Multifunctional particle comprising titanium dioxide, silver, silicon dioxide

Abstract

The present invention relates to a particle comprising titanium dioxide (TiO2), silver nanoparticles (Ag), silicon dioxide (SiO2), said particle comprising at least a fluorescent agent and / or at least a photoluminescent agent linked via heterojunction to said particle, wherein TiO2, Ag and SiO2 are linked to each other via heterojunctions, wherein the largest size of said particle is comprised between 60 nm and 70 nm. The particle according to the present invention has the advantages of being a nanomaterial that is highly compatible with finishing products, which may be used in the leather finishing process in order to give leather multifunctional properties such as protective properties, UV radiation resistance, self-cleaning properties, fluorescent and photoluminescent properties, and also improved mechanical and thermal resistance.

Description

[0001] Multifunctional particle comprising titanium dioxide, silver, silicon dioxide

[0002] Field of the invention

[0003] The present invention relates to a multifunctional particle comprising titanium dioxide, silver, silicon dioxide in particular a particle comprising titanium dioxide (TiCF), silver nanoparticles (Ag), silicon dioxide (SiCh), said particle comprising at least a fluorescent agent and / or at least a photoluminescent agent linked via heterojunction to said particle; it further relates to a process for the production of said particle, a composition comprising said particle, the use of said particle and said composition, a process for processing leather and a leather thus obtained.

[0004] Prior art

[0005] The finishing step constitutes the final step of processing the leather, the function of which is to refine the appearance of the leather and provide the desired functional features depending on the type of finished leather, with reference to

[0006] - color: desired hue, based on indications dictated by fashion or special requirements of the customer, features of transparency or coverage, reproduction of particular effects;

[0007] - brilliance: obtaining final finishes characterized by high brilliance, gloss or opacity;

[0008] - feel: achieving dry, waxy, greasy or “non-slippery” surfaces;

[0009] - resistance to mechanical stress: resistance to cracking, rubbing;

[0010] - specific mechanical features: flexibility, adhesion, extensibility;

[0011] - resistance to light, heat and other environmental agents;

[0012] - water vapor permeability;

[0013] - water resistance.

[0014] Generally, finishing operations may be divided into mechanical operations and application of surface coatings, which constitute a finishing film, the main matrix of which (net of pigments and auxiliaries, such as feel modifiers, stabilizers, etc.) is generally made up of polymers, to which most of the functions described above are appointed.

[0015] According to whether they are dissolved (or dispersed) in water or solvents, the polymers used in leather finishing are called “binders” (or “resins”) or “lacquers” (or “varnishes”), respectively. Another classification of this category of compounds may be made on the basis of the heat behavior exhibited by polymers, distinguishing them into “thermoplastics” and “thermosets”, according to whether, due to temperature, they become fluid (later returning to their original state by cooling), or harden, undergoing an irreversible chemical transformation. Naturally, these behaviors will depend substantially on the chemical constitution of the polymer and its molecular weight. Relating only to the use of polymers in the tanning industry, it is possible to find a further definition based on this criterion, according to which polymers (such as proteins and cellulose derivatives) are defined as “non-thermoplastic”, which are those polymers that, although possessing thermoplastic features, do not fluidize when the leather is subjected to mechanical and thermal treatments (with temperatures above 100°C). Finally, the polymers used in finishing may also be classified as:

[0016] - synthetics: acrylic resins, butadiene resins, polyurethane resins, polyamide resins, polyvinyl resins, epoxy resins;

[0017] - natural: casein, albumin;

[0018] - natural modified: cellulose derivatives (nitrocellulose, ethylcellulose, cellulose acetate, cellulose acetatebutyrate), casein with polyamides.

[0019] The thin finishing layer not only highlights and enhances the beauty of the leather; it is also responsible for a number of other roles and properties.

[0020] Properties of resistance to light, stain formation, oxidation, antimicrobial properties, and innovative optical properties are highly desirable for making leathers that are more durable, high-performing, and able to withstand the challenges of an increasingly globalized and demanding market.

[0021] Leather is the final substrate produced by the tanning process of animal hides such as those of cattle, sheep, goats and camels. The leather industry exists as an independent production due to the unique properties and wide use of its products in various manufactured products, such as: footwear, upholstery, gloves, garments, cases and other purposes.

[0022] The main component of natural leather is a protein called collagen. Since amino acids are the main units of collagen, leathers show functional groups such as -NH4+, -COO-, and - OH groups.

[0023] Finishing makes it possible to improve the appearance, texture, and surface roughness of leathers. It also makes it possible to protect the surface of the leather from contaminants, change its color and mask defects.

[0024] Leather finishing is one of the most crucial operations in the leather industry.

[0025] Different materials are known for leather finishing of which formulations have been developed in order to obtain leathers with specific properties.

[0026] In recent years, metallic nanoparticles have gained interest because of their wide range of potential applications. In particular, inorganic nanomaterials such as metals / metal oxides have received attention in leather finishing.

[0027] Microorganisms such as molds, yeasts, and bacteria may be a problem for leather and the leather manufacturer, their presence may in fact affect the product and performance features of leather items, including goods intended for the fashion and luxury market, such as items for footwear, leather goods, clothing, automotive, etc. Studies in the literature have concluded that the use of antimicrobial finishes may counteract microbial growth.

[0028] Traditional antimicrobial treatments, based on 2-(Methyl thiocyanate) and benzothiazole, due to the variability of microbial species and toxicity issues, are not suitable for all applications, also in view of the growing trend in this field toward the use of eco- sustainable agents and molecules.

[0029] In recent years, silver nanoparticles have been observed to exhibit interesting antibacterial activities, in part due to their large surface-to-volume ratio, which may also be used in the context of leather.

[0030] Ag nanoparticles are able to play a crucial role in inhibiting bacterial growth in aqueous and solid media. Silver-containing materials may be used to eliminate microorganisms in medical devices and on textiles or may be used for water treatment.

[0031] Silver nanoparticles, in solution or supported on substrates, are now widely used due to their efficiency related to their ability to negatively affect the metabolism of microbial cells and inhibit their growth. Studies have shown that silver deposits are nontoxic to human cells in vivo and are biocompatible.

[0032] Titanium dioxide (TiCh) nanoparticles are considered extremely promising photocatalysts. Within the scope of photocatalytic processes, TiCh nanoparticles are among the most widely used (e.g., water and air purification, surface self-cleaning, self- sterilization, optical and dielectric devices).

[0033] Modifying the TiCh nanoparticles to make them more sensitive to visible light is one of the most important goals to increase their utility.

[0034] The presence of dopant ions in the titanium dioxide structure may cause a significant shift in absorption toward the visible region with respect to pure TiCh nanopowder.

[0035] In particular, it was also found that highly active radical species, produced on the surface of TiCh under UV / visible light irradiation, participate in oxidation reactions and facilitate the destruction of organic contaminants, inactivation of microorganisms, and enhancement of heat resistance.

[0036] It is known that coupling TiCh with silica may significantly increase its photocatalytic activity.

[0037] Surface finishing of leathers with doped TiC nanoparticles has been found, in general, effective in improving some properties, e.g., self-cleaning and thermal resistance of leathers.

[0038] Silica-based materials are considered promising as flame retardants; they also promote control of the release of corrosive fumes during combustion and are environmentally friendly.

[0039] Numerous papers and patents have contributed to the development of increasingly efficient materials in leather finishing; however, in all the studies conducted, the aim was to promote the improvement of individual properties.

[0040] In general, one of the limitations in the use of nanoparticles in finishing is the use of metals and metal oxides, which even if used in trace amounts persist in a context in which the legislative landscape considers it increasingly important to contain the presence of metals in the finished product. These days, macro-particles of TiCh and SiOi are currently used massively as pigments and finishing aggregates without compromising the main features of leathers, including on the eco-toxicological level.

[0041] The possibility of having a new nanomaterial, highly compatible with finishing products, which may be used in the leather finishing process in order to give the leather, at very low concentration, multifunctional properties, such as protective properties, UV radiation resistance, self-cleaning properties, fluorescent and photoluminescent properties, as well as improved mechanical and thermal resistance is therefore a need felt on the market.

[0042] Summary of the invention

[0043] Therefore, the object of the present invention is to provide a new nanomaterial, highly compatible with finishing products, which may be used in the leather finishing process in order to give the leather, at very low concentration, multifunctional properties, such as protective properties, UV radiation resistance, self-cleaning properties, fluorescent and photoluminescent properties, and also improved mechanical and thermal resistance. Such an object is achieved by a particle, by a composition comprising said particle, by a process of preparing said particle, by the use of said particle and said composition, by a process for processing leather and the leather thus obtained, as outlined in the attached claims, the definitions of which form an integral part of this description.

[0044] Brief description of the figures

[0045] The invention will be better understood from the following detailed description of preferred embodiments thereof, given by way of non-limiting example and with reference to the accompanying figures, in which:

[0046] - Fig. 1 is an image of the particle according to the present invention when dispersed in water;

[0047] - Fig. 2 is an image of the particle according to the present invention when dispersed in a commercial product “polyurethane dispersion used in glossy coating mixtures (the so-called “top coat”)”;

[0048] - Fig. 3 is an image of the particle according to the present invention when dispersed in a commercial product “polyurethane dispersion used in opaque coating mixtures (the so-called “top coat”)”;

[0049] - Fig. 4 is an image of the particle according to the present invention when dispersed in a commercial product “polyurethane / silicone in aqueous dispersion coating mixture (the so-called “top coat”)”;

[0050] - Fig. 5 is an image of the particle according to the present invention when dispersed in a commercial product “polyacrylic derivative in aqueous / organic dispersion”;

[0051] - Fig. 6 is an image of the particle according to the present invention when dispersed in a commercial product “an aqueous dispersion of an aliphatic polyurethane”;

[0052] - Fig. 7 is an image of the particle according to the present invention when dispersed in a commercial “water-based nitroemulsion” product;

[0053] - Fig. 8 shows an XRD (X-ray diffraction) spectrum of the particle according to the present invention;

[0054] - Fig. 9 shows the morphology of the particle according to the present invention analyzed by scanning electron microscopy (SEM);

[0055] - Fig. 10 is a TEM (transmission electron microscope) image of the particle according to the present invention;

[0056] - Fig. 11 shows the results of the NTA analysis (nanoparticle tracking analysis) performed on the particle according to the present invention;

[0057] - Fig. 12 shows TG-DTG (thermogravimetric analysis) profiles of the particle according to the present invention;

[0058] - Fig. 13 shows an FT-IR (Fourier transform IR spectroscopy) spectrum of the particle according to the present invention;

[0059] - Fig. 14 shows the spectroscopic analysis of commercial products used in the composition according to the present invention, performed by ATR-IR technique (attenuated total reflectance in infrared spectroscopy).

[0060] In the accompanying figures, identical or similar elements are denoted by the same reference signs.

[0061] Detailed description of the invention

[0062] A first subject matter of the present invention relates to a particle comprising titanium dioxide (TiOi), silver nanoparticles (Ag), and silicon dioxide (SiOi), said particle comprising at least a fluorescent agent and / or at least a photoluminescent agent linked via heterojunction to said particle, wherein TiOi, Ag and SiOi are linked to each other via heterojunctions, wherein the largest size of said particle is comprised between 60 nm and 70 nm. Preferably the largest size of said particle is 65 nm.

[0063] The particle according to the present invention also preferably comprises at least a substance selected from the group consisting of: 3 -aminoprop yltriethoxysilane, tetramethylammonium 11-aminoundecanoic acid, oleic acid, polyethylene glycol, acrylic acid, citric acid and mixtures thereof. Advantageously, the presence in the particle of said at least one substance allows the hydrophilic / hydrophobic nature of the particle surface to be modulated according to the present invention, depending on the requirements or applications needed.

[0064] Preferably, said at least one substance is present in a concentration comprised between 5% by weight and 30% by weight, % expressed with respect to the weight of the particle.

[0065] Preferably, in the particle according to the present invention, the weight ratio of Si / Ag and Si / Ti is, respectively, between 10 and 4 and between 25 and 2. Even more preferably, the weight ratio of Si / Ag and Si / Ti is, respectively, 6 and 23.

[0066] The particle according to the present invention preferably has a substantially flower-like three-dimensional structure comprising pistil and petals, wherein TiCh is the pistil, Ag and SiCE are the petals.

[0067] A second subject matter of the present invention relates to a process of preparing the above particle, comprising the following steps: a) providing or synthesizing titanium dioxide (TiCE); b) providing or synthesizing silver nanoparticles (Ag); c) using TiOi of step a) and Ag nanoparticles of step b) synthesizing Ag-TiCE nanoparticles; d) providing or synthesizing silicon dioxide (SiOi); e) providing or synthesizing a fluorescent agent and / or a photoluminescent agent; f) using Ag-TiCE of step c), SiCE of step d), and a fluorescent agent and / or a photoluminescent agent of step e) synthesizing a TiOi-Ag-SiOi particle linked via heterojunction to at least a fluorescent agent and / or at least a photoluminescent agent, thereby obtaining a particle as described above.

[0068] According to a preferred embodiment of the process according to the present invention: preferably step a) is a synthesis step and comprises reacting titanium isopropoxide with deionized water under agitation for a period of time comprised between 20 minutes to 40 minutes, preferably 30 minutes, at a temperature comprised between 30°C and 50°C, preferably 40°C; separating by centrifugation the TiOi precipitate obtained from the reaction; washing and drying the TiCh, preferably washing with deionized water and methanol and drying in an oven at a temperature comprised between 70°C and 90°C, even more preferably at a temperature of 80°C. Advantageously, when the synthesis of TiOi nanoparticles is done by chemical precipitation, this approach, by allowing the precipitation of metal ions, allows a pure material to be obtained: TiCh in anatase form. Alternative synthesis routes, such as reverse micelle approaches or solvothermal methods, preferably allow TiC to be obtained with mixed anatase / rutyl forms, which may improve TiC functionalities during decolorization phenomena.

[0069] According to a preferred embodiment of the process according to the present invention: preferably step c) is a synthesis step and comprises reacting benzyl ether, silver nitrate, 1,2-hexadecanediol, oleic acid, TiOi of step a), under agitation and under nitrogen flow for a period of time comprised between 1.5 hours and 2.5 hours, preferably 2 hours, at a temperature comprised between 20°C and 300°C; washing by centrifugation in ethanol and hexane the Ag-TiO2 thus synthesized and letting it dry, preferably for a period of time comprised between 20 hours and 30 hours at a temperature comprised between 20°C and 30°C, even more preferably for a period of time of 24 hours at a temperature of 25°C. Advantageously, the synthesis just described makes it possible to easily and economically obtain monodisperse, stable nanoparticles having controlled sizes and shapes. Advantageously, the oleic acid, a biocompatible molecule, is preferably used during step c) just described in order to make the surface of the Ag-TiCh hydrophobic to allow anchoring in the next step of SiCh.

[0070] According to a preferred embodiment of the process according to the present invention: preferably step f) is a synthesis step and comprises reacting Ag-TiCh of step c), SiOi of step d), and a fluorescent agent and / or a photoluminescent agent of step e); preferably the fluorescent agent is fluorescein isothiocyanate (FITC) or rhodamine b or 4,4'-dibromobiphenyl, preferably Ag-TiCh, SiCh, and a fluorescent agent and / or photoluminescent agent are added to a microemulsion, preferably comprising branched polyoxyethylene (5) nonylphenylether and cyclohexane; separating by centrifugation the TiOi-Ag-SiOi- particle linked by heterojunction to at least a fluorescent agent and / or at least a photoluminescent agent obtained from the reaction; washing the particle by centrifugation with at least one from: acetone, isopropanol, ethanol, water; letting the particle dry.

[0071] According to an alternative embodiment of the process according to the present invention: preferably step a) is a synthesis step, preferably a hydrothermal synthesis, wherein the synthesis takes place in an aqueous solution at controlled temperature / pressure.

[0072] Advantageously, this process is used for the production of small particles.

[0073] According to this alternative embodiment of the process according to the present invention, the synthesis preferably comprises the addition of titanium tetrachloride (TiCU) in deionized water under agitation at room temperature. Preferably, after 30 minutes of agitation, the solution is transferred to a Teflon-coated stainless steel autoclave. Hydrothermal treatment preferably involves heating the autoclave to 200°C for 16 hours. The precipitate is preferably collected by repeated centrifugation and washed with ionized water.

[0074] According to an alternative embodiment of the process according to the present invention: preferably step a) is a synthesis step, preferably a synthesis by the solvothermal method, wherein the synthesis takes place in a non-aqueous type solvent. Advantageously, the solvothermal method has good control over the size distribution, shape and crystallinity of the TiCh nanoparticles thus produced.

[0075] According to this alternative embodiment of the process according to the present invention, the synthesis preferably comprises the steps of: reacting titanium butoxide (Ti(OBu)4) with urea and citric acid in ethylene glycol under agitation at room temperature. Preferably, after 30 minutes of agitation, the solution is transferred to a Teflon-coated stainless steel autoclave. The solvothermal treatment preferably involves heating the autoclave from room temperature to 200°C, the mixture is preferably kept at 200°C for 4 hours. The precipitate is preferably collected by repeated centrifugation and washed with ionized water and ethanol.

[0076] According to an alternative embodiment of the process according to the present invention: preferably step a) is a synthesis step, preferably a synthesis by the sol-gel method, wherein a colloidal suspension (or sol) is formed by the hydrolysis and polymerization reactions of precursor inorganic metal salts or organic metal compounds such as metal alkoxides, preferably titanium precursors; subsequently the complete polymerization and loss of the solvent leads to the transition from liquid sol to a solid gel phase; then the solid gel phase is subjected to a step of acid-catalyzed hydrolysis of titanium (IV) alkoxide followed by condensation at temperatures up to 500°C.

[0077] According to an alternative embodiment of the process according to the present invention: preferably step c) is a synthesis step, preferably a hydrothermal synthesis, in which the synthesis takes place in an aqueous solution at a controlled temperature / pressure.

[0078] According to this alternative embodiment of the process according to the present invention, the synthesis preferably comprises the steps of reacting the nanoparticles of TiCh of step a) with silver nitrate in water under agitation at room temperature. Preferably, after 30 minutes of agitation, the solution is transferred to a Teflon-coated stainless steel autoclave. The solvothermal treatment preferably involves heating the autoclave from room temperature to 200°C; the mixture is preferably kept at 200°C for 16 hours. The precipitate is preferably collected by repeated centrifugation and washed with ionized water.

[0079] According to an alternative embodiment of the process according to the present invention: preferably step c) is a synthesis step, preferably a synthesis by the solvothermal method, in which the synthesis takes place in a non-aqueous-type solvent.

[0080] According to this alternative embodiment of the process according to the present invention, the synthesis preferably comprises the steps of reacting TiCh nanoparticles of step a) with silver nitrate, urea and citric acid in ethylene glycol under agitation at room temperature. Preferably, after 30 minutes of agitation, the solution is transferred to a Teflon-coated stainless steel autoclave. The solvothermal treatment preferably involves heating the autoclave from room temperature to 200°C, the mixture is preferably kept at 200°C for 4 hours. The precipitate is preferably collected by repeated centrifugation and washed with ionized water and ethanol.

[0081] Advantageously, the particle according to the present invention comprises nanoparticles (NPs) of titanium dioxide (titania, TiCh), silver (Ag) and silicon dioxide (silica, SiOi) to form a three-dimensional structure that is substantially “flower-like”, coated with fluorescent and / or photoluminescent agents. As described above, the particle preparation process according to the present invention preferably comprises different steps: (a) synthesis of titanium oxide (TiCh) nanoparticles, (c) synthesis of Ag-TiCh nanoparticles, (f) synthesis of Ag-TiCh-SiCh with fluorescent and / or photophotoluminescent molecules.

[0082] Advantageously, in general, the synthesis steps of the process according to the present invention that comprise the synthesis steps of the TiCh and Ag nanoparticles may be reversed, as well as conducted by other synthesis methods.

[0083] A third subject matter of the present invention relates to a composition comprising a particle according to the present invention (and as described above) dispersed in a dispersing liquid, preferably water or a commercial product used in the finishing step of the leather process, wherein the particle has a concentration less than or equal to 0.2% by weight, % expressed with respect to the weight of the composition. Advantageously, since the particle according to the present invention is preferably coated with chains that expose hydrophilic functional groups (such as amine groups derived from 3- aminopropyltriethoxysilane) or hydrophobic groups, this allows for easy dispersion of the particle according to the present invention in water or in commercially available products commonly used in the leather finishing step.

[0084] Preferably, the commercial product used in the finishing step of the leather process is preferably chosen from: water, polyurethane dispersion used in glossy coating mixtures (the so-called “top coat”), polyurethane dispersion used in opaque coating mixtures (the so-called “top coat”), polyurethane / silicone coating mixture (the so-called “top coat”) in aqueous dispersion, polyacrylic derivative in aqueous / organic dispersion, aqueous dispersion of an aliphatic polyurethane, aqueous-based nitroemulsion or their mixtures.

[0085] A fourth subject matter of the present invention relates to the use of the particle according to the present invention (and as described above) and / or the composition according to the present invention (and as described above) in the finishing step of the leather process, in order to assign to the finished leather at least one of:protective properties against microorganisms, protective properties against UV radiation, self-cleaning properties, improved mechanical and thermal resistance, fluorescent properties, photophotoluminescent properties.

[0086] Preferably, the use of the particle according to the present invention and / or the composition according to the present invention in the finishing step of the leather process assigns to the finished leather: protective properties against microorganisms, protective properties against UV radiation, self-cleaning properties, improved mechanical and thermal resistance, fluorescent properties, photophotoluminescent properties.

[0087] A fifth subject matter of the present invention relates to a process for processing leather comprising a leather finishing step wherein a particle according to the present invention (and as described above) and / or a composition according to the present invention (and as described above) is sprayed onto the leather.

[0088] A sixth subject matter of the present invention relates to a leather finished with a particle according to the present invention (and as described above) and / or a composition according to the present invention (and as described above) having at least one of the following properties: protective property against microorganisms, protective property against UV radiation, self-cleaning property, improved mechanical and thermal resistance, fluorescent property, photoluminescent property.

[0089] Preferably, leather finished with a particle according to the present invention and / or a composition according to the present invention has the following properties: protective property against microorganisms, protective property against UV radiation, self-cleaning property, improved mechanical and thermal resistance, fluorescent property, photoluminescent property.

[0090] Advantageously, the fact of providing a particle according to the present invention having multifunctional properties makes it possible to reduce the amounts of the individual species that give each finished leather a different property. During the leather finishing step, in the event that the particle according to the present invention is not available, in order to be able to assign to the finished leather all the properties that the particle according to the present invention assigns by means of a single particle, numerous individual and different particles would be needed. Thus, the particle according to the present invention advantageously allows not only economic but also ecological savings. Indeed, the particle according to the present invention advantageously allows for the incorporation of a wide range of properties into a single particle, while also enjoying the interactions of the various chemical elements that make up the particle, linked via heterojunction, thus exhibiting new and / or enhanced properties.

[0091] Since the particle according to the present invention comprises different chemical elements each having a property, it is also possible to create particles in which the properties may vary, for example, alternately enhancing the self-cleaning property, antimicrobial resistance, oxidation, by exposing more or increasing the concentration of each chemical element component of the particle.

[0092] Advantageously, moreover, the substantially flower-like three-dimensional structure is not merely a mixture of components, but actually constitutes heterojunctions of different chemical elements, having an intimate connection and interaction with each other. Thus, advantageously, the behavior of each individual component of the particle is not simply what it would exhibit in pure form, but is amplified by the presence of the others, e.g., silica stabilizes the behavior of TiCk due to its ability to attract radicals; the antimicrobial property of silver is enhanced by the thickening of charges on its surface due to the presence of heterojunctions with less conductive oxides.

[0093] To sum up, the particle according to the present invention is, advantageously, an innovative multifunctional nanomaterial that is able to simultaneously assign antimicrobial, self-cleaning, light-resistant, fluorescent, photophotoluminescent properties, etc. to the leather.

[0094] Advantageously, the processes for preparing particles according to the present invention are inexpensive, simple, and enable particles of controlled nanometric size to be obtained. The particle according to the present invention thus enables multifunctional properties to be obtained with a single particle, which does not require complicated formulations and subsequent mixing. These properties are advantageously amplified by the fact that each particle is not a mere mixture of components, but consists of heterojunctions of different chemical elements, having an intimate connection and relative interaction with each other. Advantageously, therefore, the behavior of each individual component of the particle according to the present invention is not simply that which it would exhibit in pure form, but is enhanced by the presence of the others.

[0095] A further advantage of the particle according to the present invention is being able to modulate the composition and morphology of the particle according to the present invention in order to obtain different multifunctional properties by changing the order of the production steps, both with respect to the type of synthesis and the operating conditions.

[0096] Advantageously, therefore, the multiproperty of the particle according to the present invention is obtained by the presence in the particle of chemical elements that fulfill different properties from each other, the functions of which are amplified by the heterojunctions present among the different chemical elements that compose the particle, e.g: the silica stabilizes TiCE, the fluorescent and / or photophotoluminescent molecules are incorporated and stabilized in the silica, and the silver, which is more electronegative, promotes the thickening of negative charges on the surface of the other components of the particle, while maintaining a pronounced antimicrobial action.

[0097] Examples

[0098] Some preferred exemplary embodiments of the present invention are now provided, given by way of illustration and not limitation.

[0099] EXAMPLE 1: Preparation of the particle according to the present invention.

[0100] The preparation of the particle according to the present invention was obtained as follows: • TiCE preparation;

[0101] • preparation of Ag-TiCE nanoparticles consisting of silver / titanium dioxide coated with a dispersing agent;

[0102] • preparation of the TiCE-Ag-SiCE particle, consisting of fluorescent and / or luminescent titanium dioxide / silver / silica.

[0103] For particle preparation, the following were used: deionized water and methanol, silver nitrate (AgNCE, purity > 99), titanium isopropoxide (purity > 99.9), tetraethyl orthosilicate (TEOS, purity > 99%), (3 -aminoprop yl)triethoxy silane (APTES), cyclohexane, ammonia hydroxide, oleic acid, 1,2-hexadecanediol, benzyl ether and ethanol.

[0104] The following steps were carried out for the preparation of TiCE: 5 ml titanium isopropoxide was slowly added dropwise into 8 ml of deionized water. Next, the solution was mixed by continuous agitation at 40°C for 30 minutes. At the end of this step, a white precipitate of TiCE nanoparticles was obtained at the bottom of the beaker. The precipitate was separated from the mixture by centrifugation and washed several times with cycles of deionized water and methanol, then the precipitate was dried at 80°C in an oven for 12 hours and calcined at 400°C in air for 2 hours.

[0105] For the preparation of Ag-TiCE nanoparticles, the following were used: 200 mg of TiOi nanoparticles, benzyl ether (20 mL), silver nitrate (2 mmol), 1,2-hexadecanediol (10 mmol), oleic acid (12 mmol). All reagents were mixed in a batch reactor and agitated magnetically under nitrogen flow from 25°C to 200°C for 2 hours and then at 285°C for 1 hour. Downstream of the preparation, the mixture produced was washed through centrifugation cycles (7500 rpm; 30 minutes) in ethanol and hexane 3-4 times. Then the produced material was left to dry for 24 hours at 25 °C.

[0106] Preparation of the Ag-TiCE-SCE particle. To carry out the preparation of the Ag-TiCE-SCE particle with fluorescent agents, a conjugate consisting of fluorescein isothiocyanate (FITC) and APTES was prepared. In particular, 10 pl of a mixture of APTES and FITC, in a 2:1 molar ratio, are mixed in 2 ml of ethanol. The mixture was kept in the dark under agitation for 4 hours. Finally, the reaction product, consisting of the FITC- APTES conjugate, was stored at 4°C. At this point the actual preparation of the particle takes place, specifically a microemulsion of branched polyoxyethylene(5)nonylphenylether and cyclohexane was prepared. Subsequently, FITC-APTES conjugate and about 180 pl of Ag- TiCh nanoparticles in hexane were added to the previously prepared microemulsion. Next, 60 pl of TEOS and 72 pl of ammonia hydroxide were added. 24 hours were awaited, necessary for the hydrolysis and condensation of the silica precursor. The particle with fluorescent agents was then separated from the mixture by centrifugation. Finally, the resulting mixture was washed through centrifugation cycles (7500 rpm; 30 minutes) with acetone (1 time), isopropanol (1 time), ethanol (3-4 times) and water (3-4 times).

[0107] The obtained particle was stored in water at room temperature.

[0108] EXAMPLE 2: Characterization of the particle according to the present invention obtained in Example 1.

[0109] With reference to Fig. 1 an image of the particle according to the present invention is shown. It is possible to observe how the particles, downstream of the preparation, are perfectly dispersed in water. The particle according to the present invention downstream of the preparation was also dispersed in the water-based commercial finishing chemical products used. In particular, they were dispersed in a polyurethane dispersion used in glossy coating mixtures (the so-called “top coat”), in a polyurethane dispersion used in opaque coating mixtures (the so-called “top coat”), in an aqueous polyurethane / silicone dispersion coating mixture (the so-called “top coat”), in an aqueous polyacrylic derivative in an aqueous / organic dispersion, in an aqueous dispersion of an aliphatic polyurethane, in an aqueous-based nitroemulsion (Fig. 2-7).

[0110] With reference to Fig. 8, the XRD (X-ray diffraction) spectrum of a particle according to the present invention is shown. The typical broad halo attributed to an amorphous silica is evident. Further, peaks are present due to titania and silver nanoparticles, as indicated by the arrows.

[0111] Referring to Fig. 9: The particle morphology according to the present invention was analyzed by scanning electron microscopy (SEM). Fig. 9 shows images at various magnifications of the particle according to the present invention. As magnifications increase, the images reveal the presence of structures as small as 1 pm in size. The features of the powder and the resolution of the instrument do not allow individual nanoparticles to be well distinguished, which is on the other hand possible with the TEM (transmission electron microscope) and NTA (nanoparticle tracking analysis) characterizations that follow. In fact, a TEM image of the particle according to the present invention is shown in Fig. 10. The image shows the formation of nanoparticles of uniform size (about 65-70 nm in diameter).

[0112] Fig. 11 shows the results of the NTA analysis performed on the particle. Such an analysis makes it possible to determine the size distribution profile of small particles suspended in a liquid. The technique is used in conjunction with an ultramicroscope, which makes it possible to visualize the movement of particles in liquid suspension under the effect of Brownian motion. Computer software tracks the movements of the particles and estimates their average hydro-dynamic radius using the Stokes-Einstein equation. Analysis of the size distribution obtained by the NTA technique, as shown in the parameters below, shows a larger particle size of about 75 nm.

[0113] To study the thermal stability of the prepared particle, a thermogravimetric analysis (TG- DTG) was performed. Fig. 12 shows the TG-DTG profiles of the particle according to the present invention. The TG-DTG profile shows, up to 115°C, a weight loss of about 5% by weight, attributable to physically adsorbed water. The main weight loss, due to the coating, occurs in the 240-385°C range. The residue is 87% by weight.

[0114] FT-IR (Fourier transform IR spectroscopy) spectra were also acquired to analyze the particle according to the present invention. An FT-IR spectrum of the particle may be seen in Fig. 13. The profile shows a vibrational band around 1082 cm'1due to the asymmetric elongation of the Si-O-Si group, the vibrational band at 947 cm'1is due to the asymmetric bending of the Si-OH bond elongation. The vibrational band at 469 cm'1is due to vibrations of Ti-O-Ti bond, while the vibrational band around 1635 cm'1is due to Ti-OH bond. The vibrational bands around 2923 cm'1may be attributed to the presence of secondary amines in the FITC molecule.

[0115] Since the composition according to the present invention is a composition comprising the particle according to the present invention dispersed in a dispersing liquid, preferably water or a commercial product used in the finishing step of the leather process, the compatibility of the particle according to the present invention with the aforesaid major commercial products was tested. In fact, a characterization of the aforesaid commercial products was performed. As may be seen from Fig. 14, the spectroscopic analysis of the aforesaid commercial products, carried out by ATR-IR (attenuated total reflectance in infrared spectroscopy) technique, showed the following:

[0116] - the commercial product “polyacrylic derivative in aqueous / organic dispersion” was found to have a spectroscopic profile indicative of the presence of polyacrylates, with the following absorbances characteristic of this class of compounds: stretching vibration -C=O at 1726 cm'1; stretching vibration -C-O-C at 1240 and at 1155 cm'1;

[0117] - the commercial product “aqueous dispersion of an aliphatic polyurethane” was found to have a spectroscopic profile indicative of the presence of polyurethanes, with the following absorbances characteristic of this class of compounds: stretching vibration -NH at about 3300 cm'1; stretching vibration -C=O at 1720-1726 cm'1(amide I); banding -NH at about 1530 cm'1(amide II);

[0118] - the commercial product “water-based nitroemulsion” was found to have a spectroscopic profile indicative of the presence of nitrocellulose, with the following absorbances characteristic of this class of compounds: two strong signals related to-NCh, at 1640-1650 cm'1and 1275-1278 cm'1, to be attributed to the symmetric and asymmetric stretching vibrations of this group, respectively; stretching vibration -C-O, relative to the glucopyranosic ring, at 1070 cm'1; stretching vibration -O-NO2, at 840 cm'1.

Claims

CLAIMS1. Particle comprising titanium dioxide (TiCL), silver nanoparticles (Ag), silicon dioxide (SiCL), said particle comprising at least a fluorescent agent and / or at least a photoluminescent agent linked via heterojunction to said particle, wherein TiCL, Ag and SiCL are linked to each other via heterojunctions, wherein the largest dimension of said particle is comprised between 60 nm and 70 nm.

2. Particle according to claim 1, wherein the particle further comprises at least a substance selected from the group consisting of: 3 -aminoprop yltriethoxysilane, tetramethylammonium 11-aminoundecanoic, oleic acid, polyethylene glycol, acrylic acid, citric acid and mixtures thereof.

3. Particle according to claim 1 or 2, wherein the weight ratio of Si / Ag and Si / Ti is, respectively, between 10 and 4 and between 25 and 2.

4. Particle according to claim 3, wherein the weight ratio of Si / Ag and Si / Ti is, respectively, 6 and 23.

5. Particle according to anyone of claims 1 to 4, wherein the particle has a substantially flower-like three-dimensional structure comprising pistil and petals, wherein TiOi is the pistil, Ag and SiCL are the petals.

6. Process for preparing a particle according to any one of claims 1 to 5, comprising the following steps: a) providing or synthesizing titanium dioxide (TiCL); b) providing or synthesizing silver nanoparticles (Ag); c) using TiCL of step a) and Ag nanoparticles of step b), synthesizing Ag-TiCL nanoparticles; d) providing or synthesizing silicon dioxide (SiOi); e) providing or synthesizing a fluorescent agent and / or a photoluminescent agent; f) using Ag-TiCL of step c), SiCL of step d) and a fluorescent agent and / or aphotoluminescent agent of step e) synthesizing a TiOi-Ag-SiOi particle linked by heterojunction to at least a fluorescent agent and / or at least a photoluminescent agent, thereby obtaining a particle according to any one of claims 1 to 5.

7. Process according to claim 6, wherein: step a) is a synthesis step and comprises reacting titanium isopropoxide with deionized water under agitation for a period of time comprised between 20 minutes and 40 minutes at a temperature comprised between 30°C and 50°C; separating by centrifugation the TiOi precipitate obtained from the reaction; washing and drying the TiCh; step c) is a synthesis step and comprises reacting benzyl ether, silver nitrate, 1,2- hexadecanediol, oleic acid, TiOi of step a), under agitation and nitrogen flow for a period of time comprised between 1.5 hours and 2.5 hours at a temperature comprised between 20°C and 300°C; washing by centrifugation in ethanol and hexane the Ag-TiOi thus synthesized and letting it dry; step f) is a synthesis step and comprises reacting Ag-TiCh of step c), SiCh of step d) and a fluorescent agent and / or a photoluminescent agent of step e); separating by centrifugation the TiOi-Ag-SiCh particle linked by heterojunction to at least a fluorescent agent and / or at least a photoluminescent agent obtained from the reaction; washing the particle by centrifugation with at least one from: acetone, isopropanol, ethanol, water; letting the particle dry.

8. Composition comprising at least a particle according to anyone of claims 1 to 5 dispersed in a dispersing liquid, preferably water or a commercial product used in the finishing step of a leather process, wherein the composition has a particle concentration of less than or equal to 0.2% by weight, % expressed with respect to the weight of the composition.

9. Use of the particle according to anyone of claims 1 to 5 and / or of the composition according to claim 8, in the finishing step of a leather process, in order to assign to the finished leather at least one of: protective properties against microorganisms, protective properties against UV radiation, self-cleaning properties, improved mechanical and thermal resistance, fluorescent properties, photoluminescent properties.

10. Process for processing leather comprising a leather finishing step wherein at least a particle according to any one of claims 1 to 5 and / or a composition according to claim 8, is sprayed onto the leather.

11. Leather finished by at least a particle according to any one of claims 1 to 5 and / or by a composition according to claim 8, having at least one of the following properties: protective property against microorganisms, protective property against UV radiation, selfcleaning property, improved mechanical and thermal resistance, fluorescent property, photoluminescent property.

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