Process for the preparation of an additive comprising supported and dispersed TiO2 particles

Abstract

Process for the preparation of an additive comprising TiO.sub.2 particles dispersed on a support of pseudo-layered phyllosilicate-type, comprising the dispersion in water of the support, the acid activation of the support and the high-shear dispersion of the support with the TiO.sub.2 particles Use of the particles obtained by this process as additives with photocatalytic activity for water purification and disinfection, for purification of polluted gas streams and to provide materials, in particular construction materials, with self-cleaning, biocide, deodorization and/or pollution reduction properties in the presence of air and ultraviolet light.

Claims

1. A process for the preparation of an additive, where the additive comprises TiO.sub.2 particles supported and dispersed on a pseudo-layered phyllosilicate support, comprising the following stages: (i) the dispersion in water of the support with high shear; (ii) the acid activation of the support of stage (i); and (iii) the addition of the TiO.sub.2 particles on the support of stage (ii) with high-shear mixing, wherein high shear is performed with a high shear dispersion system capable of developing a peripheral velocity in the rotor greater than 10 m/s and which creates a shear velocity greater than 2,000 s.sup.−1; and wherein the process does not comprise a thermal treatment stage at temperatures above 350° C.

2. The process according to claim 1, further comprising the following stage after stage (iii): (iv) solid/liquid separation of the support with the TiO.sub.2 particles of the dispersion liquid, and later elimination of the residual water that remains in the support with the TiO.sub.2 particles by drying at atmospheric pressure, at low pressure or in a vacuum.

3. The process according to claim 2, where solid/liquid separation of the support with the TiO.sub.2 particles is performed by a filtration.

4. The process according to claim 1, where the support is sepiolite or attapulgite.

5. The process according to claim 4, where the support is rheological grade sepiolite or rheological grade attapulgite.

6. The process according to claim 1, where the TiO.sub.2 particles within the additive are selected from anatase phase, rutile phase, brookite phase and a mixture thereof.

7. The process according to claim 4, where the support is activated by the addition of an acid which leaches between 5% and 25% of the magnesium cations from the sepiolite.

8. The process according to claim 4, where the support is activated by the addition of an acid which leaches between 5% and 33% of the magnesium/aluminium cations from the attapulgite.

9. The process according to claim 1, where the quantity of TiO.sub.2 particles added in stage (iii) to the dispersion of the support activated with acid is adjusted so that the concentration by weight of the TiO.sub.2 of the additive is between 5% and 75% by weight of TiO.sub.2.

10. The process according to claim 9, where the quantity of TiO.sub.2 particles added in stage (iii) to the dispersion of the support activated with acid is adjusted so that the concentration by weight of the TiO.sub.2 of the additive is between 15% and 50% by weight of TiO.sub.2.

11. Additive, where the additive comprises TiO.sub.2 particles supported and dispersed on a support, obtainable by the process described in claim 1.

12. Composition that comprises the additive of claim 11.

13. The composition according to claim 12, where the composition is cement or a sol-gel coating.

14. The composition according to claim 13, comprising between 0.1% and 15% by weight of the additive.

15. The composition according to claim 12, where the composition is mortar concrete, lime mortar, mixed mortar or a plaster.

16. The composition according to claim 15, comprising between 0.1% and 15% by weight of the additive over the weight of the mortar concrete, lime mortar, mixed mortar or plaster.

17. The composition according to claim 12, where the composition is paint, a coating, emulsion or protective layer.

18. The composition according to claim 17, comprising between 0.1% and 10% by weight of the additive.

19. A material with self-cleaning, biocide, deodorization and/or pollution reduction properties in the presence of air and ultraviolet light which comprises the additive of claim 11.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1. Shows a transmission electron micrograph image of the titanium oxide particles of nanometric size agglomerated due to the high surface energy they have.

(2) FIG. 2. Shows a transmission electron micrograph image of titanium oxide particles anchored and supported homogeneously in sepiolite following the process described in the invention, with a TiO.sub.2/sepiolite weight ratio of 35/65.

(3) FIG. 3. Shows a transmission electron micrograph image of sepiolite fibres with titanium oxide nanoparticles of approximately 21 nm of size supported and homogeneously distributed with a TiO.sub.2/sepiolite weight ratio of 50/50.

(4) FIG. 4. Shows an electron scanning microscope image of a mortar whereto non-supported TiO.sub.2 nanoparticles have been added, with the distribution of the titanium performed with the EDX probe (mapping). The dispersion of TiO.sub.2 nanoparticles can be observed in mortar with the presence of large and compact agglomerates. Left: 1500 magnifications. Right: 6000 magnifications.

(5) FIG. 5. Shows an electron scanning microscope image of a mortar whereto a product has been added following the process described in the invention with 50% by weight of TiO.sub.2 nanoparticles anchored and supported on sepiolite. It shows the distribution of the titanium performed with the EDX probe (mapping). It is possible to observe the correct dispersion of TiO.sub.2 nanoparticles/Sepiolite 50/50 in mortar with few and not very compact agglomerates.

(6) FIG. 6. Shows an experimental device to assess the self-cleaning of the materials developed; the method consists of a simulation of a real façade of mortar with white cement.

(7) FIG. 7. Shows a mixture of concrete with a high water/cement ratio the Abrams cone whereof gives a value of 22 cm and shows a segregated appearance.

(8) FIG. 8. Shows the same mixture of concrete of the previous figure but after incorporating 1.5% of TiO.sub.2/Sepiolite 50/50 in the mixture; an Abrams cone of 8 cm is observed without segregation.

EXAMPLES

Example 1: Dispersion of TiO2 Nanoparticles on Sepiolite

(9) In this example commercial titanium oxide nanoparticles of anatase phase have been used, with an average size of 21 nm. FIG. 1 shows a transmission electron micrograph of the commercial TiO.sub.2 nanoparticles used which shows the presence of large agglomerates.

(10) Firstly, a dispersion is prepared of micronized sepiolite with a particle size with 99.9% less than 44 μm and 95% less than 5 μm, in water with a solid concentration of 6% (60 g of dry base sepiolite for 1000 g of pregel), mixed by a Cowles-type high shear mixer for 10 minutes, using a peripheral velocity of 18 m/s. The dispersion of clay in water has an initial pH of 8.9, and it is acidified to a pH of 3, by the addition of 50% sulphuric acid. After the addition of the acid the dispersion is stirred for another 10 minutes. On the other hand, a dispersion is prepared of the commercial titanium oxide nanoparticles in water at a weight concentration of 6% stirring with a Cowles mixture with a peripheral velocity of 18 m/s for 10 minutes. The TiO.sub.2 dispersion is added to the acidified sepiolite pregel to obtain a final concentration of TiO.sub.2 in sepiolite of 35% by weight, and it is mixed by a high shear mixer at a peripheral velocity of 18 m/s for 10 minutes to guarantee an anchoring and homogeneous dispersion of the titanium oxide on the sepiolite fibres. The dispersion is filtered and the sepiolite with TiO.sub.2 is dried at 100° C. until a final humidity of 10%.

(11) As a result monodispersed nanoparticles are obtained supported throughout the sepiolite fibres as is observed in the attached transmission electron micrograph (FIG. 2).

Example 2: Photocatalytic Effect of the TiO2 Product Supported on Sepiolite

(12) A dispersion is prepared of a rheological grade sepiolite obtained by the process disclosed in patent EP0170299, trade name PANGEL, 6% in water by a mechanical blade shaker which rotates at 1,000 rpm for 10 minutes, and is then acidified at pH 3 by the addition of 50% sulphuric acid. This dispersion is followed by stirring for another 10 minutes to achieve the surface activation of the sepiolite surface. An aqueous dispersion with 6% commercial TiO.sub.2 nanoparticles previously prepared as indicated in example 1 is added to the previous dispersion, so that the final TiO.sub.2/sepiolite ratio is 50/50. The resulting suspension is vigorously mixed in a Grindomix-type ball mill with zircon balls of between 1.6 and 2.4 mm in diameter for 10 minutes to achieve sufficient shear to completely defibrillate the sepiolite clusters and totally disperse the TiO.sub.2 nanoparticles anchored to the acid centres of the exposed surface of the sepiolite. Next, the product was filtered and dried at 105° C., until a final humidity of 10%.

(13) As is observed in the transmission electron micrograph (FIG. 3), the process of acid activation of the sepiolite together with the high shear mixing makes it possible to obtain nanoparticles homogeneously distributed throughout the sepiolite fibres even at a titanium oxide concentration of 50% by weight with respect to the sepiolite.

(14) To determine the effect of the homogeneous dispersion of the TiO.sub.2 particles supported on sepiolite on its photocatalytic activity, two slabs were compacted in the same conditions, to have the same surface roughness, thickness and TiO.sub.2 concentration, a commercial titanium oxide in anatase phase and another of this same oxide supported on sepiolite, obtained as indicated in this example, using in both cases KBr to compact the powder. The slabs obtained are homogeneously impregnated with a Rhodamine B solution used as colouring agent and subjected to different times (0, 30 min., 1, 3 and 6 hours) of exposure to UV radiation with a UVA-340 light lamp. A faster degradation of the colouring agent was observed as a result of the increase in the contact surface of the TiO.sub.2 nanoparticles as they are monodispersed in the sepiolite.

Example 3: Dispersion of the Sepiolite Product with TiO2 in a Mortar Matrix

(15) The present example compares the dispersion in a mortar of the sepiolite product with 50% TiO.sub.2 nanoparticles (sepiolite/TiO.sub.2 50/50), obtained according to example 2, in comparison with the dispersion of non-supported TiO.sub.2 nanoparticles.

(16) The process of addition of the photocatalytic additive to the mortar, both of commercial non-supported TiO.sub.2 nanoparticles and the sepiolite/TiO.sub.2 additive 50/50, has consisted of firstly dispersing the photocatalytic additive in water by mechanical shaking. To do this, a foot shaker has been used with a shaft rotating at 4,000 rpm for 15 minutes and with the rotor-stator module. Once the photocatalytic additive has been dispersed in water, the mixture with the cement and the sand are mixed in a conventional mortar mixer.

(17) The analysis of the dispersion of the different photocatalytic additives in mortar has been performed by a study of the distribution, or mapping, of titanium by the EDX of the electron scanning microscopy. FIGS. 4 and 5 show the result of said analysis. It can be seen how in the case of the commercial non-supported TiO.sub.2 nanoparticles large compact agglomerates of nanoparticles are formed. In contrast, in the case of the sepiolite/TiO.sub.2 product 50/50 the dispersion is more homogeneous and, although there are some agglomerates, they are much less compact.

(18) The better dispersion is translated into a greater photocatalytic efficacy, as can be verified in the following examples.

Example 4: Simulation of a Real Mortar Façade with White Cement. Influence of the Photocatalytic Additive in the Self-Cleaning Properties of the Mortars. Qualitative Study

(19) A qualitative method has been developed consisting of simulating a real façade and visually evaluating its self-cleaning effect in normal atmospheric conditions. This method has been based on standard ASTM G7-97.

(20) The method consists of the following: mortar specimens are prepared with the dosages considered appropriate (with and without photocatalytic additives). Once the specimens are prepared, a part of their surface is impregnated with an organic pollutant (rhodamine), simulating dirt, and the other part is left intact. The objective is to study how the organic pollutant degrades and visually analyse how the part that is not impregnated dirties over time due to environmental dirt. The specimens thus prepared are placed on the roof with an angle of 45° with respect to the horizontal. The self-cleaning is visually analysed in determined periods of time (FIG. 6).

(21) The specimens analysed have dimensions of 10×40×2 cm. Specimens have been prepared with BL A-L 42.5 white cement and different sepiolite products with TiO.sub.2 nanoparticles prepared as described in example 2, and added at different percentages. Furthermore, other types of additives have been added: 1) superplasticizers to improve the workability of the fresh mortar and 2) whiteners to enhance the whiteness of the specimens. Micrometric titanium has been chosen as whitener; however, despite being TiO.sub.2, its photocatalytic effect is minimal due to its size. By way of comparison, a sepiolite has been used with TiO.sub.2 nanoparticles synthesized in the clay fibres in accordance with the process described in patent WO2005035124. The dosages prepared are listed in the following table.

(22) TABLE-US-00001 Dosage of Dosage of whitener Type of photocatalytic Micrometric Total content of Photocatalytic additive TiO.sub.2 TiO.sub.2 and type Id* additive (%) (%) (%) A — — — B — — 1 1, micrometric C 33%   1.5 — 0.5, nanometric SepTiO.sub.2 (a) D 50% 1 — 0.5, nanometric SepTiO.sub.2 (b) E 33% 3 — 1, nanometric SepTiO.sub.2 (a) F 50% 2 — 1, nanometric SepTiO.sub.2 (b) G 33% 3 1 1, nanometric + SepTiO.sub.2 (a) 1, micrometric H 50% 2 1 1, nanometric + SepTiO.sub.2 (b) 1, micrometric I 33% 3 1 1, nanometric + SepTiO.sub.2 1, micrometric Synthesis (c) J nanoTiO.sub.2 1 1 1, nanometric + commercial (d) 1, micrometric *All the samples use BL A-L 42.5R cement, standardized sand according to standard UNE EN 196-1 (3:1 ratio with the cement) and a water/cement ratio of 0.5. (a): 33% SepTiO.sub.2: Sepiolite/TiO.sub.2 product with 33% TiO.sub.2 prepared according to example 2 (b): 50% SepTiO.sub.2: Sepiolite/TiO.sub.2 product with 50% of TiO.sub.2 prepared according to example 2 (c): 33% SepTiO.sub.2 synthesis: Sepiolite product with 33% TiO.sub.2 nanoparticles prepared by direct synthesis of the TiO.sub.2 on the sepiolite as described in patent WO2005035124 (d): Commercial TiO.sub.2 nanoparticles not supported on sepiolite

(23) As the method is qualitative and can only be appreciated correctly in situ or by colour photographs, it is necessary to establish a qualitative scale. Said scale is as follows:

(24) 1—Intense pink colouring.

(25) 2—Moderate pink tonality.

(26) 3—Slight pink tonality.

(27) 4—Traces of pink colouring can be observed.

(28) 5—No colouring is observed.

(29) The following table shows the results of bleaching/self-cleaning obtained in accordance with the established scale.

(30) TABLE-US-00002 Id t = 0 t = 1 day t = 2 days t = 3 days t = 5 days A 1 2 2 2 3 B 1 2 2 3 3 C 1 4 4 5 5 D 1 3 4 4 5 E 1 4 5 5 5 F 1 3 5 5 5 G 1 4 5 5 5 H 1 3 5 5 5 I 1 3 4 4 5 J 1 3 4 4 5

(31) Analysing the results the following can be concluded: In all cases the sepiolite-based photocatalytic additive achieves a faster self-cleaning than the samples without photocatalytic additive. There is faster self-cleaning with greater percentages of photocatalytic additive. The additive consisting of sepiolite with 33% TiO.sub.2 gives faster self-cleaning than sepiolite with 50% TiO.sub.2. The product consisting of sepiolite with 33% TiO.sub.2 nanoparticles synthesized directly on the sepiolite according to patent WO2005035124 has a self-cleaning activity appreciably greater than that obtained with the photocatalytic additive G with the same TiO.sub.2 nanoparticle content but obtained according to the process described in this invention. These results confirm the action mechanism of the additive proposed in the patent, since the sample containing TiO.sub.2 nanoparticles synthesized in sepiolite does not have rheological properties nor the water absorbed in the clay structure which would act enhancing the degradation reaction of the organic pollutant, since the TiO.sub.2 nanoparticles are obtained after the thermal treatment of the clay at high temperature (700° C.), as disclosed in patent application WO2005035124. Furthermore, the sepiolite with TiO.sub.2 synthesized on its surface appreciably yellow the mortar, despite the addition of whitener. With the same TiO.sub.2 content, product J with commercial non-supported TiO.sub.2 nanoparticles gives a self-cleaning activity that is appreciably less than that obtained with products G and H with the TiO.sub.2 anchored and supported on sepiolite following the process disclosed in this invention. This is due to the fact that the dispersion in the mortar is much more heterogeneous in the case of non-supported TiO.sub.2 nanoparticles. The addition of micrometric TiO.sub.2 achieves a whitening effect which is observed in the samples. However, the addition of micrometric TiO.sub.2 used as whitener does not cause a significant improvement in the self-cleaning effect in the case of nanometric TiO.sub.2 supported on the sepiolite. Indeed, an effect of the micrometric TiO.sub.2 is only observed on the self-cleaning activity in the case that the sample does not have sepiolite, Due to the addition of the sepiolite-based photocatalytic additive to the cement, it is necessary to use a superplasticizer in the formulation that does not interfere in the photocatalytic properties.

Example 5: Accelerated Study with UV Light Influence of the Photocatalytic Additive in the Self-Cleaning Properties of the Mortars. Semi-Quantitative Study with Analytical Software

(32) The quantification of the self-cleaning activity of photocatalytic materials has been carried out by the test detailed below. Said test is based on the initial preparation of an organic colouring agent solution, specifically, methylene blue, which is applied on the surface to be studied. Next, UV light is irradiated (500 W UV light bulbs) on the samples prepared and it is studied how the surface loses the initially acquired blue surface and recovers its initial appearance. Photographs are taken at various times and, from these, the self-cleaning capacity of a surface associated to the photocatalytic phenomena that occur is calculated. The quantification is carried out by software which analyses the captured images of the materials tested at different times, calculating the percentage of bleaching after being exposed to ultraviolet light. The software quantifies as 100% bleaching if the same tone is reached of a reference mortar without staining by methylene blue and 0% as a reference specimen recently stained with methylene blue.

(33) The samples tested by this method are the following:

(34) TABLE-US-00003 Type of Dosage of Photocatalytic photocatalytic Real TiO.sub.2 Id* additive additive (%) Content (%) 1 — 0 0 2 50% 1.5 0.75 SepTiO.sub.2 (a) (a): 50% SepTiO.sub.2: Sepiolite/TiO.sub.2 product with 50% TiO.sub.2 prepared according to example 2

(35) The results obtained from the material with the sepiolite-based photocatalytic additive and a conventional mortar without additive are detailed below: Material 1 “conventional mortar without additive” achieves 8% bleaching in 240 minutes of irradiation; and Material 2 “mortar with sepiolite-based self-cleaning additive” achieves 21% bleaching in 240 minutes.

(36) The 8% bleaching detected in the sample without additive is due to the degradation undergone by the methylene blue from UV irradiation, without this effect having anything to do with the photocatalytic activity. Therefore, the difference between both tests performed in parallel is due to the self-cleaning photocatalytic capacity of the material developed with the sepiolite-based additive, whose value is 13%, in the test conditions.

Example 6: NOx Pollution Reduction Tests. Quantitative

(37) The method used basically consists of making an airstream with a known quantity of NOx pass through a hermetic chamber containing the mortar specimens with photocatalytic additive. It analyses the evolution of the NOx concentration with and without UV radiation to determine the photocatalytic efficacy of the specimens introduced in the chamber.

(38) A heated analyser of nitrogen oxides was used to determine the concentration of nitrogen oxides by a reference method, CLD-700-AL-NO/NOx, mark ECO PHYSICS, which used the principle of chemiluminescence measurement. The test is performed at four different relative humidities of air to study the behaviour of the specimens since the relative humidity of the air is a factor which influences the process differently depending on the nature of the specimen. Furthermore, the specimens were washed with distilled water and the concentration of nitrates and nitrites of said leachate was analysed. The method used for this analysis is described in standard UNE-EN-ISO 10304-1 which uses ion chromatography with chemical suppression.

(39) The following equations have been used to calculate the NOx elimination performance and the oxidation of NO to NO.sub.2.

(40) $\mathrm{Percentage}\mathrm{of}\mathrm{NOx}\mathrm{elimination}$$\frac{{\left[{\mathrm{NO}}_x\right]}_{\mathrm{in}}-{\left[{\mathrm{NO}}_x\right]}_{\mathrm{out}}}{{\left[{\mathrm{NO}}_x\right]}_{\mathrm{in}}}\times 100$$\mathrm{Percentage}\mathrm{of}\mathrm{Oxidation}\mathrm{of}\mathrm{NO}\mathrm{to}{\mathrm{NO}}_2$$\frac{{\left[{\mathrm{NO}}_2\right]}_{\mathrm{out}}}{{\left[\mathrm{NO}\right]}_{\mathrm{in}}}\times 100$

(41) The suffixes “in” and “out” in the previous formulas refer to the concentrations in the input (in) and output (out) streams, respectively.

(42) The mortars tested are described in the following table:

(43) TABLE-US-00004 Sand (standardized according to standard UNE Water/ Photo- Real TiO.sub.2 EN 196-1): cement catalytic Content Mortar Cement cement ratio additive (%) White BL A-L 3:1 0.5 — — 42.5 R 50% BL A-L 3:1 0.5 1.5% 0.75 SepTiO.sub.2 (a) 42.5 R SepTiO.sub.2. TX Aria (b) Cement 3:1 0.5 TiO.sub.2 3.2 TX Aria nanoparticles (according to FRX analysis) (a) Mortar containing Sepiolite/TiO.sub.2 with 50% TiO.sub.2 obtained according to example 2 as photocatalytic additive. (b) Mortar containing TX Aria commercial cement which has the addition of TiO.sub.2 nanoparticles as photocatalytic additive.

(44) The activity of the photocatalytic additive sepiolite/TiO.sub.2 with 50% TiO.sub.2 obtained by the process disclosed in the present invention has been compared with a commercial photocatalytic mortar, TX Aria.

(45) The following table shows the NOx pollution reduction results obtained in the tests, at different relative humidities.

(46) TABLE-US-00005 Percentage of relative humidity Mortar 5% 25% 50% 75% White NOx elimination 3.4 2.7 0.3 2.1 NOx oxidation 7.3 7.6 6.4 6.2 50% SepTiO.sub.2 NOx elimination 48.3 42 36.0 35.6 NOx oxidation 9.2 10.2 11.4 11.5 TX Aria NOx elimination 53.5 43.3 38.4 35.7 NOx oxidation 6.8 8.9 10.2 10.9

(47) In light of the results obtained it can be verified that: Both the mortar prepared with the sepiolite-based photocatalytic additive obtained according to the present invention and the commercial mortar (TX Aria) have a much greater NOx pollution reduction capacity than the white mortar. The sample of Sepiolite/TiO.sub.2 50/50 added to the mortar in a percentage of 1.5% has an activity similar to the sample prepared with TX Aria cement, which contains a greater percentage of TiO.sub.2. In the white mortar, the percentage of NOx oxidized is much greater than that eliminated. In the other two samples, both in the sepiolite-based additive and in TX Aria, the quantity of NOx eliminated is much greater than that oxidized. The photocatalytic activity of NOx elimination decreases as the humidity in which the test is performed increases.

Example 7: TiO2 Product Supported on Sepiolite without Acid Activation

(48) To determine the effect of acid activation of the pseudo-layered phyllosilicate on the photocatalytic activity of the sepiolite product with supported TO.sub.2, a product was prepared similarly to that described in example 2, but wherein the acid activation stage of the sepiolite was omitted:

(49) A dispersion was prepared of a rheological grade sepiolite obtained by the process disclosed in patent EP0170299, trade name PANGEL, 6% in water by a mechanical blade shaker which rotates at 1,200 rpm for 10 minutes. Omitting the acidification stage, an aqueous dispersion of 6% commercial TiO.sub.2 nanoparticles previously prepared as indicated in example 1 was added to the previous dispersion, so that the final sepiolite/TiO.sub.2 ratio was 50/50. The resulting suspension was vigorously mixed in a Grindomix-type ball mill with zircon balls between 1.6 and 2.4 mm in diameter for 10 minutes to achieve sufficient shear to completely defibrillate the sepiolite clusters and totally disperse the TiO.sub.2 nanoparticles anchored to the acid centres of the exposed surface of the sepiolite. Next, the product was filtered and dried at 105° C., until a final humidity of 10%.

(50) Another product was also prepared following the same process but with a sepiolite/TiO.sub.2 ratio of 67/33, i.e. with 33% by weight of TiO.sub.2. These products were used as photocatalytic additives in example 8.

Example 8: Quantitative Test of Toluene Pollution Reduction

(51) The method used for this analysis basically consists of subjecting the mortars prepared to an airstream with a known concentration of toluene under UV radiation (5 mW/cm.sup.2). Samples are taken of the air stream at different times: 0, 2.5, 5 and 21 hours, and the toluene concentration was analysed by chromatography to determine the progressive elimination of toluene. The equipment used to determine the toluene concentration is a gas chromatograph with mass detector (GC-MS).

(52) The experimental device used to carry out the test basically consists of a chamber with a 6-liter volume with a Pyrex glass window, to introduce the UV radiation, wherein pressurized air and toluene are loaded. It has a pipe and a pump for total recirculation. The recirculation capacity is 30 L/min. To calculate the toluene elimination performance, the following equation has been used.

(53) $\frac{{\left[\mathrm{Tol}\right]}_0-{\left[\mathrm{Tol}\right]}_t}{{\left[\mathrm{Tol}\right]}_0}\times 100$
The suffixes 0 and t of the previous equation refer to the toluene concentrations in the airstream at time 0 and time t, respectively.

(54) The mortars tested are described in the following table:

(55) TABLE-US-00006 Sand (standardized according to standard Real UNE EN water/ Photo- TiO.sub.2 196-1): cement catalytic content Mortar Cement cement ratio additive (%) White BL A-L 3:1 0.5 — — 42.5 R 33% BL A-L 3:1 0.5 2.3% of 0.75 SepTiO.sub.2 42.5 R 33% (without SepTiO.sub.2. activation) (a) 33% BL A-L 3:1 0.5 2.3% of 0.75 SepTiO.sub.2 42.5 R 33% (activated) (b) SepTiO.sub.2. 50% BL A-L 3:1 0.5 1.5% of 0.75 SepTiO.sub.2 42.5 R 50% (without SepTiO.sub.2. activation) (c) 50% BL A-L 3:1 0.5 1.5% of 0.75 SepTiO.sub.2 42.5 R 50% (activated) (d) SepTiO.sub.2. Commercial BL A-L 3:1 0.5 0.75% 0.75 TiO.sub.2 (e) 42.5 R TiO.sub.2 of EVONIK TX Aria (f) TX Aria 3:1 0.5 TiO.sub.2 3.2 cement nano- (according particles to FRX analysis) (a): 33% SepTiO.sub.2 (without activation): sepiolite/TiO.sub.2 product with 33% TiO.sub.2 prepared according to example 7 omitting the acid activation stage (b): 33% SepTiO.sub.2 (activated): sepiolite/TiO.sub.2 product with 33% TiO.sub.2 prepared according to example 2 (c): 50% SepTiO.sub.2 (without activation): sepiolite/TiO.sub.2 product with 50% TiO.sub.2 prepared according to example 7 omitting the acid activation stage (d): 50% SepTiO.sub.2 (activated): sepiolite/TiO.sub.2 product with 50% TiO.sub.2 prepared according to example 2 (e): commercial TiO.sub.2 nanoparticles supplied by Evonilk. (f) Mortar containing TX Aria commercial cement which has the addition of TiO.sub.2 nanoparticles as photocatalytic additive.

(56) The following table shows results obtained of toluene pollution reduction after 21 hours of the test.

(57) TABLE-US-00007 Percentage of toluene pollution reduction Percentage of after 21 hours in the pollution photocatalytic chamber reduction/real TiO.sub.2 Mortar (%) percentage ratio White 7 9 33% SepTiO.sub.2 50 67 (without activation) (a) 33% SepTiO.sub.2 73 97 (activated) (b) 50% SepTiO.sub.2, 67 89 (without activation) (c) 50% SepTiO.sub.2 99 132 (activated) (d) Commercial TiO.sub.2 (e) 56 75 TX Aria (f) 69 22

(58) In light of the results obtained it can be concluded that: All samples containing photocatalytic additives have a toluene pollution reduction capacity much greater than mortar without additive. The samples of mortar containing the TiO.sub.2-based additive supported on sepiolite are more active than the commercial ones based on nanometric TiO.sub.2 directly dispersed in the mortar matrix with the same TiO.sub.2 content. The samples of mortar with sepiolite-based additive have a toluene pollution reduction capacity similar to the mortar made with the TX Aria cement, but the activity/TiO.sub.2 ratio is much higher in the case of sepiolite-based additives, which shows the greater efficacy of the TiO.sub.2 supported on sepiolite. The sepiolite product with 33% supported TiO.sub.2 has slightly less activity than the sepiolite product containing 50% supported TiO.sub.2 (with the same TiO.sub.2 content). The sepiolite-based products treated to generate a greater number of acid centres and silanol groups on the surface, obtained by acid activation treatment, have significantly greater activity than the sepiolite-based products not activated with acid.

Example 9: Sol-Gel Coatings

(59) Since photocatalysis is a superficial phenomenon there is also the possibility of incorporating the TiO.sub.2 nanoparticles supported on sepiolite on the surface of mortar or other materials via a coating.

(60) The coatings used in the present example are based on sol-gel technology using silicon alkoxides as reaction precursors. These precursors, once dissolved in alcohol, are hydrolyzed in water to form their respective silanes and later undergo the condensation reaction.

(61) Thus, coatings with different percentages of the sepiolite-based photocatalytic additive were applied to conventional mortars with white cement (Sepiolite/TiO.sub.2), and their self-cleaning was evaluated after being dirtied with an organic pollutant (rhodamine). This staining simulates the dirt deposited in controlled manner on the surface of said specimens. The photocatalytic activity of self-cleaning was determined according to the process described in Example 4 of the present patent, based on Standard ASTM G7-97. Exposure to solar radiation caused the disappearance of said stain with the passage of time, the material recovering its initial appearance.

(62) The results obtained from this test are included in the following table.

(63) Self-cleaning results of the different samples of white mortar with sol-gel coating.

(64) TABLE-US-00008 Percentage of Sepiolite/TiO.sub.2 50/50 with respect to the Time until Silicon quantity of achieving alkoxide Alcohol Water alcohol surface cleaning ID (mL) (mL) (mL) (%) (hours) 1 13.73 36.87 12.29 0 2,000 2 13.73 36.87 12.29 10 480 3 13.73 36.87 12.29 20 168 4 13.73 36.87 12.29 30 24

(65) In light of the results, it can be concluded that: All the mortars coated with the sol-gel solution containing sepiolite-based photocatalytic additive with supported TiO.sub.2 self-clean much before those coated with sol-gel without photocatalytic additive. The greater the content of sepiolite with TiO.sub.2 in the sol-gel solution, the sooner the degradation occurs of the organic colouring agent in the mortars coated with said sol-gel coatings.

Example 10: Rheological Modification of Concretes

(66) As commented above, the photocatalytic additive of the present invention has the quality of being a concrete viscosity regulator, in addition to providing pollution reduction and self-cleaning properties.

(67) The present example shows the rheological effect of the sepiolite-based photocatalytic additives with supported TiO.sub.2.

(68) Two concretes have been prepared, one with the photocatalytic additive and another without the same additive. The dosage has been designed so that the aggregates are segregated, to be able to evaluate the efficacy of the photocatalytic additive as rheological additive to avoid segregation in the concrete. The following table shows the two formulations prepared.

(69) TABLE-US-00009 Real dosage Dosage Real dosage with sepiolite per m.sup.3 Mixed with 0% Mixed with 1.5% Reference Standard Sepiolite/TiO.sub.2 Sepiolite/TiO.sub.2 Volume mixed 1 m.sup.3 15 L 15 L Cement, kg 300 4.50 4.50 Water, kg 222 3.35 3.35 a/c 0.74 0.74 0.74 Quartzite sand, kg 1137 17.1 17.1 Quartzite gravel, kg 886 13.3 13.3 Plasticizer, % 1 1 1 Plasticizer, kg 3.0 0.045 0.045 Sepiolite/TiO.sub.2 — 0.0 1.54 50/50 % Sepiolite/TiO.sub.2 — 0.0 0.06 50/50, kg

(70) FIGS. 7 and 8 show the result of the addition of the additive in the concrete's rheology. As can be clearly observed in the above figures, segregation occurs in the absence of the sepiolite-based additive and the Abrams cone obtained is 22 cm. In the case of the dosage with the additive (Sepiolite/TiO.sub.2) it can be verified how the concrete's appearance is very good, there is no segregation and a cone of 8 cm is obtained, which is manageable and workable.

(71) It can be concluded that in addition to providing photocatalytic properties, the additive object of the present invention also acts as a rheological modifier for concretes.

(72) Furthermore, the mechanical properties of the concrete are not harmed by the addition of the sepiolite-based photocatalytic additive with supported TiO.sub.2, as can be seen in the following table.

(73) TABLE-US-00010 28-day resistance to Reference compression (Mpa) Mixed 0% 26 Sepiolite/TiO.sub.2 50/50 Mixed 1.5% 25 Sepiolite/TiO.sub.2 50/50

(74) This example shows the dual usefulness of the sepiolite-based additive with supported TiO.sub.2 as photocatalytic additive and as rheological modifier in concretes.