Structural and surface modification of highly ordered alumina for enhanced removal of Pb2+, Cd2+ and Ni2+ from aqueous solution

The adsorption performance of three-dimensionally ordered macroporous (3DOM) alumina doped with iron oxide, and subsequently modified with (3-aminopropyl)triethoxysilane (APTES), FeAl 2 O 3 and FeAl 2 O 3 APTES, was used for enhanced Pb 2+ , Cd 2+ and Ni 2+ removal. The phase composition and the structural and surface/textural properties of the obtained adsorbents were analyzed by X-ray diffraction analysis, field emission scanning electron microscope, energy dispersive X-ray analysis, thermogravimetry, Fourier-transfer infrared spectroscopy, specific surface area of the samples and point of zero charge determination. Adsorption of selected cations was examined in the batch conditions using different contact time, adsorbent dosage and temperatures. Different models of the adsorption isotherms were used for determination of the adsorption capacities, in which the best fit of Freundlich and Langmuir model was obtained for FeAl 2 O 3 , that is, Freundlich model for FeAl 2 O 3 APTES. A significant increase of adsorption capacities: from 44.21 to 51.66 mg g –1 for Pb 2+ , 25.69 to 32.96 mg g –1 for Cd 2+ and 19.48 to 24.64 mg g –1 for Ni 2+ was obtained for FeAl 2 O 3 and FeAl 2 O 3 APTES, respectively, which indicated the significance of the macroporous structure of 3DOM alumina and subsequent amino-terminal modification. The values of the correlation coefficient (R 2 ) suggested that pseudo-second kinetic model best describes Pb 2+ , Cd 2+ and Ni 2+ adsorption on FeAl 2 O 3 APTES, and Cd 2+ and Ni 2+ onto FeAl 2 O 3 , while second kinetic model gave the highest correlation coefficients for Pb 2+ adsorption on FeAl 2 O 3 .