WO2018050459A1 - Nanoparticles fixated in porous network structure - Google Patents

Nanoparticles fixated in porous network structure Download PDF

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Publication number
WO2018050459A1
WO2018050459A1 PCT/EP2017/071992 EP2017071992W WO2018050459A1 WO 2018050459 A1 WO2018050459 A1 WO 2018050459A1 EP 2017071992 W EP2017071992 W EP 2017071992W WO 2018050459 A1 WO2018050459 A1 WO 2018050459A1
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nanoparticles
network structure
porous network
liquid
precursor
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PCT/EP2017/071992
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French (fr)
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Fei Chen
Søren Primdahl
Berit HINNEMANN
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Haldor Topsøe A/S
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/063—Titanium; Oxides or hydroxides thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/08—Silica
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/12—Silica and alumina
    • B01J35/23—
    • B01J35/39—
    • B01J35/393—
    • B01J35/613—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/031—Precipitation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/30—Preparation of aluminium oxide or hydroxide by thermal decomposition or by hydrolysis or oxidation of aluminium compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
    • C01G23/0536—Producing by wet processes, e.g. hydrolysing titanium salts by hydrolysing chloride-containing salts
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L2209/00—Aspects relating to disinfection, sterilisation or deodorisation of air
    • A61L2209/20—Method-related aspects
    • A61L2209/21—Use of chemical compounds for treating air or the like
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L9/00—Disinfection, sterilisation or deodorisation of air
    • A61L9/16—Disinfection, sterilisation or deodorisation of air using physical phenomena
    • A61L9/18—Radiation
    • A61L9/20—Ultra-violet radiation
    • A61L9/205—Ultra-violet radiation using a photocatalyst or photosensitiser
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20707—Titanium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/80—Type of catalytic reaction
    • B01D2255/802—Photocatalytic
    • B01J35/396—
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases

Definitions

  • the invention relates to a method of preparing a material, wherein nanoparticles are fixated in a porous network structure.
  • the invention moreover relates to a material, wherein nanoparticles are fixated in a porous network structure and to substances comprising such a material.
  • nanomaterials describe materials of which a single unit, a nanoparticle, is sized in at least one dimension between 1 and 100 nanometers (10 ⁇ 9 meter).
  • Nanomaterials often have unique optical, catalytic, electronic, or mechanical proper- ties. However, at least some nanomaterials are also investigated for their possible toxicity to human health and the environment. Some general considerations have impact on the toxicity of nanomaterials, no matter which actual elements constitute the nanoparticles, such as the size of the primary nanoparticles and their agglomerates, the way the nanoparticles interact with a living organism defined by the protein coat that every nanoparticle acquires when entering a living organism, and the surface charge and hy- drophobicity of a nanoparticle. Beyond these general effects of nanoparticles, individual nanoparticles may have additional, substance specific toxic effects of varying severity.
  • the invention seeks to alleviate or mitigate at least some of the health-safety and/or environmental issues associated with production, processing and use of nanomaterials. It is an object of the invention to provide a method of preparing a material, wherein nanoparticles or nanopowder are prevented from being respirable or inhala- ble during production, storage, handling, transport and further processing. Further, it is an object of the invention to allow the nanoparticles or nanopowder to be a substance in an article (as defined in REACH legislation), which is less regulated than pure nanoparticles or nanopowder. It is an object of the invention to allow fixation of nanoparticles in non-respirable particle sizes while maintaining the desired properties of the nanoparticles.
  • One embodiment of the invention provides a method of preparing a material, wherein nanoparticles are fixated in a porous network structure.
  • the method comprises the steps of:
  • the method provides a way of producing a material wherein the nanoparticles exist in a porous network structure, and where the nanoparticles have been kept non-dry so that they are not accessible in respirable form. Additionally, the nanoparticles may be produced within a reaction vessel and embedded in the porous network structure, which further ensures that the nanoparticles have not been in respirable form during their production.
  • the nanoparticles are fixated in a highly porous network material which appears in a granulated or coarse-powdered form, instead of the extremely fine nanopowder alone. Thus, no uncontrolled nanoparticles exist in accessible form during or after production and the possible toxicity due to the size of the nanoparticles to human health and the environment have been alleviated.
  • the nanoparticles created in step (c) may be present in a solvent, slurry, filter cake or any other appropriate non-dry form, which can safely be transferred or stored without release of particles to the surrounding atmosphere. Additionally, the processing of steps (c) and (d) takes place in a reaction vessel, from which the nanoparticles of step (c) cannot escape and are therefore inaccessible outside the reaction vessel until after the product is removed from the reaction vessel after step (d).
  • starting materials for a nanoparticle is meant to denote one or more compounds that participate(s) in a chemical reaction that ultimately produces the nanoparticle, whilst the term “precursor nanoparticle” is meant to denote a nanoparticle that during a subsequent process step is changed into the desired nanoparticle.
  • the nanoparticles comprise Ti0 2
  • the porous network structure comprises Si0 2 and/or Al 2 03.
  • a substantial part of the nanoparticles is Ti0 2 , and only a minor part, if any, is of other elements, in the form of a coating, a dopant, impurities or other.
  • Ti0 2 has specific uses for e.g. reduction of the level of volatile pollutants from air by heterogeneous photovoltaic oxidation or for absorption of UV radi- ation.
  • the processing of steps (c) and (d) in the method of the invention comprises the supercritical antisolvent (SAS) method, wherein the first liquid and optionally said second liquid is/are injected into a supercritical medium or substance.
  • the first and second liquids may be mixed prior to injection into the reactor for carrying out the SAS method, or the first and second liquids may be injected separately and simultaneously to the reactor for carrying out the SAS method.
  • the first liquid is injected into the SAS reactor for formation of precursor nanoparticles for further processing, or the first and second liquids are injected simultaneously. In both cases precursor nanoparticles are formed. These precursor nanoparticles are later on decomposed by heat treatment into the desired nanoparticles.
  • the precursor nanoparticles in non-dry form are generated, taken out from the SAS reactor and subsequently mixed with the second liquid for further processing in order for the second liquid to develop the porous network structure.
  • the porous network structure with the precursor nanoparticles is heat treated in order to decompose the precursor nanopar- tides into the desired nanoparticles. These desired nanoparticles are embedded in the porous network structure as was the case for the precursor nanoparticles.
  • the precursor nanoparticles and the porous network structure are formed simultaneous, with the precursor nanoparticles embedded within the porous network structure. Also in this case, a further heat treatment may be advantageous to provide the desired material properties.
  • the supercritical antisolvent is the medium of step (c) in which the nanoparticles are formed.
  • the supercritical medium may e.g. be carbon dioxide C0 2 , H 2 0, CH 4 , CH3OH, C 2 HsOH or any other appropriate medium with a supercritical point.
  • the processing of step (c) comprises a supercritical or substantially supercritical reaction step where the first liquid is exposed to elevated temperature and/or pressure to form the precursor nanoparticles or nanoparticles.
  • the exposure of the first liquid to elevated temperature and/or pressure is relatively short: as soon as the precursor nanoparticles or nanoparticles have formed, the temperature and/or pressure is/are reduced to well below the critical point, in order to suppress further reaction or agglomeration of the nanoparticles.
  • substantially supercritical is meant to denote a temperature at or above about 75% of the critical temperature, Tmticai, and/or a pressure at or above about 75% of the critical pressure, r critical ⁇
  • the processing of step (c) comprises a chemical precipitation step to form the nanoparticles or particles of a composition which can later be processed to become nanoparticles.
  • a chemical precipitation step is e.g. precipitation caused by the pH value of the first liquid.
  • Further process steps may exist between steps (c) and (d), e.g. filtration, washing and/or adding further substances.
  • Such a chemical precipitation step is a relatively cheap chemical process.
  • the processing of step (d) comprises a pH gelling method to form the porous network structure. Such a pH activated gelling step is a relatively cheap chemical process.
  • Another aspect of the invention relates to an intermediate material, wherein nanoparticles are fixated in a porous network structure, wherein the nanoparticles comprise Ti0 2 particles, and the porous network structure comprises S1O2 and/or AI2O3.
  • an intermediate material exhibits the advantages of the nanoparticles, however without their possible size-related toxicity to human health and the environment, since the nanoparticles are fixated within the porous network structure.
  • the nanoparticles are fixated in a highly porous network material which appears in a granulated or coarse-powdered form, instead of the extremely fine nanopowder alone.
  • the porous network structure of the intermediate material has a combined specific surface area of more than 50 m 2 /g, preferably more than 100 m 2 /g, more preferably more than 200 m 2 /g, most preferably more than 250 m 2 /g.
  • the nanoparticles are embedded in a network structure which does not hinder the functionality of the nanoparticles.
  • the intermediate material is present in a form as a granular powder, wherein the weight fraction of free particles with an aerodynamic diameter, D ae ro, smaller than 15 microns is less than 2%, preferably less than 0.1%. Since particles having an aerodynamic diameter, D ae ro, larger than 15 microns are seen as not respirable, the weight fraction of the respirable particles is extremely low. Thereby, the free particles of the intermediate material are not considered respirable and are not easily air- borne.
  • the aerodynamic diameter of a particle is the diameter of a sphere of density 1 g-cm 3 with the same terminal velocity due to gravitational force in calm air, as the particle, under the prevailing conditions of temperature, pressure and relative humidity (see e.g. British Standard BS EN 481:1993, Definitions).
  • the intermediate material is prepared by the method of the inven- tion.
  • the nanoparticles of the porous network structure have not been respirable during preparation of the intermediate material and thus the potential toxic effects on human and environment have been alleviated.
  • Another aspect of the invention relates to a use of an intermediate material according to the invention in a substance for reduction of the level of volatile pollutants from air by heterogeneous photocatalytic oxidation.
  • volatile pollutants or contaminants may be volatile organic compounds (VOC), such as hydrocarbons, or for example NOx or SOx.
  • Another aspect of the invention relates to the use of an intermediate material according to the invention in a substance for absorption of UV radiation.
  • Ti0 2 na noparticles find their applications in products where they provide UV-protection, UV-absorption for catalytic processes, or serve as pigments in paints, coatings, impregnations and varnishes. The ability to absorb UV light and redirect the collected energy is useful in sunscreens.
  • T1O2 na noparticles may also serve as one of the main constituents for the 'self-cleaning' properties in coatings and materials comprising such Ti0 2 nanoparticles. It should be noted however that applications listing T1O2 as a pigment are estimated to contain less than 0.1 % (w/w) Ti02-nano particles by the International Agency for Research on Cancer (IARC).
  • IARC International Agency for Research on Cancer
  • the intermediate material of the invention may also be used for antibiotic coatings of textile fibers and for cleansing of water in waste water applications.
  • EXAMPLE 1 SAS process A first liquid comprising starting materials for nanoparticles is established by dissolving 15 g/l Ti(OAc) 4 in methanol.
  • a second liquid in the form of a sol is established by hydrolysis of tetramethyl orthosili- cate (TMOS). 200ml of TMOS is mixed into 150ml methanol, thereafter 20ml of demin- eralized water and 3 ml of 0.1N HCI is added. After 24 hours under stirring at room temperature, an additional 100ml of demineralized water is added, and the second liquid is left another 24 hours under stirring.
  • TMOS tetramethyl orthosili- cate
  • a supercritical medium in the form of a C0 2 flow of 5 kg/h and a temporary carrier stream of methanol are fed to a lab scale SAS reactor at a temperature of 40°C and a pressure of 150 Barg.
  • the first liquid is injected at 5ml/h into the carrier stream of methanol, and the second liquid is injected simultaneously at 95ml/h.
  • the processing taking place within the SAS reactor of the simultaneously fed first and second liquids involves a simultaneous formation of precursor nanoparticles, viz. precursor particles for the nanoparticles, and the porous network structure.
  • the material with precursor nanoparticles fixated in the porous network structure is removed from the SAS reactor.
  • the acetate precursor nanoparticles are thereafter decomposed into the desired oxide nanoparticles at 300°C for 3h.
  • the established material with nanoparticles fixated in the porous network structure constitutes 5wt% of very fine Ti0 2 nanoparticles distributed in a Si0 2 network.
  • the first and second liquids are prepared as described in example 1, however with slight modifications: instead of using TMOS for preparing the first liquid, tetraethyl or- thosilicate (TEOS) is used; and instead of stirring the second liquid or the liquid becoming the second liquid for two times 24 hours, the second liquid is prepared by a single step of stirring for 24 hours after addition of demineralized water.
  • TMOS tetraethyl or- thosilicate
  • the first liquid is injected in the SAS reactor under conditions similar to example 1, at a rate of lOOml/h, whereby acetate precursor nanoparticles are formed.
  • the acetate precursor nanoparticles are combined with the second liquid, and 100ml of demineralized water is added, and the liquid is left another 24 hours under stirring.
  • the porous network structure is formed with the acetate precursor nanoparticles embedded.
  • the acetate precursor nanoparticles are thereafter decomposed into the desired oxide nanoparticles in the porous network structure, by heat treatment at 300°C for 3h.
  • a first liquid in the form of a solution or a suspension is formed by mixing amorphous titanyl hydroxide precipitate, ZnCI 2 and HCI and diluting the mixture with deionized water to a concentration of 5 grams of Ti0 2 per 100 grams of liquid.
  • This liquid or mixture is passed through a tubular pressure-controlled reactor at a temperature of 250°C to form the Ti0 2 nanoparticles.
  • the resultant Ti0 2 slurry is separated by filtration and washed. Thereafter ammonia and am- monium carbonate are added.
  • a second liquid is prepared by adding silicic acid to deionized water and heating to 90°C. This second liquid is added to the solvent comprising the Ti0 2 nanoparticles, at a feed rate of lOml/min for 3 hours; thereafter heating is turned off and the material is cooled and separated by filtering and drying.
  • the established material constitutes Ti0 2 nanoparticles distributed in a Si0 2 network.
  • EXAMPLE 4 Precipitation A first liquid in the form of a solution of titanium oxychloride is prepared by adding distilled water to a pure titanium chloride solution placed in an ice bath. 98% sulfuric acid is added and the solution is refluxed for two hours to provide a fine, dispersed precipitate. The precipitate is filtered and redispersed in water, and neutralized with NaOH before washing, to provide nanoparticles.
  • a second liquid in the form of a solution or a sol is formed by adding 300g AI(OC 4 Hg)3 to 1750ml water at 60°C and stirring for 2 hours, then adding 10ml of 70% sulfuric acid and an amount of solution 1 equal to 30g Ti0 2 .
  • the nanoparticles are mixed or combined with the second liquid and heated to 80°C for 1 hour while stirring, to form a gel.
  • Superfluous solvent is removed, e.g. by filtering, and the established material constitutes 10wt% Ti0 2 nanoparticles distributed in an AI2O3 or equimolar AIO(OH).
  • nH20 porous network structure The precise composition of the porous network structure depends on process time and temperature.

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Abstract

The invention relates to a method of preparing a material, wherein nanoparticles are fixated in a porous network structure. The method comprises the steps of: (a) providing a first liquid comprising starting materials for said nanoparticles, (b) providing a second liquid comprising precursors for said porous network structure, (c) processing said first liquid to form said nanoparticles or precursor nanoparticles in a non-dry form, (d) processing the second liquid together with said nanoparticles or precursor nanoparticles to form said porous network structure, whereby said nanoparticles or precursor nanoparticles are embedded within said porous network structure, and (e) optionally, heat treating said porous network structure with nanoparticles or precursor nanoparticles, whereby precursor nanoparticles are decomposed into said nanoparticles. The invention also relates to an intermediate material, wherein nanoparticles comprise TiO2 particles are fixated in a porous network structure, and where the porous network structure comprises SiO2 and/or Al2O3. Finally, the invention relates to uses of the intermediate material.

Description

Nanoparticles fixated in porous network structure
FIELD OF THE INVENTION
The invention relates to a method of preparing a material, wherein nanoparticles are fixated in a porous network structure. The invention moreover relates to a material, wherein nanoparticles are fixated in a porous network structure and to substances comprising such a material.
BACKGROUND
Within the usual definition of nanoscale, nanomaterials describe materials of which a single unit, a nanoparticle, is sized in at least one dimension between 1 and 100 nanometers (10~9 meter).
Nanomaterials often have unique optical, catalytic, electronic, or mechanical proper- ties. However, at least some nanomaterials are also investigated for their possible toxicity to human health and the environment. Some general considerations have impact on the toxicity of nanomaterials, no matter which actual elements constitute the nanoparticles, such as the size of the primary nanoparticles and their agglomerates, the way the nanoparticles interact with a living organism defined by the protein coat that every nanoparticle acquires when entering a living organism, and the surface charge and hy- drophobicity of a nanoparticle. Beyond these general effects of nanoparticles, individual nanoparticles may have additional, substance specific toxic effects of varying severity. The invention seeks to alleviate or mitigate at least some of the health-safety and/or environmental issues associated with production, processing and use of nanomaterials. It is an object of the invention to provide a method of preparing a material, wherein nanoparticles or nanopowder are prevented from being respirable or inhala- ble during production, storage, handling, transport and further processing. Further, it is an object of the invention to allow the nanoparticles or nanopowder to be a substance in an article (as defined in REACH legislation), which is less regulated than pure nanoparticles or nanopowder. It is an object of the invention to allow fixation of nanoparticles in non-respirable particle sizes while maintaining the desired properties of the nanoparticles.
SUMMARY OF THE INVENTION
One embodiment of the invention provides a method of preparing a material, wherein nanoparticles are fixated in a porous network structure. The method comprises the steps of:
(a) providing a first liquid comprising starting materials for the nanoparticles,
(b) providing a second liquid comprising precursors for the porous network structure,
(c) processing the first liquid to form the nanoparticles or precursor nanoparticles in a non-dry form, (d) processing the second liquid together with the nanoparticles or precursor nanoparticles to form the porous network structure, whereby the nanoparticles or precursor nanoparticles are embedded within the porous network structure, and
(e) optionally, heat treating said porous network structure with nanoparticles or precursor nanoparticles, whereby precursor nanoparticles are reacted or decomposed into nanoparticles.
The method provides a way of producing a material wherein the nanoparticles exist in a porous network structure, and where the nanoparticles have been kept non-dry so that they are not accessible in respirable form. Additionally, the nanoparticles may be produced within a reaction vessel and embedded in the porous network structure, which further ensures that the nanoparticles have not been in respirable form during their production. The nanoparticles are fixated in a highly porous network material which appears in a granulated or coarse-powdered form, instead of the extremely fine nanopowder alone. Thus, no uncontrolled nanoparticles exist in accessible form during or after production and the possible toxicity due to the size of the nanoparticles to human health and the environment have been alleviated.
The nanoparticles created in step (c) may be present in a solvent, slurry, filter cake or any other appropriate non-dry form, which can safely be transferred or stored without release of particles to the surrounding atmosphere. Additionally, the processing of steps (c) and (d) takes place in a reaction vessel, from which the nanoparticles of step (c) cannot escape and are therefore inaccessible outside the reaction vessel until after the product is removed from the reaction vessel after step (d). The term "starting materials for a nanoparticle" is meant to denote one or more compounds that participate(s) in a chemical reaction that ultimately produces the nanoparticle, whilst the term "precursor nanoparticle" is meant to denote a nanoparticle that during a subsequent process step is changed into the desired nanoparticle. Such process step is e.g. a heat treatment. In an embodiment, the nanoparticles comprise Ti02, and the porous network structure comprises Si02 and/or Al203. Preferably, a substantial part of the nanoparticles is Ti02, and only a minor part, if any, is of other elements, in the form of a coating, a dopant, impurities or other. Ti02 has specific uses for e.g. reduction of the level of volatile pollutants from air by heterogeneous photovoltaic oxidation or for absorption of UV radi- ation.
In an embodiment, the processing of steps (c) and (d) in the method of the invention comprises the supercritical antisolvent (SAS) method, wherein the first liquid and optionally said second liquid is/are injected into a supercritical medium or substance. The first and second liquids may be mixed prior to injection into the reactor for carrying out the SAS method, or the first and second liquids may be injected separately and simultaneously to the reactor for carrying out the SAS method.
In the SAS method, either the first liquid is injected into the SAS reactor for formation of precursor nanoparticles for further processing, or the first and second liquids are injected simultaneously. In both cases precursor nanoparticles are formed. These precursor nanoparticles are later on decomposed by heat treatment into the desired nanoparticles. If only the first liquid is injected into the SAS reactor, the precursor nanoparticles in non-dry form are generated, taken out from the SAS reactor and subsequently mixed with the second liquid for further processing in order for the second liquid to develop the porous network structure. Subsequently, the porous network structure with the precursor nanoparticles is heat treated in order to decompose the precursor nanopar- tides into the desired nanoparticles. These desired nanoparticles are embedded in the porous network structure as was the case for the precursor nanoparticles.
Alternatively, if the first and second liquids are injected into the SAS reactor, either as a mixed stream or simultaneously as two separate streams, the precursor nanoparticles and the porous network structure are formed simultaneous, with the precursor nanoparticles embedded within the porous network structure. Also in this case, a further heat treatment may be advantageous to provide the desired material properties.
Thus, in the case where the SAS method is used, the supercritical antisolvent is the medium of step (c) in which the nanoparticles are formed.
The supercritical medium may e.g. be carbon dioxide C02, H20, CH4, CH3OH, C2HsOH or any other appropriate medium with a supercritical point.
In an embodiment, the processing of step (c) comprises a supercritical or substantially supercritical reaction step where the first liquid is exposed to elevated temperature and/or pressure to form the precursor nanoparticles or nanoparticles. The exposure of the first liquid to elevated temperature and/or pressure is relatively short: as soon as the precursor nanoparticles or nanoparticles have formed, the temperature and/or pressure is/are reduced to well below the critical point, in order to suppress further reaction or agglomeration of the nanoparticles. In this context, the term "substantially supercritical" is meant to denote a temperature at or above about 75% of the critical temperature, Tmticai, and/or a pressure at or above about 75% of the critical pressure, r critical ·
In an embodiment, the processing of step (c) comprises a chemical precipitation step to form the nanoparticles or particles of a composition which can later be processed to become nanoparticles. Such a chemical precipitation step is e.g. precipitation caused by the pH value of the first liquid. Further process steps may exist between steps (c) and (d), e.g. filtration, washing and/or adding further substances. Such a chemical precipitation step is a relatively cheap chemical process. In an embodiment, the processing of step (d) comprises a pH gelling method to form the porous network structure. Such a pH activated gelling step is a relatively cheap chemical process.
Another aspect of the invention relates to an intermediate material, wherein nanoparticles are fixated in a porous network structure, wherein the nanoparticles comprise Ti02 particles, and the porous network structure comprises S1O2 and/or AI2O3. Such an intermediate material exhibits the advantages of the nanoparticles, however without their possible size-related toxicity to human health and the environment, since the nanoparticles are fixated within the porous network structure. Thus, the nanoparticles are fixated in a highly porous network material which appears in a granulated or coarse-powdered form, instead of the extremely fine nanopowder alone.
In an embodiment, the porous network structure of the intermediate material has a combined specific surface area of more than 50 m2/g, preferably more than 100 m2/g, more preferably more than 200 m2/g, most preferably more than 250 m2/g. Thereby, the nanoparticles are embedded in a network structure which does not hinder the functionality of the nanoparticles.
In an embodiment, the intermediate material is present in a form as a granular powder, wherein the weight fraction of free particles with an aerodynamic diameter, Daero, smaller than 15 microns is less than 2%, preferably less than 0.1%. Since particles having an aerodynamic diameter, Daero, larger than 15 microns are seen as not respirable, the weight fraction of the respirable particles is extremely low. Thereby, the free particles of the intermediate material are not considered respirable and are not easily air- borne. The aerodynamic diameter of a particle is the diameter of a sphere of density 1 g-cm 3 with the same terminal velocity due to gravitational force in calm air, as the particle, under the prevailing conditions of temperature, pressure and relative humidity (see e.g. British Standard BS EN 481:1993, Definitions).
I n an embodiment, the intermediate material is prepared by the method of the inven- tion. Thus, the nanoparticles of the porous network structure have not been respirable during preparation of the intermediate material and thus the potential toxic effects on human and environment have been alleviated.
Another aspect of the invention relates to a use of an intermediate material according to the invention in a substance for reduction of the level of volatile pollutants from air by heterogeneous photocatalytic oxidation. Such volatile pollutants or contaminants may be volatile organic compounds (VOC), such as hydrocarbons, or for example NOx or SOx.
Another aspect of the invention relates to the use of an intermediate material according to the invention in a substance for absorption of UV radiation. I n particular, Ti02 na noparticles find their applications in products where they provide UV-protection, UV-absorption for catalytic processes, or serve as pigments in paints, coatings, impregnations and varnishes. The ability to absorb UV light and redirect the collected energy is useful in sunscreens.
Other uses of the intermediate material are conceivable. The high opacity of the substance created by T1O2 particles is used in paints and varnishes among other applications. T1O2 na noparticles may also serve as one of the main constituents for the 'self-cleaning' properties in coatings and materials comprising such Ti02 nanoparticles. It should be noted however that applications listing T1O2 as a pigment are estimated to contain less than 0.1 % (w/w) Ti02-nano particles by the International Agency for Research on Cancer (IARC). The intermediate material of the invention may also be used for antibiotic coatings of textile fibers and for cleansing of water in waste water applications.
The following is a description of embodiments of the invention. The embodiments are examples and are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
EXAMPLE 1: SAS process A first liquid comprising starting materials for nanoparticles is established by dissolving 15 g/l Ti(OAc)4 in methanol.
A second liquid in the form of a sol is established by hydrolysis of tetramethyl orthosili- cate (TMOS). 200ml of TMOS is mixed into 150ml methanol, thereafter 20ml of demin- eralized water and 3 ml of 0.1N HCI is added. After 24 hours under stirring at room temperature, an additional 100ml of demineralized water is added, and the second liquid is left another 24 hours under stirring.
A supercritical medium in the form of a C02 flow of 5 kg/h and a temporary carrier stream of methanol are fed to a lab scale SAS reactor at a temperature of 40°C and a pressure of 150 Barg. The first liquid is injected at 5ml/h into the carrier stream of methanol, and the second liquid is injected simultaneously at 95ml/h.
The processing taking place within the SAS reactor of the simultaneously fed first and second liquids involves a simultaneous formation of precursor nanoparticles, viz. precursor particles for the nanoparticles, and the porous network structure.
After precipitation in the methanol-C02 mixture and solvent removal by C02 flushing, the material with precursor nanoparticles fixated in the porous network structure is removed from the SAS reactor. The acetate precursor nanoparticles are thereafter decomposed into the desired oxide nanoparticles at 300°C for 3h. The established material with nanoparticles fixated in the porous network structure constitutes 5wt% of very fine Ti02 nanoparticles distributed in a Si02 network.
EXAMPLE 2: SAS process + subsequent network by Sol-proces
The first and second liquids are prepared as described in example 1, however with slight modifications: instead of using TMOS for preparing the first liquid, tetraethyl or- thosilicate (TEOS) is used; and instead of stirring the second liquid or the liquid becoming the second liquid for two times 24 hours, the second liquid is prepared by a single step of stirring for 24 hours after addition of demineralized water.
The first liquid is injected in the SAS reactor under conditions similar to example 1, at a rate of lOOml/h, whereby acetate precursor nanoparticles are formed.
After removal from the SAS reactor, the acetate precursor nanoparticles are combined with the second liquid, and 100ml of demineralized water is added, and the liquid is left another 24 hours under stirring. Hereby, the porous network structure is formed with the acetate precursor nanoparticles embedded. The acetate precursor nanoparticles are thereafter decomposed into the desired oxide nanoparticles in the porous network structure, by heat treatment at 300°C for 3h.
The established material with nanoparticles fixated in the porous network structure constitutes 5wt% Ti02 nanoparticles distributed in a Si02 network. EXAMPLE 3: Supercritical + pH precipitation
A first liquid in the form of a solution or a suspension is formed by mixing amorphous titanyl hydroxide precipitate, ZnCI2 and HCI and diluting the mixture with deionized water to a concentration of 5 grams of Ti02 per 100 grams of liquid. This liquid or mixture is passed through a tubular pressure-controlled reactor at a temperature of 250°C to form the Ti02 nanoparticles. After completion of this hydrothermal reaction, the resultant Ti02 slurry is separated by filtration and washed. Thereafter ammonia and am- monium carbonate are added.
A second liquid is prepared by adding silicic acid to deionized water and heating to 90°C. This second liquid is added to the solvent comprising the Ti02 nanoparticles, at a feed rate of lOml/min for 3 hours; thereafter heating is turned off and the material is cooled and separated by filtering and drying. The established material constitutes Ti02 nanoparticles distributed in a Si02 network.
EXAMPLE 4: Precipitation A first liquid in the form of a solution of titanium oxychloride is prepared by adding distilled water to a pure titanium chloride solution placed in an ice bath. 98% sulfuric acid is added and the solution is refluxed for two hours to provide a fine, dispersed precipitate. The precipitate is filtered and redispersed in water, and neutralized with NaOH before washing, to provide nanoparticles.
A second liquid in the form of a solution or a sol is formed by adding 300g AI(OC4Hg)3 to 1750ml water at 60°C and stirring for 2 hours, then adding 10ml of 70% sulfuric acid and an amount of solution 1 equal to 30g Ti02. The nanoparticles are mixed or combined with the second liquid and heated to 80°C for 1 hour while stirring, to form a gel. Superfluous solvent is removed, e.g. by filtering, and the established material constitutes 10wt% Ti02 nanoparticles distributed in an AI2O3 or equimolar AIO(OH). nH20 porous network structure. The precise composition of the porous network structure depends on process time and temperature.
While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.

Claims

CLAIMS:
1. A method of preparing a material, wherein nanoparticles are fixated in a porous network structure, comprising the steps of: (a) providing a first liquid comprising starting materials for said nanoparticles,
(b) providing a second liquid comprising precursors for said porous network structure,
(c) processing said first liquid to form said nanoparticles or precursor nanoparticles in a non-dry form,
(d) processing the second liquid together with said nanoparticles or precursor nano- particles to form said porous network structure, whereby said nanoparticles or precursor nanoparticles are embedded within said porous network structure, and
(e) optionally, heat treating said porous network structure with nanoparticles or precursor nanoparticles, whereby precursor nanoparticles are reacted or decomposed into said nanoparticles.
2. A method according to claim 1, wherein said nanoparticles comprises Ti02, and said porous network structure comprises Si02 and/or Al203.
3. A method according to claim 1 or 2, wherein the processing of steps (c) and (d) com- prises the supercritical antisolvent (SAS) method, wherein said first liquid and optionally said second liquid is/are injected into a supercritical medium.
4. A method according to any of the claims 1 to 3, wherein the processing of step (c) comprises a supercritical or substantially supercritical reaction step where said first liq- uid is exposed to elevated temperature and/or pressure to form the nanoparticles.
5. A method according to claim 1 or 2, wherein the processing of step (c) comprises a chemical precipitation step to form the nanoparticles or particles of a composition which can later be processed to become said nanoparticles.
6. A method according to any of the claims 1 to 5, wherein the processing of step (d) comprises a pH gelling method to form said porous network structure.
7. An intermediate material, wherein nanoparticles are fixated in a porous network structure, wherein said nanoparticles comprise Ti02 particles, and said porous network structure comprises Si02 and/or AI2O3.
8. An intermediate material according to claim 7, wherein said porous network structure of said intermediate material has a combined specific surface area more than 50 m2/g, preferably more tha n 100 m2/g, more preferably more than 200 m2/g, most pref- erably more than 250 m2/g.
9. An intermediate material according to claim 7 or 8, wherein said intermediate material is present in a form as a granular powder, wherein the weight fraction of free particles with an aerodynamic diameter, Daero, smaller than 15 microns is less than 2%, pref- erably less than 0.1%.
10. An intermediate material according to any of the claims 7 to 9, wherein the intermediate material is prepared by the method of any of the claims 1 to 6.
11. Use of a material according to any of the claims 7 to 10 in a substance for reduction of the level of volatile pollutants from air by heterogeneous photocatalytic oxidation.
12. Use of an intermediate material according to any of the claims 7 to 10 in a sub- stance for absorption of UV radiation.
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