Photosensitized oxidation of substituted phenols on aluminum phthalocyanine-intercalated organoclay

Bentonite modified with cationic surfactant, cetyltrimethylammonium bromide (CTMA), was an effective sorbent for organic pollutants in water. To make the sorbent recyclable, aluminum phthalocyanine (AIPc), a representative photosensitizer for generation of singlet oxygen, was inserted successfully into the interlamellar space of CTMA-modified bentonite. Under visible light ( gimel > 450 nm) irradiation, the composite catalyst exhibited a remarkable activity for degradation of the recalcitrant pollutants phenol, 4-chlorophenol, 4-nitrophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol in an aerated aqueous medium. The initial rate of the heterogeneous photoreaction was found to increase with the initial amount of the substrate sorption onto the catalyst, the kinetics following the Langmuir-Hinshelwood equation. Loading of AIPc into the organoclay led to slight expansion of the clay basal spacings from 1.82 to 2.15 nm, but the sorption capacity was decreased notably. The optimal loading of AIPc was about 0.25 wt %. The result demonstrates that the surfactant-modified bentonite not only offers a hydrophobic zone for enrichment of organic contaminants but also provides a flexible environment for destruction of the sorbed pollutants by singlet oxygen generated in situ. It was noted, however, that during four repeated experiments, both the sorption and the degradation rate of 2,4,6-trichlorophenol were gradually decreased, due to some intermediates formed and sorbed onto the catalyst surface.