Pt-Cu Bimetallic Nanoparticles Loaded in the Lumen of Halloysite Nanotubes.

In this study, we demonstrate that Pt-Cu bimetallic nanoparticles with different compositions (Pt3Cu, PtCu, PtCu3) can be loaded in the lumen of halloysite nanotube (HNT) via a simple one-pot reduction. Increasing the pH of metallic precursor (H2PtCl6 and CuCl2)/HNT solutions enhances the dissociation of H2PtCl6, advancing the association of [PtCl6]2- with the positively charged inner surface (Al-OH) of HNT. Moreover, the shrinkage of bond length from Pt-Cl in [PtCl6]2- to Pt-O in [PtCl4(OH)2]2- due to pH-modulated ligand exchange may also assist Pt(IV) being trapped inside the halloysite. In the meantime, Cu(II) cations may complex with Pt(IV) anions via electrostatic force that would help the formation of Pt-Cu bimetallic nanoparticles inside the halloysite. The obtained PtCu3@HNT system shows a significantly enhanced catalytic performance in the reduction of 4-nitrophenol by sodium borohydride, with a mass activity approximating 60 times higher than that of unloaded Pt nanoparticles. The high catalytic efficiency can be maintained after thermal treatment at 200 or 400 °C.