Dr. Salgado-Mendoza, Pablo

Advanced oxidation processes (AOPs) are chemical systems characterized by the production of hydroxyl radicals and other reactive oxygen species. One of the most important AOP systems are the Fenton and Fenton-like reactions. The main limitation in the reactivity of these systems is the solubility and redox equilibria of Fe3+/Fe+2 species. In this way, the use of iron ligands (redox active or redox inert) is one of the most common ways to modulate the Fenton reaction. These systems are called Chelated Mediated Fenton (CMF) reaction. The 1,2-dihydroxybenzene (1,2-DHB) type ligands are one of the most used redox active compounds to drive a Fenton reaction because these ligands can chelate Fe3+ and reduce it to Fe2+ enhancing de ability of Fenton systems to generate hydroxyl radicals. These systems are called the dihydroxybezene driven Fenton reaction. In this study, the effects of five 1,2-DHBs (substituted in position 4) for driving the Fenton reaction were evaluated. The DHBs utilized were: 3,4-dihydroxybenzoic acid and 3,4-dihydroxybenzonitrile (electron-withdrawing substituents), 4-tert-butylcatechol and 4-methylcatechol (electron-donating substituents) and catechol (without substituent). The degradation of rhodamine B by different Fe3+/H2O2/1,2-DHB systems were determined at pH values between 1 and 9. These values were correlated (by a multivariate model) with the Fe+3 speciation at these pH values. To determine the Fe+3/1,2-DHB complex concentration, the stability constants for the mono, bis and tris complexes were experimentally determined. The log β1, log β2 and log β3 for the assayed 1,2-DHB were 19.30, 27.21, 45.69 for catechol; 19.52, 28.90, 44.66 for 4-methylcatechol; 19.93, 27.16, 44.77 for 4-tert-butylcatechol; 15.57, 23.46, 42.03 for 3,4-dihydroxybenzonitrile and 17.68, 29.79 and 46.27 for 3,4-dihydroxybenzoic acid, respectively. From the multivariate model (R2 = 0.994), it was determined that only Fe+3 aquocomplex, [Fe(OH)2]+ and [FeDHB]+ were significant (p < 0.05) for rhodamine B degradation, which is independent of the nature of the DHB utilized.

Wood is a complex material whose main chemical constituents are cellulose, hemicellulose, and lignin. These components are studied in various industries after the wood has been processed by chemical or mechanical methods. For the paper industry, it is relevant to determine the pentosan content in cellulose pulp because it indicates the degree of retention of hemicellulose. Hemicellulose contributes to the resistance, increasing the yield of the pulp, and therefore, high pentosan content is desirable. In this way, this research focused on the determination of the pentosan content in hard and softwood pulps between 0.81 to 18.4%. The pentosan content can be directly determined by a chemical method, although these conventional methods are long, expensive, generate a high amount of corrosive waste, and are not recommended for routine analysis. Therefore, in this research, an alternative method was developed using near-infrared spectroscopy together with partial least squares regression to predict the pentosan content in pulps. This new method is fast, inexpensive, analysis is direct and non-destructive. Finally, the pentosan calibration model was validated by cross-validation and the predicted external samples were quantified with precision between 0.008 and 0.043 and accuracy between 3.9 and 12.2%, while SEP has a variability of 1.267% of pentosan for this model.