Improved Charge Separation and Photosensitized H2 Evolution from Water with TiO2 Particles on Colloidal SiO2 Carriers

Arthur J. Frank, Itamar Willner, Zafrir Goren, Yinon Degani

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78 Scopus Citations


Laser flash photolysis and steady-state photolysis studies show that electrostatic interactions have a dramatic influence on the kinetics for charge separation and hydrogen production in aqueous systems (pH 9.8) of 20-nm diameter TiO2 modified SiO2 colloids in various combinations with an electron relay, a photosensitizer, and a Pt catalyst. Either direct excitation of the semiconductor or the photosensitizer Ru(bpy)32+(bpy = 2,2/-bipyridine), electrostatically adsorbed to the colloid, initiate electron transfer to either the zwitterionic electron relay, N,N'-bis(3-sulfonatopropyl)-4,4’-bipyridinium (PVS°), or N,N'-bis(3-sulfonatopropyl)-2,2'-bipyridinium (DQS°), or methyl viologen (MV2+). The rates and quantum yields for the formation of the radical PVS•-anion in both the TiO2-SiO2/PVS0and the TiO2-SiO2/Ru(bpy)32+/PVS0systems decline with increasing ionic strength. The rate and quantum yields for H2 production in both the TiO2-SiO2/DQS0/Pt and the TiO2-SiO2/Ru-(bpy)32+/DQS°/Pt systems also show a similar ionic strength dependence. Kinetic analysis of the data infers that repulsion of the reduced zwitterionic relay PVS•-and DQS-from the negatively charged colloidal interface inhibits back electron transfer to both the semiconductor and the surface-attached oxidized photosensitizer Ru(bpy)33+. Formation of the cation MV+radical and its back electron transfer to the semiconductor are rapid and imply that the MV2+electron relay is in close proximity to the colloid. Both the photogenerated valence-band holes and the oxidized photosensitizer Ru(bpy)33+oxidize surface Ti-O-groups of TiO2, This redox process has the important effect of recycling the photosensitizer for further reaction. The addition of the superoxide dismutase enzyme to the oxidized TiO2-(SiO2) system regenerates, in part, the activity of the semiconductor to evolve H2 and to release molecular oxygen.

Original languageAmerican English
Pages (from-to)3568-3573
Number of pages6
JournalJournal of the American Chemical Society
Issue number12
StatePublished - 1987

Bibliographical note

Work performed by Solar Energy Research Institute, Golden, Colorado and The Department of Organic Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel

NREL Publication Number

  • ACNR/JA-9907


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