Au nanoparticles supported on piranha etched halloysite nanotubes for highly efficient heterogeneous catalysis

Halloysite nanotubes (HNTs) can be conveniently used as scaffolds to load catalytic units, to enable efficient heterogeneous catalytic processes. In this contribution, we report a facile strategy to prepare a composite system based on Au nanoparticles (NPs) supported on piranha-etched HNTs. The resulting nano-system was characterized by FTIR, XPS and nitrogen physisorption to highlight its surface properties and porosity. Compared to the non-treated reference HNTs, the increase of hydroxyl groups on the etched HNTs walls allowed to graft a double amount of 3-aminopropyl silane (5.7 wt% vs. 2.8 wt%) and, consequently, to load 15.5 wt% more gold NPs. On the other hand, the interaction of the amino groups with Au NPs stabilizes positively charged NPs, thus leading to excellent catalytic activity and stability. The resulting nano-hybrid can catalyse the reduction of 4-nitrophenol to 4-aminophenol with a kinetic rate constant 53% higher than the reference reaction. In addition, it can be reused for 8 times without significant loss of activity. The supported system also demonstrates its potential in the oxidation of a sugar-derived molecule, i.e., furfural, which is converted into furoic acid with turnover frequency (TOF) 25% higher than the reference.