Surface magnetic properties of a ternary nanocomposite and its ecotoxicological properties in Daphnia magna

A ternary magnetic nanohybrid, composed of maghemite, titanium dioxide (anatase phase), and graphene oxide as synthetized by co-precipitation method and initially applied with success to arsenic removal from contaminated synthetic effluent, has its main magnetic properties (the thermal dependence of the coercive field, the saturation magnetization, and the effective anisotropy constant values) systematically studied using a modified Kneller's and modified Bloch's laws applied to magnetization data. Besides values of exchange integral and spin wave stiffness constant equal to 2.7 meV and 949 meV Ų respectively calculated, the Fe-oxide nanoparticles have ca. 11% of Fe spin in canted configuration, a result that also agreed with the description of the in-field Mössbauer spectrum. A magnetization saturation value of 47.5 emu g ⁻¹ (size of 19.6 nm) at 300 K and the Bloch's exponent of 3/2 have suggested that the ternary nanocomposite behaves like a 3D material. In order to check the impact of this ternary nanocomposite, acute toxicity tests were performed on Daphnia Magna water fleas neonates for a 24-hour exposure period due to (i) the fast metabolism of daphnids and (ii) the fact that the nanocomposite precipitates within one day at concentrations of interest for nanoremediation. Post-exposure effects were also studied after the first offspring hatched (2 weeks). A lethal concentration LC₅₀ value of 0.55 mg mL⁻¹ was found for this experiment. Analysis of morphological changes showed toxicity with little significant difference between exposed and negative control individuals. The reproductive rate test was dose dependent.