Growth of Carbon Nanocoils from K and Ag Cooperative Bicatalyst Assisted Thermal Decomposition of Acetylene

Abstract

Growth of amorphous carbon nanocoil (CNC) from acetylene on Si substrates was achieved by using nanosized Ag and K as the catalysts. The deposition of CNC was carried out inside a hot-wall reactor at 723 K using H2 as the carrier gas. Based on the observed results, we propose a cooperative bimetal catalyst enhanced vapor-liquid-solid (VLS) growth mechanism to rationalize the CNC growth. In the reaction, the liquid phase metallic K dehydrogenated acetylene into the solid-state carbon, while the Ag nanoparticle assisted the extension of carbon one-dimensionally (1-D) via a tip-growth mechanism. Due to the adhesive force between the K liquid and the carbon, the 1-D solid curled along the C-K interface into the nanocoil shape. Some CNC samples were further heat-treated at 1423 K and showed very good field emission properties. They emitted electrons (10 microA/cm2) at a turn-on field Eto of 2.51 V/microm, while Jmax reached 17.71 mA/cm2 at 5.64 V/microm. The field enhancement factor beta was calculated to be 2124, comparable to other carbon nanotube (CNT) and CNC based emitters. The CNC was also characterized by using the electrochemical behavior of K3[Fe(CN)6] via cyclic voltammetry (CV). The electrochemical surface area of a CNC electrode (geometric surface area 0.078 cm2) was calculated to be 0.143 cm2. These properties suggest that the CNC electrodes may have potential applications in field emission and electrochemical devices.

Synthesis of carbon nanocoil forests on BaSrTiO3 substrates with the aid of a Sn catalyst

“…These nanostructures have generally been referred to as carbon nanocoils (CNCs), and have been investigated for implementation in numerous applications, for instance in structural cushions (nanosprings) [3], field emission displays [4,5], and as magnetic components [6]. To fulfil the rational use of helical carbons, various approaches towards synthesis have been attempted to gain control over the structures and hence the properties of the products.…”

“…Chemical vapor deposition (CVD) is the most commonly used synthesis technique for CNCs and the catalyst material employed within the CVD reactions plays a crucial role [4,7,8]. It was shown that the size, shape, and yield of the grown nanostructures are governed by the chemical and geometrical features of the catalyst [8][9][10].…”

“…It was shown that the size, shape, and yield of the grown nanostructures are governed by the chemical and geometrical features of the catalyst [8][9][10]. To date, assorted types of catalysts have been investigated for the formation of CNCs, which mainly include Cu [7,8], Fe/Sn [11,12], Fe/In [12,13], TiC [14] and alkali compounds [4,15]. Based on these studies, several growth models have been proposed in the literature; the prevailing mechanism is based on the anisotropic extrusion of carbon from different facets/sites of catalyst particles, which is attributed to catalyst topography [7,8,16] as well as inhomogeneity of chemical composition within a particle [14,17].…”

“…Sn has been extensively reported as cooperating with Fe and/or Fe-In in synthesizing CNCs. However, to some extent, these investigations suffered from either tedious catalyst preparation procedures or low selectivity of CNC products, and also did not generate high-quality CNC forests [11,17,18], which have been shown to have great potential for various applications such as nanoelectromechanical systems and field emissions [4,12,19].…”

Fe3C/helical carbon nanotube hybrid: Facile synthesis and spin-induced enhancement in microwave-absorbing properties

“…In addition to the typical catalyst materials such as transition metals Fe, Co and Ni, several novel metal catalysts have also been developed such as Cu, Ag and K [30,31]. However, the catalytic properties of the magnetic metal oxides, a less costly and more accessible catalyst, have not received as much attention and the associated growth mechanism of HCNTs based on such catalysts remains elusive to this date.…”