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

摘要

The synthesis of the covalent linkage of Cobalt(II)tetrasulfophthalocyanine (Co(II)TSP) to the surface of titanium dioxide (TiO2) particles is described. Upon irradiation with light, which exceeds the bandgap energy of TiO2, Co(II)TSP is reduced to Co(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 O2. Hydrogen peroxide is produced upon irradiation of an aerated aqueous suspension of the 'hybrid' catalyst, TiO2-Co(II)TSP. Formation kinetics are followed in situ with a polarographic detector; quantum yields, between 0.16 and 0.49 have been determined. The reactive photocatalytic center appears to be generated by the attachment of O2 in the open apical coordination site of the hybrid Co(II)TSP complex. Formation of Co(III)TSPO2- is enhanced by the binding of TiO- 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.