Fig. 4. (a) Photocatalytic degradation of methylene blue by Au NRs, TiO₂ and annealed Au@TiO₂ core–shell nanostructures under visible light. (b) Photocatalytic degradation of methylene blue by Au NR@TiO₂, Au NC@TiO₂ and Au NS@TiO₂ core–shell nanostructures after annealing under visible light.