Halloysite Clay Nanotubes for Controlled Release of Protective Agents

Abstract

Halloysite aluminosilicate nanotubes with a 15 nm lumen, 50 nm external diameter, and length of 800 +/- 300 nm have been developed as an entrapment system for loading, storage, and controlled release of anticorrosion agents and biocides. Fundamental research to enable the control of release rates from hours to months is being undertaken. By variation of internal fluidic properties, the formation of nanoshells over the nanotubes and by creation of smart caps at the tube ends it is possible to develop further means of controlling the rate of release. Anticorrosive halloysite coatings are in development and a self-healing approach has been developed for repair mechanisms through response activation to external impacts. In this Perspective, applications of halloysite as nanometer-scale containers are discussed, including the use of halloysite tubes as drug releasing agents, as biomimetic reaction vessels, and as additives in biocide and protective coatings. Halloysite nanotubes are available in thousands of tons, and remain sophisticated and novel natural nanomaterials which can be used for the loading of agents for metal and plastic anticorrosion and biocide protection.

Competitive interactions and controlled release of a natural antioxidant from halloysite nanotubes

“…Some sources claim that molecules can penetrate also into the interlamellar space . The majority of the groups using halloysite as carrier material for active molecules assume that these latter are located within the tubes and released from there to achieve prolonged effect [2][3][4][5][6][7][8][9][10][11][12][13][14]. Unfortunately, usually not much proof is supplied for this assumption and further study and model calculations must be carried out to define the location and distribution of quercetin molecules on the surface of the halloysite unambiguously.…”

“…Halloysite is a naturally occurring mineral, which is available both in platelet like and tubular form. Numerous attempts have been made to use halloysite nanotubes as carriers for all kinds of bioactive molecules including drugs [2][3][4][5][6][7][8][9][10][11][12][13][14]. However, besides medical applications, halloysite nanotubes are used as supports in other areas as well.…”

Self-healing coatings in anti-corrosion applications

“…The only capsule materials remaining after annealing are oxides [24,48]. Halloysite nanotubes and boehmite nanoparticles are employed as reservoirs for corrosion-inhibiting compounds [57][58][59]. Cerium cations [58,[60][61][62], 8-hydroxyquinoline [48,57], benzotriazole [45,48,49,63,64], mercaptobenzimidazole (MBI) [63], dicyclopentadiene (DCPD), alkoxysilanes [65], silyl ester [24], linseed oil [37,44,66], hexamethylene diisocyanate (HDI) [40], triethanolamine (TEA) [41], monomers and catalysts for ROMP [67], magnesium ions [68], chromium(III) and cerium(IV) oxides [34] and cerium(III) chloride [60,69] are used as corrosion inhibitors.…”

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

“…Modification of the halloysite tube outer surface via covalent bond formation may open up new applications based upon molecular recognition, such as molecular separation, molecular storage, catalysis, and drug delivery Abdullayev et al, 2011;Lvov et al, 2008;Massaro et al, 2014a,b,c).…”