Aurora Santos

Bio: Aurora Santos is an academic researcher from Complutense University of Madrid. The author has contributed to research in topics: Catalysis & Persulfate. The author has an hindex of 37, co-authored 129 publications receiving 4617 citations. Previous affiliations of Aurora Santos include University of Cantabria.

Toxicity and biodegradability of imidazolium ionic liquids

Abstract: Several bioassays have been carried out to analyze the toxicity and biodegradability of several imidazolium ionic liquids (ILs) in aqueous phase. The synthetized compounds consist of an imidazolium cation with two alkyl substituents in positions 3 (R1) and 1 (R2) and a counter-ion. The alkyl substituent R1 has been fixed as a methyl group and the effect of the alkyl chain length (C1-C8) of the other substituent (R2) has been tested. Moreover, the influence of diverse counter-ions A- (Cl-, PF6, XSO4-) has been analyzed. Acute toxicity and EC50 values of each compound in the aqueous solution have been determined by using the Microtox standard procedure. Biodegradability of IL has been determined by measuring BOD5 of aqueous samples containing IL and/or D-glucose and the IL residual content and/or d-glucose concentration after this assay. The viability of the microorganisms used in the BOD5 has been related to the ATP in the samples, measured by a bioluminescence assay. All the ILs tested were not biodegradable in the considered conditions. Besides, it was found that the shorter the chain length of side chain R2, the lower the toxic effect is. On the contrary, the anion has a little effect on the IL toxicity.

Route of the catalytic oxidation of phenol in aqueous phase

Abstract: Catalytic oxidation of phenol in aqueous phase over a copper catalyst supplied by Engelhard (Cu-0203T) has been studied. A reaction pathway of phenol oxidation under intermediate temperature and pressure has been proposed. Temperatures employed were 140 and 160 °C and catalyst concentration ranged from 4 to 1550 g l −1 of liquid phase. To achieve this wide interval of catalyst concentration values, two experimental set-ups were employed: a basket stirred tank reactor (BSTR), with the liquid phase in batch, and an integral fixed-bed reactor (FBR) with co-current up-flow of gas and liquid phases. The main intermediates detected in the phenol oxidation were ring compounds (hydroquinone, catechol, benzoquinone), which break to yield CO 2 and short chain acids, mainly maleic, formic, acetic and oxalic acids, and also traces of malonic, succinic and fumaric acids. Oxalic acid was also found to form a complex with the copper which oxidizes to CO 2 . The only non-oxidizable intermediate under the conditions sets was acetic acid. In order to propose a phenol oxidation pathway, several runs were carried out where the main intermediates detected in the phenol oxidation were fed to the FBR under different temperatures and catalyst loadings. It was found that catechol oxidation does not yield either benzoquinone or maleic acid but oxalic acid which finally mineralized to CO 2 . However, benzoquinone and maleic acid are products clearly detected in the hydroquinone oxidation. Oxidation reactions of phenol and those intermediates studied take place not only on the solid surface but also in the liquid phase.

Oxidation of Orange G by persulfate activated by Fe(II), Fe(III) and zero valent iron (ZVI).

Abstract: Persulfate (PS) was employed in the oxidation of Orange G (OG), an azo dye commonly found in textile wastewaters. Activation of PS was conducted with iron to generate sulfate free radicals (SO4(-)) with high redox potential capable to oxidize most of the organics in water. Identification of oxidation intermediates was carried out by analyzing at different times organic by-products generated from treatment of a concentrate dye solution (11.6 mM) with 153 mM of PS and 20 mM of Fe(II) at 20 °C. Intermediate reaction products (mainly phenol (PH) and benzoquinone (BQ), and in less extent aniline, phenolic compounds and naphthalene type compounds with quinone groups) were identified by GC/MS and HPLC, and an oxidation pathway was proposed for the oxidation of OG with iron activated PS. The effect of iron valence (0, II and III) in the oxidation of an aqueous solution of OG (containing 0.1 mM) was studied in a 0.5 L batch reactor at 20 °C. Initial activator and PS concentrations employed were both 1 mM. Complete pollutant removal was achieved within the first 30 min when iron II or III were employed as activators. Quinone intermediates generated during pollutant oxidation may act as electron shuttles, allowing the reduction of Fe(III) into Fe(II) in the redox cycling of iron. Therefore, activation of PS by Fe(III) allowed complete OG removal. When zero valent iron (ZVI) was employed (particle diameter size 0.74 mm) the limiting step in SO4(-) generation was the surface reaction between ZVI and the oxidant yielding a lower oxidation rate of the dye. An increase in the oxidant dosage (0.2 mM OG, 2 mM Fe(III) and 6 mM PS) allowed complete pollutant and ecotoxicity removal, as well as mineralization close to 75%.

Diuron abatement using activated persulphate: Effect of pH, Fe(II) and oxidant dosage

Abstract: The high oxidation efficiencies of the free radicals (SO 4 − ), in combination with the slow rate of consumption of the oxidant, make this process very effective for the degradation of organic herbicides. Effects of pH, persulphate and Fe(II) concentration on the destruction of diuron by heat-assisted persulphate were examined in batch experiments. All the experiments were performed at 50 °C and an initial diuron concentration of 0.09 mM. The effectiveness of the process was evaluated based on the degradation of diuron and total organic carbon (TOC) removal. Under the reaction conditions, the diuron conversion is enormously influenced by the presence of Fe(II) in solution which rapidly produces the sulphate radical. Fe(II) concentration significantly accelerates diuron degradation at the first stages where the Fe(II) is oxidized to ferric iron. Increasing the persulphate concentration from 1 to 2.1 mM at natural pH accelerated the oxidation rate of diuron, which achieved 60% oxidation in 180 and 90 min, respectively. For the higher persulphate concentration (2.1 mM), complete diuron oxidation was achieved at 0.72 mM Fe(II) concentration in a few minutes. Additionally, diuron degradation by persulphate in bicarbonate-buffer solution was slower, most likely due to the presence of bicarbonate ions (radical scavengers).

Evolution of toxicity upon wet catalytic oxidation of phenol.

Abstract: This work reports on the evolution of the toxicity of phenol-containing simulated wastewater upon catalytic wet oxidation with a commercial copper-based catalyst (Engelhard Cu-0203T). The results of the study show that this catalyst enhances detoxification, in addition to its effect on the oxidation rate. The EC50 values of the intermediates identified throughout the oxidation route of phenol have been determined and used to predict the evolution of toxicity upon oxidation. The predicted values have been compared with the ones measured directly from the aqueous solution during the oxidation process. To learn about the evolution of toxicity throughout the routes of phenol oxidation, experiments have been performed with simulated wastewaters containing separately phenol, catechol, and hydroquinone as original pollutants. The significant increase of toxicity observed during the early stages of phenol oxidation is not directly related to the development of the brown color that derives mainly from catechol oxi...

Deep eutectic solvents: syntheses, properties and applications

Abstract: Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.

Activation of persulfate (PS) and peroxymonosulfate (PMS) and application for the degradation of emerging contaminants

Abstract: Sulfate radical-based advanced oxidation processes (AOPs) have been received increasing attention in recent years due to their high capability and adaptability for the degradation of emerging contaminants. Persulfate (PS, S2O82−) and peroxymonosulfate (PMS, HSO5−) can be activated by thermal, alkaline, ultraviolet light, activated carbon, transition metal (such as Fe0, Fe2+, Cu2+, Co2+, Ag+), ultrasound and hydrogen peroxide to form sulfate radical (SO4 −), which is strong oxidant and capable of effectively degrading emerging pollutants. Sulfate radical-based AOPs have a series of advantages in comparison with OH-based methods, for example: higher oxidation potential, higher selectivity and efficiency to oxidize pollutants containing unsaturated bonds or aromatic ring, wider pH range. Therefore, sulfate radicals are capable of removing the emerging contaminants more efficiently. In this review paper, various methods for the activation of PS and PMS were introduced, including, thermal, alkaline, radiation, transition metal ions and metal oxide, carbonaceous-based materials activation and so on; and their possible activation mechanisms were discussed. In addition, the application of activated PS and PMS for the degradation of emerging contaminants and the influencing factors were summarized. Finally, the concluding remarks and perspectives are made for future study on the activation of PS and PMS. This review can provide an overview for the activation and application of PS and PMS for the degradation of emerging contaminants, as well as for the deep understanding of the activation mechanisms of PS and PMS by various methods.

Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination—A review

Abstract: Nowadays there is a continuously increasing worldwide concern for development of alternative water reuse technologies, mainly focused on agriculture and industry. In this context, Advanced Oxidation Processes (AOPs) are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. Although chemical oxidation for complete mineralization is usually expensive, its combination with a biological treatment is widely reported to reduce operating costs. This paper reviews recent research combining AOPs (as a pre-treatment or post-treatment stage) and bioremediation technologies for the decontamination of a wide range of synthetic and real industrial wastewater. Special emphasis is also placed on recent studies and large-scale combination schemes developed in Mediterranean countries for non-biodegradable wastewater treatment and reuse. The main conclusions arrived at from the overall assessment of the literature are that more work needs to be done on degradation kinetics and reactor modeling of the combined process, and also dynamics of the initial attack on primary contaminants and intermediate species generation. Furthermore, better economic models must be developed to estimate how the cost of this combined process varies with specific industrial wastewater characteristics, the overall decontamination efficiency and the relative cost of the AOP versus biological treatment.

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

Abstract: Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

Modeling and optimization I: Usability of response surface methodology

Abstract: Response surface methodology (RSM) is the most popular optimization method used in recent years. There are so many works based on the application of RSM in chemical and biochemical process. On the other hand, few articles were published about the limitation and usability of it. In this paper, we looked at some of the RSM articles published during the last few years. We tried to identify common mistakes made in the application and the limitations of RSM. We asked ourselves two important questions. These questions are “Can RSM be used for optimization of all chemical and biochemical processes without any limitation?” and “Is RSM usable for other purposes (determination of reaction kinetics, stability or evaluation of kinetic constants etc.) in addition to optimization?”. We were able to answer these questions based on the observations obtained from reviewed articles. We believe that the answers will be helpful for researchers, who will use RSM in their future studies.