Synthesis of nano-hematite for possible use in sunscreens

Hematite nanoparticles were synthesized for ultraviolet filtration application by the precipitation method followed by calcination at different temperatures. A range of crystallite sizes between 37 and 85 nm (as determined by the Scherrer formula) was obtained, according to the temperature used for the calcination. An increase in the absorbance with increasing crystallite size was observed over the whole ultraviolet B and A range. The experimental band gap was 2.94 eV for the sample calcined at 500 degrees C and 3.08 eV for the sample calcined at 300 degrees C. The in vitro sun protection factor and protection factor-ultraviolet A of a water-in-oil emulsion made with the sample calcined at 500 degrees C as active ingredient were 9.21 and 8.81, respectively, which is higher than the protection factor-ultraviolet A values obtained for titanium dioxide and zinc oxide at the same mass concentration. The emulsion was found to be photostable.