What are the physical and chemical properties of nano zinc oxide?

What are the physical and chemical properties of nano zinc oxide?

physical property

Appearance and characteristics: white powder or hexagonal crystallinity. No odor, no dead star. It turns yellow after being heated, white again after cooling, and sublimates when it is heated to 1800. The covering power is half that of titanium dioxide and zinc sulfide. The coloring power is twice that of alkaline lead carbonate.

Solubility: soluble in acid, concentrated hydroxide alkali, ammonia, ammonium salt solution, insoluble in water and ethanol.

chemical property

Zinc oxide is a white pigment, commonly known as zinc coating. Its advantage is that it will not turn black when encountering H2S gas. Because ZnS is also white. When heating, ZnO gradually changes from white and light yellow to lemon yellow, and the yellow fades after cooling. Use this property to mix paint or add a thermometer to make a color change coating or color change thermometer. Because ZnO has astringency and certain bactericidal ability, it is often prepared into ointment for use in drugs, so ZnO can also be used as a catalyst.

Chemical reaction formula of nano zinc oxide:

Reaction with NaOH: ZnO+2NaOH+H2O=Na2 [Zn (OH) 4]

What is the sun protection mechanism of nano zinc oxide?

Nanometer zinc oxide uses an important and wide range of physical sunscreen agents to block the principle of ultraviolet radiation is absorption and scattering. Zinc oxide belongs to N-type semiconductor. The electrons in the valence can accept the energy conversion of ultraviolet ray, which is also the principle of absorbing ultraviolet ray. The function of scattering ultraviolet rays is related to the particle size of the material. If the size is much smaller than the wavelength of ultraviolet rays, the ultraviolet rays acted by particles can scatter in all directions, thus reducing the intensity of ultraviolet rays in the irradiation direction. In addition, if the particles of this material are too large, unnatural whitening will appear on the skin. Therefore, nano particles have considerable advantages over ordinary particles.

Nanometer zinc oxide is a stable compound, which can provide a wide range of spectral ultraviolet protection (UVA and UVB), and is an effective component in sunscreen evaluation in almost all countries. However, they are very small, have enhanced chemical activity, can be absorbed by the human body, and have potential harm to the human body and the environment. Therefore, the use of nano zinc oxide is still controversial. For example, the EU said in 2004 that nano zinc oxide could be absorbed and cause DNA damage. Australia said in a review in 2006 that it did not believe that nanoparticles were absorbed by the skin. DNA of the United States approved the use of zinc oxide in 1999, but believed that nano zinc oxide had problems and could not be used. In 2006, nano zinc oxide was approved as a new effective ingredient.

Nanoparticles worry about releasing free radicals, increasing oxidative stress, and damaging proteins, esters, and DNA in the body. Hydrogen and oxygen free radicals produced by titanium will damage DNA and cells, and hydrogen and oxygen free radicals produced by zinc will damage DNA and cell structure of skin. In addition, if you apply sunscreen to wash your face, swim or use lipstick with sunscreen coefficient, you can directly eat the nanometer sunscreen contained in it, so that the human body can directly absorb it. The research results show that when the intestine absorbs the diameter of titanium dioxide particles to 150-500nm (slightly higher than the nanometer level, it is also used for particle sunscreen equivalent to micron particles), it can reach the liver and spleen. Whether nanoparticles can enter the blood directly through the skin is still controversial. Through experiments in animals and human hands, nano zinc oxide absorbed 1.5%~2.3%. However, some people have come to the conclusion that the skin on the human hand is much thicker than the lips, eyelids, inner thighs, armpits, etc., and the absorption of the damaged parts of the skin is also different. In this case, the absorption of such particles is almost zero, which is too thoughtless, and lacks more experimental evidence.