The synthesis and characterization of ZnAl and ZnGaAl layered double hydroxides and the mixed oxides derived from their calcination is presented. The semiconducting properties of the mixed oxides were analyzed by DR-UV–Vis. It was found that all mixed oxides are semiconductors with band gaps close to that of ZnO. Also, substitution of Al3+ for 5 or 10% wt. of Ga3+ decreases the band gap below that of ZnO, despite the fact that gallium oxide is a wide band gap semiconductor. Then, the photodegrading capabilities of the mixed oxides were tested using phenol, a very recalcitrant compound, as a probe. Nearly 80% of initial 40ppm and 60% of initial 80ppm of phenol were degraded in 6h over ZnAl-3 and ZnGaAl-5% photocatalysts.