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Cobalt(II) tetrasulfophthalocyanine on titanium dioxide: a new efficient electron relay for the photocatalytic formation and depletion of hydrogen peroxide in aqueous suspensions

Journal Article · · J. Phys. Chem.; (United States)
DOI:https://doi.org/10.1021/j100292a027· OSTI ID:6629213
; ;
A novel synthesis for the covalent linkage of cobalt(II) tetrasulfophthalocyanine (Co/sup II/TSP) to the surface of titanium dioxide (TiO/sub 2/) particles (d less than or equal to 0.5 ..mu..m) is described. Upon irradiation with light that exceeds the bandgap energy (E/sub g/) of TiO/sub 2/ (i.e., lambda less than or equal to 380 nm), Co/sup II/TSP is reduced to Co/sup I/TSP under anoxic conditions both as a dry powder and in aqueous suspension. The photochemical reduction is shown to be fully reversible in the presence of molecular oxygen (O/sub 2/). Hydrogen peroxide (H/sub 2/O/sub 2/) is produced upon irradiation of an aerated aqueous suspension of the hybrid catalyst, TiO/sub 2/-Co/sup II/TSP. Formation kinetics are followed in situ with a polarographic detector (detection limit approx. 10/sup -7/ M H/sub 2/O/sub 2/); quantum yields, phi/sub H/sub 2/O/sub 2//, between 0.16 and 0.49 have been determined. The reactive photocatalytic center appears to be generated by the attachment of molecular oxygen in the open apical coordination site of the hybrid Co/sup II/TSP complex. Formation of Co/sup III/TSP-O/sub 2//sup -/ is enhanced by the binding of TiO/sup -/ surface groups in the opposite apical position. Hydrogen peroxide is produced in a two-step electron transfer from the conduction band via the Co(III) center. The involvement of free radical intermediates in this mechanism appears to be highly unlikely. On the basis of its observed chemical and photochemical stability and the high quantum yields for O/sub 2/ reduction, the newly developed hybrid material is proposed to be applicable as a potent and stable oxidation catalyst.
Research Organization:
California Institute of Technology, Pasadena
OSTI ID:
6629213
Journal Information:
J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:8; ISSN JPCHA
Country of Publication:
United States
Language:
English

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Related Subjects

14 SOLAR ENERGY
140505 -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AQUEOUS SOLUTIONS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
COBALT COMPLEXES
COMPLEXES
DATA
DISPERSIONS
EFFICIENCY
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN PEROXIDE
INFORMATION
KINETICS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PEROXIDES
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
POWDERS
QUANTUM EFFICIENCY
REACTION INTERMEDIATES
REACTION KINETICS
REDUCTION
SOLUTIONS
SYNTHESIS
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS