Abstract
MFe2O4 nanopowders (M = Ni, Co, Cu) were prepared using the precursor technique, starting from the corresponding metal
nitrates and poly(vinyl alcohol)-PVA. During the heating of metal nitrates- PVA solution, a redox reaction takes place around
150°C, leading to the formation of M(II) and Fe(III) carboxylates. These compounds were used as precursors for the ferrites
nanopowders. The desired ferrites were obtained by thermal decomposition of the carboxylates; the obtained powders were
characterized by means of Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), scanning electron
microscopy (SEM) and Brunauer-Emmett-Teller (BET) specific surface area measurements. According to the results, CoFe2O4
and NiFe2O4 were obtained at 500°C, while CuFe2O4 was contaminated with simple oxides. All powders consisted in
micrometric aggregates of nanometric particles. Magnetic measurements evidenced that all powders obtained at 500 °C exhibited
ferrimagnetic behavior. MFe2O4 nanopowders were used as adsorbents for Congo red removal from aqueous solutions. The
influence of various experimental parameters (pH value, amount of adsorbent, initial concentration and contact time) was
evaluated in batch experiments. The experimental data were analyzed using the pseudo-first-order, the pseudo-second-order and
the intra-particle diffusion kinetic models. The pseudo-second-order model best described the kinetics of the adsorption process.
The equilibrium adsorption data were fitted to Langmuir, Freundlich and Sips isotherm models. The experimental data were well
described by the Sips model.