Nano zinc oxide
Chinese name: Nano zinc oxide English name: Zinc oxide, nanometer
Alias: Nano zinc white; Zinc White nanometer
CAS RN .: 1314-13-2 Molecular formula: ZnO Molecular weight: 81.37
Nano-zinc oxide (ZnO) particle size is between 1-100 nm, is a new type of high-function fine inorganic products for the 21st century, showing many special properties, such as non-migration, fluorescence, piezoelectricity, Ability to absorb and scatter ultraviolet rays, etc., using its wonderful performance in light, electricity, magnetism, sensitivity, etc., can manufacture gas sensors, phosphors, varistor, ultraviolet shielding materials, image recording materials, piezoelectric materials, varistor, high efficiency Catalysts, magnetic materials, plastic films, etc.
Nano-zinc oxide is a versatile new inorganic material with a particle size of about 1-100 nm. Due to the miniaturization of the crystal grains, the surface electronic structure and crystal structure change, resulting in the surface effects, volume effects, quantum size effects and macro tunneling effects that are not possessed by macroscopic objects, as well as high transparency and high dispersion. In recent years, it has been found that it exhibits many special functions in catalysis, optics, magnetism, mechanics, etc., which makes it have important application value in many fields such as ceramics, chemical industry, electronics, optics, biology, medicine, etc. The particularity and use of comparison. Nano zinc oxide can be used in ultraviolet light shielding materials, antibacterial agents, fluorescent materials, photocatalytic materials, etc. in the textile field. Due to the series of nano-zinc oxide's superiority and very attractive application prospects, the research and development of nano-zinc oxide has become the focus of many scientific and technological personnel.
Metal oxide powders such as zinc oxide, titanium dioxide, silicon dioxide, aluminum oxide, and magnesium oxide. When these powders are made into nanoscale, the size of the particles is equal to or smaller than that of the light wave, and the conduction band is caused by the size effect. And the interval of the valence band increases, so the light absorption is significantly enhanced. Various powders have different differences in light shielding and reflection efficiency. When comparing zinc oxide and titanium dioxide, when the wavelength is less than 350 nanometers (UVB), the shielding efficiency of the two is similar, but when 350-400nm (UVA), the shielding efficiency of zinc oxide is significantly higher than that of titanium dioxide. At the same time, the refractive index of zinc oxide (n = 1.9) is lower than that of titanium dioxide (n = 2.6), and the diffuse reflectance of light is low, which makes the fiber more transparent and conducive to textile dyeing and finishing.
Nano zinc oxide can also be used to make far infrared reflective fiber materials, commonly known as far infrared ceramic powder. This kind of far-infrared reflecting functional fiber absorbs the heat emitted by the human body, and then radiates far-infrared rays in a certain wavelength range to the human body. In addition to increasing the blood flow in the subcutaneous tissue of the human body and promoting blood circulation, it can also block infrared rays. Reduce heat loss, so the fiber heat storage and insulation compared with the general fiber.
Zinc oxide is an electronic structure of a semiconductor catalyst. Under light irradiation, when a photon with a certain energy or a photon with an energy Eg exceeding the semiconductor band gap enters the semiconductor, an electron is excited from the valence band NB to the conduction band CB , And left a hole. Excited conduction band electrons and valence band holes can be recombined to eliminate input energy and heat. Electrons are captured at the surface state of the material, valence state electrons transition to the conduction band, and valence band holes snatch hydroxyl electrons in the surrounding environment Come to make the hydroxyl group become a free radical, as a strong oxidant to complete the degradation of organic matter (or chlorine), killing bacteria and viruses.
Japanese emerging humanization company, Teijin company, Cangluo company, Zhongfang company, Toyo company, etc. all produce deodorant, antibacterial and anti-ultraviolet fibers. For example, the Japanese barnacle company incorporated zinc oxide fine powder into polyester fibers or filaments with special cross-sections to develop anti-ultraviolet light fibers. In addition to the function of shielding ultraviolet light, it also has antibacterial, disinfection, deodorization and other functions.
Zinc oxide is a good photoluminescent material, and ultraviolet light, visible light or infrared light can be used as an excitation light source to induce its luminescence. Zinc oxide has a strong excitation binding energy at room temperature, which can produce efficient light emission at a lower excitation energy. In the past few decades, many types of emission patterns have been proposed, such as oxygen vacancies, oxygen ions in the gap, zinc ion defects, or zinc ions in the gap. Zinc oxide is a material that has luminous potential in the blue ultraviolet light and or in the visible region. Recently, it is widely used in flat panel displays or some special function pigments. Under the illumination of a certain energy, the pigment is red without light. When it is black.
Nano-zinc oxide can be used to deal with air pollution problems because it has high specific surface area, high activity, and special physical properties, making it very sensitive to the external environment (such as temperature, light, moisture, etc.), and the external environment will change rapidly. Causes a significant change in its resistance, this characteristic makes it very potential in sensing. It can be used to develop good heat resistance and corrosion resistance, fast response rate, high sensitivity, good selectivity, easy component manufacturing, and easy to be combined with a microprocessor to form a gas sensing system or portable monitor, so it is widely used It is used in home and factory environment to detect toxic gas and combustible explosive gas. The dielectric film made of zinc oxide can be widely used in automobile fuel electromagnetics, air conditioners, mobile phones and semiconductor devices.
Nano-zinc oxide has the characteristics of a semiconductor and has higher conductivity than bulk zinc oxide at room temperature, so it can play a role in electrostatic shielding. It can be made into antistatic coatings and white conductive fibers. At the same time, its color tone is better than the commonly used conductive material carbon black, so it is more widely used.
At present, the main problem that needs to be solved in the development of nano-zinc oxide at home and abroad is that we should strive to combine the relevant preparation technology, instrument analysis equipment and basic research to be able to prepare different particle size, crystal form, and appearance (spherical, rod , Needle-shaped or dendritic), making rice resistant zinc oxide suitable for various industrial applications.
Strengthen the dispersion technology in the preparation process, and no secondary aggregation occurs.
Strengthen the composite addition technology of nano zinc oxide and other nano materials or organic polymer materials and related equipment research.
Strengthen the nano-zinc oxide coating technology to make it suitable for different fields, such as anti-static, anti-ultraviolet and infrared absorption. And make the application of nano-zinc oxide produce huge economic benefits.
1. Preparation of Nanometer Zinc Oxide The preparation methods of zinc oxide are divided into three categories: direct method (also known as American method), indirect method (also known as French method) and wet chemical method. At present, many commercially available zinc oxides are mostly direct or indirect products with a particle size of micron level and a small specific surface area. These properties greatly restrict their application fields and their performance in products. The company uses the wet chemical method (NPP-method) to prepare nano-scale ultrafine activated zinc oxide. Various zinc-containing materials can be used as raw materials. Zinc is leached by acid leaching. After multiple purifications to remove impurities in the raw materials, the precipitate is then obtained to obtain basic Zinc carbonate, finally roasted to obtain nano-zinc oxide. Compared with the previous technology for preparing nano-scale ultrafine zinc oxide, this new process has the following technical innovations:
1. The combination of reaction kinetics principle and enhanced heat transfer technology under equilibrium conditions can quickly complete the calcination of basic zinc carbonate.
2. Through the adjustment of process parameters, various types of nano zinc oxide products with different purity, particle size and color can be prepared.
3. This process can use a variety of zinc-containing materials as raw materials to convert them into high value-added products.
4. A typical green chemical process belongs to an environmentally friendly process.
2. Characterization of the performance of nano-zinc oxide The outstanding feature of nano-zinc oxide is that the product particles are at the nano-scale, and have the dual characteristics of nano-materials and traditional zinc oxide. Compared with traditional zinc oxide products, it has a large specific surface area, high chemical activity, product fineness, chemical purity and particle shape can be adjusted according to needs, and has a photochemical effect and better UV shielding performance, its UV shielding rate is as high as 98 %; At the same time, it also has a series of unique properties such as antibacterial and bacteriostatic, anti-odor and anti-enzyme.
The analysis and testing center of Tsinghua University analyzed the products with transmission electron microscopy. The nano-zinc oxide particles are spherical, with a uniform particle size distribution. The average particle size is 20-30 nanometers, and the particle size of all particles is below 50 nanometers. Through the BET method test of the fully automatic F-Sorb 2400 specific surface area analyzer (Beijing Jinai Spectrum Technology Co., Ltd.), the BET specific surface area of ​​the nano-zinc oxide powder is above 35m2 / g. In addition, by adjusting the preparation process parameters, rod-shaped nano zinc oxide can also be produced. This product has been tested and identified by the Institute of Microbiology, Chinese Academy of Sciences. The results show that the addition of 0.5% to 1% of nano-zinc oxide in the rich bacterial culture medium can effectively inhibit the growth of E. coli with an antibacterial rate of more than 99.9%.
3. Surface modification of nano-zinc oxide Nano-zinc oxide has the characteristics of large specific surface area and large specific surface energy, so it is easy to reunite itself; on the other hand, the surface of nano-zinc oxide has strong polarity and is not easy to be uniformly dispersed in organic media. It has greatly restricted its nano-effects. Therefore, the dispersion and surface modification of nano-zinc oxide powder has become a necessary treatment method before the application of nano-materials in the matrix. The study of the specific surface area of ​​nano-zinc oxide is very important. The detection data of the specific surface area of ​​nano-zinc oxide is only reliable when the result is detected by the BET method. There are many instruments in China that can only be tested by the direct comparison method. eliminated. At present, the multi-point BET method is used uniformly for the specific surface area testing at home and abroad. The specific surface area measurement standards developed at home and abroad are based on the BET test method. Please refer to China's national standard (GB / T 19587-2004)-Gas adsorption BET principle Method for determining the specific surface area of ​​solid materials. The measurement of specific surface area is actually a time-consuming task. Due to the different adsorption capacity of the sample, the test of some samples may take a whole day. If the test process is not fully automated, then the tester ca n’t leave at all times. A high degree of concentration, observing the instrument panel, manipulating the knob, and a little inattention will lead to the failure of the test process, which will waste a lot of precious time of the tester. Among several domestic manufacturers of specific surface area analyzers, only the F-Sorb 2400 specific surface area analyzer of Beijing Jinyi Spectrum Technology Co., Ltd. is an instrument that can truly realize the detection function of the BET method (both with direct comparison method), and the more important Beijing Gold F-Sorb 2400 specific surface area analyzer is the only fully automated and intelligent specific surface area detection equipment in China. Its test results are highly consistent with international standards, and its stability is also very good. At the same time, it reduces human errors. Improve the accuracy of test results.
The so-called nano-dispersion refers to the reduction of various forms of agglomerates composed of dried nanoparticles into primary particles in a specific liquid medium (such as water) using various principles, methods and methods, and making them stable and uniformly distributed in the medium. technology. The surface modification of nano-powder is based on the expansion and extension of nano-dispersion technology, that is, according to the needs of the application, the surface of the dispersed nano particles is coated with a thin film of appropriate substances or the nano particles are dispersed in a certain type. Soluble solid phase carrier. The surface-modified nano-dry powder will change its adsorption, wetting, dispersion and other surface properties. Generally, it can be automatically or very easily dispersed in a specific medium, so it is very convenient to use. Generally speaking, there are three ways to modify nanoparticles: 1. Evenly coat a layer of other substances on the surface of the particle, so that the surface properties of the particles change; 2. Use charge transfer complexes (such as silane, titanic acid) Coupling agents such as esters and stearic acid, silicone, etc.) are used as surface modifiers to perform chemical adsorption or chemical reaction on the surface of nanoparticles; 3. Use high energy means such as corona discharge, ultraviolet rays, plasma, radiation, etc. To be modified.
According to the requirements of different application fields, select the appropriate surface modifier or surface modification process to modify the surface of the nano-zinc oxide, improve its surface properties, increase the compatibility between the nanoparticles and the matrix, and thus be applied to each In various fields, improve product performance and technical indicators.
Fourth, the application of nano-zinc oxide The company has paid great attention to the development of its application technology from the beginning of the preparation of nano-zinc oxide. Through the intensive research of the company's internal scientific research personnel and the technical cooperation with relevant scientific research units, a series of important results have been achieved in the application technology of nano-zinc oxide. The main application areas of the current products are:
1. Rubber tires In the rubber industry, especially in the production of transparent rubber products, nano-zinc oxide is an excellent vulcanization activator. Because nano-zinc oxide can be combined with rubber molecules at the molecular level, it can improve the performance of the rubber compound and improve the characteristics of the finished product. Taking radial tires and other rubber products as an example, the use of nano-zinc oxide can significantly improve the thermal conductivity, wear resistance, tear resistance, tensile strength and other items of the product, and its consumption can be saved by 35-50%, greatly reducing To reduce product cost; in the processing technology, it can extend the scorching time of the rubber material, which is extremely beneficial to the processing technology. Nano zinc oxide is used in rubber shoes, rain boots, rubber gloves and other labor protection products, which can greatly extend the service life of the products and improve their appearance and color. It is used in transparent or colored rubber products and has traditional activities such as carbon black. Irreplaceable effect. Nano-zinc oxide is used in products such as gas sealants and gaskets, and it also plays a good role in improving the wear resistance and sealing effect of products. At present, the company's nano-zinc oxide has been well applied in many large domestic tire and rubber products companies.
2. Paints and coatings With the improvement of people's requirements on paint color, film performance, environmental protection, etc., the application of nanomaterials in the paint industry has received more and more attention. The types of nano materials currently used in coatings are nano titanium dioxide, nano silicon dioxide, nano zinc oxide, nano calcium carbonate, etc. Among them, nano titanium dioxide and nano silicon dioxide limit their scope and number of applications due to their expensive prices. Nano-calcium carbonate has a relatively simple performance, and has a small role in improving the anti-mold and anti-ultraviolet aging properties of the coating. Therefore, nano-zinc oxide occupies a greater advantage in the application of coatings due to its excellent cost performance. Nano-zinc oxide has new properties and new uses that are unmatched by ordinary zinc oxide. It can make the coating have the functions of shielding ultraviolet rays, absorbing infrared rays, sterilization and mildew. Therefore, it can be widely used in emulsion paints and other coatings in buildings. The thickening effect also helps to improve the stability of pigment dispersion. Through joint development with relevant scientific research units, the company successfully applied nano-zinc oxide in water-based coatings to make nano-zinc oxide modified coatings. Tests have shown that the modified coatings have stain resistance, artificial aging resistance, and water resistance. Traditional mechanical properties such as alkali resistance, scrub resistance, hardness and adhesion have been greatly improved. In addition, the antibacterial and antifungal properties of nano-zinc oxide modified coatings are also under further study.
3. There are two ways to apply chemical fiber textile nanomaterials to chemical fiber textiles: One method is to directly add nanoparticles to the initial reaction solution of chemical fibers, and use conventional polymerization to synthesize functional fibers so that the nanoparticles are evenly distributed in the fibers. Internal; another method is to formulate the nanoparticles as a finishing agent in the finishing liquid of the fabric, to make the nanoparticles adsorb on the surface of the fiber by padding, or to coat the nanoparticles with a certain binder A functional coating is formed on the surface of the fabric to improve the wearability of the fabric. Jilin Chemical Fiber Group formulated the nano-zinc oxide modified by the company's surface into the spinning solution of viscose fiber to synthesize viscose fiber containing nano-zinc oxide particles. The fiber was spun and woven to obtain nano-zinc oxide added UV-resistant fabrics, compared with ordinary fabrics without added nano-zinc oxide, the UPF value (UV blocking factor) of UV-resistant fabrics is twice that of the control fabrics. The company's products can significantly improve the anti-ultraviolet and anti-bacterial functions of viscose and synthetic fiber products, and are used in the production of anti-ultraviolet fabrics, anti-bacterial fabrics, sunshades and other products. The anti-ultraviolet nanocolloid developed by the company has been tried on the parasol by Hangzhou Paradise Umbrella Industry Group Co., Ltd. Tests by the China Academy of Metrology have shown that the UPF value (ultraviolet blocking factor) is 50, and its performance index has reached the Australian standard , Exceeding EU standards.
4. Sunscreen cosmetics are damaged by the ozone layer of the earth, which leads to the continuous increase of ultraviolet radiation to the earth's biosphere. The harm caused by excessive ultraviolet radiation to human health is increasing. In order to resist the damage to human skin caused by excessive ultraviolet radiation, various sunscreens have been developed to protect the skin. Since most organic sunscreens are highly active, irritating to the skin and easily decompose after ultraviolet radiation, the sunscreen effect is not long-lasting, so people have developed inorganic sunscreens, such as nano-titanium dioxide and nano-zinc oxide. The study found that nano-zinc oxide has a stronger protective effect on ultraviolet rays than traditional nano-titanium dioxide, and has a good protective effect on both UV-A and UV-B. Therefore, the application of nano-zinc oxide in the field of cosmetics has developed rapidly. The company uses a nano-zinc oxide sunscreen produced by a special surface treatment technology, which can effectively absorb solar ultraviolet rays, especially protect the human body from UV-A and UV-B. Most traditional sunscreens can work on UV-B, but they are not effective against UV-A rays with longer wavelengths, and UV-A is increasingly considered to be related to premature skin aging and skin cancer. The average particle size of the company's zinc oxide is less than 50 nanometers. It can resist UV-A and UV-B most effectively. It is a broad-spectrum anti-UV agent, non-toxic and harmless, and is a veritable new generation of physical sunscreen.
5. Other fields With the deepening of people's understanding of the performance of nano-zinc oxide, the application field of nano-zinc oxide is continuously expanding. For example, the use of nano-zinc oxide in the ceramic industry can greatly reduce the sintering temperature of ceramic products, burnt products are as bright as mirrors, reducing the production process, reducing energy consumption, and giving ceramic products antibacterial deodorization and decomposition of organic substances. The cleaning effect greatly improves the quality of the product; nano-zinc oxide has a small size and a large specific surface area. The bond state on the surface is different from that inside the particle. It increases the reaction contact surface and improves the catalytic efficiency. It is a desulfurizer for chemical production enterprises. Nano-zinc oxide is also a good photocatalyst. Under ultraviolet irradiation, it can decompose freely moving negative electrons, leaving positively charged holes and activating oxygen in the air. Active oxygen reacts with various organic substances to kill germs and viruses. In addition, nano-zinc oxide also shows more and more broad application prospects in many fields such as sensors, capacitors, fluorescent materials, absorbing materials, conductive materials and so on.
V. Conclusion At present, some breakthroughs have been made in the preparation of nano-zinc oxide, and several industrialized manufacturers have been formed in China. However, the surface modification technology and application technology of nano-zinc oxide have not yet fully matured, and its application field has been restricted greatly, which has restricted the formation and development of the industry. Although we have made great progress in the application of nano-zinc oxide in recent years, compared with the application level in developed countries and the potential application prospect of nano-zinc oxide, there is still much work to be done. How to overcome the bottleneck of nano zinc oxide surface treatment technology and speed up its wide application in various fields has become an urgent problem faced by many nano zinc oxide manufacturers.
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