Particulate material comprising ruthenium oxide and optionally partially oxidized silver particles.

Abstract

The present invention relates to a particulate material having an average particle size (d50) in the range of 1 μm to 100 μm, the material comprising ruthenium oxide and optionally partially oxidized silver particles. The particulate material can be produced by a drying process and pyrolysis treatment carried out in a non-reducing atmosphere of an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor in the form of a ruthenium compound that can be thermally decomposed to ruthenium oxide in a non-reducing atmosphere.

Description

[Technical Field]

[0001] The present invention relates to a particulate material comprising optionally partially oxidized silver particles with ruthenium oxide (RuO2), 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 bactericidal additive, comprising particles comprising at least one support material, each of which is at least partially coated with at least two different metals. The metals are in conductive contact with each other at least via their respective surfaces. The first metal comprises at least one transition metal element, e.g., ruthenium, which has multiple oxidation states and realizes the change of oxidation state via catalytically active centers. The second metal, e.g., silver, comprises at least one conductive silver semiconductor, and the two metals form a short-circuited half-element in the presence of water and oxygen.

[0003] It is an object of the present invention to provide a material comprising silver and ruthenium, which is highly antimicrobially effective and can be produced simply and efficiently.

[0004] This object may be achieved by providing a particulate material (hereinafter also simply referred to as "particulate material according to the invention") comprising silver particles provided with ruthenium oxide and optionally partially oxidized.

[0005] The expression "comprising ruthenium oxide" as used in this patent application means that ruthenium oxide is present on the outer surface of optionally partially oxidized silver particles. The ruthenium oxide can form, for example, a discontinuous layer and / or small ruthenium oxide particles (ruthenium oxide islands).

[0006] The particulate material according to the present invention has an average particle size (d50) in the range of 1 μm to 100 μm, preferably 1 μm to 20 μm, and the silver:ruthenium weight ratio can be, for example, in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium.

[0007] The term "average particle size" as used herein refers to the volume-average primary particle size (d50), which can be measured 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 (2003-06-24), pages 145-153). Laser diffraction measurements can be performed according to the wet measurement method using a corresponding particle size measuring device, such as the Mastersizer 3000 or Mastersizer 2000 manufactured by Malvern Instruments. In the wet measurement method, the particulate sample can be dispersed in ethanol by ultrasound as part of the sample preparation.

[0008] The particulate material according to the present invention comprises particles consisting of silver particles with ruthenium oxide, optionally partially oxidized. The phrase "optionally partially oxidized" refers to two embodiments. In a first embodiment, the silver particles may comprise ruthenium oxide, and in this embodiment, the silver particles consist of elemental metallic silver (unoxidized silver particles). In a second embodiment, the silver particles may comprise ruthenium oxide and be partially oxidized, and the term "partially oxidized silver particles" refers to particles of elemental metallic silver that contain silver oxide on their surface; more precisely, these are particles consisting of a silver core with a silver oxide layer that partially or completely surrounds the silver core. The silver oxide layer may have been formed on the surface of the silver core by oxidation, for example, during the production of the particulate material according to the present invention. The silver oxide layer can be detected using conventional surface technology inspection methods, such as SEM (scanning electron microscopy) or XPS (X-ray photoelectron spectroscopy).

[0009] The particulate material according to the present invention in its first embodiment, which is made of silver particles with ruthenium oxide, can also contain silver particles and / or ruthenium oxide particles. However, the material may consist at least primarily of, for example, 90% to 100% by weight of silver particles with ruthenium oxide, and thus, a separate portion of 0% to 10% by weight may consist of silver particles and / or ruthenium oxide particles. Furthermore, the particulate material according to the present invention in its first embodiment does not contain any intentionally added materials or substances, in particular, does not contain any materials or substances that can function as support materials; rather, the silver particles themselves function as a support material for ruthenium oxide. As will be appreciated by those skilled in the art, the expression "free of intentionally added materials or substances" also excludes any intentionally performed chemical manipulation of the particulate material according to the present invention in its first embodiment, which leads to the addition or modification of materials or substances.

[0010] The particulate material according to the present invention in its second embodiment, which is partially oxidized silver particles with ruthenium oxide, can also contain partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles. However, the material may consist at least primarily of, for example, 90% to 100% by weight of partially oxidized silver particles with ruthenium oxide, and thus, 0% to 10% by weight of each separately present part may consist of partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles. Furthermore, the particulate material according to the present invention in its second embodiment does not contain any intentionally added materials or substances, particularly materials or substances that can function as support materials; rather, the partially oxidized silver particles themselves function as a support material for ruthenium oxide. As will be appreciated by those skilled in the art, the phrase "free of intentionally added materials or substances" also excludes any intentionally performed chemical manipulation of the particulate material according to the present invention in its second embodiment, which leads to the addition or modification of materials or substances.

[0011] The ruthenium oxide of the optionally partially oxidized silver particles provided therewith can be present on the outer surface of the optionally partially oxidized silver particles, for example, forming a discontinuous layer and / or small ruthenium oxide particles (ruthenium oxide islands), and as already mentioned, the optionally partially oxidized silver particles themselves function as a support material. SEM can be a suitable technique for observing such morphological characteristics.

[0012] The present invention also relates to a method for producing the particulate material according to the invention. In the method according to the invention, the particulate material according to the invention can be obtained during a drying process and a pyrolysis treatment carried out in a non-reducing atmosphere of an aqueous suspension containing water, silver particles, and at least one ruthenium oxide precursor. The pyrolysis treatment is a treatment at or above the pyrolysis temperature of the ruthenium oxide precursor, i.e., the minimum target temperature that ensures the thermal decomposition of the ruthenium oxide precursor to ruthenium oxide in a non-reducing atmosphere.

[0013] The term "non-reducing atmosphere," as used repeatedly herein, refers to an oxidizing or inert atmosphere. The term "oxidizing atmosphere" refers to an atmosphere consisting of a gas containing oxidizing properties, such as oxygen, air, or a gas mixture of oxygen and one or more inert gases, such as nitrogen, argon, and / or carbon dioxide, where the volume fraction of oxygen in such a gas mixture with an inert gas may range, for example, from 10% to 30% by volume. The term "inert atmosphere" refers to an atmosphere consisting of one or more inert gases, such as nitrogen, argon, and / or carbon dioxide.

[0014] In the method according to the invention, silver particles and at least one ruthenium oxide precursor are used.

[0015] 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) ranging from 0.5 μm to 50 μm, for example. The silver particles may have a variety of shapes, for example, spherical, substantially spherical, ellipsoidal, oval, flaky, or irregular. The silver particles are conveniently uncoated and may comprise 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. In other words, the silver particles are conveniently uncoated and are 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 available from other companies.

[0016] The ruthenium oxide precursor used in the process according to the invention is a ruthenium compound which can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere.

[0017] Any ruthenium compound that can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere can be thermally decomposed to ruthenium oxide under an oxidizing atmosphere in the method according to the present invention. Those skilled in the art can easily determine the suitability of a ruthenium compound for thermal decomposition to ruthenium oxide under an oxidizing atmosphere, for example, by thermogravimetric analysis under an oxidizing atmosphere. Examples of ruthenium compounds that are suitable in the context of a ruthenium oxide precursor include ruthenium nitrosyl nitrate, ruthenium oxalate, ruthenium acetate, and in particular ruthenium nitrosyl oxalate.

[0018] Some ruthenium compounds that can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere can be thermally decomposed to ruthenium oxide in the process according to the present invention, even under an inert atmosphere. Those skilled in the art can easily determine the suitability of a ruthenium compound for thermal decomposition to ruthenium oxide under an inert atmosphere, for example, by thermogravimetric analysis under an inert gas atmosphere. Examples of ruthenium compounds that are suitable for this purpose include ruthenium nitrosyl nitrate and, in particular, ruthenium nitrosyl oxalate.

[0019] The method of production according to the present invention comprises the steps of providing an aqueous suspension containing water, silver particles, and at least one ruthenium oxide precursor, and drying and pyrolyzing the aqueous suspension under a non-reducing atmosphere, which may be carried out sequentially or simultaneously.

[0020] 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 oxide precursor; (2) drying the aqueous suspension provided in step (1); (3) pyrolyzing the dried material obtained after completion of step (2) under a non-reducing atmosphere; The method includes the following consecutive steps:

[0021] In a second embodiment, in which steps (2) and (3) are carried out simultaneously, the method according to the invention comprises: (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor; (2+3) drying and pyrolyzing the aqueous suspension provided in step (1) under a non-reducing atmosphere; The method includes the following consecutive steps:

[0022] In step (1) according to both embodiments of the method according to the invention, an aqueous suspension is provided comprising water, silver particles, and at least one ruthenium oxide precursor. The aqueous suspension may be in the form of a thin slurry or a pulp-like, paste-like, or dough-like mass.

[0023] The aqueous suspension can be produced by adding silver particles to an aqueous solution of at least one ruthenium oxide precursor and suspending them therein. The reverse addition order is also possible.

[0024] The weight proportion of silver particles in the aqueous suspension provided in step (1) of the method according to the present invention can be, for example, in the range of 5% to 60% by weight.

[0025] The weight proportion of ruthenium in the aqueous suspension provided in step (1) of the process according to the present invention can be, for example, in the range of 0.5% to 20% by weight. The aqueous suspension provided in step (1) of the process according to the present invention can be characterized by a weight ratio of the two precious metals in the range of, for example, 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium, and generally has a significant bias towards silver.

[0026] In addition to the silver particles and the ruthenium oxide precursor, the aqueous suspension provided in step (1) of the process according to the invention generally comprises only water and, optionally, the acid from the corresponding ruthenium oxide precursor, i.e., the suspension consists at least substantially of, or preferably only of, the silver particles, the ruthenium oxide precursor and water.

[0027] In step (2) according to a first embodiment of the method according to the present invention, the aqueous suspension provided in step (1) is dried, i.e. water and any other volatile substances that may be present are removed.

[0028] The aqueous suspension is evaporated to dryness. Advantageously, the aqueous suspension is agitated during evaporation, for example by stirring and / or shaking and / or rotating, i.e., by rotating the vessel or container containing the aqueous suspension. Heat and / or negative pressure are typically applied during evaporation to remove water and any other volatile substances that may be present. During evaporation, the operation may be carried out at a temperature ranging, for example, from 40°C to 95°C. The material obtained after dryness has been achieved may be milled, if necessary.

[0029] In step (3) according to a first embodiment of the method according to the present invention, the ruthenium oxide precursor is thermally decomposed to form ruthenium oxide. For this purpose, the optionally ground material obtained after completion of step (2), i.e., the dried original aqueous suspension obtained after completion of step (2), is subjected to a pyrolysis treatment under a non-reducing atmosphere. For this purpose, the material can be heated 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, either in a stationary or moving state.

[0030] During step (3), the furnace chamber is expediently flushed with a gas containing non-reducing properties, or a gas stream is passed through the furnace chamber, which gas stream may also serve to remove gaseous decomposition products. The non-reducing atmosphere may also be at a reduced pressure.

[0031] In the combined step (2+3) according to the first variant of the second embodiment of the method according to the present invention, the aqueous suspension provided in step (1) is subjected to a drying and pyrolysis treatment under a non-reducing atmosphere. The aqueous suspension provided 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 operating it in a furnace with a time-controlled heating or temperature program that first achieves the drying temperature and then the pyrolysis temperature or pyrolysis temperature profile. Examples of types of furnaces that can be used include static furnaces, fluidized-bed reactors, and rotary kilns. In this way, the aqueous suspension provided in step (1) can first be dried, i.e., water and any other volatile substances that may be present can be removed, i.e., evaporated to dryness. During evaporation, the operation can be carried out at a drying temperature ranging, for example, from 40°C to 95°C. After drying is complete, the ruthenium oxide precursor is thermally decomposed to form ruthenium oxide by rapidly 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-reducing atmosphere.

[0032] Also, in the combined step (2+3) according to a second variant of the second embodiment of the method according to the present invention, the aqueous suspension provided in step (1) is dried and pyrolyzed under a non-reducing atmosphere. The aqueous suspension provided 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. A ruthenium oxide precursor is thermally decomposed to form ruthenium oxide. Drying and pyrolysis are carried out practically in parallel or overlapping fashion. The operations are carried out under a non-reducing atmosphere.

[0033] After completion of step (3) according to the first embodiment of the method according to the invention or the combined step (2+3) according to both variants of the second embodiment, and optionally subsequent grinding and / or classification, a particulate material according to the invention is obtained.

[0034] The 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 aspect, the invention also relates to the use of the 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, plastics in the form of plastic membranes, plastic parts or plastic fibers, textiles or textile applications, synthetic resin products, ion exchange resins, silicone products, cellulosic products, foams, cosmetics, and many others.

[0035] Particulate materials according to the present invention may also be used as heterogeneous catalysts, for example in catalysing the formation of antimicrobially active hydroxyl radicals in aqueous media that allow bacterial growth.

[0036] The particulate material according to the present invention may be used in the aforementioned applications as a dry powder, as a powder having the desired moisture content, or as a suspension.

[0037] Example 1 according to the invention (thermolytic production of silver powder according to the invention with ruthenium oxide and a silver:ruthenium weight ratio of 80:20) An aqueous suspension prepared from 5 g of silver powder (46.4 mmol of Ag, Heraeus Electronics silver powder "Ag 300-01") and 21.55 g of ruthenium nitrosyl oxalate solution (ruthenium content 5.8 wt %, 12.4 mmol of Ru) was evaporated to dryness using a rotary evaporator (90 °C / 300 mbar). The dried material was then calcined in a tube furnace under an oxygen atmosphere for a total of 10 h, first at 150 °C for 4 h and then at 200 °C for 6 h. The calcined material was then crushed using an agate mortar. ICP-OES was used to determine a silver:ruthenium weight ratio of 80:20 in the product. XPS confirmed the presence of ruthenium oxide and elemental silver on the surface.

[0038] Example 2 According to the Invention (Thermal Decomposition of Silver Powder According to the Invention with Ruthenium Oxide and a Silver:Ruthenium Weight Ratio of 80:20) An aqueous suspension prepared from 5 g of silver powder (46.4 mmol of Ag, Heraeus Electronics silver powder "Ag 300-01") and 93.98 g of ruthenium acetate solution (ruthenium content 1.3 wt.%, 12.4 mmol of Ru) was evaporated to dryness using a rotary evaporator (90 °C / 300 mbar). The dried material was then calcined in a tube furnace under an oxygen atmosphere for a total of 10 h, first at 400 °C for 5 h and then at 700 °C for 5 h. The calcined material was then crushed using an agate mortar. ICP-OES was used to determine a silver:ruthenium weight ratio of 80:20 in the product. XPS confirmed the presence of ruthenium oxide and elemental silver on the surface.

[0039] Antibacterial effect test In separate Erlenmeyer flasks, 30 mL of methicillin-resistant Staphylococcus Aureus (MRSA) cultures in tryptic soy broth (TSB) were adjusted to an optical density of 0.05. Different amounts of silver powder with ruthenium oxide, ranging from 1 mg to 50 mg, from Examples 1 and 2 according to the present invention were then weighed. The samples were incubated at 37°C and 150 rpm in a shaking incubator. The optical density at a wavelength of 600 nm (OD600) was determined at hourly intervals within a 6-hour period. Inhibition of bacterial growth was indicated by a reduced increase in optical density compared to the control sample. An MRSA culture without added antibacterial active substance served as the control sample. If bacterial growth was completely inhibited, no increase in optical density should be observed. This resulted in a minimum inhibitory concentration for the product of Example 1 according to the invention of 0.7 mg / mL and of Example 2 according to the invention of 1.6 mg / mL.

Claims

1. A particulate material having an average particle size (d50) in the range of 1 μm to 100 μm, said material comprising silver particles with ruthenium oxide and optionally partially oxidized.

2. 10. The particulate material of claim 1 having a silver:ruthenium weight ratio ranging from 1 part to 2000 parts silver:1 part ruthenium.

3. 3. The particulate material according to claim 1, comprising 90% by weight or more and 100% by weight or less of silver particles provided with ruthenium oxide, and 0% by weight or more and 10% by weight or less of silver particles and / or ruthenium oxide particles, each of which is present separately.

4. 3. The particulate material according to claim 1, comprising 90% by weight or more and 100% by weight or less of partially oxidized silver particles comprising ruthenium oxide, and 0% by weight or more and 10% by weight or less of partially oxidized silver particles, unoxidized silver particles, and / or ruthenium oxide particles, each of which is present separately.

5. A method for producing the particulate material according to any one of claims 1 to 4 of the present invention by a drying process and pyrolysis treatment carried out under a non-reducing atmosphere of an aqueous suspension comprising water, silver particles and at least one ruthenium oxide precursor in the form of a ruthenium compound that can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere.

6. 6. The method of claim 5, wherein the silver particles have an average particle size (d50) in the range of 0.5 μm to 50 μm.

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

8. 7. The method of claim 5 or 6, wherein the non-reducing atmosphere is an inert atmosphere and the at least one ruthenium oxide precursor is selected from the group consisting of ruthenium nitrosyl nitrate and ruthenium nitrosyl oxalate.

9. (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor; (2) drying the aqueous suspension provided in step (1); (3) pyrolyzing the dried material obtained after completion of step (2) under a non-reducing atmosphere; The method according to any one of claims 5 to 8, comprising the successive steps of:

10. (1) providing an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor; (2+3) drying and pyrolyzing the aqueous suspension provided in step (1) under a non-reducing atmosphere; The method according to any one of claims 5 to 8, comprising the successive steps of:

11. The method according to any one of claims 5 to 10, wherein the pyrolysis treatment is carried out at or above a pyrolysis temperature in the range of 150°C to 1000°C.

12. 12. Use of the particulate material according to any one of claims 1 to 4, or produced by the method according to any one of claims 5 to 11, 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, cellulosic products, foams and cosmetics.

13. 12. Use of a particulate material according to any one of claims 1 to 4, or produced by a method according to any one of claims 5 to 11, as a heterogeneous catalyst in the catalysis of the formation of hydroxyl radicals in an aqueous medium that allows bacterial growth.

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