Efficient removal of Congo red by magnetically separable mesoporous TiO2 modified with γ-Fe2O3

Magnetically separable mesoporous TiO2 modified with gamma-Fe2O3 was prepared and characterized by X-ray diffraction, N-2 adsorption-desorption measurements, scanning electron microscopy, UV-vis absorption and magnetic measurements. The adsorptive removal of Congo red using the binary system was performed under various experimental conditions to examine the effects of contact time, solution pH, and initial concentration of Congo red. The results show that the removal abilities and separability of mesoporous TiO2 adsorbent for Congo red can be significantly improved by modification with gamma-Fe2O3. The adsorption of Congo red on the gamma-Fe2O3-TiO2 reaches the maximum percentage removal of ca. 97 % within 60 min, showing that most of Congo red can be removed in a short time. When the pH of solution is varied from 3.4 to 10.3, the percentage removal of Congo red decreases from ca. 97 to ca. 15 %, showing that the adsorption is strongly dependent on solution pH. The adsorption kinetics of Congo red fit well with pseudo-second-order kinetic model, and the equilibrium data is best described by Langmuir adsorption model. The maximum adsorption capacity of the gamma-Fe2O3-TiO2 for Congo red is estimated to be 125.0 mg/g.