Gas Phase Photocatalytic Degradation of Volatile Organic Compounds Using Metallised Titania
Volatile organic compounds (VOCs) are major air pollutants originating from industrial processes and cause many environmental problems including air quality degradation, global warming, climate change and statospheric ozone depletion.
In recent years, photocatalytic detoxification of VOCs has been found to be generally more efficient in the gas phase than the liquid phase. However, it has been reported that the use of titania may result in its deactivation due to the formation of surface species, intermediates or by-products of higher adsorption affinity than the parent compound, limiting its practical application as a photocatalyst. Toluene is one such compound.
With an aim to address this issue, wmetals were deposited onto titania to enhance its photoactivity for the degradation of toluene as well as to inhibit its deactivation. Platinum group metals (Pt, Pd, Rh) and noble metals (Au, Ag) were deposited on Degussa P25 titania at a nominal loading of 0.5 at%. With the exception of Ag, the deposited metals delayed the onset of photocatalyst deactivation by toluene. Pd, Rh and Au desposits displayed similar improvements (~2-fold) while Pt displayed a 20-fold increase in the delay as compared to neat titania.
It has been suggested the deposition of metals on titania results in the formation of a Schottky barrier at the metal-titania interface, improving charge separation by decreasing photogenerated electron/hole recombination. However, these findings suggest the degree of photocatalysis invoked by metal deposits is governed not only by this aspect but also by other factors such as the catalytic properties of the metal.