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.

Amitriptyline (AMT) is the most widely used tricyclic antidepressant and is classified as a recalcitrant emergent contaminant because it has been detected in different sources of water. Its accumulation in water and soil represents a risk for different living creatures. To remove amitriptyline from wastewater, the Advanced Oxidation Processes (AOPs) stands up as an interesting option since generate highly oxidized species as hydroxyl radicals (OH) by environmentally friendly mechanism. In this work, the oxidation and mineralization of AMT solution have been comparatively studied by 3 Electrochemical AOPs (EAOPs) where the OH is produced by anodic oxidation of H2O (AO-H2O2), or by electro-Fenton (EF) or photoelectro-Fenton (PEF). PEF process with a BDD anode showed the best performance for degradation and mineralization of this drug due to the synergistic action of highly reactive physiosorbed BDD (OH), homogeneous OH and UVA radiation. This process achieved total degradation of AMT at 50 min of electrolysis and 95% of mineralization after 360 min of treatment with 0.5 mmol L1 Fe2þ at 100 mA cm2. Six aromatic intermediates for the drug mineralization were identified in short time of electrolysis by GC-MS, including a chloroaromatic by-product formed from the attack of active chlorine. Short-chain carboxylic acids like succinic, malic, oxalic and formic acid were quantified by ion-exclusion HPLC. Furthermore, the formation of NO3 ions was monitored. Finally, the organic intermediates identified by chromatographic techniques were used to propose the reaction sequence for the total mineralization of AMT.