ES2610658A1 - Self-cleaning, decontaminant and consolidating product for building materials (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

The present invention relates to a composite material constituted by nanoparticles of titanium dioxide and gold integrated in a silica gel, which possesses photocatalytic activity. This new material originates a self-cleansing and decontaminating effect on building materials of porous nature. Specifically, it is a product capable of: (1) providing the treated surface with self-cleaning and decontaminating capacity by simple exposure to sunlight. (2) improving its surface mechanical strength (3) to form a cohesive coating capable of adhering to the substrate. (Machine-translation by Google Translate, not legally binding)

Description

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which produces the evaporation of these compounds during the application phase in building materials or in buildings.

Description of the figures

FIGURE 1.- Comparison of self-cleaning products in which their activity decreases with increasing concentration of Au. a) Degradation curves of methylene blue on rocks treated with the products. b) Pore size distribution of the gels. c) HAADF-STEM image of the gel with 0.12% gold and corresponding EDX map for silicon (red) and titanium (blue). d) HAADF-STEM image of the gel with 0.25% gold and corresponding EDX map for silicon (red) and titanium (green).

FIGURE 2.- Comparison between the adsorption-attrition nitrogen isotherms and their corresponding pore distribution for the same material by varying the proportion of water during its synthesis.

FIGURE 3.- Image of transmission electron microscopy and size distribution of the gold nanoparticles used in the synthesis.

FIGURE 4.- Diffuse reflectance spectra of the prepared xerogels.

FIGURE 5.- Evolution of the maximum relative absorption of methylene blue in the stained samples during the self-cleaning test, general evolution and detail of the first 60 minutes.

Embodiment of the invention

The synthesis of the product, object of the present invention, includes the following steps:

First, the synthesis process undergoes slight variations depending on the way in which the gold nanoparticles are introduced into the starting sun:

(one)

Titanium dioxide is mixed with the silica oligomer and the previously synthesized gold nanoparticles are added dispersed in the volume of water used in the synthesis.

(2)

The titanium dioxide is mixed with a dispersion of previously synthesized gold nanoparticles and the dispersant is evaporated to obtain a dry powder composed of gold and titanium dioxide nanoparticles. This powder is mixed with the silica oligomer and the water necessary for the synthesis is added.

(3)

The titanium dioxide is mixed with the silica oligomer and a gold precursor and optionally a reducing agent dissolved in the volume of water to be used in the synthesis are added. In this way gold nanoparticles are formed during the synthesis of the sun.

Regardless of the type of incorporation of the nanoparticles chosen, the non-ionic surfactant is added to the mixture of silica, water, gold nanoparticles and titanium dioxide precursor and the mixture is kept under ultrasonic stirring for 10 minutes. The silicon oligomer can be TES40 WN (Wacker) and the nonionic surfactant used in the synthesis, the first amine n-octylamine. Regarding the required concentrations of each component in the starting sol, mention that if the polymer precursor is Wacker TES 40 WN and the non-ionic n-octylamine surfactant, the concentration of surfactant in the initial sol should be 0.22 M or higher, being the

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Critical micellar concentration of said surfactant at around 0.0065 M. For lower concentrations of n-octylamine, aggregation and / or precipitation of the nanoparticles occurs before the sol-gel transition occurs.

In the case of titanium dioxide, commercial particles such as Aeroxide P25 or VP Aeroperl P25 / 20 from Evonik or nanoparticles prepared in the laboratory can be used. Its proportion in the sun must be between 1 and 4% w / v with respect to the precursor, since for higher concentrations there is a significant increase in the viscosity and opacity of the suns. This prevents the penetration of the material in the porous structure of the rock, reduces its adhesion and greatly modifies the color of the treated substrate.

The gold nanoparticles must have a size between 3 and 20 nm to intensify the phenomenon of surface plasmon resonance. If a gold precursor is used, it can be tetrachlorouric acid or its potassium salt and as a sodium citrate reducer. Their concentrations should be such that the Au / TiO2 ratio does not exceed 1% w / w.

The water content in the sun must be between 0 and 1.67% v / v with respect to the silica precursor, with the maximum percentage of improvement of its characteristics around 0.83% v / v (Figure 1) , greater amount of water produces an excessively rapid gelation that prevents the application of the products.

The next stage of the process is the impregnation of the material to be treated with the prepared sun. The product can penetrate the substrate by impregnating the surface by spraying or by application by means of a roller or brush. In the case of small objects, by immersion in a tank containing the sun, or by capillary ascent by superficial contact of the product with the underside of the object. After impregnation, condensation polymerization of the silicon oligomer occurs, resulting in an Au-TiO2-Si O2 composite.

Next, and in order to illustrate in more detail, the advantages of products incorporating gold nanoparticles, results obtained in our research laboratory are described. Specifically, in example 1 the synthesis procedure is described and the characterization of the synthesized materials is performed, in which the proportion of gold nanoparticles with respect to titanium dioxide was varied between 0 and 1% w / w.

In Example 2, the same materials are applied to a building material of a stone nature, with an evaluation of its ability to adhere to the substrate and its effectiveness as a consolidant and self-cleaning.

Example 1

Evonik VP Aeroperl P25 / 20 titanium dioxide particles, with a particle diameter of 20 μm, and a surface area of 50 ± 15 m2 / g, were mixed with an aqueous dispersion of spherical gold nanoparticles with an average size of 7, 45 nm (Figure 2). Then, the water in the mixture is evaporated until a dry powder is obtained. The process is repeated to obtain titanium dioxide powders with gold contents of 0.25, 0.5 and 1% w / w. The powders are mixed with TES40 WN (hereinafter "TES40"), manufactured by Wacker and consisting of silica oligomers. The proportion of TiO2 with respect to the silicon precursor is 1% w / v. The water and the non-ionic surfactant, n-octylamine are then added, the proportion of water and octylamine with respect to TES40 is 0.83% and 0.36% (v / v), respectively. Additionally and for comparative purposes, a sun was prepared without gold nanoparticles or titanium dioxide. The five prepared suns were subjected to ultrasonic stirring (power 125 W) for 10 minutes. These

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Next, using a reflection spectrophotometer for Hunterlab ColorFlex model solids, with the following conditions: illuminant 065, 10 ° observer and CIEL standard * a * b *, the total color differences (∆E *) that the samples undergo were determined after treatment, which are shown in Table 1. This parameter is very important since high color changes are perceptible by the human eye and limits the application of the products to demanding fields such as heritage conservation (M. Drdȧckȧ et al, Mater. Struct., 45, 505, 2012). The treatment with particles of titanium dioxide produces a smaller color change than the one that does not have particles because being a white rock, TiO2 does not produce an appreciable color change. With the addition of the gold nanoparticles the color changes are greater and increase as the content of Au in the formulations increases. The limit for the application in the most restrictive fields is in the proportion of gold of 0.25% in which ∆E is around 5. All changes in the samples are uniform without stains appearing to reduce aesthetic value to the material So even the products with the highest gold content can be used for applications where color change is not a limiting factor, even giving the rock a pink-purple hue can be a desirable effect.

The degree of adhesion of the products on the stone substrate was determined by an adhesion test, according to methodology previously described by other authors (Ling L et al. Langmuir, 25, 3260, 2009; Ding, Z et al. Langmuir, 25, 9648, 2009). The treated stone surfaces and the untreated samples were subjected to the adhesion test. This test consisted of placing the adhesive tape on the stone surface and then being removed manually, exerting similar pressure in all cases. Table 1 shows the amount of material removed by the adhesive tape for each sample. In all cases, the amount of material removed is very low, even being null for ST1Au, which indicates a very good adhesion of the products on the stone substrate. In addition, the amount of material removed in the treated samples is of the order of 20 times lower than that of the untreated sample, therefore the products achieve an effective consolidating effect of the rock surface.

The self-cleaning efficacy of the products was evaluated by means of a test adapted from ISO 10678. To this end, 0.5 ml of 1 mM methylene blue solution is deposited on the samples. The spots were allowed to dry, under laboratory conditions and darkness, until constant weight. Next, the specimens were irradiated with light at 500W / m2 in a Solarbox 3000e RH solar degradation chamber of CO.FO.ME.GRA equipped with a xenon lamp as a light source. During the test the samples were subjected to a humidity of 60% and a temperature of 50 ° C. At first glance, it was observed that during the test time the stain in the untreated rock is practically not altered, however all the treated samples show degradation of methylene blue, being observed in all the treated samples a total disappearance of the staining after 300 min However, there are significant differences in degradation kinetics between products that contain Au and those that do not have this component. Specifically, degradation begins to be evident in samples treated with products containing gold nanoparticles at 15 minutes and after 60 minutes the spots have virtually disappeared. In the case of samples treated with products without Au (S0Au and ST0Au), the spots remain after 60 minutes of exposure in the chamber.

To have a quantitative measure of the degradation of methylene blue, the visible reflection spectra of the stained samples were recorded throughout the test using the solid spectrophotometer. From these spectra, the degradation curves of methylene blue were created on each sample representing the relative absorption of methylene blue (absorption ratio over time

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Claims (1)

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