A very simple method of reductive amination, based on the Leuckart reaction, is reported. This method enables not only the reduction of graphite oxide, but also results in reduced graphene oxide functionalized with amine groups, where the amination degree is 3.2 at.% as determined by XPS. The dominant nitrogen functional group was primary amine, but pyridines and lactam groups were also observed. It was found that the aminofunctionalized reduced graphene oxide is a semimetallic material because of the lack of band gap, unlike the graphite oxide that presented a band gap of 2.16 eV.
The stability and properties of the monovacancy and the divacancy in single-walled carbon nanotubes (CNTs) are addressed by spin-density functional calculations. We study these defects in four nanotubes, the armchair (6,6) and (8,8) and the zigzag (10,0) and (14,0), which have diameters of about 8 and 11Å, respectively. We also study different defect concentrations along the tube axis by increasing the supercell in this direction in order to have one defect every 13 and 26Å of CNT length. Our results show that in the equilibrium geometry CNTs with a monovacancy exhibit ferromagnetism with magnetic moments ranging from 0.3 to 0.8 µB. On the other hand, CNTs with a divacancy do not exhibit magnetism due to the full reconstruction around the defect where all C atoms are three coordinated. We observe that the presence of a monovacancy does not change drastically the CNT electronic properties, preserving their corresponding metallic or semiconducting character. However, for the divacancy both armchair and zigzag CNT become semiconductors exhibiting a energy gap of about 0.15 eV.
A series of luminescent
phenoxo-bridged dinuclear TbIII complexes with tripodal
ligands, 2,2′-[[(2-pyridinylmethyl)imino]di(methylene)]-bis(4-R-phenol),
where R = CH3 (LCH3) (I), Cl (LCl) (II), CH3O (LCH3O) (III), COOCH3 (LCOOCH3) (IV), were prepared to probe the effect of para-substitution
on the phenol ring of the ligand on the TbIII luminescence.
For these TbIII complexes a complete suppression of the
ligand-centered fluorescence is observed, which demonstrates an efficient
ligand-to-metal energy transfer. Complex IV was found
to be the one that shows the greater intensity of the emission at
room temperature. The obtained quantum yields follow the trend IV > II ≫ I > III. The quantum yield for II and IV is approximately
five times greater than those obtained for I and III, indicating that the LCl and LCOOCH3 are better sensitizers of the TbIII ions. These results
were rationalized in terms of the variation of the energy gap between
the triplet level (T1) of the ligand and the emissive 5D4 level of TbIII, due to the electron-acceptor
or electron-donor properties of the substituents. The τav values are in the millisecond range for all the studied
complexes and resulted independent of temperature. The Commission
International d’Eclairage coordinates (CIE) for all complexes
are in the green color region, being insensitive to the variation
of temperature. Moreover, the color purity (CP) is ca. 90% for all
complexes, being ca. 100% for IV. Thus, the introduction
of electron-acceptor substituents on the ligand permitted us to improve
the luminescent properties of the TbIII complexes.
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