Nucleation Mechanisms and Speciation of Metal Oxide Clusters

<div><div><div><p>The self-assembly mechanisms of polyoxometalates (POMs) are still a matter of discussion owing to the difficult task of identifying all the chemical species and reactions involved. We present a new computational methodology that identifies the reaction mechanism for the formation of metal-oxide clusters and provides a speciation model from first-principles and in an automated manner. As a first example, we apply our method to the formation of octamolybdate. In our model, we include variables such as pH, temperature and ionic force because they have a determining effect on driving the reaction to a specific product. Making use of graphs, we set up and solved 2.8·105 multi-species chemical equilibrium (MSCE) non-linear equations and found which set of reactions fitted best with the experimental data available. The agreement between computed and experimental speciation diagrams is excellent. Furthermore, we discovered a strong linear dependence between DFT and empirical formation constants, which opens the door for a systematic rescaling.</p></div></div></div>

Nucleation Mechanisms and Speciation of Metal Oxide Clusters

<div><div><div><p>The self-assembly mechanisms of polyoxometalates (POMs) are still a matter of discussion owing to the difficult task of identifying all the chemical species and reactions involved. We present a new computational methodology that identifies the reaction mechanism for the formation of metal-oxide clusters and provides a speciation model from first-principles and in an automated manner. As a first example, we apply our method to the formation of octamolybdate. In our model, we include variables such as pH, temperature and ionic force because they have a determining effect on driving the reaction to a specific product. Making use of graphs, we set up and solved 2.8·105 multi-species chemical equilibrium (MSCE) non-linear equations and found which set of reactions fitted best with the experimental data available. The agreement between computed and experimental speciation diagrams is excellent. Furthermore, we discovered a strong linear dependence between DFT and empirical formation constants, which opens the door for a systematic rescaling.</p></div></div></div>

Uso combinado de software libre y de técnicas analíticas para facilitar la comprensión de los diagramas de equilibrio químico

En el presente trabajo se han investigado las ventajas resultantes del uso combinado del software libre Spana para la realización de diagramas de equilibrio junto con diferentes técnicas experimentales de análisis químico. El software Spana se ha utilizado para representar diagramas de distribución de especies de diferentes disoluciones de ácido fosfórico y sus sales. Los diagramas resultantes se han relacionado con los resultados obtenidos mediante conductimetría y colorimetría, bajo el contexto de la realización de un trabajo fin de Máster por parte de un alumno de Ingeniería Química. Los resultados alcanzados demuestran que el uso de técnicas experimentales junto con un software fácil de usar contribuye a mejorar la comprensión de los alumnos de la relevancia que tienen los desplazamientos del equilibrio químico sobre diferentes procesos ingenieriles. La metodología propuesta reduce el tiempo del proceso de aprendizaje por parte de los alumnos y puede resultar de utilidad, no solamente para la realización de trabajos fin de máster, sino también en la realización de prácticas de laboratorio en asignaturas relacionadas con el análisis químico. In the present work, the advantages of combining the use of the freeware Spana to plot equilibrium diagrams with different laboratory analytical techniques have been investigated. The software Spana has been used to plot speciation diagrams of different solutions of phosphoric acid and its salts. The resulting diagrams have been correlated with the results obtained by conductimetric titration and colorimetry under the framework of the realization of a Master Thesis by a student of Chemical Engineering. The results achieved demonstrate that the combined use of experimental techniques and user-friendly software aid in the comprehension of the relevance that shifts in the chemical equilibrium could have on different engineering processes by students of Chemical Engineering. The proposed methodology reduces the time that students need to understand problems related to chemical equilibria and could be implemented, not only during the completion of Master Thesis’, but also in laboratory courses related with subjects of Chemical Analysis.

The revised potential – pH diagram for Pb – H2O system

Thermodynamic properties of lead species in aqueous solution are collected. The chemical equilibria between various forms of Pb(II) are considered. The speciation diagrams for the equilibria 4[PbOH]+(aq) ⇄ [Pb4(OH)4]4+(aq) and 2[Pb3(OH)4]2+(aq) ⇄ [Pb6(OH)8]4+(aq), and the thermodynamic activity - pH diagram of Pb(II) species are plotted. Basic chemical and electrochemical equilibria for lead are calculated. The potential - pH diagram for Pb - H2O system is revised.

Synthesis and thermodynamics of the reactions of [Pd(Eten)(H2O)2]2+ with ligands of biological significane with reference to the antitumour activity

Pd(Eten)Cl2 complex, where Eten = N-ethylethylenediamine , was synthesized and characterized by elemental analysis and spectroscopic techniques. The stoichiometry and stability of the complexes formed between [Pd(Eten)(H2O)2]2+ and various biologically relevant ligands as adenine, adenosine, adenosine-5’-monophosphate and some selected peptides were investigated at 25ºC and 0.1 M ionic strength. The speciation diagrams of the complexes formed in solutions are evaluated. Thermodynamic parameters for Pd(Eten)-glycylglycine complexes were estimated.

Electrodialysis of Phosphates in Industrial-Grade Phosphoric Acid

The objective of this research was to study the purification of industrial-grade phosphoric acid (P2O5) by conventional electrodialysis. The experiments were conducted using a three-compartment cell with anion and cation membranes, and industrial acid solution was introduced into the central compartment. The elemental analysis of the diluted solution indicated that the composition of magnesium, phosphates, and sodium was reduced in the central compartment. The ratios of the concentration of the ions and the phosphates were essentially unchanged by the process. Consequently, electrodialysis could not purify the acid in the central compartment, and the migration of phosphate ions to the anolyte produced a highly concentrated phosphoric acid solution containing sulfates and chlorides as impurities. However, the migration of the phosphate ions across the membrane consumed a large amount of energy. Detailed speciation diagrams were constructed in this study. These diagrams showed that metal-phosphate complexes were predominant in the industrial phosphoric acid solution. This result explains why the ratios of the concentrations of the ion metals and the phosphates did not change in the purification process. The energy consumed in the electrodialysis indicated that the metal-phosphate complexes were less mobile than the free-phosphate ions. The speciation diagrams explained the experimental results satisfactorily.