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.

In this work, the Fenton technology was applied to decolorize methylene blue (MB) and to inactivate Escherichia coli K12, used as recalcitrant compound and bacteria models respectively, in order to provide an approach into single and combinative effects of the main process variables influencing the Fenton technology. First, Box–Behnken design (BBD) was applied to evaluate and optimize the individual and interactive effects of three process parameters, namely Fe2+ concentration (6.0 × 10−4, 8.0 × 10−4 and 1.0 × 10−3 mol/L), molar ratio between H2O2 and Fe2+ (1:1, 2:1 and 3:1) and pH (3.0, 4.0 and 5.0) for Fenton technology. The responses studied in these models were the degree of MB decolorization (D%MB), rate constant of MB decolorization (kappMB) and E. coli K12 inactivation in uLog units (IuLogEC). According to the results of analysis of variances all of the proposed models were adequate with a high regression coefficient (R2 from 0.9911 to 0.9994). BBD results suggest that [H2O2]/[Fe2+] values had a significant effect only on D%MB response, [Fe2+] had a significant effect on all the responses, whereas pH had a significant effect on D%MB and IuLogEC. The optimum conditions obtained from response surface methodology for D%MB ([H2O2]/[Fe2+] = 2.9, [Fe2+] = 1.0 × 10−3 mol/L and pH = 3.2), kappMB ([H2O2]/[Fe2+] = 1.7, [Fe2+] = 1.0 × 10−3 mol/L and PH = 3.7) and IuLogEC ([H2O2]/[Fe2+] = 2.9, [Fe2+] = 7.6 × 10−4 mol/L and pH= 3.2) were in good agreement with the values predicted by the model.

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.

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.

In pursuit of a more sustainable construction material with the potential to improve bioreceptivity in marine environments, this study investigates the feasibility of incorporating three industrial residues—steel sludge (“Conox”), mytilid mussel shells, and wheat straw fibers—as partial substitutes for cement and sand. The research focuses on evaluating the physical and mechanical properties of mortar and concrete mixtures containing these residues, both individually and in combination. Additionally, it assesses the metal leaching potential of concrete incorporating Conox sludges into the environment. The results show that mixture containing 10% Conox sludges as a sand substitute exhibit the highest mechanical strength but also increased porosity, water absorption, and chloride ion diffusion. The addition of mussel shells and straw fibers generally reduced mechanical properties and increased porosity in mortars, though a 20% mussel shell substitution maintained mechanical strength and chloride ion diffusion in the concrete. The combination of mussel shells with Conox sludges allowed the concrete to retain its mechanical properties, although it also increased porosity and chloride ion penetration, which may limit its use where impermeability is key. However, this increased porosity could benefit coastal erosion control structures like breakwaters and revetments, and sea walls. Moreover, metal leaching from concrete incorporating Conox sludges remained within established safety limits. Despite these challenges, the materials show promise for non-structural applications or projects where sustainability is prioritized. Our research lays the foundation and opens new possibilities for future investigations that innovate in the combination of industrial wastes, aiming to create more sustainable construction materials with a reduced impact on biodiversity.

Water pollution, particularly from organic contaminants like dyes, is a pressing issue, prompting exploration into advanced oxidation processes (AOPs) as potential solutions. This study focuses on synthesizing Cu2O on cellulose-based fabric using Eucalyptus globulus leaf extracts. The resulting catalysts effectively degraded methylene blue through photocatalysis under LED visible light and heterogeneous Fenton-like reactions with H2O2, demonstrating reusability. Mechanistic insights were gained through analyses of the extracts before and after Cu2O synthesis, revealing the role of phenolic compounds and reducing sugars in nanoparticle formation. Cu2O nanoparticles on cellulose-based fabric were characterized in terms of their morphology, structure, and bandgap via SEM-EDS, XRD, Raman, FTIR, UV–Vis DRS, and TGA. The degradation of methylene blue was pH-dependent; photocatalysis was more efficient at neutral pH due to hydroxyl and superoxide radical production, while Fenton-like reactions showed greater efficiency at acidic pH, primarily generating hydroxyl radicals. Cu2O used in Fenton-like reactions exhibited lower reusability compared to photocatalysis, suggesting deterioration. This research not only advances understanding of catalytic processes but also holds promise for sustainable water treatment solutions, contributing to environmental protection and resource conservation.

The present study reports on phenolic compounds profile of Eucalyptus globulus leaf extracts and exhibiting their role in obtaining silver nanoparticles (AgNP) by a green method on paper and fabric supports with or without addition of NaOH. To know the mechanism involved in the formation of AgNP, FTIR, UV–Visible spectrophotometry and UHPLC-QTOF-MS analyzes were carried out of E. globulus extracts before and after the synthesis of AgNP. The FTIR, UV–Visible spectrophotometry analyzes identified phenolic compounds, and to a lesser extent reducing sugars mainly participate as reducing agents in the formation of AgNP, while phenolic compounds would participate as stabilizing agents. UHPLC-QTOF-MS analyzes identified derived from gallic acid play an important role in AgNP formation. AgNPs were characterized in their morphology and structure by SEM-EDS, TEM-SAED, XRD, UV–Vis diffuse reflectance and TGA. The results indicate the formation of Ag and/or Ag2O nanoparticles depending on the influence of NaOH in the reaction system. Furthermore, the support used (paper or fabric), it would influence the concentration of AgNPs formed, the consumption of phenolic compounds, the antibacterial activity and band-gap of AgNPs synthesized. This study provides evidence of a simple process to support AgNP on cellulose and providing key information towards the definitive clarification of the mechanism of formation of AgNP by green synthesis.

Recalcitrant compounds resulting from anthropogenic activity are a significant environmental challenge, necessitating the development of advanced oxidation processes (AOPs) for effective remediation. This study explores the synthesis of cuprous oxide nanoparticles on cellulose-based paper (Cu2O@CBP) using Eucalyptus globulus leaf extracts, leveraging green synthesis techniques. The scanning electron microscopy (SEM) analysis found the average particle size 64.90 ± 16.76 nm, X-ray diffraction (XRD) and Raman spectroscopy confirm the Cu2O structure in nanoparticles; Fourier-transform infrared spectroscopy (FTIR) suggests the reducing role of phenolic compounds; and ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis DRS) allowed us to determine the band gap (2.73 eV), the energies of the valence band (2.19 eV), and the conduction band (−0.54 eV) of Cu2O@CBP. The synthesized Cu2O catalysts demonstrated efficient degradation of methylene blue (MB) used as a model as recalcitrant compounds under LED-driven visible light photocatalysis and heterogeneous Fenton-like reactions with hydrogen peroxide (H2O2) using the degradation percentage and the first-order apparent degradation rate constant (kapp). The degradation efficiency of MB was pH-dependent, with neutral pH favoring photocatalysis (kapp = 0.00718 min−1) due to enhanced hydroxyl (·OH) and superoxide radical (O2·−) production, while acidic pH conditions improved Fenton-like reaction efficiency (kapp = 0.00812 min−1) via ·OH. The reusability of the photocatalysts was also evaluated, showing a decline in performance for Fenton-like reactions at acidic pH about 22.76% after five cycles, while for photocatalysis at neutral pH decline about 11.44% after five cycles. This research provides valuable insights into the catalytic mechanisms and supports the potential of eco-friendly Cu2O nanoparticles for sustainable wastewater treatment applications.