New porphyrin/Cu(II) porphyrin-TiO2 nanohybrids for improved photocatalytic oxidation and reduction activities

Abstract

Two new porphyrins 5,10,15,20-tetra[3-((ethoxycarbonyl)propoxy)phenyl] porphyrin (H2Pp1), 5,10,15,20-tetra[3-((carboxyl)propoxy)phenyl] porphyrin (H2Pp2) and their copper porphyrins (CuPp1, CuPp2) were synthesized and characterized spectroscopically. The corresponding porphyrin/Cu(II) porphyrin-TiO2 nanohybrids (H2Pp1-TiO2, H2Pp2-TiO2, CuPp1-TiO2, CuPp2-TiO2) were then prepared and characterized. These nanohybrids have the same anatase structure as bare TiO2 with BET specific surface area of 117.96–151.76 m2 g−1. There exists the heterojunction at the interface of porphyrin/Cu(II) porphyrin and TiO2 within nanoscale. The photocatalytic performances of these nanohybrids were investigated by 4-NP oxidative degradation, as well as reduction to 4-AP. These photocatalysts exhibit high photocatalytic activities compared with bare TiO2 and individual porphyrin/Cu(II) porphyrin. With CuPp2-TiO2 as photocatalyst, the 4-NP degradation can be finished within 25 min, and 4-NP is reduced to 4-AP in 6 min. The main active species are photogenerated hole, hydroxyl radical and superoxide free radical during the photodegradation of 4-NP. The possible photocatalytic Z-scheme mechanism is suggested. In this case, the photogenerated holes from VB of TiO2 and electrons from CB of H2Pp/CuPp are the main drive force for the high photocatalytic activity.