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Nano-scale titanium dioxide in sunscreen cosmetics application

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From the mechanism of nano-titanium dioxide sunscreen proceeding described the nanotitanium dioxide sunscreen superior performance and application prospects, analysis of nano-titanium dioxide used in sunscreen cosmetics should pay attention to the problem,more comprehensively reflect the nano-titanium dioxide in sunscreen cosmetics of the application of research in .
 
Keywords: nano-titanium dioxide; sunscreen cosmetics; optical activity
 
Ultraviolet radiation in sunlight on the human body against a larger waves. Excessive exposure to ultraviolet light, the skin will produce erythema, dark spots, skin aging, a serious lead to skin cancer [1,2]. In recent years, as people of UV awareness-raising and health awareness increases, sunscreen cosmetics of the development, application has gradually become a research hotspot. Titanium dioxide due to its high refractive index
and high optical activity, has been identified as a major sunscreen. Nano-titanium dioxide for superior performance has been much more widespread attention, was used in the new,high-quality sunscreen cosmetics research and development, step by step to demonstrate its unique advantages and wide application prospects.
 
Mechanism of nano-titanium dioxide sunscreen
 
In accordance with the different wavelengths, ultraviolet short-wave zone is divided into 190 ~280nm, Poland District 280 ~ 320nm, long-wave zone 320 ~ 400nm. Short-wavelength ultraviolet energy of the highest areas, but after was blocked from the ozone layer, therefore,impact on human health in general is a medium-wave area and long-wave ultraviolet light district [1 ~ 2].
 
The strong anti-ultraviolet titanium dioxide capacity is due to its high refractive index and high optical activity. The ability and mechanism of its anti-ultraviolet related to their size:
 
When the particle size is larger, the barrier is based on UV reflection, scattering-based, and on the medium wave ultraviolet region and long-wave zone are valid. Sun mechanism is a simple cover, a general physical sunscreen, sunscreen weak; as the particle size decreases, the light through the particles of titanium dioxide surface area of the long-wave ultraviolet reflection, scattering is not obvious, while the wave UV absorption area notably enhanced. Its mechanism of absorption of ultraviolet sun, the main UV-absorbing medium wave zone.
 
Thus, titanium dioxide on different wavelengths of UV sun protection mechanism is not the same area on the long-wave ultraviolet barrier to scattering mainly on the Polish zone of the barrier to absorb the UV-based [3].
 
Nano-titanium dioxide due to small size, active large, both reflection, scattering ultraviolet rays, can also absorb ultraviolet light, and thus a stronger barrier against UV capability.Nano-titanium dioxide to UV absorption mechanism may be [2,4]: the electronic structure of nano-titanium dioxide by the valence electron band and empty conduction band orbital composition of the formation, when its under ultraviolet irradiation, than its band gap (about 2.3eV) light energy is absorbed large, so that the valence band to the conduction band of the electronic excitation, resulting in a lack of valence electrons with holes happen to form easily movable and activity of two strong electron hole pairs. This e-2 hole right on the one hand in the
event of a variety of redox reactions with each other again in order to produce fluorescence in the form of heat, or the release of energy, on the other hand the dissociation into free movement in the crystal lattice to the lattice response surface or other areas of free holes and free electrons, and was immediately captured surface group. Under normal circumstances activation of titanium dioxide, surface water will produce surface hydroxyl groups
to capture the free holes to form hydroxyl radicals, while the free electrons will soon be free of the state with the
absorption of oxygen free radicals generated superoxide, which will be around to kill bacteria and viruses death.
Visible, ultraviolet radiation, surface water level and oxygen activation rate of titanium dioxide photocatalytic activity
of the three basic conditions.Because nano-titanium dioxide to absorb ultraviolet light would cause free radicals,
which will accelerate the skin aging, skin hazard. Therefore, the use of nano-titanium dioxide as a sunscreen when
the weakening or elimination of 3 from the basic conditions start to weaken or simply eliminate the optical activity,
thereby reducing its harmful [4].
 
Nano-titanium dioxide sunscreen properties and application prospects
 
Ultraviolet radiation on the human body as a great danger, the developed countries in recent years more emphasis
on sunscreen products, research, development, has introduced a wide range of UV fibers, plastics, film, coatings,
as well as sun cream, foundation, lipstick , mousse, ointment, etc. Fire Bureau sunscreen cosmetics. China has
also increased in recent years, sunscreen cosmetics research and production.
 
But in the past, mostly Sunscreen Benzophenone, o-amino-benzophenones, salicylic acid ester, p-amino benzoic
acid, cinnamic acid esters and other organic compounds, and therefore unstable, short life, and side effects It has
a certain toxicity and irritation, if you add too much, will have chemical allergies, and may even lead to skin cancer.
 
The nano-titanium dioxide as inorganic components, has excellent chemical stability, thermal stability and
non-migratory and strong achromatic power, hiding power, low corrosivity, excellent ease of dispersion and
non-toxic, tasteless, non-irritating, safe to use, but also the role of both bactericidal deodorant. More importantly,
as mentioned above, nano-titanium dioxide both absorb ultraviolet light, but also fired, scattering ultraviolet rays,
so anti-UV ability, with the same dose of the organic ultraviolet screening agent than its absorption in the ultraviolet
region higher; and nano-titanium dioxide on the medium wave zone and barrier effect of both long-wave ultraviolet
light district, unlike the organic anti-UV agents only a single area or long-wave area on the medium wave ultraviolet
shielding effect. In particular, because of its smaller particles, manufactures high transparency, can be transparent
to visible light by adding cosmetic use of skin whiteness of nature, to overcome some organic matter, or an opaque
pigment grade titanium dioxide, so that the skin does not show the shortcomings of the natural pale color.Because
of this, nano-titanium dioxide was soon widespread attention, and to gradually replace some of the organic anti-UV
agents, sunscreen cosmetics become the superior performance of a physics-based UV shielding agent.
 
With the improvement of people’s living standards and international competition intensifies, safe, efficient sunscreen
cosmetics research and development efforts will gradually increase. At present, the developed countries, sunscreen
cosmetics market has been demonstrating strong vitality. 1999,2000, the United States has annual sales of 100 million
U.S. dollars respectively 7.37,7.65, 2.45,2.70 England reached 100 million U.S. dollars, but in recent years were 20%, 10%
or more of the rate of growth, which the dosage of nano-titanium dioxide each year are also big rate. Japanese cosmetics
UV nano-titanium dioxide than the annual demand for the 1000t, textiles, plastics, rubber products in a greater amount.
 
From the development of sunscreen cosmetics trends, one inorganic sunscreen instead of an organic sunscreen agent,
and second, bionic sun. The latter costs more, at present difficult to promote, the former an affordable price, and the sun
superior performance, they have been generally good. In particular, nano-titanium dioxide, because of its relatively superior
performance and application prospects, and therefore a good momentum of development and market potential.
Nano-titanium dioxide in sunscreen cosmetics of the Application Selection
 
Crystal Selection
 
Titanium dioxide is commonly used square crystal, crystal with rutile and anatase two kinds, the former can be obtained by
calcining the latter, thus the lattice structure is more perfect, in the thermodynamically more stable.
 
From the refractive index point of view, 2.7 rutile, anatase is 2.3, so the launch of rutile ultraviolet, scattering a stronger ability,
while the absorption will be weak.Through the study of its surface, and found that the presence of oxygen in a case, the optical
activity of rutile than in anatase weak.This may be due to: 1) Rutile produce electronic 2 hole pairs is faster and easier with the
release of heat or other forms of solar energy; 2) rutile gradual water loss during heat treatment, reducing the surface hydroxyl
groups; 3), rutile oxygen exchange capacityis weak, the more difficult to absorb oxygen.
 
Therefore, to maintain stability, and enhance the shielding effect, reducing activity of TiO 2 to reduce the dangers of its optical point
of view, should be used in cosmetics rutile titanium dioxide [4,6].
 
The choice of particle size
 
The size of nano-titanium dioxide particles is closely related to its anti-UV capability. When its size is equal to or less than
half thewavelength, the light reflection, scattering the largest, shielding the best results. UV wavelength of 190 ~ 400nm,
and are thus nano-titanium dioxide particle size can not be larger than 200nm, preferably not more than 100nm. However,
nor is it the smaller the particle the better, size is too small easy to reunion, is not conducive to decentralization, but also
easy to plug the pores of their skin is not conducive to breathe and sweat exclusion. Generally speaking, when its diameter
is between 30 ~ 100nm, UV-shielding effect of the best, while visible light through, so that the whiteness of the skin appear
more natural beauty [6 ~ 7]. Therefore, it is best to be the size of titanium dioxide used in cosmetics control in this range.
 
The choice of preparation method
 
Preparation of nano-titania There are several ways [8], generally can be divided into two major categories of dry and wet.
Wet system were rutile titanium dioxide nano-dispersion of Bi Gan law good, but impure crystal, optical activity of a strong,
which is used in cosmetics as a sunscreen should try to avoid. The dry method was the product of rutile-type crystal of high
purity, optical activity of the small [4]. But there are also a little unsatisfactory, that is, poor dispersion. However, the surface
can be processed to resolve.
 
The choice of surface modification process
 
As the nano-titanium dioxide particles small, but in itself is a polar, more than a larger surface area, surface area can be
high, and therefore non-polar dispersion medium is not good, easy to gather in the polar medium, a direct impact on their
performance effectively; In addition, nano-titanium dioxide photocatalytic activity has a strong, direct use in cosmetics,
fragrance, and the decomposition of nutrients, oxidation of fat, so that cosmetic degenerate taste. Therefore, the need
for nano-titanium dioxide surface modification, that is, particles coated in a layer of material, we can overcome the
difficulties mentioned above. Coated material can be alumina, silica and other minerals, can also be an organic
siloxane, stearic acid and other organic compounds [9 ~ 10].Generally speaking, for inorganic package, can reach
the reduction of titanium dioxide particles of UV to reduce titanium dioxide to UV absorption, while the surface of crystalline
 particles changed, thus changing its electrochemical behavior. In this way, an increase of optical activity of inclusions and
reaction products of the reaction path for the spread of materials, an increase of electron – hole pairs have yet to be captured
before the possibility of regrouping, so as to reduce activity of a TiO 2 effective barrier, while , can increase the dispersion of
titanium dioxide particles and reduce harmful particle surface groups the opportunity to come into contact with the skin [.
In the surface of titanium dioxide particles coated organic matter, when the surface becomes non-polar, you can make it
a very good compatibility with organic media, improve the particles in the dispersion of different media; In addition, the
package is actually carried out for organic hydrophobic treatment, can reduce the surface of titanium dioxide particles
of water activation and surface hydroxyl groups to extend their adsorption and diffusion of oxygen, thereby reducing its
optical activity [6].
Through the choice of packages and parcels material conditions of the adjustment, control, can be of different nature
and effects of particle parcels. Therefore, how to prepare an appropriate particle size, particle size distribution is narrow
, long-term stability, and can be uniformly dispersed in organic molecular systems in nano-titanium dioxide particles,
is a very meaningful and has a broad application prospect research topic. In recent years, although there are some
relevant reports, but there are many issues to be studied and discussed.
 
Conclusion
 
Nano-titanium dioxide has a higher refractive index due to light and activity, superior performance they have been
become a new type of sunscreen agent in sunscreen cosmetics applications has good prospects for development.
However, to efficient and safe application of their sunscreen nature should be carefully studied in the practical
application of their unique optical activity [4], in crystal form, particle size, preparation method, surface modification
processes in areas such as a serious option to to reduce or completely eliminate the hazards of their optical activity.
This is a nano-titanium dioxide in sunscreen cosmetics applications, a new and important research topic.

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