Magnetically Recyclable Catalytic Carbon Nanoreactors

Abstract

Multifunctional nanoreactors are assembled using hollow graphitized carbon nanofibers (GNFs) combined with nanocatalysts (Pd or Pt) and magnetic nanoparticles. The latter are introduced in the form of carbon-coated cobalt nanomagnets (Co@C n ) adsorbed on GNF, or formed directly on GNF from ferrocene yielding carbon-coated iron nanomagnets (Fe@C n ). High-resolution transmission electron microscopy demonstrates that Co@C n and Fe@C n are attached effectively to the GNFs, and the loading of nanomagnets required for separation of the nanoreactors from the solution with an external magnetic field is determined using UV-vis spectroscopy. Magnetically functionalized GNFs combined with palladium or platinum nanoparticles result in catalytically active magnetically separable nanoreactors. Applied to the reduction of nitrobenzene the multifunctional nanoreactors demonstrate high activity and excellent durability, while their magnetic recovery enables significant improvement in the reuse of the nanocatalyst over five reaction cycles (catalyst loss < 0.5 wt%) as compared to the catalyst recovery by filtration (catalyst loss <10 wt%).

Palladium Nanoparticles Hardwired in Carbon Nanoreactors Enable Continually Increasing Electrocatalytic Activity During the Hydrogen Evolution Reaction

“…Compared to other materials Pt/C displayed the smallest onset potential, very close to 0 mV, in agreement with previous reports [22,24–37] . In contrast, PdNP@GNF and commercial Pd/C exhibited more negative onset potentials with similar characteristic polarization curves where two distinct potential ranges can be observed: the first between 30 and −60 mV due to electrochemical hydrogen adsorption and desorption, and the second below −60 mV due to hydrogen evolution (Figure 3a), consistent with the literature [22–37] .…”

“…The PdNP@GNF hybrid was prepared by immersing GNF into a chloroform solution of Pd 2 dba 3 tris(dibenzylideneacetone)dipalladium(0), which triggered a spontaneous growth of PdNP mainly at the graphitic step‐edges, inside the GNF (see the Experimental Section). [34] The resultant material was imaged by HRTEM confirming the formation of well‐distributed PdNP with an average diameter of 4.37±1.03 nm, with more than 80 % of the PdNP located in the interiors of the GNF (Figure 2 a).…”

Front Cover: Palladium Nanoparticles Hardwired in Carbon Nanoreactors Enable Continually Increasing Electrocatalytic Activity During the Hydrogen Evolution Reaction (ChemSusChem 22/2021)

“…Compared to other materials Pt/C displayed the smallest onset potential, very close to 0 mV, in agreement with previous reports. [22,[24][25][26][27][28][29][30][31][32][33][34][35][36][37] In contrast, PdNP@GNF and commercial Pd/C exhibited more negative onset potentials with similar characteristic polarization curves where two distinct potential ranges can be observed: the first between 30 and À 60 mV due to electrochemical hydrogen adsorption and desorption, and the second below À 60 mV due to hydrogen evolution (Figure 3a), consistent with the literature. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] The nature of the carbon support appears to have a significant impact on the electrocatalytic performance of the palladium, as PdNP@GNF displays a slightly less negative onset potential of about À 56 mV compared to Pd/ C (À 62 mV), suggesting that the fast electron transport expected for such graphitized nanocarbon structure may be beneficial for electrocatalytic performance.…”

“…[22,[24][25][26][27][28][29][30][31][32][33][34][35][36][37] In contrast, PdNP@GNF and commercial Pd/C exhibited more negative onset potentials with similar characteristic polarization curves where two distinct potential ranges can be observed: the first between 30 and À 60 mV due to electrochemical hydrogen adsorption and desorption, and the second below À 60 mV due to hydrogen evolution (Figure 3a), consistent with the literature. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] The nature of the carbon support appears to have a significant impact on the electrocatalytic performance of the palladium, as PdNP@GNF displays a slightly less negative onset potential of about À 56 mV compared to Pd/ C (À 62 mV), suggesting that the fast electron transport expected for such graphitized nanocarbon structure may be beneficial for electrocatalytic performance. Furthermore, applying the potential required to achieve a current density of À 10 mA cm À 2 , often used as a benchmark to compare the electrocatalytic activity of different materials, [38][39][40][41] resulted in the following trend Pt/C (47 mV) < Pd/C (76 mV) < PdNP@GNF (221 mV) for our electrocatalysts in their initial states (Figure 3a, Figures S4 and S5, Table S3).…”

Cerium Oxide Nanoparticles Inside Carbon Nanoreactors for Selective Allylic Oxidation of Cyclohexene

“…Like the Raman spectra, PXRD patterns of CeO 2 @GNF (Figure c) show strong evidence for the presence of GNF in the composite. The diffraction peaks of GNF at 2θ = 26.0, 42.4, 44.6, 54.4, and 77.4° correspond to the (002), (100), (101), (004), and (110) planes of the graphitic lattice , and remain unchanged in CeO 2 @GNF. In CeO 2 @GNF-1, no significant new peaks corresponding to CeO 2 are observed, which can be attributed to a low amount or very small size of CeO 2 nanoparticles.…”