Aitana Tamayo

Deep-Eutectic-Solvent-Assisted Synthesis of Hierarchical Carbon Electrodes Exhibiting Capacitance Retention at High Current Densities

Nature provides a wide range of entities and/or systems with different functions that may serve as a source of bioinspiration for material chemists. Actually, materials exhibiting a 3D porous texture (combining pores at different scales, from macroto mesoup to micropores) mimic the hierarchical structure of different systems found in living organisms (e.g., the blood circulation or the respiratory system in mammalians). Structural organization at different scales is ultimately responsible for the outstanding properties offered by hierarchical materials (not only as stationary phases in separation and catalytic processes, but also as electrodes in fuel cells and capacitors) because they offer not only large surface areas, but also accessibility to such a surface. A number of synthetic routes have been explored by using different carbonaceous precursors and either exo or endo templates to modulate the porous texture of the resulting carbon structures. Recent efforts have also been focused on the preparation of porous carbon composites containing graphitic carbon entities (e.g., carbon nanotubes and nanohorns, or even graphene oxide) the challenge of which is double and resides in 1) the achievement of a homogenous dispersion of these entities throughout the monolith structure and 2) the preservation of high surface areas. Baumann and co-workers have recently performed a quite extensive and stimulating work on single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) synthesized by resorcinol–formaldehyde polycondensation. Particularly interesting in terms of conductivity and surface area were those composites based on DWCNTs, although the authors expressed the convenience of substituting the surfactants used for carbon-nanotube (CNT) dispersion. Ionic liquids (ILs) and deep eutectic solvents (DESs, a new class of ILs obtained by complexion of quaternary ammonium salts with hydrogen-bond donors, such as acids, amines, and alcohols) have lately been the solvent of choice in a number of chemical processes because of special features: for example, they are nonreactive with water, nonvolatile, and biodegradable as well as excellent solvents for a wide variety of solutes, such as different substrates, enzymes, and even microorganisms of catalytic and biocatalytic interest. Of particular interest for the purpose of this work are those processes for which the capability both as solvents for CNT dispersion and structure-directing agents in the synthesis of different materials was demonstrated. Actually, ILs and DESs have been used as solvents for preparation of CNT-based carbon composites and even as carbonaceous precursors of both nontextured and textured carbons. In particular, we have recently described the preparation of DESs based on mixtures of resorcinol and choline chloride, the rupture of which (via resorcinol polycondensation and subsequent segregation of choline chloride) resulted in the formation of bimodal porous carbons. In this case, hierarchy was obtained through a synthetic mechanism that combined aspects from those original works used for synthesis of zeolites (i.e., based on DES rupture and controlled delivery of an organic template to the reaction mixture) and those used for synthesis of macroporous structures (i.e. , based on spinodal-like processes) . It is also worth noting the “green” character of the process as a result of the absence of residues and/or byproducts eventually released after the synthetic process, that is, one of the components forming the DES (e.g., resorcinol) becomes the material itself, whereas the second one (e.g., choline chloride) is fully recovered and can be reused in subsequent reactions. Based on these previous results, we considered that the use of DESs could open an interesting path for the preparation of hierarchical porous CNT composites. Herein, we describe the preparation of hierarchical porous multiwalled CNT (MWCNT) composites exhibiting high surface areas and outstanding conductivities through furfuryl alcohol (FA) condensation catalyzed by a protic DES based on complexes of para-toluene sulfonic acid [a] Dr. M. C. Guti rrez, Dr. D. Carriazo, Dr. R. Jim nez, Dr. J. M. Rojo, Dr. M. L. Ferrer, Dr. F. del Monte Instituto de Ciencia de Materiales de Madrid-ICMM Consejo Superior de Investigaciones Cient ficas-CSIC Campus de Cantoblanco, 28049-Madrid (Spain) E-mail : mcgutierrez@icmm.csic.es delmonte@icmm.csic.es [b] Dr. A. Tamayo Instituto de Ceramica y Vidrio-ICV Consejo Superior de Investigaciones Cient ficas-CSIC. Campus de Cantoblanco, 28049-Madrid (Spain) [c] Dr. F. Pic Centro Nacional de Investigaciones Metalurgicas-CENIM Consejo Superior de Investigaciones Cient ficas-CSIC Av. Gregorio del Amo s/n, 28040-Madrid (Spain) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101679.

Study of arsenopyrite weathering products in mine wastes from abandoned tungsten and tin exploitations.

Arsenopyrite-rich wastes from abandoned tungsten and tin exploitations were studied to determine the composition and characteristics of the secondary phases formed under natural weathering conditions so as to assess their potential environmental risk. Representative weathered arsenopyrite-bearing rock wastes collected from the mine dumps were analysed using the following techniques: X-ray powder diffraction (XRD) analysis, polarizing microscopy analysis, electron microprobe analysis (EMPA) and microRaman and Mössbauer spectroscopies. Scorodite, pharmacosiderite and amorphous ferric arsenates (AFA) with Fe/As molar ratios in the range 1.2-2.5 were identified as secondary arsenic products. The former showed to be the most abundant and present in the different studied mining areas. Its chemical composition showed to vary in function of the original surrounding rock mineralogy in such a way that phosphoscorodite was found as the mineral variety present in apatite-containing geoenvirons. Other ever-present weathering phases were goethite and hydrous ferric oxides (HFO), displaying, respectively, As retained amounts about 1 and 20% (expressed as As(2)O(5)). The low solubility of scorodite, the relatively low content of AFA and the formation of compounds of variable charge, mostly of amorphous nature, with high capacity to adsorb As attenuate importantly the dispersion of this element into the environment from these arsenopyrite-bearing wastes.

3D free-standing porous scaffolds made of graphene oxide as substrates for neural cell growth

The absence of efficient therapies for the treatment of lesions affecting the central nervous system encourages scientists to explore new materials in an attempt to enhance neural tissue regeneration while preventing inhibitory fibroglial scars. In recent years, the superlative properties of graphene-based materials have provided a strong incentive for their application in biomedicine. Nonetheless, a few attempts to date have envisioned the use of graphene for the fabrication of three-dimensional (3D) substrates for neural repair, but none of these involve graphene oxide (GOx) despite some attractive features such as higher hydrophilicity and versatility of functionalization. In this paper, we report novel, free-standing, porous and flexible 3D GOx-based scaffolds, produced by the biocompatible freeze-casting procedure named ISISA, with potential utility in neural tissue regeneration. The resulting materials were thoroughly characterized by Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopies and scanning electron microscopy, as well as flexibility testing. Embryonic neural progenitor cells were then used to investigate adhesion, morphology, viability, and neuronal/glial differentiation. Highly viable and interconnected neural networks were formed on these 3D scaffolds, containing both neurons and glial cells and rich in dendrites, axons and synaptic connections, and the results are in agreement with those obtained in initial studies performed with two-dimensional GOx films. These results encourage further investigation in vivo on the use of these scaffolds as guide substrates to promote the repair of neural injuries.

Tailoring the textural properties of hierarchical porous carbons using deep eutectic solvents

Soft-template approaches have been frequently applied for the preparation of porous carbons. Most of these processes proved highly effective for the preparation of mesoporous carbons with pore diameters below 10 nm but less explored has been the preparation of carbons with mesopores larger than 10 nm. The lack of syntheses providing large and well-interconnected mesopores is by no means a trivial issue because it limits the achievement of materials suitable for applications where pore surface accessibility is crucial – e.g. electrodes in supercapacitors or adsorbents in flow-through systems, among others. In this work, we have used deep eutectic solvents (DESs, a sort of ionic liquid, that are obtained by complexation of quaternary ammonium salts with hydrogen-bond donors) composed of resorcinol, urea and choline chloride for the preparation – via formaldehyde polycondensation and subsequent carbonization – of hierarchical porous carbons with micropores and large mesopores within the 10 to 20 nm range. The formation of large mesopores took place at the polycondensation stage via a spinodal decomposition process where some components forming the DES acted as precursors of the polymer phase, while some other ones were segregated into a polymer depleted phase. Thus, the ultimate dimension of the mesopores was controlled by the mass ratio between the segregated and condensed phases, and this mass ratio by the molar ratio of the components forming the original DES. We have finally demonstrated that carbons with larger mesopores exhibited better performance as electrodes in supercapacitor cells.

Surface properties of bioactive TEOS–PDMS–TiO2–CaO ormosils

Tetraethyl orthosilicate (TEOS)–polydimethyl siloxane (PDMS) ormosils with different amounts of Ti and Ca were prepared and characterized. Several surface properties such as specific surface area, porosity, fractality, dispersive and polar surface energies were determined and related with their in-vitro bioactivity. It has been found a dependence of the surface fractal dimension with the concentration of Ca2+ ions that induce the appearance of rough surfaces. The dispersive surface energy, γSd, increased with the incorporation of Ti or Ca and the presence of micropores, but Ca(NO3)2 precipitates in the surface coming from non-incorporated Ca lead to a decrease of the surface energy values. In relation with the polar surface energy, it has been observed that all ormosil materials presented amphoteric character with a larger presence of base surface sites than acid ones. The basicity of the surface increased with the concentration of Ti and Ca, while the acidity decreased. The in-vitro bioactivity of the surface was estimated by soaking samples in simulated body fluid (SBF) and afterwards characterized by means of X-ray diffraction (TF-XRD) and field emission scanning electron microscopy (FE-SEM). It has been observed that in vitro bioactivity is related with the polar surface characteristics of these materials, being necessary for the bioactivity, the presence of a highly polar surface with intermediate base/acid ratio and specific roughness.

Sulfur‐Doped Carbons Prepared from Eutectic Mixtures Containing Hydroxymethylthiophene as Metal‐Free Oxygen Reduction Catalysts

A template-free approach based on the use of eutectic mixtures composed of 2-hydroxymethylthiophene and furfuryl alcohol has been designed for the preparation of hierarchical sulfur-doped carbons (SPCs) in monolithic form. The temperature used for carbonization, for example, 600, 800, or 900 °C, determined most of the physicochemical properties of the resulting SPCs. Thus, the surface area increased from below 400 to up 775 m(2)  g(-1) , along with the carbonization temperature, whereas the sulfur content decreased from approximately 15 to 5 wt %. The oxygen reduction reaction performance in samples carbonized at 900 °C was good, with the four-electron-transfer reaction prevailing over the two-electron-transfer one. Interestingly, the methanol tolerance and stability of these SPCs were also remarkable, with less than 5% current decrease immediately after methanol addition, whereas, in terms of stability, the current decrease was below 8 % after 20000 s. This performance was in the range of that found not only for other SPCs, but also for many nitrogen-doped and even some dual-doped (S and N) ones.

Drug kinetics release from Eudragit – Tenofovir@SiOC tablets

A novel drug release system has been obtained in form of tablets from Eudragit® RS and tenofovir loaded on porous silicon oxycarbide glasses (SiOC). Active carbon (AC) and mesoporous silica (MCM-41) have also been used for comparative purposes. The porous silicon oxycarbide presents a bimodal mesopore size distribution that is maintained after functionalization with amino groups. We have studied the adsorption kinetics and adsorption equilibrium when the materials are loaded with tenofovir and, in all cases, pseudo-second order kinetics and Langmuir isotherm have been revealed as the most representative models describing the kinetic and thermodynamic parameters. Besides, the tenofovir adsorption on these materials turns out to be a favorable process. In vitro release of tenofovir has been studied in simulated vaginal medium by applying different release models. Continuous tenofovir release for >20days has been obtained for the SiOC material functionalized with amine groups. We concluded that the drug release occurs in two steps that involve a drug diffusion step through the material pores and diffusion through the swollen polymer. The interactions between the tenofovir drug and de amine groups of the functionalized silicon oxycarbide also play an important role in the release process.

Sustainable synthesis of N-acetyllactosamine using an immobilized β-galactosidase on a tailor made porous polymer

Porous polymer particles containing surface epoxy groups were synthesized for immobilizing β-galactosidase from Bacillus circulans. Enzyme immobilization was achieved by covalent attachment to a custom made porous polymer and the biocatalyst was characterized in terms of optimal pH and thermal stability, and its catalytic efficiency evaluated for synthesizing N-acetyllactosamine (Gal-β-(1 → 4)-GlcNAc) in different solvents and using a 1 : 5 molar ratio of donor (pNP-β-Gal) : acceptor (GlcNAc). The reaction proceeded with high conversion rates and regioselectivity. Yields up to 60% of β-(1 → 4) with biosolvent 3 were found. Reusability assays were performed with the same reaction conditions finding that the immobilized enzyme retains about 85% of its activity after twenty batches with conversion yields above 60%. Furthermore, reaction scale up, biosolvent recovery and recycling are achieved retaining catalytic activity.

Optimization of tenofovir release from mucoadhesive vaginal tablets by polymer combination to prevent sexual transmission of HIV

The use of sustained-release mucoadhesive vaginal tablets of antiretroviral drugs as microbicidal formulations can be an effective strategy for reducing the sexual transmission of HIV from men to women, which is a main problem particularly in low- and middle-income countries. Different polymers (hydroxypropylmethyl cellulose (HPMC), chitosan, guar gum and Eudragit® RS) have proven some good features for this purpose. At this work, these polymers have been combined in pairs in different proportions to enhance the advantages offered by each one individually. The in vitro release of tenofovir from the matrices, ex vivo mucoadhesive capacity (evaluated on vaginal mucosa) and the degree of swelling in simulated vaginal fluid have been assessed. A multimodal pore size distribution is observed in porosimetry studies -carried out with swelling witnesses-, due to the contribution of polymers with different swelling behaviour to the pore formation, and it is corroborated by scanning electron microscopy. X-ray diffraction technique confirms the changes in crystallinity of the formulation after swelling. We can report that the combination of HPMC and chitosan in the same formulation may be useful for the prevention of sexual transmission of HIV, since tablets can be obtained that remain adhered to the vaginal mucosa for 96h, so the drug is released in a sustained manner for 72h. When the formulation contains more chitosan than HPMC the swelling is moderate, making it more comfortable for women to apply.

Chemical oxidation of silicon oxycarbide ceramics for advanced drug delivery systems

Abstract Silicon oxycarbide particles were subjected to chemical oxidation processes to incorporate carbonyl and carboxylic functionalities on their surfaces. These materials were subjected to in vitro tests to determine their adsorption and release capabilities of the antiretroviral drug molecule acyclovir. The spectroscopic characterization revealed the distribution of the functionalities in the different nanophases contained within the silicon oxycarbide structure. This selective distribution in either the carbon or the silicon oxycarbide phase leads to a differential charge availability that in fact is responsible for the adsorption of the drug molecule on the surface of the particles. This adsorption occurs via donor–acceptor interactions with no chemical bonds involved in the drug delivery system.