Effect of metal phthalocyanine complex aggregation on the catalytic and photocatalytic oxidation of sulfur containing compounds

Water soluble zinc (II) 2,9,16,23-phthalocyanine tetrasulfonic acid [ZnPc(SO3H)(4)], zinc (II) 2,9,16,23-phthalocyanine tetracarboxylic acid [ZnPc(COOH)(4)] and sterically hindered bulky zinc(II) 2,9,16,23-tetrakis(8-quinolineoxy-5-sulfonicacid)-phthalocyanine [ZnPc(QnSO(3)H)(4)] complexes have been studied as photocatalysts for oxidation of 2-mercaptoethanol and sodium thiosulfate. The ZnPc(QnSO(3)H)(4) complex exhibited the highest photocatalytic activity due to its low aggregation degree in aqueous medium. In the presence of tetrabutylammonium chloride, quinoline and ethanol additives the monomerization degree of the ZnPc(SO3H)(4) and ZnPc(COOH)(4) complexes is increased, their photocatalytic activity being close to that of ZnPc(QnSO(3)H)(4). Because of high aggregation degree of ZnPc(SO3H)(4) and ZnPc(COOH)(4) in viscous medium, the quantum yields of singlet dioxygen generation and the photocatalytic oxidation rates of the sulfur-containing compounds are decreased. The photocatalytic activity of ZnPc(QnSO(3)H)(4) is slightly changed in viscous medium and in the presence of additives. The low aggregation degree of this complex allowed to establish enhanced and lowered rates of photocatalytic oxidation of 2-mercaptoethanol and sodium thiosulfate, respectively, on increasing medium viscosity. The effect of medium viscosity on ZnPc(QnSO(3)H)(4) photocatalyzed oxidation of the two substrates is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.