Open Access
Electrical conduction mechanism in carbon-ceramic composites
(Elsevier, 2023) Alcañiz Monge, Juan; Gil-Muñoz, Gema; Trautwein, Guido; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2
Carbon-ceramic composites (C/Cer) have been prepared by chemical vapor deposition of coal tar pitch onto clay substrates and characterized by thermogravimetric analyses, powder X-ray diffraction, Raman spectroscopy, and scanning and transmission electron microscopies (SEM and TEM). The study of the dc electrical conductivity, together with the determination of the Hall voltage sign, proves that such C/Cer composites are n-type semiconductors. Our results demonstrate that: 1) the mechanism of electrical conduction of C/Cer semiconductors proceeds through the pathways expected for amorphous solids (ie. variable-range hopping and heat-activated pathways at low and high temperatures, respectively); and 2) their transport properties are strongly dependent on the clay components, as evidenced by microscopy experiments.
Open Access
Thermally-triggered crystal dynamics and permanent porosity in the first heptatungstate-metalorganic three-dimensional hybrid framework
(Wiley, 2017) Martín Caballero, Jagoba; Artetxe, Beñat; Reinoso, Santiago; San Felices, Leire; Castillo, Óscar; Beobide, Garikoitz; Vilas, José Luis; Gutiérrez Zorrilla, Juan M.; Institute for Advanced Materials and Mathematics - INAMAT2
The hybrid compound [{Cu(cyclam)}3(W7O24)]⋅15.5 H2O (1) (cyclam=1,4,8,11-tetraaza-cyclotetradecane) was synthesized by reacting the {Cu(cyclam)}2+ complex with a tungstate source in water at pH 8. Compound 1 exhibits an unprecedented three-dimensional covalent structure built of heptatungstate clusters linked through metalorganic complexes in a POMOF-like framework that displays water-filled channels. This dynamic architecture undergoes two sequential single-crystal-to-single-crystal transformations upon thermal evacuation of water molecules to result in the partially dehydrated [{Cu(cyclam)}3(W7O24)]⋅12 H2O (2) and anhydrous [Cu(cyclam)]0.5[{Cu(cyclam)}2.5(W7O24)] (3) crystalline phases. These transitions are associated with cluster rotations and modifications in the CuII coordination geometries, which reduce the dimensionality of the original lattice to layered systems but preserving the porous nature. Phase 3 reverts to 2 upon exposure to ambient moisture, whereas the transition between 1 and 2 proved to be irreversible. The permanent microporosity of 3 was confirmed by gas sorption measurements (N2, CO2), which reveal a system of parallel channels made of wide cavities connected through narrow necks that limit the adsorption process. This observation is in good agreement with Grand Canonical Monte Carlo simulations.
Open Access
Immobilization of polyoxometalates on tailored polymeric surfaces
(MDPI, 2018) Aguado-Ureta, Saioa; Rodríguez-Hernández, Juan; Campo, Adolfo del; Pérez-Álvarez, Leyre; Ruiz-Rubio, Leire; Vilas, José Luis; Artetxe, Beñat; Reinoso, Santiago; Gutiérrez Zorrilla, Juan M.; Ciencias; Zientziak
Herein we describe the preparation of hybrid polymer–inorganic interfaces by the immobilization of polyoxometalate nanoclusters on functionalized polymer surfaces. The polymeric surfaces were made of polystyrene-b-poly(acrylic acid)/polystyrene (PS-b-PAA/PS) blends by spin coating on a silicon wafer. The functionalization of the polymer film was obtained by interfacial migration of the amphiphilic block copolymer toward the interface upon water vapor annealing. The carboxylic acid functional groups contained in the PAA block were then employed to anchor the [LnIII(α-SiW11O39)]5− polyoxometalates (Ln: Ce, Er). This purpose was achieved by immersing the films in aqueous solutions of the in situ-formed inorganic nanoclusters. X-ray photoelectron and confocal Raman spectroscopies, together with atomic force microscopy, confirmed the immobilization of the inorganic species at the interface.
Open Access
Zirconia-supported 11-molybdovanadophosphoric acid catalysts: effect of the preparation method on their catalytic activity and selectivity
(Wiley, 2018) El Bakkali, Bouchra; Trautwein, Guido; Alcañiz Monge, Juan; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa; Gobierno de Navarra / Nafarroako Gobernua
The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle.
Open Access
Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production
(Elsevier, 2018) Alcañiz Monge, Juan; El Bakkali, Bouchra; Trautwein, Guido; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
A series of materials based on the immobilization of the 12-tungstophosphoric heteropolyacid over zirconia supports have been prepared and applied as heterogeneous acid catalysts in the esterification of palmitic acid with methanol as a model reaction for the preliminary stage of the biodiesel production. The title materials have been obtained through the sol-gel method combined with a subsequent hydrothermal treatment at mild conditions, which affords catalysts with larger porosity and higher thermal and chemical stability under the esterification reaction conditions than other preparative approaches. Generating the zirconia support by hydrolysis of an alkoxyde precursor in the presence of the heteropolyacid leads to materials with homogeneously well-dispersed clusters, as well as to an increasing contribution of the tetragonal ZrO2 crystalline phase, a decreasing size of the nanoparticles and larger microporous volumes as the loading of the Keggin-type species increases. The 12-tungstophosphoric acid retains its catalytic activity in the esterification of palmitic acid with methanol at 60 °C upon immobilization over zirconia and conversions even higher than those observed under homogeneous conditions are obtained due to the active contribution of the support. The sample with a 30% mass percentage of heteropolyacid has been identified as the most efficient catalyst because it affords conversions above the 90% and shows the lower loss of activity over successive reaction runs among all of our materials. This loss of activity has been analyzed on the basis of the leaching of the catalyst and the fouling of the materials.
Open Access
Polioxometalatoak ingurune urtsuan: egitura esanguratsuenak
(Universidad de País Vasco, 2021) Ruiz-Bilbao, E.; Fernández Navarro, Leticia; Artetxe, Beñat; San-Felices, L.; Reinoso, Santiago; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Polioxometalatoen (POMen) konposizio eta egitura aniztasun ikaragarria, ur disoluzioan aurkezten dituzten oreka kimiko dinamikoen emaitza dira. Izan ere, beraien eraketa prozesuak ingurune azidotan gertatzen diren oxoanioien kondentsazio konplexuetan oinarrituta daude eta ondorioz, pH baldintza jakinetan zenbait metal-oxigeno kluster ezberdin daude orekan. Hortaz, POMei dagozkien topologia garrantzitsuenen ikuspegi orokorra aurkezten da lan honetan, pHaren arabera ur disoluzioan agertzen diren espezie nagusiei erreparatuz. Lehenik, ohiko iso- eta hetero-polioxobanadato, -polioxomolibdato eta ¿polioxowolframatoak aztertu dira eta bukatzeko hain konbentzionalak ez diren POM familietan jarri da arreta; hala nola, molibdato erraldoiak, uranio peroxo-klusterrak eta metal noblez osatutako egiturak..
Open Access
Determination of hazardous vapors from the thermal decomposition of organochlorinated silica xerogels with adsorptive properties
(Elsevier, 2024) Rosales Reina, María Beatriz; Cruz Quesada, Guillermo; Pujol, Pablo; Reinoso, Santiago; Elosúa Aguado, César; Arzamendi Manterola, Gurutze; López Ramón, María Victoria; Garrido Segovia, Julián José; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
The incorporation of organic groups into sol-gel silica materials is known to have a noticeable impact on the properties and structure of the resulting xerogels due to the combination of the properties inherent to the organic fragments (functionality and flexibility) with the mechanical and structural stability of the inorganic matrix. However, the reduction of the inorganic content in the materials could be detrimental to their thermal stability properties, limiting the range of their potential applications. Therefore, this work aims to evaluate the thermal stability of hybrid inorganic-organic silica xerogels prepared from mixtures of tetraethoxysilane and organochlorinated triethoxysilane precursors. To this end, a series of four materials with a molar percentage of organochlorinated precursor fixed at 10%, but differing in the type of organic group (chloroalkyls varying in the alkyl-chain length and chlorophenyl), has been selected as model case study. The gases and vapors released during the thermal decomposition of the samples under N2 atmosphere have been analyzed and their components determined and quantified using a thermogravimetric analyzer coupled to a Fourier-transform infrared spectrophotometer and to a gas chromatography-mass spectrometry unit. These analyses have allowed to identify up to three different thermal events for the pyrolysis of the organochlorinated xerogel materials and to elucidate the reaction pathways associated with such processes. These mechanisms have been found to be strongly dependent on the specific nature of the organic group.
Open Access
Polioxometalatoak: elhuyar anaien ametsak bizirik dirau!
(Universidad del País Vasco, 2017) Artetxe, Beñat; Reinoso, Santiago; Gutiérrez Zorrilla, Juan M.; Institute for Advanced Materials and Mathematics - INAMAT2
Polioxometalatoak (POMak) kimika ez-organikoaren munduan ezagunak diren metalez eta oxigenoz osatutako kluster anionikoak dira. Azaldu ohi duten forma, konposizio eta propietate aniztasunaren ondorioz, POMek aplikazio ugari dituzte teknologiari, ekonomiari edo ingurugiroari lotutako arlo ezberdinetan. Nahiz eta aspaldidanik aplikazio katalitikoetan erabili, gaur egun etorkizunerako garrantzitsuak izango diren esparru oso ezberdinetarako ikertzen ari dira, besteak beste, hondakin-uren tratamenduan, medikuntzan, konputazio kuantikoan, energia-iturri berriztagarrietan edota sentsore kimiko lumineszenteetan. Horrengatik guztiagatik, polioxometalatoen kimika, etorkizun handiko kimika ezorganikoaren alorreko esparru dinamikoenetariko bat dela baiezta genezake.
Open Access
A simple approach to develop tailored mesoporosity in nanostructured heteropolysalts
(Wiley, 2017) Alcañiz Monge, Juan; Trautwein, Guido; El Bakkali, Bouchra; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin‐type [PMo12O40]3− heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro‐ and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts.
Open Access
Consecutive single-crystal-to-single-crystal isomerization of novel octamolybdate anions within a microporous hybrid framework with robust water sorption properties
(Wiley, 2023) Ruiz Bilbao, Estíbaliz; Iturrospe, Amaia; Reinoso, Santiago; Artetxe, Beñat; Beobide, Garikoitz; San Felices, Leire; Lezama, Luis; Gutiérrez Zorrilla, Juan M.; Darwish, Shaza; Sensharma, Debobroto; Zaworotko, Michael J.; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The 3D hybrid framework [{Cu(cyclam)}3(kMo8O27)]· 14H2O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-singlecrystal transformations upon heating to afford two different anhydrous phases (2 a and 3a). These transitions modify the framework dimensionality and enable the isomerization of k-octamolybdate (k-Mo8) anions into λ (2 a) and μ (3 a) forms through metal migration. Hydration of 3 a involves condensation of one water molecule to the cluster to afford the γ-Mo8 isomer in 4, which dehydrates back into 3a through the 6a intermediate. In contrast, 2a reversibly hydrates to form 5, exhibiting the same Mo8 cluster as that of 1. It is remarkable that three of the Mo8 clusters (k, λ and μ) are new and that up to three different microporous phases can be isolated from 1 (2 a, 3a, and 6a). Water vapor sorption analyses show high recyclability and the highest uptake values for POM-based systems. The isotherms display an abrupt step at low humidity level desirable for humidity control devices or water harvesting in drylands.