On the toxicity behaviour of composite polyaniline-zinc oxide photocatalytic nanoparticles and their surrogate chemicals

The acute toxic effect of home-made polyaniline-zinc oxide (PANI-ZnO) nanocomposite photocatalyst samples was investigated. Toxicity behaviour was compared with that of their surrogates PANI-emeraldine base (PANI-EB), PANI-emeraldine salt (PANI-ES) and zinc oxide (ZnO). The freshwater crustacean Daphnia magna reacted more sensitively to the exposure than the marine photobacterium Vibrio fischeri and thus higher acute toxicity levels were recorded for Daphnia magna. The toxicity response increased with exposure time for both tested organisms. The hydrophobic PANI-EB was non-toxic, whereas ZnO nanoparticles were toxic towards both test organisms and the main reason of the toxicity of the PANI-ZnO composites. The toxicity behaviour changed with ZnO content rather than the PANI-ZnO nanocomposite synthesis type (in-situ polymerization or hybridization method). The acute toxicity also increased when the PANI-ZnO samples were subjected to UV-A (photocatalytic) treatment (conditions:0.25 g/L catalyst; pH=7.0; t = 180 min; I₀ =0.5 W/L). A relationship between the photo-induced Zn(II) release and acute toxicity increase after photocatalytic treatment was evident.