Optimization of the ultraviolet-visible absorption properties of nano-particle TiO2: Influence of milling, surface area and surfactants on particle-size distribution, and stability of isocyanate/acrylic paints

The ultraviolet-visible (UV-Vis) absorption properties of a range of nano-particle titanium dioxides have been optimized and interrelated to the effects of the nature of calcination versus wet milling methodologies. Different inorganic and organic surfactants and surface treatments were also assessed. The TiO2 particles as prepared were characterized using X-Ray diffraction spectrometry (XRD), transmission electron microscopy (TEM), BET, UV/Vis spectroscopy, and CPS disk centrifuge. Data are related to their spectral absorption properties and weathering stability in an isocyanate-acrylic coating via gloss retention and weight loss. The choice of particle size is a compromise between UVA absorption, UVB absorption, visible transmission, and photoactivity. It is demonstrated that TiO2 with a crystallite size of 25 nm yields a product with the optimum properties. A method using UV/visible absorption spectroscopy has been developed and found to give excellent sensitivity to particle size was shown with CPS (disk centrifuge). It is shown to be a useful way to assess nano-TiO2 dispersions. The wet milling of the base TiO2 before surface treatment was also optimized utilizing different dispersants. It was shown that using the ratio of absorbance at 300:550 nm is a good approximation for the ratio of the whole area under the curve in the UV spectrum to that in the visible region. This was used as an indication of the generation of smaller fragments generated by milling the larger aggregates. The particle-size distribution and nature of the wet-milling process significantly influenced the subsequent accelerated ATLAS weathering performance of the titania particles in an isocyanate-acrylic coating.