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

Halloysite nanotubes (HNTs) have been treated with piranha solution, in order to activate their surface and enable a higher grafting of aminopropyl silane and, in turn, a higher loading of Au nanoparticles. The resulting nanocomposites display better performance, in terms of stability and activity, for both reduction and oxidation reactions, than the non-treated HNTs. [Display omitted] •HNTs etching with piranha solution increases the surface area and Au nanoparticles loading.•The increased amount of amino propyl groups on HNTs stabilizes positively charged Au nanoparticles.•The etched heterogeneous catalyst performs better for both reduction and oxidation. 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.