Particulate material comprising silver particles equipped with ruthenium oxide and optionally partially oxidized

Abstract

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

Description

[0001] The present invention relates to a particulate material comprising silver particles provided with ruthenium oxide (RuO2) and optionally partially oxidized, and to an efficient method for its production.

[0002] EP 3 915 376 A1 discloses a hybrid material useful as an antimicrobial, antiviral, and / or antifungal additive, comprising particles each comprising at least one support material at least partially coated with at least two different metals. The metals are in conductive contact with one another at least via their respective surfaces. The first metal comprises at least one transition metal element having multiple oxidation states and allowing oxidation state changes via catalytically active centers (e.g., ruthenium). The second metal (e.g., silver) comprises at least one conductive silver semiconductor, with the two metals forming a semi-element that short-circuits in the presence of water and oxygen.

[0003] The object of the present invention is to provide a material comprising silver and ruthenium which has a high antimicrobial effect and can be produced easily and efficiently.

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

[0005] The expression "provided with ruthenium oxide" as used in this patent application means that ruthenium oxide is present on the outer surface of the optionally partially oxidized silver particles. The ruthenium oxide can, for example, form 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. Its silver:ruthenium weight ratio can be in the range of, for example, 1 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 diameter (d50) measured by laser diffraction. In this case, the equivalent circular area diameter (ECAD) is advantageously used as the measure of particle diameter (see RENLIANG XU et al.: "Comparison of sizingsmall particles using different technologies using different technologies to small particles", "Powder Technology", Elsevier, Basel (Switzerland) (POWDER TECHNOLOGY, ELSEVIER, BASEL (CH)), volume 132, phase 2-3, June 24, 2003 (2003-06-24), page 145-153). Laser diffraction measurement can be performed using corresponding particle size measuring instruments, such as Mastersizer 3000 or Mastersizer 2000 from Malvern Instruments, according to a wet assay method. In the wet assay method, as a part for sample preparation, the particulate sample can be dispersed in ethanol by ultrasound.

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

[0009] The particulate material according to the invention, in its first embodiment of silver particles equipped with ruthenium oxide, may also contain silver particles and / or ruthenium oxide particles. However, the material is at least predominantly composed of, for example, ≥90% by weight to ≤100% by weight of silver particles equipped with ruthenium oxide; thus, a proportion of ≥0% by weight to ≤10% by weight may consist of silver particles and / or ruthenium oxide particles, each present separately. Furthermore, the particulate material according to the invention, in its first embodiment, does not contain any intentionally added materials or substances, in particular, any materials or substances that could serve as a support material; rather, the silver particles themselves serve as a support material for the ruthenium oxide. It goes without saying to a person skilled in the art that the expression "without intentionally added materials or substances" also excludes any intentional chemical manipulation of the particulate material according to the invention in its first embodiment that results in the addition or modification of materials or substances.

[0010] In its second embodiment, the particulate material according to the invention, comprising partially oxidized silver particles loaded with ruthenium oxide, may also contain partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles. However, the material may consist at least predominantly of, for example, ≥90% to ≤100% by weight of partially oxidized silver particles loaded with ruthenium oxide; thus, a proportion of ≥0% to ≤10% by weight may consist of partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles, each present separately. Furthermore, the particulate material according to the invention, in its second embodiment, does not contain any intentionally added materials or substances, in particular, any materials or substances that could serve as a support material; rather, the partially oxidized silver particles themselves serve as a support material for the ruthenium oxide. It goes without saying to a person skilled in the art that the expression "without intentionally added materials or substances" also excludes any intentional chemical manipulation of the particulate material according to the invention in its second embodiment that results in the addition or modification of materials or substances.

[0011] The ruthenium oxide of the partially oxidized silver particles provided with ruthenium oxide is present on the outer surface of the optionally partially oxidized silver particles and can, for example, form a discontinuous layer and / or small ruthenium oxide particles (ruthenium oxide islands); the optionally partially oxidized silver particles themselves serve as the support material, as already mentioned. SEM can be a suitable method for observing such morphological properties.

[0012] The present invention also relates to a method for producing the particulate material according to the present invention. In the method according to the present invention, the particulate material according to the present invention can be obtained during a drying method and a pyrolysis treatment of an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor in a non-reducing atmosphere. 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 thermal decomposition of the ruthenium oxide precursor to ruthenium oxide in a non-reducing atmosphere.

[0013] As used repeatedly herein, the term "non-reducing atmosphere" refers to an oxidizing atmosphere or an inert atmosphere. The term "oxidizing atmosphere" refers to an atmosphere composed 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; in such a gas mixture with an inert gas, the volume fraction of oxygen may be, for example, in the range of 10% to 30% by volume. The term "inert atmosphere" refers to an atmosphere composed 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 are those having an average particle size (d50), for example, in the range of 0.5 μm to 50 μm. The silver particles can have a variety of shapes, for example, they can be spherical, substantially spherical, elliptical, oval, flake-shaped, or have an irregular shape. The silver particles are advantageously uncoated and can include pure silver particles (silver purity of at least 99.9% by weight) and / or silver alloy particles containing up to 10% by weight of at least one other alloying metal. In other words, the silver particles are advantageously uncoated pure silver particles (silver purity of at least 99.9% by weight) and / or silver alloy particles 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 composed of pure silver are preferred. Silver particles are commercially available. One example is the silver powder "Ag 300-01" from Heraeus Electronics. Similar powders are also available from other companies.

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

[0017] All ruthenium compounds that can be thermally decomposed into ruthenium oxide in a non-reducing atmosphere can be subjected to pyrolysis treatment in an oxidizing atmosphere in the method according to the present invention, and in this process, thermally decompose to form ruthenium oxide. Those skilled in the art can easily determine the suitability of a ruthenium compound for thermally decomposing into ruthenium oxide in an oxidizing atmosphere, for example, by thermogravimetric analysis in an oxidizing atmosphere. Examples of ruthenium compounds that are suitable as ruthenium oxide precursors in this context include ruthenium nitrate, ruthenium oxalate, ruthenium acetate, and particularly ruthenium nitrosyl oxalate.

[0018] Some ruthenium compounds that can be thermally decomposed into ruthenium oxide in a non-reducing atmosphere can be thermally decomposed in the method according to the present invention or even in an inert atmosphere, and in this process, thermally decompose to form ruthenium oxide. Those skilled in the art can easily determine the suitability of the ruthenium compound to be thermally decomposed into ruthenium oxide in an inert atmosphere, for example, by thermogravimetric analysis in an inert gas atmosphere. The example of the ruthenium compound that is suitable in this respect includes ruthenium nitrate, and particularly ruthenium nitrosyl oxalate.

[0019] The production method according to the invention comprises providing an aqueous suspension comprising water, silver particles and at least one ruthenium oxide precursor, and drying and pyrolysis treating the aqueous suspension in a non-reducing atmosphere. The drying and pyrolysis treatment can be carried out sequentially or as a combined step.

[0020] In a first embodiment, the process according to the invention comprises the following consecutive steps:

[0021] (1) providing an aqueous suspension comprising water, silver particles and at least one ruthenium oxide precursor,

[0022] (2) drying the aqueous suspension provided in step (1), and

[0023] (3) The dried material obtained after completing step (2) is subjected to a pyrolysis treatment in a non-reducing atmosphere.

[0024] In a second embodiment in which steps (2) and (3) are performed jointly, the process according to the invention comprises the following consecutive steps:

[0025] (1) providing an aqueous suspension comprising water, silver particles and at least one ruthenium oxide precursor, and (2+3) drying and pyrolyzing the aqueous suspension provided in step (1) in a non-reducing atmosphere.

[0026] 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 oxide precursor. The aqueous suspension may be in the form of a slurry or pulp, a paste or a dough.

[0027] The aqueous suspension can be produced by adding the silver particles to an aqueous solution of at least one ruthenium oxide precursor and suspending them therein. A reverse order of addition is also possible.

[0028] The weight proportion of silver particles of the aqueous suspension provided in step (1) of the method according to the invention may be in the range of, for example, 5% to 60% by weight.

[0029] The weight proportion of ruthenium in the aqueous suspension provided in step (1) of the method according to the invention can be, for example, in the range of 0.5% to 20% by weight. The aqueous suspension provided in step (1) of the method according to the invention can be characterized by a weight ratio of the two precious metals, for example, in the range of 1 to 2000 parts by weight of silver: 1 part by weight of ruthenium, and generally significantly favors silver.

[0030] In addition to 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 corresponding acid from the ruthenium oxide precursor, i.e. the suspension at least essentially or preferably consists only of silver particles, the ruthenium oxide precursor and water.

[0031] In step (2) of the first embodiment of the process according to the invention, the aqueous suspension provided in step (1) is dried, ie the water and any other volatile substances that may be present are removed.

[0032] 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., rotating the reservoir or container containing the aqueous suspension. Generally, heat and / or negative pressure are applied during evaporation to remove water and any other volatile substances that may be present. During evaporation, the temperature can be, for example, in the range of 40° C. to 95° C. The material obtained after drying can be pulverized if desired.

[0033] In step (3) of the first embodiment of the method according to the invention, the ruthenium oxide precursor is thermally decomposed to form ruthenium oxide. To this end, the material obtained after completion of step (2) and optionally pulverized (i.e., the dried initial aqueous suspension obtained after completion of step (2)) is subjected to a pyrolysis treatment in a non-reducing atmosphere. To this end, the material can be heated to a pyrolysis temperature, for example in a range of 150° C. to 1000° C., for example, in a static furnace, a fluidized bed reactor or a rotary kiln, with or without movement.

[0034] During step (3), the furnace chamber is advantageously flushed with a gas having non-reducing properties or said gas is flowed through the furnace chamber; the gas flow can also be used to remove gaseous decomposition products. The non-reducing atmosphere can also be under reduced pressure.

[0035] In the combined step (2+3) of the first variant of the second embodiment of the method according to the present invention, the aqueous suspension provided in step (1) is dried and subjected to a pyrolysis treatment in a non-reducing atmosphere. The aqueous suspension provided in step (1) can be passed through a temperature curve comprising a drying temperature and a higher pyrolysis temperature in a furnace with or without movement. This can be achieved by passing through a furnace having a temperature gradient comprising a drying temperature and a pyrolysis temperature or by working in a furnace with a time-controlled heating or temperature program that first ensures the drying temperature and then ensures the pyrolysis temperature or pyrolysis temperature curve. Examples of available furnace types include static furnaces, fluidized bed reactors, and rotary kilns. In this way, the aqueous suspension provided in step (1) can be dried first, i.e., water and any other volatile substances that may be present can be removed, i.e., evaporated to dryness. During evaporation, work can be performed at a drying temperature in the range of, for example, 40°C to 95°C. After drying is complete, the ruthenium oxide precursor is thermally decomposed to form ruthenium oxide by further heating immediately without intermediate cooling to a pyrolysis temperature, for example, in the range of 150° C. to 1000° C.; that is, the dried material is subjected to a pyrolysis treatment. The drying and subsequent pyrolysis are carried out in a non-reducing atmosphere.

[0036] In addition, in the combined step (2+3) of the second variant of the second embodiment of the method according to the present invention, the aqueous suspension provided in step (1) is dried and subjected to a pyrolysis treatment in a non-reducing atmosphere. The aqueous suspension provided in step (1) can be exposed to, for example, the pyrolysis temperature in the range of 150° C. to 1000° C. in a furnace with or without motion. Examples of available furnace types include static furnaces, fluidized bed reactors, and rotary kilns. The ruthenium oxide precursor is thermally decomposed to form ruthenium oxide. Drying and thermal decomposition are actually carried out in parallel or in an overlapping manner. Work is carried out in a non-reducing atmosphere.

[0037] After completion of step (3) according to the first embodiment or the combined step (2+3) of the two variants according to the second embodiment of the process according to the invention and optional subsequent comminution and / or classification, a particulate material according to the invention is obtained.

[0038] 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 the growth curve of the microorganisms. In this respect, the present invention also relates to the use of the particulate material according to the invention as an additive for the antimicrobial treatment of metal surfaces; coating agents such as varnishes and other paints; plasters; molding compounds; plastics in the form of plastic films, plastic parts or plastic fibers; textiles or in textile applications; synthetic resin products; ion exchange resins; silicone products; cellulose-based products; foams; cosmetics; and many others.

[0039] The particulate material according to the invention may also be used as a heterogeneous catalyst, for example for catalysing the formation of antimicrobially active hydroxyl radicals in aqueous media permissive for bacterial growth.

[0040] The particulate material according to the invention can be used in the above-mentioned uses as a dry powder, as a powder with a desired moisture content or as a suspension.

[0041] According to Example 1 of the present invention (equipped with ruthenium oxide according to the present invention and having a silver:ruthenium weight ratio of 80:20 (production of silver powder by pyrolysis) :

[0042] 5 g of silver powder (46.4 mmol 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 Ru) were prepared as an aqueous suspension and evaporated to dryness using a rotary evaporator (90°C / 300 mbar). The dried material was then calcined in an oxygen atmosphere in a tube furnace for a total of 10 hours, first at 150°C for 4 hours and then at 200°C for 6 hours. The calcined material was then crushed using an agate mortar. Using ICP-OES, the silver:ruthenium weight ratio of the product was determined to be 80:20. XPS confirmed the presence of ruthenium oxide and elemental silver on the surface.

[0043] According to Example 2 of the present invention (equipped with ruthenium oxide according to the present invention and having a silver:ruthenium weight ratio of 80:20 (production of silver powder by pyrolysis) :

[0044] 5 g of silver powder (46.4 mmol 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 Ru) were prepared as an aqueous suspension and evaporated to dryness using a rotary evaporator (90°C / 300 mbar). The dried material was then calcined in an oxygen atmosphere in a tube furnace for a total of 10 hours, first at 400°C for 5 hours and then at 700°C for 5 hours. The calcined material was then crushed using an agate mortar. Using ICP-OES, the silver:ruthenium weight ratio of the product was determined to be 80:20. XPS confirmed the presence of ruthenium oxide and elemental silver on the surface.

[0045] Testing of antimicrobial effects

[0046] In a separate conical flask, a 30mL culture of methicillin-resistant Staphylococcus aureus (MRSA) in tryptic soy broth (TSB) was adjusted to an optical density of 0.05. Different amounts of silver powder equipped with ruthenium oxide according to Examples 1 and 2 of the present invention were then weighed, with weights ranging from 1mg to 50mg. The sample was placed in a shaking incubator and cultured at a temperature of 37°C with a rotation speed of 150rpm. Over 6 hours, the optical density (OD600) at a wavelength of 600nm was measured at hourly intervals. The inhibition of bacterial growth was indicated by an increase in optical density compared to a control sample. MRSA cultures without the addition of antimicrobial active substances were used as control samples. In the case of complete inhibition of bacterial growth, no increase in optical density was observed. This resulted in a minimum inhibitory concentration of 0.7mg / mL for the product according to Example 1 of the present invention and a minimum inhibitory concentration of 1.6mg / mL for the product according to Example 2 of the present invention.

Claims

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

2. The particulate material of claim 1 , having a silver:ruthenium weight ratio in the range of 1 to 2000 parts by weight silver: 1 part by weight ruthenium.

3. The particulate material according to claim 1 , comprising ≥90% by weight to ≤100% by weight of silver particles provided with ruthenium oxide and ≥0% by weight to ≤10% by weight of silver particles and / or ruthenium oxide particles, each present individually.

4. The particulate material according to claim 1 , which consists of ≥90 wt. % to ≤100 wt. % of partially oxidized silver particles provided with ruthenium oxide and ≥0 wt. % to ≤10 wt. % of partially oxidized silver particles, non-oxidized silver particles and / or ruthenium oxide particles, each present individually.

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

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

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

9. The method according to claim 5 , comprising the following consecutive steps: (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), and (3) In a non-reducing atmosphere The dried material obtained after completing step (2) is subjected to pyrolysis treatment.

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

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

12. Use of the particulate material according to one of claims 1 to 4 or produced by the process according to one of claims 5 to 11 as an additive for the antimicrobial treatment of: metal surfaces; coating agents; plasters; moulding materials; plastics in the form of plastic films, plastic parts or plastic fibres; textiles; textile applications; Synthetic resin products; ion exchange resins; silicone resin products; cellulose-based products; foam; and cosmetics.

13. Use of a particulate material according to one of claims 1 to 4 or produced by a process according to one of claims 5 to 11 as a heterogeneous catalyst for catalyzing the formation of hydroxyl radicals in an aqueous medium permissible for bacterial growth.