JP2009046344A - Method for preparing sol - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a sol containing zinc oxide fine particles whose property of emitting fluorescence is improved much more. <P>SOLUTION: The method for preparing the sol containing zinc oxide fine particles comprises the steps of: dispersing zinc hydroxide and a cation in a solution containing at least one of di- or more-valent alcohol and alkyl ether; and heat-treating the resulting solution. As a result, the sol containing zinc oxide fine particles whose property of emitting fluorescence is improved much more can be provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a sol containing zinc oxide fine particles.

  Zinc oxide (ZnO) is known to emit fluorescence by ultraviolet irradiation or electron beam irradiation due to lattice defects contained in its crystal structure. This fluorescent light emission is currently expected to be applied to various products. For example, it is applied to a light emitting display device as a light emitter for a flat panel display.

  By the way, in order to apply zinc oxide to products, it is important to be uniform. For example, when used as a light emitter for a flat panel display, the point is how to form a uniform thin film on a substrate.

  As a method for forming a uniform thin film on a substrate, for example, a method in which a solution in which zinc oxide or a precursor thereof is dispersed is applied to the substrate and dried is cited. This is a very simple method that does not require a complicated process, and is extremely useful for cost reduction.

  As a known technique that can be suitably used for the above-described method, for example, Patent Document 1 below discloses a method in which zinc hydroxide is dispersed in a dihydric or higher polyhydric alcohol or alkyl ether and subjected to heat treatment. Has been.

JP 2007-070188 A

  Certainly, when the technique described in Patent Document 1 is used, a sol containing very small zinc oxide fine particles can be obtained. However, the above-mentioned Patent Document 1 leaves room for studying fluorescence emission characteristics.

  Therefore, an object of the present invention is to provide a method for producing a sol containing zinc oxide fine particles having further improved fluorescence emission characteristics.

  The inventors of the present invention have been diligently studying the above-mentioned problem. As a result, zinc hydroxide and a cation are dispersed in a solution containing at least one of a polyhydric alcohol and an alkyl ether, and heat treatment is performed, whereby fluorescence emission characteristics are obtained. The inventors have found that the present invention can be remarkably improved and have come up with the present invention.

  That is, in the method for producing a sol according to one means of the present invention, zinc hydroxide and a cation are dispersed in a solution containing at least one of a dihydric or higher polyhydric alcohol and an alkyl ether, followed by heat treatment.

  According to the present invention, it is possible to provide a sol containing zinc oxide fine particles capable of further improving fluorescence emission characteristics. Although there is an unclear point about this principle, the presence of cations when zinc hydroxide is heat-treated in a polyhydric alcohol solution or alkyl ether allows the cation crystal lattice to be formed during the formation of a zinc oxide crystal structure. The incorporation rate of defects such as oxygen defects is promoted in the crystal lattice, and the defect structure in the crystal lattice is thought to significantly improve the fluorescence and electrical conductivity characteristics of zinc oxide. .

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention can be implemented in many different modes and is not limited to the description of the embodiments and examples shown below. Not too long.

  The present embodiment relates to a sol manufacturing method, and the sol manufacturing method according to the present embodiment includes zinc hydroxide and a cation, at least one of a dihydric or higher polyhydric alcohol and an alkyl ether. One feature is that it is dispersed in a solution and heat-treated.

  In the present embodiment, zinc hydroxide is not limited, but it is preferably in the range of 0.001 mol / l to 0.5 mol / l with respect to the solution. By making it 0.001 mol / l or more, the production | generation reaction of zinc oxide can be accelerated, and aggregation of the zinc oxide particle produced | generated by setting it to 0.5 mol / l or less can be suppressed.

  The cation in this embodiment is not limited, but zinc ion, lithium ion, sodium ion, potassium ion, cesium ion, calcium ion, barium ion, aluminum ion, iron ion, manganese ion, cobalt ion, chromium It is preferable to include at least one of ions, ammonium ions, and tetramethylammonium ions.

  Moreover, although the cation in this embodiment is not necessarily limited, It is preferable that it is contained in 0.001 mol / l or more and 0.5 mol / l or less with respect to the said solution. When the amount is 0.001 mol / l or more, the added cation effectively acts on the growth process of the zinc oxide particles, and the physical properties can be easily controlled. When the amount is 0.5 mol / l or less, the particles are growing. The agglomeration is suppressed, and the production of particles having a uniform particle size and little aggregation is facilitated.

  Further, the cation in the present embodiment is not limited, but it is desirable to dissolve in the form of chloride, nitrate, sulfate, etc., because a salt having higher solubility in a solvent is more likely to react.

  In addition, the polyhydric alcohol in the present embodiment is not limited as long as it is divalent or higher, and various alcohols can be employed. For example, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4- It is more preferable to obtain at least one of butanediol and glycerin in order to obtain zinc oxide particles having a uniform particle diameter. In particular, a dihydric or higher polyhydric alcohol has a strong coordination interaction with a metal cation and suppresses the growth rate of zinc oxide particles. Therefore, reaction conditions that facilitate the synthesis of fine zinc oxide particles having a particle diameter of 20 nm or less can be created by using a polyhydric alcohol having a valence of 2 or more. Furthermore, by coordinating with the added cation, an effect of suppressing the occurrence of particle aggregation due to the addition of the cation can also be expected.

  In addition, the alkyl ether in the present embodiment is not limited, and various ones can be employed. For example, the inclusion of at least one of 2-methoxyethanol and 3-methoxypropanol increases the salt solubility. To preferred. Alkyl ethers often have a lower solution viscosity than polyhydric alcohols having a valence of 2 or more, and the use of alkyl ethers makes it possible to achieve uniform reaction conditions throughout the solution and to easily control particle size and the like. There is.

  Moreover, although the zinc hydroxide in this embodiment is not necessarily limited, it is also a preferable aspect that it is obtained by mixing a zinc compound and a basic solution. Zinc hydroxide obtained by this method is highly reactive and has a feature that the structure changes to zinc oxide relatively quickly even at 30 ° C., and is suitable for the synthesis of zinc oxide particles in a short time at low temperature. It becomes a precursor. The zinc compound is not limited, but is preferably zinc nitrate, zinc chloride, zinc acetate or a hydrate thereof, and the basic solution is not limited, but ammonia, sodium hydroxide, water It is preferable to contain at least one of lithium oxide, potassium hydroxide, sodium carbonate, lithium carbonate, potassium carbonate, calcium hydroxide, cesium hydroxide, and hydroxytetramethylammonium.

  In addition, the sol production method in the present embodiment is not limited, but is preferably heat-treated in a temperature range of 15 ° C. or higher and 180 ° C. or lower, more preferably 30 ° C. or higher and 120 ° C. or lower. By setting the temperature to 15 ° C. or higher, the production rate of zinc oxide particles can be increased, and by setting the temperature to 30 ° C. or higher, this effect can be made more remarkable. Moreover, aggregation of the particle | grains by excessive grain growth can be prevented by setting it as 180 degrees C or less, and this effect can be made more remarkable by setting it as 120 degrees C or less.

  In addition, the sol production method in the present embodiment is not limited, but is preferably heat-treated in the range of 15 minutes to 48 hours, more preferably 30 minutes to 24 hours. By making it 15 minutes or more, crystallization to zinc oxide can be promoted, and by making it 30 minutes or more, this effect becomes more remarkable. Further, the aggregation of particles due to grain growth can be suppressed by setting the heating time to 48 hours or less, and this effect becomes more remarkable by setting the heating time to 24 hours or less.

  According to the present embodiment, since cations are present in the solution, nucleation is promoted, and a sol in which zinc oxide nanoparticles having a particle diameter of about 20 nm or less are stably dispersed without purification is purified depending on conditions. And the defect structure on the surface of the zinc oxide particles contributing to fluorescence emission can be stably maintained. Further, since the incorporation of cations is promoted during the formation of the zinc oxide crystal lattice in the solution, oxygen defects are relatively easily introduced, and the fluorescence emission characteristics are remarkably improved. In addition to the above effects, the sol according to the present embodiment has an effect that the particle diameter can be reduced as compared with the known technique. Moreover, the production | generation speed | rate of a zinc oxide nanoparticle is accelerated | stimulated, and a zinc oxide nanoparticle can be produced | generated by the heat processing of a solution for 30 minutes by 75 degreeC heat processing.

  As described above, according to the present embodiment, it is possible to provide a sol containing zinc oxide fine particles capable of further improving the fluorescence emission characteristics.

Example 1
Hereinafter, the method for producing a sol according to the above embodiment was actually performed, and the effect was confirmed. This will be described in detail below.

(1) A step of obtaining zinc hydroxide gel by mixing zinc nitrate hexahydrate and aqueous ammonia solution.
2.97 g (0.01 mol) of zinc nitrate hexahydrate was dissolved in distilled water to make the total volume 100 ml, and 100 ml of a 0.1 mol / l zinc nitrate aqueous solution was prepared. Next, 0.66 ml of concentrated aqueous ammonia (15 mol / l) was dissolved in distilled water to make the total volume 100 ml, and 100 ml of 0.1 mol / l aqueous ammonia was prepared. When this aqueous ammonia was added to the aqueous zinc nitrate solution, white gel-like zinc hydroxide was immediately precipitated. The precipitate was centrifuged (3000 rpm, 5 min), dispersed in 100 ml of distilled water, and centrifuged under the same conditions as above. Further, after being dispersed in distilled water, the centrifugal operation was performed to remove unreacted ammonium ions and nitrate ions contained in the zinc hydroxide gel precipitate.

(2) A step of dispersing zinc hydroxide gel in ethyl glycol containing zinc ions (Zn ²⁺ ).
Zinc nitrate hexahydrate particles were weighed in a 300 ml beaker, ethylene glycol was added and completely dissolved to make the total volume 100 ml. At this time, the zinc ion concentration in the solution was set to 0 mol / l, 0.001 mol / l, 0.01 mol / l, and 0.1 mol / l. To this ethylene glycol solution in which zinc nitrate hydrate was dissolved, the gelatinous precipitate of zinc hydroxide was added and stirred with a glass rod to uniformly disperse, and then sealed.

(3) A step of heating the dispersed zinc hydroxide gel to obtain a zinc oxide nanoparticle-dispersed sol. (When temperature is 35 ° C)
A solution in which a gelatinous precipitate of zinc hydroxide was dispersed in ethylene glycol was placed in a thermostatic bath maintained at 35 ° C. and allowed to stand for 24 hours. This gave a milky white to nearly transparent sol. The obtained sol maintained a stable dispersed state without precipitation for more than 6 months.

(4) Evaluation of fluorescence emission characteristics of the zinc oxide nanoparticle-dispersed sol obtained from the above process.
Fluorescence emission characteristics of the nanoparticles contained in the obtained sol were evaluated. The sol was placed in a non-fluorescent cell and the fluorescence emission spectrum was measured with a fluorescence spectrophotometer (Shimadzu RF5300PC) at an excitation wavelength of 365 nm. The measurement results are shown in FIG. The fluorescence emission spectrum of a sol obtained by allowing zinc hydroxide to stand at 35 ° C. for 24 hours in ethylene glycol containing no zinc ions had a peak at a wavelength of 505 nm and an intensity of 195. In contrast, the fluorescence emission spectrum of a sol obtained by leaving zinc hydroxide standing at 35 ° C. for 24 hours in ethylene glycol in which zinc nitrate hexahydrate was dissolved at a concentration of 0.001 mol / l is shown in FIG. And a peak at an intensity of 290 at a wavelength of 510 nm. Furthermore, the fluorescence of the sol obtained by allowing zinc hydroxide to stand at 35 ° C. for 24 hours in ethylene glycol in which zinc nitrate hexahydrate was dissolved at concentrations of 0.01 mol / l and 0.1 mol / l. The emission spectrum had peaks with wavelengths of 514 nm and 520 nm and intensities of 710 and 990, respectively. Thus, when zinc hydroxide is allowed to stand in ethylene glycol containing zinc ions, as the zinc ion concentration increases, it is approximately five times more fluorescent than when ethylene glycol containing no zinc ions is used. It was confirmed that the emission intensity increased.

(5) Evaluation of crystallinity of zinc oxide nanoparticles obtained from the above process.
To 100 ml of the obtained sol, 100 ml of 0.2 mol / l ammonia water was added and stirred well to aggregate and precipitate the zinc oxide nanoparticles contained in the sol. The precipitate formed is 3000 r. p. m. After separating by centrifugation for 5 minutes, in order to remove and wash ethylene glycol and ammonium ions remaining in the precipitate, the precipitate is dispersed in 100 ml of distilled water and further centrifuged under the same conditions as above. It was.

  The obtained precipitate was allowed to stand at 35 ° C. for 12 hours and dried, and the powder obtained was measured with an X-ray diffractometer (MPX18 manufactured by Bruker AXS) at an acceleration voltage of 40 kV and a current of 100 mA. Measured under conditions. The result is shown in FIG. All peaks seen in this X-ray diffraction pattern are due to zinc oxide. From this, it was found that zinc hydroxide was crystallized into zinc oxide by heat treatment at 35 ° C. for 24 hours in ethylene glycol and ethylene glycol in which zinc nitrate hydrate was dissolved.

(Example 2)
In the following, zinc hydroxide is dispersed in ethylene glycol in which the zinc nitrate hexahydrate used in the above examples is dissolved and allowed to stand at 35 ° C., and water is added in pure ethylene glycol containing no cation. An example relating to the time-dependent change of the fluorescence emission intensity of the dispersion solution for the case where zinc oxide is dispersed and left at 35 ° C. will be described.

  After preparing a zinc hydroxide gel-like precipitate by the same method as shown in Example 1, in 100 ml of an ethylene glycol solution in which zinc nitrate hexahydrate was dissolved to a concentration of 0.05 mol / l. Zinc hydroxide was dispersed. Next, this solution was allowed to stand in an air constant temperature phase of 35 ° C. From this solution, 2 ml of the solution was taken every 30 minutes, and the fluorescence emission characteristics were evaluated. The sol was placed in a non-fluorescent cell and the fluorescence emission spectrum was measured with a fluorescence spectrophotometer (Shimadzu RF5300PC) at an excitation wavelength of 365 nm. FIG. 3 shows the relationship between the maximum intensity in the wavelength range of 400 nm to 600 nm and the standing time of the fluorescence emission spectrum of the collected solution. In addition, FIG. 3 also shows data obtained by using pure ethylene glycol containing no cation for comparison.

  When zinc hydroxide is dispersed in pure ethylene glycol containing no zinc ions as shown by white circles in FIG. 3 and allowed to stand at 35 ° C., the maximum intensity of fluorescence emission gradually increases as the standing time increases and 24 hours. After standing still, it became 195. On the other hand, when zinc hydroxide is dispersed in ethylene glycol in which 0.05 mol / l of zinc nitrate hexahydrate shown by the black circles in FIG. 3 is dispersed and allowed to stand at 35 ° C., the fluorescence emission intensity rapidly increases. The maximum intensity reached 850 after 12 hours of standing. The dependence of the maximum intensity of fluorescence on the standing time reflects the generation behavior of the phosphor particles. As described above, it has been clarified that by standing zinc hydroxide in ethylene glycol containing zinc ions, not only the fluorescence emission intensity increases but also the generation rate of phosphor particles increases.

(Example 3)
In the following, an example will be described in which zinc hydroxide is dispersed in ethylene glycol in which aluminum nitrate nonahydrate is dissolved instead of ethylene glycol in which zinc nitrate hexahydrate is used in the above examples.

  After preparing a zinc hydroxide gel precipitate by the same method as shown in Example 1, in 100 ml of an ethylene glycol solution in which aluminum nitrate nonahydrate was dissolved to a concentration of 0.01 mol / l. Zinc hydroxide was dispersed. Next, this solution was allowed to stand for 24 hours in an air constant temperature phase of 35 ° C. Thereby, a sol in which zinc oxide nanoparticles were stably dispersed was obtained. Fluorescence emission characteristics of the nanoparticles contained in the obtained sol were evaluated. The sol was placed in a non-fluorescent cell, and the fluorescence emission spectrum was measured with a fluorescence spectrophotometer (Shimadzu RF5300PC) at an excitation wavelength of 365 nm. The measurement results are shown in FIG. Further, for comparison, FIG. 4 shows a spectrum obtained by using pure ethylene glycol containing no cation and zinc ions in which zinc nitrate hexahydrate is dissolved so as to have a concentration of 0.05 mol / l. The fluorescence emission spectrum of the sol obtained by using the ethylene glycol solution containing it was shown.

  As shown in FIG. 4, the fluorescence emission intensity of the sol obtained by dispersing zinc hydroxide in ethylene glycol in which aluminum nitrate nonahydrate is dissolved is 10 to 80 when the fluorescence wavelength is in the range of 400 nm to 650 nm. Thus, the fluorescence emission intensity was greatly reduced as compared with ethylene glycol containing no cation. In this way, a result greatly different from the case of heat treatment in ethylene glycol containing zinc ions was obtained. This indicates that the fluorescence emission characteristics of the obtained zinc oxide nanoparticles are greatly influenced by the cation dissolved in ethylene glycol.

  The present invention can be used as a method for producing a sol, and is useful for forming a zinc oxide layer in, for example, a display using the sol, and has industrial applicability.

It is a figure which shows the fluorescence emission spectrum of the sol obtained by disperse | distributing zinc hydroxide in ethylene glycol which melt | dissolved ethylene glycol and zinc nitrate hexahydrate, and leaving still at 35 degreeC for 24 hours (excitation wavelength is 365 nm) . FIG. 3 is an X-ray diffraction pattern of particles contained in a sol obtained by dispersing zinc hydroxide in ethylene glycol in which ethylene glycol and zinc nitrate hexahydrate are dissolved and allowing to stand at 35 ° C. for 24 hours. The maximum fluorescence intensity (400 nm to 600 nm) of the fluorescence emission spectrum of the sol obtained by dispersing zinc hydroxide in ethylene glycol in which ethylene glycol and zinc nitrate hexahydrate are dissolved and allowing to stand at 35 ° C. and standing. It is a figure which shows the relationship of time. Fluorescence emission of sol obtained by dispersing zinc hydroxide in ethylene glycol in which ethylene glycol and zinc nitrate hexahydrate are dissolved and in ethylene glycol in which aluminum nitrate nonahydrate is dissolved and leaving it at 35 ° C. for 24 hours. It is a figure which shows a spectrum (excitation wavelength is 365 nm).

Claims (9)

  A method for producing a sol containing fine zinc oxide particles, wherein zinc hydroxide and a cation are dispersed in a solution containing at least one of a dihydric or higher polyhydric alcohol and an alkyl ether, and heat-treated.   The cation is at least one of zinc ion, lithium ion, sodium ion, potassium ion, cesium ion, calcium ion, barium ion, iron ion, manganese ion, cobalt ion, chromium ion, ammonium ion and tetramethylammonium ion. The method for producing a sol according to claim 1, comprising:   The method for producing a sol according to claim 1, comprising the cation in a range of 0.001 mol / l to 0.5 mol / l.   The method for producing a sol according to claim 1, wherein the polyhydric alcohol contains at least one of ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, and glycerin.   The method for producing a sol according to claim 1, wherein the alkyl ether contains at least one of 2-methoxyethanol, 3-methoxypropanol, and 3-methoxybutanol.   The method for producing a sol according to claim 1, wherein the zinc hydroxide is obtained by mixing a zinc compound and a basic solution.   The method for producing a sol according to claim 4, wherein the zinc compound contains at least one of zinc nitrate, zinc chloride, zinc acetate, or a hydrate thereof.   The basic solution contains at least one of ammonia, sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium carbonate, lithium carbonate, potassium carbonate, calcium hydroxide, cesium hydroxide, and hydroxytetramethylammonium. A method for producing the sol as described. The method for producing a sol according to claim 1, wherein the heat treatment is performed at 15 ° C. or higher and 180 ° C. or lower.