PHOTOOXIDATION OF SODIUM SULFIDE BY SULFONATED PHTHALOCYANINES IN OXYGEN-SATURATED AQUEOUS-SOLUTIONS CONTAINING DETERGENTS OR LATEXES

The water-soluble zinc and aluminum complexes and the metal-free deriv ative of tetrasulfophthalocyanine were employed as sensitizers for the photo-oxidation of sodium sulfide under irradiation with visible ligh t in oxygen-saturated aqueous alkaline solutions containing oppositely charged micelles or latex particles. With all photosensitizers the ox idation process was strongly enhanced upon irradiation, and sulfate wa s the final oxidation product. Autoxidation as well as singlet oxygen and hydrogen peroxide formed during the photoreaction contribute to th e complex overall process. The initial step is dominated by energy tra nsfer. In contrast, Co(II)-tetrasulfophthalocyanine exhibits catalytic activity in the dark, and no pronounced additional activity under irr adiation, with the formation of thiosulfate as oxidation product. In t his case an electron transfer mechanism occurs according to known resu lts. Detergents strongly increase the photoactivity of sensitizers wit h high aggregation tendency (e.g. Zn(II) -tetrasulfophthalocyanine) by stabilizing monomeric dispersions and accumulating oxygen and the sub strate. Latexes increase the photoactivity and simultaneously the phot odegradation of the sensitizer, caused by high local accumulation of t he sensitizer and consequently also O-1(2). Al(III)-tetrasulfophthaloc yanine, exhibiting a low aggregation tendency in strongly alkaline sol utions, shows high photoactivity and photostability even without deter gent.