| Abstract
| - Here we report the simultaneous Cr(VI) reduction and4-chlorophenol (4-CP) oxidation in water under visible light(wavelength > 400 nm) using commercial Degussa P25TiO2. This remarkable observation was attributed to asynergistic effect among TiO2, Cr(VI), and 4-CP. It is wellknown that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interactionbetween Cr(VI) and 4-CP is minimal if not negligible. However,we found that the combination of TiO2, Cr(VI), and 4-CPtogether can enable efficient Cr(VI) reduction and 4-CPoxidation under visible light. The specific roles of the threeingredients in the synergistic system were studiedparametrically. It was found that optimal concentrationsof Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CPoxidation. Cr(VI) was compared experimentally with othermetals such as Cu(II), Fe(III), Mn(IV), Ce(IV), and V(V).Among all these metal ions, only Cr(VI) promotes thephotocatalytic oxidation of 4-CP. The amount of 4-CPremoved was directly related to the initial concentrationof Cr(VI). The system was also tested with four other chemicals(aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurredfor organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicalsbeing oxidized during photoreaction under visible light.The synergistic effect was also found with pure anataseTiO2 and rutile TiO2. This study demonstrates a possibleeconomical way for environmental cleanup under visiblelight.
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