Synthesis and Photocatalytic Properties of Titanium-Porphyrinic Aerogels

We present novel titanium-porphyrinic gels (TPGs) and titanium-porphyrinic aerogels (TPAs), in which porphyrinic ligand tetrakis(4-carboxyphenyl)porphyrin is coordinated to Ti-oxo clusters. These hierarchically porous TPAs, with micro-, meso-, and macropores and reactant-concentration-dependent Brunauer-Emmett-Teller surface areas of 407-738 m(2) g(-1), are prepared by CO(2)critical point drying of TPGs. Although the Ti4+-> Ti(3+)photoreduction of TPAs is less efficient than that of crystalline microporous Ti-porphyrinic framework DGIST-1, prompt diffusion of O(2)and spin-trapping agents into the TPA pores causes the rapid generation of reactive oxygen species (ROS), as observed by EPR spectroscopy. When used as an ROS scavenger, large 1,3-diphenylisobenzofuran is degraded by the best-performing TPA 10 times faster than by DGIST-1, suggesting that the accessibility of molecules (reactants) to pores (reactive centers) strongly influences photocatalytic activity.