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

Abstract

MgAlCe ternary hydrotalcites-like compounds (MgAlCe-HTlc) with different Al3+/Ce3+ molar ratio were synthesized by co-precipitation method. In addition, MAlCe-HTlc (M: Co, Ni, Zn) with Al3+/Ce3+ 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 Al3+ and Ce3+ 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 Ce3+ for Al3+ ions. When Mg2+ was replaced by Co2+, Ni2+ or Zn2+, the decomposition temperatures reduced. The Ce 3d spectrum of Mg3Al0.8Ce0.2-HTlc before and after used indicated presence of mixed valence states of Ce3+ and Ce4+. The MgAlCe-HTlc exhibited a relatively high degradation capacity for methylene blue (MB), while degradation ability of Mg3Al0.95Ce0.05-HTlc/H2O2 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 Mg3Al0.95Ce0.05-HTlc/H2O2 system were all active species, while OH played a major role.