Particulate inorganic material comprising elemental silver and elemental ruthenium

Abstract

The present invention relates to a particulate inorganic material comprising elemental silver and elemental ruthenium, the material having an average particle size (d50) in the range of 50 nm to 40 μm and a particle size distribution (D) of 1 m 2 / g~1600m 2 The inorganic material itself is selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, anatase titanium dioxide, rutile titanium dioxide, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide.

Description

[Technical field]

[0001] The present invention relates to particulate inorganic materials comprising elemental precious metals in the form of elemental silver and elemental ruthenium, and to two efficient methods for their preparation.

[0002] WO 2021 / 084140(A2) discloses a method for preparing a particulate support material comprising elemental silver and elemental ruthenium, which can be used as an additive for the antimicrobial treatment of a wide variety of materials and substances.

[0003] It was an object of the present invention to provide a highly antibacterial active material based on a carrier material with elemental silver and elemental ruthenium.

[0004] The object is to provide a product in the form of a particulate inorganic material comprising elemental silver and elemental ruthenium, said inorganic material having an average particle size (d50) in the range of 50 nm to 40 μm and a particle size of 1 m 2 / g~1600m 2 This can be achieved by providing a product having a BET surface area in the range of 1000 nm / g, the inorganic material (the inorganic material itself) being selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum (alpha-aluminum oxide), titanium dioxide in the anatase form, titanium dioxide in the rutile form, pyrogenic silica (pyrogenic silicon dioxide), precipitated silica (precipitated silicon dioxide), sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. The product according to the invention is hereinafter also called "particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium". The weight proportion of silver + ruthenium formed by elemental silver and elemental ruthenium can be, for example, in the range of 0.1 wt.% (wt%) to 50 wt.% (wt%), preferably 1 wt.% to 40 wt.%, while in general, for example, the weight ratio of silver:ruthenium can be in the range of 1 part by weight of silver to 2000 parts by weight:1 part by weight of ruthenium.

[0005] The particulate inorganic material or particles of inorganic material are support materials for elemental silver and elemental ruthenium, i.e. in the particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium, the particulate inorganic material acts as a support for elemental silver and elemental ruthenium. Typically and preferably, in the particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium, only one type of support material is present.

[0006] The particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium comprises particles of inorganic material comprising elemental silver and elemental ruthenium in a proportion ranging from 95 wt.% to 100 wt.%, in particular 100 wt.%. A possible proportion not exceeding 5 wt.% can be formed by corresponding inorganic particles without precious metals. In other words, the particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium can consist of particles of inorganic material comprising 95 wt.% to 100 wt.% of elemental silver and elemental ruthenium and corresponding inorganic particles without precious metals of 0 wt.% to 5 wt.%, where the wt.% add up to 100 wt.%.

[0007] The term "average particle size" as used herein means the volume-average primary particle size (d50) that 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 according to the wet measurement method using a corresponding particle size measuring device, for example the Mastersizer 3000 or Mastersizer 2000 from 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 term "BET surface" as used herein refers to a specific surface area that can be determined by BET measurements according to DIN ISO 9277:2014-01 (according to chapter 6.3.1, static-volumetric measurement process, gas used: nitrogen).

[0009] The present invention also relates to two methods for preparing such particulate inorganic materials according to the invention comprising elemental silver and elemental ruthenium. From another point of view, the two methods can also be understood as methods for providing a corresponding particulate inorganic material with elemental silver and elemental ruthenium.

[0010] In the first method according to the invention, the particulate inorganic material according to the invention, comprising elemental silver and elemental ruthenium, can be obtained by reducing at least one silver precursor and at least one ruthenium precursor in the presence of an aqueous suspension of the corresponding inorganic material, then separating the solid formed in this method from the aqueous phase, optionally washing the separated solid with water, and optionally drying the solid.Thus, the first method according to the invention comprises the steps of reducing at least one silver precursor and at least one ruthenium precursor in the presence of an aqueous suspension of the corresponding inorganic material, separating the solid formed in the course of the reduction from the aqueous phase, optionally washing the separated solid with water, and optionally drying the separated and optionally washed solid.During the reduction, the silver and ruthenium precursors can be reduced successively or preferably simultaneously.

[0011] The silver and ruthenium precursors used in the first method according to the invention are silver and ruthenium compounds. Elemental silver or elemental ruthenium can be produced by reduction from silver and ruthenium compounds, respectively.

[0012] Examples of suitable silver compounds include silver acetate, silver sulfate, and preferably silver nitrate.

[0013] Examples of suitable ruthenium compounds include ruthenium oxalate, ruthenium acetate and especially ruthenium nitrosyl nitrate.

[0014] In the first method according to the invention, it is particularly preferred to use a combination of silver nitrate and ruthenium nitrosyl nitrate as the combination of precursor compounds.

[0015] The particles of inorganic material used in the first method according to the present invention have an average particle size (d50) in the range of 50 nm to 40 μm and a particle size of 1 m 2 / g~2000m 2 / g, the inorganic material itself being selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in anatase form, titanium dioxide in rutile form, pyrogenic silica (pyrogenic silicon dioxide), precipitated silica (precipitated silicon dioxide), sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. In other words, the particles are made of a material selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in anatase form, titanium dioxide in rutile form, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. Preference is given to the corresponding particles of titanium nitride, corundum, titanium dioxide in anatase or rutile form, pyrogenic or precipitated silica, and gamma-aluminum oxide hydroxide.

[0016] The reduction carried out in the first process according to the invention can be carried out with a reducing agent selected from the group consisting of sodium borohydride, hydrazine, hypophosphites and formates at an alkaline pH in the range of 9 to 14, preferably 10 to 12, and at a suitable temperature. For example, sodium borohydride or hydrazine can be conveniently carried out in a temperature range of 20°C to 40°C, and for example, hypophosphites or formates can be conveniently carried out in a temperature range of 60°C to 90°C.

[0017] Hydrazine can be used as such, but is preferably used as hydrazine hydrate with a hydrazine content in the range of 30 wt.% to 65 wt.%. Hydrazine can also be used as a hydrazinium salt, for example as hydrazinium sulfate. It is preferred to use hydrazine hydrate.

[0018] Hypophosphites and formates are mentioned here. These are salts, especially alkali metal salts, alkaline earth metal salts and ammonium salts (NH 4 Sodium hypophosphite and potassium hypophosphite, or sodium formate and potassium formate are preferred.

[0019] In the first method according to the present invention, the reducing agent is used in an amount equal to or more than the stoichiometrically required amount, but preferably in an amount equal to or less than 110% (hydrazine as reducing agent) or 200% (sodium borohydride, hypophosphite or formate as reducing agent) of the stoichiometrically required amount in order to completely reduce the silver and ruthenium precursors to elemental silver and elemental ruthenium. Taking the example of hydrazine as an example, this means that 1 mole of the reducing agent hydrazine can provide 4 moles of electrons with a reducing effect, and therefore 1 mole of N in the reduction 2 So, for example, 1 mole of Ag + To reduce 3+ To reduce this, 0.75 moles of hydrazine are required.

[0020] Two embodiments of the first method according to the invention for preparing a particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium are disclosed below.

[0021] In a first embodiment, the first preparation method according to the invention comprises the steps of: (1a) providing an aqueous suspension comprising water, particles of an inorganic material, at least one silver precursor and at least one ruthenium precursor; (2a) contacting the aqueous suspension with a reducing agent selected from the group consisting of sodium borohydride, hydrazine, hypophosphites and formates at an alkaline pH as described above and at a suitable temperature as described above; (3) separating the formed solids from the aqueous phase; (4) optionally washing the separated solids with water; and (5) Optionally, including the subsequent step of drying the solids.

[0022] The order of steps (1a) to (5) refers to successive steps, which may be directly successive steps without intermediate steps.

[0023] In step (1a) of the first embodiment of the first method according to the present invention, an aqueous suspension is provided comprising water, particles of inorganic material, at least one silver precursor and at least one ruthenium precursor.

[0024] The aqueous suspension may be prepared by adding particles of the inorganic material to and suspending them in an aqueous solution of at least one silver precursor and at least one ruthenium precursor.

[0025] However, it is preferred to carry out the addition of the silver precursor and the ruthenium precursor, preferably each as an aqueous solution, simultaneously or in any order (overlapping with a time delay, alternating or successively) to the initially loaded aqueous suspension of particles of inorganic material. It is particularly preferred that aqueous solutions of both precursors (an aqueous solution of at least one silver precursor and an aqueous solution of at least one ruthenium precursor) are added to the initially loaded aqueous suspension of particles of inorganic material. Generally, mixing is carried out during and also after the addition, for example by stirring. It may also be convenient to carry out the mixing at a pH of the aqueous suspension that is generally in the pH range of the following step (2a), and for this purpose a base, in particular an alkali hydroxide, in particular sodium hydroxide or potassium hydroxide, may be added to adjust the pH accordingly.

[0026] The weight proportion of particles of inorganic material in the aqueous suspension provided in step (1a) of the first embodiment of the first method according to the present invention may be in the range of, for example, 5 wt.% to 30 wt.%.

[0027] The weight fraction of the precious metals formed of silver and ruthenium in the aqueous suspension provided in step (1a) of the first embodiment of the first method according to the present invention may be in the range of, for example, 1 wt.% to 20 wt.%. The aqueous suspension provided in step (1a) of the first embodiment of the first method according to the present invention is characterized in that the weight ratio of the two precious metals is, for example, in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium, and is generally heavily biased towards silver.

[0028] In addition to the particles of inorganic material and the precious metal precursor, the aqueous suspension provided in step (1a) of the first embodiment of the first method according to the invention generally comprises only water and optionally a base used to adjust the pH.

[0029] In step (2a) of the first embodiment of the first method according to the invention, the aqueous suspension provided in step (1a) is contacted with a reducing agent selected from the group consisting of sodium borohydride, hydrazine, hypophosphites and formates at an alkaline pH as mentioned above and at a suitable temperature as mentioned above. If necessary, in this case the corresponding pH and the corresponding temperature of the aqueous suspension can be adjusted first. The alkaline pH can be adjusted using a base, in particular an alkali hydroxide, in particular sodium hydroxide or potassium hydroxide. The reducing agent is used in an amount equal to or greater than the stoichiometrically necessary to completely reduce the silver and ruthenium precursors to elemental silver and elemental ruthenium, respectively, as mentioned above. It is preferable that the reducing agent is added to the aqueous suspension in the form of an aqueous solution. The addition is preferably carried out over a period of 10 minutes to 60 minutes. During the addition and generally also after the addition, it is advantageous to carry out mixing, for example by stirring.

[0030] In a second embodiment, the first preparation method according to the invention comprises: (1b) providing an aqueous alkaline suspension comprising water, particles of inorganic material, a base, and a reducing agent selected from the group consisting of sodium borohydride, hydrazine, hypophosphites, and formates; (2b) contacting the aqueous suspension at an alkaline pH as described above and at a suitable temperature as described above (i) with an aqueous solution comprising at least one silver precursor and at least one ruthenium precursor, or (ii) with an aqueous solution comprising at least one silver precursor and then with an aqueous solution comprising at least one ruthenium precursor, or (iii) with an aqueous solution comprising at least one ruthenium precursor and then with an aqueous solution comprising at least one silver precursor; (3) separating the formed solids from the aqueous phase; (4) optionally washing the separated solids with water; and (5) Optionally, including the subsequent step of drying the solids.

[0031] The order of steps (1b) to (5) refers to successive steps, which may be directly successive steps without intermediate steps.

[0032] In step (1b) of the second embodiment of the first method according to the invention, an aqueous alkaline suspension is provided, comprising water, particles of inorganic material, a base and a reducing agent selected from the group consisting of sodium borohydride, hydrazine, hypophosphites and formates. The aqueous alkaline suspension can be prepared by adding and suspending the particles of inorganic material in an aqueous solution of the reducing agent. However, it is preferred to carry out such that the reducing agent, preferably as an aqueous solution, is added to the initially charged aqueous suspension of particles of inorganic material. The alkaline pH can be adjusted with a base, in particular with an alkali hydroxide, in particular sodium hydroxide or potassium hydroxide, generally conveniently to the pH range in the following step (2b). During the addition and generally also after the addition, it is advantageous to carry out mixing, for example by stirring.

[0033] The weight percentage of particles of inorganic material in the aqueous suspension provided in step (1b) of the second embodiment of the first method according to the present invention may be in the range of, for example, 5 wt.% to 30 wt.%.

[0034] The weight proportion of particles of reducing agent in the aqueous suspension provided in step (1b) of the second embodiment of the first method according to the present invention may be, for example, in the range of 0.5 wt.% to 10 wt.%.

[0035] In addition to particles of inorganic material and a reducing agent, the aqueous suspension provided in step (1b) of the second embodiment of the first process according to the invention generally contains only water and a base used to adjust the pH.

[0036] In step (2b) of the second embodiment of the first method according to the present invention, the aqueous suspension provided in step (1b) is contacted with (i) an aqueous solution containing at least one silver precursor and at least one ruthenium precursor, or (ii) an aqueous solution containing at least one silver precursor and then an aqueous solution containing at least one ruthenium precursor, or (iii) an aqueous solution containing at least one ruthenium precursor and then an aqueous solution containing at least one silver precursor, at an alkaline pH as described above and at a suitable temperature as described above. A single reducing agent is used in an amount equal to or greater than the stoichiometrically necessary to completely reduce the silver and ruthenium precursors to elemental silver and elemental ruthenium, respectively, as described above. It is preferable to carry out according to variant (i).

[0037] The weight fraction of the precious metals formed of silver and ruthenium in the aqueous suspension provided in step (1b) of the second embodiment of the first method according to the present invention may be in the range of, for example, 1 wt.% to 20 wt.%. The aqueous suspension provided in step (1b) of the second embodiment of the first method according to the present invention is characterized in that the weight ratio of the two precious metals is, for example, in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium, and is generally heavily biased towards silver.

[0038] Mixing is conveniently effected, for example by stirring, during and generally after the contacting according to step (2b), for a period of, for example, from 1 to 2 hours.

[0039] Steps (3) to (5) are the same in both embodiments of the first method according to the present invention.

[0040] In step (3), the solids formed in the respective step (2a) or (2b) are separated from the aqueous phase. Examples of solid-liquid separation methods suitable for this purpose include those known to the skilled artisan, such as decantation, squeezing, filtering, suction filtration, centrifugation or combinations thereof.

[0041] Step (4) of the first process according to the invention is an optional but generally convenient step in which the solid separated in step (3) can be washed with water, where water-soluble components can be removed. Washing can be carried out, for example, on a Nutsche filter.

[0042] Step (5) of the first process according to the invention is an optional, but generally convenient, step in which the solid separated in step (3) and optionally washed in step (4) can be dried. In this case, water and any other volatile components present are removed from the solid obtained after completion of step (3) or step (4). Water can be removed in the sense of substantially complete water removal or in the sense of water removal until a desired residual moisture content is reached. For this purpose, the majority of the water can be removed by conventional methods, such as squeezing, squeezing, suction filtration, centrifugation or similar methods, after which drying, optionally assisted by reduced pressure, is carried out, for example at a temperature in the range of 20°C to 150°C.

[0043] After completion of steps (3) or optionally (4) or optionally (5) and subsequent grinding and / or classification, a particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium is obtained. Silver and ruthenium can be present on the inner surface (in the pores and / or cavities) and / or on the outer surface of the originally silver-free and ruthenium-free particles of the inorganic material, thereby forming, for example, discontinuous layers and / or small silver or ruthenium particles (silver or ruthenium islands). Scanning electron microscopy can be a suitable method for observing such morphological characteristics. Silver and ruthenium are not alloyed and are statistically distributed, both precious metals being at least partially in contact with each other. It is clear to the skilled person that silver and ruthenium can contain other silver species other than elemental metallic silver and other ruthenium species other than elemental metallic ruthenium on their surface, for example the corresponding oxides, halides and / or sulfides. Such species may be formed during the performance of the first method according to the invention or subsequently during storage, use or further processing of the particulate inorganic material according to the invention comprising, for example, elemental silver and elemental ruthenium.

[0044] In a second process according to the invention, the particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium can be obtained by pyrolysis treatment under a reducing atmosphere of a previously dried preparation which, before drying, contained water, particles of the corresponding inorganic material, at least one silver precursor and at least one ruthenium precursor.

[0045] In a second method according to the invention, particles of inorganic material, a silver precursor and a ruthenium precursor are used.

[0046] The silver and ruthenium precursors used in the second process according to the invention are silver and ruthenium compounds which can be thermally decomposed under a reducing atmosphere to elemental silver and elemental ruthenium, respectively.

[0047] Examples of suitable silver compounds include silver acetate and, preferably, silver nitrate.

[0048] Examples of suitable ruthenium compounds include ruthenium oxalate, ruthenium acetate and especially ruthenium nitrosyl nitrate.

[0049] In the second method according to the invention, it is particularly preferred to use a combination of silver nitrate and ruthenium nitrosyl nitrate as the combination of precursor compounds.

[0050] The particles of inorganic material used in the second method according to the present invention have an average particle size (d50) in the range of 50 nm to 40 μm and a particle size of 1 m 2 / g~2000m 2 / g, the inorganic material itself being selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in anatase form, titanium dioxide in rutile form, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. In other words, the particles are made of a material selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in anatase form, titanium dioxide in rutile form, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. Preference is given to the corresponding particles of titanium nitride, corundum, titanium dioxide in anatase or rutile form, pyrogenic or precipitated silica, and gamma-aluminum oxide hydroxide.

[0051] The second preparation method according to the present invention comprises: (1c) providing a formulation comprising water, particles of inorganic material, at least one silver precursor and at least one ruthenium precursor; (2c) drying the preparation provided in step (1c); and (3c) the successive steps of subjecting the dried preparation obtained after completion of step (2c) to a pyrolysis treatment under a reducing atmosphere.

[0052] The order of steps (1c) to (3c) refers to successive steps, which may be directly successive steps without intermediate steps.

[0053] In step (1c) of the second method according to the invention, a preparation is provided that comprises water, particles of inorganic material, at least one silver precursor and at least one ruthenium precursor. The preparation may be in the form of an aqueous suspension or in the form of impregnated particles. The two forms (a) aqueous suspension and (b) impregnated particles differ in the presence or absence of aqueous liquid between the particles. In the case of an aqueous suspension, aqueous liquid is present between the particles, but this is not the case for impregnated particles that have the appearance of a dry or freely flowable powder and in which the aqueous liquid forms a component of the particles or is within the particles.

[0054] The aqueous suspension may be prepared by adding particles of the inorganic material to and suspending them in an aqueous solution of at least one silver precursor and at least one ruthenium precursor.

[0055] However, it is preferred to carry out such that the silver precursor and the ruthenium precursor, preferably each as an aqueous solution, are added simultaneously or in any order (overlapped with a time delay, alternating or successively) to the aqueous suspension of the particles of inorganic material that is initially loaded.It is particularly preferred that the aqueous solutions of both precursors (at least one aqueous solution of silver precursor and at least one aqueous solution of ruthenium precursor) are added to the aqueous suspension of the particles of inorganic material that is initially loaded.Generally, mixing is carried out during and also after addition, for example by stirring.

[0056] The weight proportion of particles of inorganic material in the aqueous suspension provided in step (1c) of the second embodiment of the second method according to the present invention may be, for example, in the range of 5 wt.% to 30 wt.%.

[0057] The weight proportion of the precious metals formed of silver and ruthenium in the aqueous suspension provided in step (1c) of the second method according to the present invention may be in the range of, for example, 1 wt.% to 20 wt.%. The aqueous suspension provided in step (1c) of the second method according to the present invention is characterized in that the weight ratio of the two precious metals is, for example, in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium, and is generally heavily biased towards silver.

[0058] In addition to the particles of inorganic material and the precious metal precursor, the aqueous suspension provided in step (1c) of the second process according to the invention generally comprises only water and optionally the corresponding acid from the precious metal precursor.

[0059] The preparation in the form of impregnated particles is preferred. It can be carried out by impregnating particles of inorganic material with an aqueous solution of at least one silver precursor and at least one ruthenium precursor in a manner conventional in the art. The impregnation process can be carried out once or repeatedly, in the latter case with a drying step between the individual impregnation steps.

[0060] The impregnation method must be carried out in such a way that no aqueous suspension is produced, i.e. neither a thin slurry nor a pulpy, pasty or doughy mass is produced, but rather the impregnated particles are formed in the form of a macroscopically homogeneous and freely flowable powder. In other words, the volume of the aqueous solution must be selected so that it is sufficiently small and suitable for the particles of the inorganic material to be impregnated with it. When carrying out the impregnation, it is advantageous to allow sufficient time for the particles of the inorganic material and the aqueous solution to mix. For example, it may be appropriate to mix for a sufficiently long time, in particular until said macroscopically homogeneous state of the mixed material is achieved. The volume of the aqueous solution can be selected by adjusting the respective concentration of the precious metal precursor to the amount of particles from the inorganic material that are to be brought into contact with it (in aqueous solution) and their (particles from the inorganic material) absorption behavior for the aqueous solution. If the volume is too large, the aforementioned undesirable slurries, pulps, doughs or pastes are produced. A person skilled in the art can easily determine, in the application of laboratory tests, the absorption behavior of the relevant particles of the inorganic material towards the relevant aqueous solutions and therefore determine the upper limit of the number of liters of aqueous solution per kilogram of particles of the inorganic material without any loss of said free flowability.

[0061] The weight proportion of particles of inorganic material in the impregnated particles provided in step (1c) of the second method according to the present invention may be in the range of, for example, 50 wt.% to 90 wt.%.

[0062] The weight proportion of the precious metals formed of silver and ruthenium in the impregnated particles provided in step (1c) of the second method according to the invention can be in the range of, for example, 3 wt.% to 15 wt.%. The impregnated particles provided in step (1c) of the second method according to the invention are characterized in that the weight ratio of the two precious metals is, for example, in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium, and is generally heavily biased towards silver.

[0063] In addition to the particles of inorganic material and the precious metal precursor, the impregnated particles provided in step (1c) of the second method according to the invention generally contain only water and, optionally, the corresponding acid from the precious metal precursor. The water content of the impregnated particles provided in step (1c) of the second method according to the invention may, for example, be in the range of 7 wt.% to 35 wt.%.

[0064] In step (2c) of the second process according to the invention, the preparation provided in step (1c) is dried, ie the water and any other volatile substances present are removed.

[0065] In the case of an aqueous suspension, it is evaporated to dryness. Advantageously, the aqueous suspension is agitated during concentration, for example by stirring and / or shaking and / or rotating, i.e. by rotating the vessel or container containing the aqueous suspension. Generally, heat and / or negative pressure is 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.

[0066] In the case of impregnated particles, these may be dried, for example, in an oven at a temperature in the range 40° C. to 95° C. Negative pressure may be applied to assist this. The dried material may be milled if necessary.

[0067] In step (3c) of the second method according to the invention, the precious metal precursors are thermally decomposed to form elemental silver and elemental ruthenium. For this purpose, the material obtained after completion of step (2c), optionally ground, is subjected to a pyrolysis treatment under a reducing atmosphere. For this purpose, the material can be heated, either in a stationary or moving state, to the target temperature that ensures the pyrolysis of the precious metal precursors to form the respective elemental precious metals, for example in the range of 150°C to 800°C, for example in a stationary furnace, a fluidized bed reactor or a rotary kiln.

[0068] The term "reducing atmosphere" as used herein refers to an atmosphere consisting of a gas containing reducing properties, such as hydrogen, or a mixture of hydrogen with an inert gas, such as nitrogen or argon, the latter in particular having a volume fraction in the range of 5% to 10% by volume. During step (3c), the furnace chamber is advantageously flushed with a gas having reducing properties, the gas flow also serving to remove gaseous decomposition products.

[0069] After completion of step (3c) and optionally subsequent grinding and / or classification, a particulate inorganic material according to the invention containing elemental silver and elemental ruthenium is obtained. Silver and ruthenium can be present on the inner surface (in the pores and / or cavities) and / or on the outer surface of the originally silver-free and ruthenium-free particles of the inorganic material, thereby forming, for example, discontinuous layers and / or small silver or ruthenium particles (silver or ruthenium islands). Scanning electron microscopy can be a suitable method for observing such morphological characteristics. Silver and ruthenium are not alloyed and are statistically distributed, both precious metals being at least partially in contact with each other. It is clear to the skilled person that silver and ruthenium can contain other silver species other than elemental metallic silver and other ruthenium species other than elemental metallic ruthenium on their surface, such as the corresponding oxides, halides and / or sulfides. Such species may be formed during the performance of the second process according to the invention or subsequently during storage, use or further processing of the particulate inorganic material according to the invention comprising, for example, elemental silver and elemental ruthenium.

[0070] The particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium has a correspondingly low lightness L * , for example, in the range of 35 to 45, which may be a hindrance in some applications. * is the CIEL determined spectrophotometrically with a measurement geometry of d / 8° * a * b * Specific in color space (DIN EN ISO / CIE 11664-4:2020-03) *L * and the spectrophotometric measurement of the particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium can be carried out on a sample poured into a colourless glass container to a filling height of 1 cm through the flat glass bottom of the glass container which is placed on the measuring head of the spectrophotometer used.

[0071] If desired, the particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium can be further processed to obtain a color value L in the range of, for example, 50 to 85. * For the purposes of brightening, a particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium can be contacted with at least one C1-C4 alkoxide of aluminum, magnesium, calcium, silicon, zinc, zirconium and / or titanium in the presence of at least an amount of water sufficient for complete hydrolysis of the at least one C1-C4 alkoxide. As mentioned above, a brightened particulate material, i.e. having a brightness L in the range of, for example, 50 to 85, can be formed. * It is possible to form a particulate material having a colour, for example grey, having a whitened colour. The whitened particulate material consists of a particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium, having at least partially a solid located thereon. Depending on the selection of the at least one C1-C4 alkoxide, the solid is a solid selected from the group consisting of aluminium oxide, aluminium hydroxide, aluminium oxyhydroxide, magnesium oxide, magnesium hydroxide, magnesium oxyhydroxide, calcium oxide, calcium hydroxide, calcium oxyhydroxide, silicon dioxide, silica, zinc oxide, zinc hydroxide, zinc oxyhydroxide, zirconium dioxide, zirconium(IV) oxyhydrate, titanium dioxide, titanium(IV) oxyhydrate, and combinations thereof.

[0072] The particulate inorganic material according to the invention, comprising elemental silver and elemental ruthenium, optionally brightened as described above, is characterised by a particularly high antimicrobial effect, as can be determined in conventional zone of inhibition tests or by determining the minimum inhibitory concentration from microbial growth curves. In this respect, the invention also relates to the use of the particulate inorganic material according to the invention, comprising elemental silver and elemental ruthenium, optionally brightened, as an additive for antimicrobial treatment of metal surfaces, coatings such as varnishes and other paints, plasters, moulding compounds, plastic films, plastic materials in the form of plastic parts or plastic fibres, synthetic resin products, ion exchange resins, silicone products, cellulosic products, foams, cosmetics and many others.

[0073] The particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium, optionally brightened as described above, can also be used as a heterogeneous catalyst, for example in the catalysis of the formation of hydroxyl radicals in aqueous media enabling bacterial growth.

[0074] The particulate inorganic material according to the invention comprising elemental silver and elemental ruthenium, optionally brightened as described above, can be used in the above mentioned uses either as a dry powder, as a powder with residual moisture or the desired moisture content, or as an aqueous suspension. EXAMPLES

[0075] Reference Example 1 (reduced preparation of cellulose powder with 18.9 wt.% elemental silver and 1.0 wt.% elemental ruthenium): 75.6 g (445 mmol) of silver nitrate solid and 13.94 g of ruthenium nitrosyl nitrate solution (ruthenium content 19.0 wt.%, 26.2 mmol of Ru) were dissolved in 416.8 g of deionized water, and the thus obtained aqueous precursor solution was mixed uniformly with 211.2 g of cellulose powder (Vitacel® L-600 from Rettenmaier und Sohne GmbH & Co KG) to form an orange free-flowing impregnated particulate material. 705 mL of an aqueous hydrazine solution with a pH of 13.9 [4.19 g (131 mmol) of hydrazine and 81.81 g of 32 wt.% sodium hydroxide solution (654.51 mmol of NaOH), the remainder being water] were metered into the free-flowing impregnated particulate material at room temperature under stirring at a metering rate of 30 mL / min. A homogeneous pulp was formed which became increasingly easier to stir over time. After weighing was complete, stirring was continued for 30 min until nitrogen evolution was no longer observed. The material was then filtered off by suction, washed with a total of 1,000 mL of water and dried in a drying cabinet at 105° C. / 300 mbar to a residual moisture content of 15 wt.%. The silver content of the final product was 18.9 wt.% and the ruthenium content was 1.0 wt.% (for a residual moisture of 0 wt.%) determined by ICP-OES.

[0076] Example 2 according to the invention (reductive preparation of a particulate inorganic material with 18.8 wt.% elemental silver and 1.0 wt.% elemental ruthenium): An aqueous solution prepared from 52.5 g of aqueous silver nitrate (silver content 36.2 wt.%; 176 mmol Ag) and 5.4 g of aqueous ruthenium nitrosyl nitrate (ruthenium content 18.7 wt.%; 10 mmol Ru) was added to a suspension of 80 g of silicon dioxide (Aerosil® 150 from Evonik) in 1500 mL of water. The suspension was stirred at 80° C. for 7 hours. The suspension was then cooled to 30° C. and a solution of 2.6 g of hydrazine hydrate (hydrazine content 64 wt.%; 52 mmol), 32.2 g of sodium hydroxide solution (sodium hydroxide content 32%) and 250 mL of water was metered in over the course of 10 minutes and stirred for a further 5 hours. The material was then filtered off by suction, washed with a total of 5 L of water, dried in a drying cabinet at 105° C. / 300 mbar and ground in an agate mortar. The silver content of the product was 18.8 wt.% and the ruthenium content was 1.0 wt.% (for 0 wt.% residual moisture) determined by ICP-OES.

[0077] Example 3 according to the invention (pyrolytic preparation of a particulate inorganic material with 18.3 wt.% elemental silver and 0.8 wt.% elemental ruthenium): An aqueous solution prepared from 52.5 g of aqueous silver nitrate (silver content 36.2 wt.%; 176 mmol Ag) and 5.4 g of aqueous ruthenium nitrosyl nitrate (ruthenium content 18.7 wt.%; 10 mmol Ru) was added to a suspension of 80 g of silicon dioxide (Aerosil® 150 from Evonik) in 1500 mL of water. The suspension was stirred at 80° C. for 7 h. The material was then concentrated to dryness using a rotary evaporator (90° C. / 350 mbar). The dried material was then calcined in a tube furnace under a forming gas atmosphere (5% by volume hydrogen / 95% by volume nitrogen) at 250° C. for 5 h and ground in an agate mortar. The silver content of the product, 18.3 wt.% and ruthenium content, 0.8 wt.% (for 0 wt.% residual moisture), were determined by ICP-OES.

[0078] Example 4 according to the invention (pyrolytic preparation of a particulate inorganic material with 18.0 wt.% elemental silver and 1.0 wt.% elemental ruthenium): An aqueous solution prepared from 8.8 g of aqueous silver nitrate (silver content 36.2 wt.%; 29 mmol Ag) and 0.9 g of aqueous nitrosyl ruthenium nitrate (ruthenium content 18.7 wt.%; 1.7 mmol Ru) was added to 40 g of boehmite powder (Actilox® 200SM from Nabaltec) while shaking. The material was then dried in a drying oven at 105° C. / 300 mbar. This process was repeated three times until a total of 26.2 g of aqueous silver nitrate (silver content 36.2 wt.%; 88 mmol Ag) and 2.7 g of aqueous nitrosyl ruthenium nitrate (ruthenium content 18.7 wt.%; 5 mmol Ru) was used. The material was then calcined in a tube furnace under forming gas atmosphere (5% hydrogen by volume / 95% nitrogen by volume) at 250° C. for 5 hours and ground in an agate mortar. The silver content of the product was 18.0 wt.% and the ruthenium content was 1.0 wt.% (for 0 wt.% residual moisture) determined by ICP-OES.

[0079] Example 5 (Test on the products from Reference Example 1 and Examples 2 and 3 according to the invention to compare their antibacterial effect): In separate Erlenmeyer flasks, 30 mL of culture of Methicillin-resistant Staphylococcus aureus (MRSA) in tryptic soy broth (TSB) was adjusted to an optical density of 0.05. Different amounts of the product from Reference Example 1, ranging from 1 mg to 20 mg, were then weighed. The samples were incubated at 37°C and 150 rpm in a shaking incubator. Within 6 hours, the optical density at a wavelength of 600 nm (OD600) was measured at hourly intervals. 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 antibacterial substance served as the control sample. In case of complete inhibition of bacterial growth, no increase in optical density was observed. The amounts of the corresponding samples of the products from Reference Example 1 or Examples 2-4 according to the invention were used to calculate the minimum inhibitory concentrations. This resulted in a minimum inhibitory concentration of the product of Reference Example 1 of 0.55 mg / mL, as well as a relatively low minimum inhibitory concentration of the product of Example 2 according to the invention of 0.40 mg / mL, a relatively low minimum inhibitory concentration of the product of Example 3 according to the invention of 0.40 mg / mL, and a relatively low minimum inhibitory concentration of the product of Example 4 according to the invention of 0.35 mg / mL.

Claims

1. A particulate inorganic material comprising elemental silver and elemental ruthenium, said inorganic material having an average particle size (d50) in the range of 50 nm to 40 μm and a particle size of 1 m ２ / g~1600m ２ 1. A particulate inorganic material comprising elemental silver and elemental ruthenium having a BET surface area in the range of 1 / g, the inorganic material itself being selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in the anatase form, titanium dioxide in the rutile form, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide.

2. 2. A particulate inorganic material comprising elemental silver and elemental ruthenium according to claim 1, wherein the weight ratio of silver+ruthenium formed by said elemental silver and said elemental ruthenium is in the range of 0.1 wt.% to 50 wt.%, and at the same time, the weight ratio of silver:ruthenium is generally in the range of 1 part by weight to 2000 parts by weight of silver:1 part by weight of ruthenium.

3. 3. A method for preparing a particulate inorganic material comprising elemental silver and elemental ruthenium according to claim 1 or 2, comprising the steps of reducing at least one silver precursor and at least one ruthenium precursor in the presence of an aqueous suspension of particles of the corresponding inorganic material, separating the solids formed during the reduction from the aqueous phase, optionally washing the separated solids with water, and optionally drying the separated and optionally washed solids.

4. 4. The method of claim 3, wherein the silver and ruthenium precursors are reduced sequentially or simultaneously.

5. 5. The method of claim 3 or 4, wherein the at least one silver precursor is selected from the group consisting of silver acetate, silver sulfate and silver nitrate, and the at least one ruthenium precursor is selected from the group consisting of ruthenium oxalate, ruthenium acetate and ruthenium nitrosyl nitrate.

6. The particles of the inorganic material have an average particle size (d50) in the range of 50 nm to 40 μm and a diameter of 1 m of a material selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in the anatase form, titanium dioxide in the rutile form, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. ２ / g to 2000m ２ The method according to any one of claims 3 to 5, wherein the particles have a BET surface area in the range of 1 / g.

7. 7. The method according to any one of claims 3 to 6, wherein the reduction is carried out at an alkaline pH in the range of 9 to 14, at a temperature in the range of 20°C to 40°C with a reducing agent selected from the group consisting of sodium borohydride and hydrazine, or at a temperature in the range of 60°C to 90°C with a reducing agent selected from the group consisting of hypophosphites and formates.

8. 3. A method for preparing a particulate inorganic material comprising elemental silver and elemental ruthenium according to claim 1 or 2, in which a dried preparation, which prior to drying contained water, particles of the corresponding inorganic material, at least one silver precursor and at least one ruthenium precursor, is subjected to a pyrolysis treatment under a reducing atmosphere.

9. 9. The method of claim 8, wherein the at least one silver precursor is selected from the group consisting of silver acetate, silver sulfate, and silver nitrate, and the at least one ruthenium precursor is selected from the group consisting of ruthenium oxalate, ruthenium acetate, and ruthenium nitrosyl nitrate.

10. The particles of the inorganic material have an average particle size (d50) in the range of 50 nm to 40 μm and a diameter of 1 m of a material selected from the group consisting of aluminum nitride, titanium nitride, silicon nitride, corundum, titanium dioxide in the anatase form, titanium dioxide in the rutile form, pyrogenic silica, precipitated silica, sodium aluminum silicate, zirconium silicate, zeolites, hydrotalcites and gamma-aluminum oxide hydroxide. ２ / g to 2000m ２ 10. The method of claim 8 or 9, wherein the particles have a BET surface area in the range of 1 / g.

11. (1c) providing a formulation comprising water, particles of said inorganic material, at least one silver precursor and at least one ruthenium precursor; (2c) drying the preparation provided in step (1c); and 11. The method according to any one of claims 8 to 10, comprising the successive steps of: (3c) subjecting the dried preparation obtained after completion of step (2c) to a pyrolysis treatment under a reducing atmosphere.

12. 12. The method according to claim 11, wherein the preparation provided in step (1c) is in the form of an aqueous suspension or in the form of impregnated particles.

13. The resulting particulate inorganic material comprising elemental silver and elemental ruthenium is further processed by contacting it with at least one C1-C4 alkoxide of aluminum, magnesium, calcium, silicon, zinc, zirconium, and / or titanium in the presence of water in an amount at least sufficient for complete hydrolysis of the at least one C1-C4 alkoxide to produce a color having a lightness L in the range of 50 to 85. ＊ A method according to any one of claims 3 to 12, forming a whitened particulate material having

14. 14. Use of a particulate inorganic material comprising elemental silver and elemental ruthenium according to claim 1 or 2 or a product prepared by the method according to any one of claims 3 to 13 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 applications, synthetic resin products, ion exchange resins, silicone products, cellulosic products, foams and cosmetics.

15. 14. Use of a particulate inorganic material comprising elemental silver and elemental ruthenium according to claim 1 or 2 or a product prepared by the method according to any one of claims 3 to 13, as a heterogeneous catalyst in the catalysis of the formation of hydroxyl radicals in an aqueous medium allowing bacterial growth.

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