WO2011054787A1

WO2011054787A1 - Process for preparing mesoporous materials

Info

Publication number: WO2011054787A1
Application number: PCT/EP2010/066581
Authority: WO
Inventors: Roman Zieba; Alexander Traut; Alexandra Seeber; Cornelia RÖGER-GÖPFERT; Bernd Smarsly; Torsten Brezesinski; Sebastien Sallard; Christoph Weidmann; Jan Haetge
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2009-11-09
Filing date: 2010-11-02
Publication date: 2011-05-12
Anticipated expiration: 2012-05-09

Abstract

The present invention relates to a process for preparing mesoporous materials comprising the following steps in the sequence of a-b-c-d: (a) providing at least one dispersion of metal oxide nanoparticles (A) in a solvent (C) and at least one block copolymer (B) and optionally a solid substrate (S), (b) combining the at least one dispersion of metal oxide nanoparticles (A) with the at least one block copolymer (B), (c) removing the solvent (C) thus yielding a composite material (K), and (d) removing the at least one copolymer (B) from said composite material (K), wherein the block copolymer (B) comprises at least one alkylene oxide block (AO) and at least one isobutylene block (IB). The present invention further relates to mesoporous materials thus obtainable, and to their use as an electrode material, in electronic components, sensors, and dye-sensitized solar cells. The present invention finally relates to electronic components and dye-sensitized solar cells comprising the mesoporous materials.

Description

Process for preparing mesoporous materials Description The present invention relates to a process for preparing mesoporous materials comprising the following steps in the sequence of a-b-c-d:

(a) providing at least one dispersion of metal oxide nanoparticles (A) in a solvent (C) and at least one block copolymer (B) and optionally a solid substrate (S),

(b) combining the at least one dispersion of metal oxide nanoparticles (A) with the at least one block copolymer (B),

(c) removing the solvent (C) thus yielding a composite material (K), and

(d) removing the at least one copolymer (B) from said composite material (K), wherein the block copolymer (B) comprises at least one alkylene oxide block (AO) and at least one isobutylene block (IB).

The present invention further relates to mesoporous materials thus obtainable, and to their use as an electrode material, in electronic components, sensors, and dye- sensitized solar cells. The present invention finally relates to electronic components and dye-sensitized solar cells comprising the mesoporous materials.

Mesoporous materials based on metal oxides have been developed for applications such as sensors, electrode materials and, due to the high specific surface area of mesoporous materials, catalysis. Conductive, semiconductive and dielectric transparent layers consisting of mesoporous metal oxides are of great significance for applications in electronics and optoelectronics, for example in displays, electronic paper, solar cells, touch panels and as electrode materials in fuel cells or in sensors.

The production of metal oxides by means of sol-gel processes and generation of corresponding layers is known from the prior art.

In contrast to silicas, which are frequently made by means of sol-gel processes under aqueous conditions, metal oxide materials are preferably synthesized in organic solvents, like alcohols, THF or chlorinated hydrocarbons in order to control hydrolytic and condensation processes of highly reactive metal salts. In this context, amphiphillic block copolymers have been proposed as templating agents because these block copolymers are able to form micelles even in non-polar solvents. To that end, block copolymers based on alkylene oxides have been used in the prior art.

A disadvantage of the known sol-gel based methods of making metal oxides is that the crystallinity of the metal oxide films has to be increased by calcining at high

temperature, which frequently leads to crack formation and in particular collapse of the mesoporous structure as well as to detachment of the films from the substrates.

Reducing the calcination temperature and/or increasing the stability of the mesporous structure of the materials would therefore be desirable. Methods of making mesoporous materials starting from molecular and non-crystalline precursors of metal oxides and formation of the mesostructure by means of templating agents, and subsequent thermal treatment and calcination at temperatures of more than 450°C are known from the prior art. This last step is particularly critical because the growing crystallites may destroy the mesoporous structure.

As an example, WO 99/37705 discloses that mesoscopically ordered oxide-block copolymer composites and mesoporous metal oxide films can be obtained by means of a sol-gel process starting from metal oxide precursors by using amphiphilic block copolymers in an aqueous medium. The block copolymers used are alkylene oxide block copolymers and EO-PO-EO triblock copolymers. The oxides thus obtainable include Ti0₂, Zr0₂, Si0₂, Al₂0₃, and Sn0₂.

A major disadvantage of the precursor-based methods is that the mesostructure frequently undergoes a breakdown during the final calcination step which is required to achieve the crystallinity and to remove the templating agent. The resulting ill-defined porosity is accompanied by deterioration of the electrical and physical properties.

The use of pre-formed colloidal solutions of metal oxides and their subsequent transformation into mesoporous materials in the presence of templating agents has also been reported in the prior art.

US 2003/0054954 A1 describes a process for preparing mesoporous materials starting from colloidal dispersions of nanoparticles which contain a templating agent.

Subsequently a solid composite material is formed and the templating agent is removed. As templating agents nonionic surfactants of the block copolymer type, in particular triblock copolymers according to the structure poly(ethylene oxide)- poly(propylene oxide)-poly(ethylene oxide), are used. The presence of water as a co- solvent is necessary in order to achieve micellar self assembly and formation of highly ordered mesoporous films.

Atul S. Desphande et. al., Small 2005, 1 , 313 describe the preparation of a

mesoporous Ce02 powder starting from a sol of Ce02 nanoparticles in ethanol/water. A hydrogenated polybutadiene-poly(ethylene oxide) block copolymer is used as structure-directing agent. A mesoporous Ce02 powder was obtained after calcination at 500°C. The use of water as a solvent or co-solvent is however disadvantageous because the removal of water is an energy-intensive process. The methods known from the prior art furthermore cannot generally be applied to a broad range of metal oxides but have rather been deveopled for a specific type of metal oxide which presents a disadvantage with respect to industrial applicability.

Jianhua Ba et al., Advanced Materials 2005, 17, 2509-2512 disclose the non-aqueous synthesis of tin oxide nanocrystals and their assembly into ordered porous

mesostructures. The authors used a non-aqueous sol-gel synthesis according to the benzyl alcohol route to produce monodisperse crystalline tin oxide nanoparticles sols followed by evaporation-induced self-assembly (EISA) from tetrahydrofuran (THF) under formation of the mesostructure. Polybutadiene-block-poly(ethylene oxide) copolymers are used as the template. Calcination according to this publication takes place at 500°C. However, many metal oxides are incompatible with the synthetic route disclosed in this publication. Mixtures of nanoparticles and the copolymers suggested as templating agents by the prior art frequently do not lead to transparent, optically clear solutions but rather precipitate upon addition of the copolymer. Transparent and optically clear solutions though are a pre-requisite for the preparation of transparent mesoporous films. Furthermore, the pore diameter of mesoporous materials obtained by methods of the prior art is too low for many applications.

The methods known from the prior art starting from nanoparticles are in particular not suited for the production of mesoporous antimony tin oxide (ATO).

It was an object of the present invention to avoid the disadvantages of the prior art outlined above. The mesoporous materials obtainable should have a stable mesoporous structure even at temperatures of 500°C or higher. A broad range of metal oxides should be obtainable in form of mesoporous materials using a procedure which is generally applicable to various metals. In particular, it was an object of the present invention to prepare conductive and semi-conductive oxides in the form of mesoporous transparent layers with the same or improved electrical properties. The temperature required for calcination of these films should be lower than in the prior art.

The process should substantially prevent an adverse deterioration of the mesostructure during the calcination. Furthermore, the formation of macroscopic cracks and detachment from the substrate during the crystallization should be avoided.

It was a particular object of the present invention to provide a method of making mesoporous metal oxide materials where the starting materials are used in organic solvents and the formation of the mesostructure takes place in the absence of water.

In particular, it was an object of the present invention to make it possible to obtain mesoporous transparent conductive and semi-conductive oxides as thin layers. In addition, the films should have good adhesion to a substrate and a homogeneous layer thickness in the context of customary application processes such as dip-coating. The layer thickness should additionally be adjustable precisely within the range from approx. 10 nm to approx. 100 microns. The films thus obtainable should exhibit a high transparency.

These objects are achieved by the process according to the invention and by the mesoporous materials thus obtainable.

Preferred embodiments are explained in detail in the claims and in the description which follows. Combinations of preferred embodiments, especially combinations of preferred embodiments of individual process steps, do not leave the scope of the present invention.

The process for preparing mesoporous materials according to the present invention comprises the following steps in the sequence of a-b-c-d:

(a) providing at least one dispersion of metal oxide nanoparticles (A) in a

solvent (C) and at least one block copolymer (B) and optionally a solid substrate (S),

(c) removing the solvent (C) thus yielding a composite material (K), and

The term "dispersion" denotes a stable dispersion of nanoparticles in a liquid. The liquid forming the liquid phase of the dispersion is referred to as "solvent". The term "nanoparticles" denotes particles with a number-weighted average particle diameter of below 100 nm, preferably from 0.5 to 100 nm, in particular from 1 to 50 nm, particularly preferred from 1 to 10 nm. The number average particle diameter of nanoparticles throughout the present invention is determined by means of analytical ultracentrifugation.

The term "metal oxide" throughout the present invention refers to pure or mixed metal oxides, i.e. to binary oxides containing one metal as well as to ternary or higher oxides. The same term also refers to pure oxides or mixed oxide/oxide hydrates. It is known to the person skilled in the art that metal oxides may contain -OH, -OR and/or H2O- ligands in addition to oxygen, in particular on the surface.

Mesoporous materials based on metal oxides are known to those skilled in the art as a substance class. The term "mesoporous" in the context of the present invention is used according to the lUPAC definition. A mesoporous structure is thus characterized by a number-weighted average pore diameter of from 2 to 50 nm.

Transparent conductive oxides and semi-conducting (wide band-gap) oxides are known to those skilled in the art as a substance classes as well. The term "transparent conductive oxides" in the context of the present invention denotes metal oxides which may be doped and/or may comprise extraneous atoms, and which satisfy the following criteria:

transmission at least 50% at a layer thickness of 100 nm and at a wavelength in the range from 380 nm to 780 nm to DIN 1349-2:1975;

- electrical conductivity at least 0.1 S-cnr¹ to DIN EN ISO 3915.

A transparent conductive oxide according to the present invention is additionally mesoporous. In the context of the present invention, the term "pore diameter" indicates the greatest diameter through the geometric center of a pore. The number-weighted average pore diameter is determined by means of transmission electron microscopy (TEM) and subsequent image analysis evaluation using at least 500 pores of a statistically representative sample.

The number-weighted average pore diameter of the mesoporous materials obtainable in accordance with the present invention is preferably from 10 to 45 nm, more preferably from 15 to 40 nm, especially from 20 to 35 nm.

The mesoporous materials preferred in accordance with the present invention may comprise both closed-cell and open-cell pores. Open-cell pores are capable of sorbing Kr in an adsorption measurement. The pores may have different geometry. In many cases, approximately spherical pores or pores of ellipsoidal form have been found to be suitable. The number-weighted average aspect ratio of the pores according to TEM is especially in the range from 1 to 4. When the mesoporous materials are present as a thin layer having a layer thickness in the range of 500 nm or less, an aspect ratio of from 1.2 to 3 is preferred. The mesoporous materials of the present invention are preferably crystalline.

"Crystalline" in the context of the present invention means that the proportion by mass of crystalline transparent conductive oxide relative to the total mass of transparent conductive oxide is at least 60%, preferably at least 70%, more preferably at least 80%, especially at least 90%, determined by means of X-ray diffraction (XRD).

In the context of the present invention, the crystallinity is determined by means of X-ray diffraction. In this case, the crystalline portion of the scattering is determined as a ratio to the total scatter of the sample.

The term "composite material" denotes a mixture of metal or semimetal oxide with an organic phase, in particular the at least one block copolymer (B).

The mesoporous materials according to the present invention are preferably selected from the group consisting of pure oxides or doped binary oxides and ternary oxides, where the ternary oxides may be doped. According to step (a) of the inventive method, at least one dispersion of metal oxide nanoparticles (A) in a solvent (C) and at least one block copolymer (B) and optionally a solid substrate (S) is provided. The metal oxides used in the present invention comprise at least one metal or semimetal (M). In principle, the method according to the invention is a general method for which any dispersion of metal oxide nanoparticles (A) can be used. Criteria characterizing suitable dispersions are outlined below. The at least one metal (M) is preferably selected from transition metals and main group metals provided that at least one metal (M) is neither an alkaline metal nor an earth alkaline metal.

Preferably the metal (M) comprises at least one metal selected from the group consisting of transition metals, Al, Sn, Sb, Pb, In, and Ba. It is particularly preferred if the at least one metal (M) is selected from the group consisting of Ti, Nb, Ta, Zr, Mn, Al, Fe, Cr, Sn, Sb, Pb, Ce, In, Ba and V. The at least one metal or semimetal M is particularly preferably selected from Sn, Zn, In and Cd.

If desired, doping elements M' such as Mg, Ca, Zn, Zr, V, Nb, Ta, Bi, Cr, Mo, W, Mn, Fe, Co, Ni, Pb, Ce, Sb, Al, Sn, In, Ga or mixtures thereof, preferably Mg, Ca, Cr, Fe, Co, Ni, Pb, Sb, Al, Sn, In, Ga or mixtures thereof, may be present.

The term "doping" is to be interpreted widely. It comprises both doping in the narrow sense, where the transparent conductive oxide comprises from 0.1 to 100 ppm of extraneous atoms as a result of the doping, and - this is especially preferred - doping in a wider sense, according to which the transparent conductive oxide is a mixed oxide which comprises the component which originates from the starting compound (A) to an extent of at least 50% by weight, preferably at least 70% by weight, especially at least 85% by weight. Accordingly, it is preferred when the mesoporous materials of the present invention comprise from 0.001 to 30% by weight, preferably from 0.01 to 20% by weight, especially from 0.1 to 15% by weight, of at least one doping element M', based on 100% by weight of all metals M and doping elements M'.

Doping elements M' for doping metal oxides are known to those skilled in the art. The person skilled in the art is aware that the use of doping elements M' leads to so-called mixed oxides which can in many cases lead to an increase in the electrical

conductivity. "Doping element" furthermore means that at least one M' is different from M. Useful doping elements M' include both metals or semimetals and nonmetals. "Doping element" in the context of the present invention is understood to mean that or those element(s) which is/are incorporated into the oxidic network as extraneous atoms.

As nonmetal doping element M' F, CI, Br and/or I are preferred. Particular preference is given to F. As metal or semimetal doping element M' is preferably selected from Al, Ga, B, Sb, Sn, Cd, Nb, Ta and In. The mesoporous materials of the present invention are preferably transparent conductive oxides (TCOs) or semi-conductor oxides. TCOs obtainable in accordance with the invention are preferably selected from the group consisting of ATO (Sb-doped tin oxide), ITO (Sn-doped indium oxide), Nb- and Ta-doped Sn02, F:ZnO, AhZnO, Ga:ZnO, B:ZnO, ln:ZnO, F:Sn02, Cd₂Sn0₄, Zn₂Sn0₄, Mgln₂0₄, CdSb₂Sn0₆:Y, ZnSn03, Galn0₃, Zn₂ln₂0₅, Galn03, ln Sn₃0i₂, Sn0₂, WO3, Ce0₂, aluminum oxide, iron oxide of the formula FeO_x where x may assume a value of from 1 to 1 .5, and SrTi03.

A transparent conductive oxide obtainable in accordance with the invention is most preferably antimony-doped tin oxide. Semi-conductive oxides are preferably selected from titanium dioxide and zinc oxide.

Preferably, the metal oxide nanoparticles (A) comprise at least one crystalline metal oxide. It is particularly preferred if the metal oxide nanoparticles (A) in the dispersion used in step (a) are crystalline.

As with the resulting mesopoprous materials, "crystalline" means that the proportion by mass of crystalline transparent conductive oxide relative to the total mass of transparent conductive oxide is at least 60%, preferably at least 70%, more preferably at least 80%, especially at least 90%, determined by means of X-ray diffraction (XRD).

Dispersions of metal oxide nanoparticles are known to the person skilled in the art or can be produced according to methods known from the prior art. The term "dispersion" refers to a stable dispersion of solid nanoparticles in a liquid dispersing agent which is referred to as a solvent.

In order to denote a suitable dispersion of metal oxide nanoparticles (A) in a solvent (C), the corresponding dispersions should satisfy at least one, preferably all of the following criteria:

the dispersion is free of aggregates and is therefore optically clear;

the dispersion exhibits a stability with respect to precipitation of at least 1 day, preferably at least 10 days, in particular at least 100 days at room temperature; - the number-weighted average particle diameter is from 0.5 to 50, in particular from 1 to 10 nm;

the dispersion shows no haze according to DIN EN ISO 15715:2006.

In the context of the present invention dispersions are free of aggregates, if the dispersions show no haze according to DIN EN ISO 15715:2006. For the purpose of the present invention, "no haze" shall mean an NTU (Nephelometric Turbidity Unit) or FTU (Formazine Turbidity Unit) according to DIN EN ISO 15715:2006, measurement angle 90°, of below 10, preferably of below 3, in particular of below 1 . In general, suitable dispersions of metal oxide nanoparticles (A) can be obtained by non-aqueous sol-gel synthesis, often called benzyl alcohol route due to the preferred use of benzyl alcohols for the non-aqueous synthesis. Methods for producing dispersions of metal oxide nanoparticles (A) according to a non-aqueous sol-gel synthesis are for instance described in M. Niederberger et al, Angew. Chem. Int. Ed. 2004, 43, 2270; M. Niederberger et al., Chem. Mater. 2004, 16, 1202; and unpublished European patent application EP09172909.5.

Particularly preferred dispersions of metal oxide nanoparticles (A) in a solvent (C) can be obtained according to a method of making metal oxide nanoparticles comprising the reaction of

at least one metal oxide precursor (P) containing at least one metal (M) with at least one monofunctional alcohol (Ale) wherein the hydroxy group is bound to a secondary, tertiary or oc-unsaturated carbon atom

in the presence of at least one aliphatic compound (F) according to the formula Y¹- ¹-X-R²-Y², wherein

R¹ and R² each are the same or different and independently selected from aliphatic groups with from 1 to 20 carbon atoms,

Y¹ and Y² each are the same or different and independently selected from OH, NH₂ and SH, and

- X is selected from the group consisting of chemical bond, -0-, -S-, -N R3-, and -CR⁴R⁵, wherein R³, R⁴ and R⁵ each are the same or different and represent a hydrogen atom or an aliphatic group with from 1 to 20 carbon atoms which optionally carries functional groups selected from OH, NH2 and SH;

and subsequently re-dispersing the metal oxide nanoparticles (A) so obtained in a suitable solvent (C).

This method of making particularly preferred dispersions of metal oxide nanoparticles (A) in the following is referred to as "method F" referring to the use of at least one aliphatic compound (F). Method F is known from the unpublished European patent application EP09172909.5. The content of EP09172909.5 is herewith incorporated by reference.

In the context of method F at least one metal oxide precursor (P) containing at least one metal (M) is used. The term "metal oxide precursor" refers to a metal compound which is convertible into metal oxides by means of hydrolysis, solvolysis, and/or thermal treatment. Such metal oxide precursors are known to the person skilled in the art. Method F is a general method which can be applied to the metal oxide useful for the present invention. The at least one metal (M) therefore has the same meaning as defined above. In the context of method F, preferred metal oxide precursors (P) are ionic metal compounds containing at least one metal cation and at least one anionic group frequently referred to as anion and/or ionic ligand. The precursors (P) may in addition contain non-ionic ligands. The metal oxide precursors (P) may in particular contain at least one non-ionic ligand selected from water, alcohols, in particular methanol, ethanol, isopropanol, dimethoxyethane, acetylacetone and pentanedione.

Preferred anionic groups are halides, in particular chloride or bromide, sulphates, phosphates, nitrates, carbonates, carboxylates, acetylacetonates, acetylacetates, alkoxides, in particular methoxide, ethoxide, isopropoxide, n-butoxide, iso-butoxide or tert.-butoxide and mixtures thereof. Suitable metal oxide precursors (P) may contain one sort of anionic group or two or more different anionic groups. The selection of anionic groups depends on the nature of the at least one metal (M) as well as on the nature of the alcohol (Ale). Suitable ligands are outlined in EP09172909.5 on page 5, line 14 to line 37.

Alkoxides are preferred precursors in the context of method F. Suitable alkoxides are in particular Ci-Cs-alkoxides, preferably Ci-Cs-alkoxides such as methoxides, ethoxides, n-propoxides, isopropoxides, n-butoxides, isobutoxides, sec-butoxides, tert-butoxides, n-pentoxides and isopentoxides. Particularly preferred are Ci-C4-alkoxides such as methoxides, ethoxides, n-propoxides, isopropoxides, n-butoxides, isobutoxides, sec- butoxides and tert-butoxides, in particular n-propoxides, isopropoxides, n-butoxides and isobutoxides, or mixtures thereof.

The function of the alcohol (Ale) in the context of method F is to serve as a source of oxygen for the formation of metal oxides, as reaction medium and as a dispersing liquid (referred to as a solvent). The term "monofunctional" refers to the presence of one hydroxyl group.

In principle, any monofunctional alcohol (Ale) as defined above can be used in the context of method F provided it serves as a source of oxygen during the formation of the metal oxide. It is preferred to use alcohols in which the hydroxyl group is attached to an organic rest which is capable of forming stabilized carbocations.

In the context of method F, suitable monofunctional alcohols (Ale) include benzyl alcohol, benzyl alcohols substituted in the aromatic ring, secondary alcohols such as isopropanol or higher homologues, and tertiary alcohols such as tert-butylacohol or pinacol (1 , 1 ,2,2-tetramethylethylene glycol). Preferred monofunctional alcohols (Ale) are aliphatic alcohols with from 4 to 30 carbon atoms with the hydroxyl group bound to a tertiary or benzylic carbon atom. Correspondingly the monofunctional alcohol (Ale) is advantageously a compound according to the formula R⁶-OH, wherein R⁶ is selected from tertiary alkyl groups with from 4 to 20 carbons atoms and benzylic groups with from 7 to 30 carbon atoms.

The term "benzylic group" and correspondingly "benzylic carbon atom", in accordance to the l UPAC Compendium of Chemical Terminology 2nd Edition (1997), refers to arylmethyl groups and their derivatives formed by substitution according to the general structure ArCR2- wherein each R independently represents hydrogen or a linear or branched aliphatic group or an aromatic group. Benzyl, C6H5CH2-, is the most preferred benzylic group. It is particularly preferred to use benzyl alcohol as the monofunctional alcohol (Ale). With respect to component (F) in the context of method F, preferably at least one of Y¹ and Y² represents OH and very preferably both, Y¹ and Y², represent OH. It is preferred if Y¹ and Y² are in 1 ,3-position to each other. According to a first preferred embodiment of method F, X represents an oxygen atom. Preferred compounds (F) with X = O are glycol ethers (X = O and Y¹ = Y² = OH).

Suitable glycol ethers are known to the person skilled in the art. Preferred glycol ethers are for example described in EP09172909.5 on page 13, line 31 to page 14, line 16. Glycol ethers with two hydroxyl groups (Y¹ = Y² = OH) in 1 ,3-position are preferred.

According to a second preferred embodiment of method F, X represents a sulfur atom. If X = S then bis-(2-chloroalkyl)sulfides are particularly preferred and bis-(2- chloroethyl)sulfide is very particularly preferred.

According to a third preferred embodiment of method F, X is selected from NH and NR³ with R³ having the meaning as defined above. If X = NH then diethanol amine is particularly preferred. If X = NR³ then triethanol amine is particularly preferred.

According to yet another preferred embodiment of method F, which is particularly preferred, X represents a chemical bond. It is advantageous if X is a chemical bond and Y¹ and Y² are in 1 ,3-position to each other. Preferably at least one of Y¹ and Y² represents OH and very preferably both, Y¹ and Y², each represent OH and at the same time X = chemical bond.

In the contect of method F, suitable at least bifunctional alcohols (Y¹ = Y² = OH and X = chemical bond) preferably contain from two to five hydroxyl groups. Examples are C2- C6-alkylene glycols and the corresponding di- and polyalkylene glycols, such as ethylene glycol (1 ,2-ethane diol), 1 ,2-propylene glycol (1 ,2-propane diol), 1 ,3-propane diol, 1 ,2-butylene glycol, 1 ,4-butylene glycol, 1 ,6-hexylene glycol, dipropylene glycol, glycerol and pentaerythritol as well as 1 ,2,3,4,5,6 - hexahydroxyhexane and sugars.

The function of the aliphatic compound (F) is to serve as a surface modifying agent for the metal oxide nanoparticles. Its use offers several advantages, one of which is to stabilize the surface of the nanoparticles and prevent their agglomeration during a subsequent re-dispersion. Another advantage is the significant improvement with respect to the speed and quantity of re-dispersability of the metal oxide nanoparticles.

In a very particularly preferred embodiment, method F as outlined above is used and the aliphatic compound (F) is 1 ,3-propane diol. A particularly preferred embodiment of method F - which is particularly advantageous for the present invention - comprises the following steps:

(a^*) mixing of the at least one metal precursor (P), the at least one alcohol (Ale), and the at least one aliphatic compound (F) where the components (P), (A) and (F) have the meaning as defined above,

(b^*) heating the mixture to a temperature of from 40 to 200°C and

(c^*) obtaining the metal oxide nanoparticles as a solid compound, and

(d^*) redispersing said metal oxide nanoparticles in a solvent, preferably an organic solvent, particularly preferably a polar organic solvent.

Preferred embodiments of steps (a^*), (b^*), (c^*), and (d^*) are known from EP09172909.5 and described on page 8, line 36 to page 14, line 34 therein. Step (d^*) in the context of method F is preferably applied subsequently to steps (a^*) to (c^*) as outlined above but can be applied to any solid nanoparticles suitable for the present invention.

In the context of method F, re-dispersion according to step (d^*) can be applied subsequently to steps (a^*) to (c^*) without previous drying of the nanoparticles obtained in step (c^*). Alternatively, the nanoparticulate metal oxide according to the invention can be dried under mild conditions, preferably at a temperature of from 20°C to 80°C, in particular from 40°C to 60°C, before applying step (d^*). The drying can take place at atmospheric pressure or under vacuum. The drying can take place under air or under an inert gas if required.

Preferred solvents for re-dispersing the metal oxide nanoparticles in the context of method F are identical to those which are preferred solvents (C) for the present invention.

Methods of re-dispersing metal oxide nanoparticles are known to the person skilled in the art.

The use of dispersions of nanoparticles obtained by means of method F in combination with the method according to the present invention leads to mesoporous materials with particularly high transparency. Block copolymer (B)

According to the invention, the block copolymer (B) comprises at least one alkylene oxide block (AO) and at least one isobutylene block (IB). The individual blocks of the block copolymer (B) are joined to one another by means of suitable linking groups.

The linking groups may be either functional organic groups or individual atoms.

Typically, the linking groups used are those which lead to a linear linkage. The linking groups may also have three or more than three linkage sites and thus lead to star- shaped block copolymers.

In practical terms, the linkage is effected typically by functionalizing polyisobutylene and then reacting with alkylene oxide or alkylene oxide blocks. Preferred functionalized polyisobutylenes and preferred preparation methods for the block copolymers (B) used in accordance with the invention are described below.

The alkylene oxide blocks (AO) and the isobutylene oxide blocks (IB) may each independently be linear or else have branches. They are preferably each linear. The (IB) and/or (AO) blocks may be arranged terminally, i.e. be connected only to one other block, or else they may be connected to two or more other blocks. The (IB) and (AO) blocks may, for example, be joined to one another in alternating arrangement with one another in a linear manner. In principle, any number of blocks can be used. In general, however, not more than 8 (IB) and (AO) blocks in each case are present. This results in the simplest case in a diblock copolymer of the general formula AB. The copolymers may also be triblock copolymers of the general formula ABA or BAB. It is of course also possible for several blocks to follow one another in succession, for example ABAB, BABA, ABABA, BABAB or ABABAB. In addition, the copolymers may be star-shaped and/or branched block copolymers or else comblike block copolymers in which, in each case, more than two (IB) blocks are bonded to one (AO) block or more than two (AO) blocks are bonded to one (IB) block. For example, the copolymers may be block copolymers of the general formula AB_m or BAm, where m is a natural number > 3, preferably from 3 to 6 and more preferably 3 or 4. Of course, it is also possible for a plurality of A and B blocks to follow one another in the arms or branches, for example A(BA)_m or B(AB)_m. Such block copolymers (B) are known to those skilled in the art or can be prepared by means of known processes.

Preferably, the block copolymer (B) comprises at least one alkylene oxide block (AO) and at least one isobutylene block (IB), where the number-weighted average block length of the alkylene oxide block or blocks (AO) is from 4 to 300 monomer units and the number-weighted average block length of the isobutylene block or blocks (IB) is from 5 to 300 monomer units.

Preferably, the reaction in step (a) of the process according to the invention is performed in the presence of at least one diblock copolymer (B) consisting of an alkylene oxide block (AO) and an isobutylene block (IB), i.e. the block copolymer (B) a diblock copolymer of the general structure AO-IB. The number-weighted average block lengths of the alkylene oxide blocks (AO) and of the isobutylene blocks (IB) in the aforementioned block copolymers (B) are each independently more preferably from 10 to 300 monomer units, especially from 20 to 250 monomer units, most preferably from 30 to 200 monomer units. The number- weighted average block length (via number-average molecular weight Mn) of the isobutylene blocks (IB) used and the number-average molecular weight Mn of the block copolymer obtained are determined in each case by means of gel permeation chromatography (GPC) with THF as the eluent against a polystyrene standard with a highly crosslinked styrene-divinylbenzene resin as the stationary phase. The number- weighted average block length of the alkylene oxide blocks (AO) is determined therefrom by methods known to those skilled in the art.

In a particularly preferred embodiment, the number-weighted average block length of the isobutylene blocks (IB) is from 90 to 200 monomer units and the number-weighted average block length of the alkylene oxide blocks (AO) from 80 to 200 monomer units. The block copolymer (B) is most preferably a diblock copolymer of the general structure AO-IB. The person skilled in the art determines preferred number-weighted average molecular weights from the aforementioned preferred block lengths by conversion using the known molecular weight of a monomer unit.

It has been found to be advantageous when the block copolymer (B) is of

inhomogeneous structure with regard to its molecular weight. Without being restricted to the validity of theoretical considerations, there is the perception that block copolymer molecules with comparatively low molecular weight behave as a surface-active assistant synergistically to the block copolymer molecules with a comparatively high molecular weight, thus promoting the formation of the mesostructure. It is preferred that the polydispersity index (PDI) of the block copolymer (B), which is defined as the ratio of weight-average and number-average molecular weight M_w/M_n, is from 1 .2 to 30, more preferably from 1.5 to 25, especially preferably from 2 to 20, most preferably from 4 to 15. In particular, it has been found to be advantageous, in the case of block copolymers with a high average molecular weight, simultaneously to use those with a high PDI. Accordingly, it is most preferred when the number-weighted average block length of the isobutylene blocks (IB) in the block copolymer (B) is from 90 to 200 monomer units, and the number-weighted average block length of the alkylene oxide blocks (AO) is from 80 to 200 monomer units, and the PDI of the block copolymer (B) is from 4 to 20.

The PDI of the block copolymer (B) is determined as Mw/Mn by means of gel permeation chromatography (GPC) with THF as the eluent against a polystyrene standard with a highly crosslinked styrene-divinylbenzene resin as the stationary phase. The determination of the polydispersity index (PDI) is described in general form, for example, in Analytiker-Taschenbuch [Analyst's Handbook], Volume 4, page 433 to 442, Berlin 1984.

The isobutylene blocks (IB) are referred to as such when the repeat units of the polymer block are at least 80% by weight, preferably at least 90% by weight, isobutene units, not counting the end groups and linking groups among the repeat units.

The isobutylene blocks (IB) are obtainable by polymerizing isobutene. However, the blocks may also comprise other comonomers as structural units to a minor degree. Such structural units can be used for fine control of the properties of the block.

Comonomers which should be mentioned are, as well as 1 -butene and cis- or trans-2- butene, especially isoolefins having from 5 to 10 carbon atoms such as 2-methyl-1 - butene-1 , 2-methyl-1-pentene, 2-methyl-1-hexene, 2-ethyl-1-pentene, 2-ethyl-1 -hexene and 2-propyl-1 -heptene, or vinylaromatics such as styrene and a-methylstyrene, C1-C4- alkylstyrenes such as 2-, 3- and 4-methylstyrene, and 4-tert-butylstyrene.

The proportion of such comonomers should, however, not be too great. In general, the amount thereof should not exceed 20% by weight based on the amount of all structural units of the block. The blocks may, as well as the isobutene units and comonomers, also comprise the initiator or starter molecules used to start the polymerization or fragments thereof. The polyisobutylenes thus prepared may be linear, branched or star-shaped. They may have functional groups only at one chain end or else at two or more chain ends.

The starting materials for the preparation of block copolymers (B) comprising isobutylene blocks (IB) are preferably functionalized polyisobutylenes. Functionalized polyisobutylenes can be prepared proceeding reactive polyisobutylenes, by providing them with functional groups in single-stage or multistage reactions known in principle to those skilled in the art. Reactive polyisobutylene is understood by those skilled in the art to mean polyisobutylene which has a high proportion of terminal alpha-olefin end groups. The preparation of reactive polyisobutylenes is likewise known and is described, for example, in detail in WO 04/9654, pages 4 to 8, and in WO 04/35635, pages 6 to 10.

Preferred embodiments of the functionalization of reactive polyisobutylene comprise: i) reaction with aromatic hydroxyl compounds in the presence of an alkylation

catalyst to obtain aromatic hydroxyl compounds alkylated with polyisobutylenes, ii) reaction of the polyisobutylene block with a peroxy compound to obtain an

epoxidized polyisobutylene, iii) reaction of the polyisobutylene block with an alkene which has a double bond substituted by electron-withdrawing groups (enophile), in an ene reaction, iv) reaction of the polyisobutylene block with carbon monoxide and hydrogen in the presence of a hydroformylation catalyst to obtain a hydroformylated

polyisobutylene, v) reaction of the polyisobutylene block with a phosphorus halide or a phosphorus oxychloride to obtain a polyisobutylene functionalized with phosphone groups, vi) reaction of the polyisobutylene block with a borane and subsequent oxidative cleavage to obtain a hydroxylated polyisobutylene, vii) reaction of the polyisobutylene block with an SO3 source, preferably acetyl sulfate or oleum, to obtain a polyisobutylene with terminal sulfonic acid groups, viii) reaction of the polyisobutylene block with nitrogen oxides and subsequent

hydrogenation to obtain a polyisobutylene with terminal amino groups.

With regard to all details of the performance of the reactions mentioned, we refer to the remarks in WO 04/35635, pages 1 1 to 27. Particular preference is given to embodiment i), particular preference being given to phenol as the aromatic hydroxyl compound, and to embodiment iii). In the context of iii), very particular preference is given to using maleic anhydride for the reaction. This results in polyisobutenes functionalized with succinic anhydride groups

(polyisobutenylsuccinic anhydride, PIBSA).

The alkylene oxide blocks (AO) are referred to as such when the repeat units of the polymer block are at least 70% by weight, preferably at least 80% by weight, alkylene oxide units, not counting the end groups and linking groups among the repeat units. Alkylene oxide units are, in a manner known in principle, units of the general formula -R¹-0-. In this formula, R¹ is a divalent aliphatic hydrocarbon radical which may optionally have further substituents. Additional substituents on the R¹ radical may especially be O-containing groups, for example >C=0 groups or OH groups. An alkylene oxide block (AO) may of course also comprise several different alkyleneoxy units.

The alkylene oxide units may especially be -(CH₂)₂-0- -(CH₂)3-0- -(CH₂)₄-0- -CH₂-CH(R2)-0-, -CH₂-CHOR³-CH₂-0-, where R² is an alkyl group, especially Ci-C₂4-alkyl, or an aryl group, especially phenyl, and R³ is a group selected from the group of hydrogen, Ci-C₂₄-alkyl, R¹-C(=0)- and R¹-NH-C(=0)-.

The alkylene oxide blocks (AO) may also comprise further structural units, for example ester groups, carbonate groups or amino groups. They may further also comprise the initiator or starter molecules used to start the polymerization, or fragments thereof. Examples comprise terminal R²-0- groups where R² is as defined above.

The alkylene oxide blocks (AO) preferably comprise, as main components, ethylene oxide units -(CH₂)2-0- and/or propylene oxide units -CH2-CH(CH3)-0, while higher alkylene oxide units, i.e. those having more than 3 carbon atoms, are present only in minor amounts for fine adjustment of the properties. The blocks may be random copolymers, gradient copolymers, alternating copolymers or block copolymers composed of ethylene oxide and propylene oxide units. The amount of higher alkylene oxide units should not exceed 10% by weight, preferably 5% by weight. They are preferably blocks which comprise at least 50% by weight of ethylene oxide units, preferably 75% by weight and more preferably at least 90% by weight of ethylene oxide units. They are most preferably pure polyoxyethylene blocks (AO).

The alkylene oxide blocks (AO) are obtainable in a manner known in principle, for example by polymerizing alkylene oxides and/or cyclic ethers having at least 3 carbon atoms and optionally further components. They can additionally also be prepared by polycondensing di- and/or polyalcohols, suitable starters and optionally further monomeric components.

Examples of suitable alkylene oxides as monomers for the alkylene oxide blocks (AO) comprise ethylene oxide and propylene oxide, and also 1 -butene oxide, 2,3-butene oxide, 2-methyl-1 ,2-propene oxide (isobutene oxide), 1 -pentene oxide, 2,3-pentene oxide, 2-methyl-1 ,2-butene oxide, 3-methyl-1 ,2-butene oxide, 2,3-hexene oxide, 3,4- hexene oxide, 2-methyl-1 ,2-pentene oxide, 2-ethyl-1 ,2-butene oxide, 3-methyl-1 ,2- pentene oxide, decene oxide, 4-methyl-1 ,2-pentene oxide, styrene oxide or a mixture of oxides of industrially available raffinate streams. Examples of cyclic ethers comprise especially tetrahydrofuran. It will be appreciated that it is also possible to use mixtures of different alkylene oxides. According to the desired properties of the block, the person skilled in the art makes a suitable selection among the monomers and further components.

The alkylene oxide blocks (AO) may also be branched or star-shaped. Such blocks are obtainable by using starter molecules having at least 3 arms. Examples of suitable starters comprise glycerol, trimethylolpropane, pentaerythritol or ethylenediamine.

The synthesis of alkylene oxide units is known to those skilled in the art. Details are described comprehensively, for example, in "Polyoxyalkylenes" in Ullmann's

Encyclopedia of Industrial Chemistry, 6^th Edition, Electronic Release.

The synthesis of the block copolymers (B) used in accordance with the invention can preferably be undertaken by first separately preparing the alkylene oxide blocks (AO) and reacting them in a polymer-analogous reaction with the functionalized

polyisobutenes to form block copolymers (B). The structural units for the isobutylene blocks (IB) and for the alkylene oxide blocks (AO) in this context have complementary functional groups, i.e. groups which can react with one another to form linking groups.

The functional groups of the (AO) blocks are, by their nature, preferably OH groups, but they may, for example, also be primary or secondary amino groups. OH groups are particularly suitable as complementary groups for reaction with PIBSA.

In a further embodiment of the invention, the synthesis of the blocks can also be undertaken by reacting polyisobutylenes having polar functional groups (i.e. IB blocks) directly with alkylene oxides to form (AO) blocks.

The structure of the block copolymers used in accordance with the invention can be influenced through selection of type and amount of the starting materials for the (IB) and (AO) blocks, and of the reaction conditions, especially of the sequence of addition.

The possible syntheses are described hereinafter by way of example for OH groups and succinic anhydride groups (referred to as S), without any intention that the invention thus be restricted to the use of such functional groups.

HO-[B]-OH hydrophilic blocks which have two OH groups

[B]-OH hydrophilic blocks which have only one OH group

[B]-(OH) ΐ_:χ hydrophilic blocks having x OH groups (x > 3)

[A]-S polyisobutene with a terminal S group

S-[A]-S polyisobutene with two terminal S groups

[A]-Sy polyisobutene with y S groups (y

The OH groups can, in a manner known in principle, using the succinic anhydrid groups S, be linked to one another to form ester groups. The reaction can, for example, be undertaken in bulk while heating. Suitable reaction temperatures are, for example, from 80 to 150°C. Triblock copolymers A-B-A are obtained, for example, in a simple manner by reacting one equivalent of HO-[B]-OH with two equivalents of [A]-S. This is shown by way of example hereinafter with complete formulae. One example is the reaction of PIBSA and a polyethylene glycol:

In this scheme, n and m are each independently natural numbers. They are selected by the person skilled in the art such that the block lengths defined at the outset for the (IB) and (AO) blocks are obtained.

Star-shaped or branched block copolymers BA_X can be obtained by reacting [B]-(OH)_x with x equivalents of [A]-S.

Block copolymers (B) which are particularly preferred for use in the process according to the invention are:

phenol alkylated with polyisobutylene, which is reacted with alkoxide, especially ethylene oxide,

polyisobutylene with terminal amino groups, which is reacted with alkoxide, especially ethylene oxide, and

- PIBSA, which is reacted with an alkylene oxide block, especially polyethylene oxide.

For the person skilled in the art in the field of polyisobutenes, it is clear that the resulting block copolymers, according to the preparation conditions, may also still have residues of starting materials. Moreover, they may be mixtures of different products. Triblock copolymers of the formula ABA may, for example, also comprise diblock copolymers AB, and also functionalized and unfunctionalized polyisobutene.

Advantageously, these products can be used for the application without further purification. However, it will be appreciated that the products can also be purified. The person skilled in the art is aware of suitable purification methods.

Solvent (C) The term "solvent" denotes a liquid forming the liquid phase of the dispersion. A solvent according to the present invention can consist of one compound or can be a mixture of two or more than two compounds.

Preferably, solvent (C) is a polar organic solvent or mixture of solvents, in particular at least one polar organic solvent with a boiling point of below 90°C. In principle, any polar organic solvent is suitable, in particular aliphatic polar organic solvents. Suitable aliphatic polar organic solvents include alcohols such as ethanol and methanol, ketones such as acetone, ethers such as tetrahydrofuran or halogenated

hydrocarbons.

Preferred aliphatic alcohols are monoalcohols with from 1 to 4 carbon atoms, in particular ethanol and/or methanol and/or methoxyethanol, particularly preferred ethanol and/or methanol. Preferred cyclic ethers are tetrahydrofurane and dioxane. Ethanol, methanol and/or tetrahydrofurane are very particularly preferred. Mixtures of two or more than two of the before mentioned solvents solvents are suitable, too.

Preferably the solvent (C) comprises at least one compound selected from the group consisting of aliphatic alcohols and aliphatic or cyclic ethers. The solvent (C) is more preferably selected from ethanol, methanol, tetrahydrofuran or a mixture of two or all of these solvents. The solvent (C) is most preferably ethanol.

Preferably, the solvent (C) is non-aqueous. The term "non-aqueous" denotes a water content of 1 % by weight or less, in particular 0,5 % by weight or less, particularly preferred 0,1 % by weight or less, determined by Karl-Fischer-titration.

Substrate (S) Suitable substrates (S) are especially those which satisfy the following requirements: thermal stability at temperatures of up to 600°C, preferably up to 900°C stability toward organic solvents

oxidation stability under the conditions of step (d).

In addition, the selection of the substrate (S) is determined by the later use.

Useful substrates include especially metals, silicon wafers, glass and other polar, thermally stable surfaces, preference being given to substrates (S) based on glass, silicon, ceramic or metals.

The three-dimensional form of the substrate can vary over a broad range. Preferably, the substrate is flat in one dimension and has at least one plane area. Step (b)

Step (b) according to the invention comprises combining the at least one dispersion of metal oxide nanoparticles (A) with the at least one block copolymer (B). The mass ratio between the at least one block copolymer (B) and the metal oxide nanoparticles (A) is preferably from 0.5 : 1 to 1.5 : 1 , in particular from 0.9 : 1 to 1.2 : 1 , particularly preferred from 1 .05 : 1 to 1.15 : 1.

The combination can be performed by many different means known to the person skilled in the art. Preferred methods of combining the at least one dispersion of metal oxide nanoparticles (A) with the at least one block copolymer (B) is mixing, in particular mixing under stirring. In the most preferred embodiment, solution of the surfactant in a solvent is added into the dispersion of metal oxides nanoparticles in the same solvent under stirring at room temperature. The solvents do not have to be the same but should be miscible.

The sequence of mixing doesn't play a major role. It is possible to add the at least one copolymer (B) to the dispersion or to add the dispersion to the at least one copolymer. It is advantageous if the copolymer or the copolymers are pre-solved in a solvent, preferably a solvent which is miscible with the solvent (C). Preferably the at least one copolymer (B) is pre-solved and/or pre-mixed in the solvent (C) prior to the combination of the copolymer and the dispersion of nanoparticles (A). The resulting solution can optionally be kept at a temperature from 15°C to 50°C for 1 to 24 hours, preferably at room temperature for 1 hour. Step (c)

According to the invention, step (c) comprises removing the solvent (C) thus yielding a composite material (K). The step of removing the solvent (C) may be preceded by steps influencing the form in which the composite material (K) is obtained, for instance steps preparing the formation of the composite material (K) as a film and/or coating on a substrate. The terms "film" and "coating" are used synonymously.

In a preferred embodiment, step (c) is preceded by step (c-pre) comprising applying the mixture obtained in step (b) on the solid substrate (S), preferably as a coating and/or film. During step (c-pre), the solvent may already be partly removed. Consequently, after step (b) and prior to complete removal of the solvent (C), the mixture obtained in step (b) is preferably applied to a substrate (S).

Processes for applying liquid or viscous precursor solutions of the composite material (K) to a substrate (S) are in principle known to those skilled in the art. Well-known processes such as application by immersion (especially dip-coating), application by spraying (especially spray coating), application by evaporation of the solvent, application with rotation (especially spin-coating), and printing processes are suitable. Preference is given to the application by means of coating methods.

Advantageous processes for applying layers are those which enable a controllable and simultaneously homogeneous layer thickness in the range from 10 to 500 nm. The mixture obtained in step (b) is preferably applied to a substrate (S) as a layer by dipping, spraying, spin-coating or printing, preferably under controlled air humidity. Another method of film preparation is raking preferably under controlled air humidity.

In cases which involve the removal of the substrate from a reservoir such as dip- coating, the speed of drawing of the substrate form the solution can be adjusted according to the film thickness desired and typically lies in the range 50 - 1200 mm/min, in the preferred case 400 - 800 mm/min.

The solvent (C) can be removed by many different means known to the person skilled in the art in pinciple, for instance drying and/or evaporation, for instance at increased temperature. In a preferred embodiment of step (c), the solvent (C) is removed in the presence of the substrate (S). Step (c) is performed preferably at a temperature of from 10 to 35°C, especially from 15 to 30°C, more preferably from 20 to 25°C.

Step (c) is performed preferably at a relative air humidity of from 1 to 80%, more preferably from 5 to 70%, most preferably from 10 to 60%, at a temperature of preferably from 15 to 30°C and more preferably from 20 to 25°C. The air humidity during step (c) can be determined, for example, with commercial hygrometers.

Preference is given to impedance and capacitive hygrometers. The term "air humidity" relates to the atmosphere surrounding the forming composite material (K) during step (c).

A higher air humidity than that specified above has been found to be less preferred and frequently leads, after performance of step (d), to a lower adhesion of the mesoporous material on the substrate and to the potential formation of macroscopic cracks. A lower humidity than that specified above, on the other side, may lead to a less preferable porous structure.

The composite material (K) is preferably obtained in the form of a film on a substrate (S) with a thickness of from 10 to 100000 nm. Step (d)

According to the invention step (d) comprises removing the at least one copolymer (B) from the composite material (K). In order to transform the non-porous composite material (K) into the mesoporous material according to the invention, the organic phase of the composite material needs to be removed. The removal of the block copolymer (B) is known to the person skilled in the art in principle. Possible means for removing the block copolymer (B) are application of increased temperature (which is preferred), etching, washing, and maceration.

In a preferred embodiment, step (d) comprises applying a temperature of from 100 to 600 °C to said composite material (K), in particular from 200 to 550°C. In step (d) the composite material (K) is preferably heated to a temperature of at least 350°C.

Preferably, the material (K) is pre-heated (dryed) at temperatures of from 40 to 200°C, more preferably from 60 to 120°C, in the most preferred embodiment at 80°C. At the same time, in step (d), the composite material (K) is preferably heated such that the maximum temperature does not exceed 600°C. The person skilled in the art refers to the heating of a composite material to a temperature of at least 350°C typically as "calcination". Step (d) is preferably performed in the presence of air and/or in the presence of oxygen. Calcination in the presence of oxygen leads to advantageous and complete development of a porous oxidic network.

In the process according to the invention, step (d) is preferably performed by heat treatment in at least two stages, a first stage (d1 ) involving exposure of the composite material (K) to a temperature of from 80 to 200°C for a time period of from 1 to 24 hours, and a further stage (d2) involving exposure to a temperature of from 350 to 600°C for a period of from 1 to 5 hours. In a particularly preferred embodiment, step (d1 ) itself is performed in two steps, first (d1 -a) heat treatment at a temperature of 60°C to 100°C for a period of time from 30 minutes to 2 hours and then (d1 -b) heat treatment at a temperature of from 250°C to 350°C for a time period of from 1 hour to 48 hours, in particular from 10 hours to 24 hours. The temperature rise between step (d1 -a) and step (d1 -b) is preferably achieved by steady increase of temperature within a period of from 1 hour to 5 hours, preferably 2 hours to 4 hours.

The temperature rise between step (d1 ) and step (d2) is preferably achieved by means of a heating rate from 2°C o 4°C per minute, preferably 3°C per minute.

The person skilled in the art refers to step (d1 ) typically as aging and to step (d2) typically as calcination. These terms are used hereinafter to characterize process steps (d1 ) and (d2) respectively, or, when the heat treatment is not performed in at least two stages according to the above-described preferred embodiment, the term "calcination" is used to characterize the employment of a temperature of at least 350°C.

"Aging" is understood to mean that the degree of crosslinking of the oxidic network is increased further and/or the number of reactive groups at the surface of the porous oxidic network is reduced. Preferably, in step (d1 ), the degree of crosslinking of the oxidic network of the composite material (K) is increased. In the course of calcination, the block copolymer (B) is removed from the composite material (K). Furthermore, in the course of calcination, crystallinity of the transparent conductive oxide may be increased.

The two-stage version of step (d) is preferred especially in connection with step (c), which involves application to a substrate (S).

It has been found to be advantageous to strictly control the rise in the temperature within step (d). Slow heating is of significance especially from a temperature of 200°C, since high stresses occur in the solid in the case of excessively rapid progress of aging and crystallization, which can lead to undesired degradation of the mesostructure. Moreover, there is the risk of excessively large primary crystals if the temperature is increased too rapidly proceeding from 200°C.

Heating rates of from 0.1 K to 20 K per minute have been found to be suitable.

However, it is preferred when, proceeding from a temperature of 200°C, the maximum temperature in step (d) is attained by employing a heating rate of at most 5 K/min. Below 200°C, the heating rate is less critical. It is, however, preferred to employ the abovementioned heating rates also within the temperature range of up to 200°C. Suitable means of heat treating the composite material (K) are known to those skilled in the art and are not subject to any particular restriction, provided that they enable compliance with the abovementioned conditions. Suitable equipment is, for example, heating ovens with temperature control. It is possible, for example, to use customary high-temperature, tubular, calcining or muffle furnaces. The temperature is monitored preferably by means of suitable monitoring equipment, which enables establishment and control of start and target temperatures, of heating rates and of temperature hold times.

Step (e)

It has also been found to be advantageous, after step (d), to thermally treat the resulting specimens in the presence of an oxygen-free atmosphere, preferably consisting of nitrogen or of a mixture of nitrogen and hydrogen. In many cases, this allows the conductivity of the transparent conductive oxides to be improved further.

Accordingly, preference is given to performing, after step (d), as step (e), a thermal aftertreatment of the resulting material at a temperature of from 200 to 600°C, especially from 250 to 450°C, with exclusion of oxygen. The thermal aftertreatment is effected preferably under an atmosphere composed of nitrogen or of a mixture of nitrogen and hydrogen. The temperature may remain constant or vary within a temperature program.

Step (e) can be employed by heating the fully or partly cooled material after step (d), or the already heated material is used directly in step (e).

If step (e) is carried out, it is preferable to increase the temperature by a heating rate of at most 20 K/min, especially at most 15 K/min.

When a thermal aftertreatment is carried out after step (e), the duration of the thermal aftertreatment may vary over a long period, which may be a few minutes or several hours. Preference is given to effecting the thermal aftertreatment in step (e) over a period of from 5 minutes to 3 hours, especially from 15 minutes to 1 hour.

Preferably, the mesoporous materials obtainable by means of the present invention are transparent conductive oxides, semi-conductive oxides or dielectrics. The mesoporous materials obtainable in accordance with the invention are suitable, inter alia, for applications in the sector of electronics, optoelectronics, displays, touch pads, solar cells, sensors, electrode materials and electroluminescent components. The transparent conductive oxides obtainable in accordance with the invention are preferably used in electronic components or as an electrode material or as a material for antistatic applications.

The transparent conductive oxides obtainable in accordance with the invention have a high electrical conductivity, a high transparency and an excellent homogeneity and freedom from cracks. The adhesion to substrates is very good. The layer thickness of the transparent conductive oxides obtainable in accordance with the invention is homogeneous. The mesoporous materials according to the present invention can be advantageously used in electronic components, as an electrode material, as a material for antistatic applications or in a dye-sensitized solar cell. In particular, mesoporous ΤΊΟ2 films obtained by the inventive method can be advantageously used in dye-sensitized solar cells. A further object of the present invention are therefore electronic components and dye-sensitized solar cells comprising a mesopoprous material according to the invention.

Examples

The crystallinity was determined by means of wide-angle X-ray scattering (WAXS). The analysis was carried out on a "D8 diffractometer" from Bruker AXS GmbH, Karlsruhe (Cu-Κα radiation). The films applied to an Si wafer were analyzed in "symmetrical reflection" (Θ-2Θ geometry) using a "Goebel mirror" and an energy-dispersive solid phase detector from Bruker AXS (Si-based). A Soller collimator was placed in front of the detector. The measurement was carried out in steps of 0.05° between 2Θ = 5°-120° with a recording time of 1 -5 seconds per measurement. The measurement provided the WAXS intensity against 2Θ.

The analysis of the data was carried out in three stages by means of Software

(Origin®): 1 .) Subtraction of the constant background which was determined at the points with the highest and the lowest 2Θ values of the WAXS curve; 2.) multiplication of the corrected WAXS analysis data with the square of the diffraction vector s² and of the total intensity by integration; 3.) determination of the integral intensity of the individual Bragg reflections after separation of the signals by means of the "subtract line" function such that, after subtraction, symmetrical signals were obtained and the signal base on both sides attained an intensity of zero, and formation of the sum of the integral intensities of all Bragg reflections.

The crystallinity (also known to those skilled in the art as the degree of crystallinity) can be determined from the integral intensity of the Bragg reflections and the total intensity of all reflections using the formula φ^ι = lBra_gg (lBragg+lamorphous) The number-average pore size and the geometric shape of the pores were determined by means of a scanning electron microscope and subsequent image analysis on at least 500 individual pores. The layer thickness of the films was determined by SEM measurements. The film was partly crushed and the fracture edge was analyzed. The transparency was determined as transmission in % on quartz glass with a UV-VIS spectrometer at a path length of 200 nm and at a wavelength in the range from 380 nm to 780 nm according to DIN 1349 - 2:1975.

As block copolymer (B) PIB6000-EO108, a poly(isobutylene)-block-poly(ethylen oxide) diblock copolymer with a number average block length of the isobutylene block of 108 units and a number average block length of the ethylene oxide block of 108 units was used. For comparison, a poly(ethylene-co-butylene)-block-poly(ethylene oxide) copolymer (KLE by Kraton) was used as templating agent. Example 1 : Preparation of metal oxide nanoparticles a) T1O2 nanoparticles: 3.4 g of TiCU was added into 7.9 g of ethanol under intensive stirring. The resulting solution was added to 42 g of anhydrous benzyl alcohol, followed by addition of 400 mg of 1 ,3-propanediol. The reaction mixture was stirred at 80°C for 8 hours under air. After cooling down, the nanoparticles were precipitated by addition of 8 g of the resulting solution into 18 g of cold diethyl ether. The precipitate was centrifuged at 7000 rpm for 10 minutes and then re-suspended twice in pure diethyl ether and centrifuged in order to wash out the impurities. b) Zr02 nanoparticles: 3 g of ZrCU was dissolved in 5 ml of ethanol and the resulting solution was added into 40 ml of anhydrous benzyl alcohol followed by the addition of 0,5 g of 1 ,3-propanediol. After thermal treatment at 80°C for 12 h the reaction mixture was precipitated by addition of diethyl ether and washed twice. c) ATO (antimony tin oxide) nanoparticles: 2.2 g of SnCU was dissolved in 15 mL of anhydrous benzyl alcohol under vigorous stirring, followed by solution of 193 mg of SbC in 5 mL of benzyl alcohol. The solution was filtered through a syringe filter (0.2 μηη) and transferred into the flask. The reaction mixture was stirred at 105°C for 18 h. After the liquid was removed, the solid deposit on the flask walls was collected and washed with 10 mL of acetone. The solid was separated through centrifugation at 4500 rpm. The solid was then redispersed in THF in order to obtain a dispersion containing 6 % by weight of ATO. Example 2: preparation of mesoporous films

To a clear, aggregate free dispersion of 60 mg of ΤΊΟ2 nanoparticles (Example 1 a) with average size of 4 nm in 2 g of methanol, 66 mg of the PIB6000-EO108 was added. The resulting solution was filtered using a 200 nm syringe filter. Using dip coating (speed 600 mm/min, air humidity 80 %) a thin film was deposited on the silicon wafer. The film was let dry 5 minutes under ambient atmosphere and subsequently treated thermally. The increase of temperature from 20°C to 300°C occured within a period of 2 h and was followed by a temperature ramp starting at 300°C and ending at 550°C with a heating rate of 10°C/min. Immediately after reaching the peak temperature the sample was removed from the oven and let cool down to room temperature.

Example 3

The same procedure as in example 2 was applied except that 60 mg of Zr02 nanoparticles (Example 1 b) with average particle diameter of 2.5 nm was used instead of Ti0₂. Example 4: Templating of ATO nanoparticles using PIB6000-EO108

To 1.32 g of the dispersion obtained according to example 1c), 68 mg of the PIB6000 polymer was added and the solution was used for dip coating of the silicon substrate (600 mm/min, 20 % RH). The films were tempered first at 100°C for 12 h, then at 200°C for 2 h. The temperature was the increased to 300°C within a period of 4 hours and kept at this temperature for 8 hours. Then the temperature was increased to 550°C within 25 min. After reaching this temperature the film on the substrate was removed from the oven and let cool down to room temperature. Examples 2, 3 and 4 yielded highly transparent mesoporous films with number average pore diameter of 25 nm.

Example 5V: Templating of ATO nanoparticles using KLE

Mixing of a solution of KLE block-copolymer with the ATO dispersion according to example 1 c) immediately led to precipitation and was unsuited for the production of transparent mesoporous films.

Claims

A process for preparing mesoporous materials, comprising the following steps in the sequence of a-b-c-d:

(c) removing the solvent (C) thus yielding a composite material (K), and

(d) removing the at least one copolymer (B) from said composite material (K),

wherein the block copolymer (B) comprises at least one alkylene oxide block (AO) and at least one isobutylene block (IB).

The process according to claim 1 , wherein the dispersion of metal oxide nanoparticles (A) comprise at least one crystalline metal oxide.

The process according to claim 1 or 2, wherein the number average particle diameter of the nanoparticles according to step (a) is from 0.5 to 10 nm.

The process according to claims 1 to 3, wherein the block copolymer (B) comprises at least one alkylene oxide block (AO) and at least one isobutylene block (IB), where the number-weighted average block length of the alkylene oxide block (AO) is from 4 to 300 monomer units and the number-weighted average block length of the isobutylene block (IB) is from 5 to 300 monomer units.

The process according to claims 1 to 4, wherein the reaction in step (a) is performed in the presence of at least one diblock copolymer (B) consisting of an alkylene oxide block (AO) and an isobutylene block (IB).

The process according to claims 1 to 5, wherein the block copolymer (B) has a polydispersity index of from 2 to 20.

The process according to claims 1 to 6, wherein the metal oxide nanoparticles (A) comprise oxides of at least one metal or semimetal M selected from the group consisting of Ti, Nb, Ta, Zr, Mn, Al, Fe, Cr, Sn, Sb, Pb, Ce, In, Ba and V.

The process according to claims 1 to 7, wherein the metal oxide nanoparticles (A) comprises tin as the metal or semimetal M, and antimony as the doping element Μ'.

9. The process according to claims 1 to 8, wherein the solvent (C) used is at least one compound selected from the group consisting of aliphatic alcohols and aliphatic ethers.

10. The process according to claims 1 to 9, wherein step (c) is preceded by step (c- pre) comprising applying the mixture obtained in step (b) on the solid substrate (S).

1 1 . The process according to claims 1 to 10, wherein step (d) comprises applying a temperature of from 100 to 600 °C to said composite material (K), preferably 200 to 550X.

12. The process according to claims 1 to 1 1 , wherein step (d) comprises heat

treatment in at least two stages, a first stage (d1 ) involving exposure to a temperature of from 80 to 200°C for from 1 to 24 hours, and a further stage (d2) involving exposure to a temperature of from 200 to 600°C for from 1 to 5 hours.

13. The process according to claims 1 to 12, wherein after step (d) the mesoporous material in step (e) is aged under the exclusion of oxygen, preferably at a temperature of from 200 to 600 °C.

14. A mesoporous material obtainable according to claims 1 to 13.

15. An electronic component or a dye-sensitized solar cell comprising a

mesopoprous material according to claim 14.

16. The use of the mesoporous material according to claim 14 in electronic

components or as an electrode material or as a material for sensing applications.

17. The use of the mesoporous material according to claim 14 in dye-sensitized solar cells.