Thin films of multiwalled carbon nanotubes/polyaniline nanocomposites (CNT/PAni) were synthesized through the liquid/liquid (L/L) interfacial route, deposited over glass substrates, and evaluated through cyclic voltammetry and amperometry as electrochemical sensor, using L-ascorbic acid as probe. Films with three different CNT/PAni ratios have been prepared. After the spectroscopic and morphological characterization, the electrochemical sensitivity towards L-ascorbic acid was evaluated and compared with similar sensors prepared from neat multiwalled carbon nanotubes (MWCNT) or neat polyaniline (PAni). The nanocomposite film that presented the best nanotube dispersion through the polymeric matrix presented the higher sensor sensibility, 0.237 µA (µmol L−1)−1 and a limit of detection (LOD) of 7.91 µmol L−1. These results evidenced a synergistic effect among the components, and the best response depended on strict control of the polyaniline matrix distribution surrounding the nanotubes.
Undoubtedly, the chemical element carbon is strategic for the development of any country and herein we show some specific impacts in the economical, industrial and scientific sovereignty of Brazil, with emphasis on sp2 carbn structures, namely graphite, carbon black, carbon nanotubes and graphene. Brazil comprises the second greatest natural reserve of graphite worldwide and ranks as third in world production. Carbon black also has important industrial impact in Brazil, especially in the automobile industry, specifically in tires. Some of world leading companies in the production of carbon black are installed in Brazil. Finally, carbon nanotubes and graphene are addressed as the next generation of materials that have and will have great impact in the next years. Their impressive properties have enabled innumerous commercial products worldwide and Brazil already stands out with some innovative initiatives. Indeed, Brazil has installed capacity in universities and research institutes to meet and foster demands in the area, and can be competitive worldwide.
The iron complex hexacyanoferrate (Fe4[Fe(CN)6]3), known as Prussian Blue (PB), was electrodeposited over a free-standing carbon nanotube (CNT) film assembled at the interface between two immiscible liquids, water and 1,2-dichlorobenzene. Polarization of the interface achieved through a fixed potential or under potential variation enabled iron present inside CNTs to generate a stable CNT/PB composite. We report herein on the observation that the deposition of PB is dependent on both the pH and applied potential. It was found that aqueous phases containing K3[Fe(CN)6] can decompose under an applied potential, while those containing K4[Fe(CN)6] presented more stable behavior making it a suitable precursor for PB synthesis. The electrodeposition and modification of the interface was followed by in situ spectroelectrochemical Raman spectroscopy, which indicated that an increase in signal due to PB formation was acompanied by changes in the CNT bands due to modification of the CNT walls by decoration with PB, forming a composite structure.
This work describes the preparation, characterization and properties study of multifunctional nanocomposites between poly(styrene-co -butyl acrylate) latex and different carbon nanostructures: iron-filled carbon nanotubes (CNT), graphene or graphene oxide. Different approaches were employed to prepare stable aqueous dispersions of these nanostructures, according to the specificity of each nanomaterial. The nanocomposites were characterized by Raman and Fourier transform infrared (FTIR) spectroscopy, as well as by scanning probe microscopy (SPM) at different modes, providing information regarding the nature of the interaction between the carbon nanostructures and the polymeric matrix. The synergistic effect between the components results in improved mechanical, electrical, thermal and chemical properties of the nanocomposites, when compared to the neat polymer. In addition, the iron species into CNT cavities provide an interesting and unusual magnetic property of the nanocomposites. Results show that the properties of the nanocomposites can be modulated aiming desired application by simply selecting the amount and/or the kind of carbon nanostructure. This work provides information on the features of the three systems used, showing the range of properties that can be covered by using the three nano-fillers.
The role of the different actions headed by the Brazilian Chemical Society (SBQ) for the development of the Graduate Programs in Chemistry in Brazil is highlighted herein. Specifically, the importance of the SBQ journals, such as the Quimica Nova (QN), Journal of the Brazilian Chemical Society (JBCS) and Revista Brasileira de Química (RVQ) as vehicles to disseminate the knowledge produced by the different graduate programs in chemistry is demonstrated.
Many studies have reported significant improvements in the photocatalytic degradation capacity of TiO2 immobilized in carbonaceous materials, mainly due to a well-characterized synergistic effect. The photocatalytic degradation of the estrogens 17β-estradiol and 17α-ethynylestradiol was evaluated using 1 mg L-1 aqueous solutions, employing a nanocomposite containing TiO2 and activated carbon (TiO2-AC) prepared by sol-gel technique. The synthesized materials were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). These techniques allowed to estimate the carbon proportion (11.4 wt.%), the phase composition (anatase: 80.2%, brookite: 14.0%, and rutile: 5.8%) and the superficial morphology. Using UV-A radiation provided by a high pressure mercury vapor lamp (125 W) and the synthesized photocatalysts, it was observed the almost complete removal of both estrogens in times shorter than 10 minutes. Considering the similarity between the degradation percentage of nanocomposites (TiO2 and TiO2-AC), no synergistic effects between AC and TiO2 could be assumed.
In this work the sol-gel method was used to synthesize a nanocomposite containing TiO2 and graphene oxide (GO). The photocatalytic activity of the TiO2/GO nanocomposite was evaluated regarding the degradation of a reactive dye (reactive black 5) in aqueous solution using processes assisted by UV-A radiation. Under these conditions the nanocomposite showed higher degradation efficiency than the reference photocatalyst (Degussa P25 TiO2), mainly due to the high degradation capacity of the synthesized TiO2 nanoparticles. Although contradictory to several reports in the specialized literature, no synergistic effect was observed between the nanocomposite components.
Copolymers of aniline with anthranilic acid and two esters, ethyl and methyl anthranilate, were prepared through chemical synthesis using a variety of acids as the dopant. All polymers and copolymers were characterized by UV-Vis, Fourier transform infrared (FTIR) and Raman spectroscopies, as well as scanning electron microscopy. The data support the formation of variable amounts of phenazine-like structures due to ortho-coupling polymerization that competes with the para-coupling mode for the construction of the polymer backbone. The electrical conductivity and the solubility in a diversity of solvents were determined and correlated with the spectral data. The copolymers of aniline with anthranilic esters are more soluble than the corresponding polyanilines. In addition, the conductivity of the copolymer with methyl anthranilate doped with trifluoroacetic acid is of the same order of magnitude as that observed for the regular polyanilines. Overall, higher conductivities were obtained for all polymers and copolymers doped with hydrochloric acid and trifluoroacetic acid.
Copolímeros de anilina com ácido antranílico e seus ésteres metílico e etílico foram sintetizados utilizando uma variedade de ácidos dopantes e foram caracterizados por UV-Vis, espectroscopias no infravermelho com transformada de Fourier (FTIR) e Raman, e microscopia eletrônica de varredura. Os dados apóiam a existência de reações de acoplamento para- na construção da cadeia polimérica, embora a reação de acoplamento orto- seja competitiva e leve à formação de estruturas terminais do tipo fenazina. A condutividade elétrica e a solubilidade foram determinadas em uma diversidade de solventes e os resultados correlacionados com os dados espectrais. Observou-se que os copolímeros de anilina com ésteres antranílicos são mais solúveis do que as polianilinas correspondentes. Além disso, a condutividade do copolímero com antranilato de metila dopado com ácido trifluoroacético é da mesma ordem de magnitude que a observada para polianilinas comuns. Em geral, as condutividades mais elevadas foram obtidas para os polímeros e copolímeros dopados com os ácidos clorídrico e trifluoroacético.
This work shows the influence of several reactional parameters for obtaining graphene through successive steps of oxidation and exfoliation of bulk graphite (resulting in graphene oxide), followed by chemical reduction. The results showed that changes in temperature, reaction time, reducing agent and source of primary graphite lead to different surface compositions and stability in dispersion of graphene oxide. Also, the use of different reducing agents promoted different degrees of restoration of C=C bonds in the bidimensional structure of graphene.
The synthesis and characterization of different platinum nanoparticle/carbon nanotube nanocomposite samples are described along with the application of these nanocomposites as electrocatalysts for alcohol oxidation. Samples were prepared by a biphasic system in which platinum nanoparticles (Pt-NPs) are synthesized in situ in contact with a carbon nanotube (CNT) dispersion. Variables including platinum precursor/CNT ratio, previous chemical treatment of carbon nanotubes, and presence or absence of a capping agent were evaluated and correlated with the characteristic of the synthesized materials. Samples were characterized by Raman spectroscopy, X-ray diffraction, thermogravimetric analysis and transmission electron microscopy. Glassy carbon electrodes were modified by the nanocomposite samples and evaluated as electrocatalysts for alcohol oxidation. Current densities of 56.1 and 79.8/104.7 mA cm-2 were determined for the oxidation of methanol and ethanol, respectively.