Visible light responsive metalloporphyrin-sensitized TiO2 nanotube arrays for artificial photosynthesis of methane

Abstract

The conversion of CO₂ and water into valuable chemicals under sunlight irradiation is of great significance for solving the widespread problems of both limited energy sources and global warming. In this work, new artificial photosynthesis was established through a photocatalysis process of reducing CO₂ to CH₄. A photocatalyst compounded from a porphyrin (metalloporphyrin) and TiO₂ nanotube arrays (TiO₂NTs) was prepared, and its photocatalytic performance for CO₂ reduction under Xe lamp irradiation was studied. Compared with the pure TiO₂NTs, the photocatalytic CO₂ reduction activity of metalloporphyrin-sensitized TiO₂NTs is significantly enhanced. The amount of methane produced with the cobalt tetra(4-carboxyphenyl)porphyrin/TiO₂NTs (CoTCPP/TiO₂NTs) photocatalyst is about 5.5 times higher than that produced with TiO₂NTs alone. The improvement of photocatalytic activity can be ascribed to the enhancement of light absorption ability of CoTCPP/TiO₂NTs and the inhibition of electron–hole recombination. Furthermore, according to the results of the photocatalytic and photo(electro)chemical experiments, a probable mechanism for the photoreduction of CO₂ over CoTCPP/TiO₂NTs is presented.