Rodrigo L. Lavall

Layer-by-layer assembled films of multi-walled carbon nanotubes with chitosan and cellulose nanocrystals

Chitosan solutions and cellulose nanocrystal suspensions were used to produce highly stable aqueous dispersions of multi-walled carbon nanotubes (MWCNTs). The different MWCNT dispersions, presenting positive and negative charges, were used to prepare multilayered hybrid thin films through electrostatic layer-by-layer (LBL) self-assembly. The MWCNTs are well dispersed and homogeneously distributed on each layer of chitosan and cellulose nanocrystals of the films. The nanotubes are densely packed in each multilayer, forming a random network. The surface of the LBL film exhibited a uniform and relatively smooth surface with a mean roughness value of ∼5.8±0.4nm. Electrochemical characterization revealed a decrease in two orders of magnitude in the film resistance as the number of bilayers increased from 5 to 20, which is a consequence of an increase in the amount of conductive material (MWCNT). The thin films with up to 20 bilayers exhibited transmittance higher than 90% in the visible range. The results presented in this work demonstrate the viability of the LBL technique for the deposition of active materials using the biopolymer pair chitosan/cellulose nanocrystals. The obtained films can be employed for the design of transparent and biocompatible carbon nanostructured based electrodes.

NANOCOMPÓSITOS DE POLIURETANA TERMOPLÁSTICA E NANOTUBOS DE CARBONO DE PAREDES MÚLTIPLAS PARA DISSIPAÇÃO ELETROSTÁTICA

Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 μm length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT.

Otimização do processo de dispersão de nanotubos de carbono em poliuretano termorrígido

Neste trabalho foi desenvolvido um processo empregando misturador de alto cisalhamento e moinho de rolos para dispersar MWCNTs (multiwalled carbon nanotubes) puros e modificados em poliol visando a preparacao de concentrados de 3% em massa. Condicoes otimizadas no trabalho permitiram a obtencao de suspensoes com menor numero e tamanho de agregados de MWCNTs. Compositos contendo 0,5% em massa de MWCNTs foram preparados por diluicao dos concentrados em poliol usando mistura mecânica seguida de cura. Resultados de microscopia indicaram que as melhores dispersoes foram obtidas com os MWCNTs modificados, os quais permitiram um aumento na tensao na ruptura, no alongamento e uma melhor preservacao da estabilidade termica. Alem disso, valores de condutividade eletrica sugerem que o composito possa ser empregado para dissipacao eletrostatica. Dessa forma, os resultados obtidos demonstram que a modificacao covalente da superficie dos MWCNTs e a utilizacao de estrategias eficientes de dispersao sao essenciais para melhorar as propriedades finais dos nanocompositos.

Tailored Degree of Functionalization and Length Preservation of Multiwalled Carbon Nanotubes by an Optimized Acid Treatment Process

The introduction of oxygen groups in carbon nanotubes is considered crucial for many applications. However, there is a lack of controlled functionalization methods which ensure nanotubes with specific property values according to each interest. In this work, acid treatments of multiwalled carbon nanotubes (MWCNTs) employing an optimized ultrasound process with moderate heating and stirring were studied by means of a factorial design. The functionalized nanotubes were characterized by thermogravimetry, elemental analysis, Raman spectroscopy, electron microscopy and water stability tests. Statistic models were fitted for the degree of functionalization and length reduction of MWCNTs. Temperature was identified as a key parameter to produce more functionalized MWCNTs with less structural damage. The properties of the functionalized MWCNTs can be tailored by the choice of parameters exploited in the statistical models developed to enable different end-use requests, such as for polymeric composites or biorelated applications, which is the original contribution of this work.

Use of Biodiesel Press Cake Waste to Prepare Fe/Carbon Reactive Composites for Environmental Applications: Removal of Hazardous CrVI Contaminants

In this work, Ricinus communis L. press cake waste from biodiesel production was used to produce a versatile reactive material for environmental applications. The biodiesel cake waste was impregnated with FeIII at different concentrations (19-45 wt.%) and treated at 400, 600 and 800 °C. Mossbauer, X-ray diffraction (XRD), thermogravimetric analysis (TG/DTA), scanning electron microscope (SEM), elemental analysis CHN, Raman, potentiometric titration, saturation magnetization and Brunauer-Emmett-Teller (BET) analyses showed that the materials prepared at 400 °C are composed mainly of a graphitic and amorphous carbon containing dispersed magnetite (Fe3O4). At higher temperatures, metallic iron (Fe0) and iron carbide (Fe3C) are the predominant phases well dispersed in the carbon porous structure. These reduced iron species, Fe3O4 and Fe0, are active for the reduction of different hazardous contaminants. Preliminary experiments showed very high activities for the reduction and removal of aqueous CrVI.

MELHORIA DA QUALIDADE DE TIJOLOS CERÂMICOS ATRAVÉS DA INCORPORAÇÃO DE LODO DE ESTAÇÕES DE TRATAMENTO DE ÁGUA

Sludge from water treatment units was incorporated into clay in order to produce bricks with enhanced performance on mechanical properties. The residue can be potentially reused due to mineral similarity with clay. Powder X-ray diffraction and FT-IR spectroscopy revealed that the main constituents of sludge and clay are mainly related to quartz, kaolinite, gibbsite and muscovite. Thermogravimetry assays showed good similarity on decomposition profiles, although the ash content after calcination at 1000oC was for the sludge samples. Uppon addition of 10 to 15 % of sludge, values of compressive strength and water absorption index values reached acceptable limits, whilst the performance of pureclay bricks performance was off-graded. These results demonstrate a potential recyclability of sludge in structural ceramic bricks, not only to comply with minimization of environmental impact but also to increase quality and market price of these products.