US EPA

1117696 

Journal Article 

Charge-transfer surface complex of EDTA-TiO2 and its effect on photocatalysis under visible light 

Kim, G; Choi, W 

2010 

Yes 

Applied Catalysis B: Environmental
ISSN: 0926-3373 

Elsevier BV 

100 

1-2 

77-83 

10.1016/j.apcatb.2010.07.014 

We investigated the formation of surface complex between TiO sub(2) and common electron donors (methanol, formic acid, acetic acid, triethanolamine and EDTA) that can absorb visible light through ligand-to-metal charge transfer (LMCT) mechanism. The visible light activity of TiO sub(2)-EDTA complex was outstanding among all tested TiO sub(2)-substrate complexes. The complexation of EDTA on TiO sub(2) induced a visible light absorption up to 550 nm and exhibited a marked visible light activity for both the reductive conversion of Cr(VI) and the production of H sub(2). The optimal concentration of EDTA was 100 mu M for the reduction of Cr(VI) but much higher (10 mM) for the production of H sub(2). The EDTA-adsorbed TiO sub(2) electrode also generated a significant level of photocurrent under visible light irradiation. The LMCT-excited electrons (in TiO sub(2) conduction band) are subsequently transferred to electron acceptors such as Cr(VI) and protons. The degradation of EDTA on TiO sub(2) under visible light was significant only in the presence of Cr(VI) that should scavenge electrons with inhibiting the recombination. The surface CT-complex formation between TiO sub(2) and EDTA was significantly inhibited when the surface of TiO sub(2) was fluorinated. The isoelectric point of TiO sub(2) particles suspended in water was gradually shifted to lower pH values with increasing the concentration of EDTA, which supported the formation of surface complex between TiO sub(2) and EDTA anions. The FT-IR spectra of TiO sub(2)-EDTA complex showed a band centered at 1409 cm super(-1), which is ascribed to the carboxylate group complexed with TiO sub(2) surface. The complex IR band was diminished upon fluorinating the surface of TiO sub(2). The fact that common electron donors like EDTA can form CT-complexes on the surface of TiO sub(2) and contribute to the visible light activity should be recognized in assessing and understanding the overall photocatalytic activity. 

Photocatalyst; Titanium dioxide; Ligand-to-metal charge transfer (LMCT); Surface complex; Visible light activity