Photoinduced Electron Transfer in Porous Glass

Braun, M.; Gafney, Harry D.

doi:10.1021/j100084a030

Cited by 5 publications

(3 citation statements)

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“…[24][25][26][27][28][29][30] This long lifetime of the MLCT excited state allows a number of interesting energy transfer or redox processes to occur following excitation. Photophysical and photochemical properties of Ru(bpy)32+ adsorbed onto inorganic oxides, such as Si02,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]…”

Section: Introductionmentioning

confidence: 99%

Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Liu¹,

Hug²,

Kamat³

1995

J. Phys. Chem.

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Cresyl violet, a cationic dye (CV+), forms H-aggregates on the negatively charged Si02 and Sn02 colloids. These aggregates exhibit broad absorbance around 520 nm. By coadsorbing a sensitizer, Ru(bpyb2+, we are able to characterize the triplet excited state and reduced form of dye-aggregates on the colloidal Si02 and Sn02 suspensions. On Si02 surfaces, the excited state quenching of Ru(bpy)32+ by the dye-aggregates proceeds via an energy transfer mechanism. Picosecond laser flash photolysis experiments indicate that such a surfacepromoted energy transfer is completed within 20 ps. On the other hand dye-aggregates adsorbed onto Sn02 colloids undergo photosensitized reduction since the excited sensitizer, Ru(bpy)32+\ is efficiently quenched by the semiconductor support. The role of support material in promoting energy and electron transfer processes is described.

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Section: Introductionmentioning

confidence: 99%

Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Liu¹,

Hug²,

Kamat³

1995

J. Phys. Chem.

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“…To account for the dependence of CH 4 yield on pH, the less than eighth-order dependence predicted by the Stark–Einstein law, and the ability to drive the conversion via population of the IVCT of the mixed valence oxide, we propose the tungsten oxide photocatalyst is not the source of reducing equivalents per se, but a creator of acidic and basic regions in which the reduction of chemisorbed CO 2 (reaction ) and the oxidation of chemisorbed H 2 O (reaction ) occur exergonically. The tungsten oxide transports the electrons and protons between the exergonic half reactions occurring in these regions. − Population of the WO 3 conduction band or the lower energy IVCT or polaron states of the photochromic oxide (Figure ) induces a charge polarization that creates electron deficient and electron rich regions in the metal oxide. The electron deficient region interacts with the oxygens of the silanol groups and/or adsorbed water thereby promoting their Bronsted acidity and creating an acidic region on the silica surface in which the reduction of chemisorbed CO 2 is exergonic.…”

Section: Discussionmentioning

confidence: 99%

“…The complementary electron rich region interacts with the protons of the silanol groups and/or adsorbed water creating a basic region in which the oxidation of H 2 O is exergonic. The photoexcited metal oxide creates acidic and basic regions, and by being capable of transporting protons and electrons, acts as a conduit of the protons − and electrons − between the two exergonic half reactions occurring in these acidic and basic regions…”

Section: Discussionmentioning

confidence: 99%

Photocatalyzed Conversion of CO₂to CH₄: An Excited-State Acid–Base Mechanism

Look

Gafney

2013

J. Phys. Chem. A

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Photoinduced reduction of CO2 by H2O occurs in nanoporous Vycor glass doped with tungsten oxides derived from 312 nm photolysis of physisorbed W(CO)6. In polished forms of Vycor, a hydrated precursor to monoclinic WO3 is formed, whereas in the unpolished glass, the WO3 precursor and mixed valence tungsten oxides that exhibit lower energy intervalence charge transfer (IVCT) transitions are formed. The relative amounts of the different tungsten oxide are attributed to structural differences between the polished and unpolished forms of PVG. Chemisorption converts CO2 to a formic acid-like species, and population of the conduction band of the WO3 precursor with 312 nm light or population of the IVCT state of the mixed valence oxide with ≥437 nm light photocatalyzes the reduction of chemisorbed by coadsorbed water yielding CH4 and O2. Regardless of the excitation wavelength, electronic spectra and the dependence of methane yield on absorbed energy and the energetics of the conversions implies that neither metal oxide acts as a source of reducing equivalents. Instead, excitation of the metal oxide induces a charge polarization that creates local acidic and basic regions about the oxide in which the reduction of chemisorbed CO2 and oxidation of chemisorbed H2O occur exergonically. The dependence of methane yield on surface pH, and the pH dependencies of the respective half reactions show that the pH gradient needed for the reactions to occur spontaneously fall within the range of known photoinduced changes in acid-base properties. Within this excited-state acid-base mechanism, the metal oxide is not a source of electrons, but a conduit of electrons and protons between two exergonic processes.

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SiO2 colloidal effects on the twisted intramolecular charge transfer of p-N,N-dimethylaminobenzoic acid in acetonitrile

Kim

Cheon

Yoon

et al. 1997

Chemical Physics Letters

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Photoinduced Electron Transfer in Porous Glass

Cited by 5 publications

References 13 publications

Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Photocatalyzed Conversion of CO₂to CH₄: An Excited-State Acid–Base Mechanism

SiO2 colloidal effects on the twisted intramolecular charge transfer of p-N,N-dimethylaminobenzoic acid in acetonitrile

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Photoinduced Electron Transfer in Porous Glass

Cited by 5 publications

References 13 publications

Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Photocatalyzed Conversion of CO2to CH4: An Excited-State Acid–Base Mechanism

SiO2 colloidal effects on the twisted intramolecular charge transfer of p-N,N-dimethylaminobenzoic acid in acetonitrile

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Photocatalyzed Conversion of CO₂to CH₄: An Excited-State Acid–Base Mechanism