Esteban Gallegos-Suarez

Adsorption of emerging pollutants on functionalized multiwall carbon nanotubes.

Adsorption of three representative emerging pollutants - 1,8-dichlorooctane, nalidixic acid and 2-(4-methylphenoxy)ethanol- on different carbon nanotubes was studied in order to determine the influence of the morphological and chemical properties of the materials on their adsorption properties. As adsorbents, multiwall carbon nanotubes (MWCNTs) without functionalization and with oxygen or nitrogen surface groups, as well as carbon nanotubes doped with nitrogen were used. The adsorption was studied in aqueous phase using batch adsorption experiments, results being fitted to both Langmuir and Freundlich models. The adsorption capacity is strongly dependent on both the hydrophobicity of the adsorbates and the morphology of the adsorbents. Thermodynamic parameters were determined observing strong interactions between the aromatic rings of the emerging pollutant and the nitrogen modified adsorbents.

Nitrate reduction over a Pd-Cu/MWCNT catalyst: application to a polluted groundwater.

The influence of the presence of inorganic and organic matter during the catalytic reduction of nitrate in a local groundwater over a Pd-Cu catalyst supported on carbon nanotubes was investigated. It was observed that the catalyst performance was affected by the groundwater composition. The nitrate conversion attained was higher in the experiment using only deionized water as solvent than in the case of simulated or real groundwater. With exception of sulphate ions, all the other solutes evaluated (chloride and phosphate ions and natural organic matter) had a negative influence on the catalytic activity and selectivity to nitrogen.

Comparative study of bioethanol transformation catalyzed by Ru or Pt nanoparticles supported on KL zeolite

The catalytic properties of two noble metals, Pt and Ru, supported on KL zeolite were investigated in the selective transformation of bioethanol. In aiming to have an increased basicity of the catalyst, a KL zeolite modified by the addition of Ba was also used as support for Pt catalyst. For comparative purposes, Ru supported on hydrophobic high surface area graphite (HSAG) was also prepared. The catalytic tests were conducted in a fixed bed flow reactor, by feeding either pure ethanol vapor or a mixture of 10% water/90% ethanol in an inert gas, and working at low conversions to assure kinetic conditions. All the catalysts have relatively stable catalytic performance at up to 6 hours on stream with both reactant feedings. In general, the catalytic activities of Pt-based catalysts, given as turn-over-frequencies, were one order of magnitude higher than those obtained over Ru catalysts. It was also demonstrated that the nature of the supported metal nanoparticles (Ru vs. Pt) significantly affects the product selectivities. So when comparing Pt/KL and Ru/KL, methane and carbon monoxide by-products are mainly produced on the former, indicating that degradation of the primary product acetaldehyde by decarbonylation is higher on Pt catalysts. In the case of ruthenium nanoparticles, acetaldehyde is the predominant product. Finally, the comparison of Ru supported on KL zeolite and on HSAG revealed that, in the second case, ethylene is the principal by-product and that in some extension, this ethylene can be hydrogenated to ethane, probably spending hydrogen generated in the acetaldehyde formation. DRIFTS experiments were also conducted to identify the adsorbed intermediate species present under the reaction conditions on the different catalysts. All the selectivity differences have been rationalized using appropriate reaction pathways, and it is inferred that the variation of the chosen metal–support system is decisive to obtain a given reaction product.

Effect of surfactant concentration on the morphology of MoxSy nanoparticles prepared by a solvothermal route

Abstract The preparation of MoxSy nanoparticles with different morphologies via a surfactant-assisted one-pot solvothermal route was reported. The concentration of surfactant was studied to evaluate its effects on the morphology and the size of the as obtained nanoparticles. The final products were comprehensively characterized using XRD, TEM, HRTEM, IR, TGA and XPS. It was found that at low surfactant concentration, MoS2 spherical shapes were obtained whereas tubular morphologies are formed at higher concentration. This issue has been discussed based on various relevant experimental data.

Facile solvothermal synthesis of bimetallic CoMoS2 and NiMoS2 nanospheres

Abstract Bimetallic nickel or cobalt molybdenum disulfide (MMoS2, M=Ni or Co) nanospheres, with a diameter ranging between 450 nm and 1 μm, have been successfully synthesized using a mild solvothermal method. The obtained nanomaterials have been comprehensively characterized using transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR).