Halloysite nanotubes as support for metal-based catalysts

Abstract

Halloysite nanotubes (HNTs) are clay minerals with a hollow nanotubular structure. There is growing interest in these nanomaterials, due to their biocompatibility, potential applications and availability. The surface Moreover, the presence of an empty lumen opens new perspectives for the production of nanoarchitectures with synergistic catalytic effects, due to the increase in local concentrations and confinement. The main focus of this review is the research on modified halloysite nanotubes for the preparation of valuable supports for metal nanoparticles and their applications in catalytic processes.

Palladated halloysite hybridized with photo‐polymerized hydrogel in the presence of cyclodextrin: An efficient catalytic system benefiting from nanoreactor concept

“…As the comparison of the three FT‐IR spectra reveals, the Hal characteristic bands, i.e. the bands at 1033 cm −1 (Si–O stretching), 540 cm −1 (Al‐O‐Si vibration), 3697 cm −1 and 3624 cm −1 (internal ‐OH groups), 1645 and 2923 cm −1 are observed in the FT‐IR spectra of both Pd/Hal‐H and Hal‐V, indicating that the Hal structure is preserved upon incorporation of the silane group and polymer. Notably, the FT‐IR spectrum of Hal‐V is very similar to that of pristine Hal.…”

“…It is worth noting that apart from individual Hal, various Hal‐based hybrid systems have also been designed and applied for catalytic purposes . Notably, the physical and chemical features of Hal such as tubular morphology, high chemical and mechanical stability, inert and non‐toxic nature, oppositely charged inner and outer surface, and the capability of surface functionalization render Hal a promising clay not only in the field of catalysis, but also for many scientific domains such as drug delivery, composites and polymer science …”

Palladium nanoparticles immobilized on cyclodextrin‐decorated halloysite nanotubes: Efficient heterogeneous catalyst for promoting copper‐ and ligand‐free Sonogashira reaction in water–ethanol mixture

“…According to previous reports, CD can promote the reaction rate through formation of inclusion complexes with hydrophobic guests and improving their solubility in aqueous phase and consequently increasing the yield of the reaction. On the other hand, HNTs have been reported as efficient supports for immobilization of nanoparticles . Hence, it is expected that synergistic effects between CD and HNTs can improve the catalytic activity of Pd@HNTs‐T‐CD compared to that of Pd@HNTs‐T and Pd@CD.…”

“…Similar to kaolin, the ratio of Al to Si in HNTs is 1:1. However, a monolayer of H 2 O molecules separates the unit layers in HNTs . High mechanical strength, large surface area and large internal and outer diameters (10–100 and 30–190 nm, respectively) render HNTs a promising candidate for developing (photo)catalysts, drug carriers, polymeric matrices and state‐of‐the‐art materials with the utility for separation, waste treatment and electrical applications …”

“…To manipulate the properties of HNTs and improve their potential for immobilizing catalytic species, surface functionalization is suggested . In this line, HNTs have been functionalized with various functionalities such as N ‐b‐aminoethyl‐γ‐aminopropyltrimethoxysilane, γ‐aminopropyltriethoxysilane and poly( N ‐isopropylacrylamide) .…”