Investigation of the Photocatalytic Activity of TiO₂−Polyoxometalate Systems

Abstract

The present study reports the investigation of polyoxometalate catalyzed electron transfer from the conduction band of photoexcited TiO2 to molecular oxygen. The oxidation of 1,2-dichlorobenzene (DCB) was used as an index reaction for evaluating the photocatalyst systems TiO2-PW12O40(3-), TiO2-SiW12O40,4- and TiO2-W10O32(4-) in oxygenated aqueous solution. Addition of these polyoxometalate (POM) anions to TiO2 suspensions resulted in significant rate enhancement for DCB oxidation. Photodegradation kinetics exhibited [POM] dependence, experiencing different maximum (k = 0.0318 min(-1), 0.0108 min(-1), and 0.0066 min(-1)) for each POM at different [POM] (0.1 mM PW12O40(3-), 0.07 mM SiW12O40,4- and 1 mM W10O32,4-respectively). The probability that the difference in the adsorption affinity of POMs on TiO2 surface could account for the observed ranking of photodegradation rates was ruled out by adsorption isotherm experiments that revealed similar binding constants for each POM (467 M(-1), 459 M(-1), and 417 M(-1) for PW12O40(3-), SiW12O40(4-), and W10O32(4-), respectively). DCB degradation over TiO2 with O2 or POM+O2 systems can be modeled by the Langmuir-Hinshelwood (saturation kinetics) model. The concentration-independent rate constants (kL-H) for TiO2-O2, TiO2-W10O32(4-), TiO2-SiW12O40(4-), and TiO2-PW12O40(3-) were 0.0818, 0.152, 0.421, and 0.638 min(-1), respectively. An analysis of deltaG for electron transfer from the conduction band of TiO2 to POMs in this study shows that the electron transfer takes place even when it is endothermic.

Enhancement of photocatalytic activity of nano-scale TiO2 particles co-doped by rare earth elements and heteropolyacids

“…So heteropolyacids have been frequently used as photocatalysts in the oxidation or reduction of organic or inorganic compounds in water. Ozer has reported the use of heteropolyacids such as PW 12 [16], and another report also observed that the doping heteropolyacids into TiO 2 can increase eightfold in the apparent degradation rate of 1,2-dichlorobenzene compared to TiO 2 alone [17].…”

Heteropolyacid‐Based Materials as Heterogeneous Photocatalysts

“…According to Yoon et al, the photoinduced charge-carrier generation at the HPA-TiO 2 heterojunction was very efficient and was also enhanced upon illumination of the HPA-incorporated TiO 2 with visible light as well as near-UV light. In an analogous way, Ozer et al [52] 40 . [54] HPAs as oxidants are more effective than O 2 to remove conduction band electrons from TiO 2 .…”

“…[54] HPAs as oxidants are more effective than O 2 to remove conduction band electrons from TiO 2 . [52] Mixtures of H 3 PW 12 O 40 with commercial TiO 2 Degussa P25 were used for 2,4-dichlorophenol photocatalytic degradation in aqueous media. [55] H 3 PW 12 O 40 species on the surface of TiO 2 accelerated the hydroxylation of the substrate but not its mineralization, which was somewhat suppressed in the presence of the HPA.…”

Effect of Microwave Irradiation on Morphology and Size of Anatase Nano Powder: Efficient Photodegradation of 4-Nitrophenol by W-doped Titania

“…Holeelectron recombination is a serious problem for the development of photocatalytically based technologies, since it severely limits the achievable quantum yields. 12 However, there are some strategies to reduce electron-hole recombination rates and increase photocatalyst efficiency. A common method consists of the doping of titania with transition metal ions while maintaining a good control of the primary particle size to achieve nanoscale configurations of the catalysts.…”