Luis Lartundo-Rojas

Effect of water and fluoride content on morphology and barrier layer properties of TiO2 nanotubes grown in ethylene glycol-based electrolytes

This paper studies the effect of H2O and NH4F content on morphology and barrier layer properties of TiO2 nanotubes grown by potentiostatic anodization in ethylene glycol-based electrolytes. The increase in these two variables leads to an increase in the chemical attack of the formed oxide. However, each of these variables plays a different role in the formation of TiO2 nanotubes. On the one hand, a higher percentage of H2O in the electrolyte leads to a transition from a nanoporous to a nanotubular structure, as well as to a greater diameter of the tubes and a decrease in their length and barrier layer thickness. In contrast, a higher NH4F concentration decreases nanotube diameter and increases their length modifying barrier layer properties due to insertion of F− ions into the lattice. This diminishes the barrier layer resistance, but increases both the adsorption and the diffusion coefficient of F− ions. The different roles of H2O and NH4F in film formation are also associated with the presence of sub-oxides detected by XPS.

Effect of chitosan on the performance of NiMoP-supported catalysts for the hydrodesulfurization of dibenzothiophene

Chitosan-added NiMoP catalysts supported on alumina and alumina-titania were studied in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The preparation of catalysts containing Mo (12 wt%), Ni (3 wt%), P (1.6 wt%), and chitosan/nickel = 2 (mol ratio) was accomplished by sequential pore-filling impregnation varying the order of chitosan integration. Materials were characterized by DRIFTS, TPR, TG-DTA, and XPS techniques. The TG-DTA study showed that the nature of the support influences the degradation of chitosan onto the catalytic materials and also influences the HDS of DBT and the product distribution as well. The series of catalysts supported on alumina presented the most remarkable effect of chitosan, in which the OH and NH groups of the organic molecule interact with acid sites of the support weakening the interaction between alumina and deposited metal phases. In all cases, DBT was converted mainly through direct sulfur removal. The catalysts ChP3/A (alumina support impregnated with chitosan in phosphoric acid solution, prior to NiMoP deposition) and ChP4/AT (alumina-titania support impregnated with NiMoP solution, prior to contacting with a solution comprising chitosan and phosphorus) exhibited the best performance in HDS reactions and also showed the highest selectivity in biphenyl formation. Presence of carbonaceous residua on the catalysts surface, as shown by XPS, could enhance the HDS activity over the ChP4/AT sample.

Directing photocatalytic and photoelectrocatalytic performance of TiO2 by using TEA and NH4F as doping precursors

Triethylamine (TEA) and NH4F-modified TiO2 powders and thin films were prepared by combining sol–gel and hydrothermal processes. Modification with TEA results in increased specific surface area and induces energy states below the conduction band of TiO2. On the other hand, the use of NH4F decreases the band-gap, displacing the valence band. Employing radical-scavenging agents, it was found that formation of O2* is preferred in TEA-modified TiO2, whereas generation of both O2* and OH* results from simultaneous modification. Furthermore, the photocatalytic degradation rate was directly proportional to their specific surface area. However, this trend was reversed in a photoelectrocatalytic cell, due to the fact that the photogenerated electrons are rapidly transported to the rear contact, which restrains their transfer to the dissolved oxygen to generate O2*. Therefore, the presence of OH* radicals and direct charge transfer processes appears to play a key role in the photoelectrocatalytic process.Graphical Abstract

Synthesis and characterization of Cu-doped polymeric carbon nitride

ABSTRACT Polymeric carbon nitride doped with copper through a solid-state reaction was characterized by several techniques, among them are UV-visible spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, etc. The material is a semiconductor with a wide band gap of 2.74 eV. Sites of both Cu(I) and Cu(II) were detected, apparently only coordinated by the polymer. The material comprises crumpled nanosheets, and is substantially an amorphous layered material with a prevalent 2D structure with low inter-planar interactions, as shown by X-ray diffractometry and TeraHertz spectroscopy. Photo-oxidation of benzyl alcohol was used to probe the active sites of the material, comparing them with the non-doped material. The higher activity and selectivity toward salicylic alcohol of the non-doped material can be due to both a more localized electron transfer and a longer lifetime of the hole–electron pair. Cu-CN favored the oxidation of hydroxymethyl group. Therefore, the presence of copper can favor different reaction pathways with respect to the non-doped material.

Bifunctional electrocatalysts for oxygen reduction/evolution reactions derived from NiCoFe LDH materials

Materials obtained from thermal treatment of thermally treated NiCoFe-layered double hydroxides (LDH) with different Ni:Co ratios were evaluated as bifunctional catalysts for Oxygen Reduction Evolution and Evolution Reduction Reactions in alkaline media. The structural properties of synthesized materials were characterized by X-ray diffraction, Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopies, whereas the basicity of each material was evaluated by temperature-programmed desorption of carbon dioxide. The results revealed the presence of inverse spinel structure with different compositions and a NiO phase with different amounts in the sample, while the electrochemical results showed a high activity towards oxygen reactions. The sample with higher amount of NiO and the lowest substitution grade on tetrahedral sites in the spinel-type structure exhibited the best catalytic activity.Graphical Abstract

Photocatalytic activity of a new composite material of Fe (III) oxide nanoparticles wrapped by a matrix of polymeric carbon nitride and amorphous carbon

ABSTRACT Polymeric carbon nitride was synthesized from urea and doped with Cu and Fe to act as co-catalysts. The material doped with Fe was a new composite material composed of Fe(III) oxides (acting as a co-catalyst) wrapped by the polymer layers and amorphous carbon. Furthermore, the copper doped material was described in a previous report. The photocatalytic degradation of the azo dye direct blue 1 (DB) was studied using as photocatalysts: pure carbon nitride (CN), carbon nitride doped with Cu (CN-Cu) and carbon nitride doped with Fe (CN-Fe). The catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), by X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller method (BET), etc. The adsorption phenomenon was studied using the Langmuir and Freundlich models. For the kinetic study, a solution of 500 mg L−1 of DB1 was treated with each catalyst, visible light and H2O2. The dye concentration was measured by spectrophotometry at the wavelength of 565 nm, and the removal of the total organic content (TOC) was quantified. BET analysis yielded surface areas of 60.029, 20.116 and 70.662 m2g−1 for CN, CN-Cu and CN-Fe, respectively. The kinetics of degradation were pseudo-first order, whose constants were 0.093, 0.039 and 0.110 min−1 for CN, CN-Cu and CN-Fe, respectively. The total organic carbon (TOC) removal reached the highest value of 14.46% with CN-Fe.

Copper complexes within the supramolecular solid structure of cyanuric acid and melamine

ABSTRACT A complex of copper sulfate was formed by impregnation of the cyanuric acid melamine adduct (CAM) with a solution of copper (II) sulfate. A thermal treatment at 250°C of the dried compound delivered a greenish powder. The UV-Vis spectroscopy showed that an absorption around 700 nm is compatible with a copper (II) sulfate complex coordinated inside the supramolecular structure of CAM. No copper or copper oxide particles were found by means of either transmission or scanning electron microscopy. X-ray photoelectron spectroscopy showed that on the surface there was a considerable amount of Cu(I) (66%) probably coordinated also inside the CAM channels. A brief catalytic test showed the ability of the copper complexes to oxidize sucrose to gluconic acid.