Electron transfer reactions in microporous solids. Progress report, June 1991--May 1992
We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently ``dry`` powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center_dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.
- Research Organization:
- Texas Univ., Austin, TX (United States). Dept. of Chemistry
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG05-87ER13789
- OSTI ID:
- 10159106
- Report Number(s):
- DOE/ER/13789-5; ON: DE92016222
- Resource Relation:
- Other Information: PBD: May 1992
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
RUTHENIUM COMPLEXES
EXCITED STATES
CATIONS
DIFFUSION
SEMICONDUCTOR MATERIALS
PHOTOLYSIS
PROGRESS REPORT
ELECTRON TRANSFER
POROUS MATERIALS
MICROSTRUCTURE
ZEOLITES
QUENCHING
NIOBATES
TITANATES
NUCLEAR MAGNETIC RESONANCE
MORDENITE
400500
360602
PHOTOCHEMISTRY
STRUCTURE AND PHASE STUDIES