Removal of direct yellow 12 from water using CTAB-coated core-shell bimagnetic nanoadsorbents

The present study addresses the application of core-shell bimagnetic nanoparticles coated with cetyltrimethylammonium bromide (MnFe2O4@(sic)-Fe2O3@CTAB) as adsorbents for Direct Yellow 12 (DY12) removal from water. Samples of two different mean sizes were elaborated and characterized by XRD, TEM, FTIR, BET, zetametry, and vibrating sample magnetometry. The effect of pH, shaking rate, contact time, initial dye concentration and temperature were investigated from batch studies in standard dye solutions with 0.5 g/L of nanoadsorbent. The results were analyzed using the Langmuir and Freundlich models to evaluate the maximum adsorption capacity and the adsorption mechanism. The nanoadsorbents revealed to be more efficient in pH <= 5.0, for 30 min of contact time and under a shaking rate of 400 rpm. The kinetic data followed the pseudo-second-order model. The sample based on smaller nanoparticles exhibited a maximum adsorption capacity approximately two times higher due to its larger surface area. Additionally, the adsorption capacity of the nanoadsorbents were also compared to that of uncoated precursor nanoparticles to emphasize the role of the CTAB layer in the removal efficiency. The adsorption process was spontaneous, exothermic and characteristic of physical and chemical adsorption at the same time. Finally, the nanoadsorbents were recovered from wash cycles and reused in readsorption tests keeping a good removal efficiency.