WO2024209090A1 - Titanium-oxo-cores, a coating composition containing the titanium-oxo-cores, an object having on a surface thereof a titanium oxide coating formed from the coating composition, and methods for their preparation - Google Patents

Abstract

A method of making a composition for providing an anatase phase TiO₂ coating on a substrate to produce a coated object, a method of preparing titanium-oxo-cores for use in the coating composition, a method of coating an object with an anatase phase TiO₂ coating, and a TiO₂ coated object, wherein the anatase phase TiO₂ coating has self-cleaning, antibacterial and/or antiviral properties, are disclosed.

Description

TITANIUM-OXO-CORES, A COATING COMPOSITION CONTAINING THE TITANIUM-OXO-

CORES, AN OBJECT HAVING ON A SURFACE THEREOF A TITANIUM OXIDE COATING FORMED FROM THE COATING COMPOSITION, AND METHODS FOR THEIR PREPARATION

The present invention relates to a method of preparing titanium-oxo-cores for use in forming a TiO? coating on a surface of a substrate, a method for preparing a coating composition containing the titanium-oxo-cores, a coating obtainable composition, a method of coating a surface of an object using the coating composition, and a TiCh coated object, said TiO? coating having self-cleaning, antibacterial and/or antiviral properties.

Background of the invention

Photocatalytic "self-cleaning" coatings utilise the energy in the solar light to decompose organic pollutions deposited on the surface, which bind inorganic dust to form dirt. A photocatalytic coating comprises a material, which can be activated by light of sufficient energy, which material is also referred to as a photocatalyst. These coatings also exhibit super-wetting properties (sometimes called super-hydrophilicity) that facilitate easy removal of organic decomposition products and inorganic particles that deposit on their surfaces. The decompositional acitivity of the coatings also includes decomposition of other organic matter such as biofouling. Examples of biofouling are mold, plants, bacteria and virus. Furthermore, the photocatalytic material is capable of oxidating NO_X compounds that subsequently can be washed off from the coating in the presence of oxygen and water.

The decomposition of organic groups is achieved by absorption of the ultraviolet part of the solar light to yield strongly oxidising (holes) and reducing (electron) sites in the photocatalyst. However, short wavelength visible light also contributes to the decompositional activity. These light-activated sites, together with water and oxygen, which are always present at the surface of the photocatalyst, yield oxygen and hydroxyl radicals that decompose any organics, typically fatty groups, that are present on the surface of the photocatalyst. The oxidative power of these radicals is even stronger than ozone and other oxidising disinfectant agents. Through elaborate design of the material's electronic structure and, bulk and surface atomic structure, it is possible to obtain highly efficient organic decomposition photocatalysts. This field of research has attracted enormous resources from researchers around the globe the past 50 years, in the beginning especially in Japan. It has led to many applications and demonstrators, such as photocata lytic tiles and porcelain for bathrooms, self-cleaning windows (today produced by all float glass manufacturers on large scale), photocata lytic air cleaning devices, self-cleaning concrete, and more niche products such as coated glass-wall linings along highways and wall coatings in smoke-rooms in high speed trains. Other highly potential areas are antivirus / antibacterial coatings acting by oxidising the organic groups to harmless compounds such as water and carbon dioxide. This should likely reduce the possibility of creating and spreading bacteria and viruses, since all decomposition take place with the bacteria or virus locked to the surface. The powerful oxidative action of the catalytic surface also makes it close to impossible to create a defence for a complex organic structure, such as a virus or bacteria based on carbon, oxygen, nitrogen and hydrogen.

The prevailing photocatalytic material is titanium dioxide (TiC>2) built with an atomic structure named anatase. However, there is more to it than just having an anatase structure. The quality of its atomic structure, i.e. how many defects that are present, how well the atoms are ordered in the positions of the anatase structure and the direction and quality of the surface facets, dictates the performance. Therefore, all anatases are not alike. The quality of the anatase depends on the chemical processing and the synthesis temperature. For anatase titania, higher temperatures help correcting the typically amorphous or poorly crystalline nanostructures obtained from solution or gas-phase synthesis at low temperature to yield a higher quality anatase titania. The vibrations of the titania begin to be strong enough to help correction of a low-quality structure only at ca. 400-450 °C, which has hampered low temperature synthesis of proficient photocatalyst coatings. To overcome the seemingly impossible problem indicated above, strategies of making crystalline nanoparticles in a separate route, typically by autoclaving or high temperature treatment, and combine them with a binder which can be organic or inorganic, have been proposed.

Coatings of the type described above having self-cleaning and/or antiviral properties are known e.g. from EP 1 198431 Bl (Pilkington), EP 1 512 728 Bl (Toto Ltd; Takahashi et al.), US 2013/0119305 Al (Photocat A/S; Iversen et al.).

In US 2013/0119305 Al a coating fluid composition comprising photocatalytic active nanoparticles of titania (TiO?) in a suspended form and water as a solvent is deposited on a clean, preconditioned surface, wherein the coating is performed at a temperature in the range 5-50 °C. The photocata lytic active nanoparticles of titania (TiCh) used in US 2013/0119305 Al are not prepared in the process disclosed therein, but have obviously been pre-synthesised.

In EP 1 512728 Bl a photocatalytic coating material comprising, i.a., photocatalytic oxide particles, and a hydrophobic-resin emulsion is used to coat a surface of a base material, and thereafter the coating is hardened at ordinary temperature, e.g. room temperature. The average size of the photocatalytic oxide particles, such as titanium oxide, is 5 to 50 nm.

In US 2013/0119305 Al and EP 1 512 728 Bl titania nanoparticles are combined with a binder that allows for the low temperature. However, as a consequence, the binder required for the deposition will dilute the photocatalytic TiO? part at the surface, and embed the photocatalytic particles in a binder matrix, effectively making them incapable of effecting photocatalytic decomposition of surface attached dirt and biofouling.

All-titania coatings are also made by providing an object with a coating composition, and subsequently, i.e. after applying a coating composition to the object in question, subjecting the object to a heat treatment at an elevated temperature in the range of about 400 to about 800 °C. In EP 1 198431 Bl, a titanium oxide layer is deposited on the surface of a glass wherein the substrate that is held at a temperature in the range 645 to 720 °C.

The commercial product Activ™, manufactured by Pilkington Glass, is a glass product with a clear, colourless, effectively invisible, photocatalytic coating of titania that also exhibits PSH (Photoinduced SuperHydrophilicity). This coating is however not as active as the commonly studied porous films of the powder P25 TiO? (manufactured by Degussa), which is an agglomerated nanoparticulate powder, but has vastly superior mechanical stability, reproducible activity and widespread commercial availability (millions of square meter). Activ™ is therefore a suitable benchmark photocatalyst film.

A problem with these prior art methods is that they employ high temperatures for the heat treatment. Thus, the substrates to be coated are limited to materials that can withstand the temperatures in question without degradation. Examples of substrates in the prior art are typically glass and ceramic substrates. Materials such as steel, aluminium, polymers, painted surfaces, however, cannot be coated with the prior art high temperature methods and coatings. As indicated above, in e.g. Pilkington's patent (EP 1 198431 Bl) high temperatures are employed.

Another problem with Pilkington Glass, Activ™, is that the volatile titania chemical vapour deposition precursor TiC is used in the process. The deposition precursor TiC is suitable for coating of corrosion resistive materials such as glass and ceramics, but not metals such as steel and aluminium due to the corrosiveness of the hydrogen chloride gas formed according to the reaction: TiCU + 2 H?O -> TiCh + 4 HCI.

JP 2004074006 A relates to a titania nano fine crystal dispersed thin film pattern and a method for preparing an article with the thin film pattern. The method disclosed i.a. includes bringing the film into contact with water of a temperature from room temperature to 100 °C. In general, the treatment time may be about several tens of minutes to several hours. An efficient temperature is stated to be about 90 °C. According to JP 2004074006 A, the molar ratio of the silicon alkoxides to the titanium compounds in the silicon alkoxides and titanium solutions can be adjusted to be in the SiO2:TiO2=5:l-l:3 range, more preferably about 3:1. By setting the molar ratio of the titanium compound to the silicon alkoxide to about 3:1, the photocatalytic activity of the obtained titania microcrystal dispersed thin film portion can be further enhanced.

JP 2003 253157 A relates to a coating solution of titania or titania-containing compounds excellent in storage stability. The coating solution of titania or a titaniacontaining composite oxide is improved in storage stability by modifying a hydrolysable titanium compound with a diketone compound. In the examples, a borosilicate glass substrate was immersed in the inventive coating solution and dried by heating at 90 °C for 30 minutes, and thereafter immersed in hot water at 97 °C for 1 hour to obtain a thin film.

WO 03/092886 Al discloses a method for preparing mesoporous TiO2 thin films with high photocatalytic and antibacterial properties. The method involves coating onto a substrate a TiO2 sol-gel solution prepared from hydrolysis and condensation of titanium alkoxide in the presence of a stabiliser and thermally treating the coated substrate at a temperature ranging from 400 °C to 900 °C. Mesoporous materials have a pore size in the range of 2 to 50 nm. In order to form the desired mesoporous TiCh thin films a template is added during the preparation of the TiC>2 sol-gel solution. The template can be certain polymers or surfactants, a preferred amount of the polymer being 9-20 % by weight of the TiC>2 sol-gel solution, and a preferred amount of the surfactant being 10-15 % by weight of the TiO? sol-gel solution. The invention is particularly useful for fish tank water disinfection. As noted therein in Example 2, a mesoporous TiCh thin film of the amorphous phase, as obtained at a calcination temperature of merely 300 °C, generally has a poor photocata lytic activity.

Thus, it would be desirable to be able to reduce the temperatures used in the coating process to temperatures well below those that have been used in the prior art, e.g. to lower than 300 °C, preferably lower than 200 °C, thereby making it possible to use a wider range of substrate materials and industrial deposition lines.

It would also be desirable to reduce the need for treatment of a coating with water for a prolonged period of time, especially hot water.

Furthermore, the process should use non-corrosive reactants and reaction products.

Finally, it would be desirable to use inexpensive and readily available materials for this kind of coatings.

Summary of invention

The above objects have been achieved according to the invention by the method of claim 1.

Accordingly, in a first aspect the present invention relates to a method of preparing titanium-oxo-cores for use in forming a TiCh coating on a surface of a substrate, comprising the steps of: A providing a titanium alkoxide as represented by the general formula Ti(OR)4, wherein each R is selected from the group consisting of: Ci alkyl to Ce alkyl, and Ci alkenyl to Ce alkenyl; B providing an organic bidentate ligand compound (LH); C mixing the titanium alkoxide and the organic bidentate ligand compound (LH) with each other, so as to obtain a titanium alkoxide modified with the organic bidentate ligand (L), wherein, in step C, the molar ratio of the organic bidentate ligand (LH) to the Ti(OR)4 is within the range of 2 to 0.5, which method further comprises the additional step of: D hydrolysing the resulting titanium alkoxide modified with the organic bidentate ligand from step C in the presence of an acid catalyst, thereby forming a suspension of titanium-oxo-cores. By means of the above method titanium-oxo-cores having an overall molar ratio of organic bidentate ligand (L) to Ti within the range of 2 to 0.5 are obtained, which titanium- oxo-cores can be used in preparing a coating composition for forming an anatase phase TiCh coating layer on a surface of a substrate.

Consequently, in another aspect, the invention relates to titanium-oxo-cores obtainable by means of the above method comprising organic bidentate ligands (L), and OR groups, wherein each R is selected from the group consisting of: Ci alkyl to C& alkyl, and Ci alkenyl to Ce alkenyl, and wherein the overall molar ratio of organic bidentate ligand (L) to Ti is within the range of 2 to 0.5.

In a preferred embodiment of the inventive method of preparing titanium-oxo-cores, additionally comprising the following steps: E heat treatment of the suspension of titanium- oxo-cores obtained from step D for a period of time within the range of 15-36 hours at a temperature within the range of 55-110 °C; and, F diluting the heat-treated suspension of titanium-oxo-cores from step E, so that the total molar concentration of titanium in the suspension is within the range of 0.05 M to 1.5 M, the resulting suspension of titanium-oxo- cores can be used as a coating composition.

In yet another aspect the invention relates to a coating composition for use in preparing an anatase phase TiCh coating on a surface of an object, which coating composition can be prepared from the inventive titanium-oxo-cores, comprising a suspension of titanium-oxo-cores comprising organic bidentate ligands (L), and OR groups, wherein each R is selected from the group consisting of: Ci alkyl to Ce alkyl, and Ci alkenyl to Ce alkenyl, wherein the overall molar ratio of organic bidentate ligand (L) to Ti in the titanium-oxo-cores is within the range of 2 to 0.5, and wherein the total molar concentration of titanium is within the range of 0.05 M to 1.5 M.

In yet another aspect the invention relates to a method of preparing an anatase phase TiO2 coating on a surface of an object comprising the steps of: G applying a suspension of titanium-oxo-cores comprising organic bidentate ligands (L), and OR groups, wherein each R is selected from the group consisting of: Ci alkyl to Ce alkyl, and Ci alkenyl to Ce alkenyl, wherein the overall molar ratio of organic bidentate ligand (L) to Ti in the titanium-oxo-cores is within the range of 2 to 0.5, and wherein the total molar concentration of titanium is within the range of 0.05 M to 1.5 M, to a surface of an object; and, H subjecting the coated surface obtained in step G to IR irradiation, UV irradiation, an elevated temperature of up to 300 °C, or to a combination of any thereof.

In yet another aspect the invention relates to an object having an anatase phase TiOz coating layer on a surface thereof, obtainable by means of the inventive coating method, wherein the anatase phase TiOz coating layer has a thickness within the interval of 20-300 nm.

The present invention does not rely on the use of an added binder phase, such a polymeric or SiO? binder phase. In preferred embodiments an added binder phase is absent.

The present invention does not rely on the use of a surfactant. In preferred embodiments a surfactant is not used.

The present invention does not rely on the use of an additional other metal element than Ti and/or the use of a metalloid such as Si for preparing the inventive TiOz coating. In preferred embodiments, another metal element than Ti is absent from the inventive coating composition and inventive anatase phase TiOz coating layer, except for possibly as unavoidable metal element contaminants.

The present invention does not rely on the addition of any particles, such as presynthesized TiOz particles, or SiOz particles. Accordingly, in preferred embodiments any added particles are absent. Accordingly, only titanium-oxo-core particles should be present in the inventive coating composition and in the inventive titanium-oxo-cores suspension.

In preferred embodiments, Si is not present in the inventive coating composition, except for possibly as an unavoidable contaminant.

According to the invention, the inventive anatase phase TiOz coating layer can be obtained at RT by subjecting the coated surface to UV irradiation for a duration of 10 s.

The inventive coating method is suitable for demanding large scale deposition in roll- to-roll processing at high rate, and roll-to-ro II metal sheet coating equipment which most commonly operates using a maximum temperature of approximately 300 °C.

The tests, the results of which are presented in Table 1, show that the inventive film deposited on a variety of steel, aluminium, and organic-inorganic silica hybrid substrates according to the invention is highly photocatalytically active and decompose organic material.

Another phase of TiO2 than anatase has not been detected in the coatings prepared according to the invention, which coatings are therefore believed to be 100 % of the anatase phase.

A major advantage is that the inventive methods, as opposed to the prior art processes, can be carried out at a low temperature with non-corrosive reactants. Furthermore, the materials used are inexpensive and readily available.

In general terms, the invention provides a unique low-temperature process that can be used at temperatures below 250 °C, such as room temperature, while still yielding highly photocatalytically active surfaces. More importantly, in some embodiments, the inventive TiO? coating layers can be formed within a very short period of time, such as in merely 10 sec.

Further embodiments and advantages will become apparent from the appended claims and detailed description.

Brief description of the attached drawings

Fig. 1 is a flow chart illustrating a preferred embodiment of the inventive method of the preparation of a suspension of modified titanium for film deposition comprising steps A- E.

Fig. 2 shows a typical X-ray diffractogram (XRD) of an anatase phase TiOz film prepared according to the invention.

Fig. 3a shows a schematic cross-section of an embodiment of a coated object based on an aluminium substrate.

Fig. 3b shows a schematic cross-section of an embodiment of a coated object based on a steel substrate.

Detailed description of the invention

The method according to the invention for providing self-cleaning, antibacterial and/or antiviral coatings on objects uses modified and hydrolysed alkoxides of titanium. In step C, the titanium alkoxide are modified by bidentate ligands that bind to the titanium atom of the titanium alkoxides and partially replace alkoxy groups of the titanium alkoxides. An exemplary reaction scheme is as follows:

wherein "LH" denotes the organic bidentate ligand compound provided in step B, which is selected from the group consisting of bidentate ketones and bidentate hydroxyl-group containing organic compounds. In a case wherein the organic bidentate ligand compound LH according to the invention is an alcohol, however, the alcohol could be coordinated to the titanium atom without being deprotonised. Unless indicated otherwise, as used herein, "L" is intended to refer to the organic bidentate ligand when coordinated to the titanium atom, whether deprotonised or not. The bidentate ligand (L) is also referred to herein as a modifying ligand or stabilising ligand. In the above reaction scheme, x is believed to be maximally 2.

According to the invention, the bidentate ligand compound (LH) is used in mixing step C in a molar ratio to Ti within a range of 2 to 0.5, and preferably of less than unity, i.e. x < 1 with reference to the above formula. It is believed that the inventive low amount of bidentate ligand will serve to stabilise the surface and restrict the growth of titanium oxocores to be formed in the hydrolysis in step D, thereby obtaining the inventive small sized titanium oxo-cores. The hydrolysis in step D of the modified titanium alkoxides obtained from step C, wherein the modification comprises a bidentate ligand substitution of alkoxy groups, is needed to provide a dispersion of titanium oxo-cores which after heat treatment in step E makes it possible, after deposition on a substrate, to use UV-light, I R-light or heating at below 300 °C (or combinations of them) to achieve TiO? anatase of crystallinity good enough for highly efficient photocatalytic decomposition.

In preferred titanium alkoxides as used in the inventive method of preparing the inventive titanium-oxo-cores, each R in Ti (OR)₄, represents Ci alkyl to Cg alkyl, which can be same or different, more preferably Ci alkyl to C₄ alkyl. More preferably, the titanium alkoxide is selected from the group consisting of Ti(OMe)₄, Ti(OEt)₄, Ti(OPr')₄, Ti(OPrⁿ)₄, Ti(OBu')₄, and Ti(OBuⁿ)₄, and is preferably Ti(OBuⁿ)₄, wherein OMe = methoxy; OEt = ethoxy; OPr' = 2-propoxy; OPrⁿ = 1-propoxy; OBu' = 2-butoxy; OBuⁿ = 1-butoxy. The organic bidentate ligand compound (LH) is preferably selected from the group consisting of bidentate ketones, bidentate hydroxyl compound and combinations thereof, preferably C3-C7 organic bidentate ligand compounds. An especially preferred organic bidentate ligand compound is acetylacetone (acacH). A list of suitable organic bidentate ligand compounds (LH), along with the corresponding CAS Number for each bidentate ligand compound, is given below: o 0

H₃C'^^/^'CH₃ 2,4-pentandione 123-54-6 (Acetylacetone (acacH))

2-Methyl-l,3-propanediol 2163-42-0

3-Hydroxy-2-butanone 513-86-0 (Acetoin)

2,3-Butanediol 513-85-9

2,2-Dimethyl-l,3-propanediol 126-30-7 l-Hydroxy-2-butanone 5077-67-8

4-Hydroxy-2-butanone 590-90-9

Hydroxyacetone 116-09-6

1,2-Dihydroxybenzene 120-80-9

-Dihydroxybenzaldehyde 139-85-5

2,3-Dihydroxypyridine 16867-04-2

A solvent may be used to dissolve the organic bidentate ligand compound (LH), especially when the selected organic bidentate ligand compound is a solid. Accordingly, in step B, the organic bidentate ligand compound (LH) provided may be dissolved in a suitable solvent. The solvent, when used for dissolving the organic bidentate ligand compound, is preferably present in a minimum amount. Suitable solvents can be selected from the group consisting of alcohols, and ethers, preferably alcohols, most preferred 2-propanol, 1- butanol, and ethanol.

In step C, the molar ratio of the ligand compound (LH) to Ti is more preferably 0.5-0.9, even more preferably 0.6-0.8, and especially preferred about 0.7. The mixing step C can suitably be carried out by adding the titanium alkoxide to the bidentate ligand or to the bidentate solution during stirring, whereby alkoxy groups of the titanium alkoxide are partially substituted for said bidentate ligand (L).

In step D, the resulting titanium alkoxide modified with the organic bidentate ligand (L) obtained from step C is hydrolysed in the presence of water and an acid catalyst, thereby forming a suspension of titanium-oxo-cores. The acid catalyst is added to improve the crystallisation. The hydrolysing step D preferably comprises adding, to the titanium alkoxide modified with the organic bidentate ligand (L) obtained from step C, a hydrolysis solution comprising water, and the acid catalyst, said acid catalyst being selected from the group consisting of organic and inorganic acids, such as acetic acid (HOAc), nitric acid (HNO3). The hydrolysis solution preferably additionally comprises a solvent, which is suitably selected from the group consisting of alcohols, and ethers, preferably alcohols, most preferred from 2-propanol and 1-butanol. The hydrolysis solution is preferably added during vigorous mixing. In step D, water should be provided in a molar amount corresponding to a molar ratio of water:Ti of at least 2:1. Preferably, water is provided in a molar excess, such e.g. in a ratio of about 10:1. Step D results in a suspension of titanium-oxo-cores. The appearance of the suspension should be clear. The size of the titanium-oxo-cores obtained from step D is believed to generally be within the range of 0.5-5 nm. The concentration of the suspension before heat treatment (in step E below) with respect to titanium content may typically be 1 M, the molar ratio of water to titanium atoms may typically be about 10, and the molar ratio of acid.

In step E, the suspension of titanium-oxo-cores obtained from step D is heat treated. Typically, a lower temperature will require a longer duration of the heat treatment, and vice versa. A suitable temperature can be selected in accordance with the solvent used. For example, for isopropanol as the solvent, a suitable temperature will typically be within the range of 55-85 °C, preferably within the range of 70-76 °C, and most preferably at about 74 °C, and preferably during a period of time within the range of 20-30 hours, most preferably 22-26 hours. It is believed that the inventive heat treatment will improve the crystallinity and photocata lytic properties of a film, to be formed subsequently from the titanium-oxo- cores obtained from step D.

In order to prepare the inventive coating composition, in step F, the resulting heat treated suspension of titanium-oxo-cores obtained from step E, is diluted with a solvent to a desired molar concentration of Ti, preferably of about 0.5 M. A typical molar concentration of Ti of the resulting heat treated suspension of titanium-oxo-cores obtained from step E is about 1 M. A suitable solvent for use in diluting the suspension in step F is selected from the group consisting of alcohols and ethers, preferably alcohols, most preferred 2-propanol and ethanol.

In preferred embodiments, an organic moderator or crack-inhibitor is added in step F. The organic moderator or crack-inhibitor should be selected from organic molecules having a boiling point within the range of 50-160 °C. Preferably, the organic moderator or crackinhibitor is selected from the group consisting of bidentate ketones and bidentate hydroxyl compounds, more preferably from the above listed bidentate ligand compounds (LH), more preferably beta diketones and bidentate alcohols, and most preferred (acetylacetone) 2,4- pentanedione. The organic moderator or crack-inhibitor is believed to improve the mobility of the titanium-oxo-cores during crystallisation when subjected to IR radiation, UV radiation, heat, or a combination thereof, in a subsequent step H, which step will be described below. By virtue of the improved mobility of the titanium-oxo-cores during crystallisation, it is believed that the resulting inventive film will be denser, and that the TiO? crystallites will bind stronger to each other. Accordingly, preferred embodiments of the inventive coating composition comprise an organic moderator or crack-inhibitor. When used, the moderator is typically added in an amount corresponding to a molar ratio of moderator to Ti of up to 2.5. An overly high added amount of moderator could lead to an undesired high porosity of the resulting film.

In step G, the inventive coating composition, which can be obtained from step F of the inventive method, is applied to a surface of an object, such as by spin-, dip-, roll-, slot-, spray-, flow-coating or the like. Thereby, a film of the titanium-oxo-cores will form on the surface of the substrate, and the solvent present in the composition will preferably be evaporated.

In a subsequent step H, the coated surface resulting from step G, is treated so as to crystallise the coating, preferably by IR irradiation and/or UV irradiation at about room temperature, or by heating, preferably to a temperature between 200 and 250 °C. The object to be coated in step H is preferably selected from the group consisting of a metal plate, preferably iron, steel or aluminium plate; a painted object; and a water-glass object. The crystallisation of the coating will provide the photocatalytic properties of the inventive coating.

From step H, a coated object exhibiting, on a surface thereof, a TiO? coating layer, the coating having the properties of being 20-300 nm thick, having the anatase modification of TiO?, and TiO? crystallites of about 5 nm according to x-ray diffraction (XRD) peak width measurement.

The inventive TiO? coating layer of the inventive coated object has photocatalytic properties exhibiting degradation rates of organic molecules in excess of lxlO^-3 min ^_1, preferably in excess of 4xl0^-3 min ¹, and more preferably in excess of 8xl0^-3 min ¹.

The inventive TiO? coating layer of the inventive coated object also has antibacterial properties exhibiting an antibacterial activity in excess of RL > 1, and AR > 0, preferably RL > 1.3 and AR > 0.8, and more preferably RL > 1.6, and AR > 1.3.

The efficiency of a coating as obtained by the inventive method has been measured at Uppsala University (SE) using a standard test procedure with stearic acid similar to the test procedure disclosed in EP 1 254870 Bl (Pilkington). Similar testing has also been carried out by Fraunhofer Institute for Surface Engineering and Thin Films 1ST (DE) based on the test procedure disclosed in EP 1 254870 Bl on coatings obtained using the inventive method disclosed herein. The Fraunhofer data are generally well in line with the measurements by the inventors. However, there are some considerations in the way the rate constants are calculated. In the Pilkington test, a zero-order function was used, while in the inventors' and most other researcher's cases, a first-order function was used. This is due to the different decay patterns which are related to the mechanism determining the rate of decay.

The inventive TiCh coating can also be formed on a surface of an object, the surface of which exhibits an organic material, such as an organic coating, e.g. paint or lacquer. In such case, in order to protect the organic coating layer from the organically decomposing photocatalytic reactions by the inventive photocatalytically active coating, a silica or organic- inorganic hybrid silica coating can be added as a protective intermediate layer to the organic surface, onto which protective intermediate layer the inventive coating composition can be applied.

A material generally comprising a base substrate onto which base substrate an organic material coating has been applied which is sensitive to higher temperatures, e.g. above 300 °C, is referred to herein as a "composite material", such as e.g. a base substrate provided with a creamer coating.

Accordingly, in one embodiment, the inventive coating method further comprises an additional preceding step providing an organic-inorganic hybrid-silica layer on the surface of said object before the inventive coating composition is applied.

The provision of the inorganic-organic hybrid silica layer preferably comprises the steps of making a first solution by: i) adding aqueous nitric acid to a silicon alkoxide whereby alcohol is released; ii) removing said alcohol to provide a viscous liquid; iii) diluting said viscous liquid; iv) neutralising said diluted liquid; and, v) filtering the neutralised liquid, whereby said first solution is obtained, the method further comprising the steps of vi) adding to said first solution a solution of zinc 2-ethylhexonate in toluene, wherein the mole equivalent Zn/Si = 0.001, whereby a coating solution is obtained, and, vii) applying the thus obtained coating solution to a substrate, by a suitable method, preferably selected from the group consisting of spin-, roll-, slot- and spray-coating, and finally viii) heat treating the coating at an elevated temperature, in the range 200-300 °C, preferably at about 250 °C. It is conceivable that IR radiation could alternatively be used in the heat treatment step (viii). However, heat treatment at an elevated temperature is presently preferred. Accordingly, in one embodiment, the inventive object exhibiting, on a surface thereof, an anatase phase TiCh coating layer having a thickness within the interval of 20-300 nm, additionally exhibits an intermediate protective hybrid-silica layer, onto which protective hybrid-silica layer the anatase phase TiCh coating layer is provided.

General example of a lab-scale synthesis process for providing the anatase phase TiOz coating layer according to inventive method

An example of a lab-scale synthesis process for preparing the inventive photoactive material usable for coating will be given below.

All glass-ware used in the process of making the modified titanium alkoxide are thoroughly cleaned and dried at about 150 °C before being introduced to a glovebox with a dry inert (argon) atmosphere, having a concentration of oxygen and water typically at about 1-2 ppm or lower.

Modification of the titanium alkoxide is carried out as follows. A solution of a bidentate ligand is placed in a glass flask containing a Teflon coated magnetic stirrer. The titanium alkoxide is added dropwise to the bidentate ligand or to the bidentate ligand solution during stirring at about 300 to 500 rpm. This results in a clear yellow-brown liquid.

An alternative to carrying out the above steps in a glove-box is to use a so called Schlenk-line or similar equipment.

The modified titanium alkoxide is subjected to hydrolysis by adding a water containing hydrolysis solution, thereby forming a clear solution of suspended titanium oxo-cores expected to be of sizes in the range of 0.5-5 nm. A titanium-oxo-core is a cluster of Ti and O atoms surrounded by ligands such as bidentate ligands, alkoxy groups and hydroxyl groups.

The hydrolysis solution is made up from an alcohol (e.g. 2-propanol or 1-butanol), water and an acid catalyst in the form of an organic or inorganic acid, e.g. HOAc or HNO3. Preparation of the hydrolysis solution is made in a cleaned and dried (as described above) glass flask, by adding water, then the acid cata lyst(s) and finally alcohol the while stirring. The hydrolysis solution thus prepared is then added dropwise to the modified titanium alkoxide while stirring at about 700 to 800 rpm. The resulting suspension of titanium-oxo- cores is a yellow-brown solution. In order to obtain a photoactive material, the suspension of titanium-oxo-cores, prepared as described above, are heat treated in order to obtain titanium-oxo-cores of higher crystallinity. Heat-treatment to yield the more crystalline titanium-oxo-cores is carried out in a glass vessel during stirring.

The heat treated titanium-oxo-core suspension is then diluted with a solvent and supplemented with an organic moderator or crack-inhibitor.

The suspension described in the previous paragraph is then ready for application onto metal, water glass or organic-inorganic silica hybrid surfaces using any of the application methods listed above. Finally, the applied and dried suspension (resulting from evaporation of the solvent) needs processing to form a solid coating of crystalline anatase TiCh that strongly adheres to the substrate surface and exhibits high photocata lytic activity. The processing for forming the solid photocatalytically active anatase coating encompasses irradiation by UV light, IR light or heat treatment at 200 to 300 °C, or any combination of these techniques. The final surface exhibits high photocata lytic activity and has antiviral and/or antibacterial properties.

In view of the fact that the temperatures used for the final crystallisation into the highly photocatalytically active anatase coating are so low, i.e. below 250 °C, and even so low as room temperature when using UV treatment, which is much lower than temperatures used in the prior art, it is possible with the inventive method to coat substrates that previously have not been possible to provide with this type of coating.

The process for providing an intermediate protective silica or hybrid organic-inorganic silica layer will be described in more detail below by way of a preferred example.

General example of the inventive preparation of a hybrid (silica) coating solution

The method of making an inorganic-organic hybrid silica layer requires working in dry equipment equilibrated with ambient atmosphere (20-21 °C, relative humidity RH 20-70%) for the preparation.

The method is a hydrolysis and polymerisation process in aqueous solution with an acid used as an acid catalyst for initialising said reactions, typically in an amount of less than 0.5 % by weight.

The reaction involved can be written in a general form as follows: 0.8 Si(OR¹)₃Ri (/) + 0.2 Si(OR²)₂R₂ (/) + 1.4 H₂O (/) -* SiOi.₄Ri.₂ (sol) + 2.4 R^H (/) + 0.4 R²OH (/) wherein Si(OR¹)sR and Si(OR²)₂R₂ are silicon alkoxides with (OR¹) and (OR²), respectively, denoting the alkoxide group, and R is denoting an unreactive alkyl or aryl group, wherein R¹ in each instance can be same or different, and wherein R² in each instance can be same or different. Addition of water and a catalytic amount of acid to the mixtures of the silicon alkoxides initialises the hydrolysis and polymerisation reaction. During the hydrolysis and polymerisation, Si-O-Si bonding is achieved and alcohol ROH(/) is released.

Organic-inorganic hybrid materials, usually known as Ceramers (short for "ceramic + polymer") or ORMOCERs (Organically Modified CERamics), is a class of composite materials possessing tuneable properties that can arise from the combination of organic polymer and inorganic material. The purpose of such hybrid materials is to achieve properties that a single component material cannot provide. The organic polymer components contribute with elasticity, toughness, formability and low density, while the inorganic ceramic components are hard, stiff and thermally stable. Together, these components can produce hybrid materials which adhere well to both metallic and polymeric substrates, are chemically stable, and have good abrasion resistance. These properties make these materials very attractive as coatings for items in buildings and automotive parts. Prior art examples of the above are given in scientific papers, e.g., H.H. Huang, B. Oder, G.L. Wilkes Polym. Bull., 14 (1985), p. 557 and H. Schmidt, H. Wolter J. Non-Cryst. Solids, 121 (1990), p. 428.

Fig. 2 is an X-ray diffraction study of a TiO₂ coating layer provided according to the invention. The blue bars show the position and intensity of a standard anatase TiO₂ material having an International Centre for Diffraction Data (ICDD) Number 01-070-7348. Analysis of the XRD peak width indicate a TiO₂ crystallite size of 5 nm.

In Fig. 3 is shown an overview of the composite materials consisting of aluminium and steel substrates, nascent or coated with alumina, zinc based primer or paint, an added organic-inorganic silica hybrid film and a photocata lytic anatase TiO₂ top layer according to the invention.

Fig. 3a schematically illustrates photoactive anatase TiO₂ coated according to the invention on nascent aluminium, etched or anodised aluminium, or polyester paint, forming a composite coating on aluminum comprising 4 layers of which the two top most layers are described herein.

The structure shown in Fig. 3a comprises an aluminium (3005/5005) substrate 30 on which an alumina layer 31 is provided by anodisation or etching for mechanical and corrosion protection. In the embodiment shown, a polyester paint 32 is provided, which requires a protective intermediate inorganic-organic hybrid silica coating 33, (described above) for corrosion protection. Finally, on top of the structure there is provided a TiCh anatase coating 34, 20-300 nm thick having a photoactive function.

In an alternative embodiment, the inventive top layer 34 is provided directly on the bottom aluminium substrate 30.

Fig. 3b schematically illustrates photoactive anatase TiCh coated according to the invention on steel or stainless steel comprising 4 layers of which the two top most layers are described herein. The structure shown in Fig. 3b thus comprises a steel or stainless steel substrate 35 on which a primer 36 for corrosion protection is provided, e.g. Zn, Zn/AI, Zn/Mg/AI (Magnelis®). Also, optionally, a nickel coating (not shown) could be provided for decorative purposes. This would require a protective intermediate inorganic-organic hybrid coating as described above. In the embodiment shown a polyester paint 37 is provided which requires a protective inorganic-organic hybrid silica coating 38, (described above) for corrosion protection. Finally, on top of the structure there is provided a TiO2 anatase coating 39, 20-300 nm thick having a photoactive function.

In an alternative embodiment, the inventive top layer 39 is provided directly on the bottom steel or stainless steel substrate 35.

The invention will now be further illustrated by way of the following examples.

Examples

EXAMPLE 1

General description of the preparation of modified titanium alkoxide (cf. flow chart in Fig. 1):

Titanium alkoxide: Ti(OBuⁿ)4 (Titanium n-butoxide)

Bidentate Ligand: Acetylacetone (acacH) Hydrolysis solution:

Water: H2O de-ionized water ca. 18MQ

Acetic acid: CH3COOH (cone. HOAc)

Nitric acid: cone. HNO3

Alcohol: Pr'OH (2-propanol)

Specific synthesis parameters:

Concentration of suspension before heat treatment with respect to titanium content

[ Ti ] = 1.0 M

Molar ratio of Bidentate Ligand to titanium is given as A.

A = [ L ] / [ Ti ], = 0.7

Hydrolysis ratio denotes the molar ratio of water to titanium atoms and is given as H.

H = [ H₂O ] / [ Ti ], H = 10

Molar ratio of acid (protons) to titanium atom given as H⁺

H⁺ = [ H⁺ ] / [ Ti ], H⁺ = 0.2

Coating

Heating so as to produce 50-300 nm thick films.

Synthesis of TiO₂(A,P) material for preparing dense thin films.

The Ti(OBuⁿ)4 was modified with acetylacetone (acacH) adding the titanium alkoxide drop-wise to acacH under stirring at ca. 500 rpm resulting in a clear solution.

The hydrolysis solution was prepared by adding the acetic acid to the water followed by the nitric acid and then stirring for ca. 15 min before adding the 2-propanol and stirring further ca. 15 min.

The modified titanium alkoxide was then hydrolysed by adding the hydrolysis solution drop-wise to the modified titanium alkoxide under vigorous stirring at ca. 800 rpm).

Solutions of C (Ti(OBuⁿ)₄) = 1.0 M

Modification of titanium alkoxide: m (Ti(OBuⁿ)₄ ) = 8.567 g m (acacH) = 1.768 g

Hydrolysis solution: m (H₂O) = 4.501 g m (Acetic acid) = 0.209 g m (HNO₃) = 0.104 g m (Pr'OH) = 7.718 g

The suspension was heat treated for 24 h at about 74 °C under stirring, and the resulting heat treated suspension of titanium-oxo-cores was thereafter mixed in a vial under stirring with acacH, as a moderator in a molar ratio of 2.5 of added moderator to Ti, and subsequently ethanol was added under stirring to yield a suitable concentration of Ti of 0.5 M. The suspension was spin-coated at 1500 rpm for 50 sec. on Aluminium Blue substrate producing a coating, which after UV light treatment at room temperature for 30 min had a thickness of 90 nm.

EXAMPLE 2

Coating an object.

The heat treated solution from EXAMPLE 1 was applied to a square aluminium sheet 50 x 50 mm wide by spin-coating onto the surface.

After drying by evaporation of the solvent, the surface was exposed to UV light at room temperature (85W UV light ranging ca. 290-390 nm wavelength which equals to ca. 10 mW/m²) for 30 min or light emitting diode (LED) array (200 W providing ca. 100 W at 365 nm) for 10 sec.

The resulting coating was well adhering (passing ISO Standard 2409 cross hatch test).

The coating was tested for photocata lytic activity using the method according to the Pilkington patent as mentioned in the background section. EXAMPLE 3

Making a composite material

A substrate in the form of a painted steel sheet with a polyester or PVDF paint.

An inorganic-organic hybrid silica layer is applied onto the paint by the method set forth in Example 4 below.

The procedure according to EXAMPLE 1 is followed so as to produce a coating according to the invention, and thus forming a composite material according to the invention comprising a substrate (cf. 30;35 of Fig. 3), a paint layer (cf. 32;37 of Fig. 3), an inorganic-organic hybrid silica layer (cf. 33;38 of Fig. 3) and an antiviral, anti-bacterial and self-cleaning coating (cf. 34;39 of Fig. 3).

EXAMPLE 4

Preparation of hybrid (silica) coating solution.

13.6 g (100 mmol) methyl trimethoxysilane and 3.70 g (25.0 mmol) dimethyldiethoxysilane are mixed by mechanical stirring. 4.74 g nitric acid solution in water (26.4 mol/kg) is added during 2 minutes under mechanical stirring. This results in an exothermic hydrolysis reaction wherein alcohol is released. After 1 hour the released alcohol R=OH is removed under reduced pressure (2 Pa) until a viscous liquid is attained, with a residual content of 46 mass %. The viscous liquid is immediately diluted in 9.01 g (125 mmol) 2-butanone and the solution is neutralised with an (0.137 mmol) organic amine and filtered to remove any foreign particle.

The resulting solution is referred to as Solution 1.

Preparation of hybrid silica coating:

0.093 g (0.13 mmol) of zinc 2-ethylhexonate in toluene (1.34 mol/kg) is added dropwise under mechanical stirring to Solution 1. This results in the coating solution which can be applied to a substrate by spin-, dip-, slot-, roll- or spray-coating. To achieve the final hybrid silica coating a heat treatment at 250 °C is necessary. Heating using an IR lamp could possibly be used as an alternative.

On this hybrid silica layer a coating according to the invention can be applied by a method according to EXAMPLES 1 and 2. EXAMPLE 5

Reference is made to Table 1. The photocatalytic self-cleaning performance of coated aluminum and steel substrates / samples is determined following the guidelines of EP 1 254 870 Bl. The photocatalytic activity is determined from the rate of decrease of the area of the infrared peaks corresponding to C-H stretches in the range of about 2,700 to 3,000 cm ¹ of a spin coated stearic acid thin film on the coated surface under illumination by UVA light (approx. 32 W/m² @ 351 nm). The photocatalytic activity is expressed either as the rate of decrease of the area A of the IR peaks (in units of cm ¹ min ^-1) or as tgo% (in units of min), which is the time of UV exposure to reduce the peak height (absorption) of a peak down to 10% of its initial value. Due to the opaque nature of the samples, the measurements were performed in reflection under 80 degrees of incidence instead of in transmission.

Table 1. Decomposition of stearic acid (testing carried out by Fraunhofer 1ST according to the procedure disclosed in EP 1 254870 Bl):

Reference is now made to Table 2. Antibacterial tests were performed according to ISO 27447:2019 using gram negative Escherichia Coli ATCC 8738. A BLB light source with peak intensity at 365 nm and 0.25 mW/cm² irradiance was used. The samples were illuminated for 8 h prior to analysis, and compared with non-illuminated control sample. In table 2 is shown the logarithmic decay of the bacterial count with respect to an uncoated film exposed to the same illumination treatment, R , and the decay also taking into account the bacterial decay occurring in dark for the same films, AR. RL > 1 indicates an antibacterial activity. AR > 1 signifies intrinsic light-induced antibacterial activity. Table 2 Decomposition of E-coli bacteria (by CAS according to BS ISO 27447:2019):

Reference is now made to Table 3. Anti-bacterial tests were performed using methicillin resistant staphylococcus aureus (MRSA) strain ATCC 33591 at SGS-CSTC Standards Technical Services (Shanghai, China) following ISO 27447:2019. This is a well-known antibiotic resistant bacterium. Typically, the antibacterial activity is > 99.99% MRSA killing efficiency on coated metal sheets after 4 hour and 0.25 mW/cm² UV-A illumination (typical indoor illumination close to window).

Table 3. Decomposition of MRSA bacteria (by SGS-CSTC Standards Technical Services according to 150 27447:2019):

Claims

1. A method of preparing titanium-oxo-cores for use in forming a TiOz coating on a surface of a substrate, comprising the steps of:

A providing a titanium alkoxide as represented by the general formula Ti(OR)4, wherein each R is selected from the group consisting of: Ci alkyl to C& alkyl, and Ci alkenyl to Ce alkenyl;

B providing an organic bidentate ligand compound (LH);

C mixing the titanium alkoxide and the organic bidentate ligand compound (LH) with each other, so as to obtain a titanium alkoxide modified with the organic bidentate ligand (L), characterized in that in step C, the molar ratio of the organic bidentate ligand compound (LH) to the Ti(OR)4 is within the range of 2 to 0.5, and, in further comprising the additional step of:

D hydrolysing the resulting titanium alkoxide modified with the organic bidentate ligand (L) from step C in the presence of an acid catalyst, thereby forming a suspension of titanium-oxo-cores.

2. The method of claim 1, wherein the molar ratio of the organic bidentate ligand (LH) to the Ti(OR)4 is less than 1, more preferably 0.9 to 0.5, more preferably 0.6 to 0.8, and most preferably about 0.7.

3. The method of claim 1 or 2, additionally comprising the step of:

E heat treatment of the suspension of titanium-oxo-cores obtained from step D for a period of time within the range of 15-36 hours at a temperature within the range of 55-110 °C, thereby obtaining a heat-treated suspension of titanium-oxo-cores.

4. The method according to any one of claims 1-3, wherein the titanium alkoxide is selected from the group consisting of: Ti(OMe)4, Ti(O Et)4, Ti(OPr')4, Ti(OPrⁿ)4, Ti(OBu')4, and

Ti(OBuⁿ)₄.

5. The method according to any one of the previous claims, wherein the organic bidentate ligand is selected from the group consisting of: bidentate ketones, and bidentate hydroxyl -group containing organic compounds.

6. The method according to any one of claims 3-5, further comprising the additional step of:

F diluting the heat-treated suspension of titanium-oxo-cores obtained from step E, so that the total molar concentration of titanium in the suspension is within the range of 0.05 M to 1.5 M.

7. A method of preparing a TiO? coating on a surface of an object, comprising the steps of:

G applying a suspension of titanium-oxo-cores comprising organic bidentate ligands (L), and OR groups, wherein each R is selected from the group consisting of: Ci alkyl to Ce alkyl, and Ci alkenyl to Ce alkenyl, and wherein the overall molar ratio of organic bidentate ligand (L) to Ti in the titanium-oxo-cores is within the range of 2 to 0.5, such as obtainable by means of the method of claim 6, to a surface of an object;

H subjecting the coated surface obtained in step G to IR irradiation, UV irradiation, an elevated temperature of up to 300 °C, or to a combination of any thereof.

8. The method according to claim 7, wherein the object is selected from the group consisting of: sheet metal, a metal plate, a painted object, and a water glass object, wherein the metal is preferably steel or aluminium.

9. A coated object comprising a substrate, exhibiting, on a surface thereof, an anatase phase TiOz coating layer obtainable by means of the method of claim 7 or 8, having a thickness within the range of 20-300 nm.

10. The coated object of claim 9, wherein the anatase phase TiOz coating layer comprises TiOz crystallites having a size of up to about 5 nm according to x-ray diffraction (XRD) peak width measurement.

11. The coated object according to claim 9 or 10, wherein the anatase phase TiOz coating layer has photocatalytic properties exhibiting degradation rates of organic molecules exceeding 1x10³ min S preferably exceeding 4x10³ min and more preferably exceeding 8xl0^-3 min ¹.

12. The coated object according to any one of claims 9-11, wherein the anatase phase TiOz coating layer has antibacterial properties exhibiting antibacterial activity exceeding RL > 1, and AR > 0, preferably RL > 1.3 and AR > 0.8, and more preferably RL > 1.6, and AR > 1.3.

13. The coated object according to any one of claims 9-12, wherein the substrate is selected from the group consisting of steel, aluminium, a painted surface.

14. A coating composition for forming an anatase phase TiOz coating layer on a surface of a substrate, which coating composition is obtainable by means of the method of claim 6, comprising a suspension of titanium-oxo-cores comprising organic bidentate ligands (L), and OR groups, wherein each R is selected from the group consisting of: Ci alkyl to Ce alkyl, and Ci alkenyl to Cg alkenyl, wherein the overall molar ratio of organic bidentate ligand (L) to Ti in the titanium-oxo-cores is within the range of 2 to 0.5, and wherein the total molar concentration of titanium is within the range of 0.05 M to 1.5 M.

15. Titanium-oxo-cores for use in forming an anatase phase TiCh coating layer on a surface of a substrate obtainable by means of the method of any one of the claims 1-6, comprising organic bidentate ligands (L), and OR groups, wherein each R is selected from the group consisting of: Ci alkyl to C& alkyl, and Ci alkenyl to C& alkenyl, and wherein the overall molar ratio of organic bidentate ligand (L) to Ti is within the range of 2 to 0.5.