Enhanced photocatalytic ability of Cu, Co doped ZnAl based mixed metal oxides derived from layered double hydroxides

Cu, Co doped mixed metal oxides (MMOs) were synthesized from their ternary layered double hydroxides (LDHs) precursors, ZnCu(or Co)Al-CO3 via simple calcination at different temperatures. Interestingly, MMO prepared at 400 degrees C (MMOs-400) showed only weakly crystallized ZnO phase, suggesting that other metals such as Al, Cu(or Co) remain as amorphous phase around ZnO nanoparticles. Moreover, by increasing Cu(or Co) substitution content into ZnAl-LDHs framework, the amorphous phase on the surface of MMOs was clearly observed as 'hole'-like structure by transmission electron microscopy (TEM). This amorphous phase composed of Co(or Cu) Al would play a crucial role, as doping agent of ZnO, in the improvement of photocatalytic ability towards orange II degradation, as only MMOs-400 showed significantly fast degradation rate. However, no meaningful improvement was observed for MMOs-600 or 800 that contain lower amounts of amorphous phase. Furthermore, the optimal substitution ratio of Zn/Cu(or Co) was also found to be of 19 (Zn1.9Cu0.1Al1-400), giving the best performance for dye degradation. Therefore, this report would provide a facile approach for the synthesis of efficient photocatalysts based on LDHs and their MMOs.