Magnetic Nanocomposite of TiO2 as Efficient Adsorbent for Direct Green 26 Dye: Multivariate Optimization, Kinetic and Equilibrium Isotherms

In the study, Fe3O4/TiO2 nanocomposite (FTNC) is synthesized and employed for Direct Green 26 (DG26) adsorption from aqueous solutions. The instruments of X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM) were utilized for nanocomposite characterization. The experiments were conducted based on a Box-Behnken design including the FTNC dosage (A: 0.16 - 0.40 g L-1), pH (B: 3 - 9), contact time (C: 16 - 30 min), and ionic strength (D: 0.01 - 0.05 mol L-1), as the independent variables. The obtained data were fitted to a second-order response surface model with a high correlation coefficient (R-2 = 0.9699) which predicted the optimum conditions (A = 0.40 g L-1, B = 3, C = 29 min, and D = 0.03 mol L-1) with an adsorption percentage of 97.50 +/- 0.60. The kinetic data agreed well (R-2 > 0.99) with the pseudo-second-order model. Moreover, investigating the adsorption isotherms of Langmuir, Temkin, Dubinin-Radushkevich, and Freundlich showed that DG26-FTNC adsorption system followed Langmuir model and an adsorption capacity of 200 mg g(-1) was achieved for the magnetic nanocomposite.