G. Alonso-Núñez

Synthesis of Pt and Pt-Fe nanoparticles supported on MWCNTs used as electrocatalysts in the methanol oxidation reaction

Abstract This work reports a feasible synthesis of highly-dispersed Pt and Pt-Fe nanoparticles supported on multiwall carbon nanotubes (MWCNTs) without Fe and multiwall carbon nanotubes with iron (MWCNTs-Fe) which applied as electrocatalysts for methanol electrooxidation. A Pt coordination complex salt was synthesized in an aqueous solution and it was used as precursor to prepare Pt/MWCNTs, Pt/MWCNTs-Fe, and Pt-Fe/MWCNTs using FeCl 2 ·4NH 2 O as iron source which were named S1, S2 and S3, respectively. The coordination complex of platinum (TOA) 2 PtCl 6 was obtained by the chemical reaction between (NH 4 ) 2 PtCl 6 with tetraoctylammonium bromide (TOAB) and it was characterized by FT-IR and TGA. The materials were characterized by Raman spectroscopy, SEM, EDS, XRD, TEM and TGA. The electrocatalytic activity of Pt-based supported on MWCNTs in the methanol oxidation was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Pt-Fe/MWCNTs electrocatalysts showed the highest electrocatalytic activity and stability among the tested electrocatalysts due to that the addition of ”Fe” promotes the OH species adsorption on the electrocatalyst surface at low potentials, thus, enhancing the activity toward the methanol oxidation reaction (MOR).

Aqueous solution reaction to synthesize ammonium hexachloroplatinate and its crystallographic and thermogravimetric characterization

Abstract Ammonium hexachloroplatinate (Pt(NH4)2Cl6) has been proven to be a good precursor to obtain metallic Pt by thermal decomposition, in addition to being a stable compound easily obtained from a variety of Pt recuperation processes. This work was aimed to develop a simple way to synthesize Pt(NH4)2Cl6. The crystallographic characterization by powder and single crystal XRD is reported, along with a simulation of the XRD patterns performed with the software Cerius2. A thermogravimetric analysis (TGA) allowed insight into the thermal decomposition process, which has been confirmed to take place in two steps, between 175 and 400 °C. This low decomposition temperature makes Pt(NH4)2Cl6 an ideal catalyst precursor to obtain Pt/C for polymer electrolyte membrane fuel cell (PEMFC) electrode fabrication.

Temperature Effect on the Synthesis of Multi-Walled Carbon Nanotubes by Spray Pyrolysis of Botanical Carbon Feedstocks: Turpentine, α-pinene and β-pinene

The chemistry of the different components of turpentine and the effect of temperature on the synthesis of multi-walled carbon nanotubes (MWCNTs) by spray pyrolysis using ferrocene as catalyst in a temperature range of 700–1000°C at 100°C intervals was investigated. Turpentine with high α-pinene concentration (83.4%) and low β-pinene concentration (8.22%), as well as pure α-pinene and β-pinene, were used as carbon sources. The MWCNTs were analyzed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction and thermogravimetrical analysis. When using turpentine, the optimum temperature to produce high yields of crystalline MWCNTs was 800°C. A comparative analysis between pure α- and β-pinene reveals that α-pinene produces more crystalline MWCNTs than β-pinene at 800°C, indicating that α-pinene is the active component in turpentine for the production of crystalline MWCNTs.

Friction and Wear Performance of Tetraalkylammonium Thiomolybdates in Aqueous Solutions

Aqueous solutions of three tetraalkylammonium thiomolybdates (R 4 N) 2 MoS 4 (R = methyl, propyl, or hydrogen) were prepared and their tribological performance was tested using a pin-on-disc tribometer on a steel-aluminum contact. Tests were performed at the same conditions of load, entrainment speed, sliding distance, temperature, and concentration of the solution in order to compare the activity (lubrication effect) of the thiomolybdates. Although there is a friction reduction for the three salts compared to pure water, a significant difference in the friction coefficient is observed, depending on the alkyl group. SEM/EDAX and Raman analysis of the wear tracks reveal the formation of a solid film rich in molybdenum and sulfur, which indicates the in situ formation of a MoS 2 film.

Effect of acute and long-term administration of gold nanoparticles on biochemical parameters in rat brain

The present study investigated stress oxidative parameters and activities of enzymes of the energy metabolism in various brain structures. Rats were subjected to acute and long-term administration of gold nanoparticles (GNPs) with mean diameters of 10nm and 30nm. Adult (60days old) male Wistar rats received a single intraperitoneal injection (acute administration; 70μg·kg-1) or repeated injections once daily for 28days (long-term administration; 70μg·kg-1) of saline solution or GNPs (10nm or 30nm). Twenty-four hours after administration of the final dose, the animals were killed and the cerebral structures were isolated for enzyme analysis. In this study, we observed that the thiobarbituric acid-reactive species and carbonyl protein levels were decreased after acute administration of GNPs, whereas the superoxide dismutase activity was increased after acute and long-term of GNPs. The catalase activity was affected by the administration of GNPs. Furthermore, we have not found change in the citrate synthase activity. The succinate dehydrogenase, malate dehydrogenase, complexes I, II, II-III and IV, and creatine kinase activities were altered. These results indicate that inhibition energy metabolism can be caused by oxidative stress.

In‐Situ Deposition of Nickel Nanoparticles on Carbon Nanotubes by Spray Pyrolysis

Nickel nanoparticles have been deposited on carbon nanotubes by spray pyrolysis of toluene as carbon source and nickelocene as catalyst at different temperatures. The optimum temperature to produce well‐grown Ni/carbon nanotubes was found to be 850°C. The carbon nanotubes were characterized by SEM, TEM, XRD, Raman spectroscopy and TGA‐DTA. The microscopy studies show that the produced carbon nanotubes have disorder morphologies with diameters between 60 and 100 nm and lengths of a few hundred microns. Ni particles of 40 nm are well dispersed along the carbon nanotubes. XRD patterns show the crystalline planes corresponding to graphite and metallic Ni. The TGA‐DTA results indicate a Ni loading of 20wt%. Raman spectroscopy reveals that the grown carbon nanotubes are graphitized, showing both the D and G bands at 1330 cm−1 and 1590 cm−1, respectively. The corresponding intensity ratio of these bands (ID/IG) varies with respect to synthesis temperature and catalyst concentration.

Microspherical ReS2 as a High-Performance Hydrodesulfurization Catalyst

An unsupported microspherical ReS2 catalyst, consisting in self-assembled nano-layers, was evaluated in the hydrodesulfurization (HDS) of 3-methylthiophene showing an excellent catalytic activity. The samples were characterized by X-ray diffraction, scanning electron microscopy, high resolution electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. These techniques revealed that the rhenium disulfide layers are confined to a 3D hierarchical structure with different stacking, slab size and bending, according to the annealing temperature (400 or 800 °C). The presence of a defect-rich structure in the microspheres, with short and randomly-orientated ReS2 slabs, results in the exposure of additional edge sites, which improve the catalytic performance of this material. This microspherical ReS2 composite, with good HDS performance, is a promising catalyst for the desulfurization of fuel oils; the solvothermal reaction conditions are also useful to tune and create exotic morphologies for the design of new ReS2 catalysts.Graphical Abstract

A biosensor based on Coriolopsis gallica laccase immobilized on nitrogen-doped multiwalled carbon nanotubes and graphene oxide for polyphenol detection.

Abstract The use of nanomaterials allows the design of ultrasensitive biosensors with advantages in the detection of organic molecules. Catechol and catechin are molecules that occur naturally in fruits, and their presence in products like dyes and wines affects quality standards. In this study, catechol and catechin were measured at the nanoscale by means of cyclic voltammetry. The oxidation of Coriolopsis gallica laccase immobilized on nitrogen-doped multiwalled carbon nanotubes (Lac/CNx-MWCNT) and on graphene oxide (Lac/GO) was used to measure the concentrations of catechol and catechin. Nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNT) were synthesized by spray pyrolysis and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). Covalently bonded hybrids with laccase (Lac/CNx-MWCNT and Lac/GO) were generated. Catalytic activity of free enzymes determined with syringaldazine yielded 14 584 UmL−1. With Lac/CNx-MWCNT at concentrations of 6.4 mmol L−1 activity was 9326 U mL−1, while enzyme activity measured with Lac/GO at concentration of 6.4 mmol L−1 was 9 234 U mL−1. The Lac/CNx-MWCNT hybrid showed higher stability than Lac/GO at different ethyl alcohol concentrations. The Lac/CNx-MWCNT hybrid can measure concentrations, not previously reported, as low as 1 × 10−8 mol L−1 by measuring the electric current responses.

Tribology of Aqueous Thiomolybdate and Thiotungstate Additives in Low-Pressure Contacts

The wear reducing properties of aqueous solutions of ammonium thiomolybdate and ammonium thiotungstate were evaluated using a frontal cylinder-on-cylinder test tribometer on an AISI 304 steel–steel contact. The antiwear characteristics of the lubricating solutions of thiomolybdate and thiotungstate were evaluated at 24.5, 30, and 40 N keeping fixed the entrainment speed, sliding distance, temperature, and additive concentration. Although there was a reduction in wear for the two salts compared to fluid reference, it is worth mentioning that the thiotungstate additive was slightly more effective under tested lubricating contact conditions than thiomolybdate additive. Energy-dispersive X-ray spectroscopy (EDS) analysis of a wear track lubricated with thiomolybdate showed Mo and S elements and for the track lubricated with thiotungstate W and S were detected. Raman spectra of the wear track showed peaks at 373, 404 and 208, 253, 280, 353 cm−1 corresponding to 2H-MoS2 and FeS, respectively. Ammonium thiomolybdate releases sulfur atoms that also react with the freshly exposed surface, forming FeS, which takes part in reducing wear.

Improved hydrothermal synthesis of MoS2 sheathed carbon nanotubes

MoS2 sheathed carbon nanotubes have been successfully synthesized using a hydrothermal route under controlled conditions. The resultant material was studied by XRD, EDS, HRTEM, and Raman spectroscopy. Advantages of the preparation presented here compared to other methods are: a) lower reaction temperature, b) high yield of sheathed nanotubes including ends and full body, c) simple process with non-toxic materials, and d) no damage inflicted to nanotubes.