Photocatalytic Activity of Titania: Study of Different Anatase/rutile Ratios

Viña del Mar

Congreso; XIV Encuentro LAtinoamericano de Fotoquímica y Fotobiología; 2019

ELAFOT

Titanium dioxide (TiO2) exists as three polymorph phases at atmospheric pressure: anatase, brookite and rutile. These phases have different crystal structures and consequently, different properties1. Rutile is thermodynamically stable compared with anatase and brookite. These two forms can be transformed into rutile by heating at high temperature2. Despite its unstableness, anatase has shown a higher photocatalytic activity compared with rutile1.Several works have investigated the photoactivity of anatase and rutile and, in many examples, catalysts with more weight-fraction of rutile have been more active.For instance, it has been reported that TiO2 microspheres with a rutile weight fraction of 50 % show the highest activity for the photodegradation of organic pollutants as methylene blue, rhodamine B and methyl orange in aqueous solution3. Also, a mixed-phase TiO2 powder with 40 wt% rutile exhibits the higher photocatalytic activity for the degradation of methylene blue4. Finally, TiO2 sub-micron fibers with 38 wt% of rutile phase have the optimal initial degradation rate constant for the photodegradation of phenazopyridine, a pharmaceutical contaminant5. In general, these studies concentrate on the material?s ability to photodegrade organic compounds. In contrast, here we focus our efforts to evaluate the photocatalytic activity of the different rutile fractions to accelerate organic reactions; in particular, the well-known Ullman reaction. For that we utilize a series of home-made palladium-doped titania (Pd@TiO2). Thus, the homocoupling (eq. 1) of 4-methyl iodobenzoate (1) was carried out in THF with 2 eq. of base and irradiated with 368 and 465 nm LEDs working at 0.4 and 1.9 Wcm-2 respectively, for 1 h and at room temperature (rt). We fully characterize the materials by means of X-ray diffraction, RAMAN and Diffuse reflectance spectroscopy and ICP-OES. Overall, we find optimal rutile ratios for the reaction.