Green Development of Iron Doped Silica Gel Materials for Chromium Decontamination

[Abstract] New hybrid polymeric materials were prepared by the polymerisation of sodium silicate, water, and hydrochloric acid, with the subsequent addition of iron. After the treatment with a natural reducing biomass extract, the resulting material was used in Cr(VI) decontamination processes. The preparation of the materials started with the synthesis of the polymeric base, and the successive modifications were made to maximise Cr(VI) removal. Characterization studies were carried out by SEM and EDS tests for each of the synthesised materials. The synthesised polymeric base (called GSP) was found to have a high affinity for Fe(II). An adsorption of 24.5 mg Fe(II)·g˗1 on GSP was achieved, with an associated adsorption energy of 34.5 kJ·mol˗1. In the decontamination studies, the polymeric base acts as a Supporting material for iron, while the main Cr(VI) scavenger is the adsorbed Fe. Chromium removal takes place by a combined process of Cr(VI) reduction to Cr(III) and adsorption of both chromium species at acidic pH. An adsorption model, based on statistical thermodynamics, and removal rates were used to study the process. The proposed material is sustainable, cheap and has high capacity to remove chromium from aqueous media quickly and effectively.Authors wish to thank Agencia Estatal de Investigación (AEI) (Ministerios de Ciencia e Innovación y de Economía y Competitividad) for the financial support through the research projects PID2020–117910 GB-C22 and CTQ2016–80473-P cofounded with FEDER (UE) programme. Gómez-Carnota thanks Fundación Segundo Gil Dávila for the fellowship gran

Towards the Development of Sustainable Hybrid Materials to Achieve High Cr(VI) Removals in a One-Pot Process

This article belongs to the Special Issue Nano-Adsorbents for the Removal of Heavy Metals and Dyes[Abstract] Rising manufacturing costs resulting from the current global situation make it necessary to economize at all stages of production, including waste management. Cost-effective materials that reduce the release of pollutants into the environment are becoming mandatory. In this work, a sodium silicate polymeric material, functionalized with iron, was synthesized. The material contains iron-rich nanostructures on the surface, which are responsible for the decontamination process. The inorganic material was further treated with a reducing eucalyptus extract to improve its decontamination performance. Both the inorganic and hybrid materials were used for decontamination of Cr(VI), a widely emitted chemical waste product. The hybrid material provided the best results (1.7 g Cr(VI)·g−1 Fe) in a one-pot process combining reduction and adsorption. The Langmuir–Freundlich model and a statistical thermodynamics adsorption model, together with removal rates, were used to study the processes. High adsorption energies were found, especially in the adsorption of Fe(II) on the polymeric base (33.2 kJ∙mol−1). All materials were characterized using SEM, EDS and N2 sorption, TGA, and IR analyses. In conclusion, the hybrid material synthesized in this study is cheap and easy to produce through environmentally friendly synthesis, and it is a promising adsorbent for the prevention of pollution issues in effluent discharges.This research was funded by Agencia Estatal de Investigación, Ministerio de Ciencia e Innovación, through the research project PID2020-117910GB-C22 and by Xunta de Galicia through the project ED431B 2022/40Xunta de Galicia; ED431B 2022/4

The salting coefficient and size of alkylamines in saline media at different temperatures: estimation from Pitzer equations and the mean spherical approximation

The renewed theoretical interest in the proton transfer associated to the amino group together with the scarcity of acid-base studies of amines in moderate to concentrated saline media focussed our attention on the study of the basicities of some alkylamines, namely monomethyl, dimethyl and trimethylamine, in aqueous saline solutions of KCl at various temperatures. A non-conventional analysis of stoichiometric equilibrium constants versus ionic strength data is carried out. On one hand, Pitzer’s model is easily applied to calculate the salting coefficient and the thermodynamic equilibrium constant of the alkylamines. On the other hand, the mean spherical approximation has the advantage over the Debye–Hückel based theories that it can account for effects produced by species of different sizes. Here, it is applied to predict the dependence of the salting behavior on the size of the alkylamines.Xunta de Galicia; XUGA 10310B9

Determination of biosorption mechanism in biomass of agave, using spectroscopic and microscopic techniques for the purification of contaminated water

[Abstract] Lead (Pb2+) and copper (Cu2+) are polluting metals due to their toxicity; however, the extraction of these metals is essential for economic development, so it is important to look for efficient and low-cost alternatives that can remove heavy metals from the various bodies of water. One of the alternatives used in this work is biosorption, for which an agroindustrial waste (epidermis from Agave atrovirens) was used to evaluate the affinity of removal of lead and copper in aqueous solutions; in addition, spectroscopy and microscopy techniques were used to elucidate and corroborate the removal and affinity capacity of the agave epidermis for both metals studied. The optimal pH value for the removal of both metals was 3. The adsorption isotherms yielded a qmax of 25.7 and 8.6 mg/g for lead and copper, respectively. Adjusting to the Langmuir-Freundlich model, the adsorption kinetics were pseudo-second order, and it was found that the equilibrium time was at 140 min. The spectroscopy and microscopy analyses corroborated the affinity between metals and functional groups of the agave, as well as with the elemental analysis, which reported 17.38% of lead and 4.25% of copper.[Resumen] El plomo (Pb2+) y el cobre (Cu2+) son metales contaminantes debido a su toxicidad; sin embargo, la extracción de estos metales es indispensable para el desarrollo económico, por lo que es importante buscar alternativas eficientes y de bajo costo que puedan remover metales pesados de los diversos cuerpos de agua. Una de las alternativas utilizadas en este trabajo es la biosorción, para la cual se utilizó un residuo agroindustrial (epidermis de Agave atrovirens), para evaluar la afinidad de remoción del plomo y cobre en soluciones acuosas; adicionalmente, se emplearon técnicas de espesctroscopía y microscopía que permitieron elucidar y corroborar la capacidad de remoción y afinidad que tuvo la epidermis de A. atrovirens para ambos metales estudiados. El valor óptimo de pH para la remoción de ambos metales fue 3. Las isotermas de adsorción arrojaron una qmax de 25.7 y 8.6 mg/g para el plomo y cobre, respectivamente. Ajustando al modelo de Langmuir-Freundlich, las cinéticas de adsorción resultaron de pseudo-segundo orden, se encontró que el tiempo de equilibrio es a los 140 min. El análisis espectroscópico y microscópico, corroboró la afinidad entre metales y grupos funcionales del agave, así como con el análisis elemental, el cual reportó 17.38% de plomo y 4.25% de cobre

Jornadas de Geografía y Urbanismo : Salamanca, 13, 14 y 15 de diciembre de 1984

Bibliografía

Taking the next step toward inert Mn2+ complexes of open-chain ligands: the case of the rigid PhDTA ligand

In line with our research to find inert Mn(II) complexes as contrast agents for magnetic resonance imaging, we have studied the aromatic-ring rigidified EDTA-analogue o-phenylenediamine-N,N,N′,N′-tetraacetic acid (PhDTA). The protonation constants (KHi) of PhDTA and stability constants of complexes formed between this open-chain ligand and several different biogenic metal ions (Ca2+, Mg2+, Zn2+, Cu2+, Mn2+) have been determined in 0.15 M NaCl at 25 °C and compared with the values reported in the literature previously. The protonation constants are lower than those of the corresponding cis- and trans-CDTA complexes, which might be attributed to the electron withdrawing effect of the phenylene group. The lower total basicity of the ligand leads to lower stability constants for all the examined metal complexes. On the contrary, we have found that the conditional stability constants of [Mn(PhDTA)]2− and [Mn(trans-CDTA)]2− are approximately the same, as both complexes are completely formed at pH 5 and their pM values are also comparable. The relaxivity of [Mn(PhDTA)]2− is nearly identical (r1 = 3.72 mM−1 s−1) to that determined previously for the [Mn(trans-CDTA)]2− complex (r1 = 3.62 mM−1 s−1), and its pH-dependence confirms the equilibrium model used for the fitting of the titration data. The results of the kinetic studies of the metal exchange reactions reveal that the [Mn(PhDTA)]2− complex possesses a slightly better dissociation kinetics profile than that of [Mn(trans-CDTA)]2−, which has been tested in vivo recently (including human injections). The half-life of the dissociation of the complex near physiological pH at 25 °C is 19 hours. By using the rate constant calculated for the dissociation (pH = 7.4, cCu2+ = 10 μM) and the half-life of excretion (1.6 hour), the ratio of the dissociated complex is estimated to represent 8% of the injected dose. DFT studies reveal that the metal coordination environment of [Mn(PhDTA)]2− is very similar to that of [Mn(EDTA)]2−, both containing an inner-sphere water molecule. Cyclic voltammetry studies indicate that [Mn(PhDTA)]2− is slightly more resistant towards oxidation to the Mn3+ complex than the EDTA analogue

Equilibrio ácido-base de ácidos carboxílicos en medios salinos concentrados

[Resumen] Se ha utilizado la técnica potenciométrica con electrodos de vidrio en el proceso de determinación de constantes estequiométricas de equilibrio para seis ácidos carboxílicos diferentes: benzoico, 3-nitrobenzoico, 2-clorobenzoico, acético, cloroacético y fenilacético, Como medio electrolítco se han empleado disoluciones donde la fuerza iónica se ajustaba mediante la adición de un electrolito inerte, KNO3, en amplio exceso respecto al ácido carboxílico estudiado. En el proceso de análisis se ha incorporado diferentes tipos de metodologías. Por un lado, se han aplicado cuatro modelos semiempiricos diferentes; el de Guggenheim, el de Scatchard, el de Pitzer y el modelo de cuasi-red. Gracias a estos modelos semiempíricos se han podido obtener ecuaciones explícitas que describen el comportamiento del pK estequiométrico de estos seis ácidos en función de la fuerza iónica del medio, y que resultan ser prácticamente coincidentes para cada ácido, independientemente el modelo que se utilice en el ajuste de los datos. Por otro lado, utilizando un punto de partida completamente diferente, se ha empleado la teoría MSA (Mean Spherical Approximation) en el análisis de la constante estequiométrica del ácido benzoico en diferentes medios electrolíticos. Gracias a esta teoría, se ha podido determianr el diámetro del ion benzoato a partir de datos procedentes de valoraciones potenciométricas. Aunque el diámetro calculado para el ion benzoato en KNO3 resulta ser relativamente superior al calculado en KCI y NaCI, el ajuste de los datos pK vs. I predicho con la MSA resulta satisfactorio en todo el intervalo de fuerza iónica estudiado, hasta 2.5 molar en KCI. Se ha puesto a punto, además, la técnica potenciométrica con electrodo de hidrógeno, y se ha utilizado en el proceso de estadarización del patrón de pH tetraoxalato potásico dihidratado

Thinking Outside the Blue Box: From Molecular to Supramolecular PH-Responsiveness

[Abstract] We present herein the development of a new polycationic cyclophane: the “red box”, second in a series of hydrazone-based analogues of the well-known organic receptor cyclobis(paraquat-p-phenylene)cyclophane (“blue box”). The macrocycle has been prepared in an excellent yield in aqueous media, and shows both a remarkable pH-responsiveness and unusual hydrolytic stability of the two hydrazone C[double bond, length as m-dash]N bonds, associated with charge delocalization of the amine lone pair. Whilst in aqueous media the “red box” is able to complex a variety of aromatic substrates, both in its acidic and basic form, in organic media the cyclophane is only able to capture those in the acidic form, resulting in supramolecular pH-responsiveness.Ministerio de Economía y Competitividad; CTQ2016-75629-PXunta de Galicia; ED431C 2018/39Portuguese Foundation for Science and Technology; PTDC/FIS-NAN/4662/2014Portuguese Foundation for Science and Technology; IF/00894/2015Portuguese Foundation for Science and Technology; UID/CTM/50011/201

The role of ligand to metal charge-transfer states on the luminescence of Europium complexes with 18-membered macrocyclic ligands

International audienceWe report a detailed study of the photophysical properties of Eu III and Tb III complexes with two ligands based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing either four pyridin-2yl-methyl (L 1) or four hydroxyethyl (L 2) pendant arms. The [TbL 1 ] 3+ and [TbL 2 ] 3+ complexes present moderate luminescence quantum yields upon excitation through the ligand bands (H 2 O = 7.4 and 21%, respectively). The [EuL 2 ] 3+ complex displays a relatively low quantum yield in H2O (H 2 O = 1.6%) that increases considerably in D2O (D 2 O = 5.3%), which highlights the strong quenching effect of the four ligand O-H oscillators. The emission spectrum of [EuL 1 ] 3+ is rather unusual in that it shows a relatively high intensity of the 5 D0 → 7 F5,6 transitions, which appears to be also related to the distorted D4d symmetry of the coordination polyhedron. Surprisingly, the quantum yield of the [EuL 2 ] 3+ complex is very low (H 2 O = 0.10%), considering the good protection of the Eu III coordination environment offered by the ligand. Cyclic voltammograms recorded from aqueous solutions of [EuL 1 ] 3+ display a reversible curve with a half-wave potential of-620 mV (versus Ag/AgCl), while [EuL 2 ] 3+ presents a reduction peak at more negative potential (-1040 mV). Thus, the L 1 ligand provides a rather good stabilisation of divalent Eu compared to the L 2 analogue, suggesting that the presence of a low-lying ligand-to-metal charge-transfer (LMCT) state might be responsible for the low quantum yield determined for [EuL 1 ] 3+. A density functional theory (DFT) study provides very similar energies for the ligand-centered excited singlet (1 ππ*) and triplet (3 ππ*) states of [EuL 1 ] 3+ and [EuL 2 ] 3+. The energy of the 9 LMCT state of [EuL 1 ] 3+ was estimated to be 20760 cm-1 by using all-electron relativistic calculations based on the DKH2 approach, a value that decreases to 15940 cm-1 upon geometry relaxation

MARCADORES RAPD, HERRAMIENTA PARA LA DISCRIMINACIÓN ESPECÍFICA EN EL GÉNERO Zea

Artículo de Investigació