RESUMO
One-pot synthesis of niobium carbabide (NbC) nanoparticles with ca. 30-50 nm was achieved via a rationally designed novel alkali-molten salt method using niobium oxide (Nb2O5), potassium carbonate (K2CO3), and mesoporous carbon (MPC). In this reaction, potassium niobate (KNbO3) was produced as an intermediate and carbonization of KNbO3 proceeds at a spatially limited external surface encompassed by the mesopores of MPC due to the repulsive characteristics of ionic KNbO3 toward hydrophobic MPC, which affords the size-controlled NbC nanoparticles with a narrow particle distribution. The particle sizes tended to become smaller as the pore sizes of MPCs or the temperature on the calcination under the nitrogen stream decreased. Elemental reactions along the one-pot synthesis of NbC nanoparticles were clarified by X-ray spectroscopic, thermogravimetric, and mass spectrometric measurements.
RESUMO
The influence of seed topologies on seeded supramolecular polymerization was examined using helicoidal and toroidal supramolecular polymer seeds. The addition of these seeds to a supersaturated solution of monomers led to distinct nucleation-growth kinetics, which were attributed to the significant difference between the elongation from helicoid termini and secondary nucleation catalyzed by the toroid surface.
RESUMO
Photo-induced mode change of CO2 capture/release was achieved by a rationally designed system composed of spiropyran introduced into a polar-gradient field in the interlayer of montmorillonite. DFT calculations and CO2 adsorption tests demonstrated that spiropyran can interact with CO2 through not only weak physical interaction such as Coulombic or van der Waals interactions but also electronic interaction, while photo-isomerized merocyanine was in the CO2 release mode. Photo-induced CO2 concentration systems highly contribute to the realization of carbon neutrality, hence, this study could be a breakthrough for the world's environmental issues.
RESUMO
Unique relationships between hierarchically organized biological nanostructures and functions have motivated chemists to construct sophisticated artificial nanostructured systems from small and simple synthetic molecules through self-assembly. As one of such sophisticated systems, we have investigated scissor-shaped photochromic dyads that can hierarchically self-assemble into discrete nanostructures showing photoresponsive properties. We synthesized various azobenzene dyads and found that these dyads adopt intramolecularly folded conformation like a closed scissor, and then self-assemble into toroidal nanostructures by generating curvature. The toroids further organize into nanotubes and further into helical supramolecular fibers depending on the nature of alkyl substituents. All of these nanostructures can be dissociated and reorganized through the photoisomerization of azobenzene units. On the other hand, the introduction of stilbene chromophores instead of azobenzenes leads to one-dimensional supramolecular polymerization, which upon the intramolecular photocyclization of stilbene chromophores shifts to curved self-assembly leading to helicoidal fibers with distinct supramolecular chirality.
Assuntos
Nanoestruturas , Conformação Molecular , Nanoestruturas/química , PolimerizaçãoRESUMO
Synthesis of one-dimensional nanofibers with distinct topological (higher-order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non-uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post-polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene-embedded rigid π-conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV-light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible-light irradiation followed by aging to restore fully folded structures.