D.A. Solís-Casados

Preparation and characterization of bismuth nanostructures deposited by pulsed laser ablation

Bismuth nanostructures, from nanoparticles to quasi-percolated films, were deposited by pulsed laser ablation (PLA) on different substrates using the 355 nm line of a Nd:YAG laser. The morphology and size distribution of the obtained nanostructures were investigated, as a function of the number of ablation pulses, by high resolution electron microscopy (HRTEM) and atomic force microscopy (AFM). Deposits with a small number of pulses, 50, are formed of separated isolated particles with diameters in the range from 5 to 20 nm. Further increase in the number of pulses (>100) results in coalescence of individual particles with the formation of dendritic structures and finally, for 500 pulses, quasi-percolated Bi films are obtained. Additionally, the nanostructures formed were characterized by XPS, and Raman spectroscopy in order to determine the physical and chemical properties of the deposited material.

Photocatalytic Activity under Simulated Sunlight of Bi-Modified TiO2 Thin Films Obtained by Sol Gel

The synthesis of Bi-modified TiO2 thin films, with different Bi contents, is reported. The obtained materials were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), X-ray diffraction (XRD), photoluminescence (PL), and diffuse reflectance spectroscopy (DRS), in order to obtain information on their chemical composition, vibrational features, and optical properties, respectively. Compositional characterization reveals that the bismuth content can be varied in an easy way from 0.5 to 25.4 at. %. Raman results show that the starting material corresponds to the anatase phase of crystalline TiO2, and Bi addition promotes the formation of bismuth titanates, Bi2Ti2O7 at Bi contents of 10.4 at. % and the Bi4Ti3O12 at Bi contents of 21.5 and 25.4 at. %. Optical measurements reveal that the band gap narrows from 3.3 eV to values as low as 2.7 eV. The photocatalytic activity was tested in the degradation reaction of the Malachite Green carbinol base dye (MG) as a model molecule under simulated sunlight, where the most relevant result is that photocatalytic formulations containing bismuth showed higher catalytic activity than pure TiO2. The higher photocatalytic activity of MG degradation of 67% reached by the photocatalytic formulation of 21.5 at. % of bismuth is attributed to the presence of the crystalline phase perovskite-type bismuth titanate, Bi4Ti3O12.

Preparation of nanostructured Bi-modified TiO2 thin films by crossed-beam laser ablation plasmas

The preparation and characterization of titanium dioxide thin films modified with different amounts of bismuth using a two laser ablation plasmas configuration is reported. The plasmas were produced ablating simultaneously two different targets, one of bismuth and other of titanium dioxide, using a Nd:YAG laser with emission in the fundamental line. The elemental composition, together with the vibrational and optical properties of the deposited films were investigated as a function of the parameters of the bismuth plasma. The composition of the thin films was determined from measurements of X-ray photoelectron spectroscopy (XPS) as well as by Rutherford backscattering spectroscopy (RBS). The structural modification of the deposited material, due to the incorporation of Bi, was characterized by Raman spectroscopy. The optical properties were determined from UV-Vis spectroscopy measurements. It is found that bismuth incorporation has an important effect on the optical properties of TiO2 narrowing the band gap from 3.2 to 2.5 eV.

Thermoluminescent response of C-modified Al2O3 thin films deposited by parallel laser ablation plasmas

Aluminium oxide thin films modified with different amounts of carbon were prepared using a parallel laser ablation plasmas configuration. The effect of the amount of carbon incorporated in the films on their compositional, morphological, structural, and thermoluminescent properties was studied. The results showed that films with different C content, from 11 to 33 at. %, were obtained. The structural characterization revealed the growth of an amorphous material. Surface morphology of the obtained thin films showed smooth surfaces. The films were exposed to UV and gamma radiation (Co-60) in order to study their thermoluminescence response. The results tend to indicate that carbon incorporation into the alumina favours the increase of a high temperature TL peak.

Synthesis and Characterization of Ag-Modified V2O5 Photocatalytic Materials

V2O5 powders modified with different theoretical silver contents (1, 5, 10, 15, and 20 wt% as Ag2O) were obtained with acicular morphologies observed by scanning electron microscopy (SEM). Shcherbinaite crystalline phase is transformed into the Ag0.33V2O5 crystalline one with the incorporation and increase in silver content as was suggested by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. With further increase in silver contents the Ag2O phase appears. Catalysts were active in photocatalytic degradation of malachite green dye under simulated solar light, which is one of the most remarkable facts of this work. It was found that V2O5-20Ag was the most active catalytic formulation and its activity was attributed to the mixture of coupled semiconductors that promotes the slight decrease in the rate of the electron-hole pair recombination.

Study of the Corrosion Rate of Three Contactors Materials Using the Electrochemical Technique of Tafel

The main objective of this project was to study the corrosion rate of three different structured packing materials, a metallic, one polymeric and the other one ceramic, which will be in contact with an aqueous solution of MEA (monoethanolamine) to 30% and sour gases in a countercurrent absorption column. The materials were studied in two electrochemical cells: the first one in the presence of an aqueous solution of 1N sulfuric acid, and the second in the aqueous solution of MEA 30%, the study was done using the Tafel extrapolation methods and resistance to the polarization to measure the corrosion current (I Corr), and determine the corrosion rates of the three materials structured packings. The standard procedure used was according to ASTM G59-91, following the technique ININ No. P. SC (Cl) -06, the following results were found: in the presence of 1N sulfuric acid solution the metallic material presented a rate of 7.8 x 10-4 corrosion mpy (miles per year), the polymeric material submitted a corrosion rate of 2.82 x 10-4 mpy, and the ceramic material presented a corrosion rate of 1.03 x 101 mpy. With the aqueous solution of MEA at 30% in weight, and the sour gases the results were as follows: the metallic material presented a corrosion rate of 6.42 x 10-2 mpy, the polymeric material submitted a corrosion rate of 1.48 x 10-1 mpy and the ceramic material presented a corrosion rate of 5.6 x 10-1 mpy. These results provide a basis for predicting the lifetime of the three materials, as well as chemical resistance in the absorption column. Finally, we examined the morphology of the etched surface by scanning electron microscopy and found that in the metallic material was formed a layer of Cr2O3, which is helping the passivating material to further protect the acid attacks, the polymer material has a surface smoother after the attack and in the ceramic is observed pores larger than those observed in the material before the attack.