Fabrication and Visible Light Photocatalytic Activities of TiO2 Nanomaterials Incorporated with Tin(IV) Porphyrins

Extended Abstract Photocatalytic processes using TiO2 as photocatalyst have been introduced in the seventies. However, despite lots of advantages, TiO2 must be excited in the UV region, which means that it can absorb only 3% of solar energy it receives. The majority of solar energy is concentrated in the visible region. Therefore, a photocatalyst that is active under visible light is of paramount importance as an essential element of solar photoenergy utilization. A variety of approaches has been attempted in search of visible light active materials. Porphyrins and metalloporphyrins have been widely investigated for their photochemical activity for various applications such as environmental photocatalysis, hydrogen production, and solar cell. The electrochemical potentials for the porphyrin ring being the redox center is readily dependent on the kind of central metal ions. Among a series of metalloporphyrins, tin(IV)-porphyrin has a strong oxidative capacity (porphyrin ring reduced easily) owing to the high charge on tin(IV) and the excited tin-porphyrin exhibits a high activity for the photooxidation of organic compounds under visible light [1]. We have interests in the photocatalysts based on tin-porphyrin with strong visible light absorption as an efficient visible light photocatalyst for an environmental remediation [2-4] and H2 production [5,6]. We here present TiO2 hybrid nanomaterials incorporated with tin(IV) porphyrins exhibiting visible light activities: (i) Tin(IV) porphyrins incorporated-TiO2 nanotubes with 152 m/g of surface area and 0.44 cm/g of porosity showing visible-lightactivated photocatalytic production of H2. (ii) A ternary hybrid material of semiconductor/polymer/porphyrin in which the surface of TiO2 particles coated with perfluorosulfonate polymer (Nafion) binds water-soluble cationic tin(IV) porphyrins within the Nafion layer through electrostatic attraction. H2 evolution activity in this ternary hybrid material was estimated to be 1.5 times higher than that in TiO2-porphyrin without Nafion.