Nitrogen-doped mesoporous carbon nanosheet/carbon nanotube hybrids are prepared. This metal-free catalyst exhibits remarkable catalytic performance for both OER and ORR in 0.1 M KOH solution.
Two-dimensional supramolecular assemblies of a series of 2,7-bis(10-n-alkoxycarbonyl-decyloxy)-9-fluorenone derivatives (BAF-Cn, n = 1, 3-6) consisting of polar fluorenone moieties and ester alkoxy chains were investigated by scanning tunneling microscopy on highly oriented pyrolytic graphite surfaces. The chain-length effect was observed in the self-assembly of BAF-Cn. Self-assembly of BAF-C1 was composed of a linear I pattern, where the side chains adopted a fully interdigitated arrangement. As the length of side chains increased, the coexistence of a linear I pattern and a cyclic pattern for the self-assembly of BAF-C3 was observed. Upon increasing the length of the alkoxy chain even further (n = 4-6), another linear II structure was observed in the BAF-Cn monolayer, in which the side chains in adjacent rows were arranged in a tail-to-tail configuration. It is reasonable to conclude that not only the van der Waals forces but also the dipole-dipole interactions from both the fluorenone cores and the ester alkoxy chains play critical roles in the self-assemblies of BAF-Cn. Our work provides detailed insights into the effect of intermolecular dipole-dipole and van der Waals interactions on the monolayer morphology of fluorenone derivatives.
Self-assembled
behaviors of three fluorenone derivatives substituted
by different halogen atoms, 2-(pentadecyloxy)-6-bromo-fluorenone (Br-FC15),
2-(pentadecyloxy)-6-chloro-fluorenone (Cl-FC15), and 2-(pentadecyloxy)-6-fluoro-fluorenone
(F-FC15), were investigated at the 1-phenyloctane/highly oriented
pyrolytic graphite interface by scanning tunneling microscopy combined
with density functional theory calculations in comparison with the
self-assembly of 2-pentadecyloxy-fluorenone (H-FC15). It is found
that different charge distributions on halogen substituents lead to
a subtle change of the molecular packing nanostructures. By varying
the solution concentrations, X-FC15 (X = Br, Cl, H) can self-assemble
into polymorphic nanostructures, whereas only one pattern can be observed
for the F-FC15 adlayer due to the stronger continuous C–H···F
bonds. The intermolecular C–H···OC hydrogen
bonds are the main driving forces for all the self-assembled patterns.
Particularly, the halogen-based hydrogen bonds and the type-I X···X
(X = Br, Cl) bonds act as the collaborative forces to stabilize the
alternate adlayers. Furthermore, the halogen bonds (C–Br···OC
and C–Cl···OC) make the crucial contribution
to the distinct lamellar and the dumbbell-like patterns. The investigation
suggests that the engineering of organic nanoarchitectures can be
effectively tailored by the introduction of different halogen atoms.
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