Titanium dioxide（TiO2）

Industrial application

Titanium dioxide is an important white pigment and porcelain glaze. Used in paint, ink, plastic, rubber, paper, chemical fiber, watercolor pigments, and other industries.

Titanium dioxide is the whitest thing in the world, and 1 gram of titanium dioxide can paint an area of more than 450 square centimeters white. It is 5 times whiter than the commonly used white pigment - zinc barium white, so it is the best pigment for mixing white paint. Titanium dioxide used as a pigment in the world is more than hundreds of thousands of tons a year. Titanium dioxide can be added to paper to make the paper white and opaque, the effect is 10 times greater than other substances, therefore, banknote paper and art paper add titanium dioxide [5].

In order to make the color of the plastic lighter and make the rayon luster soft, titanium dioxide is sometimes added.

In the rubber industry, titanium dioxide is also used as a filler for white rubber.

The photochemical properties of semiconductor titanium dioxide have made it useful in many fields, such as the purification of air, water, and fluids. Photocatalysts doped with carbon or other heteroatoms can also be used in sealed Spaces or areas with scattered light sources. When used as coatings on buildings, pedestrian slabs, concrete walls, or roof tiles, they can significantly increase the breakdown of airborne pollutants such as nitrogen oxides, aromatics, and aldehydes.

Ultrafine titanium dioxide has excellent UV shielding and transparency. It is widely used in cosmetics, wood protection, food packaging plastics, durable household films, man-made fibers and natural fibers, and transparent coatings. Because of its special optical effect in metallic flash coatings, it has been paid attention to and applied in high-end car paints.

Titanium dioxide is a kind of semiconductor, its particle size is small, its specific surface area is large, and loose porous, and rough surface, in the dye-sensitized solar cell photoanode material has been widely used, and the majority of researchers to titanium dioxide as a prototype, the hydrothermal method, electrospinning method and other methods to modify it, while using metal substances, inorganic substances and other doping reaction to prepare excellent performance of the photoanode. This is then assembled into dye-sensitized solar cells [9].

Titanium dioxide can effectively prevent the arbitrary growth of microorganisms through photocatalysis, thereby reducing the amount of harmful components in the environment. The antibacterial mechanism is that titanium dioxide is activated by light, the interaction between electron-hole pairs, oxygen molecules, and hydroxide ions stimulates free radicals and causes a chain reaction, destroying the protein of bacteria and achieving the effect of sterilization [4].

Food application

The U.S. Food and Drug Administration stipulates that titanium dioxide can be used as all food white pigments, with a maximum use of 1g/kg. The pigment additive titanium dioxide can be safely used in general colored food, subject to the following provisions:

(1) The amount of titanium dioxide does not exceed 1% of the weight of the food.

(2) In accordance with the special standards published in Section 401 of the Act, coloring food shall not be used unless there is a similar standard allowing the addition of coloring.

(3) For colored food, the edible color additive titanium dioxide can contain an appropriate diluent as a safe color additive, as follows: silica, as a dispersing agent, the content does not exceed 2%.

Products are suitable for cold fruit, jelly, fried food, cocoa products, chocolate, chocolate products, hard candy, polished candy, gum-based candy, puffed food, candy chocolate products coating, mayonnaise, salad dressing, jam, solid drinks, konjac gel food, etc.

Environmental protection

Purify the air

Titanium dioxide, as a catalyst for light paint pigments, is not only an environmentally safe cleaning agent, but also plays a role in saving energy and protecting environmental resources [8].

Early Japanese and British scientists coated titanium dioxide on the surface of city road paving stones to clean the road air. Titanium dioxide can be mixed with asphalt to reduce pollutants in the air. Concrete or asphalt containing titanium dioxide can purify the air as a car passes by, eliminating 25 to 45 percent of nitrogen oxides from vehicle emissions. When titanium dioxide is coated on the concrete surface, its air cleaning effect is also significant [7].

Cool the Earth

In May 2012, British scientists proposed a bold idea, they believe that by spraying enough titanium dioxide into the stratosphere to reflect sunlight, so as to achieve the purpose of cooling the earth, which can effectively offset the adverse climate factors caused by global warming.

Because titanium dioxide can effectively reflect the direct sunlight, and its nature is stable, with good covering ability, if sprayed in the stratosphere can play a long-term role. British scientists have proposed that high-altitude balloons can be used to bring this chemical into the stratosphere and then release it, and once titanium dioxide is evenly distributed in the Earth's stratosphere, it can effectively reflect sunlight, thereby cooling the Earth.

Peter Davidson, a chemical engineer and president of the British consulting firm Davison Technologies, who is leading the project, said it would take just three million tons of titanium dioxide to create a protective layer one millimeter thick in the Earth's stratosphere. The effect would be huge - enough to offset twice the greenhouse effect of the current amount of carbon dioxide in the atmosphere.

Sunscreen cosmetics

Due to the great harm of ultraviolet light to the human body, developed countries have paid more attention to the research and development of sunscreen products in recent years, and have launched a variety of anti-ultraviolet fibers, plastics, films, coatings, as well as sunscreen cream, foundation, lipstick, mousse, baking cream and other sunscreen cosmetics. In recent years, China has also increased the research and production of sunscreen cosmetics [6].

However, in the past, most sunblocks were benzophenones, o-aminophenone, salicylate, p-aminobenzoic acid, cinnamate and other organic compounds, so unstable, short life, and large side effects, with a certain toxicity and irritation, if added to excess, will produce chemical allergies, and may even lead to skin cancer. Nano titanium dioxide is an inorganic component, with excellent chemical stability, thermal stability and non-migration and strong color loss, covering power, low corrosion, good easy dispersion, and non-toxic, tasteless, non-irritating, safe to use, but also have the role of sterilization and deodorization. More importantly, as mentioned above, nano titanium dioxide can absorb ultraviolet light, but also can emit and scatter ultraviolet light, so the ability to resist ultraviolet light is strong, compared with the same dose of organic anti-ultraviolet agent, its absorption peak in the ultraviolet region is higher; Moreover, nano titanium dioxide has a blocking effect on the ultraviolet in the middle wave region and the long wave region, unlike the organic anti-ultraviolet agent which only has a shielding effect on the ultraviolet in the middle wave region or the long wave region. In particular, due to its fine particles, high transparency of the finished product, through visible light, natural skin whiteness when added to cosmetics, overcoming the shortcomings of some organic or pigment grade titanium dioxide opacity, making the skin appear unnatural pale color. Because of this, nano titanium dioxide has soon been widely valued and gradually replaced some organic anti-ultraviolet agents, becoming a physical shielding anti-ultraviolet agent with superior performance in today's sunscreen cosmetics.

With the improvement of people's living standards and the intensification of international competition, the research and development of safe and efficient sunscreen cosmetics will gradually increase. Nowadays, the sunscreen cosmetics market in developed countries has shown strong vitality. In 1999-2000, the annual sales of the United States have reached 737 million US dollars, 765 million US dollars, the United Kingdom reached 245 million US dollars, 270 million US dollars, and in recent years, respectively, at a rate of 20%, 10% or more growth, of which the amount of nano titanium dioxide also increased significantly year by year. The annual demand for nanometer titanium dioxide in Japan's anti-ultraviolet cosmetics is more than 1000t, and the amount of textile, plastic and rubber products is larger.

From the perspective of the development trend of sunscreen cosmetics, one is inorganic sunscreen instead of organic sunscreen, and the other is bionic sunscreen. The latter cost is large, it is difficult to promote today, the former price is moderate, and the sun protection performance is superior, so it is generally optimistic. Especially nano titanium dioxide, because of its superior performance and application prospects, so the development momentum and market potential is good. [1]

Sun protection mechanism

According to the different wavelength, ultraviolet light is divided into short wave region 190 ~ 280nm, middle wave region 280 ~ 320nm, long wave region 320 ~ 400nm. The ultraviolet energy in the short-wave region is the highest, but it is blocked when it passes away from the ozone layer, so the harm to the human body is generally the ultraviolet in the medium-wave region and the long-wave region.

The strong UV resistance of titanium dioxide is due to its high refraction and high light activity. Its anti-ultraviolet ability and its mechanism are related to its particle size: when the particle size is larger, the block of ultraviolet light is mainly reflected and scattered, and it is effective for the ultraviolet light in the middle wave region and the long wave region. The sun protection mechanism is a simple cover, a general physical sun protection, and the sun protection ability is weak; With the decrease of particle size, the light can pass through the particle surface of titanium dioxide, and the reflection and scattering of ultraviolet in the long wave region is not obvious, but the absorption of ultraviolet in the middle wave region is obviously enhanced. Its sunscreen mechanism is to absorb ultraviolet rays, mainly absorb ultraviolet rays in the middle wave region. It can be seen that the mechanism of titanium dioxide to different wavelengths of ultraviolet radiation is not the same, the block of ultraviolet radiation in the long wave region is mainly scattered, and the block of ultraviolet radiation in the middle wave region is mainly absorbed.

Nanoscale titanium dioxide, due to its small particle size and high activity, can not only reflect and scatter ultraviolet light, but also absorb ultraviolet light, so that it has a stronger blocking ability to ultraviolet light.

The absorption mechanism of titanium dioxide to UV may be: The electronic structure of nano-titanium dioxide is composed of a conduction band formed by a valence electron band and a vacant orbital. When it is irradiated by ultraviolet light, light with greater energy than its bandgap width (about 3.2eV) is absorbed, so that electrons in the valence band are excited to the conduction band, resulting in the absence of electrons in the valence electron band and the formation of an easily mobile and highly active electron hole pair. On the one hand, such electron hole pairs can recombine with each other during various REDOX reactions to release energy in the form of heat or fluorescence, on the other hand, they can dissociate into free holes and free electrons that migrate freely to the surface of the lattice or other reaction sites, and are immediately captured by the surface groups. Under normal circumstances, titanium dioxide will activate the surface water to produce surface hydroxyl groups to capture free holes, forming hydroxyl radicals, and the free electrons will soon combine with the absorbed state of oxygen to produce superoxide radicals, which will also kill the surrounding bacteria and viruses. It can be seen that ultraviolet irradiation, surface water activation degree and oxygen absorption rate are the three basic conditions for the photoactivity of titanium dioxide. It is precisely because nano titanium dioxide will produce free radicals after absorbing ultraviolet light, which will accelerate the aging of the skin and cause harm to the skin. Therefore, when using nano titanium dioxide as a sunscreen, it is necessary to start with weakening or eliminating three basic conditions to weaken or fundamentally eliminate its photoactivity, so as to reduce its harm.