Luis Alejandro Galeano

This study presents the first successful intercalation and pillaring of natural bentonite with mixed Al–Co species using a highly concentrated metal precursor (approx. 5.0 mol l−1). A statistical design of experiments identified optimal preparation parameters for the resulting Al/Co-pillared clay (Al/Co-PILC). The clay materials were extensively characterized by atomic absorption spectroscopy (AAS), powder X-ray diffraction (XRD), N₂ adsorption–desorption, H₂-temperature programmed reduction (H₂-TPR), cationic exchange capacity (CEC), thermal analyses (TGA/DSC), and UV-vis and IR diffuse reflectance spectroscopies (DR-UV-vis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)). The catalytic activity was assessed in the phenol degradation by sulfate radicals from sodium persulfate. The determined optimal conditions in terms of atomic metal ratio of cobalt in the interlayering solution (AMRCo ~ 10 mol%) and equivalent hydrolysis ratio (HReq. = 2.0) yielded a well-expanded Al/Co-PILC with basal spacing d001 (18.4 Å) and textural properties (SBET: 194 m² g−1; Sµp: 140 m² g−1) typical of successfully pillared Al-PILCs, alongside a significantly higher amount of cobalt was effectively incorporated as compared with previous reports. This material achieved 72.0 ± 1.24% of phenol degradation and 65.0 ± 2.13% of dissolved organic carbon (DOC) removal within 1 h of reaction under circumneutral pH and ambient conditions of temperature and pressure, with negligible cobalt leaching (approx. 0.01 mg l−1). Al/Co-PILCs so prepared are thus promising active solids for catalytic advanced oxidation of biorefractory organic contaminants in highly polluted wastewater using sulfate radicals (SR-AOP).

An Al/Fe-pillared clay catalyst (Al/Fe-PILC) prepared from low cost technical-grade reagents has been investigated in the photocatalytic Wet Peroxide Oxidation (photo-CWPO) of dissolved Natural Organic Matter (NOM) under circumneutral pH. The successful pillaring of the layered clay material was confirmed by X-ray diffraction (XRD), N₂ adsorption at −196 °C, cation exchange capacity (CEC) and simultaneous thermal analysis (TGA/DSC). High levels of mineralization of the dissolved organic carbon and color removal of a synthetic NOM surrogate solution were achieved even under natural lab’s lighting and ambient temperature and pressure, whereas the absence of radiation (in dark) was found to strongly affect the performance of the degradation. The photo-CWPO of NOM activated by the Al/Fe-PILC clay catalyst under visible light irradiation (LED lamp, 450 and 550 nm peaks) displayed a DOC mineralization of 72% and color removal of 73% in just 210 min of irradiation at neutral pH, whereas both responses decayed under ultraviolet lightning (λ: 365 nm) to 41% and 58%, respectively. This behavior is ascribed to formation of triplet states of natural organic matter (³NOM*) by absorption of visible light, which seems to synergistically improve the rate-determining step of the heterogeneous Fenton process, namely reduction of Fe³⁺ into Fe²⁺ on the surface of the clay catalyst. Interestingly, experiments performed at neutral and pH 3.0 showed very similar efficiencies under visible light irradiation; these findings may really facilitate the application of the photo-CWPO process to assist conventional drinking water treatment plants in the removal of NOM before the typical disinfection by chlorine to produce safer drinking water.

En el presente estudio se analizarán las principales incidencias que surgen de la cultura política vigente y la participación de los actores sociales en los partidos políticos existentes en el Paraguay, orientada a dirigir, o controlar, el poder del Estado. Considerando el mencionado objetivo, deviene imprescindible especificar el concepto de cultura política al que se apelará para abordar el análisis propuesto. En ese sentido, se puntualiza que la “cultura política comprende el sistema de valores, reglas morales, creencias, expectativas y actitudes compartidas por los miembros de una sociedad con relación al sistema político y al contexto social” . Más específicamente, la cultura política refleja el modo en que las personas y los grupos sociales conciben y perciben la vida política, como, al mismo tiempo, actúan hacia la autoridad, el gobierno y la sociedad. Por su parte, es pertinente sostener que “los partidos políticos son organizaciones que procuran colocar a sus líderes y cuadros en instituciones a través de los cuales pueden ejercer poder político” . En los regímenes democráticos los partidos están situados entre la Sociedad y el Estado, y su objetivo fundamental es conseguir el suficiente respaldo electoral, con el fin de dirigir las acciones del gobierno o, por lo menos, influir en ellas. También los partidos políticos suelen existir en los regímenes autoritarios, o dictatoriales, a través de organizaciones que monopolizan el poder del Estado. En lo relativo al alcance del estudio se puntualiza que, si bien el énfasis analítico de la temática adelantada estará puesto en los procesos sociopolíticos existentes en las etapas históricas más recientes y actuales, también se examinarán los procesos que se verificaron en períodos históricos precedentes. Este planteamiento parte del criterio de que, en el caso paraguayo, tanto en el ámbito de la cultura política como en el desempeño de los partidos importantes factores de antiguos antecedentes, a pesar de ciertas transformaciones, continúan teniendo vigencias significativas en la actualidad.

The modification of bentonite with Al–Fe species from different concentrated precursors at both stages: (i) the preparation of the (Al/Fe)-mixed pillaring solution and (ii) intercalation itself, was studied at lab scale. The final solids were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Cationic Exchange Capacity (CEC), textural analyses by nitrogen adsorption–desorption at 77 K, and hydrogen-temperature programmed reduction (H₂-TPR). Finally, the modified clays were assessed as active materials in the Catalytic Wet Peroxide Oxidation (CWPO) of phenol under very mild conditions through 1.0 h of reaction: T = 25.0 °C ± 0.1 °C, pH = 3.7, ambient pressure (76 kPa), and 0.5 g catalyst per dm³. Metal hydrolysis by the dissolution of elemental aluminium (final Total Metal Concentration TMC = 4.62 mol dm⁻³) achieved the best results, decreasing the volume of solution per mass unit of clay required to successfully expand the layered starting mineral by a factor of close to 75, in comparison with the widespread conventional preparation using highly diluted Al-based pillaring solutions. Even in the absence of any solvent for the clay dispersion, the intercalating/pillaring method was shown to be favourable, as a novel strategy promoting the process intensification and subsequent preparation of Al/Fe- and other Al-based pillared clays at larger scales. The best catalyst prepared from concentrated precursors exhibited 79.1% phenol conversion, 19.3% TOC mineralization, and pretty low iron leaching (0.037 mg Fe dm⁻³; ∼0.12% w/w) in such a short catalytic assessment; all these results were quite comparable or even exceeded those exhibited by the catalyst prepared from dilute precursors.

Catalytic wet peroxide oxidation (CWPO) is a novel, alternative technology to conventional disinfection methods that are widely used to control microbial parameters in drinking water. To assess its effectiveness, new studies revealing the kinetics of MS2 coliphage inactivation by CWPO technology are required. This investigation therefore aimed to perform mathematical modelling of MS2 inactivation through CWPO technology activated by an Al/Fe-pillared clay catalyst (Al/Fe-PILC) in the presence of a synthetic surrogate of dissolved natural organic matter. The inactivation constant was obtained from two different statistical approaches, and the experimental data were better fitted to the pseudo-first-order Chick-Watson model in which the inactivation rate is constant. For this model, the maximum inactivation rate was k = 0.1648 min⁻¹, which was achieved in the MS2-3 catalytic test using an initial mass ratio of peroxide to active iron (Fe_act) of 1.2 mg H₂O₂/mg Fe_act. To estimate the inactivation rate due to reactive oxygen species (ROS), we supposed that the inactivation constant depends on both ROS and Fe_act. In this case, the maximum inactivation rate due to ROS was k_r = 2.4 × 10⁻⁹ min⁻¹ (using 1.17 mg H₂O₂/mg Fe_act), which was achieved in the MS2-10 trial; both cases led to the conclusion that the optimal initial ratio of peroxide to active Fe in the catalyst in CWPO activated by Al/Fe-PILC was close to 1.2 mg H₂O₂/mg Fe_act. These kinetic studies showed that rapid inactivation takes place very early in the reaction, followed by slow inactivation during the remaining period of the recorded reaction time. This research revealed the strong potential of CWPO technology to improve microbiological parameters in drinking water due to the high catalytic performance in the heterogeneous Fenton reaction displayed by Fe sites incorporated in the Al/Fe-PILCs.

The catalytic wet peroxide oxidation (CWPO) of the industrial azo-dye methyl orange (MO) activated by an Al/Fe-pillared clay catalyst was optimized by the Response-Surface Methodology (RSM). Three sequential sets of factorial 2^k central composite experiments were required for the full optimization of the process; catalyst loading and stoichiometric dose of hydrogen peroxide were the experimental factors studied through different times of reaction by means of all, Dissolved Organic Carbon (DOC) removal, Total Nitrogen (TN) removal, reacted fraction of hydrogen peroxide, and decolorization as experimental responses to be maximized. The resulting single-response RSM optimums were combined in a multi-response Desirability function ruling out the differential effect of adsorption on the catalyst's surface by defining all responses per gram of clay catalyst. Former two statistical sets of experiments (DOE-1 and DOE-2) showed the CWPO degradation of MO to get favored at increasing both catalyst loading and time of reaction (up to 180 min). Afterwards, third final design of experiments (DOE-3) displayed 75% of DOC removal, 78% of TN removal, 97% of reacted H₂O₂, and 95% of decolorization by using a catalyst loading of 5.0 g/L of Al/Fe-PILC together with just 50% of the stoichiometric amount of H₂O₂. The multi-response optimum conditions based on the Desirability function showed excellent fitting explaining at least 99.3% of the optimal overall responses at 95% of confidence. A further analysis revealed that no one of the non-controllable variables under real conditions of industrial wastewater treatment (covariates): starting total organic carbon (TOC) (2.0–20 mg/L), temperature (5.0–25°C) or circumneutral pH (6.0–9.0), exhibited statistically significant effect (P > 0.05), suggesting the system to be almost insensitive against them within studied range of close to ambient conditions in the tropic. Finally, HPLC/PDA and GC/FID measurements identified phenol, cyclohexa-2,5-diene-1,4-dione, phenylamine, N-methylaniline and N,N-dimethylaniline in very low concentrations as main intermediates in the CWPO degradation of MO, which nevertheless disappeared over 90 min of treatment. Meanwhile, 4-aminobenzenesulfonic and oxalic acids were recorded as unique by-products at final time of reaction, but both of them fairly less toxic than the starting azo-dye.