Photocatalytic Properties and Research Applications of Nanoscale Titanium Dioxide "Photocatalytic Applications of Nanomaterials" Ma Kun, Year, Month, Day
The rapid development of high technology requires increasingly higher requirements for high-efficiency materials. The synthesis of nanometer-sized materials will provide opportunities for the development of high-performance materials. New materials and improvements to the properties of existing materials provide a new approach. Nano-titanium dioxide is a new type of high-performance material developed in recent years. Its particle size is ~, and the surface energy and surface tension increase sharply with the decrease of particle size, giving it a quantum size effect that bulk materials do not have. Volume effect and macro tunneling effect. Compared with conventional materials, nanometer titanium dioxide has unique properties such as large specific surface area, strong magnetism, good light absorption, large surface activity, good thermal conductivity, and good dispersion. It also has stable photochemical properties, high catalytic efficiency, and oxidation resistance. With the advantages of strong capability, non-toxicity and low price, it is widely used in the fields of cosmetics, plastics, coatings, fine ceramics, catalysts and environmental protection. The development and utilization of nanometer titanium dioxide has attracted widespread attention.
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Photocatalysis
Definition of photocatalysis
Photocatalysis is a substance that does not change itself under the irradiation of light, but can promote chemical reactions. Catalysis is the use of light energy existing in nature to convert the energy required for chemical reactions to produce catalysis, which excites surrounding oxygen and water molecules into free negative ions with great oxidizing power.
Types of photocatalytic materials
Compounds that can be used as photocatalysts are mostly semiconductors, such as, It is irritating to the skin, has low toxicity, and will harm people's health. Metal sulfides are unstable in aqueous solutions and will undergo photocorrosion. And toxic iron oxides will also undergo photocorrosion because of their strong oxidation ability, stable chemical properties, and non-toxicity. It has good compatibility with the human body and has become the most popular nano photocatalyst material in the world.
, Development of Photocatalysis
●In 2008, Japanese researchers discovered the photocatalytic decomposition of water on semiconductor electrodes, thus opening up a new field of semiconductor photocatalysis.
In ●, it was reported that water systems can non-selectively oxidize various organic compounds under light conditions, completely oxidizing them into water and carbon dioxide.
●Since the end of the 1990s, there have been a large number of reports on the use of semiconductor photocatalytic oxidants to treat various types of wastewater. Research on the application of photocatalytic technology in environmental protection, health care, organic synthesis, etc. has developed rapidly. Semiconductor photocatalysis has become an internationally recognized One of the most active research fields.
Mechanism of photocatalytic reaction
When semiconductor nanoparticles are irradiated by photons with energy greater than the band gap, electrons transition from the valence band to the conduction band, generating electron holes. The conduction band electrons have strong reducing properties. , the valence band holes are oxidizing, and the reaction between the holes and the particle surface generates highly oxidizing free radicals. The active free radicals can oxidize many intractable organic substances into inorganic substances such as water and carbon dioxide.
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Application of nano-titanium dioxide () photocatalysis
, nano-titanium dioxide () photocatalytic sterilization
With the improvement of living standards, people are increasingly concerned about the hygiene of their working and living environments. Pay attention to. General pesticides can inactivate cells, but after bacteria are killed, they can release heat-causing and toxic components such as endotoxins. Therefore, various environmentally friendly antibacterial functional materials have emerged and have been rapidly developed. . The photo-generated electrons and photo-generated holes generated by nano-titanium dioxide photocatalysis are adsorbed on the surface of the catalyst or form highly oxidizing superoxide ions or active hydroxyl groups, which react biochemically with bacterial cells or components within the bacteria to completely kill the bacteria. It can also degrade toxic compounds released by bacteria and prevent endotoxins from causing secondary pollution.
Researchers at the University of Texas in the United States irradiated a mixture of E. coli and nano-titanium dioxide with light greater than 100 ℃ and found that E. coli was quickly killed according to a first-order reaction kinetic equation.
Antibacterial plastics added with about nanometer titanium dioxide can be widely used in food packaging, electrical appliances, furniture, tableware, public facilities, etc. to prevent the reproduction and cross-infection of germs.
Using a single nanometer titanium dioxide powder as a food antibacterial preservative, it can effectively kill and inhibit the reproduction of a variety of bacteria that cause food spoilage. Composite nano-titanium dioxide/silica particles wrapped with porous silica () are made. Due to the sustained release effect of porous silica () on nano-titanium dioxide particles, the preservation time of food can be greatly extended.
, Nano titanium dioxide () photocatalytic air purification
With the use of indoor building decoration materials and household chemicals, indoor air pollution has attracted more and more attention. At present, hundreds of organic substances have been identified from indoor air. Research results on major indoor pollutants such as formaldehyde and toluene show that the photodegradation of pollutants is related to their concentration. Formaldehyde with a mass number below can be completely decomposed into water and carbon dioxide by titanium dioxide photocatalysis, and is oxidized into formic acid at higher concentrations. When toluene is photocatalytically degraded at high concentrations, the generated intermediate products that are difficult to decompose are concentrated around titanium dioxide, hindering the progress of the photocatalytic reaction, and the removal efficiency is very low. However, at low concentrations, toluene is easily oxidized into water and carbon dioxide.
Organic pollutants in the air can be removed by coating titanium dioxide films on the surfaces of pollution sources such as window glass, walls, carpets, sofas and cabinets in living rooms and offices, or by placing titanium dioxide photocatalytic equipment in the room, which can be effectively degraded. These organic substances achieve the purpose of purifying indoor air.
Titanium dioxide can also be used for the photocatalytic degradation of industrial waste gases in petroleum, chemical and other industries. Cars, motorcycle exhausts and industrial waste gases will emit harmful gases such as, Oxidation.
, Nano-titanium dioxide () photocatalytic deodorization
Odorous gases in the air mainly contain sulfides (such as, mercaptans, thioethers, etc.), nitrogen-containing compounds (such as amines, amides, etc.), Halogens and their derivatives (such as halogenated hydrocarbons, etc.). This year, deodorization using a mixture of titanium dioxide photocatalysts and other adsorbents has been put into practical use. The odor adsorbed by the gas adsorbent contacts titanium dioxide through diffusion. After titanium dioxide oxidizes and decomposes the gas, it not only reduces the adsorption activity of the adsorbent, but also solves the shortcomings of titanium dioxide's poor adsorption of odor and greatly improves the photolysis of odor. efficiency.
At present, the photocatalytic sheet developed by Japan's Mitsubishi Paper Company using titanium dioxide and inorganic binder has good removal performance of acetaldehyde, methyl mercaptan, ether, hydrogen sulfide, ammonia, trimethylamine and other odors. Be confirmed.
, Nano titanium dioxide () photocatalytic wastewater treatment
Daily wastewater contains a large amount of surfactants. This kind of wastewater is not only easy to produce odor and foam, but also affects the biochemistry of wastewater. Surfactants are not only difficult to degrade, but also produce toxic or insoluble intermediates. Research has proven that using nano-titanium dioxide catalysts to decompose surfactants can achieve significant results.
Printing and dyeing wastewater usually contains carcinogens such as aromatic groups, amine groups, and azo groups, and the degradation rate using general biochemical methods is usually very low. A large number of studies have found that using nano-titanium dioxide to photocatalytically degrade dyes can not only effectively destroy the chromophoric groups in the dyes, but also destroy the aromatic groups in the dye molecules to achieve complete degradation. Nanoscale titanium dioxide is used as a catalyst to degrade methylene blue dye. The research results show that when exposed to light for minutes and the dosage of titanium dioxide/hour, the degradation rate reaches.
The leachate flowing out from the garbage dump can penetrate into the ground and cause serious pollution to the groundwater. Therefore, the pollution treatment of the leachate from the garbage dump is an important aspect of environmental treatment. Nano is used for in-depth treatment of landfill leachate, and the treated water quality reaches the national first-level discharge standard. This shows that using nanometers to treat landfill leachate is very effective.
, Nano-titanium dioxide () photocatalytic anti-fouling self-cleaning
Normally, the surface of nano-titanium dioxide coating film has a large contact angle with water, but after ultraviolet light irradiation, the contact angle of water decreases As small as the following, Shenzhen can achieve it, that is, the water droplets completely infiltrate the surface of titanium dioxide, showing very strong hydrophilicity. When the contact angle on the surface of the water-damaged titanium dioxide film is less than 100%, it has high water mobility, when it is less than 10%, it has a self-cleaning effect, and when it is less than 10%, it has a mildew-proof effect. Similarly, oily liquids such as ethylene glycol, cetane, triolein, etc. will completely infiltrate into the surface of the titanium dioxide coating after being irradiated by ultraviolet light. That is, the surface of nanometer titanium dioxide has an affinity for water and oil, and is a super-amphiphilic interface material. This material can be used to treat glass, ceramic tiles, and agricultural films, and has an antifouling and self-cleaning effect.
The surface coated with nano titanium dioxide (TiO2) film has a high degree of self-cleaning effect. Once these surfaces are contaminated by oil, etc., because the surface is super hydrophilic, dirt will not easily adhere to the surface, and the attached dirt will not easily adhere to the surface. It can also be decomposed by photocatalysis. The ultraviolet rays in sunlight are enough to maintain the hydrophilic properties of the surface of the nano-titanium dioxide film, giving the surface a long-term anti-fouling self-cleaning effect. It is applied to glass, ceramics, etc., as well as the exterior walls and ceilings of high-rise buildings. It uses sunlight and ultraviolet light contained in fluorescent lamps as excitation sources to decompose oil, dust and sand. The decomposed dirt is washed away by rainwater. It can be removed, which not only helps to beautify the environment, but also reduces the inconvenience and unsafe factors caused by cleaning.
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Prospects
With its unparalleled photocatalytic performance, titanium dioxide has attracted widespread attention from scientists in materials, environment, chemistry, physics and other disciplines at home and abroad. The visible light of titanium dioxide photocatalysts Chemical research will take an important step for mankind to fully utilize solar energy and improve the human living environment. Through the joint efforts of scientists from all over the world, although the visible photochemical research on titanium dioxide has made certain progress, various modification methods of titanium dioxide have more or less improved the utilization rate of solar energy. However, judging from the current research results, visible light catalysis or energy conversion efficiency is generally low. Therefore, the development of visible light titanium dioxide photocatalysts will remain a hot research topic in the future. my country has a large number of titanium resource reserves, ranking first in the world. If we can use the abundant titanium resources to produce visible light catalysts, it will not only promote our country's economic development, but also improve our living environment.
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