Antibacterial and antiviral coatings based on niobium and copper doped titanium dioxide

Abstract

The present invention relates to niobium and copper doped titanium dioxide, and to a method for producing antibacterial and antiviral coatings with Cu, Nb doped particles and the products thereof.

Description

[Technical Field]

[0001] The present invention relates to methods for producing niobium and copper doped titanium dioxide particles and coatings thereof, their production and uses.

[0002] Nb-doped TiO (TNO) has been described in the literature as an alternative to indium tin oxide (ITO) for transparent conductive layers. This description is based on the fact that sputtered layers of this material exhibit similar optical and electrical properties to sputtered ITO layers. There have been sporadic attempts to synthesize the material using wet chemistry, for example, by preparing a sol from a precursor followed by spin or dip coating.

[0003] Nb-doped titanium dioxide particles TNO which are pressed into electrical conductors are known from WO 2019 / 129463 A1. Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide a method that allows the production of Nb- and Cu-doped TiO2 particles and layers. [Means for solving the problem]

[0005] The above-mentioned problem is solved by the invention with the features of the independent claims. Advantageous further embodiments of the invention are defined in the dependent claims. The wording of all claims constitutes the content of this specification by reference. The invention also comprises all useful, in particular all mentioned combinations of the independent and / or dependent claims.

[0006] The above-mentioned problems are solved by a method for producing an antiviral and antibacterial coating comprising Cu, Nb doped TiO particles, comprising the following steps a) to c): a) preparing a dispersion comprising Cu, Nb doped TiO2 particles; b) optionally milling the particles in the dispersion; c) applying (or coating) the dispersion onto a substrate.

[0007] The individual steps of the method are described in more detail below. The steps do not necessarily have to be performed in the order described, and the described method may include other steps not mentioned.

[0008] In the first step, a dispersion containing Cu, Nb doped TiO2 particles is prepared.

[0009] In a preferred embodiment of the invention, these are nanoparticles. Nanoparticles are understood to be particles having a particle size of less than 200 nm. This means that in a random sample of at least 100 particles, at least 50% have a diameter of less than 200 nm (measured by TEM). Particle sizes of 100 nm or less (i.e. 50% are in the range of 100 nm or less), in particular 50 nm or less, in particular 1 to 200 nm, preferably 1 to 100 nm, particularly preferably 2 to 50 nm, are particularly preferred. Particles with particle sizes of 2 to 30 nm and 2 to 20 nm are particularly preferred.

[0010] Preferably, in a random sample of at least 100 particles, all particles have a diameter of less than 200 nm, preferably less than 100 nm (as measured by TEM), particularly optionally after a milling step.

[0011] The TiO particles are Cu- and Nb-doped TiO particles. Preferably, the Cu and Nb contents are up to 30 atomic %, preferably up to 20 atomic %, based on the total of Cu, Nb, and Ti atoms. The Cu and Nb contents are preferably at least 2 atomic %, more preferably at least 4 atomic %, respectively.

[0012] Particles can typically be produced by a variety of methods, e.g., flame pyrolysis, plasma processes, colloidal techniques, sol-gel processes, controlled nucleation and growth, MOCVD, emulsion processes, etc. These methods are well described in the literature.

[0013] The dispersion also comprises at least one solvent. This may be, for example, water or an organic solvent, or a mixture thereof. Organic solvents such as alcohols, ethers, ketones, amides, or mixtures thereof are preferred. Solvents with a boiling point of less than 200°C, particularly between 30°C and 200°C, are preferred. Aliphatic alcohols (C1-C6 alcohols) such as ethanol, 1-propanol, i-propanol, sec-butanol, tert-butanol, 2-isobutyl alcohol, n-butanol, and pentanol isomers, particularly 1-pentanol, are preferred; diols such as ethylene glycol and 1,3-propanediol; or ethers of these compounds, such as ethylene glycol monoisopropyl ether (2-isopropoxyethanol).

[0014] Depending on the desired coating, the dispersion may comprise a matrix material, for example an inorganic salt solution such as an acidic or basic water glass, such as sodium, potassium or lithium water glass, or an inorganic matrix such as silica sol.

[0015] The dispersion may also contain other additives used for crosslinking, such as wetting agents, fillers, color pigments, dyes, crosslinking agents, adhesion promoters, and starters.

[0016] Preferably, the dispersion also comprises at least one wetting agent, such as a phosphate ester, which stabilizes the dispersion.

[0017] The dispersion preferably has a particle content of 10 wt% or more, more preferably 10-50 wt%. The total solids content (measured by weight after 2 hours at 500°C) is preferably 10-50 wt%.

[0018] In an optional (or required) step, the particles of the dispersion are milled, preferably by mechanical milling, especially by ball milling. This step is particularly important when the coating according to the invention is to be applied to a transparent substrate or is itself to be transparent.

[0019] The dispersion is applied to a substrate. The substrate may be any conventional material, including, for example, metal, rock, wood, paper, fabric, leather, ceramic, glass, enamel, rubber, or plastic. Metals include metal alloys, such as steel (including stainless steel), chromium, copper, titanium, tin, zinc, brass, and aluminum. Plastics include polymethyl methacrylate, polyethylene, polypropylene, polyacrylates (e.g., polymethyl acrylate), polyvinyl butyral, and polycarbonate. Glasses include float glass, borosilicate glass, lead crystal, and silica glass. Paper and fabrics can be made from plant, animal, or synthetic fibers. Stones include natural stone, such as marble, granite, or sandstone, and artificial stone, such as concrete and mortar.

[0020] In principle, the coating is suitable for any substrate or object. The object may consist of one material or several parts made of different materials. The object may have a surface layer that is at least partially coated. The coating according to the invention may be applied to the entire surface of the substrate. If required, only parts of the substrate may be provided with a coating. This may arise, for example, because these parts are particularly exposed to microorganisms or viruses, or because biofilms are particularly undesirable on these parts.

[0021] The substrate can be pre-treated in the usual way, for example by cleaning, degreasing or to achieve better adhesion with the coating.

[0022] The substrate can be provided with a surface layer, for example by metallization, enameling or painting. In many cases, it is advisable to provide it with a primer consisting of a conventional lacquer.

[0023] Of course, if only a portion of the substrate is to be coated, the portions of the substrate to be coated can first be coated separately and then joined together to form the finished product.

[0024] The dispersion can be applied to the substrate by any standard method. All common wet-chemical coating methods can be used. Examples include centrifugal coating, (electrolytic) dip coating, doctoring, spraying, spinning, drawing, spinning, casting, rolling, brushing, flood coating, film casting, knife casting, slot coating, meniscus coating, curtain coating, roller application, or conventional printing methods such as screen printing or flexographic printing. The amount of coating composition applied is selected to achieve the desired coating thickness.

[0025] After application of the dispersion, drying can be carried out, for example, at ambient temperature (below 40° C.).

[0026] The coating may be pre-dried and is generally subjected to a heat treatment to dry and / or cure the coating, the conditions selected for this depending on the substrate.

[0027] This may be, for example, a temperature treatment for at least 1 hour at a temperature above 350° C. Such a treatment removes organic residues.

[0028] The resulting coatings have several advantageous properties due to the dual doping. For example, Cu and Nb doped TiO particles have antiviral and antibacterial effects when exposed to visible light and in the absence of light. The coatings can also be produced in a simple manner without combining multiple active additives. The particles are also easy to produce.

[0029] The coating according to the invention is generally suitable for any object or part thereof that should have antibacterial and antiviral properties. Preferably, the coating according to the invention is transparent and / or on a transparent substrate.

[0030] The doped particles according to the present invention are preferably produced by a sol-gel method to form particles. In the sol-gel method, hydrolyzable compounds are typically hydrolyzed, optionally under acidic or basic catalysis, and optionally at least partially condensed. The hydrolysis and / or condensation reaction results in the formation of compounds or condensates having hydroxy groups, oxo groups, and / or oxo bridges, which function as precursors. The sol containing the particles according to the present invention can be obtained by appropriately adjusting parameters such as the degree of condensation, solvent, temperature, water concentration, time, or pH value.

[0031] The hydrolysis and condensation reaction is preferably carried out so that the hydrolyzable compound is not completely hydrolyzed to form particles, that is, the formed particles still have hydrolyzable groups on the surface. Given the task of not completely hydrolyzing the hydrolyzable compound, those skilled in the art will know how to achieve this by appropriately adjusting the above parameters. Some preferred conditions are described below. This method produces particles that are easily redispersible due to the non-hydrolyzable groups on the surface. Furthermore, the non-hydrolyzable groups can be easily controlled by selecting the compound and solvent used.

[0032] The hydrolysis and condensation can be carried out in a solvent, but can also be carried out without a solvent, in which case a solvent or other liquid component can be generated during the hydrolysis (e.g., during the hydrolysis of the alcoholate). Removal of the solvent can also include removal of any liquid component present. Removal of the solvent can be carried out, for example, by filtration, centrifugation, and / or drying (e.g., evaporation).

[0033] Preferably, the hydrolysis is carried out in a solvent. The solvent used is an organic solvent in which the hydrolyzable titanium compound, and preferably the hydrolyzable niobium compound and copper compound, are preferably dissolved. The solvent is also preferably miscible with water. Examples of suitable organic solvents include alcohols, ketones, ethers, amides, and mixtures thereof. Alcohols are preferably used, preferably lower aliphatic alcohols (C1-C6 alcohols), such as ethanol, 1-propanol, i-propanol, sec-butanol, tert-butanol, isobutyl alcohol, n-butanol, and pentanol isomers, especially 1-pentanol, and preferably methanol and ethanol, especially ethanol. Preferably, an alcohol having the same hydrocarbon chain as the preferred alkoxide is used.

[0034] Preferably, the components are dissolved and then hydrolyzed.

[0035] Preferably, the hydrolysis is carried out with a substoichiometric amount of water, i.e., the molar ratio of water to the hydrolyzable groups of the at least one hydrolyzable titanium compound is less than 1, preferably less than 0.8, particularly preferably less than 0.6, even more preferably less than 0.5, and especially less than 0.5. Preferably, the molar ratio is greater than 0.05, more preferably greater than 0.1. A preferred molar ratio is, for example, 0.1 to 0.5.

[0036] As mentioned above, hydrolysis can be catalyzed by acidic or basic methods, with acidic catalysis being preferred. Inorganic or organic acids can be used. Reactions with organic acids such as acetic acid can be incomplete, so inorganic acids are particularly preferred. When using nitric acid or sulfuric acid, additional doping with N or S atoms can occur. Particularly preferred is hydrochloric acid (HCl), particularly at a concentration of at least 2 mol / l, preferably at least 10 mol / l, and especially concentrated hydrochloric acid. Concentrated hydrochloric acid is a solution of at least 10 mol / l, especially at least 12 mol / l. Preferably, the acid (in the case of hydrochloric acid, an aqueous solution of HCl) is the only water added to generate the particles.

[0037] The hydrolysis can be carried out at room temperature (about 23° C.), but is preferably carried out under heat, for example at least 60° C., preferably at least 100° C. or at least 200° C. In a particularly preferred embodiment, the hydrolysis is carried out under heat and pressure (hydrothermal reaction), particularly preferably by heating in a closed vessel (autogenous pressure).

[0038] In a preferred embodiment of the present invention, the hydrolysis is carried out in a closed vessel at autogenous pressure and at a temperature of 200-300°C, preferably 220-260°C.

[0039] The hydrolysis is carried out until the particles according to the present invention are obtained, preferably for 30 minutes to 48 hours, more preferably for 12 hours to 36 hours, and particularly preferably for 20 hours to 36 hours.

[0040] However, suitable reaction conditions naturally depend on the starting compound used, and therefore suitable conditions can be selected from a wide range, depending, for example, on the stability of the starting compound. Those skilled in the art can easily select suitable conditions depending on the selected compound.

[0041] Alkoxides can be used as hydrolyzable compounds or precursors, but other hydrolyzable compounds can also be used, such as precursors containing acyl groups or complexed precursors such as β-diketone complexes such as acetylacetonates. Organic groups containing metal-carbon compounds can also be used.

[0042] Preferably, the hydrolyzable compound has the general formula MX n A titanium compound of formula (I), wherein M is Ti, X is a hydrolyzable group which may be the same or different, two X groups may be replaced by bidentate hydrolyzable groups or oxo groups, or three X groups may be replaced by tridentate hydrolyzable groups, and n corresponds to the valence of the element M, which is 4 for Ti. When M represents Nb, n is usually 5. When M represents Cu, n is usually 2.

[0043] The group X is preferably a low-mass group, which ensures that the particle surface is not covered with groups that are difficult to remove. Examples of preferred groups include halogen (F, Cl, Br or I, especially Cl and Br), alkoxy (preferably C 1-6 Alkoxy, especially CH 1-4 Alkoxy, such as methoxy, ethoxy, n-propoxy, i-propoxy, butoxy, i-butoxy, sec-butoxy and tert.-butoxy), aryloxy (preferably C 6-10 aryloxy, e.g., phenoxy), acyloxy (preferably C 1-6 acyloxy, for example acetoxy or propionyloxy) or alkylcarbonyl (preferably C 2-7 alkylcarbonyl, e.g., acetyl). Preferably, small groups having up to 3 carbon atoms, e.g., C 1-3 Alkoxy (ethoxy, n-propoxy, i-propoxy, etc.), C 1-3 Acyloxy (e.g., acetoxy or propionyloxy), C1-C3-alkenyloxy (e.g., vinyl or allyloxy), C1-C3-alkynyloxy or C 2-3 -Alkylcarbonyl (acetyl, etc.).

[0044] The hydrolyzable metal or metalloid compounds, such as compounds of formula (I) above, may also have complexing radicals such as β-diketones and (meth)acrylic radicals. Examples of suitable complexing agents include unsaturated carboxylic acids and β-dicarbonyl compounds such as methacrylic acid, acetylacetone, and ethylacetoacetate.

[0045] In a preferred embodiment, the Nb compound added for doping is also a compound of formula (I), where M represents Nb, which allows it to be successfully incorporated into the particles.

[0046] In a preferred embodiment, the Cu compound added for doping is a compound of formula (I), where M represents Cu.

[0047] Examples of compounds include Ti(OCH3)4, Ti(OC2H5)4, Ti(On-C3H7)4, Ti(Oi-C3H4)4, TiCl4, NbCl5, Nb(OCH3)5, Nb(OC2H5)5, Nb(On-C3H7)5, Nb(Oi-C3H7)5, Nb(Oi-C3H7)4thd (thd = 2,2,6,6-tetramethylheptane-3,5-dionate), Cu(acac)2, Cu(II)-tert.-butylacetoacetate, Cu(II)-2,2,6,6-tetramethyl-3,5-heptanedionate, Cu(OCH3)2, Cu(OOCH)2, and Cu(OOCCH3)2.

[0048] Preferably, all Nb and Ti compounds of formula (I) used are alkoxides or alkoxide-containing complexes. Preferably, they contain only carbon, hydrogen, and oxygen groups. Examples of preferred compounds are: Ti(OCH3)4, Ti(OC2H5)4, Nb(OCH3)5, and Nb(OC2H5)5. The copper compounds used are preferably carboxylates or β-dicarbonyl compounds, especially Cu(acac)2. Alkoxides are chemically more similar and can produce particularly uniform particles, especially when alcohol is used as a solvent.

[0049] Preferably, the composition does not contain other metal compounds.

[0050] Cu, Ti and Nb compounds are preferably used according to the desired doping degree.

[0051] After hydrolysis, the resulting particles are isolated by removing the solvent and obtained as a powder.

[0052] It may be necessary to neutralize excess acid by prior addition of caustic solution, especially sodium hydroxide.

[0053] Preferably, the particles are washed with deionized water until the conductivity of the wash water is 20 μS / cm or less.

[0054] In a preferred embodiment, the particles are then calcined, which removes any organic residue.

[0055] Preferably, the particles are subjected to a temperature treatment in an oxygen-containing atmosphere. The temperature is at least 200°C, preferably at least 400°C. A temperature between 200°C and 900°C is preferred, preferably between 400°C and 800°C, particularly preferably between 450°C and 800°C. Particularly good results have been obtained with a treatment between 450°C and 750°C.

[0056] The temperature treatment is carried out until the organic components are sufficiently removed. Depending on the amount of particles, the treatment takes from 1 minute to 25 hours, preferably 30 minutes to 2 hours, during which the desired temperature is maintained. Preferably, the particles are heated to the target temperature within a maximum of 4 hours.

[0057] The temperature treatment is carried out in an oxygen-containing atmosphere. This atmosphere must therefore contain a sufficient proportion of oxygen. A proportion of at least 5% by volume is preferred, and preferably at least 20% by volume. Preferably, other components include gases that are non-reactive under these conditions, such as nitrogen or argon. Up to 0.1% by volume of other gaseous components may also be present.

[0058] The temperature treatment can simply be carried out in air.

[0059] The present invention also relates to a method for producing Cu, Nb doped TiO2 particles according to the preferred embodiment of the above method.

[0060] A mixture of at least one hydrolyzable titanium compound, preferably of formula (I), at least one hydrolyzable niobium compound, preferably of formula (I), and at least one hydrolyzable copper compound, preferably of formula (I), in a substoichiometric amount, based on all hydrolyzable groups present, in an organic solvent and water is used. The mixture is treated under autogenous pressure at 200-300°C to form Cu, Nb-doped TiO particles. The treatment can be carried out for 12-36 hours. A powder of Cu, Nb-doped TiO particles is obtained by removing the solvent.

[0061] In a preferred embodiment, the hydrolyzable Nb and Ti compounds are alkoxide compounds having 1 to 3 carbon atoms, and the Cu compound is a β-diketone compound.

[0062] The present invention also relates to Cu, Nb doped titanium dioxide particles produced by the method according to the present invention.

[0063] Further details and features can be found in the following description of preferred embodiments in conjunction with the dependent claims. Each feature can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the example embodiments. For example, range specifications always include all unmentioned intermediate values ​​and all possible subintervals.

[0064] Example

[0065] Particle production

[0066] The precursors Ti(OEt)4 (65.7 g, 288.0 mmol), Nb(OEt)5 (5 at. % Nb: 5.09 g, 16.0 mmol), and copper(II) acetylacetonate Cu(acac)2 (4.19 g, 16.0 mmol) were weighed together in a glove box and then rapidly mixed with absolute ethanol (470 mL) either inside or outside the glove box. This mixture was stirred overnight (approximately 18 hours). Concentrated hydrochloric acid (37%, 6.54 g) was then added quickly with stirring. After stirring for an additional 3 hours, the reaction mixture was evenly distributed into four 200 mL Teflon containers (approximately 136 mL each). These were tightly screwed onto a steel container (at least 35 Nm) and heated in a heating block at 240 °C for 25 hours. After complete cooling, the clear supernatant was removed, and the solid was poured into a 500 mL centrifuge container containing water. After neutralizing the HCl by adding 0.5 mL of NaOH (3 M), the sample was washed at least three times with deionized water until the conductivity of the wash water reached 20 μS / cm or less. The solid was then transferred to a flask with as little water as possible, frozen in liquid nitrogen, and lyophilized.

[0067] The resulting powder was then calcined at 500°C in air for 1 hour.

[0068] Coating sol production

[0069] The particles (9 g) obtained in Example 1 were slurried in 2-isopropoxyethanol (36 g) and Byk W 9010 (1.8 g) and milled in a Retsch PM400 planetary ball mill with zirconium oxide milling balls (φ0.3 mm) in two 50 ml aluminum oxide milling vessels at 400 rpm for 4 hours without changing direction. After 2 hours at 500 °C, the solids content of the resulting dispersion was determined gravimetrically to be 19.5%.

[0070] The resulting dispersion was filtered through a Whatman ReZist Series 30 / GF92 syringe filter and applied by spin coating. Borofloat glass disks (5 cm x 5 cm, 2 mm thick) were used as substrates. 0.7 mL of the filtered dispersion was applied at each step. The following parameters were selected:

[0071] Step 1: 350 rpm; acceleration 100 rpm / sec; spin start for 5 seconds Step 2: 1000 rpm; acceleration 500 rpm / sec; spin coating for 60 seconds Step 3: 350 rpm; acceleration 300 rpm / sec; spin stop for 5 seconds

[0072] The layer was dried at 400°C for 1 hour and then characterized using ellipsometry and white light interferometry.

[0073] Antiviral and antibacterial testing

[0074] The antibacterial / viral effect of the embodiment as a coating is shown diagrammatically in the figures. Identical reference numerals in the individual figures indicate identical or functionally identical elements or elements that correspond to each other from a functional point of view. Details are as follows: [Brief explanation of the drawings]

[0075] [Figure 1] Measurement of antibacterial properties by light irradiation according to Table 1; the upper bold line indicates Rmax, and the lower bold line indicates R=2.0.

[0076] [Figure 2] Measurement of antiviral properties by light irradiation according to Table 1; the upper bold line indicates R=3.0, and the lower bold line indicates R=2.0.

[0077] [Figure 3] Measurement of antibacterial properties without light irradiation according to Table 1; the upper bold line indicates Rmax, and the lower bold line indicates R=2.0.

[0078] [Figure 4]Measurement of antiviral properties without light irradiation according to Table 1; the upper bold line indicates R=3.0, and the lower bold line indicates R=2.0.

[0079] The conditions are shown in Table 1.

[0080] The antibacterial activity or antiviral effect is expressed as an R value. The meaning of the values ​​in the antibacterial test is shown in Table 2, and the meaning of the values ​​in the antiviral test is shown in Table 3.

[0081] The R value is calculated using the following formula: R = (U t -U0)-(A t -U0)=U t -A t * R. It is calculated using

[0082] U0 is the mean logarithm of the phage titer after 0 hours of contact with the non-antiviral control sample. t A is the mean logarithm of the phage titer after 24 hours of contact with the non-antiviral sample. t R is the mean logarithm of the phage titer after 24 hours of contact with the antiviral sample. max is the maximum value calculated above. Antibacterial activity was also measured in the same way.

[0083] Figure 1 shows the results of measuring the antibacterial properties by light irradiation. The sample showed a significantly better antibacterial effect than the control (C), with an R value of over 2.5.

[0084] Figure 2 shows the results of measuring the antiviral properties by light irradiation. Compared to the control (C), the sample had an R value of over 3, indicating a sufficient antiviral effect.

[0085] Figure 3 shows the results of measuring the antibacterial properties without light irradiation. The sample still has a good antibacterial effect compared to the control (C), with an R value of approximately 3.0.

[0086] Figure 4 shows the results of measuring the antiviral properties without light irradiation. Compared to the control (C), the sample has sufficient antiviral effect, with an R value of over 3.5.

[0087] Thus, the particles according to the invention, or coatings comprising them, exhibit good to very good antibacterial and antiviral properties both with and without light irradiation.

[0088] The particles are readily available and can be produced using simple manufacturing methods, and the photocatalytic activity can reduce organic fouling, allowing the disclosed coatings to remain antibacterial and antiviral active for longer periods than pure copper-containing coatings.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

Claims

1. Cu, Nb-doped TiO ２ 1. A method for preparing an antiviral and antibacterial coating comprising particles, comprising: a) Cu, Nb-doped TiO ２ preparing a dispersion comprising particles; b) optionally milling the particles in the dispersion; c) applying the dispersion to a substrate; The method comprising:

2. 2. The method of claim 1, wherein the particles have a particle size of less than 200 nm.

3. 3. The method according to claim 1, wherein the particles have an Nb content and a Cu content of up to 30 atomic % each.

4. 4. The method according to claim 1, wherein the particles are produced by a sol-gel process.

5. 5. The method according to claim 1, wherein the particles are prepared by hydrolysis using a substoichiometric amount of water.

6. A coating produced by the method of any one of claims 1 to 5.

7. 1. A method for preparing Cu, Nb-doped titanium oxide particles, comprising: a) preparing a mixture comprising at least one hydrolyzable titanium compound, at least one hydrolyzable copper compound, and at least one hydrolyzable niobium compound in substoichiometric amounts based on total hydrolyzable groups present in an organic solvent and water; b) treating the mixture under autogenous pressure at 200°C to 300°C to form Cu, Nb-doped titanium oxide particles; The method comprising:

8. Cu, Nb-doped titanium dioxide particles produced by the method of claim 7.

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