO.sub.2 gel was then conducted with the comparative SiO.sub.2 gel following the same protocol, again in the dark.

(134) After drying, re-dispersion of the flakes, centrifugation and filtration, the leachate was analysed by UV-Visible spectroscopy.

(135) The spectrum for the leachate obtained from the SiO.sub.2 gel flakes is given in FIG. 2.

(136) The use of Beer-Lambert's law allowed determination of the concentration of Cr(VI) contained in the leachate, and hence the quantity of Cr(VI) still contained in the silica flakes. The results obtained are given in Table 3 below.

(137) TABLE-US-00003 TABLE 3 Results obtained after leaching flakes of SiO.sub.2 based gel. Absorbance at 352 nm [Cr(VI)] (leachate) [Cr(VI)] (leachate)/[Cr(VI)].sub.0 0.382 2.27 × 10.sup.−4M 0.91

(138) These results show that even after 2 h leaching of silica flakes in H.sub.2O, under mechanical agitation, 91% i.e. practically all the chromium was released into the solution.

(139) In the light of this example, the comparison between the capability of the TiO.sub.2 gel and the capability of the comparative SiO.sub.2 gel to retain chromium when the flakes were replaced in solution clearly shows the significant confining property of the TiO.sub.2 gel. The confining property of the TiO.sub.2 gel is much higher than that of the comparative SiO.sub.2 gel. Therefore, the ability of the TiO.sub.2 gel to limit release of pollution, in the event of deterioration of the flakes after treatment of contaminated surfaces, is excellent and better than that of the comparative SiO.sub.2 gel.

Example 4

(140) In this example, the decontaminating efficacy is shown of a porous surface using a gel based on TiO.sub.2 (TiO.sub.2 gel).

(141) For comparison, the same decontamination test was conducted using a «conventional» decontamination gel based on SiO.sub.2 (SiO.sub.2 gel).

(142) More exactly, the purpose in this example was to demonstrate the adsorbing property of a TiO.sub.2 gel, in particular on a porous substrate, namely here a substrate made of concrete.

(143) The tested TiO.sub.2 gel was the acid gel (pH=5), described in Example 1. It was compared with a SiO.sub.2 gel that was described in Example 3.

(144) Initially the operating protocol for the decontamination test was the same as for Example 2. Only the substrate was different: concrete being used instead of the ceramic tile.

(145) After drying and recovery of the flakes of each gel, these were dissolved under mechanical agitation in pure hydrofluoric acid at 80° C. for several hours and the solutions were analysed by Inductively Coupled Plasma—Optical Emission Spectroscopy (ICP-OES) using ThermoFisher Scientific apparatus, iCAP 6000 Series®, to determine the chromium concentrations within these flakes.

(146) The results obtained are given in Table 4 below.

(147) It is noted here the initial weight of hexavalent chromium deposited on each of the substrates was 0.26 mg.

(148) TABLE-US-00004 TABLE 4 ICP-OES results obtained after dissolution of the gel flakes obtained in Example 4. Weight HF Chromium weight % of total determined by decontami- Gel flakes volume ICP nation TiO.sub.2-based 364.8 mg 55 mL 0.1 mg 38% SiO.sub.2-based 342.6 mg 45 mL <d.l.  0% <d.l. = lower than the detection limit of the apparatus.

(149) These results therefore show the adsorbing property of the TiO.sub.2 gel. On a porous substrate such as concrete, the TiO.sub.2 gel allows decontamination at least of part of the chromium contained in the pores of the concrete, contrary to the comparative «conventional» gel not conforming to the invention and based on SiO.sub.2 (SiO.sub.2 gel).

Example 5

(150) In this example, the photocatalytic effect of the gel of the invention is demonstrated, leading to reduction of Cr(VI) and hence a decrease in the toxicity thereof.

(151) More exactly, the purpose in this example was to demonstrate the impact of UV or visible radiation on the reducing of Cr(VI) toxicity, after decontaminating a surface contaminated with Cr(VI), by applying onto this surface a TiO.sub.2 gel of the invention.

(152) For this example, and following Example 7 (in Example 6 there was no measurement of the quantity of Cr, only visual observation), measurement of the quantity of hexavalent chromium contained in the gel was performed after leaching the dry gel flakes with water, followed by UV-Visible analysis applying the protocol described in Example 3.

(153) It is considered that the ratio [Cr(VI)](leachate)/[Cr(VI)].sub.0 represents the reduction (chemical reduction) of total hexavalent chromium.

(154) Although measurement was only performed on about one third of the total chromium contained in the flakes (only 35% of the chromium contained in the flakes was released into solution after leaching with water), it is assumed that the chromium atoms adsorbed on the surface of the TiO.sub.2 particles, and still contained within the flakes, have at least the same probability of being reduced as those contained in the leachate.

(155) The gel of the invention used in this example had the following composition:

(156) TABLE-US-00005 TABLE 5 Composition of the gel used in Example 5. Weight % of Weight % of Weight % of pH pH Gel TiO.sub.2 H.sub.2O EtOH (initial) (gel) Gel H.sub.2O-40 20 40 40 3.7 5 EtOH

(157) This gel conforming to the invention was prepared as follows:

(158) Initially the TiO.sub.2 particles were dispersed in the solvent (water and ethanol) using a mechanical agitator equipped with a three-blade impeller, at a speed of 200 rpm.

(159) An opaque white liquid suspension was obtained having a pH of about 3.5.

(160) The pH was gradually increased with sodium hydroxide 0.1M NaOH, under continued agitation, until the pH reached 5 which allowed the formation of an opaque white viscous gel.

(161) When adding the sodium hydroxide, agitation was gradually increased as and when the viscosity increased to reach about 400 to 600 rpm without any splashing. The gel was then left under agitation for 5 minutes.

(162) It is noted here that the amount of added sodium hydroxide is systematically negligible relative to the quantity of solvents, and it can therefore be considered that the weight composition of 20% TiO.sub.2, 40% H.sub.2O, and 40% ethanol remains constant once the pH=5.

(163) The pH of the gel thus prepared was therefore weak acidic since it was 5.

(164) The reducing efficacy of the gels in this example was monitored by UV-Visible spectrometry from which the Cr(VI) concentration was determined.

(165) First, 0.25 mL of 10.sup.−2M K.sub.2Cr.sub.2O.sub.7 solution (from Sigma-Aldrich® having 99.0% purity, dissolved in H.sub.2O), equivalent to a 2.10.sup.−2M concentration of Cr(VI), were deposited on a ceramic tile.

(166) This operation was performed on two separate ceramic tiles.

(167) The drops were left to dry overnight, after which a spot was obtained on each of the tiles.

(168) The gel described above in this example was deposited on the spot of a first ceramic tile and the whole placed under the radiation of an UV lamp (UV lamp by Vilber®, λ=365 nm), the deposited thickness being 1.25 mm.

(169) The gel described above was also deposited to a thickness of 1.25 mm on the spot of the second ceramic tile and the whole left under visible light.

(170) The first sample was left to dry (formed of a yellow spot on which the gel was deposited) for three hours under the radiation of a UV lamp (UV lamp by Vilber®, λ=365 nm), and the second sample in full daylight under visible light.

(171) The dry gel flakes finally obtained were recovered by brushing.

(172) For the gel dried under UV, the flakes appeared slightly green (the characteristic colour in the presence of Cr(III)) or brown, whereas the gel flakes dried in daylight under visible light still have their yellow hues.

(173) Second, the dry gel flakes were re-dispersed in 20 mL of H.sub.2O for one hour.

(174) After centrifugation and filtration, the leachate was analysed by UV-Visible spectroscopy.

(175) The spectra obtained are given in FIG. 3 (for comparison the curve representing the TiO.sub.2 gel of Example 1 is given, in which the solvent was solely water and was dried in the dark).

(176) The results obtained after applying Beer-Lambert's law are summarised in Table 6 below.

(177) On the one hand, analysis of the chromium in the leachate showed that the chromium in the leachate corresponded to about 35% of the total chromium contained in the flakes, as shown in Example 3.

(178) On the other hand, the flakes contained all the initial chromium since it was shown that the gel allowed full extraction of the chromium present on the smooth substrate.

(179) Therefore, the proportion of Cr(VI) in the flakes can be estimated with the following equation:

(180) $\%{\mathrm{Cr}\left(\mathrm{VI}\right)}_{\mathrm{in}\mathrm{flakes}}=100\times \frac{{\left[\mathrm{Cr}\left(\mathrm{VI}\right)\right]}_{\mathrm{analysedin}\mathrm{flakes}}}{{0.35\left[\mathrm{Cr}\left(\mathrm{VI}\right)\right]}_0}$

(181) TABLE-US-00006 TABLE 6 Results obtained after leaching of the gel flakes obtained in Example 5. [Cr(VI)] % Cr(VI) in the Radiation Absorbance (leachate) gel flakes UV 0.001 0 0 Visible 0.032 1.9 × 10.sup.−5M 21.7%

(182) These results show that the use of UV radiation allows full reduction of hexavalent chromium to be obtained (almost 100%) whereas for the gel left to dry in daylight under visible light only a 78.3% reduction of hexavalent chromium was obtained

(183) However, this example evidences the fact that visible radiation allows at least partial activation of the TiO.sub.2 particles, since a 78.3% reduction of Cr(VI) was obtained.

Example 6

(184) In this example, the photocatalytic effect is shown of a TiO.sub.2 gel on the destruction of a chemical pollutant.

(185) More exactly, the purpose in this example was to demonstrate the photocatalytic property of a TiO.sub.2 gel on the degradation of organic compounds.

(186) As organic compound to be destroyed, degraded, an organic dye was used, Methyl Red (Sigma-Aldrich®) in the form of a 40 mg/L solution of this dye.

(187) This organic dye is red at pH values below 4.4, orange at pH values of between 4.4 and 6.2 and yellow at pH values higher than 6.2.

(188) 4 drops of the solution of this dye were deposited on a smooth substrate, namely a ceramic tile. The drops were left to dry to obtain 4 spots, and three different gels were deposited using a spatula on three of these spots whilst the last spot was left uncovered, did not receive any gel and therefore acted as control dye spot.

(189) The 3 gels were: an acidic TiO.sub.2 gel (pH=5), such as described in Example 1; a comparative SiO.sub.2 gel such as described in Example 3. This was an acidic gel (pH=4.5); a comparative Al.sub.2O.sub.3 gel. This gel was slightly basic (pH=8).

(190) The comparative Al.sub.2O.sub.3 gel was a gel with the following composition in weight percent: 17% alumina; 83% distilled water.

(191) The alumina was the alumina marketed by EVONIK® under the trade name Aeroxide® Alu C.

(192) This comparative gel containing Al.sub.2O.sub.3 was prepared in the following manner:

(193) The alumina was gradually added to the distilled water under mechanical agitation using a mechanical agitator equipped with a three-blade impeller at a speed of 200 rpm. When adding the alumina, agitation was gradually increased as and when the viscosity increased to reach about 400 to 600 rpm without any splashing. The gel was then left under agitation for 5 minutes.

(194) The pH of this gel was measured to be 8.

(195) These gels were left to dry under UV radiation (UV lamp by Vilber, λ=365 nm) for 4 h30.

(196) After drying under UV, the control dye spot was intact, the flakes of the comparative Al.sub.2O.sub.3 gel, slightly basic, were yellow tallying with the basic nature of this gel, and the flakes of the comparative acidic SiO.sub.2 gel were red tallying with the acidic nature of this gel. The organic dye was therefore not degraded by these comparative gels.

(197) On the other hand, the flakes of TiO.sub.2 gel were completely white, proving degradation of the organic dye due to the photocatalytic property, power, of TiO.sub.2 under UV radiation.

(198) It was therefore demonstrated in this example that it is possible to degrade organic compounds (such as chemical or biological contaminants) present on the surface of a material through the use of a photo-activatable gel based on TiO.sub.2.

Example 7

(199) In this example, the impact of the presence of ethanol was examined in TiO.sub.2 gels of the invention.

(200) Three gel compositions, including two gel compositions according to the invention, were studied in this example.

(201) These gels were prepared in the same manner as in Example 1 except that for the two last gels prepared, conforming to the invention, the solvent was modified and comprised a mixture of water and ethanol instead of only water (see Table 7 below).

(202) Once again, it can be considered that the weight amounts of added sodium hydroxide are negligible relative to the weights of the solvent(s), and it can therefore be considered that the weight compositions remain constant once pH=5.

(203) TABLE-US-00007 TABLE 7 Composition of the gels studied in Example 7. Weight % Weight % Weight % pH pH Gel TiO.sub.2 H.sub.2O EtOH (initial) (gel) Gel H.sub.2O 20 80 0 3.5 5 Gel H.sub.2O-24 20 56 24 3.7 5 EtOH Gel H.sub.2O-40 20 40 40 3.7 5 EtOH

(204) The reducing efficacy, efficiency, of the gels in this example was demonstrated using the same measuring protocol as in Example 5, but only drying under a UV lamp was used.

(205) After drying, re-dispersion of the flakes, centrifugation and filtration, the leachate was analysed by UV-Visible spectroscopy. For each of the examined gels, the colour of the dried flakes was green (characteristic colour of the presence of Cr(III)) or brown, and yellow traces were no longer observed on the substrate.

(206) The UV-Visible spectra are given in FIG. 4 (for comparison, the curve representing the TiO.sub.2 gel of Example 1 is added, in said gel the solvent was solely water and it was dried in the dark).

(207) The results obtained by applying Beer-Lambert's law are given in Table 8 below.

(208) The % of Cr(VI) in the flakes was calculated in the same manner as for Example 5.

(209) TABLE-US-00008 TABLE 8 Results obtained after leaching the gel flakes obtained in Example 7. Absorbance at [Cr(VI)] % Cr(VI) in gel Gel 352 nm (leachate) flakes Gel H.sub.2O 0.006 3.6 × 10.sup.−6M 4.1% Gel H.sub.2O-24 EtOH 0 0 0 Gel H.sub.2O-40 EtOH 0 0 0

(210) These results show that for the three gel compositions presented in this example, with drying under UV, excellent results were obtained since at least 95.9% of the hexavalent chromium was reduced.

(211) It is noted that the presence of ethanol in the gels of the invention, acting as sacrificial element to prevent electron-hole recombination, allows a slight improvement in the reducing efficacy of the gel to reach a 100% reduction of hexavalent chromium.

Example 8

(212) In this example, it is shown that the gels of the invention can be applied by spraying.

(213) A rheological study was conducted on two of the three gels described in Example 7, namely the «H.sub.2O» gel and the «H.sub.2O-40 EtOH» gel of the invention, and showed that these gels are suitable for application by spraying.

(214) For application of these gels using a spray method, they must have the properties of a rheofluidifying, thixotropic fluid having a very short reset time (less than one second) and with a threshold stress typically higher than 15-20 Pa.

(215) Different rheological measurements were made using a rheometer by TA Instruments® AR-1000 in vane geometry, and are given in this example.

(216) First, the viscosity of the gel was measured as a function of shear rate. After pre-shearing for 5 minutes at a shear rate of 20 s.sup.−1 then 1 minute at 6.72×10.sup.−3 s.sup.−1, several shear rate plateau values were applied ranging from 6.2×10.sup.−3 s.sup.−1 to 100 s.sup.−1 measuring viscosity every 30 seconds.

(217) FIG. 5 gives the change in viscosity (Pa.Math.s) of the two gels examined in this example as a function of shear rate (s.sup.−1) for shear rates of between 6.72×10.sup.−3 and 100 s.sup.−1.

(218) For each of the gels, a drastic drop in viscosity was observed with shear rate, characteristic of rheofluidifying behaviour.

(219) Additionally, it was found that the presence of ethanol in the gel conforming to the invention tends to make the rheofluidifying behaviour of the gel more perfect. The viscosity value of the «H.sub.2O-40 EtOH» gel of the invention as a function of shear rate progresses in a more linear way than that of the «H.sub.2O» gel which has jumped in a fairly irregular way.

(220) Also, the threshold stress values of these two gels described in Example 7 («H.sub.2O» gel and «H.sub.2O-40 EtOH» gel of the invention) were determined by measuring the changes in shear stress and their strain under an imposed shear rate.

(221) A low shear rate (6.72×10.sup.−3 s.sup.−1) was constantly applied to each gel to obtain deformation thereof starting from rest, and thereby determine their flow threshold.

(222) FIG. 6 shows shear stress as a function of strain obtained for the two gels described in Example 7.

(223) The two curves have the same shape: two states are observed. First, stress is strongly increased and the material is in solid state (elastic deformation). A change in behaviour is then observed, stress reaches the flow threshold and the material moves into liquid state (stationary flow). The threshold stress then corresponds to the yield stress of the gel i.e. 52 Pa for the «H.sub.2O» gel and 36 Pa for the «H.sub.2O-40 EtOH» gel. This threshold stress is therefore much higher than 20 Pa which will enable the gel to adhere to a wall in thicknesses of between 0 and at least 2 mm.

(224) To conclude for this example, the H.sub.2O and H.sub.2O-40EtOH gels indeed have adequate rheological properties allowing them to be easily sprayed onto different types of surfaces (whether or not horizontal). The presence of ethanol in the gel has a significant impact on the rheology of the gel: first it allows the tending towards a more pronounced rheofluidifying nature, but secondly the gel has a slightly lower threshold stress and will therefore flow more easily.

Example 9

(225) In this example, it is shown that the gels of the invention can be applied by spraying.

(226) For being able to be applied using a spray technique, the gels of the invention must have the properties of a rheofluidifying fluid.

(227) Two gel compositions conforming to the invention were studied in this example.

(228) These gels were prepared in the same manner as in Example 1.

(229) Once again, it can be considered that the weight amounts of added sodium hydroxide are negligible relative to the solvent weights.

(230) TABLE-US-00009 TABLE 9 Compositions of the gels studied in Example 9. Weight % Weight % Weight % pH pH Gel TiO.sub.2 H.sub.2O EtOH (initial) (gel) Ti15_pH 5.5 15 42.5 42.5 3.7 5.5 Ti15_pH 9 15 42.5 42.5 3.7 9

(231) Rheological measurements were carried out using a TA Instruments® AR-1000 rheometer in vane geometry, and are given in this example.

(232) The viscosity of the gel was measured as a function of shear rate.

(233) After pre-shearing for 5 minutes at a shear rate of 0.01 s.sup.−1, several shear rate plateau values were applied ranging from 0.01 s.sup.−1 to 100 s.sup.−1 and the viscosity was measured.

(234) FIG. 9 gives the change in viscosity (Pa.Math.s) of the two gels studied in this Example 9 as a function of the shear rate (s.sup.−1) for shear rates of between 0.01 and 100 s.sup.−1.

(235) For each of the gels, a drastic drop in viscosity with shear rate was observed, characteristic of a rheofluidifying behaviour.

(236) To conclude this example, it can be said that the two gels in this example, Ti15_pH 5.5 and Ti15_pH 9 are indeed rheofluidifying and can therefore be applied by spraying.

Example 10

(237) In this example, it is shown that the gels of the invention are able to hold, adhere with a thickness of several millimetres onto non-horizontal surfaces such as a wall or ceiling.

(238) To do so, the studied gels must have a sufficiently high flow threshold i.e. a threshold stress higher than 10 Pa.

(239) Four gel compositions were examined in this example. These gels were prepared in the same manner as in Example 1.

(240) Among these four gel compositions, two conformed to the invention namely the gel compositions designated «Ti15_H.sub.2O/EtOH pH 5.5» and «Ti15_H.sub.2O/EtOH_pH 9».

(241) Once again, it can be considered that the weight amounts of added sodium hydroxide are negligible relative to the solvent weights.

(242) TABLE-US-00010 TABLE 10 Compositions of the gels studied in Example 10. Weight Weight Weight % % % pH pH Gel TiO.sub.2 H.sub.2O EtOH (initial) (gel) Ti15_H.sub.2O_pH 5.5 15 85 0 3.7 5.5 Ti15_ H.sub.2O_pH 9 15 85 0 3.7 9 Ti15_H.sub.2O/EtOH_pH 5.5 15 42.5 42.5 3.7 5.5 Ti15_ H.sub.2O/EtOH_pH 9 15 42.5 42.5 3.7 9

(243) The threshold stress values of the gels described in this example were determined by measuring the change in their shear stress and their strain under an imposed shear rate.

(244) Measurements were carried out with a TA Instruments® AR-1000 rheometer in vane geometry, and are given in this example.

(245) A low shear rate (0.01 s.sup.−1) was constantly applied to each gel to obtain deformation thereof starting from rest, and thereby determine their flow threshold.

(246) FIG. 10 gives the shear stress as a function of the deformation obtained for the four gels described in this example.

(247) The four curves display the same shape: two states are observed. First stress increases strongly and the material is in solid state (elastic deformation).

(248) Thereafter a change in behaviour is observed, stress reaches the flow threshold and the material changes over to liquid state (stationary flow). The threshold stress then corresponds to the yield stress of the gel i.e. 12 Pa for the «Ti15_H.sub.2O_pH 5.5» gel and 11 Pa for the «Ti15_H.sub.2O_pH 9» gel, 14 Pa for the «Ti15_H.sub.2O/EtOH_pH 5.5» gel and 29 Pa for the «Ti15_H.sub.2O/EtOH_pH 9» gel. These threshold stresses are therefore much higher than 10 Pa which will enable the gels to adhere to a wall in thicknesses of between 0 and at least 1 mm.

(249) It is additionally observed that the presence of ethanol in the gels of the invention allows an increase in the flow threshold of the gel, and hence the possibility to deposit a greater gel thickness on non-horizontal surfaces such as walls or ceilings.

Example 11

(250) In this example, it is shown that after application and drying, the gels of the invention are vacuumable, suctionable.

(251) More exactly, the purpose in this example was to show that the gels of the invention, described in the preceding examples, dry within a reasonable time of a few hours, that they fractionate producing non-powdery flakes of millimetric size that can be easily vacuumed, suctioned.

(252) The impact of the presence of ethanol is also shown in this example, in particular regarding drying time.

(253) To conduct this study, the «H.sub.2O» gel and the «H.sub.2O-24 EtOH» gel of the invention were each left to dry in a Binder® climate chamber having a set temperature and relative humidity percentage of 25° C. and 50% respectively.

(254) The gels were spread over a boat made of stainless steel machined to obtain a controlled thickness of 2 mm of gel in the boat.

(255) In the climate chamber, a Sartorius® precision balance was installed together with a Moticam® camera surrounded by a circular LED lamp (VWR) positioned on the top of the balance.

(256) The balance and Moticam® camera were connected to a computer positioned outside the climate chamber allowing simultaneous acquisition, throughout drying under a controlled atmosphere, of the weight and images of the boat filled with gel.

(257) It is to be noted that the weighing boat containing the gel was placed in the precision balance and that all the doors of the balance were closed with the exception of the door opposite the blower which was 3 cm ajar (to maintain the controlled atmosphere within the balance whilst limiting the airflow related to the operating of the climate chamber). Weight recording throughout drying allows monitoring of drying kinetics. All the results are given in FIG. 7.

(258) It is observed that the two gels examined in this example dry well within a maximum time of only a few hours, namely 580 minutes i.e. 9 hours and 40 minutes for the «H.sub.2O» gel, and 480 minutes i.e. 8 hours for the «H.sub.2O-24 EtOH» gel conforming to the invention.

(259) The presence of ethanol in the gel formulation therefore allows a reduction in gel drying time since the evaporation of ethanol takes place at a lower temperature than the evaporation of water.

(260) With regard to fractionation, a photograph of the dry flakes obtained with the H.sub.2O-24 EtOH gel of the invention deposited in a weighing boat of depth 2 mm, is given in FIG. 8.

(261) It can be seen that the number of flakes formed and especially the size thereof conform well since these flakes are of millimetric size and are not powdery.

REFERENCES

(262) [1] Faure, S., et al., “Procédé de traitement d′une surface par un gel de traitement, et gel de traitement”, 2003, FR-A1-2 827 530. [2] Faure, S., P. Fuentes, et Y. Lallot, “Gel aspirable pour la décontamination de surfaces et utilisation”, 2007, FR-A1-2 891 470. [3] Cuer, F. et S. Faure, “Gel de décontamination biologique et procédé de décontamination de surfaces utilisant ce gel”, 2010, WO-A1-2012001046. [4] Ludwig, A., F. Goettmann, et F. Frances, “Gel alcalin oxydant de décontamination biologique et procédé de décontamination biologique de surfaces utilisant ce gel”, 2013, WO-A1-2014154818.