Heteropoly Acid-Incorporated TiO₂ Colloids as Novel Photocatalytic Systems Resembling the Photosynthetic Reaction Center

Abstract

TiO 2 colloids are very useful photocatalytic systems, capable of converting solar energy to chemical or electrical energy and environmental cleaning. The key step in enhancing photocatalytic efficiency is improving photoinduced interfacial electron transfer like plant photosynthesis. It remains difficult to modify TiO 2 particles as a real analogue of the photosynthetic reaction centers of green plants. We attempted to incorporate a photoreactive heteropoly acid (HPA) such as H 3 PW 12 O 40 into TiO 2 colloids in aqueous polyvinyl alcohol (PVA) (0.1%) solution, and found that two light reactions appear to operate in a series. Upon illumination of the HPA/TiO 2 system with near-UV light (300-375 nm), interfacial electron transfer takes place from the conduction band of TiO 2 to the incorporated HPA, which is also excited to catalyze photoreduction of Methyl Orange. The extent of the photoinduced reduction of the HPA adsorbed on TiO 2 particles depends on the concentration ratio of the HPA and TiO 2 colloids, irradiation wavelength, and intensity of radiation. It is found that the interfacial electron-transfer mechanism of HPA/TiO 2 is quite analogous to the "Z-scheme" mechanism for plant photosynthetic systems. The photoinduced charge-carrier generation at the heterojunction is very efficient, and the photoreduction of Methyl Orange has been observed to be synergistically enhanced upon illumination of the HPA-incorporated TiO 2 with visible light as well as near-UV light.

Synthesis, Characterization and Applications in Catalysis of Polyoxometalate/Zeolite Composites

“…5-8 cm´1 compared to the values of pure HPW 12 . This shift was much the same as that observed when HPW 12 was interacting with TiO 2 in a colloidal solution [31]. The system was 20 times more active than the same system without titanium for the photodegradation of methyl orange [29] (see below a detailed explanation of the mechanism of this reaction).…”

Visible-light photocatalytic H2 evolution over a series of transition metal substituted Keggin-structure heteropoly blues

“…HPB possesses adsorption in the visible light region (400-800 nm), which results from d-d and/or intervalence charge-transfer band excitation [23]. Recently, the photo-activity of HPB under visible light has attracted much attention, and HPBs have shown visiblelight photocatalytic activity in some reactions [24][25][26].…”

Heteropolyacid‐Based Materials as Heterogeneous Photocatalysts

“…[49] Tachikawa et al [50] experimentally demonstrated the one-electron oxidation and reduction processes reported in Figure 4 in the HPA-mediated TiO 2 photocatalytic reaction by using the two-color two laser flash photolysis technique. [50] The efficiency of this electron transfer increased by using PW 12 O 40 3-instead of SiW 12 O 40 4-.…”