Noble metals supported on carbon nanotubes using supercritical fluids for the preparation of composite materials: A look at the interface

Abstract

Carbon nanotubes (CNTs) have attracted great interest from scientific and industrial communities thanks to their remarkable properties. However, even if their mass production is nowadays well-known, the methods commonly used lead to bundles made of hundreds of single nanotubes with inert surface. Through the description of a simple, rapid and green procedure to uniformly decorate CNTs with metal nanoparticles (Ag, Pd), this paper presents a look at the CNTs-metal interface as a function of the functionalization technique.Three types of CNTs are considered for deposition: raw CNTs, CNTs functionalized with the reference HNO3/H2SO4 method and CNTs functionalized with our approach using CO2/EtOH/H2O/H2O2 under temperature and pressure. For functionalized CNTs the Pd atoms and CNTs are linked by oxygen atoms and the coating is made of metallic palladium nanoparticles while palladium oxide nanoparticles are formed on raw CNTs, the functionalization having an influence on the nucleation and growth phenomenon. Furthermore the surface treatment of CNTs in acidic solution has a major drawback with CNTs contamination that is why a functionalization with CO2/EtOH/H2O/H2O2 under temperature and pressure is preferred. In addition, electron tomography has shown that the use of supercritical fluids leads to a uniform deposition of metal inside the bundles of CNTs. The orientation relationship between palladium nanoparticles and CNTs has also been determined; the {111} planes of palladium nanoparticles are parallel to the CNTs graphite planes. The supercritical fluids chemical deposition method appears as an interesting alternative process for the uniform decoration of CNTs with strong interfaces for the preparation of composite materials.