Importance of the embedding environment on the strain within small rings in siliceous materials

The effect of the local environment on the energetic strain within small (SiO)N rings (with N=2,3) in silica materials is investigated via periodic model systems employing density functional calculations. Through comparison of the energies of various nonterminated systems containing small rings in strained and relatively unstrained environments, with alpha quartz, we demonstrate how small ring strain is affected by the nature of the embedding environment. We compare our findings with numerous previously reported calculations, often predicting significantly different small-ring strain energies, leading to a critical assessment of methods of calculating accurate localized ring energies. The results have relevance for estimates of the strain-induced response (e.g., chemical, photo, and radio) of small silica rings, and the propensity for them to form in bulk glasses, thin films, and nanoclusters.

Modeling nitrogen adsorption in spherical pores of siliceous materials by density functional theory

Adsorption of nitrogen in spherical pores of FDU-1 silica at 77 K is considered by means of a nonlocal density functional theory (NLDFT) accounting for a disordered structure of pore walls. Pore size distribution analysis of various FDU-1 samples subject to different temperatures of calcination revealed three distinct groups of pores. The principal group of pores is identified as ordered spherical mesopores connected with each other by smaller interconnecting pores and irregular micropores present in the mesopore walls. To account for the entrances (connecting pores) into spherical mesopores, a concept of solid mass distribution with respect to the apparent density was introduced. It is shown that the introduction of the aforementioned distribution was sufficient to quantitatively describe experimental adsorption isotherms over the entire range of relative pressures spanning six decades.

Effect of the Concentration of Siliceous Materials Added to Tobacco Cigarettes on the Composition of the Smoke Generated during Smoking

Two as-synthesized meso- and macro-porous siliceous materials (MPSMs), i.e., Al-MCM-41 and SBA-15, were mixed with tobacco to study their effect on tobacco smoke chemistry. A reference cigarette, 3R4F, and a commercial cigarette, Fortuna, containing different percentages of MPSM were smoked in a smoking machine, and the mainstream smoke was analyzed. SBA-15 showed the highest reductions of nicotine; close to 90% when it was added at 8 mass %. The superb behavior of these materials may be related to their high particulate matter filtering efficiency in combination with their catalytic activity. The selectivity of these materials with respect to nicotine was also analyzed. Al-MCM-41 presents higher selectivity for condensed compounds than for gases, whereas SBA-15 presents similar ratios for both fractions. The highest selectivity was obtained for the liquid fraction when smoking 3R4F cigarettes mixed with Al-MCM-41.

Dye adsorption onto mesoporous materials: PH influence, kinetics and equilibrium in buffered and saline media

Mesoporous materials were used as adsorbents for dye removal in different media: non-ionic, buffered and saline. The mesoporous materials used were commercial (silica gel) as well as as-synthesised materials (SBA-15 and a novel mesoporous carbon). Dye adsorption onto all the materials was very fast and the equilibrium was reached before 1h. The pH has a significant influence on the adsorption capacity for the siliceous materials since the electrostatic interactions are the driving forces. However, the influence of the pH on the adsorption capacity of the carbonaceous material was lower, since the van der Waals interactions are the driving forces. The ionic strength has a great impact on the siliceous materials adsorption capacity, being their adsorption capacity in a buffered medium six times higher than the corresponding to a non-ionic medium. Nevertheless, ionic strength does not influence on the dye adsorption on the mesoporous carbon. Overall, the as-synthesised carbon material presents a clear potential to treat dye effluents, showing high adsorption capacity (q_e≈200mg/g) in all the pH range studied (from 3 to 11); even at low concentrations (C_e≈10mg/L) and at short contact times (t_e<30min).

The trapping and decomposition of toxic gases such as hydrogen cyanide using modified mesoporous silicates

Selected silicas were modified with the covalently bound ligand 2,6-bis(benzoxazoyl)pyridine (BBOP), equilibrated with copper(II) nitrate, then challenged with toxic vapour containing HCN (8000 mg m(-3) at 80% relative humidity). The modified SBA-15 material (Cu-BBOP-SBA-15) had an improved breakthrough time for HCN (36 min at a flow rate of 30 cm(3) min(-1)) when compared to the other siliceous materials prepared in this study, equating to a hydrogen cyanide capacity of 58 mg g(-1), which is close to a reference activated carbon adsorbent (24 min at 50 cm(3) min(-1)) that can trap 64 mg g(-1). The enhanced performance observed with Cu-BBOP-SBA-15 has been related to the greater accessibility of the functional groups, arising from the ordered nature of the interconnected porous network and large mesopores of 5.5 nm within the material modified with the Cu(II)-BBOP complex. Modified MCM-41 and MCM-48 materials (Cu-BBOP-MCM-41 and Cu-BBOP-MCM-48) were found to have lower hydrogen cyanide capacities (38 and 32 mg g(-1) respectively) than the Cu-BBOP-SBA-15 material owing to the restricted size of the pores (2.2 and <2 nm respectively). The materials with poor nano-structured ordering were found to have low hydrogen cyanide capacities, between 11 and 19 mg g(-1), most likely owing to limited accessibility of the functional groups. (C) 2004 Elsevier Inc. All rights reserved.

Minerals of bulk samples and the fine-grained (<2-µm) fractions from DSDP Leg 67 Holes

Leg 67 sample sediments are mainly composed of biogenic carbonate and biogenic siliceous materials. Apart from calcite, crystallized minerals are scarce; however, they are better represented in sites near the continent and in all Quaternary sediments. These minerals are: quartz, feldspars, smectite, and, rarely, chlorite, dolomite, and zeolite.

Modelización del registro y proceso de datos espectrales, referidos a superficies líticas, en un ámbito arqueológico.

La determinación del origen de un material utilizado por el hombre en la prehistoria es de suma importancia en el ámbito de la arqueología. En los últimos años, los estudios de procedencia han utilizado técnicas que suelen ser muy precisas pero con el inconveniente de ser metodologías de carácter destructivo. El fenómeno de la minería a gran escala es una de las características que acompaña al Neolítico, de ahí que la revolución correspondiente a este periodo sea una de las etapas más importantes para la humanidad. El yacimiento arqueológico de Casa Montero es una mina de sílex neolítica ubicada en la Península Ibérica, de gran importancia por su antigüedad y su escala productiva. Este sitio arqueológico corresponde a una cantera de explotación de rocas silícicas desarrollada en el periodo neolítico en la que solamente se han encontrado los desechos de la extracción minera, lo cual incrementa la variabilidad de las muestras analizadas, de las que se desconoce su contexto económico, social y cultural. Es de gran interés arqueológico saber por qué esos grupos neolíticos explotaban de forma tan intensiva determinados tipos de material y cuál era el destino de la cadena productiva del sílex. Además, por ser una excavación de rescate, que ha tenido que procesar varias toneladas de material, en un tiempo relativamente corto, requiere de métodos expeditivos de clasificación y manejo de dicho material. Sin embargo,la implementación de cualquier método de clasificación debe evitar la alteración o modificación de la muestra,ya que,estudios previos sobre caracterización de rocas silícicas tienen el inconveniente de alterar parcialmente el objeto de estudio. Por lo que el objetivo de esta investigación fue la modelización del registro y procesamiento de datos espectrales adquiridos de rocas silícicas del yacimiento arqueológico de Casa Montero. Se implementó la metodología para el registro y procesamiento de datos espectrales de materiales líticos dentro del contexto arqueológico. Lo anterior se ha conseguido con la aplicación de modelos de análisis espectral, algoritmos de suavizado de firmas espectrales, reducción de la dimensionalidad de las características y la aplicación de métodos de clasificación, tanto de carácter vectorial como raster. Para la mayoría de los procedimientos se ha desarrollado una aplicación informática validada tanto por los propios resultados obtenidos como comparativamente con otras aplicaciones. Los ensayos de evaluación de la metodología propuesta han permitido comprobar la eficacia de los métodos. Por lo que se concluye que la metodología propuesta no solo es útil para materiales silícicos, sino que se puede generalizar en aquellos procesos donde la caracterización espectral puede ser relevante para la clasificación de materiales que no deban ser alterados, además, permite aplicarla a gran escala, dado que los costes de ejecución son mínimos si se comparan con los de métodos convencionales. Así mismo, es de destacar que los métodos propuestos, representan la variabilidad del material y permiten relacionarla con el estado del yacimiento, según su contenido respecto de las tipologías de la cadena operativa. ABSTRACT: The determination of the origin of a material used by man in prehistory is very important in the field of archaeology. In recent years the provenance studies have used techniques that tend to be very precise but with the drawback of being destructive methodologies. The phenomenon of mining on a large scale is a feature that accompanies the Neolithic period; the Neolithic revolution is one of the most important periods of humanity. The archaeological site of Casa Montero is a Neolithic flint mine located in the Iberian Peninsula of great importance for its antiquity and its scale. This archaeological site corresponds to a quarry exploitation of silicic rocks developed in the Neolithic period, in which only found debris from mining, which increases the variability of the samples analyzed, including their economic, social and cultural context is unknown. It is of great archaeological interest to know why these Neolithic groups exploited as intensive certain types of material and what the final destination of flint was in the productive chain. In addition, being an excavation of rescue that had to process several tons of material in a relatively short time requires expeditious methods of classification and handling of the material. However, the implementation of any method of classification should avoid the alteration or modification of the sample, since previous studies on characterization of silicic rocks have the disadvantage of destroying or partially modify the object of study. So the objective of this research wasthe modeling of the registration and processing of acquired spectral data of silicic rocks of the archaeological site of Casa Montero. The methodology implemented for modeling the registration and processing of existing spectral data of lithic materials within the archaeological context, was presented as an alternative to the conventional classification methods (methods destructive and expensive) or subjective methods that depend on the experience of the expert. The above has been achieved with the implementation of spectral analysis models, smoothing of spectral signatures and the dimensionality reduction algorithms. Trials of validation of the proposed methodology allowed testing the effectiveness of the methods in what refers to the spectral characterization of siliceous materials of Casa Montero. Is remarkable the algorithmic contribution of the signal filtering, improve of quality and reduction of the dimensionality, as well the proposal of using raster structures for efficient storage and analysis of spectral information. For which it is concluded that the proposed methodology is not only useful for siliceous materials, but it can be generalized in those processes where spectral characterization may be relevant to the classification of materials that must not be altered, also allows to apply it on a large scale, given that the implementation costs are minimal when compared with conventional methods.

Determinación del contenido de alúmina reactiva de las adiciones puzolánicas naturales y artificiales, por termogravimetría y por el método de Rietveld

Tanto el tema de esta investigación, como sus objetivos, fundamentos, materiales seleccionados y parte experimental para alcanzarlos, han sido promovidos por la situación y el estado de las construcciones de hormigón armado que se comenzaron a realizar en España a partir del año 1975, con hormigones y morteros de cemento que contenían cenizas volantes hasta un 20 %, en principio, y hasta un 35 %, más tarde, de su dosificación de cemento Portland (CP), los cuales y en contra de lo esperado, han demandado y continúan demandando, muy a pesar de sus aparentes bondades de todo tipo que se les atribuían, una necesidad de mejora de sus prestaciones, especialmente, debido a un nivel inesperadamente bajo de la durabilidad de algunas obras construidas con los mismos. Todo era debido, en definitiva, a que las adiciones puzolánicas, naturales y artificiales, tales como las cenizas volantes, referidas antes, se vienen utilizando reglamentariamente para la fabricación de cementos y/o de sus productos derivados, hormigones, morteros y pastas, en la mayor parte de los países industrializados, desde hace ya más de tres décadas aproximadamente, en las mismas condiciones e idénticos usos constructivos que los hormigones y morteros de CP puro, viniendo además, dictada dicha utilización de estos materiales residuales, hoy sub-productos industriales, por cuestiones medioambientales y/o económicas, principalmente, motivo por el cual esta Tesis Doctoral ha pretendido responder también, adecuadamente y de manera esquemática (en forma de diagrama de flujo), a los criterios que deben de tenerse en cuenta a la hora de su selección y caracterización normalizada y reglamentada de estas adiciones minerales activas, sobre todo, antes de su dosificación y uso en forma del denominado cemento Portland con puzolana, o con ceniza volante, o con esquistos calcinados o con puzolanas calcinadas o con humo de sílice, cemento Portland mixto, cemento puzolánico o cemento compuesto, para que dichos problemas no se le produzcan al hormigón armado ni en masa. De aquí el enfoque tan particular y especial de esta investigación, al haberla circunscrito únicamente a las puzolanas naturales y artificiales, por considerarlas todas ellas, independientemente de por su origen, como materiales constituidos por pequeñas fracciones cristalinas distribuidas aleatoriamente en una matriz mayoritariamente vítrea y/o amorfa, la cual es la que le confiere su reactividad con el hidróxido de calcio en forma de cal apagada o de portlandita procedente de la hidratación del CP. A su vez, dichas fracciones vítreas y/o amorfas están constituidas, en su mayor parte, por sílice reactiva, SiO2r-, alúmina reactiva, Al2O3r-, y óxido de hierro reactivo, Fe2O3r-, recibiendo además, en conjunto, el nombre específico de "factores hidráulicos" de la puzolana, los cuales, por lo común, difieren cuantitativamente de sus contenidos totales, determinados por fusión alcalina mediante procedimientos normalizados. De los tres óxidos reactivos mencionados y desde el punto de vista técnico, los más importantes por su mayor presencia en casi todas las puzolanas naturales y artificiales y, también, transcendencia en la durabilidad química que les pueden llegar a conferir al hormigón armado y en masa, mortero o pasta de cemento que las contenga, son la SiO2r- y la Al2O3r-. El primero de los dos, la SiO2r-, reacciona nada más que con la portlandita (y el Ca(OH)2) para formar geles C-S-H, más tarde transformados en tobermoritas o en jennitas, semejantes a los que originan la alita y la belita del CP en su hidratación. Y desde el punto de vista normativo, la presencia de esta fracción silícica reactiva en las puzolanas viene regulada por la norma EN 197-1, de modo general, siendo además referida por la norma EN 450-1:2006, en el contexto de las cenizas volantes en su adición al hormigón, como "un polvo fino de partículas principalmente de forma esférica y cristalina, procedentes de la combustión de carbón pulverizado, que tiene propiedades puzolánicas y que está compuesto fundamentalmente de SiO2 y Al2O3". Además y de acuerdo con la primera de las dos normas, "El contenido de dióxido de silicio reactivo (definido y determinado según la norma EN 196-2 o su equivalente la UNE 80225) no debe ser inferior al 25 % en masa". Por su parte, cuantiosos estudios experimentales realizados por Talero solo y con otros investigadores, han demostrado que si la puzolana no es adecuada en calidad ni en cantidad, la durabilidad del cemento del que forme parte, y, por consiguiente, de los productos derivados que con él se fabriquen, hormigones, morteros, pastas y prefabricados, puede llegar a ser anormalmente baja, porque la alúmina reactiva, Al2O3r-, o alúmina tetra- o penta-coordinada que la constituye, se implica como tal, de una forma muy directa y con resultados totalmente contrapuestos incluso, en los ataques químicos agresivos naturales que se les producen, provenientes de terrenos y aguas selenitosas (sulfatos, que atacan en su caso al propio material hormigón, mortero y pasta que la contiene para formar ettringita de rápida formación, ett-rf, la cual puede llegar incluso a provocar un ataque rápido del yeso), del rocío marino y de las sales de deshielo (cloruros, que atacan, en cambio, a las armaduras de acero del hormigón provocándoles su corrosión electroquímica por "picadura", si bien, en este otro ataque químico, dicha Al2O3r- lo que origina es sal de Friedel de rápida formación, sF-rf, también, cuyo efecto es, en cambio, colmatador y protector, en definitiva, de dicha corrosión electroquímica), del agua de mar (acción agresiva mutua de cloruros y sulfatos), de la carbonatación, de la reactividad árido-álcali, además de intervenir en la liberación del calor de hidratación, así como también, en el comportamiento reológico de sus pastas, etc., acortándoles de este modo su durabilidad prevista y, en ocasiones, muy seriamente incluso. Pero lo más paradójico de todo es, que a pesar de su referido comportamiento totalmente contrapuesto, frente a sulfatos y cloruros, - aún no se dispone de un método de análisis químico para su determinación cuantitativa, que sea además relativamente sencillo en su operatividad, veraz, preciso, de respuesta rápida, desde el punto de vista técnico de la construcción (no más de 28 días), repetible, reproducible, que no implique peligro alguno para la seguridad vital de las personas que lo tengan que manipular y poner en práctica, económico, y que sirva también tanto para investigación -vertiente científica-, como, sobre todo, para control de calidad -vertiente técnica-, - y ni mucho menos tampoco se dispone todavía, de especificación química alguna que precise el contenido máximo de Al2O3r- (%) que tiene que poseer una puzolana natural o artificial, para poder ser añadida al cemento Portland y/o al hormigón que va a estar sometido a un determinado ataque químico agresivo de los mencionados antes, y, en especial, a sulfatos, a cloruros o al agua de mar. Y para mayor justificación de ambas necesidades, se ha de decir también que la vigente Instrucción de Hormigón Estructural EHE-08 no contempla tampoco especificación química alguna sobre los "factores hidráulicos", en general, ni del contenido de Al2O3r-(%) de las cenizas volantes, muy en particular, en su Artículo 30º "Adiciones", ni en ningún otro Artículo, a pesar de que sí contempla, en cambio, - otras especificaciones químicas que carecen del necesario significado en cuanto a la necesidad de llevar explícita o implícitamente, el mensaje de la Durabilidad Química deseado, y - el Artículo 37º, el cual y para mayor abundamiento se titula paradójicamente "Durabilidad del hormigón y de las armaduras". Asimismo, tampoco se contempla en la última versión que acaba de publicarse de la norma EN 197-1 titulada: "Cementos. Parte 1: Composición, especificaciones y criterios de conformidad de los cementos comunes". Ni tampoco, en la norma EN 450-1:2006 titulada "Cenizas volantes para hormigón. Parte 1: Definiciones, especificaciones y criterios de conformidad", ni en la vigente Instrucción española para la Recepción de Cementos, RC-08, ni en la norma ASTM C618-03 tampoco. La única especificación química que ambas normas, la europea y la norteamericana, refieren es aquella que dice que la suma de los contenidos porcentuales de SiO2 total, Al2O3 total y Fe2O3 total, de la puzolana natural o artificial, ha de ser mayor o igual que 70 %, definiendo, además, a las puzolanas de este modo tan genérico: "materiales silíceos o silíceos y aluminosos, que por sí mismos no poseen valor cementante alguno, pero que finamente divididos y en presencia de humedad, reaccionarán químicamente con hidróxido de calcio a temperaturas ordinarias para formar compuestos que poseen propiedades cementantes". Por consiguiente y de acuerdo con todo lo anterior, el objetivo primordial de esta Tesis Doctoral ha sido: Diseñar y poner a punto un nuevo método analítico de utilidad técnica (que la duración máxima del ensayo no sea mayor de 28 días), para determinar el contenido de alúmina reactiva, vítrea o amorfa, Al2O3r-, de las puzolanas naturales y artificiales. Y una vez puesto a punto, validarlo a nivel de su repetibilidad, de acuerdo con parámetros estadísticos apropiados, poniendo especial énfasis en los criterios de aceptación establecidos por la American Association of Official Analytical Chemists (AOAC). Y para conseguirlo, la innovación de esta investigación se ha basado en los siguientes fundamentos generales, a saber: - Toda la alúmina de cualquier puzolana natural o artificial, capaz de ser atacada, disuelta y lixiviada en 28 días, por la portlandita o por el hidróxido de calcio, Ca(OH)2, en medio acuoso, es considerada como alúmina reactiva, Al2O3r-. - Dicha fracción alumínica reactiva de la puzolana natural o artificial se tiene que encontrar, además, en el estado físico-químico de poder reaccionar químicamente también, en presencia de hidróxido de calcio, cloruro de sodio y agua, para originar monocloro¿aluminato de calcio hidratado, C3A·CaCl2·10H2O, o sal de Friedel. Además, dicho estado físico-químico de la puzolana ha de ser acorde con la definición de alúmina reactiva adoptada en esta investigación en razón de las prestaciones reales de durabilidad química que le puede llegar a conferir a los cementos de mezcla y a sus productos derivados, hormigones, morteros y pastas, que se fabriquen con la misma. - La originalidad de este nuevo método analítico, respecto a los demás métodos ya existentes, reside en que la cuantificación de dicha fracción alumínica reactiva de la puzolana natural o artificial, se realiza mediante cálculo estequiométrico, basándose, para ello, en dicha reacción química de formación de sal de Friedel precisamente, tras 28 días de hidratación básica-salina acelerada de la puzolana natural o artificial, habiéndose realizado, además, en esta investigación dicha determinación cuantitativa de la cantidad de sal de Friedel originada por cada puzolana, mediante dos técnicas analíticas instrumentales que fueron las siguientes: el análisis termogravimétrico (variante I ó I-I en su caso) y el método de Rietveld con la difracción de Rayos X en polvo (variante II). - La reacción química de formación de sal de Friedel tras 28 días de hidratación básica-salina acelerada de las puzolanas que se analicen, se optimizó para asegurar que el único compuesto químico de aluminio y cloro formado fuese sal de Friedel nada más (dosificando para ello en cantidad adecuada los reactivos químicos necesarios: Ca(OH)2, NaCl y agua destilada), manteniendo, además y por otra parte, el compromiso apropiado entre el máximo rendimiento de dicha reacción química (ataque, disolución y lixiviación en 28 días, de toda la alúmina reactiva de la puzolana) y el modo y medios más adecuados de acelerarlo para conseguirlo fue a 40°C de temperatura, con agitación constante y cierre hermético del reactor. - La aplicabilidad y selectividad del nuevo método analítico, objeto de esta Tesis Doctoral, fue estudiada con una serie de puzolanas naturales y artificiales españolas, silíceas y/o silíceas y aluminosas en naturaleza, que fueron las siguientes: M0 (metacaolín 0), M1 (M0 con 50 % de cuarzo), C y L (puzolanas naturales de las Islas Canarias), CV10 y CV17 (cenizas volantes), A (puzolana natural de Almagro), O (puzolana natural de Olot) y HS (humo de sílice). - Todas las adiciones minerales anteriores cumplieron con los principales requisitos físicos y químicos que son preceptivos para poder considerarlas, antes de todo, como puzolanas, lo que era indispensable y de obligado cumplimiento, para poderles determinar su contenido total de Al2O3r- (%) mediante el nuevo método analítico. Estos condicionantes fueron los siguientes: grado adecuado de finura de molido o tamaño medio de partícula (según la norma EN 451-2), haber sido analizadas químicamente antes de todo (según la norma EN 196-2 ó la ASTM C311), con el fin de determinarles especialmente, sus contenidos totales de SiO2 (%), Al2O3 (%) y Fe2O3 (%), haberles determinado, además, su contenido de sílice reactiva, SiO2r- (%) (según la norma UNE 80225), y haber cumplido con el ensayo de puzolanicidad o de Frattini (según la norma EN 196-5) a la edad de 28 días al menos. Este último requisito, otrora de obligado cumplimiento hasta el año 1988, para cualquier puzolana natural y artificial que una fábrica de cementos pretendiera introducir en el proceso de fabricación de un nuevo cemento puzolánico o cemento tipo CEM IV, ha logrado así, que se tenga que volver utilizar de nuevo de forma obligada con esta Tesis Doctoral. Y los resultados obtenidos con el nuevo método analítico de los contenidos de Al2O3r-(%) de las puzolanas seleccionadas, fueron los siguientes: - Mediante su variante I: M0 29.9 %, M1 16.9 %, CV10 11.4 %, L 12.3 %, C 12.6 %, A 8.0 %, CV17 9.5 % y O 6.3 % de Al2O3r-, y - Mediante su variante II: M0 30.7 %, M1 15.4 %, CV10 14.7%, L 11.8 %, C 11.1 %, A 8.9 %, CV17 9.6 % y O 6.8 % de Al2O3r-. Finalmente, todos ellos fueron contrastados, además, mediante la calibración y validación del nuevo método analítico, con los valores de referencia obtenidos de esas mismas puzolanas, los cuales se les habían determinado mediante el método de Florentín, consistente en atacar, disolver y lixiviar también toda la fracción alumínica soluble de la puzolana (y además, aquella silícica y férrica que la constituyen a la par), pero, en especial, su contenido total de alúmina reactiva, mediante un ataque básico (con Ca(OH)2 en medio acuoso a temperatura del laboratorio, habiendo sido, además, su duración hasta 1 año), seguido de otro ácido (con HCl, d = 1.12), habiéndose obtenido esta vez los siguientes resultados de sus contenidos de Al2O3r- (%): M0 28.8 %, M1 16.7 %, CV10 9.7 %, L 11.2 %, C 12.2 %, A 13.0 %, CV17 10.6 % y O 9.5 %. Dicha validación realizada ha puesto de manifiesto, en términos generales, que el nuevo método analítico es más fidedigno que el de Florentín, por lo que resulta ser totalmente apropiado para obtener los resultados que se han pretendido, además de proporcionarlos en un espacio de tiempo relativamente corto (28 días a lo sumo) y a un coste económico razonable por no elevado (salvo error u omisión y libre de impuestos directos e indirectos, el coste económico estimado de la variante I estaría en torno a 800.00 - 900.00 €/puzolana -caso más probable-, y aproximadamente una tercera parte nada más, en el caso de que la edad máxima del ensayo acelerado sea 7 días nada más -caso menos probable-), y, por consiguiente, técnicamente aceptable, al cumplir, además, en todo el rango considerado de variabilidad posible de concentraciones o contenidos del analito buscado en la puzolana, con tales parámetros de validación como son: linealidad (los resultados obtenidos son directamente proporcionales a la señal-respuesta instrumental recibida), sensibilidad, precisión excelente, repetibilidad satisfactoria de los valores obtenidos de los contenidos de Al2O3r- de todas y cada una de las adiciones puzolánicas seleccionadas, confirmando, por ello, la universalidad de su uso. Finalmente, las ventajas del nuevo método analítico, respecto a los métodos ya existentes recopilados de la bibliografía (el método de Florentín, el método de López Ruiz -HF 40 % y HNO3 2N-, el método de Murat y Driouche para arcillas -HF 0.5M-, el método de Arjuan, Silbee y Roy para cenizas volantes -HF 1 %- y su modificación por Fernández-Jiménez y cols. -HF 1 %, 27Al NMR MAS y XRD (método de Rietveld)-, y el método de determinación de la relación SiO2r-/Al2O3r- para arcillas y cenizas volantes por Ruiz-Santaquiteria y cols. -HF 1 %, NaOH 8M y ICP-AES-) son, principalmente, estar exento de peligro alguno para la seguridad vital de las personas que lo tengan que manipular y poner en práctica, ser bastante apropiado para control de calidad además de para investigación, su considerable menor coste económico, su relativamente corto espacio de tiempo que se necesita para obtener la respuesta-resultado pretendida (28 días a lo sumo), así como su universalidad y selectividad, puesto que además, su aplicabilidad es para todo tipo de adiciones puzolánicas naturales o artificiales, como así lo demuestran los resultados obtenidos de los materiales puzolánicos naturales y artificiales seleccionados y analizados, en un rango de concentraciones del analito -contenido de alúmina reactiva, Al2O3r- (%)-, desde el 5 % hasta el 30 % en masa, rango éste que, por otra parte, comprende prácticamente TODAS las adiciones puzolanas naturales y artificiales existentes en el mercado transnacional y las aún por existir. Por consiguiente y de acuerdo con lo anterior, el nuevo método analítico, ya sea realizado mediante su variante I o la II, debido, - en primer lugar, a los fundamentados planteamientos relativos a su procedimiento experimental -modus operandi- el cual ha sido aplicado a una amplia gama de puzolanas naturales y artificiales, y - en segundo lugar, debido a la calidad de los resultados obtenidos con un grado de precisión y repetibilidad excelentes, ha demostrado poseer una gran utilidad científica -para investigación-, pero, sobre todo, técnica -para control de calidad de adiciones puzolánicas naturales y artificiales que se adicionan habitualmente al cemento Portland en fábrica y/o a sus hormigones y morteros en planta-, además de ser representativos los valores obtenidos mediante el mismo respecto a la más que probable durabilidad química que cada una de ellas puede llegarle a conferir al hormigón armado y en masa, mortero y pasta del que forme parte, así como también su cantidad adecuada de sustitución parcial de cada cemento Portland para conseguirla, acorde con sus propias prestaciones químico-físicas o físico-químicas que puede llegarle a conferir, según sea su carácter químico (alumínico, alumínico-silícico, silícico-alumínico, silícico-férrico-alumínico o silícico), forma y tamaño medio de su partícula. Por último, el nuevo método analítico ha demostrado cumplir además, con todos los requisitos de obligado cumplimiento que establece la norma ISO/IEC 17025 sobre la calidad y fiabilidad de nuevos métodos o procedimientos analíticos no normalizados todavía, para poder ser propuesto en un futuro próximo, ante la Comisión de AENOR correspondiente, con objeto de comenzar un expediente para su certificación y normalización. ________________________________________________________________________________ Both the subject of this research, its objectives, fundamentals, materials selected and experimental part to achieve, have all been promoted by the situation and the state of reinforced concrete constructions that began performing in Spain from 1975, with concrete and mortars cement containing fly ash up to 20 %, in principle, and later, up to 35 % to its content of Portland cement, which and against expected, demanded a need to improve their performance, especially due to an unexpectedly low level of durability of some works built with them, despite, however, its apparent benefits of all kinds are ascribed to them. Ultimately, the natural or artificial pozzolanic additions, such as fly ash specially, referred to above, have been used with regulation to manufacture cements and/or its derivatives, concretes, mortars, cement pastes, in the most industrialized countries. More than three decades ago, under the same conditions and identical construction mainly uses concretes and mortars plain Portland cement, besides coming, given that use of these waste materials, industrial by-products today for environmental and/or economic issues. For this reason, this Doctoral Thesis aims to answer properly and schematically (in the form of flow chart), the criteria to be taken into account when selection and characterization standardized for these active mineral additions, especially prior to choosing and use in the so-called Portland Cement (PC) pozzolan, or with fly ash or with calcined shales or with calcined pozzolans or with silica fume or PC mixed or pozzolanic cement or compound cement, for that such pathology problems will not occur when reinforced concretes nor mass concretes are used for building. Hence the very particular and special focus about this research, having confined only to the natural or artificial pozzolans, considering them all, regardless of their origin, approach as materials consisting of small crystalline fractions randomly distributed in a largely vitreous and/or amorphous matrix, which confers their reactivity with calcium hydroxide in the form of slaked lime or portlandite from PC. In turn, these vitreous and/or amorphous fractions consist in its greater part, by reactive silica, SiO2r-, reactive alumina, Al2O3r-, and reactive iron oxide, Fe2O3r-, which also receive, in conjunction, the specific name of "hydraulic factors" of the pozzolan. Usually, they all differs in quantity of their respective total contents of the SiO2 (%), Al2O3 (%) and Fe2O3 (%) determined the pozzolan by alkaline fusion by means of standard procedures. Of the three above-mentioned oxides reagents and from the technical point of view, the most important for its increased presence in every one of the natural or artificial pozzolans and also significance in the chemical durability that can get them to give the concrete mortar or cement paste which contain them, are SiO2r- and Al2O3r-. From the first two, the SiO2r- reacts with portlandite only, released in the hydration of the PC (and with Ca(OH)2), to form C-S-H gels, transformed in tobermorites or jennites later on, similar to C-S-H gels also originating from the alite and belite hydration in the CP. From the standardization criteria point of view, the presence of this silicic fraction in pozzolans is regulated at first, by the European standard EN 197-1, in general, also being referred by the EN 450-1:2006, in the context of the fly ash in addition to the concrete, as a "fine powder of spherical particles mainly crystalline form. It is from the combustion of pulverized coal, which have pozzolanic properties and is mainly composed of SiO2 and Al2O3". In addition and according to the EN 197-1 standard, the reactive silica content (which can be defined and determined in accordance with EN 197-1 standard or its UNE 80225 standard) must not be lower than 25 % of its mass. Meanwhile, considerable experimental studies by Talero and Talero et al, have shown that if the pozzolan is not adequate in quality nor quantity, the durability of cement that is part and, therefore, of its derivative products, concretes, mortars and pastes cement, can become abnormally low because its reactive alumina, Al2O3r- (%), content or tetra- or penta-coordinated alumina which involves itself in a very direct and totally mixed and conflicting results even at all aggressive chemical attack natural to produce to the concrete, mortar and paste with inadequate natural and/or artificial pozzolans, such as those from the selenitous land and waters (sulfates, strikes if the material itself concrete, mortar and paste that contain them, for rapid forming ettringite form, ett-rf, which can even cause rapid gypsum attack to said concrete). In contrast, sea spray and de-icing salts (chlorides strikes the reinforced steel concrete causing them electrochemical corrosion by "bite", although in that other chemical attack, such Al2O3r- causes rapid Friedel's salt formation, Fs-rf, too, to cause protector effect of the electrochemical corrosion of reinforcements for these chlorides), seawater (mutual aggressive action of chlorides and sulfates), carbonation, alkali-silica reaction, and, in addition, to influence the release of hydration heat, as well as in the rheological behavior of the pastes, etc., decreasing/shorting them thus their expected durability and sometimes even very seriously. But the most ironic thing is, that despite its referral totally opposed, compared to sulfates and chlorides, behaviour, - far not available is, a chemical analysis method for its quantitative determination, which is also relatively simple in operation, accurate, precise, rapid response, from a technical point of view for building (no more than 28 days), repeatable, reproducible, not involving danger to life safety of the people who need to manipulate and implement, economic, and also serve for both scientific research and technical side, and - has yet to be any chemical specification that sets maximum levels for Al2O3r-(%) in the natural or artificial pozzolan to be added to the cement and/or to the concrete that will be subject to a particularly aggressive chemical attack from those mentioned above, and in particular, to sulphates, chlorides or sea water. And for the sake of and justification of this need, it has to be said that the current Spanish Instruction for Structural Concrete EHE-08 does not provide any specification on "hydraulic factors" in general, nor the content of Al2O3r- (%) in fly ash, very particular, as Article 30º "Additions", or any other Article, although does provide, however, other chemical specifications lacking the necessary meaning in terms of the message Chemical Durability mentioned, nor the Article 37º which and for greater sake, is paradoxically entitled "Durability of the concrete and of their reinforcements". It has also not contemplated in the latest version just released from EN 197-1 standard entitled "Cement Part 1: Composition, specifications and conformity criteria for common cements". Nor, in EN 450-1:2006 entitled "Fly ash for concrete Part 1: Definitions, specifications and conformity criteria", nor by current Spanish Instruction for Cement Reception, RC-08, nor the ASTM C618-03 Standard either. The only chemical specification that both Standards, European and American, refer is one that says that the sum of the total contents of SiO2 (%), Al2O3 (%) and Fe2O3 (%) of natural and artificial pozzolan, must be greater than or equal to 70 % , defining pozzolans thus: "siliceous or aluminous and siliceous materials, which themselves do not have any cementitious value but finely divided and in the presence of moisture it reacts with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties". Consequently and according to everything related before, the primary objective of this Doctoral Thesis has been: To design and start-up a new quantitative analytical method of technical utility (the maximum test duration is not more than 28 days), to determine the content of reactive alumina content, Al2O3r- (%), vitreous or amorphous alumina, of natural and artificial pozzolans. And once designed, validate at repeatability level and in accordance with appropriate statistical parameters with special emphasis on the acceptance criteria established by the American Association of Official Analytical Chemists (AOAC). And to achieve this, the innovation of this research has been based on the following general principles, namely: - All the alumina in any pozzolan, natural or artificial, that can be attacked, dissolved and leached by portlandite or calcium hydroxide, Ca(OH)2, in aqueous medium, is considered reactive alumina, Al2O3r-. - This aluminic fraction of natural or artificial pozzolan to analyze and study, has to be in such physical-chemical state that it can react in the presence of calcium hydroxide, sodium chloride and water status and to cause monochloro-aluminate hydrated calcium, C3A·CaCl2·10H2O or Friedel's salt. Moreover, such physical-chemical state of the pozzolan must be consistent with the definition of reactive alumina adopted in this research because of the actual performance of chemical durability that can reach confer on blended cements and their derivatives, concretes, mortars and pastes that are manufactured with the same. - The originality of this new analytical method, compared to the other methods for determining reactive alumina existing (collected in abbreviated form in the state of the art of this report), is the quantification of such aluminic fraction of natural or artificial pozzolans is performed by stoichiometric calculation based on this, in the chemical reaction of Friedel's salt formation after 28 days of the analysis of saline-basic hydration accelerated natural or artificial pozzolan also performed in this research, and the quantitative determination of the Friedel's salt has been performed by two instrumental analytical techniques known as thermogravimetric analysis (variant I), and Rietveld method with X-ray powder diffraction (variant II). - The chemical reaction of Friedel's salt formation after 28 days of accelerated saline-basic hydration of the selected natural and artificial pozzolan, was optimized to ensure that the single chemical compound of aluminium and chlorine formed was Friedel's salt only (dosing for this purpose in amount suitable chemical reagents: Ca(OH)2, NaCl and distilled water), and, on the other hand, maintaining the appropriate compromise between the highest yield from the chemical reaction (attack, dissolution and leaching in 28 days, all reactive alumina of pozzolan) and to accelerate the etching media, which were 40°C temperature, constant stirring and sealing the reactor. - The applicability and selectivity of the new analytical method, the subject of this Doctoral Thesis, was studied with a series of Spanish natural and artificial pozzolans, siliceous or siliceous and aluminous in nature, which were as follows: M0 (metakaolin 0), M1 (M0 with 50 % quartz), L and C (natural pozzolans of the Canary Islands), CV10 (fly ash 10), CV17 (fly ash 17), A (natural pozzolan of Almagro), O (natural pozzolan of Olot), and HS (silica fume). - All mineral admixtures were selected satisfied the physical and chemical requirements proposed to consider them as pozzolan, which was mandatory, so its Al2O3r- (%) content can determine by the new analytical method. These conditions were as follows: adequate degree of fineness of grind or average particle size (according to EN 451-2 standard), have been analyzed chemically (according to EN 196-2 or ASTM C311 standards), in order to determine their total contents of SiO2 (%), Al2O3 (%) and Fe2O3 (%), mainly, having also determined its reactive silica content, SiO2r- (%) (UNE 80225 standard), and fulfilled with testing of pozzolanicity or Frattini test (according to EN 196-5 standard) at 28 days age at least. The last criteria was mandatory until 1988, for any natural and artificial pozzolan to a factory intended to introduce cements in the manufacturing process of a new Portland cement type CEM IV pozzolanic additions, and with this Doctoral Thesis has made is to be used once again mandatory. And the results obtained using the new analytical method, of the Al2O3r- (%) content for each selected pozzolan, were as follows: - by its variant I: M0 29.9 % , M1 16.9 % , CV10 11.4 % , L 12.3 % , C 12.6 % , A 8.0 % , CV17 9.5 % and O 6.3 % of Al2O3r-, and - by its variant II: M0 30.7 % , M1 15.4 % , CV10 14.7% % , L 11.8 % , C 11.1 % , A 8.9 % , CV17 9.6 % and O 6.8 % of Al2O3r-. Finally, they would all be further contrasted by the calibration and validation of new analytical method, with reference values obtained from these same natural and artificial pozzolans, which had been given by the method of Florentin, consisting of attack, dissolve and leached with a basic attack (with Ca(OH)2 in aqueous medium and laboratory temperature, having also been its duration up to 1 year), followed by another acid attack (HCl, d = 1.12), all soluble aluminic fraction of pozzolan, and in particular their total content of reactive alumina, Al2O3r-(%), was this time as follows: M0 28.8 %, M1 16.7 %, CV10 9.7 %, L 11.2 %, C 12.2 %, A 13.0 %, CV17 10.6 % and O 9.5 % (and their siliceous and iron contents that are at par). This validation has shown on the new analytical method is more reliable than Florentin method, so it turns out to be entirely appropriate to get the results that have been tried by the same, besides providing them a relatively short space of time (28 days at most) and reasonably no high economic cost (unless mistake -free direct and indirect taxes, such economic cost would be between 800.00 - 900.00 €/pozzolan (most likely case), and about an one-third part around, in the event that the maximum age of the accelerated test is 7 days only (less likely case). So it is technically acceptable, to consider the range of possible variability of concentrations or contents pozzolan analyte with validation parameters such as: linearity (the results obtained are directly proportional to the instrumental response signal received), excellent sensitivity and accuracy, satisfactory repeatability values from the contents of each and Al2O3r- (%) each selected pozzolan, confirming therefore universal use. Finally, the advantages of the new analytical method over existing methods compiled from literature (Florentin method , the Lopez Ruiz method -HF and HNO3 40 % 2N-, the method of Murat and Driouche for clays -0.5M HF-, the method of Arjuan, Roy and Silbee for fly ash -HF 1 %- and its modification by Fernández-Jiménez et al -HF 1 %, 27Al MAS NMR and XRD (Rietveld method)-, and the method for determining the SiO2r-/Al2O3r- clay and fly ash ratio of Santaquiteria Ruiz et al -HF 1 %, NaOH 8M and ICP-AES-) are primarily and relatively short time get the result intended answer (28 days at most), its considerable lower cost, free from danger to the life safety of the people who need to manipulate and put in practice as well as its universality and selectivity, since it is applicable for all types of natural or artificial pozzolans, as it has been shown by the results of selected natural and artificial pozzolanic materials and analyzed in a range of analyte concentrations -reactive alumina, Al2O3r- (%) content- from 5 % to 30 % by mass, this range, on the other hand, includes virtually ALL existing transnational market in natural and artificial pozzolans and still exist. Therefore and in accordance with the above, the new analytical method is already performed by the variant I or II, because, - firstly, grounded to experimental approaches concerning its experimental procedure -"modus operandi"- which has been applied to a wide range of natural and artificial pozzolans, and - secondly, due to the quality of the results obtained with a great degree of accuracy and repeatability, it has been shown to possess significant scientific value in the research, but especially technical value -for quality control of natural and artificial pozzolans commonly added to Portland cement factory and/or directly to their concrete and mortar in plant-, and also be representative enough of the values obtained by the same probable chemical durability that each of them can reach out to give the concrete mortar and paste to which it belongs, as well as proper amount of partial replacement of Portland cement. To get in line with their own chemical-physical or physical-chemical features which can come to confer, as its chemical character (aluminic, silicic-aluminic, aluminic-silicic, aluminic-ferric-silicic or ferric-silicic), form and medium size of its particle is. Finally, the new analytical method has proven to meet all mandatory requirements established by ISO/IEC 17025 on the quality and reliability of new methods or analytical procedures are not standardized yet, in order to be considered appropriate this new analytical method, in this Doctoral Thesis it is to be proposed in the near future, before the corresponding AENOR (Spanish Association for Standardization and Certification) Commission, to start a procedure for certification and standardization.

SBS as template to synthesize 3D siliceous mesostructured cellular foams

A mesostructured cellular foam (MCF) with three-dimensional (313) disordered strutlike structure is prepared by using triblock copolymer (poly(styrene-b-butadiene-b-styrene), SBS, M-W = 140K) as template under strong acid conditions. It is the first report to use triblock copolymer with both hydrophobic head and tail groups instead of hydrophilic head and hydrophobic tail copolymers to synthesize siliceous mesostructured cellular foams. The resulted materials have high pore volume (0.92 cm(3)/g) and relatively narrow pore size distributions with a large pore size of 7.9 nm, which will allow for the fixation of large active complexes, reduce diffusional restriction of reactants and enable reactions involving bulky molecules to take place, especially.

Comparative study on the photoluminescent properties of siliceous MCM-41 with silica particles and xerogels

The samples of as-synthesized siliceous MCM-41, extracted MCM-41, amorphous silica particles and silica xerogels were heat treated from room temperature to 1000degreesC. Their photoluminescence (PL) spectra at room temperature excited by 254nm and 365nm ultraviolet light (UV) were investigated and compared. Excited by 254nm UV the MCM-41 samples do not display PL but amorphous silica particles and silica xerogels show PL, which changes with the heat treatment conditions for the samples. However, when excited by 365nm UV the PL spectra for the MCM-41 and the amorphous samples are similar. The carbon impurity and E' center mechanisms can be ruled out as the origin of PL in siliceous MCM-41 under UV excitation. The PL of MCM-41 series samples probably originates from oxygen-related defect center like dropSi-O-. according to the present work.

Effects of SBS addition and temperature on 3D siliceous mesostructured cellular foam

Siliceous mesostructured cellular foam with three-dimensional (3D) wormhole structure (MSU-type) is prepared by using triblock copolymer (poly(styrene-b-butadiene-b- styrene), SBS) with both hydrophobic head and tail group as template in strong acid condition via microemulsion method. The effects of SBS addition and temperature on the morphology and physicochemical properties, such as pore diameters, surface areas and pore volumes of the materials have been investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and nitrogen adsorption-desorption analysis. The results show that the pore volumes, pore sizes and specific surface areas depend strongly on the SBS amount and forming micelles temperature. Moreover, the materials obtained with high wall thickness exhibit a relatively good thermal stability.

The unique skeleton of siliceous sponges (Porifera; Hexactinellida and Demospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review

Sponges (phylum Porifera) had been considered as an enigmatic phylum, prior to the analysis of their genetic repertoire/tool kit. Already with the isolation of the first adhesion molecule, galectin, it became clear that the sequences of sponge cell surface receptors and of molecules forming the intracellular signal transduction pathways triggered by them, share high similarity with those identified in other metazoan phyla. These studies demonstrated that all metazoan phyla, including Porifera, originate from one common ancestor, the Urmetazoa. The sponges evolved prior to the Ediacaran-Cambrian boundary (542 million years ago [myr]) during two major "snowball earth events", the Sturtian glaciation (710 to 680 myr) and the Varanger-Marinoan ice ages (605 to 585 myr). During this period the ocean was richer in silica due to the silicate weathering. The oldest sponge fossils (Hexactinellida) have been described from Australia, China and Mongolia and are thought to have existed coeval with the diverse Ediacara fauna. Only little younger are the fossils discovered in the Sansha section in Hunan (Early Cambrian; China). It has been proposed that only the sponges possessed the genetic repertoire to cope with the adverse conditions, e.g. temperature-protection molecules or proteins protecting them against ultraviolet radiation. The skeletal elements of the Hexactinellida (model organisms Monorhaphis chuni and Monorhaphis intermedia or Hyalonema sieboldi) and Demospongiae (models Suberites domuncula and Geodia cydonium), the spicules, are formed enzymatically by the anabolic enzyme silicatein and the catabolic enzyme silicase. Both, the spicules of Hexactinellida and of Demospongiae, comprise a central axial canal and an axial filament which harbors the silicatein. After intracellular formation of the first lamella around the channel and the subsequent extracellular apposition of further lamellae the spicules are completed in a net formed of collagen fibers. The data summarized here substantiate that with the finding of silicatein a new aera in the field of bio/inorganic chemistry started. For the first time strategies could be formulated and experimentally proven that allow the formation/synthesis of inorganic structures by organic molecules. These findings are not only of importance for the further understanding of basic pathways in the body plan formation of sponges but also of eminent importance for applied/commercial processes in a sustainable use of biomolecules for novel bio/inorganic materials.

Novel microporous silicates and mesoporous MCM materials derivatised with inorganic and organometallic complexes

Os materiais microporosos e mesoporosos são potenciais catalisadores heterogéneos. Os zeólitos e outros materiais microporosos do tipo zeolítico tradicionais, têm átomos tetracoordenados no esqueleto. Nos últimos anos, um vasto número de titanossilicatos contendo Ti(IV) hexacoordenado e Si(IV) tetracoordenado, com estruturas tridimensionais, têm sido alvo de grande interesse. Um dos objectivos desta tese foi preparar silicatos microporosos, contendo átomos metálicos com número de coordenação superior a quatro, e possuindo quer novas estruturas quer propriedades físicas e químicas interessantes. Neste contexto, foi preparado um novo ítriossilicato de sódio, AV-1, análogo do raro mineral montregianite, Na4K2Y2Si16O38·10H2O. Este material é o primeiro sólido microporoso que contem quantidades estequiométricas de sódio (e ítrio) no esqueleto. Foi, também, sintetizado um silicato de cério, AV-5, análogo estrutural do mineral montregianite com potencial aplicação em optoelectrónica. Nesta tese é, ainda, descrita a síntese e caracterização estrutural de um silicato de cálcio hidratado, AV-2, análogo do raro mineral rhodesite (K2Ca4Na2Si16O38.12H2O). Na continuação do trabalho desenvolvido em Aveiro na síntese de novos titanossilicatos surgiu o interesse de preparar novos zirconossilicatos microporosos por síntese hidrotérmica. Foram preparados dois novos materiais análogos dos minerais petarasite Na5Zr2Si3O18(Cl,OH)·2H2O (AV-3) e kostylevite, K2Si3O9·H2O (AV-8). Foram, também, obtidos análogos sintéticos dos minerais parakeldyshite e wadeite, por calcinação a alta temperatura de AV-3 e de umbite sintética. A heterogeneização de complexos organometálicos na superfície de materiais mesoporosos do tipo M41S permite associar a grande actividade catalítica e a presença de sítios activos localizados típicos dos complexos organometálicos, com a robustez e fácil separação, características dos materiais mesoporosos siliciosos. Nesta dissertação relata-se a derivatização dos materiais MCM-41 e MCM-48 através da reacção de [SiMe2{(h5-C5H4)2}]Fe e [SiMe2{(h5-C5H4)2}]TiCl2 com os grupos silanol das superfícies mesoporosas. Os materiais MCMs derivatizados com ansa-titanoceno foram testados na epoxidação de cicloocteno a 323 K na presença de hidrogenoperóxido de t-butilo. Estudou-se a heterogeneização dos sais de complexos com ligação metal-metal [Mo2(MeCN)10][BF4]4, [Mo2(m-O2CMe)2(MeCN)6][BF4]2 e [Mo2(m- O2CMe)2(dppa)2(MeCN)2][BF4]2 via imobilização nos canais do MCM-41. A imobilização dos catalisadores homogéneos na superfície do MCM-41 envolve a saída dos ligandos nitrilo lábeis, preferencialmente em posição axial, através da reacção com os grupos Si-OH da sílica. Verificou-se que a ligação Mo-Mo se mantém intacta nos produtos finais. É provável que estes materiais sejam eficientes catalisadores heterogéneos em reacções de polimerização. As técnicas de caracterização utilizadas nesta tese foram a difracção de raios-X de pós, a microscopia electrónica de varrimento, a espectroscopia de ressonância magnética nuclear do estado sólido (núcleos 13C, 23Na e 29Si), as espectroscopias de Raman e infravermelho com transformadas de Fourier, as análises termogravimétricas e as análises de adsorção de água e azoto.

Coordination of Eu3+ ions in siliceous nanohybrids containing short polyether chains and bridging urea cross-links

Infrared and photoluminescence spectroscopies have been used to investigate the local environment of the Eu3+ ions in luminescent sol-gel derived materials-di-ureasils-based on a hybrid framework represented by U(600). This host is composed of a siliceous backbone grafted, through urea cross-links, to both ends of polymer segments incorporating 8.5 oxyethylene repeat units. The active centers have been introduced as europium perchlorate, Eu(ClO4)3. Samples with compositions n = 232, 62, 23, 12, and 6 (where n denotes the ratio of (OCH2CH2) moieties per lanthanide ion) have been examined. The combination of the information retrieved from the analysis of characteristic bands of the FTIR spectra-the perchlorate and the Amide I/Amide II features-with that obtained from the photoluminescence data demonstrates that at compositions n = 232 and 62 the anions are free, whereas the Eu3+ ions are complexed by the heteroatoms of the polyether chains. At higher salt concentration, the cations are bonded, not only to the ClO4 - ions, but also to the ether oxygen atoms of the organic segments and to the carbonyl oxygen atoms of the urea linkages. The dual behavior of U(600) with respect to cation coordination has been attributed to the presence in this nanohybrid of strong hydrogen-bonded urea-urea structures, which, at low salt content, cannot be disrupted, thus inhibiting the formation of Eu3+-O=C(urea) contacts and promoting the interaction between the lanthanide ions and the (OCH2CH2) moieties. The present work substantiates the claim that the activation of the coordinating sites of the di-ureasil framework can be tuned by varying either the guest salt concentration at constant chain length or the length of the.organic segments at constant salt concentration. This relevant property opens challenging new prospects in the fields of application of this class of hybrids. © 2001 American Chemical Society.