Evaldo José Corat

Kinetics study of diamond electrodes at different levels of boron doping as quasi-reversible systems

Abstract Electrochemical reversibility was investigated for diamond electrodes with different boron concentrations for two redox couple. Diamond electrodes presented quasi-reversible electrochemical behavior for both electrolytes. In the range of scan rate and doping level analyzed diamond electrodes presented heterogeneous electron-transfer rate constant k 0 values of approximately 10 −4 –10 −3 cm/s for ferri/ferrocyanide and of approximately 10 −6 –10 −5 for quinone/hydroquinone. It was observed a maximum k 0 value when the electrode reaches a semi metallic behavior, associated to its higher crystalline quality and lower impurity incorporation. The acceptor concentrations were evaluated in the range of 10 18 –10 21 cm −3 from the Mott–Schottky plot curve slope. The results were compared with platinum and glassy carbon electrodes. Scanning electron microscopy (SEM) has also shown diamond crystallites decreasing with boron doping increasing. Raman spectroscopy has evidenced a drastic decrease of 1332 cm −1 peak, characteristic of boron-doped diamond. Atomic force microscopy (AFM) measurements have also demonstrated the electrode topography and its real active area for electrochemical response.

Antibacterial activity of DLC films containing TiO2 nanoparticles

Diamond-like carbon (DLC) films have been the focus of extensive research in recent years due to their potential applications as surface coatings on biomedical devices. Titanium dioxide (TiO2) in the anatase crystalline form is a strong bactericidal agent when exposed to near-UV light. In this work we investigate the bactericidal activity of DLC films containing TiO2 nanoparticles. The films were grown on 316L stainless-steel substrates from a dispersion of TiO2 in hexane using plasma-enhanced chemical vapor deposition. The composition, bonding structure, surface energy, stress, and surface roughness of these films were also evaluated. The antibacterial tests were performed against Escherichia coli (E. coli) and the results were compared to the bacterial adhesion force to the studied surfaces. The presence of TiO2 in DLC bulk was confirmed by Raman spectroscopy. As TiO2 content increased, I(D)/I(G) ratio, hydrogen content, and roughness also increased; the films became more hydrophilic, with higher surface free energy and the interfacial energy of bacteria adhesion decreased. Experimental results show that TiO2 increased DLC bactericidal activity. Pure DLC films were thermodynamically unfavorable to bacterial adhesion. However, the chemical interaction between the E. coli and the studied films increased for the films with higher TiO2 concentration. As TiO2 bactericidal activity starts its action by oxidative damage to the bacteria wall, a decrease in the interfacial energy of bacteria adhesion causes an increase in the chemical interaction between E. coli and the films, which is an additional factor for the increasing bactericidal activity. From these results, DLC with TiO2 nanoparticles can be useful for producing coatings with antibacterial properties.

Residual stresses and crystalline quality of heavily boron-doped diamond films analysed by micro-Raman spectroscopy and X-ray diffraction

Abstract X-ray diffraction analysis and micro-Raman spectroscopy measurements have been used for stress studies on HFCVD diamond films with different levels of boron doping. The boron incorporation in the film varied in the range 10 18 –10 21 boron/cm 3 . The grain size, obtained from SEM images, showed grains with 2–4-μm average size, which decreases when the doping level increases. The thickness of the films obtained by SEM cross-section view decreased from 8 to 5 μm as the doping level increased from 0 (undoped film) to 10 21 boron/cm 3 . The total residual stress was determined by measuring, for each sample, the (331) diamond Bragg diffraction peak for Ψ -values ranging from −60° to +60°, and applying the sin 2 ψ method. For the micro-Raman spectroscopy the spectral analysis performed on each sample allowed the determination of the residual stress, from the diamond Raman peak shifts, and also the diamond purity, which decreases from 99 to 75% as the doping level increases. The type and magnitude of the residual stress obtained from X-ray and micro-Raman measurements agreed well only for undoped film, disagreeing when the doping level increased. We attributed this discrepancy to the domain size characteristic of each technique.

Dispersion liquid properties for efficient seeding in CVD diamond nucleation enhancement

Abstract We investigated diamond seeding as an efficient method of enhancing the nucleation density in chemical vapor deposition (CVD) diamond growth. We prepared substrates by ultrasonification for a short time in a 0.25 m diamond powder suspension and studied the effects of several dispersion liquids on seeding. We identified five key liquid properties for efficient seeding: zero or low dipole moment, low density, high vapor pressure, low surface tension and low viscosity. n-Hexane and n-pentane are the most suitable liquids, and yield seeding at the limit of the powder grit. We also observed the phenomenon of chemical consolidation of diamond particles onto silicon substrates during the initial growth stages. This consolidation ensures film adherence comparable with that obtained by other methods of nucleation enhancement.

Fast Preparation of Hydroxyapatite/Superhydrophilic Vertically Aligned Multiwalled Carbon Nanotube Composites for Bioactive Application

A method for the electrodeposition of hydroxyapatite films on superhydrophilic vertically aligned multiwalled carbon nanotubes is presented. The formation of a thin homogeneous film with high crystallinity was observed without any thermal treatment and with bioactivity properties that accelerate the in vitro biomineralization process and osteoblast adhesion.

Graphene and carbon nanotube nanocomposite for gene transfection

Graphene and carbon nanotube nanocomposite (GCN) was synthesised and applied in gene transfection of pIRES plasmid conjugated with green fluorescent protein (GFP) in NIH-3T3 and NG97 cell lines. The tips of the multi-walled carbon nanotubes (MWCNTs) were exfoliated by oxygen plasma etching, which is also known to attach oxygen content groups on the MWCNT surfaces, changing their hydrophobicity. The nanocomposite was characterised by high resolution scanning electron microscopy; energy-dispersive X-ray, Fourier transform infrared and Raman spectroscopies, as well as zeta potential and particle size analyses using dynamic light scattering. BET adsorption isotherms showed the GCN to have an effective surface area of 38.5m(2)/g. The GCN and pIRES plasmid conjugated with the GFP gene, forming π-stacking when dispersed in water by magnetic stirring, resulting in a helical wrap. The measured zeta potential confirmed that the plasmid was connected to the nanocomposite. The NIH-3T3 and NG97 cell lines could phagocytize this wrap. The gene transfection was characterised by fluorescent protein produced in the cells and pictured by fluorescent microscopy. Before application, we studied GCN cell viability in NIH-3T3 and NG97 line cells using both MTT and Neutral Red uptake assays. Our results suggest that GCN has moderate stability behaviour as colloid solution and has great potential as a gene carrier agent in non-viral based therapy, with low cytotoxicity and good transfection efficiency.

Effect of ultrasound irradiation on the production of nHAp/MWCNT nanocomposites

Large amounts of nanohydroxyapatite (nHAp)-multiwall carbon nanotube (MWCNT) nanocomposites are produced by two different aqueous precipitation methods. The ultrasonic irradiation (UI) and slow-drip addition under continuous magnetic stirring (DMS) methods were used to investigate the precipitation of nHAp acicular crystals. Calcium-nitrate, diammonium hydrogen phosphate, and ammonium hydroxide were used as precursor reagents. Superhydrophilic MWCNT were also employed. XPS analysis evidences that the functionalized MWCNTs are composed of 18 to 20 at.% of oxygen and that this property influences the nHAp formation. The high surface area of the MWCNT decreases the mean free path of ions, favoring the nHAp formation assisted by UI. The crystallinity was evaluated using the Scherrer equation. Semi-qualitative energy dispersive spectroscopy (EDS) analysis showed that the main components of HAp powders were calcium and phosphorus in the ratio Ca/P around of 1.67. Bioactivity properties of the nHAp/MWCNT-UI nanocomposites could be evaluated after 14 days soaking in simulated body fluid medium. Scanning electron microscopy, EDS, Fourier transform infrared attenuated total reflection spectroscopy, and X-ray diffraction techniques proved that the apatites formed on the surface and to points that the nHAp/MWCNT-UI have potential biological applications.

Biomineralization of Superhydrophilic Vertically Aligned Carbon Nanotubes

Vertically aligned carbon nanotubes (VACNT) promise a great role for the study of tissue regeneration. In this paper, we introduce a new biomimetic mineralization routine employing superhydrophilic VACNT films as highly stable template materials. The biomineralization was obtained after VACNT soaking in simulated body fluid solution. Detailed structural analysis reveals that the polycrystalline biological apatites formed due to the -COOH terminations attached to VACNT tips after oxygen plasma etching. Our approach not only provides a novel route for nanostructured materials, but also suggests that COOH termination sites can play a significant role in biomimetic mineralization. These new nanocomposites are very promising as nanobiomaterials due to the excellent human osteoblast adhesion.

Cutting characteristics of dental diamond burs made with CVD technology

The aim of this study was to determine the cutting ability of chemical vapor deposition (CVD) diamond burs coupled to an ultrasonic dental unit handpiece for minimally invasive cavity preparation. One standard cavity was prepared on the mesial and distal surfaces of 40 extracted human third molars either with cylindrical or with spherical CVD burs. The cutting ability was compared regarding type of substrate (enamel and dentin) and direction of handpiece motion. The morphological characteristics, width and depth of the cavities were analyzed and measured using scanning electron micrographs. Statistical analysis using the Kruskal-Wallis test (p < 0.05) revealed that the width and depth of the cavities were significantly greater when they were prepared on dentin. Wider cavities were prepared when the cylindrical CVD bur was used, and deeper cavities resulted from preparation with the spherical CVD bur. The direction of handpiece motion did not influence the size of the cavities, and the CVD burs produced precise and conservative cutting.

Efficiency study of perforated diamond electrodes for organic compounds oxidation process

Abstract The electrochemical oxidation of organic compound by bulk electrolysis has been analyzed for diamond electrodes used as anode. Boron-doped diamond thin films were grown on titanium alloy substrates (Ti6Al4V) with a geometric area of 12.2 cm 2 at 870 K and at 6.5×10 3 Pa. By using hot filament chemical vapor deposition technique and perforated and non-perforated substrates, the films were grown in both sample sides. The electrodes were characterized from their electrochemical behavior as a function of film quality, morphology and surface area, for boron concentrations of approximately 10 18 /cm 3 . The electrode performance was determined by cyclic voltammetry measurements in acid and neutral solutions and the reversibility behavior of the Fe(CN) 6 3−/4− at the Ti6Al4V/diamond electrode were also studied. High performance liquid chromatography (HPLC) and total organic carbon (TOC) techniques were used to study the oxidation products. These techniques are important to quantify the different compounds in the oxidation process steps permitting to observe the diamond electrodes efficiency. The results have shown a TOC decrease of approximately 85% and for HPLC it was observed almost complete phenol combustion to CO 2 . Scanning electron microscopy and Raman scattering spectroscopy were also used for morphology and diamond quality evaluation, respectively.