Electron transfer reactions in microporous solids
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; USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG05-87ER13789
- OSTI ID:
- 7069873
- Report Number(s):
- DOE/ER/13789-5; ON: DE92016222
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
CATIONS
DIFFUSION
RUTHENIUM COMPLEXES
EXCITED STATES
SEMICONDUCTOR MATERIALS
PHOTOLYSIS
ELECTRON TRANSFER
MICROSTRUCTURE
MORDENITE
NIOBATES
NUCLEAR MAGNETIC RESONANCE
POROUS MATERIALS
PROGRESS REPORT
QUENCHING
TITANATES
ZEOLITES
CHARGED PARTICLES
CHEMICAL REACTIONS
COMPLEXES
CRYSTAL STRUCTURE
DECOMPOSITION
DOCUMENT TYPES
ENERGY LEVELS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IONS
MAGNETIC RESONANCE
MATERIALS
MINERALS
NIOBIUM COMPOUNDS
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
REFRACTORY METAL COMPOUNDS
RESONANCE
SILICATE MINERALS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
400500* - Photochemistry
360602 - Other Materials- Structure & Phase Studies