Abstract Montmorillonite clays (natural and commercial (KSF and K-10)) were modified by impregnation with TiO2 from TiCl4 solution. The natural and KSF clays were also pillared with Al polyhydroxication and after that, these were impregnated with TiO2. Photocatalysts were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy X-ray (EDX) and Infrared Spectroscopy (IR) in order to understand their catalytic potential properties. Photocatalysts were used in a decomposition reaction of methylene blue (MB) and all catalysts demonstrated photocatalytic activity for degradation of dye (20 to 45%); however, K-10 sample showed the best results (more than 98% of elimination) due to its high superficial area and TiO2 dispersion. The results obtained using photocatalysts were compared with electrochemical oxidation process using Ti/Pt anode, showing that the photocatalysis reaction is more efficient. At present, our results demonstrate the potential of these catalysts for environment applications.

Resumen Las arcillas de montmorillonita (naturales y comerciales (KSF y K-10)) se modificaron por impregnación con TiO2 a partir de una solución de TiCl4. Las arcillas naturales y KSF también se agruparon con polihidroxilación de Al y, posteriormente, se impregnaron con TiO2. Los fotocatalizadores se caracterizaron mediante difracción de rayos-X (XRD), microscopía electrónica de barrido (SEM), espectroscopía de rayos-X de dispersión de energía (EDX) y espectroscopia de infrarrojo (IR) con el objetivo de comprender sus propiedades catalíticas. Los fotocatalizadores se emplearon en una reacción de descomposición de azul de metileno (MB) y todos los materiales sintetizados mostraron actividad fotocatalítica para la degradación del colorante (20 a 45%). Sin embargo, el fotocatalizador K-10 mostró los mejores resultados (más del 98% de eliminación) debido a su alta área superficial y la dispersión de TiO2. Los resultados obtenidos utilizando los fotocatalizadores se compararon con el proceso de oxidación electroquímica utilizando ánodo Ti/Pt, evidenciando que la reacción de fotocatálisis es más eficiente. Nuestros resultados muestran el potencial de estos catalizadores para aplicaciones ambientales.

The performance of an electrocoagulation (EC) system with aluminium and iron electrodes for removing heavy metal ions (Cd2+, Cu2+, Cr3+, Sr2+ and Zn2+) present in synthetic produced water on laboratory scale was studied systematically. Experimental parameters such as applied current, flow effluent and sacrificial electrodes were investigated in order to understand their influence on the EC process. Increasing the current density accelerated the electrocoagulation process, but made it less efficient. Cd2+, Cu2+, Sr2+ and Zn2+ showed similar removal rates, under similar conditions, indicating a uniform electrochemical behavior. The study gave indications on the removal mechanisms of the investigated metals. Cd2+, Cu2+ and Zn2+ ions are hydrolyzed and co-precipitated as hydroxides. Cr4+, was proposed to be reduced first to Cr3+ at the cathode before precipitating as hydroxide. The process expenditure was estimated and reported showing the viability of this process as a green alternative, obtaining modest costs using Fe electrodes.

A simple differential pulse voltammetric method based on chitosan modified glassy carbon was used to pre-concentrate copper ions in the chitosan film. After, this electrode was employed for the quantitative determination of cysteine. The modified electrode exhibits a clear improvement of the current response. The method allowed quantifying the analyte in the range in buffer solution and a limit of detection range from 1.0×10-6 to 1.4×10-6 M was achieved. This value seems quite higher than those previously published by other authors. The results are described and discussed in the light of the existing literature.

In this study, advanced oxidation processes (AOPs) such as the UV/H2O2 and Fenton processes were investigated for the degradation of 2-hydroxybenzoic acid (2-HBA) in lab-scale experiments. Different [H2O2]/[2-HBA] molar ratios and pH values were used in order to establish the most favorable experimental conditions for the Fenton process. For comparison purposes, degradation of 2-HBA was carried out by the UV/H2O2 process under Fenton experimental conditions. The study showed that the Fenton process (a mixture of hydrogen peroxide and Fe2+ ion) was the most effective under acidic conditions, leading to the highest rate of 2-hydroxybenzoic acid degradation in a very short time interval. This same process led to a six-fold acceleration of the oxidation rate compared with the UV/H2O2 process. The degradation of 2-hydroxybenzoic acid was found to follow first-order kinetics and to be influenced by the type of process and the experimental conditions. The experimental results showed that the most favorable conditions for 2-HBA degradation by the Fenton process are pH around 4-5, [Fe2+] = 0.6 mmol.L-1, and [H2O2]/[2-HBA] molar ratio = 7. The hydroxylation route is explained here for the two processes, and the results are discussed in the light of literature information.

El presente estudio se centró en la monitorización de la distribución de nitrógeno en los productos de oxidación de compuestos orgánicos nitrogenados (urea, colorante Blue 4, acetonitrilo, formamida, guanidina y piridazina) sobre ánodos de titanio platinado y de óxidos de rutenio. La mineralización del nitrógeno produce contaminantes inorgánicos (NH3/NH4 + y/o NO2 -/NO3 -). Los compuestos amídicos y amínicos reaccionan tanto en fase homogénea (hidrólisis acida) como en fase heterogénea (electroxidación directa), con una velocidad que depende del estado inicial de oxidación del nitrógeno en la molécula orgánica. Las moléculas con enlaces múltiples y heterocíclicos fueron convertidas eficazmente con una mineralización del nitrógeno despreciable, dada la elevada estabilidad de los compuestos intermedios de su oxidación. Los resultados obtenidos (elevada producción de nitratos) evidencian la necesidad de acoplar la electroxidación directa con otros procesos para, de esta forma, limitar la concentración de nitratos a niveles aceptables. Los procesos estudiados, diálisis (del catión amonio) más oxidación indirecta (mediante cloro activo), demostraron ser alternativas validas para este objetivo.

The electro-oxidation, over platinized titanium and ruthenium oxide anodes, of nitrogen containing molecules (urea, reactive Blue 4 dye, acetonitrile, formamide, guanidine and pyridazine) was investigated, monitoring the products distribution. The N-mineralization leads to have inorganic pollutants (NH3/NH4+ and/or NO2-/NO3-). Amidic and aminic compounds react both in homogeneous (acid hydrolysis) and in heterogeneous phase (direct electroxidation) with a rate depending on the original state of oxidation of nitrogen. Heterocyclic and multiple-bond carbon-nitrogen molecules were effectively converted with negligible mineralization of nitrogen due to the stability of their first oxidation intermediates. The obtained results (high rate of nitrate generation) evidence the need of coupling of the direct electroxidation with other process to limit the nitrate concentration to an accepted level; in accordance, dialysis (of the ammonia cation) and indirect oxidation (chlorine-mediated) were proved to be valid alternatives.

O objetivo deste trabalho é discutir a oxidação eletroquímica do ácido oxálico (AO), analisando a influência do NaCl e NaBr. Experimentos foram realizados em eletrodos de diamante dopados com boro (DDB), em meio alcalino. Eletrodos DDB têm uma baixa adsortividade superficial, portanto sua grande estabilidade frente à oxidação permite que a reação ocorra com reagentes e intermediários não adsorvidos. O processo é significativamente acelerado pela presença de sal de halogênio na solução; curiosamente, o processo mediado não depende da densidade de corrente aplicada. Com base nos resultados, o brometo foi selecionado como um mediador apropriado durante a oxidação de AO em DDB. Br- age primeiramente no volume da solução, com a formação de oxidantes fortes, enquanto a ação do Cl- mostrou melhoras mais baixas na oxidação do AO em BDD, com relação aos resultados relatados usando eletrodo de Pt. Finalmente, os parâmetros de eficiência de remoção e consumo de energia para a incineração eletroquímica de AO foram calculados.

Aim of this work is to discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr. Experiments were carried out at boron-doped diamond (BDD) electrodes, in alkaline media. BDD electrodes have a poor superficial adsorptivity so their great stability toward oxidation allows the reaction to take place with reactants and intermediates in a non-adsorbed state. The process is significantly accelerated by the presence of a halogen salt in solution; interestingly, the mediated process does not depend on applied current density. Based on the results, bromide was selected as a suitable mediator during OA oxidation at BDD. Br- primarily acts in the volume of the solution, with the formation of strong oxidants; while Cl- action has shown lower improvements in the OA oxidation rate at BDD respect to the results reported using Pt electrode. Finally, the parameters of removal efficiency and energy consumption for the electrochemical incineration of OA were calculated.