Synthesis of Rh–carbon nanotube based heterostructures and their enhanced field emission characteristics

Abstract

Selective decoration of Rh nanospheres on acid functionalized carbon nanotubes has been demonstrated using Al as a sacrificial substrate. Remarkable field emission has been observed for this heterostructure as a high current density of 170 lA cm À2 is generated at an ultra-low threshold of 300 V lm À1 , compared to much smaller values for Rh nanospheres and carbon nanotubes separately.Metal nanostructures of tunable size and shape have been the central focus of current research due to their unusual electronic, optical and magnetic properties that are often different from those of their bulk counterparts. 1 The exploitation of the electronic structure of these materials at the nanoscale has strong implications for the development of high-throughput electronic devices, like those based on field emission. 2 Field emission from nanostructured materials, in particular, has captured extensive attention in the past few years due to the enormous field enhancement possible at sharp tips anticipated as a function of their size and shape in the nanoscale. 3 Moreover, carbon-based materials such as diamond, carbon nanotubes (CNTs), graphenes etc. are more favorable in terms of their stability and mechanical strength. 4 Unfortunately, their higher resistivity diminishes their replenishment and transport of electrons, thereby requiring higher threshold fields with time to sustain a constant emission current. 5 Since carbon nanotubes are already considered to be good emitters, 6 their desirable properties may be further enhanced by making use of the electronic properties (work function and the structure of density of states) of metal decorated CNT heterostructures since some of these can operate remarkably well (lower applied voltages) below the intrinsic current limit due to their thermal effects. 7 Current strategies of binding nanoparticles to carbon nanotubes (CNTs) often make use of small organic bridging molecules to improve the adhesion between the nanostructures and CNTs. 8 This not only complicates the process but also results in indirect and poorer contact between different phases. Indeed, the consequential increase in the barrier for electron transport can adversely affect materials performance in emission applications. 9 Enormous improvements have been made, to date, in metal/CNT heterostructures using silver (Ag), platinum (Pt), nickel (Ni), palladium (Pd), rhodium (Rh) and gold (Au) despite the poor durability issues for some of these heterostructures. 8,10 Among these, Rh/CNTs could especially be promising due to their features such as excellent electrical performance, chemical inertness, mechanical strength, remarkable thermal stability, lower electron affinity and significant stability toward ion bombardment. 11 Herein we report such an enhanced field emission from Rh nanospheres decorated multiwalled carbon nanotubes (MWNTs) as compared to Rh nanospheres and acid functionalized MWNTs. Raman spectroscopic analysis reveals conclusive mechanistic evidence for oxidative functionalization followed by effective dec...

Graphite carbon nitride/boron-doped graphene hybrid for efficient hydrogen generation reaction

“…A high degree of structural disorder of the graphene planes, and some defect sites formed, arising from the oxidation process of the graphite. In addition, some of the basal (and peripheral) carbon atoms of the graphite were functionalized with −SO 3 H, hydroxyl, carboxyl, and the epoxy groups [28][29][30]. Boron was doped into the carbon plan by subjecting the graphene to high-temperature reduction with boron oxide.…”

Metal-free B-doped graphene with efficient electrocatalytic activity for hydrogen evolution reaction

“…In this process, some of the graphite's sp 2 carbon atoms are transformed into sp 3 carbon atoms as the graphite undergoes oxidation and its basal (and edge) plane carbons were functionalized with -COOH, -SO 3 H, -OH and epoxy groups by the strong acid solution. 26 Additionally, after such chemical treatment (i.e., graphite with such strong acids), the resulting material (GO) is well-known to have ill-defined distribution of C atoms, or some defect sites and a high degree of structural disorder on its basal planes. 14,24 Thus, the as-obtained GO was chemically reduced and converted into DeG in order to partially restore the material's sp 2 C platform, and thereby its conductivity, so that it would be suitable for making electrocatalysts with.…”

Rhodium nanoparticle–carbon nanosphere hybrid material as an electrochemical hydrogen sensor

“…This is further supported by the red shift in the D and G bands and an increase in the D/G ratio. 20 This presumably is related to the strong bond between the surfaceoxidized functionalities of the CNSs (surface carbon defects) and the Rh nanoparticles. Moreover, the sharp vibration peak observed in the Raman spectrum after the acid functionalization of the CNSs (Fig.…”