The production of singlet oxygen with tetra(4-carboxyphenyl)porphyrin adsorbed on SiO2 irradiated with visible light (λ > 500 nm) was evidenced by EPR spectra of TEMPO formed by oxidation of 2,2,6,6-tetramethyl-4-piperidone(TEMP) with 1O2. The formation of singlet oxygen was also evidenced by the formation of anthraquinone and oxanthrone as oxidation products of anthracene with 1O2. The absence of the EPR DMPO-O2− signal evidenced that superoxide anion was not present. No other oxygen radicals were detected. TCPP and TCPP/SiO2 were characterized with UV–vis, UV–vis diffuse reflectance and FT-IR spectroscopy.