Porous Nanoarchitectures from Delaminated Clays

Layered silicates belonging to the smectite clays family can be delaminated or exfoliated in the formation of the well-known polymer-clay nanocomposites initially developed by Fukushima and Inagaki at the Toyota Central Laboratories [54]. In a similar way, Letaief and Ruiz-Hitzky [55] using silicon alkoxides able to promote sol-gel processes have successfully achieved the hydrolysis and polycondensation of Si(OR)4 compounds within the interlayer space of smectite clays giving rise to a silica network with the concomitant delamination of the silicate layers [8,55-57] 

Layered silicate (organoclay) TMOS TEOS ETEOS 

The organoclay/alkoxide ratio in these experiments ranged from 0.5/1 to 1/5 (w/w). vf very fast formation of gel ( 0.5 h) f fast formation of gel (0.5-2 h) s slow formation of gel ( 1 day), a) No gel is formed after 2 weeks (data from Refs [55,56]). 

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. 

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]. 

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