Textura porosa de la akageneita sintética

Tesis - Universidad Complutense de Madrid, 1979.Depto. de Química InorgánicaFac. de Ciencias QuímicasTRUEProQuestpu

High resolution transmission electron microscopy: A key tool to understand drug release from mesoporous matrices

This work demonstrates that high resolution transmission electron microscopy (HRTEM) is an essential tool to understand drug delivery performance of mesoporous silica materials, mainly those submitted to functionalization processes involving harsh conditions that may affect the mesostructure. Herein an SBA-15-type mesoporous material bearing Si(CH2)(2)P(O)(OCH2CH3)(2) groups was synthesized following the co-condensation route. Then, the resulting material was treated with 37 wt% HCl to convert ethylphosphonate groups to ethylphosphonic acid groups. The proper dealkylation of ethoxy groups following acid treatment was confirmed by FTIR and CP-MAS H-1 -> C-13 solid state NMR, which indicated the presence of Si(CH2)(2)P(O)(OH)(2) functionalities in the treated sample. Characterization of mesoporous materials by XRD diffraction and N-2 adsorption points to well-ordered SBA-15 structures in both untreated and acid-treated samples. Nonetheless, a deep study by HRTEM reveals that the acid-treatment provokes noticeable loss of mesostructural order, only remaining small crystalline domains. This structural damage does not influence cargo loading but it severely affects the release of molecules confined into the mesopores, as concluded from in vitro delivery tests using cephalexin as model drug. Thus, whereas untreated sample showed a sustained diffusion-controlled drug release during more than 2 weeks, 100% of the loaded drug was released only after 10 h from treated sample. This abrupt burst effect cannot be explained on the basis of the existing matrix-drug interactions, whose nature and extension is quite similar under the release conditions for both samples. Thus, it can be only understood on the basis of the mesostructural damage revealed by HRTEM studies. (C) 2016 Elsevier Inc. All rights reserved

Evaluation of the Nanodomain Structure in In-Zn-O Transparent Conductors

The optimization of novel transparent conductive oxides (TCOs) implies a better understanding of the role that the dopant plays on the optoelectronic properties of these materials. In this work, we perform a systematic study of the homologous series ZnkIn2Ok+3 (IZO) by characterizing the specific location of indium in the structure that leads to a nanodomain framework to release structural strain. Through a systematic study of different terms of the series, we have been able to observe the influence of the k value in the nano-structural features of this homologous series. The stabilization and visualization of the structural modulation as a function of k is discussed, even in the lowest term of the series (k = 3). The strain fields and atomic displacements in the wurtzite structure as a consequence of the introduction of In3+ are evaluated.Depto. de Química InorgánicaFac. de Ciencias QuímicasTRUEMinisterio de Ciencia, Innovación y Tecnología /Ministerio de EconomíaComunidad de Madridpu

Study of Cr2O3 nanoparticles supported on carbonaceous materials as catalysts for O2 reduction reaction

A series of chromium oxides (Cr2O3) nanoparticles supported on different carbonaceous material, namely: graphene, graphene oxide (GO) and graphite, were synthetized by precipitation of the salt precursors with precipitant (ammonia) and the subsequent thermal treatment. The catalytic activity of these composites and the Cr2O3 nanoparticles have been analysed by Koutecky-Levich (KL) and rotating ring-disc electrode methods and the results have been discussed following a model proposed here, which considers the O2 electrosorption as the rate determining step. Among them, graphite and graphene based composites have better catalytic activities and their behaviours agree with the proposed treatment: logarithm dependent of the intercept and nondependent slopes values of the KL plots with the potential. Cr2O3-graphite shows a mechanism interchanging 4 e-, which has been attributed to a graphite- Cr2O3 nanoparticles interaction. Besides, Cr2O3-graphite-based electrodes have been tested as cathode in a Zn/PVA-KOH/air battery, confirming its good properties to be applied as positive electrode in metal-air batteries.The authors thank the financial support from Fundación Séneca (Región de Murcia, Spain; Ref: 20985/PI/18), Spanish Agencia Estatal de Investigación (PID2019-104272RB-C55/AEI/10.13039/501100011033, CTQ2017-90659-REDT and PID2019-106097 GB/AEI/10.13039/501100011033), MINECO (projects MAT2017-84118-C2-2-R and MAT2017-82252-R) and Banco Santander-UCM (project PR87/19-22613). The authors also acknowledge Victor Galindo Garre for providing R-Studio scripts for data analysis

Hybrid Enzyme-Polymeric Capsules/Mesoporous Silica Nanodevice for In Situ Cytotoxic Agent Generation

A novel nanocarrier based on functionalized mesoporous silica nanoparticles able to transport a non-toxic pro-drug and the enzyme responsible for its activation is presented. This nanodevice is able to generate in situ cytotoxic species once accumulated in the tumoral cell. Enzymes are sensitive macromolecules which can suffer denaturalization in biological media due to the presence of proteases or other aggressive agents. Moreover, the direct attachment of enzymes to the silica surface can reduce their activity by conformational changes or active site blockage. For these reasons, in order to create a robust system able to work in living organisms, the enzymes are previously coated with a protective polymeric shell which allows the attachment on the silica surface preserving their activity. The efficacy of this hybrid nanodevice for antitumoral purposes is tested against several human tumoral cells as neuroblastoma and leukemia showing significant efficacy. It converts this device in a promising candidate for further in vivo studies for oncology therapy

Complex structural ordering of the oxygen deficiency in La_-0.5 Ca_2.5Mn_2O_7-delta Ruddlesden-Popper phases

Ruddlesden-Popper oxides, (AO)(ABO_3))_n, occupy a prominent place in the landscape of materials research because of their intriguing potential applications. Compositional modifications to the cation sublattices, A or B, have been explored in order to achieve enhanced functionalities. However, changes to the anionic sublattice have been much less explored. In this work, new oxygen-deficient manganese Ruddlesden-Popper-related phases, La_0.5Ca_2.5Mn_2O_6.5, and La_0.5Ca_2.5Mn_2O_6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La_0.5Ca_2.5Mn_2O_7. A complete structural and compositional characterization, by means of neutron diffraction, electron diffraction and atomically resolved scanning transmission electron microscopy and electron energy-loss spectroscopy techniques, allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO_2] layers along [031] and [013] directions. The gradual decrease of the Mn oxidation state, accommodated by short-range ordering of anionic vacancies, reasonably explains the breaking of ferromagnetic interactions reinforcing the emergence of antiferromagnetic ones. Additional short-range order-disorder phenomena of La and Ca cations have been detected in the reduced La_0.5Ca_2.5Mn_2º_7-delta, as previously reported in the parent compound

Crystallographically uniform arrays of ordered (In)GaN Nanocolumns

In this work, through a comparative study of self-assembled (SA) and selective area grown (SAG) (In)GaN nanocolumn (NC) ensembles, we first give a detailed insight into improved crystallographic uniformity (homogeneity of crystallographic tilts and twists) of the latter ones. The study, performed making use of: reflective high energy electron diffraction, X-ray diffraction and scanning electron microscopy, reveals that unlike their SA counterparts, the ensembles of SAG NCs show single epitaxial relationship to both sapphire(0001) and Si(111) underlying substrates. In the second part of the article, making use of X-ray diffraction, we directly show that the selective area growth leads to improved compositional uniformity of InGaN NC ensembles. This further leads to improved spectral purity of their luminescence, as confirmed by comparative macro-photoluminescence measurements performed on SA and SAG InGaN NC ensembles. An improved crystallographic uniformity of NC ensembles facilitates their integration into optoelectronic devices, whereas their improved compositional uniformity allows for their employment in single-color optoelectronic applications

Light-Emitting-Diodes based on ordered InGaN nanocolumns emitting in the blue, green and yellow spectral range

The growth of ordered arrays of InGaN/GaN nanocolumnar light emitting diodes by molecular beam epitaxy, emitting in the blue (441 nm), green (502 nm), and yellow (568 nm) spectral range is reported. The device active region, consisting of a nanocolumnar InGaN section of nominally constant composition and 250 to 500 nm length, is free of extended defects, which is in strong contrast to InGaN layers (planar) of similar composition and thickness. The devices are driven under pulsed operation up to 1300 A/cm2 without traces of efficiency droop. Electroluminescence spectra show a very small blue shift with increasing current, (almost negligible in the yellow device) and line widths slightly broader than those of state-of-the-art InGaN quantum wells

SrMnO3 thermochromic behavior governed by size-dependent structural distortions

The influence of particle size in both the structure and thermochromic behavior of 4H-SrMnO related perovskite is described. Microsized SrMnO suffers a structural transition from hexagonal (P6/mmc) to orthorhombic (C222) symmetry at temperature close to 340 K. The orthorhombic distortion is due to the tilting of the corner-sharing MnO units building the 4H structural type. When temperature decreases, the distortion becomes sharper reaching its maximal degree at ∼125 K. These structural changes promote the modification of the electronic structure of orthorhombic SrMnO phase originating the observed color change. nano-SrMnO adopts the ideal 4H hexagonal structure at room temperature, the orthorhombic distortion being only detected at temperature below 170 K. A decrease in the orthorhombic distortion degree, compared to that observed in the microsample, may be the reason why a color change is not observed at low temperature (77 K)

Influence of doping and controlled sn charge state on the properties and performance of SnO nanoparticles as anodes in li-ion batteries

Li-ion batteries (LiB) play nowadays a major role in several technological fields. In addition to enhanced high capacity and long cyclability, some other issues regarding safety, materials sustainability, and low cost remain unsolved. Tin oxide (SnO_2) presents several of those advantages as an anode material; however, some aspects still require to be investigated such as capacity fading over cycles. Herein, tin oxide nanoparticle-based anodes have been tested, showing high capacities and a significant cyclability over more than 150 cycles. A complementary strategy introducing doping elements such as Li and Ni during the synthesis by hydrolysis has been also evaluated versus the use of undoped materials, in order to assess the dependence on SnO_2 quality and properties of battery performance. Diverse aspects such as the Sn charge state in the synthesized nanoparticles, the variable incorporation of dopants, and the structure of defects have been considered in the understanding of the obtained capacity