Fábio dos Santos Grasel

Bio: Fábio dos Santos Grasel is an academic researcher from Universidade Federal do Rio Grande do Sul. The author has contributed to research in topics: Acacia mearnsii & Fourier transform infrared spectroscopy. The author has an hindex of 8, co-authored 23 publications receiving 281 citations. Previous affiliations of Fábio dos Santos Grasel include Pontifícia Universidade Católica do Rio Grande do Sul.

A rapid and non-invasive method for the classification of natural tannin extracts by near-infrared spectroscopy and PLS-DA

Abstract: Vegetable tannins are plant extracts that have traditionally been used to tan leather. These extracts are polyphenolic compounds that are widely distributed in plants and have the ability to precipitate proteins since their structures are rich in hydroxyls. Tannins can be classified into two groups: the hydrolyzable tannins and the proanthocyanidins, also called condensed tannins. In this study, 49 samples of vegetable tannin extracts, representing six commercially available types, were analyzed by near infrared and multivariate analyses (HCA and PLS-DA). The first derivative of the NIR spectra proved useful in the differentiation of the extracts, as it provided information on the main absorption bands, which are related to the chemical composition and structure. A well-defined separation between condensed (quebracho and mimosa) and hydrolyzable tannins (tara, myrobalan, chestnut and valonea) was observed by HCA (unsupervised method). The PLS-DA supervised method showed excellent results regarding classification, with a sensitivity and specificity of 100%. From the results, we concluded that this method may be useful for the quality control of commercial tannins and correct identification, as well as in mitigating fraud since other extracts and products can also be detected.

Mercury removal by magnetic biochar derived from simultaneous activation and magnetization of sawdust.

Abstract: Novel magnetic biochars (MBC) were prepared by one-step pyrolysis of FeCl3-laden biomass and employed for Hg0 removal in simulated combustion flue gas. The sample characterization indicated that highly dispersed Fe3O4 particles could be deposited on the MBC surface. Both enhanced surface area and excellent magnetization property were obtained. With the activation of FeCl3, more oxygen-rich functional groups were formed on the MBC, especially the C═O group. The MBC exhibited far greater Hg0 removal performance compared to the nonmagnetic biochar (NMBC) under N2 + 4% O2 atmosphere in a wide reaction temperature window (120–250 °C). The optimal pyrolysis temperature for the preparation of MBC is 600 °C, and the best FeCl3/biomass impregnation mass ratio is 1.5 g/g. At the optimal temperature (120 °C), the Fe1.5MBC600 was superior in both Hg0 adsorption capacity and adsorption rate to a commercial brominated activated carbon (Br-AC) used for mercury removal in power plants. The mechanism of Hg0 removal was pr...

Theoretical Insights Into the Excited State Double Proton Transfer Mechanism of Deep Red Pigment Alkannin.

Abstract: As the most important component of deep red pigments, alkannin is investigated theoretically in detail based on time-dependent density functional theory (TDDFT) method. Exploring the dual intramolecular hydrogen bonds (O1–H2···O3 and O4–H5···O6) of alkannin, we confirm the O1–H2···O3 may play a more important role in the first excited state than the O4–H5···O6 one. Infrared (IR) vibrational analyses and subsequent charge redistribution also support this viewpoint. Via constructing the S1-state potential energy surface (PES) and searching transition state (TS) structures, we illuminate the excited state double proton transfer (ESDPT) mechanism of alkannin is the stepwise process that can be first launched by the O1–H2···O3 hydrogen bond wire in gas state, acetonitrile (CH3CN) and cyclohexane (CYH) solvents. We present a novel mechanism that polar aprotic solvents can contribute to the first-step proton transfer (PT) process in the S1 state, and nonpolar solvents play important roles in lowering the potenti...