M. Luisa Ruiz-González

Supramolecular mechanisms in the synthesis of mesoporous magnetic nanospheres for hyperthermia

The present work deals with the preparation of magnetic mesoporous nanocomposites with potential application for cancer treatment. The supramolecular mechanisms that govern the incorporation of γ-Fe2O3 nanoparticles into mesoporous silica spheres have been deeply analyzed. The modification of γ-Fe2O3 nanoparticles during the encapsulation into mesoporous SiO2 has been studied. The alkaline conditions of these processes lead to an enlargement of maghemite nanoparticles. We hypothesize that this particle enlargement results from Fe3+ cations present in solution. The results presented in this work indicate the importance of the appropriate surface functionalization to incorporate nanosystems into mesoporous silica materials, as well as the modifications that magnetic nanoparticles undergo during the process. Finally, the ability to produce magnetic hyperthermia makes this material a very promising candidate for multifunctional thermoseeds for cancer treatment.

A novel zwitterionic bioceramic with dual antibacterial capability

A novel zwitterionic SBA-15 type bioceramic with dual antibacterial capability has been synthesized. The co-condensation route has been employed to functionalize SBA-15 with primary and secondary amine groups. The resulting material exhibits textural and nanostructural properties comparable to those of pure silica SBA-15, as confirmed by XRD, HR-TEM and N2 adsorption porosimetry. The presence of -NH3 ⊕/-SiO⊖ and >NH2 ⊕/-SiO⊖zwitterionic pairs on the material surface is evidenced by FTIR and 1H →13C CP/MAS solid state NMR. The homogeneous distribution of this zwitterionic pairs agrees with the results derived from STEM-EDS studies. ζ-Potential measurements indicate that the zwitterionic nature of this material is preserved at the physiological pH of 7.4. In vitro bacterial assays using S. aureus demonstrate that the zwitterionic material is capable of inhibiting 99.9% of the bacterial adhesion compared to pure silica SBA-15. Moreover, cephalexin loading and delivery assays indicate that the zwitterionic sample is capable of releasing antibiotic molecules over long time periods. This dual antibacterial capability, i.e. antibiofouling and bactericidal, opens up promising expectations for the treatment of bone implant infections.

Magnetic Structure and Electronic Study of Complex Oxygen-Deficient Manganites

Neutron diffraction and X-ray absorption near-edge structure (XANES) studies have been performed in La0.5Ca0.5MnO2.5, La0.5Sr0.5MnO2.5 and Nd0.5Sr0.5MnO2.5 oxygen-deficient perovskite compounds obtained by topotactic reduction. They all exhibit a brownmillerite structure with G-type antiferromagnetic ordering. Mn2+, Mn3+ and Mn4+ coexist at the octahedral sites, whereas only Mn2+ is placed in the tetrahedral positions. A magnetic moment of 1.6 microB has been detected at the tetrahedral layers, which can be explained by assuming Mn2+ is in a low-spin configuration.

Thiol grafted imine-based covalent organic frameworks for water remediation through selective removal of Hg(II)

An imine-linked covalent organic framework ([HCC]0.5-TPB-DMTP-COF), endowed with reactive ethynyl groups on the walls of one-dimensional pores, has been used as a platform for pore-wall surface engineering with triazole and thiol groups to yield TPB-DMTP-COF-SH, which is suitable to interact very efficiently with mercury ions. The evaluation of the carefully designed TPB-DMTP-COF-SH is addressed as an effective and selective system for mercury sorption. The obtained results reveal an extraordinary capacity and a great efficiency of the polymeric material with a very high distribution coefficient value Kd = 3.23 × 109. Thus, the level of mercury of a highly concentrated aqueous solution, 10 mg L−1 of Hg(II), is dramatically decreased, below the limits of what is considered to be drinking water, upon treatment with TPB-DMTP-COF-SH for a few minutes. The TPB-DMTP-COF-SH retention value of Hg(II) from water is 99.98% within 2 minutes and its record uptake capacity is 4395 mg g−1 which represents the highest value reported so far. Besides TPB-DMTP-COF-SH captures other extremely toxic heavy metal ions such as Sn(II) and Pb(II) being quite selective versus Cd(II) or As(III). These results suggest that TPB-DMTP-COF-SH constitutes a realistic alternative for the remediation of contaminated spaces from an environmental perspective.

Magnetoresistance in La0.5Sr0.5MnO2.5

Resistance measurements indicate the presence of magnetoresistance in the La(0.5)Sr(0.5)MnO(2.5) brownmillerite related compound. An 80 % of magnetoresistance is found at 75 K. In spite of the partial break-up occurring at the 3D network of octahedra sharing corners, characteristic of the full oxygen content perovskite phase, the oxygen deficient compound exhibits complex magnetic and electric properties. Such behavior can be explained on the basis of ferromagnetic and metallic clusters randomly distributed at the octahedral layers separated from each other by an insulating antiferromagnetic matrix. AC susceptibility measurements suggest spin glass behavior at low temperature as a consequence of the competition between different magnetic interactions.

Experimental Evidence of the Origin of Nanophase Separation in Low Hole-Doped Colossal Magnetoresistant Manganites

While being key to understanding their intriguing physical properties, the origin of nanophase separation in manganites and other strongly correlated materials is still unclear. Here, experimental evidence is offered for the origin of the controverted phase separation mechanism in the representative La1-xCaxMnO3 system. For low hole densities, direct evidence of Mn(4+) holes localization around Ca(2+) ions is experimentally provided by means of aberration-corrected scanning transmission electron microscopy combined with electron energy loss spectroscopy. These localized holes give rise to the segregated nanoclusters, within which double exchange hopping between Mn(3+) and Mn(4+) remains restricted, accounting for the insulating character of perovskites with low hole density. This localization is explained in terms of a simple model in which Mn(4+) holes are bound to substitutional divalent Ca(2+) ions.

Chemical Analysis at Atomic Resolution of Isolated Extended Defects in an Oxygen‐Deficient, Complex Manganese Perovskite

A general approach to the structural and analytical characterization of complex bulk oxides that exploits the advantage of the atomic spatial resolution and the analytical capability of aberration-corrected microscopy is described. The combined use of imaging and spectroscopic techniques becomes necessary to the complete characterization of the oxygen-deficient colossal magnetoresistant La(0.56)Sr(0.44)MnO(2.5)-related perovskite. In this compound, the formation of isolated (La/Sr)O and MnO rock-salt-type planar defects are identified from atomically resolved High Angle Annular Dark Field (HAADF) images. The location of the oxygen atomic columns from Annular Bright Field (ABF) images indicates edge-sharing MnO6 octahedra in the MnO planes and the study performed by Electron Energy Loss Spectroscopy (EELS) reveals different Mn oxidation states derived from the corner- or edge-sharing MnO6 octahedra environment.

Chapter 44:Nano and Mesoporous Materials: A Study by HREM

Host–guest materials comprise a wide group of great interest due to their intrinsic properties that allow the development of classic and new applications. Among them, silica ordered porous materials constitute a very interesting example. There are materials with different pore sizes that can be used...