*2.4.1 Hard-template method*

In principle, this method is for the preparation of one-dimensional hollow materials. Materials used as hard-templates are polymer microspheres, porous membranes, plastic foam, ion exchange resins, carbon fiber, and anodic aluminum oxide (AAO) [28, 29]. Because the templates and the resulting target products have a unique structure and influence the particle size range, they play an important role in many areas of application. Furthermore, after the desired target is obtained so that a template used is moved/separated or modified.

One example of using the hard template method is making the ordered mesoporous CeO2 prepared via a hard-template method using SBA-15 as a structuredirecting agent. Leaching with NaOH and thermal treatment at 500°C enabled the removal of the inorganic template, thus resulting in the formation of long-range ordered CeO2. Nevertheless, small amounts of silica were present in the final oxides. The resulting CeO2 samples were used as supports for Au nanoparticles as shown in **Figure 6** below.
