Figure 7.

Hierarchical macro-mesoporous structures. Hierarchical macro-mesoporosity can be created in (a) two or (b) one step(s). (a) To create hierarchical macro-mesoporosity in two steps, an inverse opal (IO) is first generated, which can be backfilled by mesoscale templates to form a colloidal crystal within the IO (CC in IO). Infiltrating this structure and removing the mesoscale templates yield a mesoporous IO structure within a macroporous IO structure (IO in IO). Backfilling the (IO in IO) or (CC in IO) structure with a support sol–gel precursor and removing all the previous structures yield the inverted (CC in CC) or (IO in CC) macro-mesostructures, respectively. (b) Hierarchical macro-mesoporosity can be created in one step by simultaneous colloidal assembly of both the macro- and meso- scale colloidal templates with the support sol–gel precursor(s) (SiO₂, in this example) and/or nanocrystals. Note that in both methods, NPs can be incorporated before, during, or after each colloidal templating step, as shown in Figure 3a–c. (a) adapted with permission from ref (120). Copyright 2013 Wiley-VCH. (b) adapted with permission from ref (29). Copyright 2006 American Chemical Society.