Dry Sintered Metal Coating of Halloysite Nanotubes

Abstract

Abstract:Halloysite nanotubes (HNTs) are a naturally-occurring aluminosilicate whose dimensions measure microns in length and tens of nanometers in diameter. Bonding defects between the alumina and silica lead to net negative and positive charges on the exterior and interior lumen, respectively. HNTs have been shown to enhance the material properties of polymer matrices and enable the sustained release of loaded chemicals, drugs, and growth factors. Due to the net charges, these nanotubes can also be readily coated in layered-depositions using the HNT exterior lumen's net negative charge as the basis for assembly. These coatings are primarily done through wet chemical processes, the majority of which are limited in their use of desired chemicals, due to the polarity of the halloysite. Furthermore, this restriction in the type of chemicals used often requires the use of more toxic chemicals in place of greener options, and typically necessitates the use of a significantly longer chemical process to achieve the desired coating. In this study, we show that HNTs can be coated with metal acetylacetonates-compounds primarily employed in the synthesis of nanoparticles, as metal catalysts, and as NMR shift reagents-through a dry sintering process. This method was capable of thermally decaying the metal acetylacetonate, resulting in a free positively-charged metal ion that readily bonded to the negatively-charged HNT exterior, resulting in metallic coatings forming on the HNT surface. Our coating method may enable greater deposition of coated material onto these nanotubes as required for a desired application. Furthermore, the use of chemical processes using toxic chemicals is not required, thus eliminating exposure to toxic chemicals and costs associated with the disposal of the resultant chemical waste.

Zinc Doped Halloysite Cooperating with Polylactic Acid for Bone Regeneration

“…Halloysite nanotubes (HNTs) are cyto-and biocompatible 20 . They have attracted increasing attention in biomedical research due to its physicochemical stability, the potential for chemically modification, and ease of doping substances within its lumen, including therapeutic agents [21][22][23][24] , enzymes 25 , nucleic acid 26 , and metal nanoparticles 27 . In addition, HNTs have been proven to enhance mechanical properties for numerous materials, such as alginate 25 , chitosan 28,29 , epoxy 30 , nylon 24 , rubber 31 , and calcium phosphate 32 .…”

Sulfonated halloysite nanotubes as a novel cation exchange material for solid phase extraction of toxic pyrrolizidine alkaloids

“…[27][28][29][30] Structurally, halloysite nanoclay is a two-layered aluminosilicate with water molecules in between and a hollow tubular structure with walls formed through the rolling of 15 to 20 aluminosilicate layers. 27,29,[31][32][33] The outer shell, which is built out of silicium dioxide with free hydroxy groups on the surface, can easily be modied and presents itself therefore as an ideal substrate. 33 The size of the tubes varies from 50 to 70 nm in external diameter and 10 to 20 nm in lumen diameter.…”

Bi-Functionalized Clay Nanotubes for Anti-Cancer Therapy

“…Additionally, several recent studies have demonstrated that HNTs are cytocompatible [20,[24][25][26]. In one study, HNTs were added to cultures of epithelial adenocarcinoma and human breast cancer cells up to a concentration as high as 75 µg/mg) and cell proliferation was not affected [24].…”

“…In one study, HNTs were added to cultures of epithelial adenocarcinoma and human breast cancer cells up to a concentration as high as 75 µg/mg) and cell proliferation was not affected [24]. In fact, most studies have shown that the HNTs do not produce cytotoxic effects [20,[24][25][26]. Recently, Cervini-Silva et al in 2012 showed that HNTs also have anti-inflammatory properties [27].…”