Zn-Al layered double hydroxides: Synthesis, characterization and photocatalytic application

Zn/Al-LDHs with cationic ratio of 1-4 were prepared by the co-precipitation method at constant pH. The XRD patterns showed that additional phase is present in all samples due to the lattice strains created when more Zn2+ is added and the longer periods of hydrothermal treatment. The as-synthesized samples were calcined at different temperatures and the phase transformations were fully investigated by XRD, IR, TG/DTG, UV-vis-DR, N-2 adsorption/desorption, SEM and EDX methods. Infrared spectroscopy revealed that the characteristic layered double hydroxide structure is not fully destroyed. The EDX analysis showed that the increase of the calcination temperature leads to a diffusion of the Zn2+ cations to the surface of the particles. The photocatalytic activity was evaluated for the degradation of the methyl-orange dye. The band gap energy decreases as the calcination temperature increases indicating that less energy is needed for the photocatalytic process. The photocatalytic activity increases with the increase of the cationic ratio and the calcination temperature. 93% of the dye could be removed by the Zn/Al-LDH with the cationic ratio of 4 and calcined at 500 degrees C. (C) 2007 Elsevier Inc. All rights reserved.