Chemical and spectroscopic characterization of humic acids extracted from the bottom sediments of a Brazilian subtropical microbasin

International audienceHumic substances (HS) perform a fundamental role in aquatic environments, exhibiting different levels of reactivity in retaining metal ions and organic pollutants. Also, they control the primary production of these ecosystems and act in the carbon sequestering process. In order to improve our understanding vis-à-vis the structural and functional features of HS from aquatic systems, this study aimed to chemically and spectroscopically characterize humic acids (HA) isolated from bottom sediment samples of a stream in a Brazilian subtropical microbasin by elemental analysis, and infrared (FT-IR), ultraviolet and visible (UV-Vis) and solid-state 13C nuclear magnetic resonance (CP-MAS 13C NMR) spectroscopies, thermogravimetry (TG), and scanning electron microscopy (SEM). Although all samples originated from the same environment, the data showed that the HA have distinct chemical and spectroscopic properties, and that the location and characteristics of the sampling points from which the sediments were collected played an important role in the differences observed. Furthermore, vascular plant matter is probably the main contributor to these samples

Removal of the hormones 17β-estradiol and 17α-ethinylestradiol from aqueous solutions employing a decomposed peat as adsorbent material

REMOVAL OF THE HORMONES 17b-ESTRADIOL AND 17a-ETHINYLESTRADIOL FROM AQUEOUS SOLUTIONS EMPLOYING A DECOMPOSED PEAT AS ADSORBENT MATERIAL. This paper describes the adsorption of 17b-estradiol (E2) and 17a-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

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

Avaliação do Ensino de Empreendedorismo entre Estudantes Universitários por meio do Perfil Empreendedor

Entrepreneurship is a socioeconomic phenomenon that has been valued for its influence on the growth and development of regional and national economies. The main promoter of this phenomenon are entrepreneurs, subjects endowed with multiple features that make up their profiles. They are dynamic and results oriented, benefitting from the fruits of their own personal efforts. Entrepreneurial education is highlighted as one of the most efficient ways to promote an entrepreneurial culture and train new entrepreneurs. However, some difficulty has been observed in assessing the effectiveness of teaching and learning this subject. The objective of this study was to analyze, by means of multivariate techniques, an instrument whose function is to measure the learning of Entrepreneurship, verifying the change in entrepreneur profiles of 407 college students participating or not in an entrepreneurial training process. The results showed that students who participated in Entrepreneurship educational training activities showed significant changes in their entrepreneurial profiles. The main contributions showed growth in the Self-realization, Planner, Innovative and Risks Assumed dimensions

Fluorescence fingerprint of fulvic and humic acids from varied origins as viewed by single-scan and excitation/emission matrix techniques

Excitation/emission matrix (EEM), single-scan excitation and synchronous fluorescence spectra of a series of FA and HA from distinct environments are presented. The EEM plots show at least four spectral features whose corresponding Ex/Em pairs relate to the α', α, β and γ (or δ) fluorophores previously found in natural waters spectra. The α' and α peaks, which identify typical humic-like components, are present in all samples, independently of the organic matter (OM) source. In FA, their Ex/Em pairs are ~260 nm/460 nm and ~310 nm/440 nm, respectively. In HA their excitation and emission maxima are red-shifted, the corresponding Ex/Em pairs being located at ~265 nm/525 nm and ~360 nm/520 nm, respectively. The appearance of β and γ (or δ) peaks is dependent both on the OM origin and on HS aging. The former (Ex/Em ~ 320 nm/430 nm), that has been associated with the incidence of marine humic-like material, is present only in a few marine and estuarine HA. It emerges as a shoulder on the α peak and its detection is dependent on a balance between its magnitude and the magnitude and emission maxima location of the α peak. The γ (or δ) peak (Ex/Em ~ 275 nm/315 nm in FA, and ~275 nm/330 nm in HA), on the other hand, is better visualized in FA than in HA diagrams. It has typical protein-, mainly tryptophan-like, fluorescence properties and appears with varied significance in a few marine and estuarine samples being hardly detected in samples from exclusively terrestrial environments. It is also shown in this study that with selected λex, λem and Δλ values, regular emission, excitation and synchronous spectra can, together, provide a good picture of the OM sources and aging for extracted HS. \textcopyright 2004 Elsevier Ltd. All rights reserved

Removal of methylene blue from aqueous solutions using a solid residue of the apple juice industry: full factorial design, equilibrium, thermodynamics and kinetics aspects

International audienceThe use of adsorbent materials derived from agro-industrial residues represents a simple, easy and low-cost process for the removal of dyes from aqueous solutions. In this context, this study aimed to evaluate the use of a solid residue from the apple juice industry in the removal of methylene blue (MB) dye. Several different analytical techniques, including elemental analysis, Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance, nitrogen adsorption/desorption and determination of pH at zero-point charge, were used to investigate the physico-chemical properties of the apple pomace. Conventional bath experiments were carried out by simultaneously optimizing five variables (initial MB concentration, amount of adsorbent, pH, stirring frequency and temperature) using a full 2k factorial design with central point. In general, the characterization analyses evidenced the presence of several types of oxygenated functional groups in the adsorbent chemical structure and a favorable morphology for dye removal. Furthermore, the initial MB concentration, the amount of adsorbent and the pH of the medium had the strongest effect on the response variables, including their interactions and quadratic terms. In terms of equilibrium, it was found that the Langmuir model gave a good fit to the data, while the thermodynamic parameters indicated that the process was spontaneous and exothermic in nature. Moreover, kinetic studies revealed that the MB removal rate followed a pseudo-second-order model, suggesting an adsorption controlled by either diffusion on the stagnant film covering the adsorbent particles or intraparticle diffusion. Finally, the data acquired in this study also emphasized the interest to use materials derived from agro-industrial residues as potential adsorbents in the light of its properties for the removal of basic dyes, including MB

Elemental compositions, FT-IR spectral and thermal behavior of sedimentary fulvic and humic acids from aquatic and terrestrial environments

Studies on elemental analysis, Fourier transform infrared spectroscopy (FT-IR) and thermal decomposition (thermogravimetry, TG; and derivative thermogravimetry, DTG) of sedimentary fulvic (FA) and humic acids (HA) from marine, estuarine, lacustrine and terrestrial environments are presented. In general, H/C and N/C atomic ratios, as well as the infrared spectra, reflected the extent of the influence of algal and/or terrestrial organic matter sources on the samples, the aquatic (both, marine and freshwater) humic substances (HS) being richer in nitrogen and more saturated, than terrestrial materials. Comparison of properties of FA and HA from the same parent sediments showed that the latter are relatively richer in nitrogen and unsubstituted aliphatic chains and poorer in carboxylic groups. FT-IR spectra showed that the nitrogen present is mostly as forming part of amide groups. Concerning thermal degradation, two main steps were observed for all samples: the first, relative to the loss of moisture, being located between 40°C and 100°C and the second between 270°C and 440°C. FT-IR spectra of the samples which had been heated to 90°C, 400°C and 900°C showed that, upon heating, the carboxyl content decreases (especially for FA), the aliphaticity decreases and the aromaticity increases (especially for HA), indicating that the 270°C-470°C degradation step might be related to decarboxylation and unsaturation losses. In spite of this, both kinds of HS, were shown to be highly thermo-resistant materials retaining most of their typical original infrared spectral features, even after being heated to 400°C. \textcopyright 2004 by The Geochemical Society of Japan

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

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