Clay minerals in Gamalama volcanic soil have not yet been identified thoroughly. The soil is estimated to contain nanoscale natural clays, such as halloysite or imogolite. The occurrence of nanoclays in the soil will support the development of many applications in nanotechnologies from nature. The objective of the present study was to characterize soil samples from five different locations around the volcano at three different depths from the soil surface. A total of 50 g of dry soil sample was stirred slowly in 300 mL of distilled water. Stirring was stopped after the addition of 10 mL of 30% H2O2 and then allowed to stand for 24 h. The small floating particles with dimensions of <2 μm were separated from the mixture and collected using a centrifuge at 4000 rpm (1790×g) for 30 min. About 5 g of solid sample was obtained for further characterization. X-ray diffraction results showed the presence of halloysite, allophane, and kaolinite. Morphology analysis by scanning and transmission electron microscopy of some representative samples showed short tubes 10–20 nm in diameter and 50–100 nm long with the halloysite structure. Halloysite was found at 70 cm depth from the soil surface at almost all locations. The surface area determined by the surface area analyzer using the BET equation was as much as 112.51 m2/g. This surface area is thought to be the largest ever determined for a natural nanoclay, paving the way for future application as catalytic or photocatalytic-supporting materials.

Several procedures for hydrothermal synthesis of saponite can be found in the literature. They differ in terms of the preparation conditions of the precursor and of the synthesis temperature. The objective of the present study was to investigate how these two parameters influence the structure of the final synthesis product. The precursor was prepared from Mg(NO3)2, Al(NO3)3, and Na4SiO4 in three different ways: as a gel, a dried gel, and a calcined gel. The influence of the synthesis temperature on the structure of saponite was investigated in the range 90–200°C. The results showed that the use of a calcined precursor yielded a single mineral phase, saponite, with up to 90% aluminum in tetrahedral configuration. In comparison, the use of a gel precursor resulted in a product with only 60% aluminum in the tetrahedral configuration. The synthesis temperature had no significant effect on the saponite structure. The reported synthesis method showed the possibility of obtaining saponite with superior characteristics, in terms of crystallinity, surface acidity, and thermal stability compared to the natural mineral, even at 90°C, and thus with greater potential for industrial application.

Because of their large potential for agricultural, industrial and medicinal applications, nanomaterials have been the focus of much research during the past few decades. Nanoclays are natural nanomaterials that occur in the clay fraction of soil, among which montmorillonite and allophane are the most important species. Montmorillonite is a crystalline hydrous phyllosilicate (layer silicate). Organically-modified montmorillonites or ‘organoclays’, formed by intercalation of quaternary ammonium cations, have long been used as rheological modifiers and additives in paints, inks, greases and cosmetics and as carriers and delivery systems for the controlled release of drugs. Perhaps the largest single usage of organoclays over recent years has been in the manufacture of polymer-clay nanocomposites. These organic–inorganic hybrid materials show superior mechanical, thermal and gas-barrier properties. Organoclays are also useful in pollution control and water treatment. Allophane is a non-crystalline aluminosilicate derived from the weathering of volcanic ash. A large proportion of the agricultural land in Chile is covered by volcanic soils,the clay fraction of which is dominated by allophane. Consisting of nanosize (3.5–5.0 nm) hollow spherules, allophane is a suitable support material for enzyme immobilization. Allophane is also effective at adsorbing phenolic compounds and colour from kraft mill effluents and phosphate from water and wastewater.