Recent developments in inorganically filled carbon nanotubes: successes and challenges

Abstract

Carbon nanotubes (CNTs) are a unique class of nanomaterials that can be imagined as rolled graphene sheets. The inner hollow of a CNT provides an extremely small, one-dimensional space for storage of materials. In the last decade, enormous effort has been spent to produce filled CNTs that combine the properties of both the host CNT and the guest filling material. CNTs filled with various inorganic materials such as metals, alloys, semiconductors and insulators have been obtained using different synthesis approaches including capillary filling and chemical vapor deposition. Recently, several potential applications have emerged for these materials, such as the measurement of temperature at the nanoscale, nano-spot welding, and the storage and delivery of extremely small quantities of materials. A clear distinction between this class of materials and other nanostructures is the existence of an enormous interfacial area between the CNT and the filling matter. Theoretical investigations have shown that the lattice mismatch and strong exchange interaction of CNTs with the guest material across the interface should result in reordering of the guest crystal structure and passivation of the surface dangling bonds and thus yielding new and interesting physical properties. Despite preliminary successes, there remain many challenges in realizing applications of CNTs filled with inorganic materials, such as a comprehensive understanding of their growth and physical properties and control of their structural parameters. In this article, we overview research on filled CNT nanomaterials with special emphasis on recent progress and key achievements. We also discuss the future scope and the key challenges emerging out of a decade of intensive research on these fascinating materials.

Carbon nanotubes prepared by anodic aluminum oxide template method

“…Wetness impregnation is a commonly used method for filling foreign matters into the hollow core of CNTs [132]. The precursor used in the wetness impregnation method is usually a soluble salt that contains the element intended to fill.…”

Electronic and magnetic properties of Fe clusters inside finite zigzag single-wall carbon nanotubes

“…This is confirmed by experiments using high-resolution electron microscopy, 40 showing that there is not free space between the metal and the carbon walls and that elongated iron aggregates condensate separated by empty regions along the nanotube. 6,40 For this reason, we shall focus on an isomer of Fe 12 having an elongated geometry that fits well inside the (10,0) and (11,0) ZNTs considered in this paper. Moreover, we will investigate the icosahedral structure of Fe 12 and a second elongated isomer based on tetrahedral units.…”

“…This justifies the iron-filled tubes produced experimentally. 6,7,40 Free iron clusters exhibit large magnetic moments (see Table I). The magnetic moments of the encapsulated iron clusters, shown in Table III, are reduced with respect to the moments of the free clusters, except for Fe 2 , whereas there is an enhancement in the net magnetization of the ZNT.…”

“…Nanotubes filled with Fe have potential uses in medicine, 1 in spintronic devices, 2 including spin valves, 3 and can also be used as probes for magnetic force microscopy. 4,5 Recent reviews on the preparation of filled carbon nanotubes 6,7 indicate the activity in the field. In general, free metallic magnetic nanoparticles are oxide coated, but the encapsulation of Fe clusters and nanowires in carbon nanotubes, where these metallic nanostructures are protected from the oxidating environment, 8 has been shown to be feasible.…”

Hybrid systems based on metal oxide and nanocarbons: electronic properties and applications for photocatalysis

“…The inner channel of the CNTs has been filled by metals, alloys or inorganic nanoparticles. [Gautam et al 2010;Eliseev et al 2009;Cabana et al 2014] However, for energy application, the inorganic generally needs to have its surface accessible to gas or liquid molecules. Therefore, the deposition of the second compound on the nanocarbon surface (coating them) in general results more interesting for the formation of hybrid materials for energy applications.…”