Clickable halloysite nanotubes for interfacial strain promoted azide-alkyne cycloaddition of Au25 nanoclusters

Abstract

Halloysite nanotubes (HNT) are naturally occurring biocompatible tubular clay minerals, susceptible to functionalization because of their inherent siloxane, silanol and aluminol functionality, that has made them attractive nanomaterials for modification and further applications. Interfacial strained promoted alkyne-azide cycloaddition (I-SPAAC) is a well-known click reaction that can be used to generate new hybrid HNT based nanomaterials. Herein, both azide and bicyclononyne strained alkyne modified HNT are prepared enabling I-SPAAC reactions with suitable reaction partners. I-SPAAC was demonstrated on both and was used to covalently bond azide-modified [N(C₈H₁₇)₄][Au₂₅(SCH₂CH₂-C₆H₄-N₃)₁₈] (Au₂₅) nanoclusters to HNT without need for catalyst and without nanocluster core alterations. Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed HNT functionalization and that the Au₂₅ nanocluster was covalently bound to HNT through analysis of N 1s high resolution XPS spectra. Transmission electron microscopy (TEM) with EDX confirmed that gold nanoclusters are homogeneously distributed over HNT. Diffuse reflectance spectra displayed Au₂₅ HOMO-LUMO transitions indicative that the metal core of the nanocluster remains unaltered. The successful covalent bonding of modified HNT capable of I-SPAAC enables the delivering of function to these solid supports for future applications, including nanohybrid gold nanoclusters for use in solid state reactions or heterogeneous catalysis.