Halloysite clay minerals — a review

Abstract

Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur in a variety of particle shapes and hydration states. Diversity also characterizes their chemical composition, cation exchange capacity and potassium selectivity. This review summarizes the extensive but scattered literature on halloysite, from its natural occurrence, through its crystal structure, chemical and morphological diversity, to its reactivity toward organic compounds, ions and salts, involving the various methods of differentiating halloysite from kaolinite. No unique test seems to be ideal to distinguish these 1:1 clay minerals, especially in soils. The occurrence of 2:1 phyllosilicate contaminants appears, so far, to provide the best explanation for the high charge and potassium selectivity of halloysite. Yet, hydration properties of the mineral probably play a major role in ion sorption. Clear trends seem to relate particle morphology and structural Fe. However, future work is required to understand the possible mechanisms linking chemical, morphological, hydration and charge properties of halloysite.

Natural halloysite nanotubes as mesoporous carriers for the loading of ibuprofen

“…The first slow loss at approximately 50-400°C is attributed to dehydration of the physically adsorbed water and the gradual loss of the residual interlayer water [45]. The second substantial loss at approximately 400-600°C is ascribed to dehydroxylation of the structural aluminol groups (AlOH), which is in agreement with the observation that the dehydroxylation of halloysite occurs at approximately 450-600°C [25]. The two mass losses correspond to the two endothermic peaks at 80 and 521°C in the DSC curve of Hal/120, clearly attributed to dehydration and dehydroxylation, respectively.…”

“…Interlayer water is favorable for the intercalation of organic compounds. The dehydrated halloysite was only partly intercalated by formamide and ethylene glycol [25]. As the studied thermally treated halloysite was dehydrated and the IBU had only one carboxyl group (-COOH) per molecule, both of these characteristics prevent the intercalation of IBU into halloysite.…”

“…The tubular morphology of halloysite results from the wrapping of halloysite layers that is driven by a mismatch between the oxygen-sharing tetrahedral SiO 4 sheet and the adjacent octahedral AlO 6 sheet in the 1:1 layer under favorable crystallization conditions and geological occurrences [23,24]. Generally, tubular halloysite is approximately 0.02-30 lm long [25] and has an external diameter of 30-190 nm and an internal diameter of 10-100 nm [23,26,27]. These sizes vary in different halloysite deposits [28].…”

Pharmaceutical properties of supramolecular assembly of co-loaded cardanol/triazole-halloysite systems

“…Among the materials that have porous structure, halloysite (HNT), a natural aluminosilicate clay with a hollow tubular structure, is enable to load and to release biomacromolecules and drugs (Joussein et al, 2005;Price et al, 2001;Shchukin et al, 2005).…”

Structural reinforcement of microvascular networks using electrostatic layer-by-layer assembly with halloysite nanotubes

“…Lvov and coworkers have demonstrated the assembly of halloysite and the polycation poly(diallyldimethyl ammonium) chloride (PDADMAC) onto planar glass substrates with reasonable uniformity. 41 Halloysite is a naturally occurring aluminosilicate nanotube 42 with a net negative surface charge, used as a toughening agent in thermoset epoxies. [43][44][45] Here we seek to use the halloysite/PDADMAC multilayer system to modify the channel structure of scaffold-assembled microvascular network materials by depositing directly onto network template surfaces and thereby transferring the particles to the subsequent matrix.…”