Effects of monometallic and bimetallic Au–Ag supported on sol–gel TiO2 on photocatalytic degradation of 4-chlorophenol and its intermediates

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.

Research Highlights
► A thorough investigation on how Au and Ag affect the degradation of 4-chlorophenol were carried out.
► The addition of Au or Ag significantly increased the degradation of 4-chlorophenol.
► Au and Ag differently affected the intermediate formation and reaction pathway.
► Effects of the bimetallic Au–Ag on TiO2 on the degradation were reported.