Azael Martínez de la Cruz

Lithium in W18O49: synthesis and characterization of novel phases

Electrochemical lithium insertion into W18O49 has allowed the determination of the existence of a range of intercalated phases, LixW18O49. For x < 22 the phases form through an intercalation reaction and four single-phase regions are detected: x= 0–2.6, 3.4–10, 11–15, 15.5–22. In the last of these composition ranges and by reaction with n-butyllithium, a new phase, Li17W18O49, can be isolated that has a multiple cell, with respect to the starting phase. By following this chemical route, the maximum lithium content corresponds to Li40W18O49. Electrochemical experiments showed that lithium is not reversibly intercalated in this last phase.

Mesoporous titania nanofibers by solution blow spinning

Fast and large-scale production of mesoporous titania nanofibers was achieved by solution blow spinning. The blow spinning setup provides a method to prepare titania nanofibers in a safe and scalable way without using a high-voltage electric field. Titania microstructure and porosity can be modified by adding a suitable template, such as pluronic polymers. The blow spun titania nanofibers had a good performance on the photocatalytic degradation of tetracycline and could be easily removed from the tetracycline aqueous solution due to their large aspect ratio. Solution blow spinning method has a great potential for the large-scale production of titania nanofibers with good photocatalytic properties.Graphical Abstract

Optimized photocatalytic degradation of caffeic acid by sol–gel TiO2

TiO₂anatase powder was prepared by means of the sol-gel method with titanium(IV) butoxide as precursor. The formation of a tetragonal crystal structure of TiO₂anatase at 500 °C was confirmed by X-ray powder diffraction. The characterization of the samples synthesized was complemented by scanning electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, nitrogen adsorption-desorption isotherms (Brunauer-Emmett-Teller) and diffuse reflectance spectroscopy. The photocatalytic activity of the TiO₂anatase powder was evaluated in the degradation of caffeic acid in aqueous solution under ultraviolet radiation. A central composite circumscribed design was used to assess the weight of the experimental variables, pH and amount of catalyst in the percentage of caffeic acid degraded and the optimal conditions. The optimized conditions were found to be pH = 5.2 and a load of TiO₂of 1.1 g L⁻¹. Under these conditions more than 90% of caffeic acid degradation was achieved after 30 min of lamp irradiation. At this time the mineralization reached was almost 60%.

New Visible-Light Active Semiconductors

So far, the anatase TiO2 polymorph has been the most studied semiconductor photocatalyst due to its high activity under UV irradiation, high stability against photocorrosion process, and low cost. Nevertheless, from the whole solar energy spectrum that radiates the earth, UV irradiation only represents 4 %. In the same way, other semiconductors such as ZnO, Fe2O3, CdS, ZnS, Nb2O5, Ta2O5, and BiTaO4 have been reported with excellent performance as photocatalysts, among others. In particular, oxides with perovskite structure formed by TaO6 or NbO6 octahedra layers have shown the capability to develop an important catalytic activity have reported photocatalytic activity in tantalates and niobates of the type NaMO3 (M = Ta and Nb) for the stoichiometric decomposition of water. In the same way, photocatalytic activity better than TiO2 has been observed on laminar oxides such as BaLi2Ti6O14, MTaO3 (M = Li, Na, K), and SrM2O7 (M = Nb, Ta) for the degradation of organic pollutants. However, most of these have the same drawbacks that TiO2 has in relation with their limited range of light absorption and an inefficient charge separation which leads to a high recombination process with the concomitant diminishing of their photocatalytic activity.

Photocatalytic Degradation of RhB with Microwave Prepared PbMoO4

Abstract Synthesized PbMoO4 from H2MoO4 and Pb(NO3)2 with microwaves was compared, in terms of its photocatalytic activity as catalyzer for decomposing rhodamine B (RhB), against samples prepared by hydrothermal and sonochemical methods from the same precursors. Microwave synthesis lasted 20 minutes; hydrothermal, 10 minutes and sonochemical method, 1 hour. X-rays diffraction patterns show that PbMoO4 prepared by these three routes is compounded by the same phase. It is found that microwave synthesized PbMoO4 particles are rounder, in an intermediate size (250 nm), compared to sonochemical (100 nm) and hydrothermal (500 nm) routes; microwave particles also exhibit higher photocatalytic activity for degradation of RhB under a xenon lamp. This difference is not explicable in terms of surface area measurements, but could be explained by UV light scattering by the rounder particles produced by means of the microwave processing, which are about one half size compared to the wavelength.

Artificial neural network for optimization of a synthesis process of γ -bi 2 moo 6 using surface response methodology

In this work an artificial neural network was utilized in order to optimize the synthesis process of γ-Bi2MoO6 oxide by co-precipitation assisted with ultrasonic radiation. This oxide is recognized as an efficient photocatalyst for degradation of organic pollutants in aqueous media. For the synthesis of γ-Bi2MoO6 three variables were considered, the exposure time to ultrasonic radiation, calcination time and temperature. The efficiency of photocatalysts synthesized was evaluated in the photodegradation of rhodamine B (rhB) under sun-like irradiation. A set of experimental data were introduced into the neural network, a multilayer type perceptron with a back-propagation learning rule was used to simulate the results by modifying one of the three input variables and observing the efficiency of photocatalysts using besides a response surface methodology.