Thelma Serrano

Synergistic effects of transition metal substitution in conversion electrodes for lithium-ion batteries

Different solid solutions in the FexCo1−xC2O4·2H2O system have been prepared in the form of nanoribbons by a reverse micelles method. The orthorhombic crystallographic structure differs from the monoclinic massive products FeC2O4·2H2O and CoC2O4·2H2O. The dehydration process is studied by thermal analysis to prepare the anhydrous solid solution oxysalts, in which the nanoribbon-shaped particles are preserved and a porous system is developed. Anhydrous mixed oxalates are used for the first time as high-capacity lithium storage materials with improved rate performance, and display synergistic effects as compared with the end members. Fe0.75Co0.25C2O4 displays a reversible capacity ca. 600 mA h g−1 at 5C rate with a very good capacity retention after 75 cycles by a hybrid mechanism. The solids display faradaic capacities due to a novel conversion reaction that produces nanodispersed transition metals, which is responsible for the high energy density, and a capacitive response that leads to high power densities in Li-ion batteries. The low temperature synthesis of these materials makes them an inexpensive option for this purpose.

Template assisted synthesis of poly(3-hexylthiophene) nanorods and nanotubes: growth mechanism and corresponding band gap

Abstract Poly(3-hexylthiophene) (P3HT) dense film and P3HT nanorods and nanotubes were synthesized on ITO and anodic aluminium oxide (AAO) substrate respectively. The growth mechanism of one-dimensional P3HT was investigated by changing the monomer concentration of 5 mM, 15 mM and 30 mM resulting in different polymer morphologies. By applying the transmittance spectra in the wavelength range of 1 100 to 400 nm, band gaps of 2.1, 1.9 and 1.55 eV were obtained for P3HT dense film, nanotubes and nanorods respectively. Tuning the band gap was achieved by changing the monomer concentration in electrochemical synthesis of P3HT on AAO substrate. Also the conductivity of 3.26 S · cm−1 for rod-shape P3HT and 1.06 S · cm−1 for dense film was calculated indicating better charge transport for nanorods.

Synthesis of PbS/Cu2S/ZnS nanoparticles and their optical properties

The use of simple stabilizers, such as trisodium citrate and 3-mercaptopropionic acid, with the colloidal solution-phase growth method is successful in synthesizing PbS/Cu2S core/shell nanoparticles with emission in the visible range and with improved luminescence properties. The core/shell arrangement for particles with different crystalline structures is achieved, and, in addition, the first reported synthesis of the PbS/Cu2S/ZnS core/shell/shell system. The absorption and photoluminescence spectra and scanning electron microscopy images provide direct proof of the formation of PbS/Cu2S cores with sizes around 20 nm and a ZnS secondary shell 8 nm thick. According to the ultraviolet–visible absorption and photoluminescence spectra, the optical characteristics observed in the synthesized material correspond to a PbS/Cu2S/ZnS system with higher confinement than the PbS/Cu2S nanoparticles. The quantum yield improves by 14% from the PbS/Cu2S to the PbS/Cu2S/ZnS nanoparticles.

Modification of the luminescent properties of ZnS nanoparticles by the adsorbed species

Abstract We report the modification of the luminescent properties of ZnS nanoparticles by the adsorbed chemical species. ZnS nanoparticles were prepared via microwave-assisted synthesis. The effects of the concentrations of citrate and SO42− ions on the optical properties were analyzed by means of UV-Vis and photoluminescence spectrophotometries, and Fourier-transform IR spectroscopy. ZnS nanoparticles were also analyzed by means of X-ray diffraction and transmission electron microscopy. The results confirm that the luminescent properties of the synthesized particles are affected by the adsorbed chemical species (citrate and SO42− ions). ZnS nanoparticles synthesized with 30 and 45 mM Na2SO4, and 2 mM trisodium citrate exhibit higher intensity of luminescence than those synthesized with 15 mM Na2SO4. The average diameter of the ZnS nanoparticles synthesized under these last experimental conditions is about 20 nm.

Hydrophobization and evaluation of absorption capacity of Aloe vera, Opuntia ficus-indica and Gelidium for oil spill cleanup

Abstract Natural sorbent materials have practical advantages for the oil spill cleanup, whose advantages are their low-cost, feasibility for real-life applications and environmental adaptability. In this work, absorption capacity was determined for lyophilized aloe, nopal and agar and their composites with silica, Fe3O4/polysterene and multi-wall carbon nanotubes (MWCNTs). Freeze-drying was performed in order to preserve the structure and increase the internal volume of sorbents. The structures of lyophilized sorbents and composites were analyzed by scanning electron microscopy (SEM). SEM images for lyophilized sorbents show a tridimensional arrangement formed by plant-derived materials, which allows the oil absorption. The composites keep their tridimensional structure after freeze-drying and composite formation and exhibit coupling between both materials. Absorption capacity of aloe, nopal and agar are 9 g/g, 3 g/g, and 26 g/g, respectively without any pretreatment. Composites with Fe3O4/polysterene own capacities of 5.8 g/g, 2.8 g/g, and 14 g/g, respectively. Finally, for MWCNT composites, capacities are 7.8 g/g, 2.9 g/g and 23 g/g. A significant difference of adsorption capacity between lyophilized sorbents and composites is attributed to lyophilized materials absorbing oil, water and other compounds. Meanwhile, for composites the absorption is a more selective process, since the hydrophobization does not allow the absorption of water. Graphical Abstract

Highly Luminescent PbS/ZnS Nanoparticles Synthesized by a Microwave Method

Abstract Nanoparticles with PbS core of 12 nm and shell of approximately 3 nm were synthesized at PbS:ZnS ratios of 1.01:0.1 using Merca Ptopropionic Acid as stabilizing agent. PbS/ZnS nanoparticles present a dramatically increase of Photoluminescence intensity, confirming the confinement of the PbS core by increasing the Quantum Yield from 0.63 to 0.92 by the addition of the ZnS shell. In this case, the synthesis by microwave method allows obtaining nanoparticles with enhanced optical characteristics in shorter reaction time than those of nanoparticles synthesized by colloidal method.