Visible light photodegradation of 4-chlorophenol with a coke-containing titanium dioxide photocatalyst

Photocatalysts based on titanium dioxide have been prepared by a modified sol–gel process using different alkoxide precursors. Depending on the precursor and the calcination temperature of the gels, carbon-containing catalysts with large surface areas, capable to photodegrade p-chlorophenol (4CP) with visible light (λ>400 nm), have been obtained. Photodegradation and mineralisation were confirmed by HPLC and TOC measurements. The catalysts were characterised by physisorption of argon, elemental analysis, EPR, UV/VIS, X-ray powder diffraction (XRD), FT-IR and high-resolution transmission electron microscopy (HRTEM). A highly condensed, carbonaceous species formed during calcination is responsible for the photosensitisation. When used as a photoelectrode, the appearance of a photocurrent indicated the semiconductor nature of these novel materials. The catalysts exhibit a surprisingly good long-time stability despite of the carbonaceous nature of the sensitising species. It is also shown, that commercially available TiO2 can be photosensitised by impregnation with suitable alcohols followed by pyrolysis.