Visible light photocatalysts based on homogeneous and heterogenized tin porphyrins

Visible light photocatalysis using water-soluble tin porphyrin (s-SnP, [Sn(OH2)(2)((TPyP)-P-H)](NO3)(6)) and water-insoluble tin porphyrin Sn(OH)(2)(TPP) (ins-SnP) immobilized on SiO2 (hetero-SnP) was investigated. The visible light photocatalytic activities of s-SnP and hetero-SnP were demonstrated successfully for the degradation of 4-chlorophenol (4-CP) and acid orange 7 (AO7) in water. The visible light activity of hetero-SnP increased with the ins-SnP loading and was saturated above 77 mg/g-SiO2, which corresponded to the homogeneous concentration of [ins-SnP] = 50 mu M. It is the Q band of SnP (500-650 nm) that is photocatalytically active under visible light, not the Soret band (420-430 nm) whose absorption intensity is much higher. When applied to the degradation of 4-CP and AO7, hetero-SnP was particularly stable and could be used repeatedly without losing the activity whereas the activity of s-SnP was reduced gradually with repeated uses. The photocatalytic degradation reactions of 4-CP, AO7, and other organic substrates were studied systematically to show that the operating mechanisms are very different depending on the kind of substrates. The properties and activities of s-SnP and hetero-SnP as visible light photocatalysts were investigated in various ways and discussed in detail.