Adsorption of Ferrocene on Carbon Nanotubes, Graphene, and Activated Carbon

Abstract

Ferrocene could be adsorbed on activated carbon, carbon nanotube surfaces, graphite, and graphene in the absence of a solvent at room temperature in spite of its high melting point (174 °C). In each case only monolayers formed via self-adsorption and the transition to surplus polycrystalline material was abrupt, with no multiple layers occurring. Variable-temperature multinuclear solid-state NMR spectroscopy was applied to study the mobilities of the surface-adsorbed ferrocene molecules. It has been demonstrated that on favorable supports the major anisotropic interactions that usually broaden the solid-state NMR signals of polycrystalline and amorphous materials were reduced or completely eliminated due to the mobility of the adsorbed ferrocene. In favorable cases the chemical shift anisotropy (CSA) and the dipolar and quadrupolar interactions were reduced to a degree that allowed the recording of the spectra of the solid materials on a conventional solution NMR spectrometer.

Structures and Dynamics of Secondary and Tertiary Alkylphosphine Oxides Adsorbed on Silica

“…Indeed,t he 31 Pw ideline and MAS spectra ( Figure 9) of 4a show that the CSA is only reduced, but not averaged out entirely.T he size of the molecule andt he long alkyl chains are not expected to slow the motion of an adsorbed species because it has been demonstrated earlier that paraffin, cyclododecane, or metallocenes with cycloalkyl substituents are highly mobile on silica and other surfaces. [13][14][15][16] Upon adsorption of 4 to form 4a all CSA parameters and the span of the signal are changed significantly,t he latter by nearly 100 ppm (Table2). Therefore, it can be concluded that both P=Og roups in the molecule are interacting equallyw ith the surfaceo fs ilica, but they actually do impedee ach other's mobility to some extent.…”

“…Encouraged by the meaningful results obtained with 1 Hw ideline NMR of adsorbed metallocenes [12][13][14][15][16] andm obile species in polymers [50] we probed 4 and 4a with this technique. The proton wideline spectrum of 4 shows as ignal that is broadened by large homonuclear dipolar interactions [17][18][19] and spans from about À110ppm to + 120 ppm, with ah alfwidth of ca.…”

“…Early research in our group resulted in a study of paramagnetic chromocenes in polycrystalline and adsorbed form, while Oprunenko and Günther investigated biphenylene chromium tricarbonyl complexes . Later, we studied diverse diamagnetic and paramagnetic metallocenes and demonstrated that they can be adsorbed as solids on amorphous high surface area silica gel and on various carbon supports …”

“…[11] Later,w e studied diverse diamagnetic and paramagnetic metallocenes and demonstrated that they can be adsorbed as solids on amorphous high surface area silica gel [12][13][14][15] and on various carbon supports. [16] In all the cases of successful solid/solid adsorption described in the literature, [6,7,9,[11][12][13][14][15][16] unique solid-state NMR [17][18][19][20] features were found due to the high translational mobilities of the adsorbate molecules on the surfaces. Importantly,t he adsorbed speciest ravel on spiraling trajectories within the pores of the support or on curveds urfaces, which mimic the molecular reorientation occurring in solution.…”

“…Therefore, the anisotropic interactions dominating the signal shapes of crystalline solids, [17][18][19][20] dipolar and quadrupolar interactions, as well as the Chemical Shift Anisotropy (CSA) [17,18] of the signals of the adsorbeds pecies, are averaged out. [6,7,9,[11][12][13][14][15][16] Signals with larger residual linewidths, but devoid of rotational sidebands, result. The broader isotropic lines are ac onsequence of the less uniform surroundings of the nuclei on the support surfaces, as compared to their environment in asingle crystal.…”