A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT) was performed. The influence of ultrasonic cavitation and solid/liquid interface was indirectly evaluated by statistical characterization of MWCNT aspect ratio and degree of functionalization. MWCNT aspect ratio was determined through hundreds of electron microscopy images. Degree of functionalization of MWCNT was characterized by elemental analysis and thermogravimetry. Distribution of different oxygen-containing functional groups was assessed by potentiometric titration. MWCNT aqueous dispersions were evaluated by electrophoretic mobility and dynamic light scattering. An acid volume over 90% lower than usually reported in literature guaranteed MWCNTs with significantly larger aspect ratio, higher proportion of carboxylic groups and a more negative zeta potential in aqueous suspension. These results can be related to a more localized ultrasonic cavitation in MWCNTs/acid interface for reduced liquid volumes. This distinguished influence of ultrasonic cavitation may be a valuable contribution to more eco-friendly processes with nanomaterials.

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 bio-related applications, which is the original contribution of this work.

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. Mössbauer, 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.

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.

The fact that alpha- and beta-chitin adopt different arrays in the solid state is explored to emphasize their different properties and distinct spectral characteristics and X ray diffraction patterns. The methods for their extraction from the biomass in view of the preservation of their native structures and aiming to fulfill the claims of purity and uniformity for potential applications are discussed. The different arrays adopted by alpha- and beta-chitin also result in distinct reactivities toward the deacetylation reaction. Thus, the deacetylation of beta-chitin is more efficient owing to the better accessibility to amide groups due to the lower crystallinity of this polymorph.