Marcelo Giovanela

Characterization of Microwave-Devulcanized Composites of Ground SBR Scraps

The recycling of waste rubber has considerable significance in terms of environmental protection and energy conservation. Considering that most of the relevant literature is concerned with tire recycling, the objective of this study is to develop and characterize styrene-butadiene rubber composites containing only industrial rubber scraps devulcanized by microwave. The styrene-butadiene rubber extruded profile scraps were collected and ground under ambient conditions. The obtained powder styrene-butadiene rubber-r was physically, thermally, and chemically characterized. From the devulcanized styrene-butadiene rubber-r two composites were prepared, varying the exposure time of the powder in the microwave (3 and 4 min). These composites were compared to a control sample supplied by the industry from which the styrene-butadiene rubber extruded profile scraps were collected. Vulcanization parameters were determined by oscillatory disk rheometry. Vulcanized composites were characterized by crosslink density and physical-mechanical properties (Shore A hardness, tensile and tear strength, and compression set) before and after a postcure process. The mechanical properties of the compositions were ∼25% for tensile strength and 41% for tear strength compared to the control sample. The results for the crosslink density verified those for the mechanical properties of the composites.

Nonionic organoclay: A ‘Swiss Army knife’ for the adsorption of organic micro-pollutants?

A Na exchanged montmorillonite (Mt) was used as a starting layered material for the preparation of two organoclays synthesized with benzyl decyltrimethyl ammonium (BDTA) cationic surfactant and the tri-ethylene glycol mono n-decyl ether(C10E3), a nonconventional nonionic surfactant. The adsorption of the surfactants was performed at an amount of 0.7 times the cation exchange capacity (CEC) for BDTA and below the critical micelle concentration (cmc) where C10E3 is in a monomer state, leading to the intercalation of a lateral monolayer surfactant arrangement within the interlayer space and about 5-7% organic carbon content in organoclays. The environmental properties of both nonionic (C10E3Mt) and cationic (BDTAMt) organoclays were compared to those of the starting Mt clay with the sorption of three micro-pollutants: benzene, dimethyl-phthalate and paraquat. The adsorption isotherms and the derivative data determined through the fitting procedure by using Langmuir, Freundlich and Dubinin-Radushkevitch equation models explicitly highlighted the importance of the chemical nature of the micropollutants, which play on the adsorbents efficiency. The adsorption data combined with FTIR and XRD supplementary results suggest that C10E3Mt nonionic organoclay, although being less efficient for the retention of the different micropollutants, turned out to be the most polyvalent adsorbent since such hybrid material could adsorb the entire studied organic compounds.

3D-fluorescence spectroscopic analysis of HPLC fractionated estuarine fulvic and humic acids

Seis amostras de acidos fulvicos (AF) e humicos (AH) estuarinos foram fracionadas por meio de cromatografia liquida de alta performance em fase reversa, num gradiente de polaridade agua → acetonitrila, com deteccao por fluorescencia. Diferencas entre os cromatogramas mostraram que os AH contem mais componentes hidrofobicos que os AF. Os espectros de fluorescencia tridimensional das fracoes foram bastante similares entre si e tambem ao da amostra original, indicando que, apesar das polaridades distintas, a complexidade e as principais caracteristicas do material original se mantem. Um mesmo grupo de fluoroforos parece ser responsavel pelas caracteristicas de fluorescencia, dos dois tipos de substâncias humicas. Um deslocamento batocromico dos espectros de emissao das solucoes originais, com relacao aqueles das fracoes, foi atribuido a uma maior proximidade destes fluoroforos, possivelmente devido a formacao de agregados. Em geral, os resultados confirmam o conceito de que as “macromoleculas” humicas consistem de associacoes de estruturas menores com caracteristicas quimicas semelhantes. Six estuarine fulvic (FA) and humic acids (HA) were fractionated with reversed-phase high performance liquid chromatography in a water/acetonitrile gradient, with fluorescence detection. Differences between FA and HA chromatograms pointed to a higher incidence of hydrophobic components in the latter. Excitation-emission matrix fluorescence diagrams of most fractions were similar to those of the bulk samples indicating that, in spite of their distinct polarities, the complexity and main spectral characteristics of the materials persisted. A primary group of fluorophores, which are present in most of the fractions, seems to be at the origin of the fluorescence properties of both kinds of HS. A bathochromic shift of the bulk solutions spectra in relation to the fraction emissions was attributed to a greater proximity of these fluorophores, possibly due to the formation of aggregates. Generally, the results reinforced concepts that humic macromolecules consist of assemblages of structurally similar building blocks.

Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions.

Among pharmaceutical products (PPs) recalcitrant to water treatments, diclofenac shows a high toxicity and remains at high concentration in natural aquatic environments. The aim of this study concerns the understanding of the adsorption mechanism of this anionic PP onto two organoclays prepared with two long-alkyl chains cationic surfactants showing different chemical nature for various experimental pH and temperature conditions. The experimental data obtained by a set of complementary techniques (X-ray diffraction, elemental analyses, gas chromatography coupled with mass spectrometry, and Fourier transform infrared spectroscopy) and the use of Langmuir, Freundlich and Dubinin-Radushkevish equation models, reveal that organoclays show a good affinity to diclofenac which is enhanced as the temperature is under 35°C and for pH above 4.5 (i.e. >pKa of diclofenac) while the chemical nature of surfactant appears to play a minor role. The thermodynamic parameters derived from the fitting procedure point out the strong electrostatic interaction with organic cations adsorbed within the interlayer space in the organoclays for the adsorption of diclofenac. This study stress out the application of organoclays for the adsorption of a recalcitrant PPs in numerous aquatic compartments that can be used as a complement with activated carbon for waste water treatment.

Remoção dos hormônios 17β-estradiol e 17α-etinilestradiol de soluções aquosas empregando turfa decomposta como material adsorvente

This paper describes the adsorption of 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) from aqueous solution by decomposed peat. The peat presented a good adsorption process, close to 76.2% for E2 removal and approximately 55.0% for EE2. Moreover, the results indicated a probable multi-layered process. Adsorption isotherms were well fitted by Freundlich model. The data were evaluated considering the pseudo-first-order and pseudo-second-order approaches, being the second more significant mechanism in the rate-controlling step. Thermodynamic data revealed that hormones adsorption onto peat is spontaneous under the employed experimental conditions. The results confirmed the potential of this adsorbent to be employed for effluents treatment.

Nutrient contents in bottom sediment samples from a southern Brazilian microbasin

The nutrients, carbon, nitrogen and phosphorus, significantly affect the quality of aquatic environments, especially when present at concentrations above natural levels. In this context, the sedimentary column can act as an environment for storage or accumulation of these nutrients and for the reprocessing of such substances in the water column and aquatic biota. In this context, this study aimed to estimate the concentration of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), inorganic phosphorus (IP) and organic phosphorus (OP) in seven sediment samples that were collected from the Marrecas Stream microbasin (Caxias do Sul, Rio Grande do Sul State, Brazil). The relationships among the sediment nutrient concentrations and the levels of organic matter (OM), fine material (silt–clay) and the concentration of the metal species, Al, Fe and Mn, as well as the possible nutrient sources to the stream studied were also evaluated. The data set suggest that the TOC and IP appear to have a direct correlation with the vast riparian vegetation present in areas adjacent to the sampling points and to the physico-chemical properties of the water and sedimentary column. Moreover, the results obtained for TN suggest that its concentration possibly suffers interference from the temperature of the water and its oxygenation, in addition to other biological activities. On the other hand, one cannot rule out human interference, mainly in the levels of OP, possibly due to the inflow of domestic sewage to the stream.

Fluorescence properties of well-characterized sedimentary estuarine humic compounds and surrounding pore waters.

Structural and spectroscopic properties of sedimentary estuarine humic compounds (HC) and surrounding pore waters were investigated. Elemental analysis showed that sedimentary HC exhibit a molecular design compatible with a mixed continental-marine environment. In some respects, they are well correlated with the marine organic matter (e.g. low C/H ratio), while in others they are better associated to terrestrial material (e.g. high C/N ratio). High rates of microbiological activity, combined with a tide-dependent contribution of an aliphatic marine-like source of organic matter, may account for such results. Chemical anomalies were not observed in samples from polluted sites, indicating that moderate anthropogenic disturbances will affect chemical processes related to humic compounds rather than their chemical design. With respect to fluorescence properties, sedimentary humus exhibits a single and wide emission peak (λex = 313 nm), with λmax ∼ 431 nm for fulvic acid and λmax ∼ 446 nm for humic acids. For humic acids a shoulder at around 515 nm is also observed. HC corrected excitation spectra (λem = 445 nm) are similar to those previously observed for HC from aquatic environments, presenting two peaks of variable intensities, the first being more intense, located around 250 nm, and the second located in the range 320-350 nm. Pore waters extracted from the same sediment samples as those of HC exhibited fluorescence properties comparable to that of fulvic acids but exhibiting emission maxima around 424 nm. The significance of hydrophilic substances in relation to the fluorescence properties of natural waters is discussed.

Potentiometric acidity determination in humic substances influenced by different analytical procedures

Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-Hasselbalch model (MHHM). In the case of IHSS samples, the fitting data depended on the analytical procedure undertaken. Whilst high CA and low PhA were usually recorded using the MHHM, the opposite trend was observed employing the BEST7 algorithm. In contrast, in the case of model compounds the acidity values matched well with theoretical data regardless of the procedure. In order to better understand the reasons for such discrepancies changes in the titrations procedure (e.g.: fast or slow) were also considered. General data strongly suggest that acidity determination of humic substances (HS) by potentiometric methods is extremely dependent on both the choice of mathematical model to fit experimental data points as well as the experimental conditions employed.

Bactericidal Performance of Chlorophyllin-Copper Hydrotalcite Compounds

Copper hydrotalcites with and without adsorbed chlorophyllin exhibit a bactericidal effect that depends on the copper release and the basicity, which can be tuned through the chlorophyllin adsorption. The prepared solids performed well for the elimination of Escherichia coli, Enterobacter aerogenes, Salmonella enterica, and Staphylococcus aureus bacteria. The results showed that the copper-containing hydrotalcite with the adsorbed chlorophyllin is the most active material. Wastewaters from a metal industry were treated with these hybrid compounds, and the bactericidal effect was comparable with the results reported using more complex methods such as photocatalysis. Furthermore, one main advantage of these hybrid compounds is its low human toxicity compared with silver-containing materials.

Removal of Congo red dye from aqueous solutions using a halloysite-magnetite-based composite

Adsorption has been considered as one of the most effective methods to remove dyes from aqueous solutions due to its ease of operation, high efficiency and wide adaptability. In view of all these aspects, this study aimed to evaluate the adsorption capacity of a halloysite-magnetite-based composite in the removal of Congo red dye from aqueous solutions. The effects of stirring rate, pH, initial dye concentration and contact time were investigated. The results revealed that the adsorption kinetics followed the pseudo-second-order model, and equilibrium was well represented by the Brunauer-Emmett-Teller isotherm. The thermodynamic data showed that dye adsorption onto the composite was spontaneous and endothermic and occurred by physisorption. Finally, the composite could also be regenerated at least four times by calcination and was shown to be a promising adsorbent for the removal of this dye.