Functional Kaolinite

Abstract

The world resources of all clays are extremely large. Among the various types of clays, the world mine production of kaolin in 2016 was 37.0 Mt, the largest mined clay. Kaolin is traditionally used in ceramics, refractories and as paper coating and filling. But kaolin, as it is demonstrated in this paper, has a bright potential for use in non-traditional, high value-added, applications. This is particularly true for its principal component: the mineral species kaolinite which has a chemical structure allowing its functionalization, leading to a variety of potential applications. Kaolinite is a layered 1 : 1 clay mineral, the layer being made of two different sheets, a tetrahedral silica sheet and an octahedral alumina sheet. Large dipole-dipole interactions, in addition to a network of H-bonds, link the siloxane surface of a layer to the aluminol surface of another layer, making intercalation of guest species in kaolinite challenging. There is however a limited number of molecular units (molecules or salts) that can directly intercalate in kaolinite to form "pre-intercalates". Once intercalated these molecular units can be exchanged by a large number and variety of guests, providing access to the interlayer space of kaolinite, and to its reactive aluminol internal surfaces. The intercalation of molecules of pharmacological interest showed the potential of kaolinite to act as a slow-releasing agent for drugs, and the intercalation of polymers resulted in the creation of intercalated nanocomposites. The intercalation of ionic liquids gave materials with ionic conductivity properties in the solid-state. Intercalates are however unstable in water. One needed to make these organo-inorgano nanohybrid materials resistant to hydrolysis and more thermally stable. The network of aluminol groups on the internal surfaces of kaolinite offers the opportunity to design and create controlled organo-inorgano nanohybrid materials, taking advantage of their reactivity, in particular with hydroxyl groups of organic compounds, to form Al-O-C bonds. A functional, two-dimensional, spatially restricted, environment can be created with controlled nanoarchitecture. The grafting of organic groups on the aluminol internal carpets has allowed applications in catalysis, in sensing, in heavy metals adsorption, in exfoliated nanocomposite, in luminescence, and in structural modifications to form nanoscrolls or nanorolls. This paper shows how the future of the use of kaolinite will shift from its traditional uses in ceramics, tiles and paper coating to more sophisticated, high value-added, uses. In particular, research should amplify in the years to come to design an efficient and cost-effective method to produce kaolinite with nanotubular morphology. One can foresee also that efficient, easy-to-use, electrochemical devices based on modified kaolinite, will be created to quantify selectively a variety of pollutants in waste waters.

Kaolinite Clay Mineral Reactivity Improvement through Ionic Liquid Functionalization

“…If these processes occur with some delay, the expanded layers will collapse and the parent kaolinite regenerated. Using this approach, several compounds were successfully intercalated and used for several environmental, energy and medical applications As other clay minerals, kaolinite displays functional groups (silanol (Si‐OH) and mainly aluminol (Al‐OH) functions) on particles basal surfaces and borders that can be functionalized.…”

“…If these processes occur with some delay, the expanded layers will collapse and the parent kaolinite regenerated. Using this approach, several compounds were successfully intercalated and used for several environmental, energy and medical applications …”

“…Using this approach, several compounds were successfully intercalated and used for several environmental, energy and medical applications. [29,36,37] -As other clay minerals, kaolinite displays functional groups (silanol (Si-OH) and mainly aluminol (Al-OH) functions) on particles basal surfaces and borders that can be functionalized. For several clay minerals, these reactive sites are scarce.…”

Dual application of natural clay material for decolorization and adsorption of methylene blue dye

“…The ability of clay materials or their composites to remove color from materials or oils often gave such clays the name "bleaching earth" (Beshara and Cheeseman, 2014;Ming et al, 2003;Udomkun et al, 2018). The structural features of clays are described by their octahedral (Al 3+ , Fe 2+ , Fe 3+ , or Mg 2+ ) and tetrahedral (Si 4+ ) arrangements of atoms and they can further be modified through intercalation of cations at elevated temperatures (Detellier, 2018;Paineau et al, 2012;Vaculíková et al, 2019). Most clay materials obtained from archaeological contexts have been widely linked to specific medical practices including but not limited to preservation of human remains, removal of hazardous contaminants from wastewater or healing rituals which are probably due to their porous and complex topography that allows the use of the materials for such applications compared to soils and sand (Christopoulou-Aletra et al, 2006;Insoll, 2009;Van Dongen et al, 2011).…”

Flow and Tableting Behaviors of Some Egyptian Kaolin Powders as Potential Pharmaceutical Excipients

“…Kaolinite is a generally inexpensive, ubiquitous and biologically safe raw geomaterial to be used in pharmaceutical formulations at specific high purity grades. This phyllosilicate mineral exhibits a simple pseudohexagonal platy-form of stacking layered structure, with excellent physical and chemical properties that make it suitable as excipient (e.g., diluent, binder, disintegrant, pelletizing, granulating, amorphizing and film coating, emulsifying and suspending agents and drug carrier) in solid and semi-solid dosage formulations, besides its therapeutic activity in many biomedicinal applications [2][3][4][5][6][7][8][9][10][11][12][13]. Kaolinite particles and its polymorph halloysite nanotubes surfaces exhibit adsorption affinities to many active ingredients including the organic drug and agrochemical molecules, biomolecules and non-toxic bioactive metals [14][15][16][17].…”