Efficacious Removal of Organic Contaminants from Water Using a Novel CoO–NiO@MgAl₂O₄ Nanocomposite

Herein, novel MgAl₂O₄-based quadruple nanocomposites containing different contents of Co/Ni bimetallic doping were synthesized employing gelatin as a green capping agent. Typically, MgAl₂O₄ (MgAl₂O₄-1), 5% NiO-5% CoO@MgAl₂O₄ (MgAl₂O₄-2), 2.5% CoO-5% NiO@MgAl₂O₄ (MgAl₂O₄-3), and 5% CoO-2.5% NiO@MgAl₂O₄ (MgAl₂O₄-4) were synthesized via a one-pot method. The prepared quadruple nanocomposites were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), surface analysis, and Fourier transform infrared spectroscopy (FTIR) spectroscopy. MgAl₂O₄-1, MgAl₂O₄-2, MgAl₂O₄-3, and MgAl₂O₄-4 exhibited surface areas of 75.4, 118.4, 141.1, and 123.0 m² g^-1, respectively, and possessed q_t values of 46.8, 60.9, 72.4, and 60.2 mg g^-1, respectively, toward the indigo carmine (INCR) dye. The INCR sorption onto MgAl₂O₄-1, MgAl₂O₄-2, MgAl₂O₄-3, and MgAl₂O₄-4 followed the pseudo-second-order model, and the liquid film diffusion model controlled the INCR sorption onto MgAl₂O₄-1, MgAl₂O₄-2, MgAl₂O₄-3, and MgAl₂O₄-4 nanocomposites. MgAl₂O₄-3 was selected as the best sorbent for eliminating INCR, and it exhibited enhanced performance at pH 6.0. The MgAl₂O₄ q_t value increased proportionally with the INCR concentration (20 to 100 mg L^-1), and increasing the temperature affected the sorption positively, indicating endothermic sorption. The Langmuir model best fitted among the tested isotherm models, and it predicted a maximum adsorption capacity of 181.0 mg g^-1. MgAl₂O₄-3 was tested for removing INCR from tap water, groundwater, and seawater at 313 K, and it showed an average efficiency of 97.1%, with a standard deviation of 2.4%.