Adsorption of toxic metal ion Cr(VI) from aqueous state by TiO2-MCM-41: Equilibrium and kinetic studies

Highlights: ► Adsorption of toxic Cr(VI). ► Immobilization of various weight percentage of titania on MCM-41. ► Equilibrium, kinetic and thermodynamic study of adsorption of Cr(VI) onto TiO2-MCM-41. - Abstract: This paper deals with the immobilization of various weight percentage of TiO2 on mesoporous MCM-41, characterization of the materials by X-ray diffraction (XRD), nitrogen adsorption–desorption, Fourier Transform Infrared (FTIR) analysis, UV–vis diffuse reflectance spectroscopy (DRS) and evaluation of the adsorption capacity toward Cr(VI) removal. It is found that the MCM-41 structure retained after loading of TiO2 but the surface area and pore diameter decreased due to pore blockage. Adsorption of Cr(VI) from aqueous state was investigated on TiO2-MCM-41 by changing various parameters such as pH, metal ion concentration, and the temperature. When TiO2 loading was more than 20 wt.%, the adsorption activity (25)TiO2-MCM-41 reduced significantly due to considerable decrease in the surface area. It is also observed that TiO2 and neat MCM-41 exhibits very less Cr(VI) adsorption compared to TiO2-MCM-41. The adsorption of Cr(VI) onto (20)TiO2-MCM-41 at pH ∼ 5.5 and temperature 323 K was 91% at 100 mg/L Cr(VI) metal ion concentration in 80 min. The experimental data fitted well to Langmuir and Freundlich isotherms. The adsorption of Cr(VI) on TiO2-MCM-41 followed a second order kinetics with higher values of intra-particle diffusion rate. Thermodynamic parameters suggested that the adsorption process is endothermic in nature and desorption studies indicated a chemisorption mode.