Mixed oxides derived from layered double hydroxides as novel catalysts for phenol photodegradation

The removal of organic pollutants is nowadays a very challenging aspect of the environmental research. There are strong interests to develop novel semiconducting photocatalysts able to efficiently promote advanced oxidation reactions. The development of photocatalysts based on the mixtures of mixed oxides derived from layered double hydroxides (LDHs) - a family of naturally occurring anionic clays - might offer novel environmental-friendly solutions for the cost effective removal of organic pollutants. This work presents ZnO/ZnAl₂O₄, ZnO/Zn₂TiO₄ and ZnO/ZnCr₂O₄ as novel photocatalytic formulations for phenol degradation under UV irradiation. They were obtained by the controlled thermal treatment of the layered double hydroxides matrices (LDHs), as precursors materials, type ZnM-LDH (M = Al³⁺, Cr³⁺ or Ti⁴⁺). The LDHs were synthesized by the co-precipitation method at a constant pH. Controlled calcination at 650^°C gives rise to solutions of mixed metal oxides. The structural and nanoarchitectonics characteristics of the studied catalysts were described by: XRD, SEM/TEM and TG/DTG techniques. Results show that in the photocatalytic process of the phenol degradation from aqueous solutions, ZnO/ZnCr₂O₄ and ZnO/ZnAl₂O₄ showed the best performance degrading ∼98% of phenol after 3.5 hs and 5 hs, respectively; while ZnO/Zn₂TiO₄ has degraded almost 80 % after 7.5 hs of UV irradiation. These results open new opportunities in the development of new cost effective photoresponsive formulations able to facilitate the photo-degradation of the organic pollution as "green" solution for removal of dangerous pollutants.