Modification of Photocatalytic Properties

8.5.3.1 Deposition of Noble Metals

A substantial number of reports have been accumulated on the effect of noble metals, such as Pt, on the photocatalytic performance of TiO2 [81-92]. This data indicates that the photocatalytic activity depends on surface dispersion of Pt, forming small islets, and the related ratio of the Pt/TiO2 areas.

Sakthvitel et al. [91] reported photocatalytic oxidation of dichloroacetic acid at dif­ferent Pt load (the studies also included Au and Pd). The data reported by Sakthvitel et al. [91] on the effect of Pt on photocatalytic properties is represented in Figure 8.33. As shown in Figure 8.34, the Pt-activated TiO2 catalysts exhibit optimum per­formance at 0.8 wt% of the Pt load.

In most cases platinum results in enhanced performance, which is consistent with basic theoretical models. However, due to cost reasons, there is a need to find an alternative solution to activate cathodic sites. The cathodic sites may also be formed by the deposition of small islets of oxides that exhibit high WF, such as WO3 [83].

FIGURE 8.34 Effect of Pt content on photocatalytic degradation of acid green 16 (leather dye) in terms of normalized concentration versus Pt content, according to Sakhtivel et al. [91]. (Reprinted from Water Res, 38, S Sakhtivel, MV Shankar, M Palanichamy, B Arabindoo, DW Bahnemann, V Murugesan, Enhancement of photocatalytic activity by metal deposi­tion: Characterisation and photonic efficiency of Pt, Au and Pd deposited on TiO2 catalyst, 3001-3008, Copyright 2004, with permission from Elsevier.)

In summary, while the effect of noble metals on photocatalytic performance of TiO2 is relatively well established, these metals are unlikely to be the components of commercial photocatalysts due to their costs.