Photochemistry of ZnTPP induced by cadmium sulfide nanoparticles in 2-propanol

Abstract

Addition of ZnTPP to non-stoichiometric CdS nanoparticles in 2-propanol leads to adsorption of ZnTPP molecules onto the surface of the nanoparticles. A limiting adsorption of about 13% ZnTPP molecules onto the surface of 2 × 10 −4 M CdS nanoparticles was determined by ultrafiltration (100 Å membrane filters). It corresponds to 6.15 × 10 −3 × m ZnTPP molecules adsorbed onto the surface of an average-size CdS nanoparticle; m is the number of CdS units in such a nanoparticles. Both the quenching of the recombination luminescence of CdS (e tr − / h tr +) by ZnTPP and the photoreactivity of ZnTTP in the presence of CdS nanoparticles are linked to the extent of adsorption of ZnTPP onto CdS. The adsorption of ZnTPP onto the surface of CdS nanoparticles is described by Langmuir-type plots. UV irradiation of ZnTPP in the presence of CdS nanoparticles leads to the formation of intermediate photoproducts, characterized with absorption bands in the red region of the spectrum, which subsequently convert to more stable photoproducts. The former photoproducts are attributed to reactions of O 2 − with ZnTPP whereas the latter may be linked to the reduction of ZnTPP, substitution at the exodouble bonds of ZnTPP and to open macrocyclic structures.