Applications of Pillared or Intercalated Layered Solids

The applications of expanded layered solids (LDHs or clays) are largely due to their large surface area and variation in their chemical and physical properties. These properties may be enhanced by the ability to

Figure 8 Illustration of terephthalate intercalated LDH.

tailor them for specific uses. In general these materials have found use as catalysts, ion exchangers and adsorbents and are also useful in gas and liquid separation processes (where they exhibit molecular sieving properties similar to those of zeolites). Some examples are:

1. Organoclays containing molecules such as (CH3)4N+ are especially suited for certain separation processes due to their hydrophobic nature and high affinity for certain organic compounds.

2. Clays and their oxide-pillared derivatives have found use as: (i) scavengers for hazardous organics (especially from effluent streams); (ii) selective adsorbents of heavy metals from effluent streams; and (iii) purifiers for edible oils where the clays adsorb compounds such as carotenoids and chlorophyll to give the oil its clear look and taste. Indeed acid activated clays are the industry standard for the decolorizing of oil.

3. LDHs have found use as excellent acid residue scavengers.

Greater use of layered materials in separation processes can be achieved when the materials are used in the form of membranes where they act as ionic and molecular filters or sieves.

See also: Il/Ion Exchange: Historical Development; Novel Layered Materials: Phosphates; Organic Ion Exchangers; Organic Membranes.

C. Luca, 'Petra Poni' Institute of Macromolecular Chemistry, Lasi, Romania

Copyright © 2000 Academic Press

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