W. Spiller et al., PHOTOOXIDATION OF SODIUM SULFIDE BY SULFONATED PHTHALOCYANINES IN OXYGEN-SATURATED AQUEOUS-SOLUTIONS CONTAINING DETERGENTS OR LATEXES, Journal of photochemistry and photobiology. A, Chemistry, 95(2), 1996, pp. 161-173
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.