In situ preparation of a novel organo-inorganic 6,13-pentacenequinone–TiO2 coupled semiconductor nanosystem: a new visible light active photocatalyst for hydrogen generation

Abstract

Previous studies related to the synthesis of stable UV-visible light active photocatalysts for hydrogen generation have been limited to inorganic semiconductors and their nano- and hetero-structures. We demonstrate here the use of an organo-inorganic 6,13-pentacenequinone (PQ)–TiO₂ coupled semiconductor nanosystem as an efficient photocatalyst active in visible light for the production of hydrogen. Anatase TiO₂ nanoparticles (3–5 nm) were uniformly decorated on thin sheets of monoclinic PQ by an in situ solvothermal method. These as-prepared PQ–TiO₂ coupled semiconductor nanosystems had a band gap in the range 2.7–2.8 eV. The strong emission at 590 nm can be attributed to the transfer of electrons from the LUMO energy level of TiO₂ to combine with the holes present in the HOMO level of PQ. This electron–hole recombination makes availability of electrons and holes in LUMO of PQ and HOMO of TiO₂, respectively. This hybrid semiconductor coupled nanosystem resulted in a rate of hydrogen evolution of 36 456 μmol h⁻¹ g⁻¹ from H₂S under UV-visible light; this is four times higher than the rate obtained with TiO₂ in earlier reports of UV-visible light active photocatalysts. These results open up a new path to explore inorganic systems coupled with PQ as new photoactive hybrid catalysts in a number of chemical and physicochemical processes.