Noemí Montoya

Preparation of Hg2+ selective fluorescent chemosensors based on surface modified core–shell aluminosilicate nanoparticles

A synthetic procedure for the preparation of functional structured inorganic–organic hybrid materials consisting of boehmite-silica core–shell nanoparticles and anthracene-containing amines covalently attached to the nanoparticles surface is reported. The system functionalised with the monoamine chain shows a very high sensing performance for Hg2+ detection in pure water reaching a detection limit of 0.2 ppb. Two additional advantages of these systems are their stability over a wide pH window and the feasibility to be recovered by a simple procedure.

Electrochemical anion sensing using electrodes chemically modified with Au(I)–Cu(I) heterotrimetallic alkynyl cluster complexes containing ferrocenyl groups

A novel family of electrochemical anion sensors operating in aqueous media, based on the heterometallic Au(I)–Cu(I) [{Au3Cu2(C2R)6}Au3(PPh2C6H4PPh2)3](PF6)2 (L1, R = Fc; L2, R = C6H4Fc) alkynyl cluster complexes, is presented. Upon attachment to graphite and gold electrodes, these compounds exhibit a well-defined, essentially reversible, solid-state electrochemistry in contact with aqueous media, based on ferrocenyl-centered oxidation processes involving anion insertion, leading to distinctive pH-independent electrochemical responses for fluoride, chloride, bromide, perchlorate, bicarbonate, carbonate, phosphate, hydrogen phosphate, dihydrogen phosphate, and nitrate anions. Cluster-modified electrodes can be used as potentiometric sensors as a result of the reversible, diffusion-controlled electrochemistry obtained for the anion-assisted electrochemical oxidation of L1 and L2.

Tuning the size and shape of nano-boehmites by a free-additive hydrothermal method

A synthetic procedure allowing the control of boehmite micro and nanoparticles is presented. The proposed hydrothermal synthetic procedure is based on the control of three reaction parameters, the pH and temperature of precipitation of xerogels and the water/xerogel ratio for the hydrothermal process, carried out at 200 °C for 48 h. Results obtained by measurements on transmission electron microscopy (TEM) images indicate that at pH 5 micro or nanorods of controlled length between ca. 300 and 50 nm were obtained depending on the temperature of precipitation of the xerogel (25 or 100 °C) and the water/xerogel ratio used (1/1, 6/1, 15/1). On the contrary, at pH 10, nanoplatelets with major basal dimensions ranging between 50 and 25 nm were prepared with the same values of the mentioned parameters. The implemented methodology for the particle-length determination based on the accumulation of measurements on TEM images was in good agreement with the results obtained from dynamic light scattering (DLS) measurements for properly dispersed boehmite nanoparticles, validating its application in the study of these materials. On the basis of X-ray diffraction (XRD) broadening analysis, high-resolution transmission electron microscopy (HRTEM) images and zeta potential (ζ) results, some details on the mechanism of formation of the final boehmites prepared by hydrothermal aging of precipitated xerogels have been proposed.

Identification of vegetal species in wooden objects using in situ microextraction-assisted voltammetry of microparticles

A method for identifying vegetal species in wooden objects using microextraction-assisted voltammetry of microparticles is described. The proposed methodology, aimed at facilitating tasks of patrimony conservation, is based on the recording of the voltammetric response of microparticulate films of compounds resulting from microextraction with organic solvents (ethanol, acetone, and chloroform) of micro- or sub-microsamples of wood in contact with aqueous buffers. Upon application of bivariate and multivariate chemometric techniques, the obtained voltammetric responses led us to identify different taxonomic groups from the characteristic voltammetric profiles. Application to a series of samples of wooden objects of cultural heritage of different European and American provenances dated to ca. 375–350 BC and to historical periods, namely 14th and 17–19th centuries, is described.

Separation of the ionic and electronic contributions to the overall thermodynamics of the insertion electrochemistry of some solid Au(I) complexes

Water-insoluble alkynyl-triphosphine tetranuclear Au(I) complexes containing ferrocenyl motifs, [Au4(C2R)2{(PPh2CH)2PPh}2](PF6)2 (L1, R = Fc; L2, R = C6H4Fc) produce, in contact with aqueous electrolytes, anion-assisted reversible solid-state oxidation/reduction reactions in voltammetry and a pure anion transfer reaction determining the open circuit potential in potentiometric measurements. The mid-peak potentials determined in voltammetry and the open circuit potential determined in potentiometry exhibit differences, which allow accessing the individual contributions of Gibbs energies of electron and ion transfer. This is the second example of a solid compound where this separation is possible. Monitoring of anion insertion by electron microscopy (field emission scanning microscopy/energy-dispersive X-ray analysis (FESEM/EDX)) experiments is reported.

Bisferrocenyl-functionalized pseudopeptides: access to separated ionic and electronic contributions for electrochemical anion sensing

Pseudopeptidic receptors containing ferrocene fragments have been prepared and their response to a series of anions was measured by a voltammetry of microparticles methodology. Such water-insoluble compounds yield anion-assisted reversible solid-state oxidations differing in their open-circuit potential and their midpeak potential recorded in cyclic voltammetric measurements. The difference between those potentials provides the individual thermodynamic contributions of electron and proton transfer, revealing that the mechanism of an ion-sensitive electrode can differ in potentiometry and voltammetry. The studied receptors are potentially interesting for potentiometric sensing, showing relatively high selectivity for H2PO4− and HPO42− anions.

Crystal structure and microstructure of synthetic hexagonal magnesium–cobalt cordierite solid solutions (Mg2−2xCo2xAl4Si5O18)

Co(2+)-containing cordierite glasses, of nominal compositions (Mg(1-x)Co(x))2Al4Si5O18 (with x = 0, 0.2, 0.4, 0.6, 0.8 and 1), were prepared by melting colloidal gel precursors. After isothermal heating at 1273 K for around 28 h, a single-phase α-cordierite (high-temperature hexagonal polymorph) was synthesized. All materials were investigated using X-ray powder diffraction and field-emission scanning electron microscopy. The crystal structure and microstructure were determined from X-ray diffraction patterns. Rietveld refinement confirmed the formation of magnesium-cobalt cordierite solid solutions. The unit-cell volume increased with the increase of cobalt content in the starting glass. The crystalline microstructure of the cordierites was interpreted using a mathematical model of a polycrystalline material and characterized by prevalent crystallite shape, volume-weighted crystallite size distribution and second-order crystalline lattice-strain distribution. Hexagonal prismatic was the prevalent shape of α-cordierite crystallites. Bimodality in the size distribution was observed and interpreted as a consequence of two paths of the crystallization: the nucleation from glass of μ-cordierite, which transformed into α-cordierite with annealing, or the nucleation of α-cordierite directly from glass at high temperatures. Scanning electron microscopy images agreed well with crystalline microstructure characteristics determined from the X-ray diffraction line-profile analysis.

Electrochemical analysis of gold embroidery threads from archeological textiles

A methodology for characterizing archeological gold embroidery threads based on two analytical techniques is described: Field emission scanning electron microscopy (FESEM-EDX) and voltammetry of immobilized microparticle (VIMP) methodologies. After the analysis of the chemical composition of the metallic foil, we analyze specific voltammetric features associated with the oxidation of gold in contact with aqueous H2SO4 and HCl electrolytes. Cyclic and square wave voltammetries (VMP) have been used to get information about the elemental composition and the corrosion products of the samples. AFM, FESEM-EDX, and FESEM-FIB-EDX methodologies complete the study and bring us closer to the composition of the alloys and the embroidery manufacture techniques. This technique actualizes the VIMP data and evidences the morphological and elemental differences between them; in particular, it is confirmed that Au-Ag-Cu alloys, with notably differences in Ag content depending on the provenance, were used.

Electrochemical identification of toxigenic fungal species using solid-state voltammetry strategies

An electrochemical methodology for the characterization of mycotoxin-producing fungal species from the genera Aspergillus and Fusarium using solid-state voltammetry is described. Upon attachment of fungal colony microsamples to glassy carbon electrodes in contact with aqueous acetate buffer, characteristic voltammetric signals mainly associated to the oxidation of polyphenolic metabolites are recorded. The possibility of fungi-localized electrochemical processes was assessed by means of electron microscopy and field emission scanning electrochemical microscopy coupled to the application of oxidative potential inputs. Using pattern recognition methods, the determined voltammetric profiles were able to discriminate between mycotoxin-producing fungi from different sections and to identify selected toxigenic species of the Aspergillus and Fusarium genera isolated from grapes and cereals.