Photocatalyzed oxidation of alcohols and organochlorides in the presence of native TiO2 and metallized TiO2 suspensions. Part (I): Photocatalytic activity and pH influence

Photocatalytic oxidations of methanol, ethanol and chloroform, trichloroeth ylene (TCE), and dichloropropionic acid (DCP) in M/TiO2 aqueous slurries ar e studied. In the presence of oxygen, the intermediates of methanol oxidati on, such as formaldehyde: and formic acid, were not detected by GC in the s lurries of TiO2, Pt/TiO2, or Pd/TiO2, and CO2 was the only product detected . The distribution of intermediates for ethanol photocatalytic oxidation va ries with different catalysts: under the same reaction conditions, the rati o of acetaldehyde:acetic acid is 30:1 on TiO2, and 0.23:1 on Pt/TiO2, with the acetaldehyde concentration being 130 limes higher or. TiO2 than on Pt/T iO2. Thus, a further oxidation is achieved easily on the Pt/TiO2. The CO2 p roduction depends on the initial reaction pH: Acidic pH produces CO2 immedi ately in alcohol oxidation, but alkaline pH retards the mineralization subs tantially. Little effect of Pd metallization on TiO2 was observed for photo catalytic oxidation of chloroform, TCE or DCP. Pt/TiO2 only enhances DCP de chlorination and has no effect on its decarboxylation. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.