JP4520088B2 - Method for synthesizing mesoporous oxides with high three-dimensional regularity - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for synthesizing a mesoporous metal oxide having a three-dimensional highly ordered pore structure, particularly a three-dimensional hexagonal structure, or a three-dimensional cubic structure, in particular, a mesoporous metal oxide is relatively simple and has high reproducibility. It is related with the method of synthesizing with.
[0002]
[Prior art]
The mesoporous metal oxides produced so far are mainly two-dimensionally regular, that is, two-dimensional hexagonal regular. Therefore, when a thin film having the structure is formed, the above-described mesoporous metal oxide is formed on the film surface. There is a problem that it is difficult to form a structure in which hexagonals are arranged vertically and with high regularity.
[0003]
There are several examples of synthesizing mesoporous metal oxides having a three-dimensional structure (References 1 and 2), but the synthesis method has a problem that the reproducibility is not good and the manufacturing method has complicated conditions.
[0004]
Document 1 describes the following. Because amphiphilic block copolymers are useful as templates that can rationally regulate the interaction between inorganic and organic species and self-assembly, their use as a surfactant as a template material has increased. Being. As a compound for synthesizing a mesoporous material, it has been studied to use a material selected from non-silica metal oxides such as Nb, Ti, and Ta. When conventional low molecular weight surfactants are used, only <4 nm mesoporous pores can be obtained. The walls that make up the pores are almost amorphous.
[0005]
The above metal oxide-block copolymer was conceived to synthesize a high-density, ie, improved crystallinity, fine particle having a large pore size, that is, up to ˜14 nm. complexes by the interaction of the block copolymer and the inorganic metal compound, said also to guess would be formed that desired mesoporous structure, it mentions that attempted an experiment. In the experimental section, commercially available EO ₂₀ PO ₇₀ EO ₂₀ (P-123 manufactured by BASF), EO ₁₀₆ PO ₇₀ EO ₁₀₆ (Pluronic F-127 manufactured by BASF), and EO _{75 are used} as the block copolymer. Using BO ₄₅ (manufactured by Dow Chemical), this is dissolved in ethanol (butanol in the case of Hf), and a metal compound such as a metal chloride that forms the metal oxide is used as a precursor while stirring vigorously. To add. Gel the obtained solution in an open petri dish at 40-60 ° C. The aging time of the gel should be adjusted according to the metal species. In the case of forming a mesoporous metal oxide thin film layer, it is applied by dip coating and dried at 30 to 60 ° C., and the resulting gel is baked at 300 to 600 ° C. to remove the block copolymer surfactant, thereby removing the mesoporous metal. It has been reported that oxides were obtained. Then, the characteristics of the obtained mesoporous metal oxide are measured by examining the temperature adsorption characteristics such as XRD, TEM, and nitrogen gas, and the pore size distribution by the BJH method.
[0006]
When TiO ₂ was synthesized by the above method using EO ₂₀ PO ₇₀ EO ₂₀ (P-123 manufactured by BASF) as a structure-regulating surfactant, a two-dimensional hexagonal meso structure having lattice constants α ₀ = 142 and 117 お よ びWas obtained. Further, when EO ₇₅ BO ₄₅ (manufactured by Dow Chemical) [OH (CH ₂ CH ₂ O) ₇₅ (CH ₂ CH (CH ₂ CH ₂ ) O) ₄₅ ] is used as a structure-regulating surfactant, cubic meso is used. It is described that a phase is formed. Furthermore, when Nb ₂ O ₅ was synthesized by the above method using EO ₂₀ PO ₇₀ EO ₂₀ (P-123 manufactured by BASF) as a structure-regulating surfactant, a two-dimensional hexagonal having lattice constants α ₀ = 122 and 92Å A meso structure was obtained. However, none of the described metal oxide XRDs can find a 002-plane diffraction peak around θ = 1 °, which shows high regularity of a three-dimensional hexagonal structure.
[0007]
Reference 2 describes in a paper entitled “Ligand-Assisted Liquid Crystal Template in Mesoporous Nb Oxide Molecular Sieve Formation”, the ratio of surfactant to metal, and the novel hexagonal P63 / mmc spatial structure and layered (Nb-TMS2) phase. And the formation of a novel cubic phase (Nb-TMS3) due to an increase in the chain length of the surfactant (chemical structure of the template surfactant). However, there is no mention of the synthesis of a three-dimensional highly ordered mesostructure.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for synthesizing a mesoporous oxide having a three-dimensional high regularity, and in particular, the synthesis method having a good reproducibility and relatively easy. In the synthesis of mesoporous metal oxides using the sol-gel method, it is important to establish a system that forms the basic structure of mesoporous by self-assembly. However, although the prior art describes establishment of a technique for regulating the structure of the obtained mesoporous metal oxide, there is no teaching how to establish three-dimensional high regularity. The present inventors assumed that the presence of ionic species in the formation of the sol may have some influence on the process of self-organization, and the presence of alkali and chloride ions, their concentrations and the resulting mesoporous metal oxides. It has been found that there is a correlation with the structure, and the problems of the present invention have been solved.
[0009]
[Means for Solving the Problems]
The present invention provides (1) a nonionic surfactant comprising a block copolymer composed of a polyethylene oxide chain (CH ₂ CH ₂ O) _m and a polypropylene oxide chain [CH ₂ CH (CH ₃ ) O] _n (where, m and n are 10 to 70, and the terminal of the polymer is etherified with H, alcohol or phenol), and a non-silica Nb or Ti compound aliphatic alcohol solution is used as a metal oxide precursor. In the method of forming a mesoporous metal oxide by hydrolysis, aging, and calcination by a sol-gel method, when a non-silica Nb compound is used as a precursor in the sol-gel reaction system , Water having a cation concentration selected from alkali or alkaline earth ions of 0.01 mol to 0.1 mol In addition to the solution of the non-silica Nb compound so that the alkali or alkaline earth ion is 0.05 mol to 0.5 mol with respect to 1 mol of the nonionic surfactant, a Ti compound is also used. Is used as a precursor, an aqueous solution having a chlorine anion concentration of 10M to 12M is used as water to promote hydrolysis, so that the anion is 40 mol to 50 mol with respect to 1 mol of the nonionic surfactant. In addition , the non-silica Nb has a three-dimensional hexagonal structure, and has a three-dimensional high regularity characterized by hydrolysis, and a three-dimensional cubic when a Ti compound is used as a precursor. This is a method of synthesizing a mesoporous oxide having a structure. Preferably, (2) aliphatic alcohol is methanol, ethanol, propanol, butanol, pentanol, hexanol or high three-dimensional according to (1), characterized in that mixtures of two or more thereof A method for synthesizing a non-silica metal mesoporous oxide having regularity, more preferably (3) Nb having enhanced three-dimensional high regularity as described in (1) or (2) above In the method for synthesizing mesoporous oxides, a three-dimensional hexagonal structure in which NbCl ₅ is used as a precursor compound and 0.25 mol of a cation selected from alkali or alkaline earth ions is added to 1 mol of a nonionic surfactant. This method synthesizes mesoporous niobium oxide.
[0010]
(4) In the method of synthesizing a titanium mesoporous oxide having three-dimensional high regularity in the above (1) or (2), Ti [(CH ₃ ) ₂ CHO] ₄ is used as a Ti compound , and chlorine This is a method of synthesizing cubic mesoporous TiO ₂ having a three-dimensional high regularity by adding an anion to 45 mol with respect to 1 mol of a nonionic surfactant and hydrolyzing it.
[0011]
[Embodiments of the present invention]
The present invention will be described in more detail.
A. As the surfactant used for forming nano-sized pores in the present invention, it is preferable to use the nonionic surfactant used in the above-mentioned document 1. That is, there are polyalkylene oxide block copolymers comprising ethylene glycol oligomers (including polymers), propylene glycol oligomers (including polymers), and compounds obtained by etherifying the ends of the block copolymers with alcohol, phenol, or the like. . These are preferable surfactants from the viewpoint of low toxicity. Specifically, for example, P123 [trade name, BASF _{Corp.: (HO (CH 2 CH 2} O) 20 (CH 2 CH (CH 3) O) 70 (CH 2 CH 2O) 20) H ], and items name; P85 _{[(HO (CH 2 CH 2 O} ) 26 (CH 2 CH (CH 3) O) 39 (CH 2 CH 2 O) 26) H ], P103 _{[(HO (CH 2 CH 2 O} ) 56 ( CH ₂ CH (CH ₃ ) O) ₁₇ (CH ₂ CH ₂ O) ₅₆ ) H] (manufactured by Asahi Denka Kogyo Co., Ltd.).
[0012]
In the present invention, the nonionic surfactant is combined with a metal salt or alkoxide that forms the metal oxide, and a cation selected from alkali or alkaline earth, or water containing a chlorine anion is added to the nonionic surfactant. It was discovered that by adding an appropriate number of moles to 1 mole of the agent, the pore structure regularity in the sol-gel process can be strengthened and a metal oxide having three-dimensional highly ordered pores can be synthesized. Has characteristics.
[0013]
B, a cation selected from the alkali or alkaline earth, or water added with a chlorine anion preferably has a concentration in the range of 0.02 mol% to 0.1 mol% in the case of a cation. The cation is preferably added in a ratio of 0.05 mol to 0.5 mol with respect to 1 mol of the nonionic surfactant, and in the case of chlorine anion, the concentration is 20 mol% to 30 mol%. As a result of many trials and errors, it is preferable to add the chlorine anion concentration water so that the chlorine anion is in a ratio of 40 mol to 50 mol with respect to 1 mol of the nonionic surfactant. found.
[0014]
C, the metal salt and alkoxide compounded per gram of the surfactant is 0.003 to 0.01 mol, and the average maximum pore length is 2 nm to 50 nm, and the pore structure period is three-dimensional. In particular, it has been found to be preferable for producing a Ti oxide having a hexagonal arrangement structure or a cubic structure.
It has been found that even when Nb or the like is used in place of D and Ti, a mesoporous metal oxide crystal having a three-dimensional hexagonal structure can be obtained.
[0015]
F, The characteristics of the obtained mesoporous oxide were measured by the following method.
1, XRD (Rigaku RINT 2100, CuKa line) method: X-ray diffraction method: A periodic structure of mesopores is observed by a low angle (1-6 °) peak pattern.
2. Nitrogen adsorption isotherm (Coulter SA3100): Corresponds to the rapidly increasing relative pressure (P / P0) (X axis) region of nitrogen adsorption (Y axis / volume (mL / g)) and pore diameter To do. The degree of rise is related to the pore volume.
3, TEM: Transmission electron microscope (JEOL JEM 2010F, acceleration voltage 200 kV): A TEM image of a hexagonal array structure of mesoporous NbTa oxide was observed.
4, Electron diffraction image (JEOL JEM 2010F, acceleration voltage 200 kV): An image of six spots regularly arranged at equal distances around one spot perpendicular to the pore, or other Since a regular array of pores on the crystal plane can be seen for each electron beam irradiation surface, a three-dimensional hexagonal array structure of pores or a three-dimensional cubic structure was observed.
[0016]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not interpreted limitedly by this illustration.
Example 1
Synthesis of three-dimensional hexagonal structure mesoporous niobium oxide Nonionic surfactant comprising polyethylene oxide chain (CH ₂ CH ₂ O) _n and polypropylene oxide chain [CH ₂ CH (CH ₃ ) O] _m [( HO (CH ₂ CH ₂ O) ₂₆ (CH ₂ CH (CH ₃ ) O) ₃₉ (CH ₂ CH ₂ O) ₂₆ ) H] [trade name; Pluronic P-85, manufactured by Asahi Denka Kogyo Co., Ltd.] And a 10% by weight surfactant solution. Thereto, 0.007 mol of niobium chloride per 1 g of surfactant is added and dissolved with stirring for 20 to 60 minutes. At that time, water containing 0.05 M alkali or alkaline earth ions (Li ⁺ , Na ⁺ , Mg ²⁺ , Ca ²⁺ , Ba ²⁺ ) (similar results are obtained using any cation). 0.5 to 2 milliliters (mL) (0.25 mole of cation per mole of nonion) is added to promote hydrolysis and self-assembly of the inorganic substance. Here, as described above, the alkaline water has an important effect on the structural regulation in the self-organization in relation to the inorganic cation and the ratio to the nonion. The obtained sol is aged in the range of 35 ° C. to 60 ° C. in air for 2 to 10 days to gel. The obtained gel was baked at 400 ° C. to 500 ° C. to remove the nonionic surfactant as the template, thereby obtaining the desired mesoporous metal oxide.
[0017]
FIG. 1 shows the XRD characteristics of the mesoporous niobium oxide having a three-dimensional hexagonal structure obtained by the manufacturing method. The 002 diffraction peak near 2θ = 1 ° reflects a three-dimensional hexagonal structure. FIG. 2 shows a nitrogen gas adsorption isotherm of the niobium oxide. An isotherm hysteresis appears, showing a uniform pore distribution. The pore size distribution is shown in FIG. From this, it was found that the average pore diameter was 5 nm. The BET specific surface area was 200 to 250 m ² / g. Also, the two-step desorption curve suggests a three-dimensional pore structure that is regularly ordered. In a transmission electron microscope (not shown) and electron diffraction, a regular pore structure is seen on each electron beam irradiation surface, confirming the formation of a three-dimensional pore structure on the entire particle. It was done.
[0018]
Example 2
Synthesis of three-dimensional cubic mesoporous TiO _{2 As} a nonionic surfactant, it is composed of a polyethylene oxide chain (CH ₂ CH ₂ O) _n and a polypropylene oxide chain [CH ₂ CH (CH ₃ ) O] _m [(HO ( CH ₂ CH ₂ O) ₂₆ (CH ₂ CH (CH ₃ ) O) ₃₉ (CH ₂ CH ₂ O) ₂₆ ) H] (trade name Pluronic P-85) as a solvent and 10% by weight surfactant Make a solution. Thereto, 0.01 mole of titanium tetraisopropoxide per 1 g of surfactant is added and dissolved by stirring for 20 to 60 minutes. At that time, 0.8 to 1 ml of 37% hydrochloric acid is added to promote hydrolysis and self-assembly of the inorganic substance in the previous period. Here, as described above, hydrochloric acid plays an important role in structural regulation in self-organization in relation to being an anion and the ratio to the nonion. The obtained sol is aged in the range of 35 to 60 ° C. in air for 2 to 14 days to gel. The obtained gel was baked at 300 ° C. to 400 ° C. to remove the nonionic surfactant as the template, and the above-mentioned target mesoporous metal oxide was obtained.
[0019]
FIG. 4 shows the XRD characteristics of mesoporous TiO ₂ having a three-dimensional cubic structure obtained by the manufacturing method. The diffraction peaks near 2θ = 1.1 and 1.6 reflect the three-dimensional cubic structure. FIG. 5 shows the nitrogen gas adsorption isotherm of TiO ₂ . An isotherm hysteresis appears, showing a uniform pore distribution. The pore size distribution is shown in FIG. From this, it was found that the average pore diameter was 5 nm. The BET specific surface area was 200 to 350 m ² / g.
[0020]
【The invention's effect】
As described above, according to the method of the present invention, when a mesoporous oxide having three-dimensional high regularity is used as a precursor in the sol-gel reaction system with non-silica Nb and Ta compounds, alkali or alkali When a cation selected from earth ions or a non-silica Ti compound is used as a precursor, an excellent effect can be obtained that it can be obtained by a relatively simple means of adding chlorine ions. When a mesoporous oxide having a thin film structure is formed by using the method of the present invention, since the structural regularity of the mesoporous metal oxide is three-dimensionally regular, an array of regular pores can be formed on the entire surface. is there.
[0021]
Reference 1; P. Yang, D. Zhao, DI Margolese, BF Chemlka, GD Stucky, "Block copolymer templating syntheses of mesoporous metal oxides with largeordering lengths and semicrystalline framework." Chemistry of Materials, 1999, 11, 2813-2826.
Reference 2: DM Antonelli, A. Nakahira, JY Ying, "Ligand-assisted liquid crystal templating in mesoporous niobium oxide molecular sieves." Inorganic Materials, 1996, 35, 3126-3136.
[Brief description of the drawings]
1 is an XRD characteristic of a mesoporous niobium oxide having a three-dimensional hexagonal structure in Example 1. FIG. 2 is a nitrogen gas adsorption isotherm of the niobium oxide in Example 1. FIG. pore size distribution [4] example 2 of a three-dimensional cubic characteristics of XRD of mesoporous TiO ₂ structure [5] a nitrogen gas adsorption isotherm of mesoporous TiO ₂ of example 2 of 6 example 2 mesoporous Distribution of pore diameter of TiO ₂

Claims (4)

Nonionic surfactant comprising a block copolymer composed of a polyethylene oxide chain (CH ₂ CH ₂ O) _m and a polypropylene oxide chain [CH ₂ CH (CH ₃ ) O] _n (where m and n are from 10 to 70) And the end of the polymer is etherified with H, alcohol or phenol) as a templating agent, a non-silica Nb or Ti compound aliphatic alcohol solution as a metal oxide precursor, and hydrolyzed by a sol-gel method. In the method of forming a mesoporous metal oxide by aging and calcination, when a non-silica Nb compound is used as a precursor in the sol-gel reaction system, as water for proceeding hydrolysis, from alkali or alkaline earth ions Using an aqueous solution having a selected cation concentration of 0.01 mol to 0.1 mol, In addition to the solution of the non-silica Nb compound so that the alkali or alkaline earth ion is 0.05 mol to 0.5 mol with respect to 1 mol of the nonionic surfactant, a Ti compound is used as a precursor. In some cases, the hydrolysis is carried out by adding an aqueous solution having a chlorine anion concentration of 10M to 12M as water so that the anion becomes 40 mol to 50 mol with respect to 1 mol of the nonionic surfactant. The mesoporous oxide having a three-dimensional high regularity and having a three-dimensional hexagonal structure in the case of the non-silica Nb and a three-dimensional cubic structure in the case of using a Ti compound as a precursor How to synthesize.   The non-silica system having three-dimensional high regularity according to claim 1, wherein the aliphatic alcohol is selected from methanol, ethanol, propanol, butanol, pentanol, hexanol or a mixture of two or more thereof. A method for synthesizing mesoporous oxides of metals. 3. The method of synthesizing a strengthened three-dimensional highly ordered Nb mesoporous oxide according to claim 1 or 2 , wherein NbCl ₅ is used as a precursor compound, and an alkali or alkali is used with respect to 1 mol of a nonionic surfactant. A method for synthesizing a mesoporous niobium oxide having a three-dimensional hexagonal structure in which 0.25 mol of a cation selected from earth ions is added and strengthened. The method for synthesizing a titanium mesoporous oxide having three-dimensional high regularity according to claim 1 or 2, wherein Ti [(CH ₃ ) ₂ CHO] ₄ is used as a Ti compound, and the chlorine anion is a nonionic surfactant 1. A method of synthesizing mesoporous TiO ₂ having cubic structure having three-dimensional high regularity by adding 45 mol to mol and hydrolyzing.

Images