Improved photocatalytic degradation of phenolic compounds with ZnAl mixed oxides obtained from LDH materials

ZnAl layered double hydroxides (LDHs) with different M_II/M _III molar ratio (0.89-3.81) were synthesized by the co-precipitation method and calcinated at 723 K. High specific surface areas (228-155 m ²/g) and semiconductor properties (band gap values from 3.32 to 3.07 eV) were obtained. The mixed oxides were reconstructed to the crystalline LDHs (memory effect) after being put in contact with aqueous solutions containing phenol and p-cresol. Using UV light, a maximum in photoactivity as a function of the Zn²⁺/Al³⁺ molar ratio was observed. The sample with a Zn²⁺/Al³⁺molar ratio of 1.48 photodegrades up to 95% of phenol and p-cresol after 4 and 6 h of irradiation, respectively. These values are lower than that obtained with ZnO and commercial P-25 TiO₂ photocatalysts. The results show the applicability of alternative photocatalysts for the degradation of organic pollutant compounds rather than others such as TiO₂.