Cobalt(II) Tetrasulfophthalocyanine on Titanium Dioxide: A New Efficient Electron Relay for the photocatalytic Formation and Depletion of Hydrogen Peroxide in Aqueous Suspensions

Article abstract of DOI:10.1021/j100292a027

A novel synthesis for the covalent linkage of cobalt(II) tetrasulfonaphthalocyanine (Co(II)TSP) to the surface of titanium dioxide (TiO2) particles (dg) of TiO2 (i.e., λa dry powder and in aqueous suspension.The photochemical reduction is shown to be fully reversible in the presence of molecular oxigen (O2).Hydrogen peroxide (H2O2) is produced upon irradiation of an aerated suspension of the hybrid catalyst, TiO2-Co(II)TSP.Formation kinetics are folowed in situ with a polarographic detector (detection limit ca./= 1E-7 M H2O2); quantum yields, Φ_H2O2, 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(II)TSP complex.Formation of Co(III)TSP-O2(1-) radical is enhanced by the binding of TiO2(1-) 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 O2 reduction, the newly developed hybrid material is proposed to be applicable as a potent and stable oxidation catalyst.