Metal oxide hierarchical nanostructures

Soler-Illia, G.J.A.A. Sanchez, C. Lebeau, B. Patarin, J. Chemical strategies to design textured silica and metal oxide-based organised networks from nanostructured networks to hierarchical structures. Chem. Rev. 2002, 102, 4093. 

Conducting polymers can be mixed with or electrochemically deposited onto transition metal oxides to achieve better performances as electrode materials. However, the wrapping of conducting polymers on metal oxides may reduce the effective contact area between metal oxides and electrolytes. This will further impede insertion of alkali ions into metal oxides and result in poor rate performance with low specific capacitance. A rational strategy is to use conducting polymers as active electrode materials directly and optimize their structures. To this end, a hierarchically nanostructured conductive polymer hydrogel was synthesized by a facile interfacial polymerization (Shi et al., 2014). 

More complex in preparation and expensive, hierarchically nanostructured porous group V metal oxides synthesized via a spontaneous autoformation process from alkoxide precursors were used as supports for palladium in total oxidation of toluene (Figure 18.8) [40]. In addition to the effect of the support cation, multimodal porosities of these supports facilitate both the dispersion of the noble metal nanoparticles and the internal transport of the substrates. 

Rooke, J.C., Barakat, T., Brunet, Li, Y Finol, M.F., Lamonier, J.-F., Giraudon, J.-M., Cousin, R., Siffert, S., and Su, B.L. (2015) Hierarchically nanostructured porous group Vb metal oxides from alkoxide precursors and their role in the catalytic remediation of VOCs. Appl Catal B Environ., 162, 300-309. 

Examples of dense silica, hybrid silica, metal oxides, solid-state metal oxide solutions, or colloidal self-assembly are unlimited. However, the recent developments to accurately control processing conditions (e.g., atmosphere, temperature, and motion) led to films with unique properties (see Figure 9.6) [52,53]. These progresses concern mesoporous coatings with controlled pore size and structure [26], hard template infiltration and/or replication [54-58], nanostructured epitaxial low-quartz thin films [59], ultrathin nanostructured supported networks [60,61], ultrathick porous Ti02 layer prepared from aqueous solutions [51], coatings with hierarchical porosity [62], multilayer porous stacks [63], colloidal MOF layers [64,65], pillar planar nanochannels (PPNs) for nanofluidics [66], and so on. 

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