Víctor Sánchez-Mendieta

Green Synthesis of Noble Metal (Au, Ag, Pt) Nanoparticles, Assisted by Plant-Extracts

The physicochemical and optoelectronic properties of metallic nanoparticles are strongly dependent on the size and size-distribution, but also nanoparticles shape contributes significantly to the control of their properties. Wide varieties of physical and chemical procedures have been developed in order to synthesize nanoparticles of different compositions, sizes, shapes and controlled polydispersity. Nevertheless, the routinely physicochemical techniques for nanoparticle production such as photochemical reduction [1], laser ablation [2], electrochemistry [3], lithography [4] or high energy irradiation [5], either remain expensive or employ hazardous substances, such as organic solvents, and toxic reducing agents like sodium borohydride and N,N-dimethylformamide. In addition, due to the high surface energy of the nanoparticles, these tend to form aggregates; therefore, surface passivating and capping reagents are frequently added to the reaction systems to avoid coalescence. The development of reliable, eco-friendly processes for the synthesis of nanomaterials is an important aspect of nanotechnology. Nanotechnology also requires the synthesis of nanomaterials of different chemical compositions, sizes and morphology with an excellent control over these characteristics.

Cr(VI) reduction in wastewater using a bimetallic galvanic reactor.

The electrochemical reduction of Cr(VI)-Cr(III) in wastewater by iron and copper-iron bimetallic plates was evaluated and optimized. Iron has been used as a reducing agent, but in this work a copper-iron galvanic system in the form of bimetallic plates is applied to reducing hexavalent chromium. The optimal pH (2) and ratio of copper to iron surface areas (3.5:1) were determined in batch studies, achieving a 100% reduction in about 25 min. The Cr(VI) reduction kinetics for the bimetallic system fit a first order mechanism with a correlation of 0.9935. Thermodynamic analysis shows that the Cr(VI) reduction is possible at any pH value. However, at pH values above 3.0 for iron and 5.5 for chromium insoluble species appear, indicating that the reaction will be hindered. Continuous column studies indicate that the bimetallic copper-iron galvanic system has a reduction capacity of 9.5890 mg Cr(VI) cm(-2) iron, whereas iron alone only has a capacity of 0.1269 mg Cr(VI) cm(-2). The bimetallic copper-iron galvanic system is much more effective in reducing hexavalent chromium than iron alone. The exhausted plates were analyzed by SEM, EDS, and XRD to determine the mechanism and the surface effects, especially surface fouling.

Efficient removal of crystal violet dye from aqueous solutions by vitreous tuff mineral

Textural, structural and morphological characteristics of the vitreous tuff were determined by means of several physicochemical techniques. The nitrogen adsorption isotherm at 77 K was fitted with the Brunnauer–Emmet–Teller model and together with the results of the average pore distribution showed a mesoporous material. Samples of vitreous tuff were used as adsorbent to study the removal of crystal violet from aqueous solution. The presence of -OH moieties in the material seems to be responsible for the removal of the dye showing that vitreous tuff can be used as an organic dye adsorbent material. The pseudo-second-order model was the best fit model for describing the sorption process of crystal violet; intraparticle diffusion being the controlling step in the process. The experimental adsorption isotherm was fitted with Langmuir, Freundlich and Langmuir–Freundlich models, showing better correlation with the second one. The adsorption capacity was 170.01 mg/g, being among the highest compared with other inorganic and organic common sorbent materials. The design of single stage of the adsorber can predict the behaviour to potential scale up. This mineral has a very good potential as an adsorbent material for organic dyes.

Synthesis of silver nanoparticles using aqueous extracts of Heterotheca inuloides as reducing agent and natural fibers as templates: Agave lechuguilla and silk.

Silver nanoparticles (Ag NPs) were synthesized using a one-pot green methodology with aqueous extract of Heterotheca inuloides as a reducing agent, and the support of natural fibers: Agave lechuguilla and silk. UV-Vis spectroscopy, X-Ray photoelectron spectroscopy XPS and transmission electron microscopy TEM were used to characterize the resulting bionanocomposite fibers. The average size of the Ag NPs was 16nm and they exhibited low polydispersity. XPS studies revealed the presence of only metallic Ag in the nanoparticles embedded in Agave. lechuguilla fibers. Significant antibacterial activities against gram-negative Escherichia coli and gram-positive Staphylococcus aureus were determined. AgO as well as metallic Ag phases were detected when silk threads were used as a substrates hinting at the active role of substrate during the nucleation and growth of Ag NPs. These bionanocomposites have excellent mechanical properties in tension which in addition to the antibacterial properties indicate the potential use of these modified natural fibers in surgical and biomedical applications.

Formation of silk-gold nanocomposite fabric using grapefruit aqueous extract

Gold nanostructures were synthesized by reduction of gold ions using aqueous extract of grapefruit pulp (Citrus paradisi). This eco-friendly bioreduction method allows the formation in solution and support of gold nanostructures on silk fibers. Bioreduction techniques involve biomolecules of grapefruit extract for reducing a gold precursor to obtain different kinds of nanostructures. Carbohydrates and organic acids, present in C. paradise, are believed to be responsible for the formation of nanoparticles. Analysis of gold–silk nanocomposites by electron microscopy shows gold nanostructures with quasi-spherical, hexagonal, and triangle shapes. The evolution of functional groups in the silk fibers before and after the bioreduction process was followed by infrared spectroscopy. Diffuse reflectance spectroscopy (DRS) and laser scanning confocal microscopy (LSCM) were used to probe surface plasmon resonance and fluorescent behavior in the silk–gold composite. This simple and novel methodology for obtaining these types of nanocomposite may have important applications in the development of functional fibers.

XPS Study of the Chemical Structure of Plasma Biocopolymers of Pyrrole and Ethylene Glycol

An XPS study about the structure of plasma biocopolymers synthesized with resistive radio frequency glow discharges and random combinations of ethylene glycol, pyrrole, and iodine, as a dopant, is presented in this work. The collisions of molecules produced structures with a great variety of chemical states based in the monomers, their combinations, crosslinking, doping, fragmentation, and oxidation at different levels in the plasma environment. Iodine appears bonded in the copolymers only at high power of synthesis, mainly as C–I and N–I chemical bonds. Multiple bonds as C≡C, C≡N, C=O, and C=N were found in the copolymers, without belonging to the initial reagents, and were generated by dehydrogenation of intermediate compounds during the polymerization. The main chemical states on PEG/PPy/I indicate that all atoms in pyrrole rings participate in the polymerization resulting in crosslinked, partially fragmented, and highly oxidized structures. This kind of analysis can be used to modify the synthesis of polymers to increase the participation of the most important chemical states in their biofunctions.

Size-controlled synthesis of Fe2O3 and Fe3O4 nanoparticles onto zeolite by means of a modified activated-coprecipitation method: effect of the HCl concentration during the activation

Synthetic sodium type A zeolite bearing Fe2O3 and Fe3O4 nanoparticles composites have been prepared by means of a coprecipitation method with two different activation methodologies, one using Sn and the other using Sn/Pd nanoparticles as activators. Sn activation generates hematite nanoparticles while Sn/Pd produces magnetite nanoparticles. Amount of HCl used during the activation of the zeolite with SnCl2 showed a correlation between the stannous activating species and the particle size. Both Sn and Sn–Pd activated nanocomposites show nearly narrow size distributions but only those iron oxides obtained with Sn–Pd showed supermagnetism.

Facile Solventless Synthesis of a Nylon-6,6/Silver Nanoparticles Composite and Its XPS Study

Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10 nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for in situ reduction of silver ions and for the formation and stabilization of Ag nanoparticles. Transmission electron microscopy (TEM) analysis showed that silver nanoparticles are well dispersed throughout the nylon fibers. Furthermore, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy (XPS).

1D and 3D supramolecular structures exhibiting weak ferromagnetism in three Cu(II) complexes based on malonato and di-alkyl-2,2’-bipyridines

Abstract Three new Cu(II) complexes composed of malonato (mal), methylmalonato (memal), 4,4′-di-tert-butyl-2,2′-bipyridine (tbpy) and 5,5′-dimethyl-2,2′-bipyridine (mebpy) ligands, Cu(H2O)(mal)(tbpy) (1), Cu(H2O)(memal)(tbpy) (2) and Cu4(H2O)4(memal)4(mebpy)4·11H2O (3) were synthesized by simple one-pot solution reactions at ambient conditions. Single-crystal X-ray diffraction analyses reveal that the Cu(II) ions exhibit a distorted five-coordinate square pyramidal geometry. These three complexes display supramolecular arrays due to hydrogen-bonding interactions. Complexes 1 and 2 show 1-D supramolecular structures; 1 forms a double-ion chain, unlike 2, which only generates a single-ion chain. In 3, there are two identical monomers in the asymmetric unit with Z″ = 2; its high number of noncoordinated water molecules, along with hydrogen-bonding interactions between aqua ligand and memal ligand, generate a supramolecular tetramer, which mimics to produce a 3-D supramolecular framework. Besides this fascinating and yet uncommon crystallographic phenomenon in 3, the structural differences found in these complexes arise from the substituted groups in the malonato dianion and in the bipyridine ligands. These compounds exhibit weak ferromagnetic-exchange interactions.

Synthesis and structural characterization of tris (methacrylato)chromium(III)

A straightforward synthetic route to produce tris(methacrylato)chromium(III), Cr(O2C(CH3)C=CH2)3, by reacting sodium methacrylate with an aqueous solution of CrCl3 gave a blue microcrystalline powder, insoluble in most common solvents. Electronic spectroscopy (UV-Vis), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), were employed to characterize Cr(O2C(CH3)C=CH2)3. Morphology and elemental composition of this compound were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), respectively. Spherical particles of approximately 2.5 µm in diameter were obtained. Thermal stability of the product was investigated via thermogravimetric analysis (TGA). The spectroscopic studies revealed that the coordination sphere around the chromium ion corresponds to a chelating bidentate carboxylate-Cr(III) complex. Thermal stability above 350°C, and spherical shape particles of few micrometers in diameter, suggest a potential application of this novel compound as a catalyst in oxidation reactions.