USE OF TiO_2 NANOPARTICLES AS INORGANIC UV FILTERS: EFFECT OF OPERATING CONDITIONS ON THE CHARACTERISTICS OF THE FINAL PRODUCT

摘要

Fine titanium dioxide particles are added to sunscreen lotions to efficiently attenuate UVB (290-320 nm) and UVA (320-400 nm) sunlight radiation. The size, the particle size distribution, the structure and the composition of TiO_2 nanopowders have a considerable influence on UV light. The present study consists in improving TiO_2 synthesis in supercritical carbon dioxide (SC-CO_2) in order to increase the UV attenuation factor. Experiments have been carried out first by batch process and secondly in a semi-continuous reactor. The effects of the operating conditions on the final product and their influence in the different steps of the process have been studied. Results have shown that product crystallinity, mean particle size and particle size dispersion influence the UV attenuation factor. Thus, well crystallized TiO_2 anatase particles of about 15 nm in diameter have been obtained working at 250-300°C, 30 MPa with residence time of 5 min. Such particles show good radiation protection properties and specific surface area BET of around 100 m~2·g~(-1).