JP3146351B2 - Method for producing layered compound having interlayer crosslinked structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing a layered compound having an interlayer crosslinked structure useful as a photocatalyst or the like by using a layered perovskite type compound and utilizing an intercalation reaction.

[0002]

2. Description of the Related Art A semiconductor photocatalytic reaction utilizing a metal compound having photoresponsive semiconductor characteristics represented by titanium oxide is disclosed by the discovery of photodecomposition of water at a semiconductor electrode [Industrial Chemistry Magazine, Vol. Pages 108 to 113 (1969
Years)], many studies have been conducted as a promising means of converting light energy into chemical energy.
The potential utility in various fields is emerging.

A metal compound having photoresponsive semiconductor properties, a so-called photocatalyst, has a "forbidden band" which is an energy gap between a valence band and a conduction band in a crystal molecule.
When light having energy equal to or greater than is absorbed, electrons in the valence band are photoexcited into the conduction band, free electrons are generated in the conduction band, and holes are generated in the valence band. The photocatalytic reaction proceeds by causing the oxidation reaction.

However, in order for photodecomposition of water to occur by the semiconductor photocatalyst, the bandwidth of the semiconductor must be equal to the electrolytic pressure of water (theoretical value 1.23 V + overvoltage 0.4 V = 1.63 V).
It must be larger, moreover, electrons in the conduction band must be able to reduce water and holes in the valence band must be capable of oxidizing water. That is, the lower end of the conduction band must be located on the minus side of the hydrogen generation potential from water, and the upper end of the valence band must be located on the plus side of the oxygen generation potential.
Due to this limitation, the types of semiconductors that can completely decompose water theoretically are limited.

A photocatalyst such as a metal compound (T
As a method for producing a photocatalyst mainly composed of iO ₂ ), a method of directly sintering a high temperature using an inorganic material powder or a chemical treatment to impart more excellent photoresponsiveness to the semiconductor by chemical treatment, A method of adsorbing an aqueous solution of a metal compound and then oxidizing, reducing or partially oxidizing the metal or the metal compound adsorbed on the semiconductor, a sol-gel method, and the like have been known.

However, in a photocatalyst using a metal compound having photoresponsive semiconductor characteristics, the visible light portion of sunlight cannot be absorbed because the bandwidth of the semiconductor is too large, and almost only near-ultraviolet light contributes to the reaction. In addition, since electrons and holes generated by excitation by light energy easily recombine, there is a disadvantage that the reaction quantum yield in various reaction systems is low.

Recently, a layered composite oxide, for example, layered perovskite type KCa ₂ Nb ₃ O ₁₀ has been proposed as a photocatalyst having photoresponsive semiconductor properties. Such a layered perovskite compound can be variously combined with the element to be used, for example, K [Ca ₂ Nan _- 3Nb
It has the advantage that the _{n O} 3n _{+ 1]} Various compounds represented by may be prepared.

In general, when preparing a highly functional photocatalyst, for example, a catalyst for completely decomposing water into hydrogen and oxygen by visible light using a layered compound, how to modify the layers becomes an important issue. However, in the case of a layered perovskite, the interlayer charge density is high, so that it is difficult to increase the interlayer distance, it is difficult to modify the interlayer, and it is difficult to obtain a highly functional photocatalyst.

[0009]

SUMMARY OF THE INVENTION Under such circumstances, the present invention provides a method for efficiently producing a layered compound useful as a high-performance photocatalyst by increasing the interlayer distance of the layered compound and modifying the layers. The purpose of this is to provide.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for modifying the interlayer of a layered compound, and as a result, have found that a layered layer prepared by reacting NaNbO ₃ and KCa ₂ Nb ₃ O ₁₀ at a high temperature. Using a perovskite compound,
After this is subjected to a proton exchange treatment, a long-chain alkylamine intercalation treatment, a treatment with tetraalkoxysilane, and a calcination treatment are sequentially performed, whereby a layered compound having an interlayer crosslinked structure having silica pillars between layers can be easily obtained. This led to the completion of the present invention based on this finding.

[0011] That is, the present invention relates to NaNbO ₃ and KC
a ₂ Nb ₃ O ₁₀ is reacted at a temperature of 1150 to 1350 ° C. to obtain a general formula K [Ca ₂ Na _n-3 Nb _n O _{3n + 1} ] (I) (where n is a number of 4 to 6) , Nb may be substituted with at least one metal selected from Ni, V, Cu, Cr and W at a ratio of 10 atomic% or less) to prepare a layered perovskite compound represented by the formula: After proton exchange treatment, intercalate the long-chain alkylamine, then react with tetraalkoxysilane, and further calcine at 400-600 ° C under an oxygen-containing gas atmosphere to form silica pillars between layers. It is intended to provide a method for producing a layered compound having an interlayer crosslinked structure, characterized in that the method comprises:

[0012]

In DETAILED DESCRIPTION OF THE INVENTION The present invention method, as layered compound, the generally formula layered perovskite compound represented by (I) is used, the layered perovskite type compound, NaNbO ₃ and KCa ₂ Nb ₃ O ₁₀ at a high temperature of 1150-1350 ° C. Nb in the general formula (I) is 10 atomic%.
Ni, V, Cu, Cr or W or a combination of two or more thereof may be substituted at the following ratio.

The layered perovskite compound represented by the general formula (I) is selected from commonly used methods, for example, niobium oxide powder, calcium carbonate powder, potassium carbonate powder and optionally used sodium carbonate powder. The metal compounds are mixed at a predetermined ratio, and this powder mixture is calcined in an atmosphere containing oxygen such as air at a temperature within the above range to obtain NaNbO.
₃ and KCa ₂ Nb ₃ O ₁₀ are separately prepared, and then both are mixed at a predetermined ratio and fired. In the layered perovskite compound thus obtained, the interlayer distance increases as n in the general formula (I) increases from 4 to 6.

In the method of the present invention, it is necessary that the layered perovskite compound represented by the general formula (I) thus prepared is subsequently subjected to a proton exchange treatment. This proton exchange treatment can be carried out by stirring the layered perovskite compound in an acid solution, for example, an aqueous solution of nitric acid of an appropriate concentration at room temperature for about 50 to 100 hours. This process, the layered perovskite type compound represented by the general formula _{H [Ca 2 Na n-3} Nb n O 3n + 1] (II) or considering the electronic ^{_{value, H + [Ca 2 Na n}} -3 Nb n O 3n + 1] ^- (II ') wherein n has the same meaning as described above.

Next, a long-chain alkylamine is intercalated into the proton exchange layered compound. As the long-chain alkylamine used at this time, one having about 5 to 15 carbon atoms is preferable, and n-hexylamine is particularly preferable. This intercalation reaction can be performed by contacting the long-chain alkylamine with the above-mentioned proton conversion layered compound in a suitable solvent such as a lower alcohol at room temperature for about 50 to 200 hours. By this reaction, a long-chain alkylamine is intercalated between the layers of the layered compound, and the interlayer distance is increased.

Next, a tetraalkoxysilane is reacted with the layered compound in which the long-chain alkylamine has been intercalated as described above. As the tetraalkoxysilane used at this time, those in which the alkoxyl group is a lower alkoxyl group such as a methoxy group, an ethoxy group, an n-propoxy group, and an isopropoxy group are preferable, and tetraethoxysilane is particularly preferable. This reaction generally takes 40
This is performed at a temperature of about 80 ° C. for about 50 to 200 hours.

Finally, in an oxygen-containing gas atmosphere such as air, a baking treatment is performed at a temperature in the range of 400 to 600 ° C. to burn organic substances in the interlayer. By this calcination treatment, an interlayer bridge represented by the general formula SiO ₂ —Ca ₂ Na _n−3 Nb _n O _{3n + 1} (III) (wherein n has the same meaning as described above) and having silica pillars between the layers A layered compound of the structure is obtained. This is a porous body, has a large surface area, and has good high-temperature stability.

[0018]

According to the present invention, a layered perovskite compound containing a plurality of alkali metals and alkaline earth metals is used, and the intercalation reaction is used to increase the interlayer distance of the silica compared with the conventional silica. It is possible to efficiently produce a porous body composed of a layered compound having an interlayer cross-linking structure having the above-mentioned pillars. This is useful as a highly functional photocatalyst, for example, in the field of synthetic chemistry using photochemical conversion or light, or in the field of removal of environmental pollutants using photocatalysis.

[0019]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Reference Example 1 Preparation of KCa ₂ Nb ₃ O ₁₀ Niobium (V) oxide powder [purity 9 manufactured by Wako Pure Chemical Industries, Ltd.]
9.9%] 0.03 mol, calcium carbonate powder [manufactured by Wako Pure Chemical Industries, Ltd., reagent grade] 0.04 mol and potassium carbonate powder [Katayama Chemical Industry Co., Ltd., reagent first grade] 0.01
After thoroughly mixing 1 mol, the mixture obtained by calcining in air at 1200 ° C. for 7 hours is pulverized, and again in air,
It was baked at 1200 ° C. for 7 hours. Next, this is sufficiently washed with distilled water, and then dried at 110 ° C.
KCa ₂ Nb ₃ O ₁₀ powder was prepared. The X-ray diffraction pattern of this is shown in FIG.

Reference Example 2 Preparation of KCa ₂ NaNb ₄ O ₁₃ Niobium (V) oxide powder [Wako Pure Chemical Industries, Ltd., purity 9
9.9%] 0.045 mol, calcium carbonate powder [manufactured by Wako Pure Chemical Industries, Ltd., reagent grade] 0.06 mol and potassium carbonate powder [Katayama Chemical Industry Co., Ltd., reagent first grade] 0.0
After well mixing 165 moles, the mixture was calcined in air at 1000 ° C. for 20 hours, and the resultant was pulverized and calcined again in air at 1000 ° C. for 20 hours. Then
After sufficiently washing this with distilled water, it was dried at 500 ° C. for 3 hours to prepare KCa ₂ Nb ₃ O ₁₀ powder.
On the other hand, niobium oxide (V) powder [manufactured by Wako Pure Chemical Industries, Ltd.
[Purity 99.9%] and 0.02 mol of sodium carbonate powder [Wako Pure Chemical Industries, Ltd., first class reagent] are mixed well, and then calcined in air at 1050 ° C. for 6 hours to obtain NaNbO. _Three powders were obtained. The thus obtained KCa ₂ Nb ₃ O ₁₀ powder 0.025 mol and NaN
After sufficiently mixing 0.025 mol of bO ₃ powder, the mixture was calcined at 1230 ° C. for 10 hours in air to obtain KCa ₂ N
aNb ₄ O ₁₃ powder was prepared. The X-ray diffraction pattern of this is shown as b in FIG.

REFERENCE EXAMPLE 3 Preparation of KCa ₂ Na ₂ Nb ₅ O ₁₆ KCa ₂ NaNb ₄ O ₁₃ powder obtained in Reference Example 2 0.01
Mol and 0.01 mol of the NaNbO ₃ powder obtained in Reference Example 2 were thoroughly mixed, fired in air at 1260 ° C. for 15 hours, pulverized, and fired again in air at 1300 ° C. for 10 hours. KCa ₂ Na ₂ Nb ₅ O ₁₆ powder was prepared. The X-ray diffraction pattern of this is shown as c in FIG.

REFERENCE EXAMPLE 4 Preparation of KCa ₂ Na ₃ Nb ₆ O ₁₉ KCa ₂ NaNb ₄ O ₁₃ powder obtained in Reference Example 2 0.01
Mol and 0.02 mol of the NaNbO ₃ powder obtained in Reference Example 2 were mixed well, calcined in air at 1320 ° C. for 5 hours, pulverized, and calcined again in air at 1320 ° C. for 5 hours. KCa ₂ Na ₃ Nb ₆ O ₁₉ powder was prepared. The X-ray diffraction pattern of this is shown in FIG. 1 as d.

From the above Reference Examples 1 to 4, the above-mentioned general formula (I)
In shown are _{K [Ca 2 Na n-3} Nb n O 3n + 1]
(N = 3 to 6) are the backbone _{[Ca 2 Na n-3 Nb} n O
_{3n + 1} ] and a layered perovskite compound in which the interlayer K is combined. It can be seen that as n increases, the thickness of the skeleton increases. As a result of identification by X-ray diffraction, it was found that when n was changed from 3 to 4, 5, 6, the interlayer distances increased in the order of 2.94 nm, 3.72 nm, 4.47 nm, and 5.24 nm, respectively. That is, the layered perovskite compound obtained in Reference Example is
It allows for modification of its backbone.

Comparative Example 1 2.5 g of KCa ₂ Nb ₃ O ₁₀ prepared in Reference Example 1 was added to 6
N nitric acid [Wako Pure Chemical Industries, Ltd., reagent grade] aqueous solution 10
After stirring for 3 days while stirring at room temperature, the mixture was filtered, washed and dried to give HC
It was obtained a ₂ Nb ₃ O ₁₀ powder.

The thus obtained HCa ₂ Nb ₃ O ₁₀
2.2 g of the powder was placed in a mixed solution of 50 ml of n-hexylamine [manufactured by Wako Pure Chemical Industries, Ltd., reagent first grade] and 25 ml of ethanol [manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent], and the mixture was stirred at room temperature. After reacting for 7 days while stirring, the mixture was filtered, washed and dried to obtain [C ₆ H ₁₃ NH ₃ ] [Ca
To obtain a ₂ Nb ₃ O _10] powder.

[C ₆ H ₁₃ NH ₃ ] thus obtained.
2.0 g of [Ca ₂ Nb ₃ O ₁₀ ] powder was placed in 50 ml of tetraethoxysilane [Wako Pure Chemical Industries, Ltd., reagent grade], reacted at 65 ° C. for 3 days with stirring, filtered, and then ethanol. And then dried. Thereby, tetraethoxysilane could be introduced between the layers. Next, this is calcined in air at 500 ° C. to form a pillar of silica between the layers, and SiO ₂ —Ca ₂ Nb ₃ O ₁₀ which is a layered compound having an interlayer cross-linking structure is formed.
Was manufactured. When an intercalation reaction with n-hexylamine was performed, the interlayer distance was changed from 1.47 nm to 2.87 nm, and when pillars were formed using tetraethoxysilane, the interlayer distance was 3.03 nm.

Example 1 Using the KCa ₂ NaNb ₄ O ₁₃ powder prepared in Reference Example 2, a silica column was formed between layers by the same method as in Comparative Example 1, and SiO ₂ , an interlayer compound having an interlayer cross-linking structure, was formed.
The -Ca ₂ NaNb ₄ O ₁₃ was prepared. When the intercalation reaction with n-hexylamine was performed, the interlayer distance was changed from 1.86 nm to 3.30 nm, and when the pillar was formed with tetraethoxysilane, the interlayer distance was 3.40 nm.

Comparative Example 2 Niobium (V) oxide powder [manufactured by Wako Pure Chemical Industries, Ltd., purity 9]
9.9%] 0.029 mol, calcium carbonate powder [Wako Pure Chemical Industries, Ltd., reagent grade] 0.04 mol, potassium carbonate powder [Katayama Chemical Industry Co., Ltd., reagent first grade] 0.01
1 mol of chromium nitrate nonahydrate _{[Cr (NO 3) 3 ·} 9
H ₂ O] powder [Katayama Chemical Industry Co., Ltd., reagent grade]
002 mol was added to 100 ml of distilled water and evaporated to dryness while stirring. Drying the resulting solid at 110 ° C.
Next, it was baked in air at 1200 ° C. for 5 hours, and then pulverized. The pulverized material was fired in air at 1200 ° C. for 10 hours, sufficiently washed with distilled water, and dried at 110 ° C. to prepare KCa ₂ Nb _2.9 Cr _0.1 O ₁₀ powder.

The thus obtained KCa ₂ Nb _2.9 C
4.0 g of r _0.1 O ₁₀ powder was placed in 150 ml of 6N nitric acid [Wako Pure Chemical Industries, Ltd., reagent grade] aqueous solution, and stirred at room temperature for 3 days for proton exchange, followed by filtration, washing and drying. And HCa ₂ Nb _2.9 Cr _0.1 O
₁₀ powders were obtained. Next, the HCa ₂ Nb _2.9 Cr
2.8 g of _0.1 O ₁₀ powder is mixed with 80 ml of n-hexylamine [manufactured by Wako Pure Chemical Industries, Ltd., first grade reagent] and 40 ml of ethanol [wako Pure Chemical Industries, Ltd., special grade reagent]. After stirring at room temperature for 7 days, the mixture was filtered, washed and dried to obtain [C ₆ H ₁₃ NH ₃ ].
[Ca ₂ Nb _2.9 Cr _0.1 O ₁₀ ] powder was obtained. Next, this [C ₆ H ₁₃ NH ₃ ] [Ca ₂ Nb _2.9 Cr
_0.1 O ₁₀ ] powder (2.0 g) is placed in 50 ml of tetraethoxysilane [Wako Pure Chemical Industries, Ltd., reagent grade] for 50 days with stirring at 65 ° C. for 7 days (in the meantime, 20 ml of tetraethoxysilane is added twice) After the reaction, the mixture was filtered, washed with ethanol, and dried. Then
By baking at 500 ° C. in air, pillars of silica were formed between the layers, and SiO ₂ —Ca ₂ Nb _2.9 Cr _0.1 O ₁₀ which was a layered compound having an interlayer cross-linking structure was produced. When an intercalation reaction with n-hexylamine is carried out, the interlayer distance becomes 1.46 nm to 2.46 nm.
When the thickness became 73 nm, and further when pillars were formed with tetraethoxysilane, the interlayer distance became 2.95 nm.
When the temperature is changed and firing is performed at 400 ° C., 500 ° C., and 600 ° C., the interlayer distances are 2.61 nm and 2.
45 nm and 2.39 nm, which was recognized to be slightly reduced by burning organic substances.
Those fired at 00 ° C. had 292 m ² / g) and high temperature stability was also observed. FIG. 2 shows an X-ray diffraction diagram of the product obtained at each stage. In FIG.
(A) untreated KCa ₂ Nb ₃ O ₁₀
(B) is obtained by treating (a) with a 6N nitric acid aqueous solution,
(C) is a product obtained by intercalating (b) with hexylamine, (d) is a product obtained by substituting hexylamine of (c) with tetraethoxysilane, and (e) is a product obtained by replacing (d) by 3
(F) is obtained by firing (d) at 500 ° C.

Example 2 In the same manner as in Example 1, KCa ₂ NaNb ₄ O ₁₃ powder was used, followed by treatment with a 6N aqueous nitric acid solution, treatment with n-hexylamine and treatment with tetraethoxysilane. Fired at ℃. FIG. 3 shows X-ray diffraction patterns at each of these stages. In FIG.
(A) untreated KCa ₂ NaNb ₄ O ₁₃ , (b) (a) treated with 6N nitric acid aqueous solution,
(C) is a product obtained by intercalating (b) with hexylamine, (d) is a product obtained by substituting hexylamine of (c) with tetraethoxysilane, and (e) is a product obtained by replacing (d) by 3
(F) is obtained by firing (d) at 500 ° C.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a layered perovskite compound obtained in Reference Examples 1 to 4.

FIG. 2 is an X-ray diffraction diagram of KCa ₂ Nb ₃ O ₁₀ and a processed product thereof.

FIG. 3 is an X-ray diffraction diagram of KCa ₂ NaNb ₄ O ₁₃ and a processed product thereof.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-196912 (JP, A) JP-A-63-503538 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 33/00 B01J 23/20 CA (STN)

Claims (1)

(57) [Claims] 1. A reaction between NaNbO ₃ and KCa ₂ Nb ₃ O ₁₀ at a temperature of 1150 to 1350 ° C. to obtain a general formula K [Ca ₂ Na _n-3 Nb _n O _{3n + 1} ] (where n is 4 to ₁ ). 6, and Nb may be substituted by at least one kind of metal selected from Ni, V, Cu, Cr and W at a ratio of 10 atomic% or less.) After proton exchange treatment, a long-chain alkylamine is intercalated, then tetraalkoxysilane is reacted, and further calcined at a temperature of 400 to 600 ° C. under an oxygen-containing gas atmosphere to form an interlayer. A method for producing a layered compound having an interlayer crosslinked structure, wherein pillars of silica are formed.