Gustavo M. do Nascimento

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint.

In the present work, the resonance Raman, UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about approximately 300 nm in diameter) and nanofibers (about approximately 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of bands at 578, 1400 and 1, 632 cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609 cm(-1) of PANI fibers is correlated with the extended PANI chain conformation.

Structural and Vibrational Characterization of Polyaniline Nanofibers Prepared from Interfacial Polymerization

This work deals with the structural and vibrational characterization of PANI nanofibers prepared through interfacial polymerization using different concentrations of HCl aqueous solution. The results were compared to those obtained by PANI prepared through the conventional route. X-ray diffraction and small-angle X-ray scattering techniques showed that high concentrations of HCl solutions used in the preparation of the PANI nanofibers reduce their crystallinity. The increase of regions with granular morphology was also observed in the scanning electron microscopy images. The changes in the resonance Raman spectra from 200 to 500 cm (-1), FTIR spectra, and the EPR data of the PANI nanofibers reveal an increase in the torsion angles of C ring-N-C ring segments owing the formation of bipolarons in the PANI backbone higher than the PANI samples prepared by conventional route.

Spectroscopic Characterization of the Inclusion Compound Formed by Polyaniline and β-Cyclodextrin

The encapsulation of emeraldine base (EB) was achieved by the thread of several β-CD units onto the polymer chain. The formation of the inclusion compound was confirmed by X-ray powder diffraction, IR and Raman spectroscopies. It was shown that despite encapsulation EB is still prone to the doping effect of HCl or iodine vapours.

Elucidando os estados de oxidação do nitrogênio através da espectroscopia de absorção de raios-X na borda K do nitrogênio

The potentialities of X-ray Absorption Near Edge Spectroscopy (XANES) of the N K edge (N K) obtained with the spherical grating monochromator beam line at the Brazilian National Synchrotron Light Laboratory are explored in the investigation of poly(aniline), nanocomposites and dyes. Through the analysis of N K XANES spectra of conducting polymers and many other dye compounds that are dominated by 1s®p* transitions, it was possible to correlate the band energy value with the nitrogen oxidation states. An extensive N K XANES spectral database was obtained, thus permitting the elucidation of the nature of different nitrogens present in the intercalated conducting polymers.

Interionic interactions in imidazolic ionic liquids probed by soft X-ray absorption spectroscopy.

This work investigates pure ionic liquids (ILs) derived from an imidazolium ring with different carbonic chains and halides or bis(trifluoromethanesulfonilimide) (TFSI(-)) as anions, using X-ray absorption near edge spectroscopy (XANES) at different energies (N, S, O, F, and Cl edges) to probe the interionic interactions. XANES data show that the interaction with the anion is weaker when the cation is an imidazolium than when the salt is formed by smaller cations, as lithium, independently of the length of the carbonic chain attached to the imidazolium cation. The results also show that, for all studied ILs, it is not observed any influence of the anion on the XANES spectra of the cation, nor the opposite. 1-Methylimidazolium with Cl(-), a small and strongly coordinating anion, presents in the N K XANES spectrum a splitting of the band corresponding to nitrogen in the imidazolic ring, indicating two different chemical environments. For this cation with TFSI(-), on the contrary, this splitting was not observed, showing that the anion has a weaker interaction with the imidazolic ring, even without a lateral carbonic chain.

Human Hair as Adsorbent of Palladium(II) in Solution: A Precursor of Well-Dispersed Size-Controlled Pd Nanoparticles

This work describes, for the first time, the preparation of palladium nanoparticles supported in thermally-treated human hair. Human hair showed to be an efficient adsorbent of Pd in aqueous media, reaching nearly 100% of adsorption from a 100 ppm solution. The thermal treatment of hair containing Pd at 200 °C under nitrogen atmosphere led to the formation of an N, S-containing material presenting 0.5 wt.% of palladium. The material was extensively characterized by elemental analysis (CHN and inductively coupled plasma optical emission spectroscopy (ICP OES)), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and Raman spectroscopies, and by thermogravimetry (TG), thermogravimetry coupled to mass spectrometry (TG-MS), scanning electron miscroscopy (SEM), transmission electron microscopy (TEM) and dispersive X-ray spectroscopy (EDS) analyses. It was possible to observe that the surface structure of hair was preserved during thermal treatment, presenting palladium nanoparticles with particle sizes of approximately 4 nm. This material was used as heterogeneous catalyst in a preliminary application in nitrobenzene reduction to aniline in aqueous medium using sodium borohydride.