There are currently a variety of applications for multiwalled carbon nanotubes (MWCNTs), but considerable concerns exist regarding their release into the environment. Their potential accumulation by aquatic organisms could lead to transfer throughout food chains. Considering the divergences in experimental data published on the ecotoxicity of carbon nanotubes, further research is required. The dispersion of MWCNTs in aqueous culturing media of organisms as well as the determination of concentrations are relevant aspects to obtain accurate ecotoxicity results. Ultraviolet-visible spectroscopy is one of the most reported techniques to analyze concentration quickly and economically, but the methodologies to prepare dispersions and selecting the wavelengths for ultraviolet-visible measurements have not yet been clearly defined. The present study demonstrates that dispersion procedures influence absorbance, and an approach to determine the most appropriate measurement wavelength is proposed. Ecotoxicity tests with MWCNTs were performed on Vibrio fischeri bacteria, and divergences in the results were observed with respect to those previously reported. The present study contributes to the attempt to overcome the lack of standardization in the environmental assessment of MWCNTs.
Summary: Polyamide 6 (PA6)/multiwall carbon nanotubes (MWCNTs) nanocomposites have been prepared by an extrusion process assisted by ultrasounds. The ultrasounds system has been incorporated at the extrusion die, when the material is flowing through the exit channel. The application of an ultrasound field to a polymer melt has been shown a very efficient method to improve productivity of the process. When ultrasounds are applied, the extrudate flow is highly enhanced maintaining the same processing conditions. In addition, the ultrasounds contribute to the deagglomeration of CNTs into the matrix, as can be conclude from the drop in the electrical resistivity values of the nanocomposites observed when ultrasounds are applied. For the system PA6/MWCNT 7wt%., the electrical resistivity increases three orders of magnitude when ultrasounds are employed during the extrusion. In addition, a high reduction in the electrical percolation index is obtained for nanocomposites extrudated by the assistance of ultrasounds.
Heterogeneous Fenton/photo Fenton type processes using a Fe-exchanged zeolite of Y-type have been applied for the degradation of a model textile synthetic water based on Black B azodye. Research work has been directed to compare process efficiency and to establish their advantages over corresponding homogenous Fenton type processes. By optimizing the amount of reactants and process conditions, a complete decolorization of the effluent and a reduction greater than 80 per cent in the total organic carbon content is achieved. The influence of solar radiation on the heterogeneous process has been also studied. Homogeneous and heterogeneous Fenton processes yielded similar decolorization and mineralization, but the concentration of Fe ions in the bulk after the treatment was not significant in the latter case. Moreover, the catalyst support can be reused in successive cycles without significant loss of effectiveness. The use of solar radiation as a source of energy for operating the process accelerates the decomposition of azodye, making the process economical and environmentally sustainable.
During operations using biodegradable oil for lubrication, the chemical structure of the biolubricant changes and, as a consequence, its biodegradability tends to decrease. Despite the fact that the biodegradability of most of the fresh biodegradable oils has been well determined, the monitoring of the biodegradability of oil during its aging has not been studied. Thus, the development of a monitoring method for on-line measuring of lubricant biodegradability could provide a significant advance in lubrication and environmental management. In the present paper, the prediction of the biodegradability of a lubricant by means of near infrared (NIR) spectroscopy combined with advanced statistical techniques like PLS is presented. Three fully formulated ester oils and a biodegradable base oil without additives were selected for performing laboratory oxidation in a batch reactor at 140ºC using an air flux and aided by mechanical stirring.During the aging process of the oils, 35 aliquots were sampled at different degradation times, in order to build a mathematical model which allowed the biodegradability of oil to be predicted.
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