macla nº 9. septiembre ‘08 revista de la sociedad española de mineralogía 15 Clay Minerals as an Ancient Nanotechnology: Historical Uses of Clay Organic Interactions, and Future Possible Perspectives / GIORA RYTWO Environmental Sciences Department, Tel Hai Academic College, Upper Galilee (Israel) e-mail: [email protected] INTRODUCTION. for bleaching fleece and clothes, and Johnston (1996) develops the concept of removal of grease and stains from it "active sites" adopted from biological The world "clay" has ambivalent (Beneke and Lagaly, 2002; Robertson, macromolecules, and defines six definitions (Bergaya, 2000). On one 1986). Additional uses along history different types of sites that may appear hand it is used to define any soil particle included very thin ceramics in China in clay minerals, contributing to its smaller than 2 μm, but on the other (Weiss, 1963), cosmetics, internal and interaction with other substances, hand it includes a large group of external medicine, art and religion, yielding unique results: (a) "broken microcrystalline secondary minerals construction, sealing and proofing, and edge" sites and exposed surface based on hydrous aluminum or assorted uses in the food industry. aluminol and silanol groups, (b) magnesium silicates that have sheet isomorphic substitutions, (c) like structures (Manahan, 2000). There are at least two points that make exchangeable cations, (d) hydrophobic clay minerals so active in natural silanol surfaces, (e) hydration shell of Clay minerals have been part of human processes, and became the key for their exchangeable cations, and (f) existence since antiquity (Murray, 1997; wide applications: (a) The very large hydrophobic sites on adsorbed organic Yuan, 2004) and were used as natural surface area that arises from the tiny molecules. nanomaterials along history for size of the particles (nano-scale), and (b) industrial and commercial uses. The first The fact that those particles are The latter active site leads to very recorded applications were more than electrically charged, leading to relatively interesting interactions between clay 5000 years ago, in Cyprus and Greece, strong electrostactic interactions. minerals and organic chemicals. Changes on the surface of the clay mineral make it specifically optimized chitosan - montmorillonite crude montmorillonite for interactions with different types of X1000 X1000 chemical compounds: Natural clay are negatively charged, and cations can easily bind to their natural surface while negative or non polar hydrophobic chemicals will be rejected. An hydrophilic behavior will be observed, based mainly on hygroscopic water bound as hydration shell on the exchangeable cations (Lahav, 1983). Adsorption of organic cations (as ammonium based compounds deriving from decaying urine, e.g.) to the clay charged sites, exchanging the original chitosan - montmorillonite crude montmorillonite inorganic cations, might exhibit X8000 X8000 hydrophobic moities toward the outside surface of the "organoclay" composite. Such new surface might be optimal to bind non polar chemicals. In some cases organic cations may be even loaded in excess (charge reversal), leading to interactions with negatively charged chemicals. Morphological properties of the surface also change due to such interactions (see Fig.1): Whereas natural smectite shows dense platelets, a sponge-like structure can be obtained by fig 1. An example of the modification in the morphology of a clay mineral (Crude SWy-1 montmorillonite, the binding of the natural organic right pictures) due to the adsorption of organic cations (chitosan-montmorillonite, left pictures). Images cationic polymer chitosan, to are shown at x1000 (upper row) and x8000 magnifications. 16 montmorillonite (Rytwo and Dultz, 2007, penetrated into the crystal lattice and most of them positively charged and unpublished results). increased the distance between the with relatively low molecular weight. kaolinite layers from 7.2 to 10.7 A. When the temperature of the wine TYPICAL USES OF CLAY MINERALS. Rheological behavior of kaolin does increases due to exposure to sun or high indeed increase strongly with this heat at transport conditions- those Several typical examples of the use of pretreatment. A kaolin of low thixotropy proteins coagulate, forming tiny clays along the history might be subjected to this treatment yields a aggregates that disperse light, and wine presented. This work will focus only on a material surpassing the best ceramic becomes turbid, usually without any few of them. kaolins and approximating sodium influence on the taste (Eisenman,1998). bentonites. The positive charge of the PR proteins 1. The use of clay minerals in laundry makes them suitable for binding to and bleaching of wool and cloth: The 3. Cosmetic uses: Clay has been used negatively charged clay minerals. Thus, term "fullers' earth" usually used for clay around the world for centuries by clayey soils or bentonite were added to minerals arrives from the Latin term indigenous people as an important wine at very low concentrations at “fullo”, which indicates "working in the medicinal and cosmetic tool ("Mountain various stages of preparation. The PR removal of oil from clothes" (Robertson, Rose Herb", 2008). Clays, as French proteins are bound to the clay, and sink 1986). As mentioned above, the oldest Green clay (illite) and Rhassoul clay (a as relatively larger aggregates. The archeological findings of clay used for smectite), are used externally for skin process of adding a flocculant to avoid such purpose was found in Cyprus, at conditions and for cosmetic purposes. the turbidity due to heating is usually wool dumps dated from 5000 BC. In In Mesopotamia mixtures of clays were known as “fining”, and is used until now Rome, clay and soil were combined with used as soap an other facial- and skin- in most wineries along the world. “Low decaying urine to enhance the process, care ointments. In Egypt, “red ochre” (a stability wines” are, therefore, white indicating one of the oldest reported pigment made from naturally tinted clay wines with high PR-proteins. Several uses of clay-organic interactions. minerals, with relatively large amounts fining agents are in use, as bentonite, Romans even developed a commercial of hydrated Fe(III)) was used for lips and polymers, gelatin, polysacharides and system dedicated to collect products cheeks other large organic molecules as dried- from public urinals, in order to sell the milk solids (casein) or dried “egg-white” products for laundry use. 4. Medicinal uses: In the second century (albumin) (Morris & Main, 1995). A.D., Galen, the Greek philosopher and 2. Chinese Porcelain:. Porcelain has physician, was the first to record the use Amount and exact type of protein been made in China probably since the of clay by sick or injured animals changes with the grape variety, soil type, 6th or 7th century A. D. Quartz, feldspar, (AboutClay.com, 2006). Uses appear to weather, etc- and differs considerably and kaolin were then, as now, the raw be worldwide: The Essenians (near the from year to year (Ferreira et al., 2002). materials employed. The name “kaolin”, Dead Sea), The Amargosians Thus, winemakers usually make for china clay derived from old deposits (predecessors to the Aztecs ), and other preliminary “try and error” experiments on the mountain Kao- ling in China. natives in North, Central and South in order to know the amount of clay to Observations had been made since the America, Africa and Australia recognized add. Large amount might cause 9th century about the fact that “chinese the benefit of clays as a dietary unwanted side-taste, and changes in have particularly fine clay which they supplement or as a healing aid. Several color. Added amounts are usually 0.1-5 use to make drinking vessels with the clay providers' web sites propose g/L (0.01-0.5%). Figure 2 shows a test delicacy of glass; although they are therapeutical applications. Uses are performed with several clay minerals in made of clay.” Such items had great wide and some of them even have order to avoid turbidity after heating in strength, were shaped perfectly by hand, special definitions, (“Pelotherapy”: Sauvignon Blanc wine from Galil and have wall thickness of less than medical treatment by mud baths). Mountain Winery, 2006 (Rytwo and 0.4mm! During Mongol domination Although some uses are rather esoteric, Lang, 2007, unpublished results). It can (1280-1368) the knowledge was lost. part of the proposed applications are be seen that smectites (SWy-1 and Ceramics from the following Ming well-understood: adsorption of toxins KWK) are considerably more effective in dinasty was not as thin as before, even from skin or internally by clay organic fining than other clay minerals. This is they tried to use the most plastic kaolin interaction processes, adsorption of ascribed to the large negatively charged deposits they found. Only till the end of mercury and other heavy metals by ion surface area. However, it is interesting to the Ming dinasty (1644) thin ceramics exchange (Eyton's Earth, 2006), use as notice that the fining strongly depends appear again, but in this case those an alkalizing agent, supplying alkali on the grape variety: performing the were made from illite, which has a-priori exchangeable cations, etc. same experiment on Viognier white wine a considerably higher plasticity than from the same winery- sepiolite yielded kaolin, making it easier to handle. The 5. Fining and clarification of juices, oils the best fining results. We assume that secret of ancient Chinese kaolin-based and wines: Clays were and still are the remaining proteins in Viognier on porcelain must therefore lie in some applied in order to avoid secondary that season might be non-charged. technique enabling delicate items to be turbidity, especially in white wines. The Since sepiolite adsorbs effectively formed from kaolin of poor plasticity, scientific base of this application lies on organic molecules to neutral silanol which would normally be expected to the fact that during fermentation, most sites (Rytwo et al, 1998) at amounts require clays of extremely good proteins in wine decompose due to the considerably larger than smectites, plasticity.