Enhanced photoactivity for the phenol mineralization on ZnAlLa mixed oxides prepared from calcined LDHs

• ZnAl and ZnAlLa oxides were obtained by thermal treatment of LDH materials.
• High specific surface areas were obtained in ZnAlLa mixed oxides.
• Mineralization over 90% was reached with ZnAlLa vs. 48% of ZnAl catalyst.
• Lanthanum presence helps to avoid recombination in the ZnO.

ZnAlLa layered double hydroxides (La/Zn molar ratio of 0.005, 0.01 and 0.03) were synthesized by the co-precipitation method and calcined at 500 °C. XRD patterns showed lamellar type materials in fresh solids (dried) and a diminishing basal parameter denoting the incorporation of La in the ZnAl LDH structure. At low content of La, XRD does not show the formation of La2O3, which become detectable only in the sample with high La content. After calcination, the formation of zincite was detected in the LDH, indicating the destruction of the lamellar structure. The Eg band of the sample with low content of La, calculated from the UV–Vis spectra, showed a shift to low energy, while for the samples with high content of La the Eg shift is displaced to high absorption energy. Evaluation of the photoactivity in the degradation of phenol using a low intensity UV–Vis lamp (254 nm and 4400 μW/cm2), showed the maximum values in phenol mineralization 88–66% with the ZnAlLa samples, in comparison to that obtained with the ZnAl oxide (48%). These results show that ZnAlLa mixed oxides prepared from the thermal treatment of ZnAlLa LDH are promising materials for an effective phenol mineralization.

Photocatalytic behavior of ZnAl and ZnAlLa LDHs like materials calcined at 500 °C in the photodegradation of phenol in aqueous solution (40 ppm) in presence of UV light. La improves the photodegradation when it is present at low concentration (La/Zn 0.005 molar ratio) in the Zn–Al lamellar structure.Figure optionsDownload high-quality image (98 K)Download as PowerPoint slide