A 3D monolithic CNT block structure as a reductant, support and scavenger for nanoscopic gold, platinum and zinc oxide

Abstract

ZnO (8–10 nm), gold (10–50 nm), and platinum (2–5 nm) nanoparticles were deposited on monoliths of regularly arranged three-dimensional (3D) carbon nanotubes of 40 nm diameter and length up to 30 μm. The single-source precursor complex di-aqua-bis[2-(methoxyimino)propanato]₂Zn(II) in dimethylformamide was used for the deposition of nanoparticulate ZnO on an ordered 3D CNT scaffold by solution-phase deposition at temperatures as low as 150 °C. Au and Pt nanoparticles were deposited by the spontaneous reduction of aqueous solutions of HAuCl₄ and K₂PtCl₄ on the surface of the macroscopic 3D CNT scaffolds. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) indicate the crystalline nature and nanosize structure of the deposited ZnO, Au and Pt nanoparticles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations revealed a dense and homogeneous decoration of the individual CNTs throughout the 3D CNT scaffold structure. Thus the nanovoids of the carbon scaffold structure are therefore completely accessible leading to a homogenous particle deposition on the complete CNT outer surface. The kinetics of the spontaneous reduction of gold(III) and platinum(II) ions on the CNTs of the scaffold was followed by UV–vis spectroscopy and indicate (i) first-order reaction kinetics with respect to Au³⁺ and Pt²⁺ concentration and (ii) that the rate of reduction of Au³⁺ is one order of magnitude slower than that of Pt²⁺.