Construction of Size-Controllable Hierarchical Nanoporous TiO₂ Ring Arrays and Their Modifications

TiO₂ hierarchical nanoporous ring arrays are constructed on a solid surface by an annealed template-induced sol-soaking strategy. The ring size can be controlled by changing the sol concentration and varying the annealing time of the polystyrene sphere colloidal monolayer. The sol−gel process generates porous nanocrystalline networks in the ring walls, which can be modified by incorporating functional particles into the pores. This strategy allows the fabrication of specific metal oxides and semiconductor ring arrays on both flat and curved surfaces.