Carbon nanospheres: synthesis, physicochemical properties and applications

Abstract

The discovery of carbon nanostructures, essentially carbon nanotubes (CNT) and carbon nanofibres (CNF) has led to a big effort devoted to their synthesis, characterization, surface modification and use. Indeed, these structures have encountered application in a wide range of technological fields, such as adsorption, catalysis, hydrogen storage or electronics. Apart from the filamentous arrange of graphene sheets conducting to CNT or CNF, carbon can bond in other different ways to create structures with dissimilar properties. The pairing of pentagonal and heptagonal carbon rings can result in the formation of carbon nanospheres (CNS). This novel nanostructure has only now started to attract significant research activity. In its spherical arrangement, the graphite sheets are not closed shells but rather waving flakes that follow the curvature of the sphere, creating many open edges at the surface. Contrary to the chemically inert C 60 , the unclosed graphitic flakes provide reactive ''dangling bonds'' that are proposed to enhance surface reactions, establishing CNS as good candidates for catalytic and adsorption applications. Despite the embryonic stage of the field and the existing data being too scattered, this work is aimed to provide a comprehensive review of the existing literature related to CNS, exploring the different preparation routes employed, the critical characterization results as well as the applications studied so far.

CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties

“…The common broadness of the peaks in the carbon sphere spectra indicates a low range in the structural order. 10,28 According to Bragg's equation, the interlayer spacing d 002 of our CS is 0.356 nm, which agrees with the literature, 30,31 with a low deviation for the ideal d 002 space (0.343 nm) in a graphitic structure (JCPDS-ICDD Card No. ).…”

“…0.80, showing a higher degree of graphitization (lower I D /I G ) than most of the other CVD carbon spheres reported to date. 10,33,37,38 Lower I D /I G ratios can be achieved in the presence of MnO 2 or Ni doping. 39,40 In any case, our results are in accordance with the graphitization trend reported by Nieto-Márquez et al: graphite 4 carbon nanotubes/nanofibers 4 carbon nanospheres 4 activated carbon.…”

“…35 Anyway, it is worth noting that this coalescence is related to the presence of reactive dangling bonds on the surface, which gives them a high surface reactivity. 4,10 Indeed, the EDAX analysis of the sample revealed a carbon content of 93.2 atomic% and an oxygen content of 6.8%. These results are corroborated by C, H, N elemental analysis, with a carbon content of 93.3% (atomic ratio) and 0.4% of H. No N was detected.…”

“…39,40 In any case, our results are in accordance with the graphitization trend reported by Nieto-Márquez et al: graphite 4 carbon nanotubes/nanofibers 4 carbon nanospheres 4 activated carbon. 10 A further comparison of all the synthesized spheres in this work can be found in SI 3 (ESI †).…”

“…Furthermore, their unclosed graphitic flakes give rise to dangling bonds throughout the surface of the spheres, increasing their reactivity and boosting their applicability in adsorption, lubricants, tribological coatings, catalysis, batteries, supercapacitors or fuel cells among others. [10][11][12][13][14][15] Conversely, when it comes to their transport and magnetic properties, the list of examples is very scarce, 16,17 despite their potential for use as electronically active reinforcing agents of functional composites. 18,19 Indeed, the recent discovery of organic magnetoresistance (OMAR) in graphene and other related nanocarbons has significantly attracted increasing attention to these systems, as they are promising materials for flexible, low-cost and transparent electronics.…”