WO2014118372A1 - An aqueous dispersion comprising tio2 particles - Google Patents

An aqueous dispersion comprising tio2 particles Download PDF

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Publication number
WO2014118372A1
WO2014118372A1 PCT/EP2014/052060 EP2014052060W WO2014118372A1 WO 2014118372 A1 WO2014118372 A1 WO 2014118372A1 EP 2014052060 W EP2014052060 W EP 2014052060W WO 2014118372 A1 WO2014118372 A1 WO 2014118372A1
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Prior art keywords
particles
aqueous dispersion
dispersion
group
range
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PCT/EP2014/052060
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French (fr)
Inventor
Robert William Corkery
Andreas Westermoen
Matti Ben-Moshe
Michael Kheyfetz
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Joma International A/S
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Publication of WO2014118372A1 publication Critical patent/WO2014118372A1/en

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    • B01J35/39—
    • 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
    • B01J35/23—
    • 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
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
    • B01J27/053—Sulfates
    • 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
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/14—Phosphorus; Compounds thereof
    • B01J27/16—Phosphorus; Compounds thereof containing oxygen, i.e. acids, anhydrides and their derivates with N, S, B or halogens without carriers or on carriers based on C, Si, Al or Zr; also salts of Si, Al and Zr
    • B01J27/18—Phosphorus; Compounds thereof containing oxygen, i.e. acids, anhydrides and their derivates with N, S, B or halogens without carriers or on carriers based on C, Si, Al or Zr; also salts of Si, Al and Zr with metals other than Al or Zr
    • B01J35/33—
    • 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
    • B01J37/0215—Coating
    • B01J37/0219—Coating the coating containing organic compounds
    • 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
    • B01J37/0215—Coating
    • B01J37/0232—Coating by pulverisation

Definitions

  • the present invention relates generally to an aqueous dispersion
  • the invention also provides a method of manufacturing the dispersion.
  • TiO2 nanoparticles are useful for a range of applications, including
  • the particles in order to add the active particles to the desired system, the particles must usually be modified in ways that decrease their performance such as drying to powder.
  • EP 2130587 discloses a method to achieve well dispersed T1O2 at pH above the iso-electric point using phosphoric acid as stabilizer. This method however is limited to pH below 7 and also requires the presence of tungsten oxide nanoparticles.
  • EP1997860 and EP202448 disclose dispersions based on re-dispersing ⁇ 2 powders.
  • EP1997860 discloses the presence of an amine in a well dispersed photocatalytic coating precursor, but teaches dispersion of the ⁇ 2 particles from powder using a polymer dispersant.
  • aqueous solution comprising titanium ions or titanium complexes, keeping the temperature lower than 70°C and hydrolyzing, adjusting the conditions by at least one of a) heating at least 1 °C, b) changing pH at least 0.1 units, and c) diluting by at least 20%.
  • the pH is increased from below about 5 to a value between 5 and 1 1 by addition of an alkalizing agent such as acyclic alkonol monoamines.
  • US 7,763,565 discloses a method of preparing stable, transparent
  • photocatalytic titanium dioxide sols which involves thermal treatment of a dispersion of amorphous titanium dioxide in the presence of certain alpha- hydroxy acids.
  • the sots comprise titanium dioxide particles in the anatase form having a crystallite size less than about 10 ⁇ .
  • US2010234209 discloses a nano-particle comprising: a core of a size
  • the shell thickness is less than or equal to the core size.
  • an aqueous dispersion comprising
  • the particles wherein the particles have a size in the range 2-500 nm wherein the particles comprise ⁇ 2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the aqueous dispersion comprises at least one amine and wherein the pH of the aqueous dispersion is above the iso-electric point of the particles comprising ⁇ 2.
  • a method of manufacturing an aqueous dispersion comprising the steps of: a) providing an acidic aqueous dispersion comprising particles wherein the particles have a size in the range 2-500 nm, wherein the particles comprise ⁇ 2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, b) adding at least one amine to the aqueous dispersion and adjusting the pH value to above the iso-electric point of the T1O2 particles.
  • Fig. 1 shows the volumetric distribution of colloidal particle sizes
  • the dashed line indicates the neutral dispersion according to the invention, diluted with acid to prepare the DLS sample.
  • the dots-and-dashed line indicates an initially stable acidic solution where simple dilution with water has led to formation of aggregates.
  • a dispersion as used herein refers to a system in which particles are
  • dispersion includes but is not limited to suspensions, colloids, and sols.
  • the particle dispersion can be used for many different purposes.
  • One of the particles dispersion can be used for many different purposes.
  • One of the particles dispersion can be used for many different purposes.
  • the catalytic properties of the particles in the dispersion can also be utilized even if the particles are not adsorbed onto a surface.
  • the inventors believe that the catalytic action of the particles can be described as a two-step process, in particular for particles comprising at least one core and an at least partially surrounding layer.
  • the compound to be reacted is in a first step adsorbed to the surrounding layer. Subsequently the compound to be reacted is transported to the core(s). The majority of the molecules to be reacted react at the core(s).
  • a good catalytic particle should thus have a surrounding layer where the adsorption of the compound to be reacted is adsorbed in a good way and a core(s) at which the catalyzed reaction can take place.
  • the high fraction 50wt% or more, even 60wt% or more
  • the particles contain a significant fraction of Ti leachable in HCI 37%.
  • the leachability is determined by treating T1O2 particles in 37% HCI at 55°C for an extended period of several hours, such as at least 5 hours or more such as 17 hours.
  • the treatment time should be sufficiently long to reach a plateau value for the concentration of leached material in the HCI.
  • the skilled person can perform a routine experiment as already described in this application and verify a sufficiently long treatment time to reach
  • the particles should be leached until equilibrium. A skilled person realizes that in theory equilibrium may not be reached even after many hours, but in practice a value of ⁇ 1 wt% within the true equilibrium value is considered to be equilibrium.
  • the leached Ti in solution is measured and the fraction of leached Ti can be calculated. All fractions are calculated by weight.
  • the leached Ti in solution is measured and the fraction of leached Ti can be calculated. All fractions are calculated by weight.
  • the leachable fraction does to a large extent comprise amorphous material. As shown in example 4, the fraction of amorphous material can be reduced by thermal treatment. Since the particles can show a high leachable fraction while XRD analysis of the crystalline material shows 100wt% anatase, this leachable fraction is concluded to consist of one of more amorphous forms of titanium oxides (T1O2 or substochiometric TiO(2 -x )) and/or hydrated T1O2, containing -Ti-OH moieties.
  • the layer with a high content of Ti leachable in 37% HCI is rich in hydroxyl groups.
  • the high amorphous content nanoparticles i.e. particles with a high fraction of Ti leachable in 37% HCI are observed to give better transparency and dispersion stability in the precursor dispersion. Powders with high amorphous content in the nanoparticles are also observed have better redispersability than highly crystalline powders.
  • the particles When the particles have for instance been standing, and/or exposed to heat they may form a gel, but the gelation process is reversible and by shaking it is possible to regain the aqueous dispersion.
  • a model of the particles as at least one crystalline core surrounded by a layer of amorphous material can explain the advantages in crosslinking, dispersion stability and powder redispersability since all of these are connected to surface mechanisms and not bulk composition.
  • particles at pH above the iso-electric point comprising at least one amine.
  • the ability to provide stable nanoparticle dispersion at basic pH is useful for adding active nanoparticles to materials, where adding acidic T1O2 dispersions would cause a reaction that typically leads to unwanted aggregation of the T1O2 nanoparticles and degradation.
  • materials include but are not limited to cement.
  • the ability to provide stable nanoparticle dispersion at neutral pH or at a pH slightly above neutral allows the application of active nanoparticles via equipment that is vulnerable to corrosion, allows application of active nanoparticles to substrates, binders and formulations were acid pH is undesirable.
  • the claimed dispersion can be made with solid concentrations at least up to 30wt%, but concentrations up to about 15wt% give added advantages in transparency, sprayability and colloidal stability.
  • the dispersion can easily be diluted to obtain lower concentrations.
  • concentration of the particles in the aqueous dispersion is 1 -45wt%.
  • the concentration of the particles in the aqueous dispersion is 10- 20wt%.
  • the transparency of the dispersion is an indication of aggregation stability, since large aggregates will scatter visible light and make the dispersion turbid.
  • the dispersion is transparent. In one embodiment the dispersion is semi-transparent.
  • the dispersion shows no visible sign of nanoparticle aggregation. In one embodiment of the invention, the dispersion shows no visible sign of nanoparticle aggregation and the DLS size distribution of the dispersion is similar to that of the starting aqueous solution.
  • the particles have at least one core which is at least partially surrounded by a surrounding layer. Since most of the crystalline material is in the at least one core, the at least one core can also be referred to as the crystal phase.
  • the at least one core of the particles comprises at least 75wt% anatase.
  • the at least one core of the T1O2 particles comprises at least 95wt% anatase.
  • the at least one core of the T1O2 nanoparticles comprises 100wt% anatase, or essentially 100wt% anatase.
  • nanoparticles comprises 99wt% anatase
  • the T1O2 nanoparticles contain at least 50wt% Ti that is leachable in 37% HCI. In an embodiment of the invention, the ⁇ 2 nanoparticles contain at least 50wt% Ti that is leachable in 37% HCI.
  • the pH of the final dispersion can be modified to any target pH at least in the range 6-12 by adjusting the amount of amine and base added.
  • the pH is neutral or near neutral. In an alternative embodiment the pH is in the range 9-10. In one embodiment the pH is matched to a cementitous substrate.
  • the dispersion has controlled viscosity and is sprayable with generic
  • the solid concentration can easily be reduced by dilution, which is observed to decrease the viscosity.
  • the dispersion can be produced by increasing the pH value of an acidic T1O2 dispersion. Taking the pH through the isoelectric point can be done with or without the presence of amines, but addition of amines gives significantly improved transparency in the final dispersions.
  • an aqueous dispersion comprising
  • the particles wherein the particles have a size in the range 2-500 nm wherein the particles comprise T1O2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the aqueous dispersion comprises at least one amine and wherein the pH of the aqueous dispersion is above the iso-electric point of the particles comprising T1O2.
  • At least of part of said particles comprise at least one core and an at least partially surrounding layer, wherein more than 90wt% of the total amount of Ti leachable in 37% HCI is in the surrounding layer. In an alternative embodiment more than 95wt% of the total amount of Ti leachable in 37% HCI is in the surrounding layer.
  • the embodiments with at least one core and a surrounding layer is often several cores embedded in a surrounding layer.
  • the average size of the particles is in the range 5-50 nm.
  • the particles in the dispersion are titanium oxide
  • the particles comprise sub stoichiometric T1O2.
  • the preparation of the dispersion is not observed to have any significant effect on the basic nanoparticle properties such as crystal phase, crystal size, specific surface and porosity, only on what additives and/or stabilizers are present on the particle surface.
  • the T1O2 nanoparticles are in the XRD size range 5-50 nm. In another embodiment of the invention, the T1O2
  • nanoparticles are in the XRD size range 10-30 nm.
  • the T1O2 nanoparticles are in the DLS size range 5-50 nm. In another embodiment of the invention, the TiO2 nanoparticles are in the DLS size range 15-30 nm. [0049] In one embodiment at least a part of the particles comprise at least one core and an at least partially surrounding layer, and wherein the at least one core comprises at least 95wt% anatase.
  • the dispersion comprises at least one selected from the group consisting of monoethanolamine, diethanolamine, and triethanolamine. In one embodiment the dispersion comprises ethanolamine.
  • the dispersion comprises at least one alpha hydroxy acid.
  • the dispersion comprises at least one molecule, wherein said molecule comprises at least one chemical group selected from the group consisting of a carboxylic group, a sulphate group, and a phosphate group.
  • the pH of the aqueous dispersion is in the range 6-8. In an alternative embodiment the pH is in the range 8-12. In yet another embodiment the pH is in the range 9-10.
  • the particles have a monomodal size distribution.
  • Monomodal is interpreted so that at least 99wt% of the particles fall within the monomodal size distribution. I.e. 1wt% of the particles can have sizes which are not monomodal.
  • the concentration of said particles is 1 -45wt%
  • the aqueous dispersion comprises up to 10wt% amines. In an alternative embodiment of the invention, the dispersion comprises 2-8wt% amines. In one embodiment the concentration is at least 1wt%. In one embodiment the concentration is at least 5wt%. In one embodiment the concentration is at least 10wt%. In one embodiment the concentration is at least 20wt%. In another embodiment of the invention, the dispersion comprises 3wt% MEA. In yet another embodiment of the invention, the dispersion comprises 3wt% MEA and 3wt% TEA.
  • a method of manufacturing an aqueous dispersion comprising the steps of: a) providing an acidic aqueous dispersion comprising particles wherein the particles have a size in the range 2-500 nm, wherein the particles comprise ⁇ 2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the pH of the acidic aqueous dispersion is below the isoelectric point of the particles comprising ⁇ 2, b) adding at least one amine to the aqueous dispersion and adjusting the pH value to above the iso-electric point of the ⁇ 2 particles.
  • the particles have not undergone a powder stage.
  • the pH value is adjusted by adding at least one selected from the group consisting of an organic amine and an inorganic base.
  • an inorganic base is used to increase the pH above the iso-electric point.
  • amines are used to increase the pH from below neutral to the final pH.
  • At least one alpha hydroxyl acid is added.
  • At least one molecule is added, wherein said molecule comprises at least one chemical group selected from the group consisting of a carboxylic group, a sulphate group, and a phosphate group.
  • Example 1 preparation of high stability neutral 15% TiO? dispersion
  • Example 4 investigation of amorphous content of nanoparticles
  • the vial was shaken at 55°C for 24 hours.
  • Example 5 comparative investigation of colloidal particle size and stability

Abstract

There is disclosed an aqueous dispersion comprising TiO2 particles, the have a size in the range 2-500 nm, wherein the particles comprise TiO2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCl, wherein the aqueous dispersion comprises at least one amine, and wherein the pH of the aqueous dispersion is above the iso-electric point of the particles comprising TiO2. One advantage is that it is possible to adjust the pH of the dispersion to adapt the pH to sensitive materials, in particular materials sensitive for low pH values. Another advantage is that the higher fraction of Ti leachable in 37% HCl gives better transparency and dispersion stability. Further it gives better redispersability.

Description

AN AQUEOUS DISPERSION COMPRISING TIO2 PARTICLES
Technical field
[0001 ]The present invention relates generally to an aqueous dispersion
comprising T1O2 nanoparticles and which further comprises an amine. The invention also provides a method of manufacturing the dispersion.
Background
[0002]TiO2 nanoparticles are useful for a range of applications, including
photocatalytic breakdown of organic pollutants. However in order to add the active particles to the desired system, the particles must usually be modified in ways that decrease their performance such as drying to powder.
[0003]Husken et al (2007) teaches that for air purifying paving stones, having well dispersed and small particles is more important than the amount of T1O2 added, and that adding the nanoparticles as dispersion increases the performance compared to powders. However T1O2 dispersions produced by hydrolysis of TiCU or T1OCI2 are strongly acidic due to the excess of HCI, and unsuitable for insertion into systems such as cement or paints. Increasing the pH towards the iso-electric point eliminates electrostatic stabilization and leads to aggregation unless stabilized by other means. The process of aggregation irreversibly affects to the surface, so that aggregating and re-dispersing a product generally gives a different particle size distribution with larger particles.
[0004]Several disclosures detail dispersions of T1O2 nanoparticles at non-acidic pH, but do not give methods to go from acidic to non-acidic pH without changing the particle size distribution.
[0005] EP 2130587 discloses a method to achieve well dispersed T1O2 at pH above the iso-electric point using phosphoric acid as stabilizer. This method however is limited to pH below 7 and also requires the presence of tungsten oxide nanoparticles. [0006] EP1997860 and EP202448 disclose dispersions based on re-dispersing ΤΊΟ2 powders. EP1997860 discloses the presence of an amine in a well dispersed photocatalytic coating precursor, but teaches dispersion of the ΤΊΟ2 particles from powder using a polymer dispersant.
[0007]WO 2007/074436 discloses a method for production of TiO2 particles
comprising the steps of providing an aqueous solution comprising titanium ions or titanium complexes, keeping the temperature lower than 70°C and hydrolyzing, adjusting the conditions by at least one of a) heating at least 1 °C, b) changing pH at least 0.1 units, and c) diluting by at least 20%. There is disclosed a step to dehydrate particles at a calcination temperature in a range 90-900°C.
[0008] US 2,819,174 discloses a process for manufacturing a titania hydrate
dispersion. The pH is increased from below about 5 to a value between 5 and 1 1 by addition of an alkalizing agent such as acyclic alkonol monoamines.
[0009]US 7,763,565 discloses a method of preparing stable, transparent
photocatalytic titanium dioxide sols which involves thermal treatment of a dispersion of amorphous titanium dioxide in the presence of certain alpha- hydroxy acids. The sots comprise titanium dioxide particles in the anatase form having a crystallite size less than about 10 μιτι.
[0010]US2010234209 discloses a nano-particle comprising: a core of a size
having a first electrically conducting or semiconducting material, a shell of a thickness having a second dielectric or semiconducting material, wherein the composition of said second material is different from the composition of said first material, and wherein the shell thickness is less than or equal to the core size.
[001 1 ] Even if dispersions according to the prior art are used today there is still room for an improvement regarding for instance the pH of the aqueous dispersion. Further the stability of a dispersion of particles is also desired to improve. Summary
[0012] It is an object of the present invention to obviate at least some of the
disadvantages in the prior art and to provide an improved dispersion as well as a method for manufacturing the dispersion.
[0013] In a first aspect there is provided an aqueous dispersion comprising
particles, wherein the particles have a size in the range 2-500 nm wherein the particles comprise ΤΊΟ2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the aqueous dispersion comprises at least one amine and wherein the pH of the aqueous dispersion is above the iso-electric point of the particles comprising ΤΊΟ2.
[0014] In a second aspect there is provided a method of manufacturing an aqueous dispersion, said method comprising the steps of: a) providing an acidic aqueous dispersion comprising particles wherein the particles have a size in the range 2-500 nm, wherein the particles comprise ΤΊΟ2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, b) adding at least one amine to the aqueous dispersion and adjusting the pH value to above the iso-electric point of the T1O2 particles.
[0015] Further aspects and embodiments are defined in the appended claims, which are specifically incorporated herein by reference.
[0016]One advantage is that it is possible to adjust the pH of the dispersion to adapt the pH to sensitive materials, in particular materials sensitive for low pH values.
[0017]Another advantage is that the higher fraction of Ti leachable in 37% HCI gives better transparency and dispersion stability. Further it gives better redispersability. Brief description of the drawings
[0018] The invention is now described, by way of example, with reference to the accompanying drawings, in which:
[0019] Fig. 1 shows the volumetric distribution of colloidal particle sizes
(hydrodynamic diameter) measured by DLS. The dashed line indicates the neutral dispersion according to the invention, diluted with acid to prepare the DLS sample. The dots-and-dashed line indicates an initially stable acidic solution where simple dilution with water has led to formation of aggregates.
Detailed description
[0020] Before the invention is disclosed and described in detail, it is to be
understood that this invention is not limited to particular compounds,
configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.
[0021 ] It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.
[0022] If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.
[0023] A dispersion as used herein refers to a system in which particles are
dispersed in a continuous phase of a different composition. The term
dispersion includes but is not limited to suspensions, colloids, and sols.
[0024]The particle dispersion can be used for many different purposes. One
purpose is for preparing a surface with adsorbed particles where the catalytic properties of the particles are utilized. The catalytic properties of the particles in the dispersion can also be utilized even if the particles are not adsorbed onto a surface. The inventors believe that the catalytic action of the particles can be described as a two-step process, in particular for particles comprising at least one core and an at least partially surrounding layer. The compound to be reacted is in a first step adsorbed to the surrounding layer. Subsequently the compound to be reacted is transported to the core(s). The majority of the molecules to be reacted react at the core(s). A good catalytic particle should thus have a surrounding layer where the adsorption of the compound to be reacted is adsorbed in a good way and a core(s) at which the catalyzed reaction can take place. The high fraction (50wt% or more, even 60wt% or more)
[0025] According to the invention, the particles contain a significant fraction of Ti leachable in HCI 37%. The leachability is determined by treating T1O2 particles in 37% HCI at 55°C for an extended period of several hours, such as at least 5 hours or more such as 17 hours. The treatment time should be sufficiently long to reach a plateau value for the concentration of leached material in the HCI. The skilled person can perform a routine experiment as already described in this application and verify a sufficiently long treatment time to reach
equilibrium. The particles should be leached until equilibrium. A skilled person realizes that in theory equilibrium may not be reached even after many hours, but in practice a value of ±1 wt% within the true equilibrium value is considered to be equilibrium. The leached Ti in solution is measured and the fraction of leached Ti can be calculated. All fractions are calculated by weight.
[0026] The leached Ti in solution is measured and the fraction of leached Ti can be calculated. All fractions are calculated by weight. The leachable fraction does to a large extent comprise amorphous material. As shown in example 4, the fraction of amorphous material can be reduced by thermal treatment. Since the particles can show a high leachable fraction while XRD analysis of the crystalline material shows 100wt% anatase, this leachable fraction is concluded to consist of one of more amorphous forms of titanium oxides (T1O2 or substochiometric TiO(2-x)) and/or hydrated T1O2, containing -Ti-OH moieties.
[0027]The layer with a high content of Ti leachable in 37% HCI is rich in hydroxyl groups.
[0028]The high fraction of Ti leachable in 37% HCI at 55°C is obtained by carefully controlling the growth of nanoparticles. It is possible to start with a
solution/dispersion of titanic acid which is heated to initiate growth of nanoparticles. When the nanoparticles are formed the layer which to a large extent is leachable in 37% HCI at 55°C grows first and when the material which is leachable in 37% HCI has formed the crystalline material starts to grow. The crystalline material is not or only to a very minor extent leachable in 37% HCI. Thus it is possible to abort the heating early in order to obtain particles with a high fraction of leachable material.
[0029]The high amorphous content nanoparticles, i.e. particles with a high fraction of Ti leachable in 37% HCI are observed to give better transparency and dispersion stability in the precursor dispersion. Powders with high amorphous content in the nanoparticles are also observed have better redispersability than highly crystalline powders. When the particles have for instance been standing, and/or exposed to heat they may form a gel, but the gelation process is reversible and by shaking it is possible to regain the aqueous dispersion. A model of the particles as at least one crystalline core surrounded by a layer of amorphous material can explain the advantages in crosslinking, dispersion stability and powder redispersability since all of these are connected to surface mechanisms and not bulk composition.
[0030]There is disclosed a concentrated stable aqueous dispersion of T1O2
particles at pH above the iso-electric point, comprising at least one amine.
[0031 ]The ability to provide stable nanoparticle dispersion at basic pH is useful for adding active nanoparticles to materials, where adding acidic T1O2 dispersions would cause a reaction that typically leads to unwanted aggregation of the T1O2 nanoparticles and degradation. Examples of such materials include but are not limited to cement. The ability to provide stable nanoparticle dispersion at neutral pH or at a pH slightly above neutral allows the application of active nanoparticles via equipment that is vulnerable to corrosion, allows application of active nanoparticles to substrates, binders and formulations were acid pH is undesirable.
[0032]The claimed dispersion can be made with solid concentrations at least up to 30wt%, but concentrations up to about 15wt% give added advantages in transparency, sprayability and colloidal stability. The dispersion can easily be diluted to obtain lower concentrations. In one embodiment the concentration of the particles in the aqueous dispersion is 1 -45wt%. In an alternative
embodiment the concentration of the particles in the aqueous dispersion is 10- 20wt%.
[0033]The transparency of the dispersion is an indication of aggregation stability, since large aggregates will scatter visible light and make the dispersion turbid. In one embodiment of the invention, the dispersion is transparent. In one embodiment the dispersion is semi-transparent.
[0034] In one embodiment of the invention, the dispersion shows no visible sign of nanoparticle aggregation. In one embodiment of the invention, the dispersion shows no visible sign of nanoparticle aggregation and the DLS size distribution of the dispersion is similar to that of the starting aqueous solution.
[0035] In one embodiment the particles have at least one core which is at least partially surrounded by a surrounding layer. Since most of the crystalline material is in the at least one core, the at least one core can also be referred to as the crystal phase. In an embodiment with particles having at least one core surrounded at least partially by a layer, the at least one core of the particles comprises at least 75wt% anatase. In an alternative embodiment of the invention, the at least one core of the T1O2 particles comprises at least 95wt% anatase. In another embodiment of the invention, the at least one core of the T1O2 nanoparticles comprises 100wt% anatase, or essentially 100wt% anatase. In one embodiment of the invention the at least one core of the T1O2
nanoparticles comprises 99wt% anatase
[0036] In an embodiment of the invention, the T1O2 nanoparticles contain at least 50wt% Ti that is leachable in 37% HCI. In an embodiment of the invention, the ΤΊΟ2 nanoparticles contain at least 50wt% Ti that is leachable in 37% HCI.
[0037]The pH of the final dispersion can be modified to any target pH at least in the range 6-12 by adjusting the amount of amine and base added.
[0038] In one embodiment of the invention, the pH is neutral or near neutral. In an alternative embodiment the pH is in the range 9-10. In one embodiment the pH is matched to a cementitous substrate.
[0039]The dispersion has controlled viscosity and is sprayable with generic
equipment at least up to 20wt% solid content. The solid concentration can easily be reduced by dilution, which is observed to decrease the viscosity.
[0040]The dispersion can be produced by increasing the pH value of an acidic T1O2 dispersion. Taking the pH through the isoelectric point can be done with or without the presence of amines, but addition of amines gives significantly improved transparency in the final dispersions.
[0041 ] In a first aspect there is provided an aqueous dispersion comprising
particles, wherein the particles have a size in the range 2-500 nm wherein the particles comprise T1O2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the aqueous dispersion comprises at least one amine and wherein the pH of the aqueous dispersion is above the iso-electric point of the particles comprising T1O2.
[0042] It is understood that the beneficial effects of a high fraction of Ti leachable in 37% HCI start already at 50wt%, but that the beneficial effects are improved at 55wt% and more pronounced at 60wt%. At even higher fractions of leachable material the advantages can be further pronounced. However one drawback of a very high fraction of leachable material (such as 70-80wt% Ti) is that the yield during the manufacturing process is impaired. Thus in one embodiment at least 50wt% of the Ti in the particles is leachable in 37% HCI. In another embodiment at least 55wt% of the Ti in the particles is leachable in 37% HCI. In yet another embodiment at least 60wt% of the Ti in the particles is leachable in 37% HCI. In a further embodiment at least 65wt% of the Ti in the particles is leachable in 37% HCI. In another embodiment at least 70wt% of the Ti in the particles is leachable in 37% HCI.
[0043] In one embodiment at least of part of said particles comprise at least one core and an at least partially surrounding layer, wherein more than 90wt% of the total amount of Ti leachable in 37% HCI is in the surrounding layer. In an alternative embodiment more than 95wt% of the total amount of Ti leachable in 37% HCI is in the surrounding layer. The embodiments with at least one core and a surrounding layer is often several cores embedded in a surrounding layer.
[0044] In one embodiment the average size of the particles is in the range 5-50 nm.
[0045] In one embodiment the particles in the dispersion are titanium oxide
particles with primary particle size in the range 5-50 nm as measured by XRD and where the crystal form comprises mainly anatase T1O2. In one embodiment the particles comprise sub stoichiometric T1O2.
[0046]The preparation of the dispersion is not observed to have any significant effect on the basic nanoparticle properties such as crystal phase, crystal size, specific surface and porosity, only on what additives and/or stabilizers are present on the particle surface.
[0047] In one embodiment of the invention, the T1O2 nanoparticles are in the XRD size range 5-50 nm. In another embodiment of the invention, the T1O2
nanoparticles are in the XRD size range 10-30 nm.
[0048] In one embodiment of the invention, the T1O2 nanoparticles are in the DLS size range 5-50 nm. In another embodiment of the invention, the TiO2 nanoparticles are in the DLS size range 15-30 nm. [0049] In one embodiment at least a part of the particles comprise at least one core and an at least partially surrounding layer, and wherein the at least one core comprises at least 95wt% anatase.
[0050] In one embodiment the dispersion comprises at least one selected from the group consisting of monoethanolamine, diethanolamine, and triethanolamine. In one embodiment the dispersion comprises ethanolamine.
[0051 ] In one embodiment the dispersion comprises at least one alpha hydroxy acid.
[0052] In one embodiment the dispersion comprises at least one molecule, wherein said molecule comprises at least one chemical group selected from the group consisting of a carboxylic group, a sulphate group, and a phosphate group.
[0053] In one embodiment the pH of the aqueous dispersion is in the range 6-8. In an alternative embodiment the pH is in the range 8-12. In yet another embodiment the pH is in the range 9-10.
[0054] In one embodiment the particles have a monomodal size distribution.
Monomodal is interpreted so that at least 99wt% of the particles fall within the monomodal size distribution. I.e. 1wt% of the particles can have sizes which are not monomodal.
[0055] In one embodiment the concentration of said particles is 1 -45wt%,
preferably 10-20wt%. In an embodiment of the invention the aqueous dispersion comprises up to 10wt% amines. In an alternative embodiment of the invention, the dispersion comprises 2-8wt% amines. In one embodiment the concentration is at least 1wt%. In one embodiment the concentration is at least 5wt%. In one embodiment the concentration is at least 10wt%. In one embodiment the concentration is at least 20wt%. In another embodiment of the invention, the dispersion comprises 3wt% MEA. In yet another embodiment of the invention, the dispersion comprises 3wt% MEA and 3wt% TEA. [0056] In a second aspect there is provided a method of manufacturing an aqueous dispersion, said method comprising the steps of: a) providing an acidic aqueous dispersion comprising particles wherein the particles have a size in the range 2-500 nm, wherein the particles comprise ΤΊΟ2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the pH of the acidic aqueous dispersion is below the isoelectric point of the particles comprising ΤΊΟ2, b) adding at least one amine to the aqueous dispersion and adjusting the pH value to above the iso-electric point of the ΤΊΟ2 particles.
[0057] In one embodiment the particles have not undergone a powder stage.
[0058] In one embodiment the pH value is adjusted by adding at least one selected from the group consisting of an organic amine and an inorganic base.
[0059] In one embodiment of the invention, an inorganic base is used to increase the pH above the iso-electric point. In one embodiment of the invention, amines are used to increase the pH from below neutral to the final pH.
[0060] In one embodiment at least one alpha hydroxyl acid is added.
[0061 ] In one embodiment at least one molecule is added, wherein said molecule comprises at least one chemical group selected from the group consisting of a carboxylic group, a sulphate group, and a phosphate group.
[0062]Other features and uses of the invention and their associated advantages will be evident to a person skilled in the art upon reading the description and the examples.
[0063] It is to be understood that this invention is not limited to the particular
embodiments shown here. The embodiments are provided for illustrative purposes and are not intended to limit the scope of the invention since the scope of the present invention is limited only by the appended claims and equivalents thereof. Examples
[0064]AII percentages are calculated by weight if not clearly stated otherwise.
[0065]27.1 kg of T1OCI2 was diluted with 13.8 kg deionized water and left
overnight. The diluted T1OCI2 solution was neutralized with 77.2 kg of aqueous NaOH and 16.2 kg of (Na)2CO3 in a stirred reactor to yield a final solution pH below 5. To this was added a solution of 63.7 kg T1OCI2 and 1 .9 kg surfactant yielding a transparent solution with a temperature of 40.4°C. To this clear solution, 1 .9 kg of acetylacetone was added followed by heating for 35 minutes until the temperature was 81 .9° C. The temperature was held constant for a further 75 minutes, followed by cooling from 81 .7°C to 50.9°C. The resulting 198.8 kg nanotitania dispersion yielded 196.6 kg of reaction product. The product was filtered through a nanofiltration unit combining washing and concentration steps to obtain a final pH of 1 .1 and approximately 20% weight concentration of T1O2. These particles were utilized for the following examples unless otherwise is clearly stated.
Example 1 : preparation of high stability neutral 15% TiO? dispersion
[0066]To 840g of a Joma acidic (pH=1 ) 18% TiO2 dispersion was added 30g lactic acid, 70g of 20% KOH, 30g of water and 30g of MEA (Monoethanolamine), bringing the final pH to neutral and the T1O2 content to 15%. All additions were done slowly and with good stirring in order to homogenize the dispersion between each step. The dispersion remained translucent or semi-transparent during the whole process with no signs of particle sedimentation or visible aggregation.
Example 2: preparation of high stability basic 15% TiO? dispersion
[0067]To 840g of a Joma acidic (pH=1 ) 18% TiO2 dispersion was added 30g lactic acid, 70g of 20% KOH, 30g of MEA (Monoethanolamine) and 30g of TEA (Triethanolamine), bringing the final pH to 10 and the T1O2 content to 15%. All additions were done slowly and with good stirring in order to homogenize the dispersion between each step. The dispersion remained translucent or semi- transparent during the whole process with no signs of particle sedimentation or visible aggregation.
Example 3: sprayability of high stability 15% and 20% TiO? dispersions
[0068] In one experiment, a dispersion containing 15%wt ΤΊΟ2, 3% TEA and 3% MEA was sprayed onto a brick surface using a generic spraying unit. The dispersion showed good sprayability with no clogging of the equipment, and the resulting liquid layer appeared homogeneous.
[0069] In a different experiment, a dispersion containing 20%wt T1O2, TEA and MEA was sprayed onto a substrate using a consumer spray pump. The dispersion showed good sprayability with no clogging of
[0070]the equipment, suggesting that even higher concentrations are sprayable and the resulting liquid layer appeared homogeneous.
Example 4: investigation of amorphous content of nanoparticles
[0071 ]Various samples containing T1O2 nanoparticles were dissolved in
concentrated HCI in an amount of ca 10g HCI 37% per gram of TiO2- containing product, enough to leach any amorphous T1O2 present in the product.
[0072]Two different Joma acidic T1O2 dispersions were treated with nano filtration, cationic and anionic exchangers until a pH=6.2 was reached. Excess amounts of 37% HCI was added to the samples. The vials were shaken at 55°C for 17 hours.
[0073]Two samples of the second Joma dispersion, after treatment to pH=6.2, were dried at 60°C and sintered at different temperatures. The sintered samples were added to excess amounts of 37% HCI. The vials were shaken at 55°C for 17 hours.
[0074]A third Joma dispersion, after treatment to pH=6.2, was dried at 100 °C and sintered at 200 °C. The samples were added to excess amounts of 37% HCI. The vials were shaken at 55°C for 18 hours and the solid fraction weighed after washing and air drying for 96 hours followed by heating at 50°C for 1 hour.
[0075]Two different Cristal Millenniunn product samples (dispersion) were mixed with excess amounts of 37% HCI. The vials were shaken at 55°C for 6-40 hours.
[0076]Evonik Degussa P25 powder was added to excess amounts of 37% HCI.
The vial was shaken at 55°C for 24 hours.
In all the Initial TiOwt% Leaching time Clear solution Unleached/initi cases the Ti[aq]wt% al TiO2 resulting
almost clear
samples were
analysed for Ti
content
Sample
Joma sample 0.68 17h 0.30 0.25
A
Joma sample 1 .02 17h 0.44 0.27
B
Joma sample 2.44 17h 0.72 0.71
B sintered at
300°C for
90min
Joma sample 2.19 17h 0.24 0.89
B sintered at
500°C for
30min Joma sample 7.75 18h 0.54
C
Joma sample 7.75 18h 0.64
C sintered at
200°C for 18h
Cristal 4.09 6h 0.386 0.84
Millennium
S5300A
2.95 24h 0.616 0.64
40h 0.637 0.63
Cristal 4,45 18h 0.69 0.73
Milennium
PC500
Degussa P25 17.5 24h 0.27 0.974
In all the Initial TiO2wt% Leaching time Clear solution Unleached/initi cases the Ti[aq]wt% al TiO2 resulting
almost clear
solutions were
analysed for Ti
content
Sample
Joma sample 0.68 17h 0.30 0.25
A
Joma sample 1 .02 17h 0.44 0.27
B
Joma sample 2.44 17h 0.72 0.71
B sintered at
300°C for
90min
Joma sample 2.19 17h 0.24 0.89
B sintered at
500°C for
30min Cristal 4.09 6h 0.386 0.84
Millennium
S5300A
2.95 24h 0.616 0.64
40h 0.637 0.63
Cristal 4.45 18h 0.69 0.73
Milennium
PC500
Degussa P25 17.5 24h 0.27 0.974
[0077]The results show that Joma ΤΊΟ2 nanoparticles have a significantly higher fraction of leachable Ti than other tested products, but that this fraction can be reduced by thermal treatment.
Example 5: comparative investigation of colloidal particle size and stability
[0078]A sample of neutral dispersion prepared according to example 1 was diluted with water and analyzed by DLS. A single peak was observed in the volumetric size distribution with the maximum value in the around 23 nm, as shown by the solid lines in figure 1 . The experiment was repeated and reproduced the result.
[0079]A sample of acidic dispersion at pH=1 identical to the starting dispersion used in example 1 was diluted with water and analyzed by DLS. The dilution corresponds to a pH increase to about pH=3.5. Two peaks were observed in the volumetric size distribution, shown by the dashed lines in figure 1 , with the dominant peak having a maximum value around 70nm range and a smaller peak having a maximum around 25nm. The experiment was repeated and reproduced the result.
[0080]To the diluted acidic dispersion sample was added a few drops of NaOH, quickly bringing it to basic pH. Instant aggregation was visually observed. The resulting dispersion was too polydisperse to be analyzed by DLS, with aggregate sizes up to several microns.

Claims

1 . An aqueous dispersion comprising particles, wherein the particles have a size in the range 2-500 nm, wherein the particles comprise ΤΊΟ2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the aqueous dispersion comprises at least one amine and wherein the pH of the aqueous dispersion is above the iso-electric point of the particles comprising ΤΊΟ2.
2. The aqueous dispersion according to claim 1 wherein at least of part of said particles comprise at least one core and a surrounding layer, at least partially surrounding the at least one core, wherein more than 90wt% of the total amount of Ti leachable in 37% HCI is in the surrounding layer.
3. The aqueous dispersion according to any one of claims 1 -2, wherein the average size of the particles is in the range 5-50 nm.
4. The aqueous dispersion according to any one of claims 1 -3, wherein at least a part of the particles comprise at least one core and a surrounding layer, at least partially surrounding the at least one core, and wherein the at least one core comprises at least 95wt% anatase.
5. The aqueous dispersion according to any one of claims 1 -4, wherein the dispersion comprises at least one selected from the group consisting of
monoethanolamine, diethanolamine, and triethanolamine.
6. The aqueous dispersion according to any one of claims 1 -5, wherein the dispersion comprises ethanolamine.
7. The aqueous dispersion according to any one of claims 1 -6, wherein the dispersion comprises at least one alpha hydroxy acid.
8. The aqueous dispersion according to any one of claims 1 -7, wherein the dispersion comprises at least one molecule, wherein said molecule comprises at least one chemical group selected from the group consisting of a carboxylic group, a sulphate group, and a phosphate group.
9. The aqueous dispersion according to any one of claims 1 -7, wherein the pH is in the range 6-8.
10. The aqueous dispersion according to any one of claims 1 -7, wherein the pH is in the range 8-12.
1 1 . The aqueous dispersion according to any one of claims 1 -7, wherein the pH is in the range 9-10.
12. The aqueous dispersion according to any one of claims 1 -1 1 , wherein the particles have a monomodal size distribution.
13. The aqueous dispersion according to any one of claims 1 -12, wherein the concentration of said particles is 1 -45wt%, preferably 10-20wt%.
14. A method of manufacturing an aqueous dispersion, said method comprising the steps of: a) providing an acidic aqueous dispersion comprising particles
wherein the particles have a size in the range 2-500 nm, wherein the particles comprise T1O2, wherein at least 50wt% of the Ti in the particles is leachable in 37% HCI, wherein the pH of the acidic aqueous dispersion is below the isoelectric point of the particles comprising T1O2, b) adding at least one amine to the aqueous dispersion and adjusting the pH value to above the iso-electric point of the T1O2 particles.
15. The method according to claim 14, wherein the pH of the aqueous dispersion in step a) is below 3.
16. The method according to claim 14, wherein the pH of the aqueous dispersion is adjusted to a value of 9 or higher in step b).
17. The method according to claim 14, wherein the pH of the aqueous dispersion is adjusted to a value in the range 6-8 in step b).
18. The method according to claim 14, wherein the pH of the aqueous dispersion is adjusted to a value in the range 8-12 in step b).
19. The method according to any one of claims 14-18, wherein the particles have not undergone a powder stage.
20. The method according to any one of claims 14-19, wherein the particles have a monomodal size distribution.
21 . The method according to any one of claims 14-20, wherein the concentration of said particles is 1 -45wt%, preferably 10-20wt%.
22. The method according to any one of claims 14-21 , wherein the pH value is adjusted by adding at least one selected from the group consisting of an organic amine and an inorganic base.
23. The method according to any one of claims 14-22, wherein at least one alpha hydroxyl acid is added.
24. The method according to any one of claims 14-23, wherein at least one molecule is added, wherein said molecule comprises at least one chemical group selected from the group consisting of a carboxylic group, a sulphate group, and a phosphate group.
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