M.R. Baldan

Anodic oxidation of wastewater containing the Reactive Orange 16 Dye using heavily boron-doped diamond electrodes.

Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0 × 10(21)atoms cm(-3), respectively. The boron levels were evaluated from Mott-Schottky plots also corroborated by Ramans spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (111) and (100). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process.

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Porous silicon (PS) samples were obtained by anodization etching process of n-type silicon wafer phosphorus-doped. Electrochemical oxidation of PS was investigated in aqueous hydrofluoric acid (HF) containing additive such as ethanol or acetonitrile. Pore formation was studied with the variation of type and resistivity of the silicon wafer, taking into account the most important anodization process parameters such as: acid concentration, current density and anodization time. Scanning Electron Microscopy (SEM) and Raman Scattering Spectroscopy measurements were used to characterize the macropore morphology changes and sample photoluminescense responses, respectively. PS layer formed in HF-acetonitrile solution showed more uniform and homogeneous macropore distributions with different shapes and sizes. Behavior may be explained because acetonitrile surface tension is greater than that of ethanol. Therefore, acetonitrile molecules might passivate the silicon surface dissolved during the anodization process.

Lead detection using micro/nanocrystalline boron-doped diamond by square-wave anodic stripping voltammetry

Monitoring heavy metal ion levels in water is essential for human health and safety. Electroanalytical techniques have presented important features to detect toxic trace heavy metals in the environment due to their high sensitivity associated with their easy operational procedures. Square-wave voltammetry is a powerful electrochemical technique that may be applied to both electrokinetic and analytical measurements, and the analysis of the characteristic parameters of this technique also enables the mechanism and kinetic evaluation of the electrochemical process under study. In this work, we present a complete optimized study on the heavy metal detection using diamond electrodes. It was analyzed the influence of the morphology characteristics as well as the doping level on micro/nanocrystalline boron-doped diamond films by means of square-wave anodic stripping voltammetry (SWASV) technique. The SWASV parameters were optimized for all films, considering that their kinetic response is dependent on the morphology and/or doping level. The films presented reversible results for the Lead [Pb (II)] system studied. The Pb (II) analysis was performed in ammonium acetate buffer at pH 4.5, varying the lead concentration in the range from 1 to 10 μg L(-1). The analytical responses were obtained for the four electrodes. However, the best low limit detection and reproducibility was found for boron doped nanocrystalline diamond electrodes (BDND) doped with 2000 mg L(-1) in B/C ratio.

Nanodiamond Films for Applications in Electrochemical Systems

The purpose of the present paper is to give an overview on the current development status of nanocrystalline diamond electrodes for electrochemical applications. Firstly, we describe a brief comparison between the general properties of nanocrystalline diamond (undoped and boron-doped) and boron-doped microcrystalline diamond films. This is followed by a summary of the nanodiamond preparation methods. Finally, we present a discussion about the undoped and boron-doped nanocrystalline diamond and their characteristics, electrochemical properties, and practical applications.

Numerical simulation of HFCVD process used for diamond growth

Hot-filament chemical vapour deposition (HFCVD) is a common method employed for diamond deposition. Typically in this method a dilute mixture of carbon containing gas such as methane in hydrogen is thermally activated at sub atmospheric pressures by a hot filament. Due to the filament-substrate proximity, large temperature variation across the substrate is possible. In this work we investigate the role of fluid flow and heat transfer from the filament to substrate in determining the quality of diamond growth. The commercial software CFX was used to calculate velocity field, temperature distribution and fluid flow. A vortex was identified on the substrate.

Growth of vertically aligned carbon nanotubes on carbon fiber: thermal and electrochemical treatments

Composite electrodes of vertically aligned carbon nanotubes (VACNT) were synthesized on carbon fiber (CF) substrate by pyrolysis of camphor/ferrocene using a SiO2 interlayer as a barrier against metal diffusion into the substrate. Two treatments were used to remove iron from CF/VACNT structure: thermal annealing at high temperature under inert atmosphere and electrochemical oxidation in H2SO4 solution. The composites were characterized by scanning electron microscopy and Raman scattering spectroscopy. Besides, the electrochemical behavior of CF/VACNT was analyzed by cyclic voltammetry and charge/discharge tests. CF/VACNT composite submitted to the electrochemical oxidation showed the best electrochemical performance, with high specific capacitance, which makes it very attractive as electrode for supercapacitors.

From micro to nanocrystalline diamond grown on 3D porous titanium matrix

This study aims to give an overview on the growth process and characterization of electrodes produced by coating three-dimensional (3D) titanium (Ti) substrates with diamond films. Powder metallurgy (P/M) was the technique used to obtain the desired and controlled 3D porosity in the Ti matrix. As an important role, in the first place, the effect of a hydrogenation process on the 3D Ti substrate during the diamond growth is presented and discussed. In addition, a detailed description was done about the main growth parameters to obtain these 3D diamond electrodes in the micro and nano scale. The experimental parameters analyzed were the pressure inside the reactor, the methane and the argon gas concentrations, and the temperature at the substrate surface. Scanning electron microscopy, Grazing incident X-ray diffraction and Raman spectroscopy were the techniques used to characterize all the diamond films in the point of view of their morphology, structure, and sp2/sp3 ratio. Finally, the results concerning the electrochemical characterization of these 3D micro and nanocrystalline diamond electrodes are discussed.

Efeito do tratamento térmico na microestrutura, turbostraticidade e superfície de carbono vítreo reticulado analisado por XPS, espalhamento Raman e voltametria cíclica

The structural and surface properties of reticulated vitreous carbon (RVC) were discussed as a function of its heat treatment temperature (HTT), for samples produced in the range from 700 to 2000 oC, using the furfuryl precursor resin. The samples were analyzed by x-ray photoelectron spectroscopy, first and second order Raman scattering as well as electrochemical response. Exploring the material turbostraticity concept, the interdependence between the RVC chemical surface variation and its defects were demonstrated. The influence of heteroatom presence was discussed in the material ordering for HTT lower than 1300 oC while the graphitization process evolution was also pointed out for HTT higher than 1500 oC.

Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites

Carbon fiber/polyaniline composites (CF/PAni) were synthesized at three different deposition time of 30, 60 and 90 min by oxidative polymerization. The composite materials were morphologically and physically characterized by scanning electron microscopy and by Raman spectroscopy, respectively. Their electrochemical responses were analyzed by cyclic voltammetry, by galvanostatic test, and by electrochemical impedance spectroscopy. The influence of the PAni layer thickness deposited on carbon fibers for the composite formation as well as for their electrochemical properties was discussed. The CF/PAni-30 showed a nanometric thickness with more homogeneous morphology compared to those formed in deposition times of 60 and 90 min. It also showed, from the electrochemical impedance spectroscopy measurements, the lowest charge transfer resistance value associated to the its highest value for the double-layer capacitance of 180 Fg-1 making it a very strong candidate as a supercapacitor electrode.

Micro, Nano and Ultranano-Crystalline Diamond Deposition

This is a comparative experimental study of the micro, nanoand ultranano-crystalline diamond deposition. The Hot Filament Chemical Vapor Deposition (HFCVD) reactor deposits the films using different deposition parameters. Scanning Electron Microscopy and Field Emission Scanning Electron Microscopy let morphology inspection. Visible-Raman scattering loaded to estimating relative induced stress, by the graphite peak shift and associated with the defect incorporation and sp2 bond enhancement. The x-ray diffraction confirmed the diamond crystallinity, where Scherrer ́s equations estimate crystallite size and diamond renucleation rates. In this work we propose a defect increasing relative graphite incorporation with the transition of micro, nanoto ultranano-crystalline diamond deposition. Besides this, we propose that this increase defects follows the increase diamond renucleation rates and decreases in the induced stress films. Included is a discussion of the possible reasons for these observations.