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

Abstract

The invention relates to a particulate material which has an average particle size (d50) ranging from 1 to 100 µm, said material comprising silver particles which are equipped with ruthenium oxide and are optionally partially oxidized. The particulate material can be produced by means of a drying process and a thermalytic treatment, which is 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 which can be thermally decomposed into ruthenium oxide in a non-reducing atmosphere.

Description

[0001] Particulate material comprising silver particles provided with ruthenium oxide and optionally partially oxidized

[0002] The invention relates to a particulate material comprising silver particles provided with ruthenium oxide (RuCh) and optionally partially oxidized, as well as to an efficient process for its production.

[0003] EP 3 915 376 A1 discloses a hybrid material usable as an antimicrobial, antiviral, and / or fungicidal additive, comprising particles each comprising at least one carrier material at least partially coated with at least two different metals. The metals are in electrically conductive contact with each other, at least via their respective surfaces. The first metal comprises at least one transition metal element that has multiple oxidation states and allows a change of oxidation states via catalytically active centers, for example, ruthenium. The second metal, for example, silver, comprises at least one electrically conductive silver semiconductor, wherein the two metals form half-elements that are short-circuited in the presence of water and oxygen.

[0004] The object of the invention was to provide a material comprising silver and ruthenium that can be produced easily and efficiently and has a pronounced antimicrobial effect.

[0005] The object can be achieved by providing a particulate material comprising silver particles provided with ruthenium oxide and optionally partially oxidized, hereinafter also referred to simply as “particulate material according to the invention”.

[0006] The term "coated with ruthenium oxide" used in this patent application means that the 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).

[0007] The particulate material according to the invention has an average particle size (d50) in the range from 1 to 100 μm, preferably 1 to 20 μm. Its silver:ruthenium weight ratio can, for example, be in the range from 1 to 2000 parts by weight of silver:1 part by weight of ruthenium. The term "average particle size" used herein means the volume-average primary particle diameter (d50) determinable by laser diffraction. The so-called equivalent circular area diameter (ECAD) can expediently be used as a measure of the particle diameter (cf. RENLIANG XII ET AL: "Comparison of sizing small particles using different technologies", POWDER TECHNOLOGY, ELSEVIER, BASEL (CH), Vol. 132, Nos. 2-3, June 24, 2003 (2003-06-24), pages 145-153).Laser diffraction measurements can be performed using the wet method with a suitable particle size measuring device, such as a Malvern Instruments Mastersizer 3000 or Mastersizer 2000. With the wet method, particulate samples can be dispersed in ethanol using ultrasound during sample preparation.

[0008] The particulate material according to the invention comprises particles of silver particles provided with ruthenium oxide and optionally partially oxidized. The wording "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 partially oxidized; in this case, the term "partially oxidized silver particles" refers to particles of elemental metallic silver which have silver oxide on their surface; more precisely, these are particles consisting of a silver core with a silver oxide layer partially or completely surrounding 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 invention. The silver oxide layer can be detected using conventional surface analysis 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 can also comprise silver particles and / or ruthenium oxide particles. However, it consists at least predominantly, for example, of >90 to <100 wt.%, silver particles equipped with ruthenium oxide; accordingly, the >0 to <10 wt.% portion can consist of separately present silver particles and / or ruthenium oxide particles. Furthermore, the particulate material according to the invention in its first embodiment does not comprise any deliberately added material or substances, in particular any material or substances that could serve as a carrier material; rather, the silver particles themselves serve as the carrier material for the ruthenium oxide.It goes without saying for the person skilled in the art that the expression “no deliberately added material or substances” also excludes any deliberately carried out chemical manipulation of the particulate material according to the invention in its first embodiment that leads to the addition or modification of material or substance.

[0010] The particulate material according to the invention, in its second embodiment of partially oxidized silver particles provided with ruthenium oxide, may also comprise partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles. However, it consists at least predominantly, for example, of >90 to <100 wt.%, partially oxidized silver particles provided with ruthenium oxide; accordingly, the >0 to <10 wt.% portion may consist of separately present partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles.

[0011] Furthermore, the particulate material according to the invention in its second embodiment comprises no deliberately added material or substances, in particular no material or substances that could serve as a carrier material; rather, the partially oxidized silver particles themselves serve as the carrier material for the ruthenium oxide. Needless to say, the expression "no deliberately added material or substances" also excludes any deliberately performed chemical manipulation of the particulate material according to the invention in its second embodiment that leads to the addition or modification of material or substance.

[0012] The ruthenium oxide of the possibly partially oxidized silver particles thus coated is present on the outer surface of the possibly partially oxidized silver particles and can, for example, form a discontinuous layer and / or small ruthenium oxide particles (ruthenium oxide islands); the possibly partially oxidized silver particles themselves act as the carrier material, as already mentioned. SEM can be a suitable method for observing such morphological properties.

[0013] The invention also relates to a process for producing the particulate material according to the invention. In the process according to the invention, the particulate material according to the invention can be obtained by drying and thermolytic treatment, under a non-reducing atmosphere, of an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor. The thermolytic treatment is a treatment at or above the thermolysis temperature of the ruthenium oxide precursor(s), i.e., the minimum object temperature that ensures thermal decomposition of the ruthenium oxide precursor(s) to ruthenium oxide under a non-reducing atmosphere.

[0014] The term "non-reducing atmosphere" used repeatedly herein refers to an oxidizing or inert atmosphere. The term "oxidizing atmosphere" refers to an atmosphere consisting of a gas having 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; the volume fraction of oxygen within such a gas mixture with inert gas can, for example, be in the range of 10 to 30 ol%. The term "inert atmosphere" refers to an atmosphere consisting of one or more inert gases, such as nitrogen, argon, and / or carbon dioxide.

[0015] The process according to the invention uses silver particles and at least one ruthenium oxide precursor.

[0016] The silver particles mentioned herein, or the silver particles used as a starting material in the process according to the invention, are those with an average particle size (d50), for example, in the range from 0.5 μm to 50 μm. The silver particles can have a wide variety of shapes, for example, they can be spherical, substantially spherical, elliptical, egg-shaped, flake-shaped, or irregular. The silver particles are advantageously uncoated and can comprise particles of pure silver (silver purity of at least 99.9 wt.%) and / or particles of silver alloys with up to 10 wt.% of at least one other alloying metal. In other words, the silver particles are advantageously uncoated particles of pure silver (silver purity of at least 99.9 wt.%).-%) and / or those made of silver alloys with up to 10 wt.% 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. The silver particles are commercially available. One example is the silver powder "Ag 300-01" from Heraeus Electronics. Comparable powders are also available from other companies.

[0017] The ruthenium oxide precursor(s) used in the process according to the invention are ruthenium compounds that can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere.

[0018] All ruthenium compounds that can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere can be thermolytically treated in the process according to the invention under an oxidizing atmosphere and thereby thermally decomposed to ruthenium oxide. The skilled person can easily determine the suitability of a ruthenium compound for thermal decomposition to ruthenium oxide under an oxidizing atmosphere, for example, thermogravimetrically under an oxidizing atmosphere. Examples of ruthenium compounds suitable as ruthenium oxide precursors in this context include ruthenium nitrosyl nitrate, ruthenium oxalate, ruthenium acetate, and especially ruthenium nitrosyl oxalate.

[0019] Some ruthenium compounds that are thermally decomposable to ruthenium oxide under a non-reducing atmosphere can even be thermolytically treated in the process according to the invention under an inert atmosphere, thereby thermally decomposing them to ruthenium oxide. The skilled person can easily determine the suitability of a ruthenium compound for thermal decomposition to ruthenium oxide under an inert atmosphere, for example, thermogravimetrically under an inert gas atmosphere. Examples of ruthenium compounds suitable in this regard include ruthenium nitrosyl nitrate and, in particular, ruthenium nitrosyl oxalate.

[0020] The production process according to the invention comprises providing an aqueous suspension comprising water, silver particles, and at least one ruthenium oxide precursor, as well as drying and thermolytically treating the aqueous suspension under a non-reducing atmosphere. The drying and thermolytic treatment can be carried out sequentially or as a joint step.

[0021] In a first embodiment, the method according to the invention comprises the successive steps:

[0022] (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

[0023] (3) thermolytically treating the dried material obtained after completion of step (2) under a non-reducing atmosphere.

[0024] In a second embodiment with steps (2) and (3) carried out together, the method according to the invention comprises the successive steps:

[0025] (1) Providing an aqueous suspension comprising water, silver particles and at least one ruthenium oxide precursor, and

[0026] (2+3) Drying and thermolytically treating the aqueous suspension provided in step (1) under a non-reducing atmosphere.

[0027] In step (1) according to both embodiments of the process according to the invention, an aqueous suspension is provided which comprises water, silver particles, and at least one ruthenium oxide precursor. The aqueous suspension can be in the form of a low-viscosity slurry or a slurry, paste, or dough-like mass.

[0028] The aqueous suspension can be prepared by adding the silver particles to an aqueous solution of the at least one ruthenium oxide precursor and suspending them therein. The reverse addition sequence is also possible.

[0029] The weight fraction of the silver particles in the aqueous suspension provided in step (1) of the process according to the invention can, for example, be in the range from 5 to 60 wt.%.

[0030] The ruthenium weight fraction of the aqueous suspension provided in step (1) of the process according to the invention can, for example, be in the range from 0.5 to 20 wt.%. The aqueous suspension provided in step (1) of the process according to the invention can be characterized by a weight ratio of the two precious metals, for example, in the range from 1 to 2000 parts by weight of silver to 1 part by weight of ruthenium, and is generally significantly favored by silver.

[0031] In addition to the silver particles and the ruthenium oxide precursor(s), the aqueous suspension provided in step (1) of the process according to the invention generally comprises only water and optionally corresponding acid from the ruthenium oxide precursor(s), ie said suspension consists at least essentially or preferably only of the silver particles, the ruthenium oxide precursor(s) and water.

[0032] In step (2) according to the first embodiment of the process according to the invention, the aqueous suspension provided in step (1) is dried, ie freed from water and any other volatile substances present.

[0033] The aqueous suspension is evaporated to dryness. The aqueous suspension is advantageously agitated during the evaporation process, for example by stirring and / or shaking and / or rotation, i.e., rotation of the vessel or container containing the aqueous suspension. Generally, heating and / or vacuum are applied during the evaporation process to remove water and any other volatile substances present. During the evaporation process, temperatures in the range of 40 to 95°C, for example, can be used. The material obtained after reaching dryness can be comminuted if necessary.

[0034] In step (3) according to the first embodiment of the process according to the invention, the ruthenium oxide precursor(s) are thermally decomposed to form ruthenium oxide. For this purpose, the optionally comminuted material obtained after completion of step (2), i.e., the dried, originally aqueous suspension obtained after completion of step (2), is subjected to a thermolytic treatment in a non-reducing atmosphere. For this purpose, the material can be heated, either in motion or in agitation, to a thermolysis temperature, for example, in the range of 150 to 1000°C, for example in a static furnace, a fluidized-bed reactor, or a rotary kiln.

[0035] During step (3), the furnace chamber is expediently purged or flowed through with the gas having non-reducing properties; the gas stream can also serve to remove gaseous decomposition products. The non-reducing atmosphere can also be pressure-reduced.

[0036] In the combined step (2+3) according to a first variant of the second embodiment of the process according to the invention, the aqueous suspension prepared in step (1) is dried and thermolytically treated in a non-reducing atmosphere. The aqueous suspension prepared in step (1) can be moved or immobilized within a furnace and undergo a temperature profile comprising a drying temperature and a higher thermolysis temperature. This can be achieved by passing through a furnace with a temperature gradient comprising drying temperature and thermolysis temperature, or by working in a furnace with a time-controlled heating or temperature program that first ensures the drying temperature and subsequently the thermolysis temperature or thermolysis temperature profile. Examples of usable furnace types include static furnaces, fluidized-bed reactors, and rotary kilns.Thus, the aqueous suspension prepared in step (1) can first be dried, i.e., freed from water and any other volatile substances present, i.e., concentrated to dryness. During concentration, the drying temperature can be, for example, in the range of 40 to 95°C. After drying is complete, the ruthenium oxide precursor(s) are thermally decomposed to form ruthenium oxide by being immediately heated further, without intermediate cooling, to a thermolysis temperature, for example, in the range of 150 to 1000°C; i.e., the dried material is subjected to a thermolytic treatment. Said drying and the immediately subsequent thermolysis take place in a non-reducing atmosphere.

[0037] In the combined step (2+3) according to a second variant of the second embodiment of the process according to the invention, the aqueous suspension prepared in step (1) is also dried and thermolytically treated under a non-reducing atmosphere. The aqueous suspension prepared in step (1) can be subjected to the thermolysis temperature, for example, in the range of 150 to 1000°C, within a furnace, either in motion or in a stationary state. Examples of usable furnace types include static furnaces, fluidized-bed reactors, and rotary kilns. The ruthenium oxide precursor(s) are thermally decomposed to form ruthenium oxide. Drying and thermolysis take place virtually in parallel or overlapping. The process is carried out under a non-reducing atmosphere.

[0038] After completion of step (3) according to the first embodiment or the combined step (2+3) according to both variants of the second embodiment of the process according to the invention and optionally subsequent comminution and / or classification, the particulate material according to the invention is obtained.

[0039] The particulate material according to the invention is characterized by a pronounced antimicrobial effect, as can be determined in conventional inhibition zone tests or by determining the minimum inhibitory concentration from growth curves of microorganisms. The invention therefore also relates to the use of the particulate material according to the invention as an additive for the antimicrobial treatment of metal surfaces; coating materials such as lacquers 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;

[0040] Silicone products; cellulose-based products; foams; cosmetics; and much more.

[0041] The particulate material according to the invention can also be used as a heterogeneous catalyst, for example in the catalysis of the formation of antimicrobially active hydroxyl radicals within aqueous media that allow bacterial growth.

[0042] The particulate material according to the invention can be used in the aforementioned applications as a dry powder, as a powder having a desired moisture content or as a suspension.

[0043] Inventive Example 1 (Thermolytic production of a silver powder according to the invention containing ruthenium oxide with a silver : ruthenium weight ratio of 80 : 20):

[0044] An aqueous suspension prepared from 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) was evaporated to dryness in a rotary evaporator (90 °C / 300 mbar). The dry material was then calcined in a tube furnace under an oxygen atmosphere for a total of 10 hours, initially for 4 hours at 150 °C and then for 6 hours at 200 °C. The calcined material was then crushed with an agate mortar. Using ICP-OES, a silver:ruthenium weight ratio of 80:20 was determined for the product. XPS confirmed that the surface consisted of ruthenium oxide and elemental silver.

[0045] Inventive Example 2 (Thermolytic production of a silver powder according to the invention containing ruthenium oxide with a silver : ruthenium weight ratio of 80 : 20):

[0046] An aqueous suspension prepared from 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) was evaporated to dryness using a rotary evaporator (90 °C / 300 mbar). The dry material was then calcined in a tube furnace under an oxygen atmosphere for a total of 10 hours, initially for 5 hours at 400 °C and subsequently for 5 hours at 700 °C. The calcined material was then crushed using an agate mortar. Using ICP-OES, a silver:ruthenium weight ratio of 80:20 was determined for the product. XPS confirmed that the surface consisted of ruthenium oxide and elemental silver.

[0047] Testing for antimicrobial effect

[0048] In various Erlenmeyer flasks, 30 mL of a culture of methicillin-resistant Staphylococcus aureus (MRSA) in trypticase soy broth (TSB) medium were adjusted to an optical density of 0.05. Subsequently, varying amounts of the ruthenium oxide-coated silver powders from Examples 1 and 2 according to the invention, ranging from 1 to 50 mg, were weighed in. The samples were incubated in a shaking incubator at 37°C and 150 rpm. The optical density at a wavelength of 600 nm (OD600) was determined at hourly intervals over a period of 6 hours. The inhibition of bacterial growth was evident by a reduced increase in optical density compared to the control sample. The control sample was an MRSA culture without the addition of an antimicrobial agent. With complete inhibition of bacterial growth, no increase in optical density was observed.This resulted in a minimum inhibitory concentration of 0.7 mg / mL for the product from Example 1 according to the invention and of 1.6 mg / mL for the product from Example 2 according to the invention.

Claims

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

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

3. Particulate material according to claim 1 or 2, consisting of >90 to <100 wt.% silver particles containing ruthenium oxide and >0 to <10 wt.% silver particles and / or ruthenium oxide particles present separately.

4. Particulate material according to claim 1 or 2, consisting of >90 to <100 wt.% partially oxidized silver particles containing ruthenium oxide and >0 to <10 wt.% partially oxidized silver particles, non-oxidized silver particles, and / or ruthenium oxide particles present separately.

5. A process for producing the particulate material according to the invention according to any one of claims 1 to 4 by means of drying and a thermolytic treatment 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 which can be thermally decomposed to ruthenium oxide under a non-reducing atmosphere.

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 pm to 50 pm.

7. The method of 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 process 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. Method according to one of claims 5 to 8, comprising the successive 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) thermolytically treating the dried material obtained after completion of step (2) under a non-reducing atmosphere.

10. Method according to one of claims 5 to 8, comprising the successive steps: (1) Providing an aqueous suspension comprising water, silver particles and at least one ruthenium oxide precursor, and (2+3) Drying and thermolytically treating the aqueous suspension provided in step (1) under a non-reducing atmosphere.

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

12. Use of a particulate material according to any one of claims 1 to 4 or produced by a process according to any one of claims 5 to 11 as an additive for the antimicrobial treatment of metal surfaces; coatings; plasters; Molding compounds; plastics in the form of plastic films, plastic parts or plastic fibers; textiles; textile applications; synthetic resin products; ion exchange resins; silicone products; cellulose-based products; foams; and cosmetics.

13. Use of a particulate material according to any one of claims 1 to 4 or produced by a process according to any one of claims 5 to 11 as a heterogeneous catalyst in catalyzing the formation of hydroxyl radicals within aqueous media permitting bacterial growth.

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