Comparison of the Photoelectronic and Photocatalytic Activities of Various Anatase and Rutile Forms of Titania in Pure Liquid Organic Phases and in Aqueous Solutions

Abstract

Various titania samples of industrial origin (Degussa and Tioxide) have been characterized by electrical photoconductance measurements and tested as photocatalysts in various liquid media (either pure organic liquids or aqueous solutions) as a function of their structure (anatase versus rutile). Anatase was constantly found more active than rutile, whatever the reaction chosen (mild oxidation of pure cyclohexane and 2-propanol; total degradation of phenol and nitrophenol isomers in water). In identical conditions, Degussa was found more active, but the intrinsic activity, expressed in moles converted per hour and per square meter of active surface, was found slightly higher for anatase Tioxide. The higher activity of anatase with respect to that of rutile could be explained by the interpretation of the photoconductance measurements, which evidence the higher aptitude of anatase (i) to photoadsorb oxygen, in O2 - and O- forms; (ii) to photodesorb it; and (iii) to have a lower relative electron−hole recombination rate. The origin of the differences in the photocatalytic behavior of titania leading to mild oxidation in pure liquid organic phase and total oxidative degradation in aqueous medium is also analyzed.

Does nanoparticle activity depend upon size and crystal phase?

“…Similar to the photocatalytic activity of TiO 2 that is not directly proportional to the total surface area but to the availability of active sites (Sclafani and Herrmann 1996), the same is true for ROS activity of TiO 2 . The discontinuous crystal planes or defects in the crystal structures of nanomaterials play an important role in reactive oxygen species generation; and hence nanoparticle activity is related to the available surface defect sites (Arenz et al 2005;Rajh et al 2002).…”

“…as H 2 O) Vittadini et al 1998). Oxygen in the form of O 2 -, O -and dissociated water molecules on the anatase crystal faces facilitate the ROS formation (Sclafani and Herrmann 1996). Though only chemical activity was measured in this study, this is very relevant to toxicological studies.…”

“…The observation that anatase TiO 2 has higher ROS activity than rutile TiO 2 is consistent with the results of other activity tests. It has been reported that anatase is more photocatalytically active than rutile (Carp et al 2004;Sclafani and Herrmann 1996). The lead (Pb) absorption affinity and capacities of anatase were demonstrated to be higher than that of rutile (Giammar et al 2007).…”

“…The higher activity of anatase with respect to that of rutile could be explained by their surface chemistry difference, i.e. the higher aptitude of anatase to adsorb oxygen in the form of O 2 -and O - (Sclafani and Herrmann 1996) and the dissociative adsorption of water molecules to anatase faces (i.e. as H + and OH -) against the nondissociative water adsorption to rutile faces (i.e.…”

Capturing Irradiation with Nanoantennae: Plasmon‐Induced Enhancement of Photoelectrolysis

“…In addition, surface-bonded peroxo species are present in anatase, in contrast to their absence on rutile surfaces 96 . However, for 650°C annealing, the IPCE apparently drops again, due to the fact that TiO 2 is now partially of a denser rutile form, which is less efficient in creating long-lived electron-hole pairs, crucial for photocurrent generation 97 . The nature of all TiO 2 structures has been verified by subsequent Raman measurements, which will be discussed in Section 5.4.1.…”