Unsupported bimetallic particulate materials

Abstract

The present invention relates to a carrier-free bimetallic particulate material comprising elemental metallic silver and elemental metallic ruthenium, having an average particle size (d50) in the range of 1 μm to 100 μm, preferably 1 μm to 20 μm, and having a silver:ruthenium weight ratio in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium.

Description

[Technical Field]

[0001] The present invention relates to a carrier-free bimetallic particulate material comprising elemental metallic silver and elemental metallic ruthenium, and an efficient method for its production.

[0002] EP 3915376 (A1) discloses a hybrid material that can be used as an antibacterial, antiviral, and / or fungicidal additive, each comprising particles comprising at least one support material at least partially coated with at least two different metals. The metals are in conductive contact with each other at least on their respective surfaces. The first metal has multiple oxidation states and includes at least one transition metal element, such as ruthenium, that allows oxidation state changes via catalytically active centers. The second metal, such as silver, constitutes at least one conductive silver semiconductor, and the two metals form semi-elements that are short-circuited in the presence of water and oxygen.

[0003] The object of the present invention was to provide a material that has a high antimicrobial effect, can be produced easily and efficiently and is based on a carrier material comprising elemental silver and elemental ruthenium.

[0004] This objective can be achieved by providing a carrier-free bimetallic microparticle material, which contains elemental metallic silver and elemental metallic ruthenium, has an average particle size (d50) in the range of 1 μm to 100 μm, preferably 1 μm to 20 μm, and has a silver:ruthenium weight ratio in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium, and which will hereinafter be referred to simply as "carrier-free bimetallic microparticle material."

[0005] The term "average particle size" as used herein refers to the volume-average primary particle size (d50), which can be determined by laser diffraction. In this case, what is known as the equivalent circular area diameter (ECAD) can be advantageously used as a measure of particle size (see Renliang Xu et al.: "Comparison of sizing small particles using different technologies," Powder Technology, Elsevier, Basel (CH), vol. 132, no. 2-3, June 24, 2003 (06-24-2003), pages 145-153). Laser diffraction measurements can be performed using a corresponding particle size measuring device, such as the Mastersizer 3000 or Mastersizer 2000 from Malvern Instruments, according to the wet measurement method. In the wet measurement method, the particulate sample can be dispersed in ethanol by ultrasound as part of the sample preparation.

[0006] The carrier-free bimetallic particulate material according to the present invention comprises particles consisting of silver particles accompanied by elemental ruthenium. This material may also comprise silver particles, ruthenium particles, and / or ruthenium particles accompanied by elemental silver. However, this material may consist at least primarily, for example, from 90% to 100% by weight, of silver particles accompanied by elemental ruthenium, and therefore 0% to 10% by weight or less may consist of silver particles, ruthenium particles, and / or ruthenium particles accompanied by elemental silver. The carrier-free bimetallic particulate material according to the present invention does not comprise any carrier material. In addition to the silver particles accompanied by elemental ruthenium and any silver particles, ruthenium particles, and / or ruthenium particles accompanied by elemental silver that may be present, the carrier-free bimetallic particulate material according to the present invention does not comprise any intentionally added materials or substances, in particular any materials or substances that can be used as carrier materials, and furthermore does not comprise vitamins, vitamin derivatives, ascorbic acid, or ascorbic acid derivatives.

[0007] The elemental ruthenium of the provided silver particles is present on the outer surface of the silver particles, and can form, for example, a discontinuous layer and / or small ruthenium particles (ruthenium islands), with the silver particles themselves serving as a support material. Scanning electron microscopy can be a suitable method for observing such morphological characteristics. Silver and ruthenium are not alloyed but are statistically distributed, and both precious metals are at least partially in contact with each other. It will be clear to those skilled in the art that the silver and ruthenium on the surface of the carrier-free bimetallic particulate material according to the present invention may contain silver species other than elemental metallic silver and ruthenium species other than elemental metallic ruthenium, such as the corresponding oxides, halides, and / or sulfides. Such species may be unintentionally and unavoidably produced as small amounts of impurities during or after the production of the carrier-free bimetallic particulate material according to the present invention, for example, during storage, use, or further processing.

[0008] The present invention also relates to a method for producing the carrier-free bimetallic particulate material of the present invention. In the method of the present invention, the carrier-free bimetallic particulate material of the present invention can be obtained by drying and pyrolysis of an aqueous suspension containing water, silver particles, and at least one ruthenium precursor in a non-oxidizing atmosphere. The pyrolysis is a treatment in a non-oxidizing atmosphere at or above the pyrolysis temperature, i.e., above the minimum target temperature required to ensure the thermal decomposition of the ruthenium precursor to form elemental ruthenium.

[0009] As used herein, the term "non-oxidizing atmosphere" refers to a reducing or inert atmosphere. The term "reducing atmosphere" refers to an atmosphere consisting of a gas having reducing properties, such as hydrogen and / or carbon monoxide, or a gas mixture of a gas having reducing properties with an inert gas, such as nitrogen, argon, and / or carbon dioxide, where the volume fraction of the gas having reducing properties in the gas mixture with the inert gas may be, for example, in the range of 5% to 10% by volume. The term "inert atmosphere" refers to an atmosphere consisting of an inert gas, such as nitrogen, argon, and / or carbon dioxide.

[0010] The method according to the invention uses silver particles and at least one ruthenium precursor.

[0011] The silver particles referred to herein or used as starting material in the method according to the present invention have an average particle size (d50), for example, in the range of 0.5 μm to 50 μm. The silver particles can have various shapes, for example, they can be spherical, substantially spherical, ellipsoidal, oval, flaky, or irregularly shaped. The silver particles are advantageously uncoated and may include particles of pure silver (at least 99.9% silver purity by weight) and / or particles of a silver alloy containing up to 10% by weight of at least one other alloying metal. Examples of suitable alloying metals are copper, gold, nickel, palladium, platinum, and aluminum. Silver particles made of pure silver are preferred. Silver particles are commercially available. One example is the silver powder "Ag 300-01" manufactured by Heraeus Electronics. Similar powders are also available from other companies.

[0012] The ruthenium precursor used in the process according to the invention is a ruthenium compound that can be thermally decomposed in a non-oxidizing atmosphere to form elemental ruthenium.

[0013] All ruthenium compounds that can be thermally decomposed in a non-oxidizing atmosphere to form elemental ruthenium can be thermally decomposed in a reducing atmosphere in the process according to the invention to form elemental ruthenium in this process. Examples of suitable ruthenium compounds in this regard include ruthenium nitrosyl nitrate, ruthenium oxalate, ruthenium acetate, and especially ruthenium nitrosyl oxalate.

[0014] Some ruthenium compounds that can be thermally decomposed to form elemental ruthenium under a non-oxidizing atmosphere can also be thermally decomposed under an inert atmosphere in the method according to the present invention, and in this process can be thermally decomposed to form elemental ruthenium. Those skilled in the art can easily determine the suitability of a ruthenium compound for thermal decomposition under an inert atmosphere to form elemental ruthenium, for example, by using thermogravimetric analysis under an inert gas atmosphere. Examples of suitable ruthenium compounds in this regard include ruthenium oxalate, ruthenium acetate, and in particular ruthenium nitrosyl oxalate.

[0015] The method of the present invention comprises providing an aqueous suspension containing water, silver particles, and at least one ruthenium precursor, and drying and pyrolyzing the aqueous suspension in a non-oxidizing atmosphere, which can be performed sequentially or in a combined step.

[0016] In a first embodiment, the method according to the invention comprises: (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium precursor; (2) drying the aqueous suspension prepared in step (1); (3) subjecting the dried material obtained after completion of step (2) to pyrolysis in a non-oxidizing atmosphere; The process includes the following continuous steps.

[0017] In a second embodiment, in which steps (2) and (3) are carried out together, the method according to the present invention comprises: (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium precursor; (2+3) drying and pyrolyzing the aqueous suspension prepared in step (1) in a non-oxidizing atmosphere; The process includes the following continuous steps.

[0018] In step (1) of both embodiments of the method according to the invention, an aqueous suspension is provided comprising water, silver particles, and at least one ruthenium precursor. The aqueous suspension may be in the form of a thin slurry or a pulp-, paste-, or dough-like mass.

[0019] The aqueous suspension can be produced by adding silver particles to and suspending them in an aqueous solution of at least one ruthenium precursor. The reverse addition order is also possible.

[0020] The weight percentage of silver particles in the aqueous suspension prepared in step (1) of the method according to the present invention may be, for example, in the range of 5% to 60% by weight.

[0021] The weight proportion of ruthenium in the aqueous suspension prepared in step (1) of the method according to the present invention can be, for example, in the range of 0.5% to 20% by weight. The aqueous suspension prepared in step (1) of the method according to the present invention is characterized by a weight ratio of the two precious metals in the range of, for example, 1 part to 2000 parts by weight of silver:1 part by weight of ruthenium, and is generally heavily biased towards silver.

[0022] In addition to the silver particles and the ruthenium precursor, the aqueous suspension provided in step (1) of the method according to the invention generally comprises only water and, optionally, the corresponding acid from the ruthenium precursor, i.e., the suspension consists at least substantially, and preferably only, of silver particles, ruthenium precursor and water.

[0023] In step (2) according to the first embodiment of the method according to the invention, the aqueous suspension provided in step (1) is dried, i.e. water and any other volatile substances present are removed.

[0024] The aqueous suspension is concentrated to dryness by evaporation. Advantageously, the aqueous suspension is agitated during concentration, for example by stirring and / or shaking and / or rotating, i.e., rotating the vessel or container containing the aqueous suspension. Heat and / or negative pressure are typically applied during concentration to remove water and any other volatile substances that may be present. During concentration, the operation can be carried out at a temperature in the range of, for example, 40°C to 95°C. The material obtained after drying has been achieved can be milled, if necessary.

[0025] In step (3) of the first embodiment of the method according to the present invention, the ruthenium precursor is pyrolyzed to form elemental ruthenium. To this end, the optionally pulverized material obtained after completion of step (2) (i.e., the dried initial aqueous suspension obtained after completion of step (2)) is subjected to a pyrolysis treatment in a non-oxidizing atmosphere. To this end, the material can be heated, either stationary or in motion, to pyrolysis temperatures, for example in the range of 150°C to 1000°C, for example in a static furnace, a fluidized bed reactor or a rotary kiln.

[0026] During step (3), the furnace chamber is advantageously flushed with a gas having non-oxidizing properties, the gas flow also serving to remove gaseous decomposition products. The non-oxidizing atmosphere may also be at a reduced pressure.

[0027] In the combined step (2+3) according to the first variant of the second embodiment of the method of the present invention, the aqueous suspension prepared in step (1) is subjected to drying and pyrolysis in a non-oxidizing atmosphere. The aqueous suspension prepared in step (1) can be passed through a temperature profile in a furnace, either moving or stationary, including a drying temperature and a higher pyrolysis temperature. This can be achieved by passing it through a furnace with a temperature gradient including the drying temperature and the pyrolysis temperature, or by passing it through a furnace with a time-controlled heating or temperature program that first ensures the drying temperature and then the pyrolysis temperature. Examples of furnace types that can be used include static furnaces, fluidized-bed reactors, and rotary kilns. In this way, the aqueous suspension prepared in step (1) can first be dried, i.e., water and any other volatile substances present can be removed, i.e., concentrated to dryness by evaporation. During the evaporative concentration, the operation can be carried out at a drying temperature, for example, in the range of 40°C to 95°C. After drying is complete, the ruthenium precursor is pyrolyzed to form elemental ruthenium by immediate further heating without intermediate cooling to a pyrolysis temperature, e.g., in the range of 150°C to 1000°C, i.e., the dried material is subjected to a pyrolysis process, with the drying and immediate pyrolysis being carried out in a non-oxidizing atmosphere.

[0028] Also, in the combined step (2+3) according to the second variant of the second embodiment of the method according to the present invention, the aqueous suspension prepared in step (1) is dried and pyrolyzed under a non-oxidizing atmosphere. The aqueous suspension prepared in step (1) can be exposed to this pyrolysis temperature, for example, in the range of 150°C to 1000°C, in a furnace, with or without movement. Examples of furnace types that can be used include static furnaces, fluidized bed reactors, and rotary kilns. The ruthenium precursor is pyrolyzed to form elemental ruthenium. Drying and pyrolysis are carried out in parallel or overlapping in practice. The operation is carried out under a non-oxidizing atmosphere.

[0029] After completion of step (3) according to the first embodiment of the method according to the invention, step (2+3) according to both variants of the second embodiment, and optionally subsequent grinding and / or classification, the carrier-free bimetallic particulate material according to the invention is obtained.

[0030] The carrier-free bimetallic particulate material according to the invention is characterized by a particularly strong antimicrobial effect, as can be determined in conventional inhibition zone tests or by determining the minimum inhibitory concentration from microbial growth curves. In this regard, the invention also relates to the use of the carrier-free bimetallic particulate material according to the invention as an additive for the antimicrobial treatment of metal surfaces, coatings such as varnishes and other paints, plasters, molding compounds, plastic materials in the form of plastic films, plastic parts or plastic fibers, textiles or textile applications, synthetic resin products, ion exchange resins, silicone products, cellulose-based products, foams, cosmetics, and many others.

[0031] The support-free bimetallic particulate material according to the present invention may also be used as a heterogeneous catalyst, for example in catalyzing the formation of antimicrobially active hydroxyl groups in aqueous media that allow bacterial growth.

[0032] The carrier-free bimetallic particulate material according to the present invention can be used in the aforementioned applications as a dry powder, as a powder having a desired moisture content, or as a suspension.

[0033] Example 1 of the present invention (thermal decomposition of silver powder according to the present invention with ruthenium, consisting of 80% by weight of elemental silver and 20% by weight of elemental ruthenium) An aqueous suspension prepared from 5 g of silver powder (46.4 mmol of Ag, silver powder "Ag 300-01" from Heraeus Electronics) and 21.55 g of ruthenium nitrosyl oxalate solution (ruthenium content 5.8 wt. %, 12.4 mmol of Ru) was concentrated to dryness by evaporation using a rotary evaporator (90 °C / 300 mbar). The dried material was then calcined at 200 °C in a tube furnace under nitrogen atmosphere for 21 h and ground using an agate mortar. The product, with a silver content of 80.0 wt. % and a ruthenium content of 20.0 wt. % (relative to 0 wt. % residual moisture), was determined by ICP-OES.

[0034] Example 2 of the present invention (thermal decomposition of silver powder according to the present invention with ruthenium, consisting of 80% by weight of elemental silver and 20% by weight of elemental ruthenium) An aqueous suspension prepared from 5 g of silver powder (46.4 mmol of Ag, silver powder "Ag 300-01" from Heraeus Electronics) and 93.98 g of ruthenium acetate solution (ruthenium content 1.3 wt. %, 12.4 mmol of Ru) was concentrated to dryness by evaporation using a rotary evaporator (90 °C / 300 mbar). The dried material was then calcined at 800 °C in a tube furnace under nitrogen atmosphere for 21 h and ground in an agate mortar. The product, with a silver content of 80.0 wt. % and a ruthenium content of 20.0 wt. % (relative to 0 wt. % residual moisture), was determined by ICP-OES.

[0035] Antibacterial effect test In separate Erlenmeyer flasks, 30 mL of a culture of methicillin-resistant Staphylococcus aureus (MRSA) in tryptic soy broth (TSB) was adjusted to an optical density of 0.05. Then, different amounts of ruthenium-loaded silver powder ranging from 1 mg to 50 mg from Examples 1 and 2 according to the present invention were weighed out. The samples were incubated at 37°C and 150 rpm in a shaking incubator. Optical density at a wavelength of 600 nm (OD600) was measured at hourly intervals within 6 hours. Inhibition of bacterial growth was indicated by a reduced increase in optical density compared to the control sample. An MRSA culture without the addition of an active antimicrobial substance served as the control sample. For complete inhibition of bacterial growth, no increase in optical density should be observed. This resulted in a minimum inhibitory concentration of 0.4 mg / mL for the product from Example 1 according to the present invention and 1.6 mg / mL for Example 2 according to the present invention.

Claims

1. 1. A carrier-free bimetallic particulate material comprising elemental metallic silver and elemental metallic ruthenium, having an average particle size (d50) in the range of 1 μm to 100 μm, preferably 1 μm to 20 μm, and having a silver:ruthenium weight ratio in the range of 1 part by weight to 2000 parts by weight silver:1 part by weight ruthenium.

2. 2. The carrier-free bimetallic fine particle material according to claim 1, comprising 90% by weight or more to 100% by weight of silver particles accompanied by elemental ruthenium, and 0% by weight to 10% by weight or less of silver particles, ruthenium particles, and / or ruthenium particles accompanied by elemental silver.

3. 3. A method for producing the carrier-free bimetallic particulate material of claim 1 or 2 by drying and pyrolysis treatment carried out in a non-oxidizing atmosphere of an aqueous suspension comprising water, silver particles, and at least one ruthenium precursor in the form of a ruthenium compound that can be pyrolyzed in a non-oxidizing atmosphere to form elemental ruthenium.

4. 4. The method of claim 3, wherein the silver particles have an average particle size (d50) in the range of 0.5 μm to 50 μm.

5. 5. The method of claim 3 or 4, wherein the non-oxidizing atmosphere is a reducing atmosphere and the at least one ruthenium precursor is selected from the group consisting of ruthenium nitrosyl nitrate, ruthenium oxalate, ruthenium acetate, and ruthenium nitrosyl oxalate.

6. 5. The method of claim 3 or 4, wherein the non-oxidizing atmosphere is an inert atmosphere and the at least one ruthenium precursor is selected from the group consisting of ruthenium oxalate, ruthenium acetate, and ruthenium nitrosyl oxalate.

7. (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium precursor; (2) drying the aqueous suspension prepared in step (1); (3) subjecting the dried material obtained after completion of step (2) to pyrolysis in a non-oxidizing atmosphere; The method according to any one of claims 3 to 6, comprising the successive steps of:

8. (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium precursor; (2+3) drying and pyrolyzing the aqueous suspension prepared in step (1) in a non-oxidizing atmosphere; The method according to any one of claims 3 to 6, comprising the successive steps of:

9. The method according to any one of claims 3 to 8, wherein the pyrolysis treatment is carried out at a pyrolysis temperature or higher in the range of 150°C to 1000°C.

10. 10. Use of the carrier-free bimetallic particulate material according to claim 1 or 2, or produced by the method according to any one of claims 3 to 9, as an additive for the antimicrobial treatment of metal surfaces, coatings, plasters, moulding compounds, plastics in the form of plastic films, plastic parts or plastic fibres, textiles, textile utility products, synthetic resin products, ion exchange resins, silicone products, cellulose-based products, foams and cosmetics.

11. 10. Use of a carrier-free bimetallic particulate material according to claim 1 or 2, or produced by the method according to any one of claims 3 to 9, as a heterogeneous catalyst in the catalysis of the formation of hydroxyl groups in an aqueous medium that allows bacterial growth.

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