Photoactive polymer–nanoclay hybrid photosensitizer for oxidation of phenol in aqueous media with the visible light

The intercalation of a photoactive polymer, polyethylene glycol (PEG2000) containing covalently attached 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin chromophores (p-THPP), in Cloisite® 30B (C30B) resulted in formation of a hybrid photosensitizer C30B/p-THPP-PEG2000. The photosensitizer acts as an efficient generator of singlet oxygen in aqueous medium on irradiation with visible light. Structural and photophysical properties of C30B/p-THPP-PEG2000 were determined using complementary physicochemical techniques: X-ray diffraction, laser scanning fluorescence confocal microscopy, and electronic absorption/emission spectroscopies. The C30B/p-THPP-PEG2000 was found to act as an efficient photosensitizer for oxidation of phenol in aqueous solution under irradiation with light at λ > 470 nm. The mechanism and the quantum yield of that process were shown to be strongly pH dependent. The pH effect on acid–base equilibria of porphyrin associated with imine N-protonation as well as the ionization of the phenol molecule were evaluated.