Alvaro Mayoral

University of Zaragoza, Caesaraugusta, Aragon, Spain

Are you Alvaro Mayoral?

Claim your profile

Publications (95)382.96 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Copper(II) complexes with commercial chiral bis(oxazoline)s were for the first time directly coordinated onto amine-modified mesoporous phenylene and biphenylene silicas. All final materials maintained the 2D ordered mesoporous structure. The copper metal coordinates directly to the amine groups within the walls of the materials. The materials were tested as asymmetric heterogeneous catalysts in the kinetic resolution of hydrobenzoin. They were active, selective, and enantioselective in this reaction. The material containing the (S)-(-)-2,2'-isopropylidene-bis(4-phenyl-2-oxazoline) (Me2PhBox) ligand, the best ligand in the homogeneous phase, presented the highest enantioselectivity of all the materials in the first cycle (73%). The 2,2'-methylenebis[(4S)-4-phenyl-2-oxazoline] (PhBox) ligand rendered the catalyst more stable, independent of the anion or organic moiety in the periodic mesoporous organosilica material; this catalyst was reused over five cycles without any significant loss of catalytic activity or enantioselectivity. This type of ligand plays an important role in the stability of the corresponding copper(II) complex upon immobilization and in the robustness of the heterogeneous catalyst upon reuse.
    Full-text · Article · Dec 2015 · Berichte der deutschen chemischen Gesellschaft
  • [Show abstract] [Hide abstract]
    ABSTRACT: A series of selected TiO2-Zeolite hybrid photocatalytic materials have been systematically synthesized and analyzed. The synthesized samples were characterized by X-ray diffraction (XRD), elemental analysis (ICP-OES), N2 adsorption–desorption isotherms, diffuse reflectance UV–Vis spectroscopy (DRS), and transmission electron microscopy (STEM/HAADF/EDS/EELS). The photocatalytic activity of the samples was tested for the degradation of methyl orange (MO) and real wastewaters from the textile industry of Ethiopia. A 10% loaded TiO2-Zeolite Y (CBV 760) yielded up to 20 times higher mass normalized turnover rate (TORm) than pristine TiO2. The reusability of this photocatalyst was tested and only a 5% decrement was observed after three cycles. Furthermore, the photocatalytic activity was tested for real textile wastewater of Ethiopia resulting in 84 and 49% removal of total organic carbon (TOC) using 10% loaded TiO2-Zeolite Y and pristine TiO2, respectively. The enhanced photocatalytic activity of the hybrid system is attributed to the dual role of the zeolite surface and to the electronic modification of the TiO2 photocatalyst.
    No preview · Article · Dec 2015 · Microporous and Mesoporous Materials
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a systematic study on the structural and magnetic properties of CoxFe3�xO4 magnetic nanoparticles with sizes between 5 and 25 nm, prepared by thermal decomposition of Fe(acac)3 and Co(acac)2. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42K<TB<345K for 5<d<13 nm) and large coercive fields (HC�1600 kA/m for T¼5 K). The smallest particles (hdi¼5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the Neel–Arrhenius relaxation framework by including the thermal dependence of the magnetocrystalline anisotropy constant K1(T), without the need of ad-hoc corrections. This approach, using the empirical Br€ukhatov- Kirensky relation, provided K1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (s0�10�10s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener’s relation between K1(T) and M(T).
    Full-text · Article · Nov 2015 · Journal of Applied Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Zeolites are porous aluminosilicate materials that have found applications in many different technologies. However, although simulations suggest that there are millions of possible zeolite topologies, only a little over 200 zeolite frameworks of all compositions are currently known, of which about 50 are pure silica materials. This is known as the zeolite conundrum-why have so few of all the possible structures been made? Several criteria have been formulated to explain why most zeolites are unfeasible synthesis targets. Here we demonstrate the synthesis of two such 'unfeasible' zeolites, IPC-9 and IPC-10, through the assembly-disassembly-organization-reassembly mechanism. These new high-silica zeolites have rare characteristics, such as windows that comprise odd-membered rings. Their synthesis opens up the possibility of preparing other zeolites that have not been accessible by traditional solvothermal synthetic methods. We envisage that these findings may lead to a step change in the number and types of zeolites available for future applications.
    Full-text · Article · Oct 2015 · Nature Chemistry
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Super-resolution (SR) software-based techniques aim at generating a final image by combining several noisy frames with lower resolution from the same scene. A comparative study on high-resolution high-angle annular dark field images of InAs/GaAs QDs has been carried out in order to evaluate the performance of the SR technique. The obtained SR images present enhanced resolution and higher signal-to-noise (SNR) ratio and sharpness regarding the experimental images. In addition, SR is also applied in the field of strain analysis using digital image processing applications such as geometrical phase analysis and peak pairs analysis. The precision of the strain mappings can be improved when SR methodologies are applied to experimental images.
    Full-text · Article · Oct 2015 · Journal of Microscopy
  • [Show abstract] [Hide abstract]
    ABSTRACT: This work presents the highest resolution micrographs reported so far of two beam-sensitive microporous materials: Ti-doped AlPO4-5 (TAPO-5) and the metal–organic framework Zn–MOF-74. They were registered by means of Cs-corrected STEM. The high-resolution images of the TAPO-5 along the [0 0 1] orientation allows a clear observation of the aluminophosphate-five (AFI) type framework, and illustrates the atomic distribution of the “T” atoms of the structure. However, no definitive conclusions about Ti substitution mechanism could be afforded because of the high symmetry of the AFI framework. In the case of Zn–MOF-74, the images were also obtained at 300 kV proving that under certain conditions of beam current this technique can provide invaluable information of an ever-increasing variety of molecular sieves.
    No preview · Article · Sep 2015 · ChemCatChem
  • Source
    Zheng Zhang · Alvaro Mayoral · Ignacio Melián Cabrera
    [Show abstract] [Hide abstract]
    ABSTRACT: Porosity development of mesostructured colloidal silica nanoparticles is related to the removal of the organic templates and co-templates which is often carried out by calcination at high temperatures, 500-600 °C. In this study a mild detemplation method based on the oxidative Fenton chemistry has been investigated. The Fenton reaction involves the generation of OH• radicals following a redox Fe3+/Fe2+ cycle that is used as catalyst and H2O2 as oxidant source. Improved material properties are anticipated since the Fenton chemistry comprises milder conditions than calcination. However, the general application of this methodology is not straightforward due to limitations in the hydrothermal stability of the particular system under study. The objective of this work is three-fold: 1) reducing the residual Fe in the resulting solid as this can be detrimental for the application of the material, 2) shortening the reaction time by optimising the reaction temperature to minimize possible particle agglomeration, and finally 3) investigating the structural and textural properties of the resulting material in comparison to the calcined counterparts. It appears that the Fenton detemplation can be optimized by shortening the reaction time significantly at low Fe concentration. The milder conditions of detemplation give rise to enhanced properties in terms of surface area, pore volume, structural preservation, low Fe residue and high degree of surface hydroxylation; the colloidal particles are stable during storage. A relative particle size increase, expressed as 0.11%·h-1, has been determined.
    Full-text · Article · Aug 2015 · Microporous and Mesoporous Materials
  • Source

    Full-text · Dataset · Jul 2015
  • Source

    Full-text · Dataset · Jul 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract The amination reaction of biphenylene moieties in crystal-like mesoporous silica (Bph-PMO) is successfully achieved with a density of 3.17 mmol g-1. The amination occurs approximately in every aromatic ring of the biphenylene bridge in the position 2 and 2', leading to above 50% of the biphenylene group di-aminated. The structural integrity of the synthetized material is preserved during the strong acid treatment to achieve the amine funcionalization of Bph-PMO. The aminated mesoporous organosilica is highly active (initial turnover frequency 2193 h-1 or 37 min-1) and almost 100% selective in the Knöevenagel condensation. Moreover, the amine-modified periodic mesoporous biphenylene-silica is effective for direct metal coordination.
    Full-text · Article · Jul 2015 · Microporous and Mesoporous Materials
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a systematic study on the structural and magnetic properties of Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between 5 to 25 nm, prepared by thermal decomposition of Fe(acac)_{3} and Co(acac)_{2}. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42 K < T_B < 345 K for 5 < d <13 nm ) and large coercive fields (H_C \approxeq 1600 kA/m for T = 5 K). The smallest particles ( d=5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the Néel-Arrhenius relaxation framework without the need of ad-hoc corrections, by including the thermal dependence of the magnetocrystalline anisotropy constant K_1(T) through the empirical Brükhatov-Kirensky relation. This approach provided K_1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (tau_0 \simeq 10^{-10} s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener's relation between K_1(T) and M(T).
    Full-text · Article · Jul 2015 · Journal of Applied Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work we investigate the formation of PtAu monodisperse alloyed nanoparticles by ageing pure metallic Au and Pt small nanoparticles (sNPs), nanoparticle size <5 nm, under certain conditions. We demonstrate that those bimetallic entities can be obtained by controlling the size of the initial metallic sNPs separately prepared and by selecting their appropriate capping agents. The formation of this spontaneous phenomenon was studied using HR-STEM, EDS, ionic conductivity, UV-Vis spectroscopy and cyclic voltammetry. Depending on the type of capping agent used and the size of the initial Au sNPs, three different materials were obtained: (i) AuPt bimetallic sNPs showing a surface rich in Au atoms, (ii) segregated Au and Pt sNPs and (iii) a mixture of bimetallic nanoparticles as well as Pt sNPs and Au NPs. Surface segregation energies and the nature of the reaction environment are the driving forces to direct the distribution of atoms in the bimetallic sNPs. PtAu alloyed nanoparticles were obtained after 150 h of reaction at room temperature if a weak capping agent was used for the stabilization of the nanoparticles. It was also found that Au atoms diffuse towards Pt sNPs, producing a surface enriched in Au atoms. This study shows that even pure nanoparticles are prone to be modified by the surrounding nanoparticles to give rise to new nanomaterials if atomic diffusion is feasible.
    No preview · Article · Jun 2015 · Nanoscale
  • [Show abstract] [Hide abstract]
    ABSTRACT: Nano-hydrotalcite (nano-HT), particles have been supported on silica and tested for chromium(VI) retention through anion exchange mechanism. Ultra high resolution has been achieved in the structural characterization of the nano-hydrotalcite particles allowing identification of the Cr within few layers of the nanoparticles. Compared to a reference hydrotalcite (HT), in which the Cr(VI) retention takes place via memory effect, nano-HT/SiO2 exhibits better adsorption capacity, for 4 mg/L Cr(VI) solutions, even when the adsorption mechanism of the later is anion exchange. This higher adsorption capacity can be attributed to the considerable smaller size of the crystals, which would favor adsorption kinetics and would minimize possible hindrances between the layers of hydrotalcite. The adsorption behavior of nano-HT/SiO2 can be described by a Freundlich isotherm suggesting a non-uniform surface, which is consistent to their arrangement in nanocrystallites observed by TEM.
    No preview · Article · May 2015 · Journal of Environmental Chemical Engineering
  • [Show abstract] [Hide abstract]
    ABSTRACT: Super-paramagnetic iron oxide-based nanoparticles (SPIONS) have attracted an enormous amount of attention for their potential use in biomedical applications, due to their good biocompatibility and low toxicity. The current study considers citric acid-conjugated manganese ferrite and its synergy to be used in MRI and in hyperthermia treatment, thus showing theragnostic applications. High colloidal stability was obtained with this functionalisation. SPIONS with super-paramagnetic behaviour of crystal sizes of approximately 20 nm were obtained via an electrochemical synthesis method. One of the highest specific absorption rate (SAR) values was achieved in this work (1661 W g-1), under a magnetic field of 30 mT at 717 kHz frequency, compared with other magnetic ferrites in the literature. These nanoparticles dissipate heat through Néel relaxation, and together with the high SAR value obtained indicate an excellent material for hyperthermia treatment of cancer. In addition, these nanoparticles exhibit transverse relaxivity behaviour, with an r2 value of 394 mM-1 s-1, i.e., at least two times higher than the value of a commercial magnetic contrast agent based on iron oxides. Finally, no toxicity effects of these nanoparticles are evidenced; as a result, these nanoparticles are appropriate for in vivo application.
    No preview · Article · Mar 2015 · The Journal of Physical Chemistry C
  • Source
    Alvaro Mayoral · Daniel Llamosa · Yves Huttel
    [Show abstract] [Hide abstract]
    ABSTRACT: Core@shell Co@Au nanoparticles of around 8 nm have been produced by inert gas condensation method, revealing for the first time that most of the nanoparticles present an icosahedral shape in agreement with the theoretical prediction. Additionally, we report the existence of a novel morphology which consists of a Co icosahedron surrounded by fcc Au facets, reported here for the first time.
    Full-text · Article · Feb 2015 · Chemical Communications
  • [Show abstract] [Hide abstract]
    ABSTRACT: The synthesis of nano-sized ZIF-11 with an average size of 36±6 nm is reported. This material has been named nano zeolitic imidazolate framework-11 (nZIF-11). It has the same chemical composition and thermal stability properties and analogous H2 and CO2 adsorption properties as the conventional microcrystalline ZIF-11 (i.e. 1.9±0.9 µm). nZIF-11 has been obtained following the centrifugation route, typically used for solid separation, as a fast new technique (pioneering for MOFs) for obtaining nanomaterials where the temperature, time and rotation speed can easily be controlled. Compared with traditional synthesis consisting of stirring + separation, the reaction time was lowered from several hours to a few minutes when using this centrifugation synthesis technique. Employing the same reaction time (2, 5 or 10 min), micro-sized ZIF-11 was obtained in the traditional synthesis while nano-scale ZIF-11 was achieved only by using centrifugation synthesis. The small particle size obtained for nZIF-11 allowed the use of the wet MOF sample as a colloidal suspension stable in chloroform. This helped to prepare mixed matrix membranes (MMMs) by direct addition of the membrane polymer (polyimide Matrimid®) to the colloidal suspension, avoiding particle agglomeration resulting from drying. The MMMs were tested in H2/CO2 separation, improving the pure polymer membrane performance, with permeation values of 95.9 Barrer of H2 and a H2/CO2 separation selectivity of 4.4 at 35 ⁰C. When measured at 200 ⁰C, these values increased to 535 Barrer and 9.1.
    No preview · Article · Feb 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Metal nanoparticles with precisely controlled size are highly attractive for heterogeneous catalysis. However, their poor thermal stability remains a major concern in their application at realistic operating conditions. This paper demonstrates the possibility of synthesizing gold nanoparticles with exceptional thermal stability. This has been achieved by using a simple conventional deposition-precipitation technique. The material employed as catalyst consists of gold supported on a TiO2-impregnated SiO2 bimodal mesoporous support. The resulting material shows gold nanoparticles with a narrow size distribution around 3.0 nm, homogeneously dispersed over the TiO2/SiO2 material. Most interestingly, the gold nanoparticles show exceptional thermal stability; calcination temperatures as high as 800 °C have been employed, and negligible changes in the gold particle size distribution are apparent. Additionally, the presence of an amorphous titanium silicate phase is partially preserved, and these factors lead to remarkable activity to catalyze a range of oxidation reactions.Keywords: heterogeneous catalysis; gold nanoparticles; stability; mesoporous materials; catalytic oxidation
    Full-text · Article · Feb 2015 · ACS Catalysis
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The effect of synthesis pH and H2O/EtOH molar ratio on the textural properties of different aluminium trimesate metal organic frameworks (MOFs) prepared in the presence of the well-known cationic surfactant cetyltrimethylammonium bromide (CTAB) at 120 °C was studied with the purpose of obtaining a MOF with hierarchical pore structure. Depending on the pH and the solvent used, different topologies were obtained (namely, MIL-96, MIL-100 and MIL-110). On the one hand, MIL-110 was obtained at lower temperatures than those commonly reported in the literature and without additives to control the pH; on the other hand, MIL-100 with crystallite sizes as small as 30 ± 10 nm could be easily synthesized in a mixture of H2O and EtOH with a H2O/EtOH molar ratio of 3.4 at pH 2.6 in the presence of CTAB. The resulting material displays a hierarchical porosity that combines the microporosity from the MOF and the non-ordered mesopores defined in between the MOF nanoparticles. Interestingly, the maximum of the pore size distribution could be varied between 3 and 33 nm. Finally, at pH 2.5 and using water as a solvent, platelets of MIL-96, a morphology never observed before for this MOF, were synthesized with a (001) preferential crystal orientation, the (001) plane running parallel to the bipyramidal cages of the MIL-96 topology.
    Full-text · Article · Feb 2015 · CrystEngComm
  • [Show abstract] [Hide abstract]
    ABSTRACT: A ca. one-μm single crystal of MOF MIL-53(Al) was attached to a glass support surface via covalent bonding.•The breathing behavior of MOF MIL-53(Al) was monitored in real-time with the help of environmental SEM.•This allowed the attribution of porosity to the geometry in MIL-53(Al) crystals.•The new characterization and the corresponding crystallographic calculations were in agreement with the previous related literature.
    No preview · Article · Feb 2015 · Microporous and Mesoporous Materials
  • Source

    Full-text · Dataset · Jan 2015

Publication Stats

664 Citations
382.96 Total Impact Points

Institutions

  • 2010-2015
    • University of Zaragoza
      • Department of Chemical Engineering and Environmental Technology
      Caesaraugusta, Aragon, Spain
  • 2014
    • Klinikum Darmstadt
      Darmstadt, Hesse, Germany
  • 2009-2012
    • University of Texas at San Antonio
      • Department of Physics and Astronomy
      San Antonio, Texas, United States
  • 2007-2010
    • University of Birmingham
      • School of Chemistry
      Birmingham, England, United Kingdom
  • 2007-2008
    • Stockholm University
      • Department of Materials and Environmental Chemistry
      Tukholma, Stockholm, Sweden