TWI401117B - Stable dispersion of nano metal / inorganic clay complex and its manufacturing method - Google Patents

Description

Stable dispersed nano metal/inorganic clay composite and preparation method thereof

The invention relates to a stable dispersed nano metal particle/inorganic clay composite and a preparation method thereof, which use sheet-like inorganic clay as a carrier to disperse a spherical structure metal material to prepare a stable metal-free nano metal particle. The liquid is further dried to form a powder; the product can be applied to chemical catalysis and biological antibacterial, including biology, medicine, chemistry, chemicals, materials, and the like.

Nano silver particles have a proven antibacterial effect, killing more than 600 kinds of bacteria, and tens of times more bactericidal function than chlorine used for sterilization of tap water. Nano silver has 99.99% inhibition effect on Escherichia coli, Staphylococcus aureus, Salmonella and Pseudomonas aeruginosa in multiple dilutions. When the bacteria are killed by silver ions, the silver ions will be released from the dead bacteria, and the repeated action on the living bacteria will continue until all the bacteria are eliminated. It can be seen that the efficacy of nano silver is a long-acting antibacterial agent. Silver is a non-toxic substance, and pure nano-silver is also edible, so it is harmless to the human body. The US Food and Drug Administration also emphasized that such products can be used in commodities and continue to be mass-produced. Among the published literature, the most famous reports on nano-silver treatment are acne, AIDS, anti-allergy, appendicitis, arthritis, anti-cancer, diabetes and so on. Through the nanotechnology, the activity of the silver particles can be increased, the surface area is increased, and the bactericidal function is enhanced to about 200 times that of silver.

At present, a method for preparing nanoparticles has a high-energy laser that cleaves bulk phase solid matter into nanometer-sized particles. Some are gasification of metal solid materials into gaseous metal vapors, which are then aggregated into metal nanoparticles by condensation. Alternatively, nano silver can be prepared by an oxidation reaction using an organic solution. In the preparation process, the operation is complicated, the required equipment also greatly increases the production cost, and in the process of operation or manufacturing, the concentration must be carried out at a scale of ppm. If the concentration of silver ions is increased, silver particles are easily formed during the reduction. Aggregation, reducing the efficacy of the product, so the operating range is limited, coupled with the low concentration of nano silver prepared, the total amount is not high, the reaction area is small, so that the catalytic and antibacterial effects are limited. At the time of preparation, the organic solvent and the organic surfactant used are also a burden on the environment, and it is still unknown whether it can be applied to medical or other materials for the purpose of antibacterial and sterilization.

In order to stabilize the nano metal particles and prevent the particles from agglomerating, it is usually necessary to add a dispersing agent or a protective agent in the preparation of the metal nanoparticles. The mode of action of the protective agent includes: (1) by electrostatic repulsion, the surface of the particle is adsorbed to form an electric double layer, and the surface of the particle carries the same electric charge. When the two particles are close to each other, the Coulomb repulsive force increases, preventing the particle from being arrested. Condensed. If the anion adsorbed on the surface is replaced by a neutral adsorbate, the surface charge will decrease and the van der Waals force will agglomerate the particles. In addition, under the high concentration of particles or the increase of the ionic strength of the solution, the electric double layer is compressed due to the enhancement of the dielectric strength, which is unsatisfactory for the stability of the particles; (2) by the steric hindrance, if there is an adsorption protectant on the surface of the particle, The organic molecules form a protective agent layer on the surface of the metal particles, and the aggregation of the hindered particles is called steric stabilization. Commonly used types of protective agents include: water-soluble polymers (such as PVP, PVA, polymethylvinylether, PAA, etc.), surfactants, ligands or chelating agents.

In order to solve many problems of the conventional process, the present invention uses clay as a dispersant or a protective agent for metal particles, and prepares a nano metal particle/inorganic clay composite by a chemical reduction method.

The object of the present invention is to provide a stably dispersed nano metal particle/inorganic clay composite and a preparation method thereof, which can reduce the cost of biological and chemical materials and improve the efficiency thereof. The present invention utilizes a nano-sheet clay having an aspect ratio of 100 to 1,000 to become a steric obstacle, and to disperse spherical nano-silver particles having an aspect ratio of 1 to avoid aggregation thereof, such as the first The figure shows. In addition, clay has a special ionic valence and can be moistened in water, which also helps to evenly disperse.

A preferred embodiment of the present invention is a layered tantalate clay mineral having a tetrahedral and an aluminum octahedron of 2:1 as a carrier. Ag ⁺ exchange layer cations are adsorbed on the clay colloid by negative charge. Through chemical reduction, Ag ^{0 is} fixed on the clay surface. The clay has strong adsorption to silver, and the particles are not easy to attract each other. Structural barriers avoid aggregation and achieve uniform dispersion.

Materials used in preferred embodiments of the invention include: 1. Synthetic layered silicate clay mineral: SWN, cation exchange capacity (CEC) = 0.67 mequiv/g, manufactured by CO-OP Chemical Co. 2. Silver nitrate: AgNO ₃ exchanges the Na ⁺ between the clay layers to form nano silver particles after reduction. 3. Sodium borohydride: NaBH ₄ , strong reducing agent. 4. Methanol: CH ₃ OH, 95%, weak reducing agent.

The operation steps of the preferred embodiment are described in detail below, in which Examples 1 to 16 are prepared by the methanol reduction method, wherein Example 16 is irradiated with a xenon lamp during the reduction process; and Examples 17 to 19 are reduced by NaBH _{4 .} Nano silver was prepared by the method in which Example 19 was irradiated with a xenon lamp during the reduction process.

Example 1 First, a SWN solution (1.0 wt%) and an AgNO ₃ solution (1.0 wt%) were prepared, and then AgNO _{3 (aq)} (1.0 wt%, 0.68 g) was slowly added to the SWN solution (30 g, 1.0 wt%). The ratio of Ag ⁺ /CEC is 0.2, and Ag ⁺ replaces Na ⁺ between the clay layers, and the solution will be pale beige. Next, a sufficient amount of methanol (MeOH, about 6-8 mL) was added to the solution, at which time the solution did not change significantly. After heating to 70-80 ° C by water, the color of the solution slowly changes, and the reaction of silver ions between the layers of methanol reduction is performed. After 2 to 3 hours of reaction, the solution will appear dark red wine, which is the product after shaking.

The operation steps of Examples 2 to 15 were the same as those in Example 1, except that the dose of AgNO _{3 (aq)} (1 wt%) was increased so that the ratio of Ag ⁺ /CEC was 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, respectively. 5.0, 8.0, 10, 20, 30, 35, 200; methanol (MeOH) also increased moderately according to the ratio.

The operation of Example 16 was the same as in Example 5 except that the reduction reaction was carried out while heating with water, and the solution was irradiated with a xenon lamp.

Example 17 First, a SWN solution (1.0 wt%) and an AgNO ₃ solution (1.0 wt%) were prepared, followed by AgNO _{3 (aq)} (1.0 wt%, 0.68 g), and slowly added to the SWN solution (30 g, 1.0 wt%). The ratio of Ag ⁺ /CEC is 0.2, and Ag ⁺ replaces Na ⁺ between the clay layers, and the solution will be pale beige. Next, powdered NaBH ₄ (0.0075 g) is added to the solution in portions, and the solution immediately exhibits a deep yellow-green color. After stirring and shaking, the solution is a product.

The procedure of Example 18 was the same as in Example 17, except that the ratio of Ag ⁺ /CEC was changed to 1.0.

The procedure of Example 19 was the same as in Example 18 except that NaBH ₄ was added for the reduction reaction, and the solution was irradiated with a xenon lamp.

Product analysis

1 ml of the product Ag-SWN solution obtained in the above examples was dropped on a 1 × 1 cm ² glass substrate, and placed in an oven at 80 ° C for 2 hours, and then the glass substrate was subjected to carbon plating for observation to carry out the following analysis.

1. Uniform Dispersibility The powdery products of Examples 5 and 18 were observed by SEM, and the results are shown in Fig. 2 and Fig. 3, respectively. It is obvious in the figure that the nano-silver/inorganic clay composite prepared by using methanol and NaBH ₄ as reducing agents has good dispersibility and uniformity; the nano-silver/inorganic clay composite obtained by methanol reduction method The uniformity of the material is better than that of the NaBH ₄ reduction method.

Figures 4 and 5 show the products of Examples 16 and 19. Compared with Figures 2 and 3, the particle size of the nano-silver particles obtained by the xenon lamp irradiation is significantly smaller; this is due to the increase in energy. The molecules produce a large interference behavior with each other, and particles having a smaller particle size are formed.

Compared with the traditional process, the organic solvent is used as the reaction medium, and the product is not easily dispersed after drying, and the particles are easy to aggregate, and can only be observed by TEM. If applied to the surface of the material, after drying or air drying, the same aggregation problem will occur, which is difficult in material application.

In addition, when the SEM sample was produced, it was found that the product was closely adsorbed on the glass slide because the clay itself had a large adsorption force, so that the solution was evenly distributed on the slide. This feature allows the product to be used in a wide variety of materials and can be applied or sprayed as needed.

2. Particle size analysis Table 1 is the average particle diameter of the powdery products of Examples 1 to 19; wherein the nano silver/inorganic clay composite obtained by the methanol reduction method has an average particle diameter of only about half of the NaBH ₄ reduction method. . Since the nano silver particles produced by the present invention have a very small particle diameter, they have a large surface area, and the effects of the antibacterial and catalytic agents are also increased by the increase in the total reaction area.

The nano-silver particle size produced by the methanol reduction method is smaller than the NaBH ₄ reduction method. This is because methanol is a weak reducing agent, and the silver ion reduction reaction must be performed by heating with water, so that the formation rate of the nano-silver is slow, and the formed particles are formed. small. On the contrary, NaBH ₄ is a strong reducing agent, and the reduction rate is fast, and the particle diameter of the formed nano silver is large. However, the two reduction processes are carried out between the clay layers, so the size of the nanosilver is limited, and the particles produced will be smaller than the conventional methods.

Fig. 6 further shows the average particle diameters of the powdery products of Examples 1 to 15 as a graph, showing that the higher the Ag ⁺ /CEC ratio, the larger the average particle diameter of the composite. In particular, even if the Ag ⁺ /CEC ratio is increased to 35, the average particle size of the resulting nanosilver/inorganic clay composite is only 125 nm. That is, the method of the invention can achieve the dispersion effect of the protective agent by using a small amount of clay, and can prepare a high concentration nano silver solution, thereby reducing the preparation scale or increasing the total preparation amount under the same reaction conditions to achieve the concentration effect. Improve the efficiency of the entire process.

The invention uses water as a reaction medium instead of a traditional organic solvent, and the raw material is derived from natural clay, so it does not burden or harm the environment or the human body.

Although the preferred embodiment of the present invention uses SWN, different clays can also be used as carriers, such as montmorillonite, synthetic mica, hydrotalcite, etc., CEC, chip size, specific surface area, charge density and three-dimensional structure. There will be differences, but they can all be used as protective agents to produce nano silver. As for the ionic properties of the interlayer charge, the valence, the strength of the electrostatic attraction, the uniformity of the distribution between the layers, the charge density and the amount of the ions, the exchange process of the ions is such that the subsequent reduction reaction also has an effect.

The reducing agent of the present invention is also not limited to methanol and NaBH ₄ . Although different reducing agents have different reducing powers, the effect of metal ion reduction, such as ethanol and other alcohol reducing agents, can still be achieved.

The metal ions of the embodiments of the present invention are not limited to silver ions and may be gold, copper, iron or other suitable metals. The silver ion source is also not limited to silver nitrate as long as it can appropriately supply silver ions, for example, AgBrO ₃ , AgBr, AgClO ₃ , AgCl.

Compared with the general preparation process, the invention has a simpler process, thereby effectively reducing production equipment and operating costs. In addition, clay is a sheet-like nanomaterial with a high specific surface area (750 m ² /g) and a high charge density (1 ion/nm ² ). It is used in catalyst materials and has high mechanical properties and thermal stability. Sexual and gas barrier properties, can expand the application of its nano metal.

1 is a schematic view showing the dispersion of spherical silver nanoparticles by using a nano-sheet clay according to the present invention; FIGS. 2 to 5 are SEM images of the powdery products of Examples 5, 18, 16, and 19; The average particle size of the powdery products of Examples 1 to 15.

Claims (11)

A method for producing a stably dispersed nano metal particle/inorganic clay composite obtained by mixing a metal ion compound, a flaky inorganic clay and a reducing agent in water, wherein an aspect ratio of the inorganic clay is obtained Is 10 to 100,000 as a dispersant or protective agent for the metal to achieve nano-scale dispersion; wherein: the metal particles are gold, silver, copper or iron; the flaky inorganic clay is selected from Synthetic layered silicate clay, montmorillonite, synthetic mica, kaolin, talc, attapulgite, vermiculite or LDH; the cation exchange capacity of the flaky inorganic clay is 0.1 mequiv/g~ 5.0 mequiv/g; the ratio of the ionic equivalent of the metal particle to the cation exchange equivalent of the flaky inorganic clay is 0.1-200; the reducing agent is selected from the group consisting of methanol, ethanol, formaldehyde, ethylene glycol and dodecanol Group. The method of claim 1, wherein the metal is silver. The method of claim 1, wherein the metal compound is AgNO ₃ , AgCl, AgBr, AuBr ₃ , AuCl or HAuCl ₄ . 3H ₂ O. The method of claim 1, wherein the flaky inorganic clay has an aspect ratio of 100 to 1,000. The method of claim 1, wherein the flaky inorganic clay has a structure of a tetrahedron: an aluminum octahedron of about 2:1. The method of claim 1, wherein the reduction reaction is carried out at 70 to 80 ° C, and the reaction time is 2 to 3 hours. The method of claim 1, wherein the reducing reaction is carried out under irradiation with a xenon lamp. A method for producing a stably dispersed nano metal particle/inorganic clay composite by mixing a metal ion compound, a flake inorganic clay and a reducing agent sodium borohydride (NaBH ₄ ) in water, and performing a reduction reaction under irradiation with a xenon lamp The inorganic clay has an aspect ratio of 10 to 100,000 as a dispersant or a protective agent for the metal, so that the metal reaches a nanometer dispersion; wherein: the metal particle is gold, Silver, copper or iron; the flaky inorganic clay is selected from the group consisting of synthetic layered silicate clay, montmorillonite, synthetic mica, kaolin, talc, attapulgite, vermiculite or LDH; The cation exchange capacity of the inorganic clay ranges from 0.1 mequiv/g to 5.0 mequiv/g; the ratio of the ionic equivalent of the metal particles to the cation exchange equivalent of the flaky inorganic clay is from 0.1 to 200. The method of claim 8, wherein the metal is silver. The method of claim 8, wherein the metal compound is AgNO ₃ , AgCl, AgBr, AuBr ₃ , AuCl or HAuCl ₄ . 3H ₂ O. The method of claim 8, wherein the flaky inorganic clay has an aspect ratio of 100 to 1,000.