Iron impregnation on the amorphous shell of vapor grown carbon fibers and the catalytic growth of secondary nanofibers

Abstract

Vapor grown carbon fibers (VGCFs) with diameters of several microns were synthesized and investigated by high resolution transmission electron microscopy. It was found that the shell of the VGCFs consisted of densely-packed domains embedded in loosely-packed matrix, and both were highly amorphous. Regular edge planes as observed on the surface of fishbone nanofibers do not exist on VGCFs. Hence, surface treatment is more important for the deposition of catalysts. Ammonium ferric citrate (AFC) was employed for the impregnation of iron, where the high viscosity of the aqueous solution of AFC is beneficial. Calcination was found to be a key step to improve the dispersion of the iron particles, which can be attributed to enhanced interactions between iron and carbon due to the gasification of carbon occurring at the iron-carbon interface. Quantitative analysis by X-ray photoelectron spectroscopy showed that the calcination of the supported AFC led to a higher atomic concentration of iron on the surface, indicating smaller particle size and higher dispersion. Secondary carbon nanofibers were grown subsequently on the VGCFs from cyclohexane. The specific surface area was enhanced considerably, from less than 1 m 2 g -1 to 106 m 2 g -1 after the growth of the secondary nanofibers. The obtained composites are promising materials as structured support in heterogeneous catalysis.

Fabrication and characterization of buckypaper-based nanostructured electrodes as a novel material for biofuel cell applications

“…38 Here, Raman spectra revealed an increase in the ratio of I D /I G , confirming the apparent increase of surface defects of MWCNTs after acid treatment. 7 Before fabrication of the BPs, the suspensions consisted typically of 1 mg CNTs in 2 ml Triton solution (1 wt% of Triton X-100 in de-ionized water). These were mixed together and ultra-sonicated to make a stock solution, which was subjected to zeta potential measurements to investigate the colloidal stability of the dispersions.…”

“…For functionalization, the as-received Baytubes samples were treated following a reported procedure. 7 They were heated under reflux at 140 1C with (65%) concentrated nitric acid for 3 h, cooled, centrifuged (2700 rpm for 15 min), re-dispersed, filtered with normal filter paper and washed after filtration with distilled water until a neutralization of the filtrate was reached and finally vacuum dried at 50 1C overnight to ensure that all of the moisture and HNO 3 traces were removed from the functionalized Baytubes (f-Baytubes).…”

“…Surface functionalization could increase the affinity of CNTs with organic solvents and provide new pathways for further functionalization based on modification of the attached chemical groups. Usually, surface functionalization can be achieved via oxidation using thermal heating under air, 6 concentrated acid treatment under reflux, 7 oxygen plasma processes, 8 UV-ozonolysis 6 or vapour acid treatment 9 to create surface defect sites and oxygen-containing functional groups in CNTs which can act as anchor sites for nanoparticles.…”

Metal‐Free Heterogeneous Catalysis for Sustainable Chemistry

“…On the molecular level it is useful to grow dendritic structures of CNTs or CNFs onto each other to maximize the exposed surface area and to provide molecular roughness for entanglement of, for example, polymer strands. [120] It is further possible to grow or immobilize CNT or CNFs on activated carbon [121][122][123] and carbon fibers [124][125][126] for catalytic applications. The use of such hierarchically structured carbons in scaled up reactors is still challenging.…”

Nanocarbons for the Development of Advanced Catalysts

“…On the molecular level it is potentially useful to grow dendritic structures of CNTs/CNFs onto each other to maximize the surface area exposed and to provide molecular roughness for entanglement of, for instance, polymer strands. A hierarchical organization of the nanocarbon units on itself to form small objects and on a robust carrier structure in larger dimensions is highly desirable, for instance, to immobilize CNTs on carbon macrofibers. − This kind of carbon hierarchy shows satisfying performance as catalyst for the ODH of ethylbenzene to styrene. , Carbon nanofiber–nanotube hierarchy could be prepared by replacing metal particles inside CNTs (acting as a container) followed by the CVD process . With this approach it is possible to grow CNFs inside large CNTs, developing thus a further level of hierarchy.…”