KR100843190B1 - Method of fabrication of zinc oxide by freeze drying at low temperature - Google Patents

Abstract

A method for manufacturing nano-size zinc oxide is provided to produce the zinc oxide in a simpler manner and at a lower cost than the conventional production methods, and to enable the control of particle size ranging from several nm to several dozen nm according to temperature control. A method for manufacturing nano-size zinc oxide by low-temperature freeze drying includes the steps of: dissolving a zinc oxide powder having a particle size of 0.5 micron or larger in an organic acid to prepare a zinc salt precursor solution; adding an aqueous base solution and a complex-forming agent to the prepared zinc salt precursor solution, and mixing the admixture; aging and crystallizing the aqueous mixture solution at low temperature ranging from -5 °C to 5 °C; freeze-drying the aged aqueous mixture solution; and washing, filtering, and drying the lyophilized powder of the aqueous mixture solution. Further, the aqueous base solution is at least one selected from sodium hydroxide, potassium hydroxide, ammonia and lithium hydroxide.

Description

Manufacturing method of nano zinc oxide by low temperature lyophilization {METHOD OF FABRICATION OF ZINC OXIDE BY FREEZE DRYING AT LOW TEMPERATURE}

The present invention relates to a method for producing nano zinc oxide by low temperature lyophilization, and more particularly to a method for producing uniform ultrafine zinc oxide particles having a size of 10 nm by low temperature lyophilization method rather than conventional high temperature hydrothermal method. It is about.

Zinc oxide (ZnO) is a catalyst for the synthesis of varistors, electrophotographic photosensitizers and methanol from traditional applications such as rubber crosslinkers, ferrites, paint film reinforcements, glass, pigments and anti-inflammatory agents, and traditional applications such as wires, batteries and white colorants. It is used in many fields such as gas sensor and phosphor.

In addition, since the ultraviolet ray blocking effect is large, the surface of zinc oxide can be used as a ultraviolet absorber by treating it with silica or the like, and is used in fields such as UV cut cosmetics. On the other hand, in order to efficiently remove impurities such as sulfur oxides, halogens and dust contained in coal gas, absorbents have been developed that combine iron oxide having a high rate of sulfur absorption and zinc oxide having excellent dehydration performance.

There are many other new features found in zinc oxide, with the potential for new applications in the future.

Conventional methods for producing zinc oxide include sol-gel method, flame pyrolysis, spray pyrolysis, gas-phase method, calcination, calcining method sintering, milling and the like have been used.

Among them, the conventional milling method of producing fine particles is practically impossible to make nano-sized particles, and it is difficult to control the particle size distribution of nano-sized particles.

For example, according to a paper published by Dea Jong Seo et al., Zinc acetate dehydrate and zinc nitrate hexahydrate are used as raw materials of ZnO, and the temperature is 900 to 1,900 ° C. A method for producing ZnO powders using flame pyrolysis is disclosed (Journal of nanoparticle Research 5: 199-210p, (2003)).

Although small particles having a size of 30 nm were obtained by this method, there was a problem in that crystallinity was not good.

In addition, a method for producing ZnO from ZnS by calcination method after hydrothermal synthesis using Zn (CH ₃ COO) ₂ .2H ₂ O as a raw material [Hao-Ying Lu, etc., Journal of Crystal Growth 269: 385-391p. , (2004)], Zn (NO ₃ ) ₂ as a raw material to obtain ZnO by centrifugation by precipitation method [AB Kashyout, etc., Materials Chemistry and Physics 90: 230-233p, (2005)], etc. Although a method for producing nanoparticles has been proposed, there is a problem in that a complicated manufacturing process is required by the above method.

In the nano ZnO manufacturing method, the sol-gel method is to make various kinds of inorganic network from a metal alkoxide unit precursor such as silicon. This method was first discovered in the late 1800's and actively studied since the 1930's. However, in the 1970's, a single inorganic gel made it possible to convert from low temperatures to glass without melting at high temperatures.

Unlike the traditional method of making inorganic glass by melting at high temperature, this process can produce homogeneous inorganic oxides with good properties such as hardness, transparency, chemical stability, controlled porosity and thermal conductivity at room temperature. By applying these sol-gel processes to make glass or ceramics, special methods have been developed to obtain single monoliths, thin films, fibers, and single-size powders by molding into various shapes in the gel state. This method can be used to make optical materials, protective and porous films, optical coatings, window insulators, dielectric and electronic material coatings, high temperature superconductors, reinforcing fibers, fillers, and catalysts.

However, even by the conventional sol-gel method, a separate high temperature hydrothermal process is required, there is a disadvantage in that a method such as a high pressure reactor and supercritical drying is used, and there is a problem that there is a limit in obtaining spherical uniform crystals. have.

The present invention is to solve the above problems, the object of the manufacturing process is simple compared to the conventional gas phase method, mechanical milling, calcination method, etc., but also inexpensive in terms of manufacturing cost, the particle size of several nano to several tens of nanometers under temperature control The present invention provides a method for manufacturing nano zinc oxide that can be controlled.

In addition, it is an object of the present invention to provide a method for preparing nano zinc oxide, which can produce nanoparticles of high purity by low temperature aging and freeze-drying without sol-gel method, by low temperature aging and lyophilization.

The method for producing nano zinc oxide powder by low temperature freeze drying according to the present invention for solving the above problems comprises the steps of preparing a precursor to prepare a zinc salt precursor solution by dissolving zinc oxide powder having a particle size of 0.5 μm or more in an organic acid; A mixing step of adding and mixing a basic aqueous solution and a complex forming agent to the zinc salt precursor solution produced by the precursor preparing step; A low temperature aging step of crystallizing the mixed aqueous solution formed after the mixing step at a low temperature of −5 to 5 ° C .; A freeze drying step of freeze drying the mixed aqueous solution aged after the low temperature aging step; It comprises a washing step of washing and filtering the frozen powder of the mixed aqueous solution having completed the freeze-drying step and dried.

Here, the freeze-drying step, the freezing step of solidifying the material by cooling the aged mixed aqueous solution to -100 ℃ to -10 ℃ temperature; And a sublimation step of subliming the water contained in the freeze powder by lowering the pressure to 4.6torr or less in a state where the temperature is kept constant in the freeze powder of the mixed aqueous solution formed after the freezing step.

In addition, the organic acid used in the precursor manufacturing step, it is preferable to use at least one of carboxylic acid, palmitic acid, formic acid, oxalic acid, tartaric acid, sulfonic acid, sulfinic acid alone or in combination for optimal properties.

The base aqueous solution used in the mixing step is preferably at least one aqueous solution of sodium hydroxide, potassium hydroxide, ammonia, lithium hydroxide.

In addition, the volume ratio of the zinc salt precursor solution and the base aqueous solution used in the mixing step is 1: 1.5 to 1: 2.5 is preferred in order to implement the minimum particle size and uniform crystal grains.

In addition, the volume ratio of the zinc salt precursor solution and the complexing agent used in the mixing step is preferably 200: 1 to 20: 1 to prevent deagglomeration of the final product.

In addition, the complexing agent used in the mixing step is preferably a mixture of at least one of triethanolamine, diethanolamine, monoethanolamine, ethylenediamine, thioacetamide alone or mixed.

In addition, the mixing step is preferably performed at a low temperature of -10 to 10 ℃ in order to limit the crystal growth as much as possible.

In addition, the low temperature aging step is preferably carried out for 15 to 120 minutes for economical and efficient low temperature aging.

According to the present invention, the manufacturing process is simpler than the conventional gas phase method, mechanical milling, calcining method, etc., and the manufacturing cost is low, and the manufacturing method of nano zinc oxide which can control the particle size from several nanometers to several tens nanometer by temperature control. To provide.

In addition, by the sol-gel method, it is possible to provide a method for producing nano zinc oxide that can produce a high-purity nano-sized particles of less than 10nm by low temperature aging and freeze-drying without high temperature hydrothermal process.

Hereinafter, a method for producing nano zinc oxide by low temperature freeze drying according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart sequentially showing a method for producing nano zinc oxide by low temperature freeze drying according to the present invention.

As shown in Figure 1, the method for producing nano zinc oxide by low temperature lyophilization according to the present invention is a precursor manufacturing step (S10) to prepare a zinc salt precursor solution by dissolving zinc oxide powder having a particle size of 0.5㎛ or more in an organic acid Wow; A mixing step (S20) of adding and mixing a basic aqueous solution and a complex forming agent to the zinc salt precursor solution produced by the precursor preparing step (S10); A low temperature aging step (S30) of aging the mixed aqueous solution formed after the mixing step at -5 to 5 ° C at low temperature to crystallize; Freeze drying step (S40) for lyophilizing the aged mixed aqueous solution; It comprises a washing step (S50) of washing and filtering the frozen powder of the mixed aqueous solution that has completed the freeze-drying step to dry.

First, a precursor producing step (S10) is carried out by preparing a zinc precursor solution containing Zn ^{2 +} ions by dissolving zinc oxide (ZnO) or more of the raw material particle size 0.5㎛ high purity (over 99.98%) in an organic acid.

Here, the particle size is different depending on the type of organic acid used. The organic acid is carboxylic acid (R'-COOH) such as acetic acid (CH ₃ COOH), butyric acid (C ₃ H ₇ COOH), palmitic acid (CH ₃ (CH ₂ ) ₁₄ COOH), oxalic acid (C ₂ H ₂ O ₄ ) , Organic acids, such as tartaric acid (C ₄ H ₆ O ₆ ), sulfonic acid (R-SO ₃ H), sulfinic acid (R-SO ₂ ) may be used alone or in combination, preferably acetic acid (CH ₃ COOH) use. Here, R represents an alkyl group and R 'represents an alkyl group or a hydrogen group.

Thus, the particle size of the final product ZnO powder can be minimized by using an organic acid instead of the conventional method using a nitrate aqueous solution. Here, since impurities may exist in the solution, it is used after filtering.

The mixing step (S20) is the precursor producing step (S10) of zinc precursor solution of triethanolamine (triethanolamine, TEA) as a complexing to form a dispersed Zn ^{2 +} ions the complex (chelate compound) in generated from di At least one of ethanolamine (DEA), monoethanolamine (MEA), ethylenediamine, thioacetamide (TAA), more preferably triethanolamine (TEA), diethanolamine ( An aqueous solution of at least one of DEA) alone or mixed is added thereto, followed by mixing by addition of a basic aqueous solution to form an amorphous ZnO.nH ₂ O compound through a hydrolysis and condensation step by an acid group reaction. That is, a nucleus or seed of crystal growth of ZnO is generated. Here, the order of addition of the complexing agent and addition of the base aqueous solution may be changed.

The base aqueous solution includes an alkali metal hydroxide or aqueous ammonia solution, preferably at least one of an aqueous solution of sodium hydroxide (NaOH), potassium hydroxide (KOH), aqueous ammonia (NH ₄ OH), lithium hydroxide (LiOH) alone or It can be mixed and used.

The zinc oxide particle size changes depending on the type of base. The volume ratio of the basic aqueous solution to the zinc salt precursor solution is preferably 1: 1.5 to 1: 2.5, more preferably 1: 1.8 to 1: 1.2. When the volume ratio of the base aqueous solution to the zinc salt precursor aqueous solution is less than 1: 1.5, and the amount of the base aqueous solution is small, the shape of the particles exhibits a needle shape, resulting in inferior uniformity. There is a problem that becomes large.

When a complexing agent, such as TEA, is added to an aqueous solution of a zinc salt precursor, initially a chelating compound (complex) around Zn ^{2 +} ions is formed, and the zinc ions are ligands of the chelate compound during the process. By forming a nucleus and growing in a protected state by, it is effective in the deagglomeration in the final ZnO powder production.

The volume ratio of the complexing agent to the zinc salt precursor solution is preferably 200: 1 to 20: 1, more preferably 150: 1 to 10: 1. If the volume ratio of the complexing agent is less than 0.5% (200: 1) relative to the zinc salt precursor solution, it is not good for the deagglomeration of the particles. If the amount is more than 5% (20: 1), the size of the ZnO particles is not affected. However, the manufacturing cost due to the consumption of the complexing agent is increased. In the mixing step (S20), a conventional mechanical mixing method is used.

The hydrolysis and condensation reaction in the mixing step (S20) is preferably carried out at a low temperature of -10 to 10 ℃, more preferably -5 to 5 ℃, even more preferably -2 to 2 ℃. . The reason for proceeding the mixing step (S20) by the low temperature reaction is to reduce the solubility as much as possible to suppress the growth of the particles to reduce the particle size.

When the temperature at which the hydrolysis and condensation reaction is performed is -10 ° C. or less, there is a problem in that the rate of the reaction is too slow. On the other hand, when the temperature is 10 ° C. or more, the size of the crystalline ZnO particles is increased to 10 nm or more by a fast reaction. high portential.

Here, even if the mixing step (S20) is not carried out at a low temperature, there is no significant effect because it maintains a low temperature in the low temperature aging step (S30), but by performing a low temperature reaction from the mixing step (S20) to obtain more fine particles Can be.

The low temperature aging step (S30) is a mixture of the resulting solution through the mixing step (S20) for a predetermined time of preferably at -5 to 5 ℃, more preferably -2 to 2 ℃ temperature of the seed (seed) This step is to slow down the crystallization reaction (crystal growth) as much as possible.

Here, when the aging temperature is -5 ℃ or less, there is a problem that the rate of the reaction is too slow, when 5 ℃ or more, on the contrary, the size of the crystalline ZnO particles by the rapid reaction is likely to increase to 10 nm or more.

The ripening time is preferably 15 minutes to 120 minutes, more preferably aged for 30 to 60 minutes. If the aging time is less than 15 minutes, the ZnO crystal nuclei grow rapidly, which may increase the particle size.If aging for more than 120 minutes, there is no big problem, but it is not preferable for the rapid process because sufficient aging time has already passed. Can not do it.

Freeze drying step (S40) is a technical feature of the present invention in addition to the low temperature aging step (S30). By slowing the crystal growth as much as possible in the low temperature aging step (S30) and removing all the water contained in the particles by the freeze-drying step (S40), rather smaller nanoparticles can be produced without a high temperature hydrothermal process.

The freeze-drying step (S40) is a freezing step (S41) for solidifying the material by cooling the mature mixed solution to -100 ℃ to -10 ℃ temperature; It comprises a sublimation step (S42) for subliming the water contained in the freeze powder by lowering the pressure to below the triple point of water in the state of maintaining a constant temperature in the freezing powder of the mixed aqueous solution formed by the freezing step (S41) desirable.

That is, the freeze-drying step (S40) is to freeze the mature mixed solution to -100 ℃ to -10 ℃ temperature, more preferably -80 ℃ to -30 ℃ temperature (S41), the pressure at the freezing temperature of water 3 By lowering below the middle point (6mbar, 4.6torr) is a process of removing all the water present in the mixed solution through the process of sublimating the ice present in the mixed solution directly to the steam (S42).

If the freezing temperature is less than -100 ℃ can lead to excessive energy waste, if it is more than -10 ℃, there may be a problem that the freezing is not performed properly.

The washing step (S50) uses a general method. For example, after removing all impurities present in the particles by distilled water while filtering the impurities using distilled water, the process of drying the generated particles through a dryer, for example, an oven is performed. .

Hereinafter, by the examples and comparative examples of the present invention to look at the results of the application of the present invention.

Example

28 g of zinc oxide powder with 0.5 μm, 99.98% purity A mixed aqueous solution obtained by mixing a small amount of 1 M TEA solution (98%) with 350 ml of zinc acetate aqueous solution (Zn-acetate) dissolved in 2 M acetic acid (CH ₃ COOH) solution at a flow rate of 71 ml / min, and 735 ml of 1 M NaOH aqueous solution It was supplied into the mixer using a metering pump at a flow rate of 145 ml / min, mixed by mechanical mixing for 5 minutes, and the mixed solution of Zn-acetate-NaOH-TEA was mixed in a low temperature container at 0 ° C. for 30 minutes. After aging at low temperature, the resultant was placed in a lyophilizer (D8508PT of ILSHIN LAB CO. LTD.), Lyophilized for 48 hours at a pressure of 4.5 torr under -70 ° C, and then the zinc oxide powder formed was subjected to X-ray diffraction (XRD), BET. Observation was made using the Brunauer-Emmett-Teller method.

The XRD results of the frozen powders run before washing are shown in FIG. 2.

XRD results and TEM photographs of the frozen powder after washing are shown in FIGS. 3A and 3B, respectively.

Comparative example  One

After the low temperature aging step, the same manufacturing method as in Example was performed except that the washing was performed at room temperature (25 ° C.) without undergoing lyophilization.

XRD results and TEM images of the ZnO powders are shown in FIGS. 4A and 4B, respectively.

Comparative example  2

After the low temperature aging step was subjected to the same production method as in Example, except that the aging was performed for 24 hours at room temperature (25 ℃) without undergoing lyophilization.

XRD results and TEM images of the ZnO powders are shown in FIGS. 5A and 5B, respectively.

Comparative example  3

After the low-temperature aging step was subjected to the same production method as in Example, except that the aging for 24 hours at 60 ℃ without undergoing lyophilization.

XRD results and TEM images of the ZnO powders are shown in FIGS. 6A and 6B, respectively.

Comparative example  4

After the low temperature aging step was subjected to the same production method as in Example, except that after aging for 24 hours at 100 ℃ without lyophilization.

XRD results and TEM images of the ZnO powders are shown in FIGS. 7A and 7B, respectively.

Table 1 below summarizes the particle size obtained by TEM image, the observation result of crystal size, and the size and surface area measurement result by BET. Here, the grain size is derived from the Scherrer formula based on XRD data.

Table 1 Unit: Particle Size (nm)

Surface area (m ² / g)

Classification TEM particle size XRD Grain Size BET particle size Surface Area (BET) nm m ² / g Example 10 9 13 79 Comparative Example 1 100 to 200 22 52 20 Comparative Example 2 100 to 200 19 - - Comparative Example 3 50 to 200 20 - - Comparative Example 4 50 to 100 23 55 19

Looking at the results for the above example, first, the frozen powder before washing, as shown in FIG. 2, ZnO particles were not produced (only on XRD), only the crystal phase of sodium acetate (CH ₃ COONa) appeared. In addition, as shown in Figures 3a and 3b, as the lyophilized amorphous ZnO? NH ₂ O undergoes dehydration or condensation during washing (at room temperature), as shown in <Table 1>, as small as 10nm or less Particles were produced. In addition, the specific surface area per weight reaches 79 m ² / g.

However, as shown in Figures 4a and 4b, ZnO particles dried and washed at room temperature without lyophilization of Comparative Example 1 is in the shape of leaves due to growth and aggregation by room temperature condensation reaction, as shown in Table 1 Likewise, the particle size was 100 nm or more and the surface area per weight was prepared at 20 m ² / g.

Similarly, in the case of Comparative Example 2, as shown in Figs. 5A and 5B, the particle size becomes large (particle size 100 to 200 nm). 6A and 6B, it can be seen that the particle size is increased (50 to 200 nm) in a triangular shape, and in Comparative Example 4, as shown in FIGS. 7A and 7B, The particle size is smaller (50 to 100 nm) than at room temperature and 60 ° C. However, it can be seen that the particle size is larger than the case of lyophilization, and the surface area per weight is as small as 19 m ² / g.

It has been described in detail above with reference to a preferred embodiment and comparative example of the present invention. However, the scope of the present invention is not limited to the above embodiments, but may be embodied in various forms of embodiments within the appended claims. Without departing from the gist of the invention as claimed in the claims, any person skilled in the art to which the invention pertains is considered to be within the scope of the claims of the invention to the various possible modifications possible.

1 is a flow chart of a method for producing nano zinc oxide by low temperature freeze drying according to the present invention

2 and 3 are XRD results and TEM photographs of nano zinc oxide powder prepared according to an embodiment of the present invention

4 is an XRD result and TEM photograph of the nano zinc oxide powder prepared by Comparative Example 1 of the present invention

5 is an XRD result and TEM photograph of the nano zinc oxide powder prepared by Comparative Example 2 of the present invention

6 is an XRD result and TEM photograph of the nano zinc oxide powder prepared by Comparative Example 3 of the present invention

7 is an XRD result and TEM photograph of the nano zinc oxide powder prepared by Comparative Example 4 of the present invention

Claims (9)

In the manufacturing method of nano zinc oxide powder, A precursor preparation step of preparing a zinc salt precursor solution by dissolving zinc oxide powder having a particle size of 0.5 μm or more in an organic acid; A mixing step of adding and mixing a basic aqueous solution and a complex forming agent to the zinc salt precursor solution produced by the precursor preparing step; A low temperature aging step of crystallizing the mixed aqueous solution formed after the mixing step at a low temperature of −5 to 5 ° C .; A freeze drying step of freeze drying the mixed aqueous solution aged after the low temperature aging step; Method for producing nano zinc oxide powder by low temperature lyophilization characterized in that it comprises a washing step of washing and filtering the frozen powder of the mixed aqueous solution that has completed the freeze-drying step. The method of claim 1, The freeze drying step, the freezing step of cooling the aged mixed solution to -100 ℃ to -10 ℃ temperature to solidify the material; And a sublimation step of subliming the water contained in the freeze powder by lowering the pressure to 4.6torr or less in a state in which the freezing powder of the mixed aqueous solution formed after the freezing step maintains the cooling temperature of the freezing step constant. Method for producing nano zinc oxide powder by low temperature freeze drying. The method of claim 1, The organic acid used in the precursor preparation step, nano zinc oxide powder by low temperature lyophilization, characterized in that at least one of carboxylic acid, palmitic acid, formic acid, oxalic acid, tartaric acid, sulfonic acid, sulfinic acid, or used in combination. Manufacturing method. The method of claim 1, The base aqueous solution used in the mixing step is a method for producing nano zinc oxide powder by low temperature lyophilization, characterized in that the aqueous solution of at least one of sodium hydroxide, potassium hydroxide, ammonia, lithium hydroxide. The method of claim 1, The volume ratio of the zinc salt precursor solution and the base aqueous solution used in the mixing step is 1: 1.5 to 1: 2.5 method for producing nano zinc oxide powder by low temperature lyophilization. The method of claim 1, The volume ratio of the zinc salt precursor solution and the complexing agent used in the mixing step is 200: 1 to 20: 1 method for producing nano zinc oxide powder by low temperature lyophilization. The method of claim 1, Complex forming agent used in the mixing step of the nano zinc oxide powder prepared by low temperature freeze-drying, characterized in that at least one of triethanolamine, diethanolamine, monoethanolamine, ethylenediamine, thioacetamide alone or mixed Way The method of claim 1, The mixing step is a method of producing nano zinc oxide powder by low temperature lyophilization, characterized in that carried out at a low temperature of -10 to 10 ℃. The method of claim 1, The low temperature aging step is a method for producing nano zinc oxide powder by low temperature lyophilization, characterized in that performed for 15 minutes to 120 minutes.

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