In this research, magnetic nickel ferrite NiFe2O4/hazelnut-shell-based activated carbon (NiFe2O4/AC) was used to eliminate anionic dyes (Direct Red 31(DR31) and Direct Blue 78 (DB78)) from aqueous solution. The morphological, structural, particle size and surface charge properties of as-prepared nanoadsorbent were characterized. TEM (Transmission electron microscopy) images revealed that the size of NiFe2O4 particles in the structure of AC was in the range of 8-12 nm, which is compatible with the results obtained by the analysis of DLS (Dynamic light scattering). The results of the BET (Brunauer-Emmett-Teller) analysis indicated that the surface area, the pore volume and average pore diameters of the NiFe2O4 were 288 m2/g, 0.3338 cm3/g and 5.05nm, respectively. The as-prepared nanocomposite showed excellent adsorption capacity for DR31 and DB78 dyes with the highest adsorption capacity obtained at pH=2.0 and rapid dye adsorption equilibrium attained after 20 and 25 min for DR31 and DB78, respectively. The equilibrium study showed the maximum adsorption capacity (qmax) of 299.67 mg/g and 209.13 mg/g for DR31 and DB78, respectively. In addition, thermodynamic study revealed the endothermic and spontaneous nature of adsorption process. The adsorption of DR31 and DB78 onto the NiFe2O4/AC is a physisorption process, during which electrostatic adsorption was the main driving force.
Keywords: DB78; DR31; NiFe2O4 nanoparticles; adsorption; magnetic separation.