Structure, Ecotoxicity, Redox and Bactericidal Activity of Cu-Containing Nanocrystalline Ferrites

Cu-modified ferrites, prepared by solvothermal syntheses, at up to 200 oC, show the presence of copper metal particles, embedded in ferrite nanocrystalline particle agglomerates. Notably, these metallic copper micron sized crystallites are dramatically reduced in size, down to a few tens of nanometers, when part of the copper dopant is replaced by zinc. All materials are magnetic due to the presence of the cubic spinel phase, being ferrimagnetic, with a narrow hysteresis of 6 kOe for the largest particle size copper ferrite material of 15 nm, to superparamagnetic for the zinc-doped, 9-10 nm average particle size ferrite. The oxidant activity of the materials was studied in free-radical oxidation reactions (pH 7.4, physiological and pH 8.5, optimal for the generation of ROS) by the chemiluminescent method with: i) Fenton`s reagent (.OH, .OOH); ii) H2O2; iii) with O2.- radicals. All materials showed moderate inhibitory activities, converted to prooxidant at pH 7.4, except for the largest isolated copper particles containing material, which remained inhibitory. Materials antimicrobial potential was checked on Gram-positive and Gram-negative bacteria, Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 via two classical methods namely the spot and well diffusion tests in agar medium. Тhe above tests included also a nanocrystalline CuO, tenorite, as a reference material too. Daphnia magna ecotoxicity test show that all investigated materials are rather toxic and since daphnia are a key component in freshwater ecosystems, the toxicity even at low concentrations may have significant consequences for the ecological balance. This requires careful monitoring and assessment of the possible use or disposal of these nanomaterials in the environment.