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, trichloroethylene (TCE), and dichloropropionic acid (DCP) in M/TiO2 aqueous slurries are studied. In the presence of oxygen, the intermediates of methanol oxidation, such as formaldehyde and formic acid, were not detected by GC in the slurries of TiO2, Pt/TiO2, or Pd/TiO2, and CO2 was the only product detected. The distribution of intermediates for ethanol photocatalytic oxidation varies with different catalysts: under the same reaction conditions, the ratio of acetaldehyde:acetic acid is 30:1 on TiO2, and 0.23:1 on Pt/TiO2, with the acetaldehyde concentration being 130 times higher on TiO2 than on Pt/TiO2. Thus, a further oxidation is achieved easily on the Pt/TiO2. The CO2 production depends on the initial reaction pH: Acidic pH produces CO2 immediately in alcohol oxidation, but alkaline pH retards the mineralization substantially. Little effect of Pd metallization on TiO2 was observed for photocatalytic oxidation of chloroform, TCE or DCP. Pt/TiO2 only enhances DCP dechlorination and has no effect on its decarboxylation.