Carlos Perez Bergmann

Adsorption of Reactive Red M-2BE dye from water solutions by multi-walled carbon nanotubes and activated carbon

Multi-walled carbon nanotubes and powdered activated carbon were used as adsorbents for the successful removal of Reactive Red M-2BE textile dye from aqueous solutions. The adsorbents were characterised by infrared spectroscopy, N(2) adsorption/desorption isotherms and scanning electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium at 298K was fixed at 1h for both adsorbents. The activation energy of the adsorption process was evaluated from 298 to 323K for both adsorbents. The Avrami fractional-order kinetic model provided the best fit to the experimental data compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. For Reactive Red M-2BE dye, the equilibrium data were best fitted to the Liu isotherm model. Simulated dyehouse effluents were used to check the applicability of the proposed adsorbents for effluent treatment.

Environmental and technical aspects of the utilisation of tannery sludge as a raw material for clay products

This paper is a report on the results of a feasibility study on the immobilisation of tannery sludge by producing a ceramic product. The main purpose of this work was to test the clays used in the manufacture of a ceramic that could incorporate tannery sludge. The raw materials, tannery sludge and clay, were mixed together in different proportions. The ceramic specimens were characterised with respect to water absorption, porosity, linear shrinkage and transverse rupture strength. Leaching tests, in accord with the Brazilian and German regulations, were done on ceramic bodies made with different additions of sludge. In order to evaluate the possibility of air contamination during the firing process, preliminary studies of air emissions were carried out The mechanical properties of the samples evaluated were similar to those specified for ceramic bricks. All the leaching tests have shown that the main sludge contaminant i.e. chromium, could be immobilised within a finished ceramic product. The studies of air emissions have shown that zinc and chlorine are mainly collected from gas emissions and hence are not immobilised by the ceramic system. The study shows that the properties of the ceramic materials produced are acceptable for applications such as bricks for the building industry.

Thin, conductive, carbon nanotube networks over transparent substrates by electrophoretic deposition

A new method was developed for deposition of carbon nanotube networks (CNTNs) over transparent and electrically non-conductive substrates. This method allows the deposition of functionalized or surfactant-stabilized carbon nanotubes dispersed in water. The nanotube films can be applied over complex geometries, on non-conductive rigid or flexible substrates and over large areas in a continuous manner. The carbon nanotube films are deposited by electrophoretic deposition (EPD) using a thin film layer of conductive metal, such as aluminium or titanium. The metal layer oxidizes during the EPD, becoming transparent. The carbon nanotube films can be easily patterned using this technique.

The addition of nanostructured hydroxyapatite to an experimental adhesive resin

OBJECTIVES Was produced nanostructured hydroxyapatite (HAnano) and evaluated the influence of its incorporation in an adhesive resin. METHODS HAnano was produced by a flame-based process and was characterized by scanning electron microscopy. The surface area, particle size, micro-Raman and cytotoxicity were evaluated. The organic phase was formulated by mixing 50 wt.% Bis-GMA, 25 wt.% TEGDMA, and 25 wt.% HEMA. HAnano was added at seven different concentrations: 0; 0.5; 1; 2; 5; 10 and 20 wt.%. Adhesive resins with hydroxyapatite incorporation were evaluated for their radiopacity, degree of conversion, flexural strength, softening in solvent and microshear bond strength. The data were analyzed by one-way ANOVA and Tukeys post hoc test (α=0.05), except for softening in solvent (paired t-test) and cytotoxicity (two-way ANOVA and Bonferroni). RESULTS HAnano presented 15.096 m(2)/g of specific surface area and a mean size of 26.7 nm. The radiopacity values were not different from those of 1-mm aluminium. The degree of conversion ranged from 52.2 to 63.8%. The incorporation of HAnano did not influence the flexural strength, which ranged from 123.3 to 143.4MPa. The percentage of reduction of the microhardness after immersion in the solvent became lower as the HAnano concentration increased. The addition of 2% nanostructured hydroxyapatite resulted in a higher value of microshear bond strength than the control group (p<0.05). CONCLUSIONS The incorporation of 2% of nanostructured hydroxyapatite into an adhesive resin presented the best results. CLINICAL SIGNIFICANCE The incorporation of nanostructured hydroxyapatite increases the adhesive properties and may be a promising filler for adhesive resin.

Niobium pentoxide as a novel filler for dental adhesive resin.

OBJECTIVES The purpose of this study was to develop an adhesive resin with incorporation of niobium pentoxide and evaluate its properties. METHODS Niobium pentoxide was characterised by X-ray diffraction, surface area, particle size, micro-Raman, scanning electron microscopy and the effectiveness of silanisation process by Fourier Transform Infrared (FTIR). An experimental adhesive resin was formulated with 0, 5, 10 and 20wt% Nb(2)O(5). The formulated adhesive resins were evaluated based on microhardness, degree of conversion, radiopacity and interface (resin/dentine) characterisation by micro-Raman. RESULTS The particles used in this study presented a monoclinic crystalline phase with typical chemical groups and micrometre mean size. Microhardness and radiopacity increased with higher amounts of Nb(2)O(5), and the particles were able to penetrate into the hybrid layers. CONCLUSIONS Therefore, Nb(2)O(5) may be an alternative for polymer-based biomaterials. CLINICAL SIGNIFICANCE Niobium pentoxide could be used to produce adhesive resins with enhanced properties.

Nanostructured hydroxyapatite as filler for methacrylate-based root canal sealers.

AIM   To evaluate the effect of different concentrations of nanostructured hydroxyapatite on the radiopacity, flow and film thickness of an experimental root canal sealer. METHODOLOGY   An experimental dual-cured root canal sealer was produced with a methacrylate-based co-monomer blend. Nanostructured hydroxyapatite/calcium tungstate solutions (ratios 10:90, 20:80, 30:70 and 40:60) were added to produce the sealer. Radiopacity was evaluated using a digital system and an aluminium step wedge (n=5). Flow and thickness tests were conducted in accordance with ISO 6876 (n=3). The data were analysed using one-way anova and Tukeys test (α=0.05). RESULTS   All groups had levels of radiopacity in accordance with ISO 6876. The flow of the experimental sealers was not significantly different (P=0.204). All groups had a film thickness in accordance with ISO 6876 and with no statistical difference (P = 0.654). CONCLUSION The addition of up to 40% HA(nano) to root canal sealers did not alter their radiopacity and film thickness.

Recycling of iron foundry sand and glass waste as raw material for production of whiteware

The purpose of this study was to evaluate the production feasibility of triaxial whiteware using sand from cast iron moulds as a raw material instead of silica, and recycled glass in place of feldspar. Formulations were prepared using sand, glass waste, and white-firing clay such that only 50% of the composition was virgin material (clay). The ceramic bodies were formed by pressing and fired at different temperatures (between 1100 and 1300°C). Specimens were characterized in terms of green density prior to firing; and their flexural strength, linear shrinkage, and water absorption were measured after firing. The microstructure was determined by scanning electron microscopy. Possible environmental impacts of this recycling process were also evaluated, through solubility and leaching tests, according to Brazilian standards. Gaseous emissions during the firing process were also analysed. The results showed that it is possible to produce triaxial ceramics by using such alternative raw materials.

Vitrification: an alternative to minimize environmental impact caused by leather industry wastes.

The main purpose of this work was the investigation of the immobilization of chromium ion present in the ash from the incineration of chromium-tanned leather shavings (ACS) by means of vitrified ceramic bodies. To achieve the immobilization samples were initially produced adding soda-lime glass to ACS. After that, new formulations were produced with the addition of pure oxides, TiO(2) and MgO, to the soda-lime glass and ACS sample. These samples were conformed by pressing and fired in an eletrical furnace, at temperatures of 750, 800, 950 and 1000 degrees C. The ceramic bodies were evaluated with respect to their physical properties and mineralogical composition by X-ray diffraction and energy dispersive spectroscopy (EDS) mapping. The chromium immobilization was characterized by leaching tests according to Brazilian Regulations (NBR 10005). The results confirmed the immobilization of the chromium ion within the allowed limits of Brazilian Regulations, NBR 10004 (5mg/L), with the use of glass and vitrification/densification agents such as titanium and magnesium oxides.

Nanostructured materials for engineering applications

1 INTRODUCTION 2 NANOMATERIALS PROPERTIES 3 NANOMAGNETIC MATERIALS 4 OPTOELECTRONIC AND FERROELECTRIC APPLICATIONS 5 NANOSTRUCTURED MATERIALS FOR ENERGY APPLICATIONS 6 MATERIALS FOR BIO-APPLICATIONS 7 NANOMATERIALS AND CATALYSIS 8 NANOREINFORCEMENTS FOR NANOCOMPOSITE MATERIALS 9 NANOMATERIALS FOR APPLICATIONS IN REFRACTORY MATERIAIS 10 MATERIALS FOR ADSORBENT APPLICATIONS 11 USE OF NATURAL AND MODIFIED NATURAL NANOSTRUCTURED MATERIALS

Electrospun TiO2 Fiber Composite Photoelectrodes for Water Splitting

This work has focused on the development of electrospun TiO2 fiber composite photoelectrodes for hydrogen production by water splitting. For comparison, similar photoelectrodes were also developed using commercial TiO2 (Aeroxide P25) nanoparticles (NPs). Dispersions of either fibers or P25 NPs were used to make homogenous TiO2 films on fluorine-doped SnO2 (FTO) glass substrates by a doctor blade (DB) technique. Scanning electron microscopy (SEM) analysis revealed a much lower packing density of the DB fibers, with respect to DB-P25 TiO2 NPs; this was also directly reflected by the higher photocurrent measured for the NPs when irradiating the photoelectrodes at a light intensity of 1.5AM (1 sun, 1000 W/m(2)). For a better comparison of fibers vs. NPs, composite photoelectrodes by dip-coating (onto FTO) TiO2 sol-gel (SG) matrixes containing an equal amount (5 or 20 wt %) of either fibers or P25 NPs were also investigated. It emerged that the photoactivity of the fibers was significantly higher. For composites containing 5 wt % TiO2 fibers, a photocurrent of 0.5 mA/cm(2) (at 0.23 V vs Ag/AgCl) was measured, whereas 5 wt % P25 NPs only provided 0.2 mA/cm(2). When increasing to 20 wt % fibers or NPs, the photocurrent decreased, because of the formation of microcracks in the photoelectrodes, because of the shrinkage of the sol-gel. The high photoactivity of the fiber-based electrodes could be confirmed by incident photon to current efficiency (IPCE) measurements. Remarkably, the IPCE of composites containing 5 wt % fibers was between 35% and 40% in the region of 380-320 nm, and when accounting for transmission/reflection losses, the absorbed photon to current efficiency (APCE) was consistently over 60% between 380 nm and 320 nm. The superior photoactivity is attributed to the enhanced electron transport in the electrospun fibers, with respect to P25 NPs. According to this study, it is clear that the electronic connectivity ensured by the sol-gel also contributes positively to the enhanced photocurrent.