In this work, photocatalytic degradation of 4-chlorophenol (4-CP) was investigated using TiO2, Au/TiO2, Ag/TiO2, and Au-Ag/TiO2 photocatalysts prepared by a sol-gel method. Experiments were carried out in a batch reactor with a photocatalyst suspended in a reaction solution under irradiation from an 11-W low-pressure mercury lamp emitting UV light in the wavelength range of 200-280 nm. Qualitative analysis of the reaction solution was performed by means of both a high performance liquid chromatograph (HPLC) and a total organic carbon (TOC) analyzer. The amounts of intermediates obtained from the 4-CP degradation were also determined. The results showed that the loading of a small amount (0.1%) of either Au or Ag onto the TiO2 significantly improved the photocatalytic activity, but the loading of 0.1% Au onto the 0.1% Ag/TiO2 slightly affected the photocatalytic activity, exhibiting almost the same photocatalytic activity as the host 0.1% Ag/TiO2. However, both the 0.1% Ag/TiO2 and 0.1% Au-0.1% Ag/TiO2 provided the highest photocatalytic activity in terms of TOC reduction. (C) 2011 Elsevier B.V. All rights reserved.