Effect of Ce3+ on the photocatalytic activity of MAlCe ternary hydrotalcites-like compounds in methylene blue photodegradation

MgAlCe ternary hydrotalcites-like compounds (MgAlCe-HTlc) with different Al 3+ /Ce 3+ molar ratio were synthesized by co-precipitation method. In addition, MAlCe-HTlc (M: Co, Ni, Zn) with Al 3+ /Ce 3+ molar ratio 0.95: 0.05 were also synthesized. The attained LDH were characterized by SEM, EDX, XRD, FT-IR, TG-DTA, XPS and UV-Vis DRS techniques. The results indicated that the synthesized MgAlCe-HTlc appeared to be the typical layered structure when it contains Al 3+ and Ce 3+ ions simultaneously. Three kinds of attained MAlCe-HTlc also had typical layered structure of LDH. Furthermore, the thermal stability of MgAlCe-HTlc decreased by the substitution of Ce 3+ for Al 3+ ions. When Mg 2+ was replaced by Co 2+ , Ni 2+ or Zn 2+ , the decomposition temperatures reduced. The Ce 3d spectrum of Mg 3 Al 0.8 Ce 0.2 -HTlc before and after used indicated presence of mixed valence states of Ce 3+ and Ce 4+ . The MgAlCe-HTlc exhibited a relatively high degradation capacity for methylene blue (MB), while degradation ability of Mg 3 Al 0.95 Ce 0.05 -HTlc/H 2 O 2 was highest. The remaining rate of the MB was about 6.46% after irradiation for 80 min. The order of degradation effects about MB was as follow: MgAlCe-HTlc>ZnAlCe-HTlc>CoAlCe-HTlc≈NiAlCe-HTlc. In addition, the effects of different parameters such as pH of the solution, catalyst type and dosage, concentration of MB, as well as the stability of catalyst were investigated. The photocatalytic degradation mechanism of MB showed that the OH, h + and superoxide anion produced in Mg 3 Al 0.95 Ce 0.05 -HTlc/H 2 O 2 system were all active species , while OH played a major role.