Ti oxide films were made by reactive magnetron sputtering under conditions yielding "penniform" structures with large porosity. X-ray diffractometry showed that rutile-like and anatase-like films were produced depending on the oxygen content in the sputter plasma. Rutherford backscattering spectrometry documented some oxygen overstoichiometry. Spectral optical measurements were used to analyze the absorption around the fundamental band gap and to give evidence of some hydration and hydroxylation in the films. The various Ti oxide films were brought in contact with 4-chlorophenol (4-CP), whose photo-electrocatalytically induced degradation under ultraviolet irradiation was investigated in a reactor allowing optical probing of 4-CP as well as of intermediate reaction products such as benzoquinone. A rutile-like structure was conducive to the degradation of 4-CP, which can be reconciled with the band gap being suitable for producing photoinduced holes capable to effecting oxidation of the pollutan t. © 2001 Kluwer Academic Publishers.