The influences of nanoscale titanium dioxide particle size and crystal structure on light absorbance

Nanoscale titanium dioxide is an important physical sun-block material and is widely used in sunscreen. In our test, the influences of the particle size and crystal structure on light absorbance were examined. The experiment shows that the absorbance (Abs) of nanoscale titanium dioxide in UV-ray district is much higher than it in visible light district under the same concentration (0.04 g/L). The Abs of nanoscale rutile keeps increasing, reaches the highest at 360 nm, and then starts to decrease as the wavelength becomes shorter. The nanoscale anatase has the similar light absorbance characteristic, with the highest Abs peak at 320 nm. In the UVA district, the rutile has stronger absorbance ability than the anatase, while in UVB and UVC, there is a similar absorbance between rutile and anatase. Compared with the bulk titanium dioxide, the nanoscale titanium dioxide is capable of absorbing the UV-ray more effectively and let the visible light pass through more easily. Since the anatase is of the stronger activity than rutile and thus probably harms the skin more easily, the nanoscale rutile should be the best selection used for sunscreen. However, when the particle size of rutile is too small, for example, smaller than 10 nm, its Abs tends to be much higher in UVB and UVC district, but lower in UVA and visible light district. Therefore the appropriate particle size and crystal structure should be considered when nanoscale titanium dioxide is applied for sun-block effect. The detailed test optimizations are being carried out in our lab.