Nano-layered Silicates with High Chemical Reactivity
The smectite family of layered silicate minerals, the so-called "swelling clays," have theoretical surface areas of 700 meters per gram or larger. However, accessing this surface area for important materials applications such as catalysis, adsorption, and polymer-clay nanocomposite formation is not readily achievable; the elementary one-nanometer thick nanolayers stack to form tactoids, thus reducing the effective surface area for useful chemical reactions. The tactoids can be swelled by a swelling solvent to access interlayer regions. However, this approach is inconvenient and limits applications to only swelling solvents. Other approaches, e.g., pillared clays, result in limited gains in effective surface area of the clays. It would be desirable to have a more effective approach that avoids the formation of tactoids.
Description of Technology
The invention provides reactive layered silicate materials with a novel nano-layered structure and reactive silanol groups. The invention prevents the stacking of nanolayers and resulting formation of tactoids. The silicate layers of this invention contain silanol groups in tetrahedral sheets. The compositions of the invention differ from existing alternatives in that a substantial fraction of silicon atoms in the tetrahedral sheets are bonded to hydroxyl groups. The dimensions of the nanolayers vary from one to 200 nanometers, and the nanolayers are aggregated into particles less than 2 microns in size. The preparation of the silicate uses a reaction mixture containing a silica source, a divalent metal oxide source and water forming a paste or slurry (optionally with a base) with a molar ratio of silica to divalent metal oxide source between 1.33 and 1.60, allowing the mixture to react at a temperature between 60° C and 225° C to form the product.
- High surface area for chemical reactions: The invention provides low-cost synthetic layered silicate phases primarily in pre-exfoliated, unstacked nanolayer form, with surface areas in excess of 500 square meters per gram.
- Breadth of applications: The formation of nanolayered silicate phases in unstacked form holds great promise for applications in chemical catalysis, adsorption, polymer-nanocomposite formation, and many other materials applications.
- Potential for water purification: The invention enables the removal of heavy metal cations from contaminated water.
The invention has materials applications such as chemical catalysis, adsorption, and polymer-clay nanocomposite formation. Other potential applications include water purification in the removal of heavy metal cations from contaminated water.
US 2006/0021945 (published US application)
Thomas Pinnavaia, Mihai Polverejan
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Michigan State University