Visible Light Photocatalysts Based on Homogeneous and Heterogenized Tin Porphyrins

Visible light photocatalysis using water-soluble tin porphyrin ( s -SnP, [Sn(OH 2 ) 2 (TPy H P)](NO 3 ) 6 ) and water-insoluble tin porphyrin Sn(OH) 2 (TPP) ( ins -SnP) immobilized on SiO 2 ( 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-SiO 2, which corresponded to the homogeneous concentration of [ ins -SnP] = 50 μM. 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.