Enlargement of Halloysite Clay Nanotube Lumen by Selective Etching of Aluminum Oxide

Abstract

Halloysite clay tubes have 50 nm diameter and chemically different inner and outer walls (inner surface of aluminum oxide and outer surface of silica). Due to this different chemistry, the selective etching of alumina from inside the tube was realized, while preserving their external diameter (lumen diameter changed from 15 to 25 nm). This increases 2-3 times the tube lumen capacity for loading and further sustained release of active chemical agents such as metals, corrosion inhibitors, and drugs. In particular, halloysite loading efficiency for the benzotriazole increased 4 times by selective etching of 60% alumina within the tubes' lumens. Specific surface area of the tubes increased over 6 times, from 40 to 250 m(2)/g, upon acid treatment.

Modified Halloysite Nanotubes: Nanoarchitectures for Enhancing the Capture of Oils from Vapor and Liquid Phases

“…3 The data in Table 1 show that for all of the surfactants this value is never reached, indicating the presence of void space in the hollow cavity. If one assumes that the adsorbed surfactant generates a monolayer, then by considering the average specific area of the inner surface 19 (6.9 m 2 g −1 ) and the occupied area of the surfactant at the water/alumina interface 20 (0.41 nm 2 molecule −1 ) a loading value of 1.2 wt % is calculated. From these results, one may deduce that NaC11 likely forms a monolayer in the lumen, whereas NaC12 and NaC14 generate structure that require larger amounts of surfactant.…”

Eco-friendly functionalization of natural halloysite clay nanotube with ionic liquids by microwave irradiation for Suzuki coupling reaction

“…The non-covalent functionalization of HNTs external surface, with ionic liquids (ILs) was, also, reported. The interaction between 1-butyl-3-methyl-imidazolium hexafluorophosphate [BMIm]PF 6 and HNTs, proposed by hydrogen bonds, was verified by various spectral results and the IL-coated-HNTs were used as reinforcement for styrene-butadiene rubber [17].…”

“…Halloysite is a naturally occurring mineral nanoclay with a tubular shape and a stoichiometry of Al 2 Si 2 O 5 (OH) 4 $2H 2 O which is different to kaolinite only for the presence of two molecules of water located between the adjacent clay layers [6]. As concerns the size, HNTs are quite polydisperse with a length ranging between 0.1 and 2 mm while the outer and inner diameters are ca.…”

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

“…The first step is consistent with the presence of adsorbed cardanol, while the second mass loss process can be related to cardanol strongly interacting with the p-HNT lumen or interlayers. Going further, based on geometrical consideration on the p-HNT size (Abdullayev et al, 2012), the loading amount of 10.2% estimated from the mass loss at 350 C indicates a complete filling of the p-HNT cavity. These results prove that the incorporation of cardanol is a very slow process.…”