Edson Nossol

Transparent films from carbon nanotubes/Prussian blue nanocomposites: preparation, characterization, and application as electrochemical sensors

The preparation of a homogeneous, transparent and electroactive film of a carbon nanotube/Prussian blue nanocomposite is described for the first time. Transparent films of iron- and iron oxide-filled multi-walled carbon nanotubes (CNTs) were prepared on top of ITO electrodes from NMP dispersions of CNTs. Prussian blue (PB) was electrosynthesized as nanocubes over the CNT walls through a heterogeneous reaction between ferricyanide ions in an aqueous solution and the iron-species encapsulated into CNTs. The resulting nanocomposites exhibited intimate contact between PB and CNTs, which improved the stability and redox properties of PB. The electrodeposition of PB and the chemical interaction between PB and CNTs were confirmed by cyclic voltammetry, X-ray diffraction, UV-Vis and Raman spectroscopies and Raman spectroelectrochemistry. The amount of PB obtained in the films was directly proportional to the amount of CNTs deposited initially. In addition, these electrodes were employed as hydrogen peroxide amperometric sensors, which demonstrated very low detection limits (4.60 × 10−9 mol L−1) and very high sensitivity (97.2 A cm−2 M−1).

Synthesis, characterization and morphology of reduced graphene oxide–metal–TCNQ nanocomposites

A simple method has been developed to synthesize reduced graphene oxide (rGO)–AgTCNQ and rGO–copper–TCNQ nanocomposite films (TCNQ = 7,7,8,8-tetracyanoquinodimethane) from electrodeposited rGO–Ag and rGO–Cu films. The method is based on voltammetric co-reduction of a dispersion containing graphene oxide and a silver or copper metal cation precursor followed by reaction of the rGO–metal films with TCNQ. The morphologies of the organic charge transfer nanomaterials, AgTCNQ and copper–TCNQ, are reaction time dependent. Introduction of the metal–TCNQ nanostructures leads to p-doping of reduced graphene oxide. Pure phase II AgTCNQ nanorods/nanocubes were generated in the reduced graphene oxide film whereas pure phase I copper–TCNQ micro/nanorods grew along the reduced graphene oxide structure. In the Cu case, the bulk material was fully consistent with formation of microcrystalline CuTCNQ but evidence for an underlying film which includes nanocrystalline CuTCNQ (1.3 : 1 Cu : TCNQ ratio) and Cu2+ species was also obtained. The achievement of semiconducting phase II AgTCNQ or phase I CuTCNQ in the reduced graphene oxide structure may provide a route for the development of electronic switching devices.

Carbon nanotube/Prussian blue thin films as cathodes for flexible, transparent and ITO-free potassium secondary battery.

Thin films of either unpurified single-walled carbon nanotubes (SWCNT) or iron-filled multi-walled carbon nanotubes (MWCNT) were deposited through the liquid-liquid interfacial route over plastic substrates, yielding transparent, flexible and ITO-free electrodes. The iron species presented in both electrodes (inside of the MWCNT cavities or outside of the SWCNT bundles, related to the catalyst remaining of the growth process) were employed as reactant to the electrosynthesis of Prussian blue (PB), yielding carbon nanotubes/Prussian blue nanocomposite thin films, which were characterized by Raman spectroscopy, scanning electron microscopy, atomic force microscopy, cyclic voltammetry and galvanostatic charge/discharge measurements. The nanocomposite films were employed as cathodes for flexible, transparent and ITO-free potassium batteries, showing reversible charge/discharge behavior and specific capacitance of 8.3mAhcm(-3) and 2.7mAhcm(-3) for SWCNT/PB and MWCNT/PB, respectively.

Carbon nanotube/Prussian blue nanocomposite film as a new electrode material for environmental treatment of water samples

The use of carbon nanotube/Prussian blue nanocomposite film as a new electrode material for the environmental treatment of water samples is reported. The application of photochemical, electrochemical and photoelectrochemical-based Fenton processes were investigated for methyl orange dye degradation. The effect of the operating parameters, such as hydrogen peroxide concentration and applied potential, was established using factorial experimental design. Surface-contour plots revealed how the interaction of the parameters influenced the system response maximum. A methyl orange degradation of 98% was achieved at neutral pH, room temperature, small amount of catalyst, low overpotential (0.0 V vs. Ag/AgCl) and very low amount of H2O2 (1.0 mmol L−1). Moreover, since the carbon nanotube/Prussian blue nanocomposite film is very stable and can be reused without a loss of catalytic activity, this new electrode material is shown to be applicable to wastewater treatment.

Non-Synergistic UV-A Photocatalytic Degradation of Estrogens by Nano-TiO2 Supported on Activated Carbon

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.

DEGRADAÇÃO FOTOCATALÍTICA DE CORANTE UTILIZANDO-SE NANOCOMPÓSITO TiO2/ÓXIDO DE

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.

Highly-sensitive voltammetric detection of trinitrotoluene on reduced graphene oxide/carbon nanotube nanocomposite sensor

This work presents the highly-sensitive detection of 2,4,6-trinitrotoluene (TNT) on reduced graphene oxide/multi-walled carbon nanotube (rGO/MWCNT) nanocomposite sensor. The formation of a thin film of this nanocomposite occurred at the cyclohexane/water immiscible interface of a mixture of MWCNT and rGO in the biphasic solution. The film was transferred to a boron-doped diamond (BDD) electrode for the square-wave voltammetric detection of TNT, which presented improved analytical characteristics in comparison with bare BDD and after modification with precursors. Electrochemical impedance spectroscopy also revealed the faster electron transfer for a redox probe on the nanocomposite modified surface. The synergistic properties of both carbon nanomaterials in the thin film modified surface resulted in a TNT sensor with a detection limit of 0.019 μmol L-1 within a wide linear range (0.5-1100 μmol L-1), with superior performance in comparison with other electrochemical sensors produced with carbon nanomaterials. This new material provides great promises for the highly-sensitive detection of other nitroaromatic explosives as well as other analytes. Moreover, the interfacial method enables the production of homogeneous and stable films on large coated areas as well as the large-scale production of electrochemical sensors.