Silica-clay nanoarchitectures

The resulting silica-clay nanoarchitectures are produced in a three-step process (Figure 14.5) ... 

Figure 14.5 Scheme showing the formation of porous silica-clay nanoarchitectures (D) in the following steps (i) Elomoionic charged layered silicates (smectites and vermiculites)... 

Table 14 J Values of specific surface area (Sbet). total pofo volume (VJ, and micropore volume (Vm) from f plot calculations of the silica-clay nanoarchitectures prepared from different layered silicates treated with CTAB, in the reaction with TMOS and calcined at 500 °C as indicated in Figure 14.6, compared with the natural pristine silicates.

As reported by Fuentes-Alventosa et al. [60], more complex silica-clay nanoarchitectures can also be prepared by sol-gel chemistry coupled with intercalation procedures combining montmorillonite and silica from TEOS, but in this case in the presence of a polysaccharide (pullulan). The resulting bionanocomposite is of... 

Similar silica-montmorillonite nanoarchitectures have also been prepared by sol-gel, as reported by Qian et al., using TEOS and another type of clay (from Zhangjiakou, China), corroborating the usefulness of this methodology in the development of silica-silicate-based porous materials [58]. 

The presence of silica NPs assembled to fibrous clays could be of interest for their use as nanofillers in polymers reinforcement Preliminary attempts in the use of silica-sepiolite nanoarchitectures, as well as the intermediate silica-organosepiolite materials, as nanofillers of epoxy resins show a moderate mechanical improvement [57,74], Further modifications of the silica NPs assembled to sepiolite could produce organic-inorganic hybrids that can be considered as promising new functional materials for diverse applications, from sensing devices to polymer reinforcement. 

One of the most typical clay-based nanoarchitectures is the so-called pillared clays (PILCs). They are built by incorporation of diverse species in the interlayer region of layered silicates, such as smectites, which provoke a permanent separation of the structural layers as do pillars in the building constructions. PILCs are mainly prepared in two-step processes in which polyoxocations of diverse type of metal (e.g., Al(III), Cr(III), Fe(III), and Ga(III)) are first intercalated by ion exchange reactions and further transformed into oxide particles by an adequate thermal treatment [8]. In certain cases, for instance, in the preparation of silica. 

The clay delamination as well as the development of the silica matrix give rise to an enhancement of the surface area and porosity compared with the pristine layered silicates (Table 14.2). An extraordinary increase (>20 times) in the BET surfece area and in the total pore volume ( 100 times) is observed in the nanoarchitectures prepared from vermiculite, making these materials of potential interest as adsorbents, support of catalysts, and nanofillers of polymers. 

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