Nanostructured porous solids self-assembled

Various nanoscale architecture can be designed, including solid spheres, hollow spheres, tubes, porous particles, solid particles, and branched structures (Table 2).To achieve such nanostructures, different fabrication methods are used depending on the types of material. The methods used for nanoscale assembly include molecular self-assembly, bioaggregation, nanomanipulation, photochemical patterning, molecular imprinting, layer-by-layer electrsostatic deposition, and vapor deposition. 

One of the targets in the formation of 2D porous nanostructures is to define and control the size of the cavities. The obvious approach is to extend the distance between the carboxylic acid groups and the center of the molecule, for instance by a phenyl group. 1,3,5-Benzenetribenzoic acid (BTB) is a rigid molecule and self-assembles also at the liquid-solid interface into honeycomb-type networks (Fig. 21 A) [55]. The circular cavities have a diameter of about 2.8 nm. In case of TMA, the cavity diameter is about 1 nm only. 

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. 

---