Tin-porphyrin sensitized TiO 2 for the production of H 2 under visible light

Abstract

Hydrogen was successfully produced under visible light irradiation in a tin porphyrin (SnP)-sensitized TiO 2 system in the wide pH range (pH 3-11) although SnP hardly adsorbs on TiO 2. The number of H 2 produced in the SnP/TiO 2 system after 9 h irradiation corresponds to the turnover number of 410. The apparent photonic efficiency for H 2 evolution was estimated to be 35% with the monochromatic radiation of 550 ± 10 nm. The photochemical production of hydrogen is mediated through the formation of the π-radical anion (SnP ) that subsequently transfers electron to TiO 2. The photogenerated SnP was monitored by transient absorption spectroscopy and its lifetime is long enough to survive the slow diffusion from the solution bulk to the TiO 2 surface, which makes the adsorption of SnP on TiO 2 not required for hydrogen production. This is clearly contrasted with the common ruthenium complex-sensitized TiO 2 system where the adsorption of the sensitizer complex is essentially required and the hydrogen production is limited to the acidic condition where the adsorption of the sensitizers on TiO 2 is allowed. The photocatalytic activity of SnP was mainly attributed to the Q-band (500-650 nm), not to the Soret band (420-430 nm) of which absorption intensity is much higher. © 2010 The Royal Society of Chemistry.