KR100725444B1 - Method for producing zinc oxide nanoparticles - Google Patents

Abstract

The present invention relates to a method for producing zinc oxide nano powder by mechanochemical process. The method according to the invention involves the synthesis of ultrafine zinc oxide nanoparticles by mechanochemical process with zirconia vol. These balls mechanically activate the solid phase substitution reaction, induce a salt matrix and then wash and centrifuge the milled powders to remove NaCl. The heat treatment of the washed powder yields a light yellow powder, which is significantly prevented from flocculation of the particles after milling and subsequent removal of the soluble reaction by-products.

The method for producing zinc oxide nanopowders according to the present invention has the advantage of being able to mass-produce ZnO nanoparticles at low cost by the above configuration.

Description

A method for preparing zinc oxide nanoparticles

1 is a graph showing the XRD crystal size and BET particle size distribution according to the size of the zirconia ball after washing and heat treatment at 500 ℃.

FIG. 2 is a graph showing the XRD pattern of ZnCl ₂ + Na ₂ CO ₃ powder mixture after (a) washing and centrifugation with deionized water and (b) microchuck

3 is an X-ray curve of ZnO powder after firing at various temperatures for 2 hours.

4 shows zirconia balls and powders in various volume ratios {(a) ball: powder = 4: 1, (b) ball: powder = 5: 1, (c) ball: powder = 7: 1 and (d) ball: TEM image of ZnO particles after milling with powder = 10: 1}.

5 is a TEM image of ZnO particles when ZnCl ₂ : Na ₂ CO ₃ is a molar ratio of (a) 1: 1, (b) 1: 2 and (c) 2: 1.

6 is a UV-Vis absorption spectrum of ZnO and TiO ₂ nanopowders.

The present invention relates to a method for producing zinc oxide nanoparticles.

Zinc oxide Nano powder  Use and manufacturing method

Because of their electrical and optical properties, zinc oxide (ZnO) is used in a variety of fields such as varistors, dyes, and cosmetics. However, since zinc oxide easily aggregates, there is a limit in dispersibility. Zinc oxides used in gas sensors, catalysts, solar cells, electrodes, light emitting diodes (LEDs), cosmetics or biomaterials are very expensive. Oxides of Zn, Sn, In, Cd and Ga are used as semiconductors. Among these oxides, zinc oxide reacts at low temperatures, is chemically stable, and has excellent electrical conductivity and permeability.

GaN is mainly used as LED and laser diode (LD). However, zinc oxide is considered as a next generation light emitting device material due to process uniformity, number rate, reduction of film thickness, and its excellent properties and entropy.

In addition, these semiconductor materials can be classified into thermistors and varistors. In addition, zinc oxide inhibits ultraviolet radiation and has a high conductive band gap (3.27 eV) and binding energy (60 meV). In addition, the low temperature process of producing zinc oxide is very efficient. Zinc oxide is useful in a variety of applications because of its ability to take various forms such as nanowalls, nanorings, nanobridges, nanonail, nanorods and nanoneedles.

In particular, titanium oxide (TiO ₂ ) and zinc oxide may be used as a photocatalyst to block ultraviolet rays. Zinc oxide is a nanopowder composed of a material that inhibits the UV-A wavelength with a band gap of 3.27 eV, and TiO ₂ has a band gap inhibition of 2.99 eV in the UVB range. These UV inhibitions are useful in high quality paints such as cosmetics or coating materials.

Recently, zinc oxide doped with TiO ₂ has been developed into composites using silica beads. This composite is a highly efficient nanopowder material that blocks both UV-B and UV-A wavelengths. Common methods for preparing nanoparticles include precipitation, sol-gel, solvent evaporation, sputtering, pyrolysis, hydrothermal processes, ultrasonic spray pyrolysis, and mechanochemical processes. However, mechanochemical processes have been used in the production of ultrafine powders, which induce reactions during the milling process or at low temperature heat treatment to form a composite powder consisting only of fully dispersed ultrafine particles embedded in soluble salt byproducts. Recently, a wide range of nanoparticles have been synthesized by mechanochemical processes, for example SeO ₂ , SnO ₂ , ZnO, CdS, ZrO ₂ , CeO ₂ , LiMn _{2 -x} Co _x O ₄ , and LiB ₂ O ₇ . Mechanochemical synthesis is a simple and inexpensive process and therefore particularly suitable for mass production.

Hereinafter, the sunscreen which is the main use of zinc oxide is demonstrated.

About UV rays and sunscreen

Sunlight is composed of ultraviolet light, visible light, infrared light, and the like, which is invisible to the human eye in the electromagnetic spectrum and has a wavelength range of 100 to 3800 angstroms. Although it has less permeability than ordinary X-rays or gamma rays, it has higher energy than visible light, and thus affects human skin and small organisms.

Ultraviolet rays can have beneficial effects, such as bactericidal action and vitamin D synthesis, but they can also have a number of adverse effects on the skin. When exposed to UV rays, blackening reactions (skin tanning) occur immediately. After two to three hours, it disappears, but after several hours, a sunburn occurs, such as erythema (reddening of the skin locally) or edema, and pigmentation occurs. Temporarily, the skin will not only dry out, but in the long run it will be uneven. Chronic exposure to UV rays may cause skin wrinkles, sagging, and serious skin cancer.

There are three types of ultraviolet rays: UVA, UVB, and UVC. Among them, UVB is contained in a small amount in the sun, but it causes spots, freckles, DNA destruction, skin cancer, etc., and a sunscreen applied to the skin to block UV rays mainly blocks UVA and UVB.

The blocking of ultraviolet light can be achieved by the application of a physical blocker or a chemical blocker. Among them, physical barrier agents include physical properties that reflect and scatter ultraviolet rays, such as TiO ₂ (titanium dioxide), ZnO (zinc oxide), iron oxides, and magnesium oxides. In the case of using such an inorganic raw material, the skin irritation feeling is low, but since the cream or lotion should be mixed in a lot, the feeling of use becomes heavy, and when the product is applied, white opacity (aka cloudy phenomenon) has a disadvantage. On the other hand, chemical blocking agents are substances that absorb ultraviolet rays by being trapped in a molecule and exhibit a blocking effect, and stability problems to the human body such as contact dermatitis, photoallergy or cancer have been raised. The importance of physical blockers is increasing.

Currently, inorganic sunscreens include zinc oxide having excellent blocking effect in the UV-A region and titanium oxide having excellent blocking effect in the UV-B region. Since zinc oxide is advantageous in terms of dispersibility as compared to titanium oxide as a UV blocking agent, research on zinc oxide is currently becoming the mainstream. When the size of the zinc oxide particles is smaller than the wavelength of the visible light, the visible light may pass through the zinc oxide dispersion. In addition, as the size of the zinc oxide particles decreases, it effectively scatters and absorbs the absorbed ultraviolet rays. Therefore, it is excellent in dispersibility and manufacturing nano-sized zinc oxide particles is advantageous in terms of ultraviolet absorption and visible light transmittance.

Conventional zinc oxide particles have been mainly used in a gas phase process, that is, a method in which zinc metal is vaporized and then reacted with oxygen gas present in the air. However, in the case of the zinc oxide particles produced using the gas phase method, zinc metal that does not react with oxygen is present, and the zinc oxide particle size distribution formed cannot be controlled. When these unreacted metal zinc particles are present in applications such as cosmetics, paints, plastics, and the like, they react with air, moisture, and organic materials to generate unwanted gases.

In addition, the liquid phase method also requires a number of cleaning processes, there is a problem that the yield is low.

Developed in this way, zinc compounds (zinc sulfide, zinc chloride, zinc acetate, etc.) are dissolved in water and precipitated in the form of zinc carbonate, followed by the mechanochemical method of producing oxides through washing, filtering and calcination processes. For example, ZnCl ₂ (Cerac, 99.5%, -8mesh) and Na ₂ CO ₂ (Aldrich, 99 +%, -20mesh) powder were added with the substitution agent NaCl (Aldrich, 99.8%, ˜0.5 mm bead). It is made to react using hardened steel vial and hardened steel ball (6.4mm). At this time, the specific gravity of the ball and powder is used as 10: 1. After 4 hours of reaction, it was calcined at 400 ° C., washed in a centrifuge, and NaCl removed to synthesize 10-40 nm zinc oxide particles (“ZnO nanoparticles synthesized by mechanochemical processing”, Takuya Tsuzuki and Paul G. McCormick, Scripta). mater. 44 (2001) 1731-1784.

However, the technique of the above document has a disadvantage in that the reaction time is long, the hassle of substitution reaction with NaCl, the resulting yield is reduced, and a plurality of equipments are required.

The present invention has been made to overcome the disadvantages of the prior art described above. That is, the present invention is a method for producing zinc oxide nanoparticles to be used as a sunscreen, it is possible to reduce the raw material using an industrial sample, have a high yield, dozens of nano-size white when used as a sunscreen for skin It aims to provide a method for producing nano-sized zinc oxide, which is skin-friendly, light yellow and similar to skin, and is uniform and dispersible.

In order to achieve the above object, the present invention provides a method for producing zinc oxide nanoparticles, characterized in that after the ZnCl ₂ and NaCO ₃ is mixed with zirconia balls, ZnO nanoparticles are prepared by heating, washing and centrifugation. .

In the present invention, determining the particle size of the zinc oxide nanoparticles is achieved by the size of the zirconia ball. Zirconia balls apply local heating and pressure at the contact surface, thus promoting low temperature chemical reactions.

Example

C ₁₆ H ₁₆ N ₄ ZnCl ₂ (DaeJung), anhydrous sodium carbonate (Na ₂ CO ₃ , DeaJung) and zirconia balls (3.5 mm, 5 mm, 6 mm, 9.5 mm; DAIHAN) were used as starting materials.

In this example, sodium carbonate was used as a catalyst for promoting the hydrolysis reaction. The reaction mixture was milled in a hardened steel vial using a vibrating Spex 8000 mixer / mill with zirconia balls. The mass ratio of the ball to the powder was prepared from 4: 1 to 10: 1, and the milling time was 1 to 4 hours.

To remove the byproduct NaCl, the milled powder was washed with deionized water in an ultrasonic bath and centrifuged. The washed powder was dried at 10 ° C. for 24 hours and heat treated for 2 hours at a temperature between 200 and 500 ° C. under a sealed N ₂ atmosphere. Particle size and dispersion of ZnO were analyzed by dynamic light scattering (DLS, ELS-8000, Otsuka Co.). The surface area of the powder was measured using a BET (Gemini 2360, Micromeritics) surface area analyzer. The size and morphology of the zinc oxide powder were characterized by electron transmission microscopy (TEM, JEM2010, JEOL) and the optical properties were investigated by UV-Vis spectrometer (Ultrospec 2000, Pharmacia Biotech).

1 shows the change in XRD crystal size and BET particle size. The particle size of the crystal was analyzed from the measurement width of the diffraction curve. For correct processing, we followed the Scherrer equation t = 0.9 / Bcosθ _B for hexagonal peaks. The average particle size is estimated from the measurement of the specific surface area through a relationship of D = 6 / Sρ (where D is the average diameter, S is the specific surface area and ρ is the particle density). In order to obtain monodisperse ZnO particles, zirconia balls of various sizes were used for mixing. As a result of the test, the XRD crystal size and the BET particle size gradually decreased with the size of the zirconia ball, but the BET crystal size increased more homogeneously by calcining at 500 ° C. after 2 hours milling, like the XRD size.

2 shows ZnCl ₂ for powder (a) washed and centrifuged and finely divided powder (b) after 2 h polishing + XRD pattern of Na ₂ CO ₃ mixed powder. ZnCl _{2 in} milled powder The presence of + Na ₂ CO ₃ suggests that an exchange reaction occurred during polishing. After this exchange reaction, the detected NaCl peaks in the milling powder were two broad diffraction peaks at a 2θ value of 31.7. After washing to remove NaCl, only ZnO phase remained. The average crystal size of this washed and unwashed milling powder ranged from 3 to 5 nm using Scherrer's equation.

3 shows the XRD pattern of ZnO powder calcined at different temperatures for 2 hours. All NaCl remaining after washing and centrifugation was removed by firing. The intensity of the diffraction peaks increased with increasing heat treatment temperature.

4 is a TEM image of a ZnO powder after milling using a ball: powder ratio of (a) 4: 1, (b) 5: 1, (c) 7: 1, and (d) 10: 1. Will be shown. The mixture of ZnO powder and zirconia ball was made nonuniformly at a molar ratio of 1: 7. The average particle size was nearly 50 nm and the size distribution was narrow. In this work, the mechanochemical process used several ratios of zirconia balls. Since zirconia has a high specific gravity, the polishing efficiency is good and the productivity can be improved. This is due to the low temperature chemistry and the reaction initiated by the balls due to local heat and pressure at the contact surface. The chemical reaction of the powder was separated by a salt matrix and low temperatures allowed for control of particle formation. After the powder was heat treated, particle agglomeration was prevented by solid phase chemicals. This salt was removed by a simple washing step.

5 is a TEM image of ZnO particles at various molar ratios of ZnCl ₂ and Na ₂ CO ₃ . Reaction Equation ZnCl ₂ A mechanochemical mixture of starting powders corresponding to + Na ₂ CO _3- > ZnO + 2NaCl + CO ₂ was prepared with zirconia balls. For Zn, sodium carbonate was used as a catalyst to accelerate the substitution reaction. The powder mixture in stoichiometric ratio 1: 1 (FIG. 5A) showed an average size of nearly 30 nm. Self-assembled into well-arranged, hexagonal, dense structures. Samples with a molar ratio of 1: 2 (FIG. 5B) resulted in an increase in Na ₂ CO ₃ leading to high pH (high concentration of hydroxyl ions), promoting rate reduction, producing large amounts of growth spices, Growth moves away from the diffusion limiting process. Samples with a molar ratio of 2: 1 (FIG. 5C) showed that the reaction rate decreased as the concentration of chlorine ions increased. As a result, the supply of growth species, zerovalent Zn atoms, slows down and favors diffusion-limited growth of the original Zn nucleus.

Figure 6 shows the UV-Vis absorption spectrum development of ZnO and TiO ₂ nanoparticles. The results of the UV-Vis spectrum above 250-600 nm (Ultrospec 2000, Pharamacia Biotech) give information that the ranges reaching the UV-A and UV-B wavelengths may be blocked. Strong absorption peaks were observed for TiO ₂ in the range of 300-320 nm. It is assumed that TiO ₂ has a band gap of 2.99 eV and can block the UV-B range. A strong absorption peak for ZnO was observed in the range above 370-390 nm, which assumes that ZnO can block the UV-A region with a band gap of 3.27 eV.

Heat treatment of the powder milled at 500 ° C. reduced the level of agglomeration that occurred during the process. The heated powder is light yellow, similar to the skin, and therefore would be applicable to cosmetics.

The present invention relates to the synthesis of ultrafine zinc oxide nanoparticles by mechanochemical process with zirconia ball. These balls mechanically activate solid phase substitution reactions and induce salt matrices. The milled powders are then washed and centrifuged to remove NaCl. Heat treatment of the washed powder yields a light yellow powder which, after milling, removes the heat treatment and subsequent soluble reaction by-products, which significantly prevents agglomeration of the particles. In conclusion, this mechanochemical process has the effect of being a viable and inexpensive procedure for mass production of ZnO nanoparticles.

Claims (3)

A method of producing zinc oxide nanoparticles, the method comprising: preparing ZnO nanoparticles by mixing ZnCl ₂ and NaCO ₃ powders with zirconia balls, followed by washing, centrifugation, and heat treatment. The method of claim 1, wherein the mass ratio of the ball to the mixed powder is 4: 1 to 10: 1. The method according to claim 1 or 2, wherein the heat treatment is performed at a temperature of 200 to 500 ° C.

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