Inorganic hybrid materials integrating carbon nanotubes with osmium compounds: formation mechanisms, structure and reactivity

Abstract

The formation of inorganic nanomaterials is highly sensitive to the local environment. When environmental conditions are carefully selected, they enable precise control over the composition, shape and dimensionality of inorganic nanostructures, which, in turn, influences their functional properties. In this study, we explore the impact of single-walled carbon nanotubes (SWNTs) on the sequential transformation of triosmium dodecacarbonyl (Os3(CO)12) into osmium iodide (OsI) and subsequently osmium disulphide (OsS2). Initially, the nanotubes form a van der Waals complex with Os3(CO)12, allowing the molecules to retain their structure and properties, unaffected by the presence of the SWNT, as determined by direct imaging using high-resolution transmission electron microscopy (HRTEM) and evaluation of metal atom valence states by X-ray photoelectron spectroscopy (XPS). When iodine is introduced, it triggers a chemical transformation of the metal carbonyl to iodide (OsI) in a NaCl-like cubic phase. The nanotubes play a crucial role by providing electrons from their valence band, as evidenced by resonance Raman spectroscopy. The structure of OsI depends significantly on its position relative to the nanotube: disk-like particles measuring 4-6 nm form on the exterior, while sub-nanometer-wide wires form within the internal cavity, the latter exhibiting tumbling motion within SWNT, resulting in different projections in HRTEM images. The hybrid OsI-SWNT material shows ionic character and readily reacts with hydrogen sulphide, converting into OsS2. During this reaction, SWNTs regain their electrons and become charge neutral. OsS2 nanoparticles consist of two distinct phases: a standard pyrite-like cubic phase forms the core of the particles, while a hexagonal phase creates the shell (h-OS2@c-OsS2). Inside SWNTs, however, OsS2 forms a nanowire that is one unit cell wide and twists along the length of the nanotube. The nanotube serves as a protective shell for the undercoordinated osmium atoms located at the edges of the nanowire. We showed that in inorganic transformations, the SWNT acts both as a template for the growth of osmium-based nanoparticles and an analytical platform for the detailed characterisation and comparison of nanostructures formed with and without spatial constraints, facilitating the discovery of new crystal phases such as OsI and hybrid nanostructures of h-OS2@c-OsS2 reported in this study.