Dr. Valdes-Morales, Hector

The influence of surface physical-chemical characteristics of Chilean natural zeolite on the catalytic ozonation of toluene is presented in this article. Surface characteristics of natural zeolite were modified by acid treatment with hydrochloric acid and ion-exchange with ammonium sulphate. Prior to catalytic ozonation assays, natural and chemically modified zeolite samples were thermally treated at 623 and 823 K in order to enhance Brønsted and Lewis acid sites formation, respectively. NaturalandmodifiedzeolitesampleswerecharacterisedbyN2 adsorptionat77K,elementalanalysis, X-ray fluorescence, and Fourier transform infrared (FTIR) spectroscopy, using pyridine as a probe molecule. The highest values of the reaction rate of toluene oxidation were observed when NH4Z1 and 2NH4Z1 zeolite samples were used. Those samples registered the highest density values of Lewis acid sites compared to other samples used here. Results indicate that the presence of strong Lewis acid sites at the 2NH4Z1 zeolite surface causes an increase in the reaction rate of toluene oxidation, confirming the role of Lewis acid sites during the catalytic ozonation of toluene at room temperature. Lewis acid sites decompose gaseous ozone into atomic oxygen, which reacts with the adsorbed toluene at Brønsted acid sites. On the other hand, no significant contribution of Brønsted acid sites on the reaction rate was registered when NH4Z1 and 2NH4Z1 zeolite samples were used.

En este trabajo se investigaron las variables de diseño y los parámetros operacionales en el proceso de adsorción de compuestos orgánicos volátiles clorados (COVs-Cl) utilizando zeolita natural modificada con metales de transición (ZMt). Se establecieron los niveles de las variables de diseño: temperatura de desgasificación [350 550 OC], tipo de metal de transición [Fe, Mn, Ag, Co, Cu, Ni], concentración del metal depositado [0,05; 0,1 M], método de deposición del metal [impregnación, intercambio iónico], posttratamiento del metal depositado [desgasificación con Ar, calcinación con O2, reducción con H2], y como parámetros operacionales: tipo de COVs-Cl [percloroetileno, clorobenceno], concentración de COVs-Cl [1,5; 9,5 μmol dm-3], temperatura de adsorción [20; 100 OC], flujo volumétrico de COVs-Cl [50; 100 cm3 min-1], masa de ZMt [0,15; 0,3 g]. Se utilizó el diseño de experimento D-Optimal, con el que el número de experimentos a realizar fue reducido de 2.048 a 139. Los experimentos de adsorción se llevaron a cabo en un adsorbedor de lecho fijo, siguiendo la concentración del COVs-Cl por cromatografía de gases. Los resultados experimentales se ajustaron a un modelo de regresión lineal de segundo orden. El análisis de varianza (ANOVA) demostró que el modelo ajustado es altamente significativo y con una satisfactoria bondad de ajuste. Los resultados del ANOVA también indicaron que entre las variables significativas, las zeolitas intercambiadas con Fe y Cu tienen un efecto positivo en la capacidad de adsorción de la ZMt. La concentración de COVs-Cl y temperatura de adsorción muestran la mayor influencia en la eliminación de COVs-Cl entre las variables de operación estudiadas.

Three-dimensional (3D) bismuth selenide (Bi2Se3) nanostructures were synthesized by microwave synthesis using water as a solvent and hydrazine hydrate as a reducing agent and exfoliated into few layers of Bi2Se3. Bi2Se3- Few Layers (Bi2Se3- FL) exhibited localized surface plasmon resonance and enhanced electrocatalytic behavior. The scanning electron microscope (SEM) and transmission electron microscopy (TEM) characterization indicated the layered structure of Bi2Se3. The electrocatalytic properties of the Bi2Se3-FLmodified GC electrode towards nonenzymatic glucose oxidation were evaluated by cyclic voltammetry (CV) and chronoamperometry. The designed non-enzymatic glucose sensor showed a low detection limit of 6.1 μM, a linear range from 10 μM to 100 μM of glucose concentration and a current sensitivity of 0.112 μAμM 1 .The electrochemical sensor constructed using Bi2Se3-FL attained steady-state level within 3 s upon adding glucose and remained stable even after 19 days with only 17% loss in current signal. The obtained electrodes can be applied for determining glucose in urine samples. The results obtained here are of great significance to use nanostructured Bi2Se3-FL electrode as a potential candidate for non-enzymatic glucose detection.

Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 ◦C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation.

This study describes theoretical and experimental considerations to optimize the photocatalytic degradation of caffeic acid in water using 3D-BiOBr based materials under visible light irradiation. Three BiOBr materials were synthesized through the solvothermal method using different bromide sources, namely potassium bromide (KBr) and the ionic liquid (IL) 1-butyl-3-methylimidazolium bromide. Morphological and chemical changes were observed in IL based 3D-BiOBr materials. The theoretical optimization of the experimental conditions in heterogeneous photocatalysis tests (pH and dose of catalyst) were simulated using the MODDE 12.0.1 software. A central composite design (CCD) was applied to obtain a response surface to elucidate the optimal conditions. This model predicted that the maximum photocatalytic degradation can be achieved at pH of 6.7 and a photocatalyst dose of 344 mg L−1. The optimal experimental conditions were tested using the three synthesized 3D-BiOBr materials. The results showed that the highest degradation efficiency and mineralization yield were obtained using the BiOBr microspheres synthesized with the IL at 145 °C.

In this work, we prepared bismuth oxide (Bi2O3) nanoparticles with and without fuels (citric acid and urea) using a one-pot solid-state combustion method at 400 °C for visible light photocatalytic degradation of acid blue 25 (AB). The nanoparticle prepared with fuel greatly influences the Bi2O3 properties such as morphology, chemical, structural, and optical properties. Bi2O3 prepared with citric acid as fuel act as an effective photocatalyst for the breakdown of acid blue 25 within 60 min under visible light irradiation. The enhanced photocatalytic property of Bi2O3 is due to the narrow band gap, high crystallinity, flower-like morphology with high active sites, and light stability of the material. Furthermore, an effective photogenerated charge separation, high charge transfer, and lower band gap, improved the absorbing capacity in the visible region of Bi2O3 (1) and enhanced its photocatalytic ability. In the photocatalytic process, the superoxide radicals (O2·) anion played a significant role during the degradation of acid blue 25. The Bi2O3 (1) maintained its effectiveness after three reaction cycles without suffering any appreciable change in structural and functional stability. These findings demonstrated an easy method for treating the hazardous effluents into non-toxic small molecules, which can be potentially applied to purify the various textile effluent.

Cationic doping of TiO2 anatase with sulphur represents a facile method to improve catalytic and photocatalytic activity for hydrogen production and extend the action spectrum of TiO2 into the visible light region. However, there is a lot of misunderstanding when trying to explain the experimental findings and suggest theoretical models. In the present computational research work, novel theoretical models are put forward representing fully hydroxylated small anatase nanoparticles with S(IV) and S(VI) doping in various surface positions and in the bulk. It was found that sulfur in the doped anatase nanoparticles preserves its typical coordination geometries of trigonal pyramid for S(IV) and tetrahedron for S(VI). Doping in the anatase surface is much more energetically favorable compared to doping in the bulk. Doping with S(IV) causes decrease of the band gap from 3.22 to 2.65 eV while S(VI) doping could decrease Eg only to 2.96 eV. Location of photogenerated electrons and holes depends strongly on the position of dopant atoms and their valent state. Contrary to some experimental works, no strong and extended visible light absorption bands could be found with cationic doped hydroxylated anatase nanoparticles. However, improved charges separation is observed indeed and causes improved photocatalytic hydrogen production.

Tomatoes (Solanum lycopersicum L.) are widely cultivated and consumed, but ripening should be carried out in controlled storage conditions to extend their shelf life and avoid economic losses. The aim of this study was to investigate the effects of visible artificial light on the ripening and quality of fresh market tomatoes stored at a low temperature and high humidity. The postharvest performance with respect to the ripening of organically grown tomatoes in the Toscano cultivar, with a long storage life, was studied in the presence and the absence of visible LED light. The maturation kinetics of the tomatoes was modeled using the Power Law equation. Results showed that tomatoes stored in the presence of light exhibited an increased respiration rate and a faster preclimacteric phase. Lycopene content, total soluble solids, and maturity index increased in the presence of light. Hence, light increased the postharvest ripening of tomatoes, affecting their shelf life.

Synthesis and characterization of bismuth oxychloride (BiOCl) has received much attention due to its excellent photocatalytic properties, and low toxicity that allow its potential application for environmental decontamination processes. In this work, experimental conditions (temperature and reaction time) were established to synthesize BiOCl microspheres by a solvothermal method with high photocatalytic efficiency on the degradation of 3,4,5-trihydroxybenzoic acid (gallic acid). BiOCl materials were synthesized according to a design of experiment (DoE) where temperature and reaction time were selected as varying parameters. Obtained BiOCl materials with the highest and lowest degradation toward gallic acid, were characterized using several techniques. Results showed that the applied temperature is the most important parameter during solvothermal synthesis, which influences not only morphology and structure of BiOCl, but also its thermal stability and optical properties. Response surface methodology (RSM) analysis indicated that the highest photocatalytic efficiency of synthesized BiOCl material, is obtained when the temperature and reaction time are fixed at 155 °C and 18 h, respectively. Finally, a reaction mechanism of photocatalytic oxidation of gallic acid was proposed based on an experimental tests by adding different radical’ scavengers.

In the last decades, air pollution control has received much attention due to the increase of environmental and health problems. The design of new materials with potential applications in air pollution control systems is a challenge nowadays. In this work, BiOI nanostructured materials were synthesized and used for photocatalytic oxidation of nitric oxide (NO). A microwave-assisted solvothermal method was successfully applied for BiOI synthesis at 126 °C, using ethylene glycol (EG) as a solvent. Several samples were prepared by varying the microwave irradiation time between 5 and 120 min. Resulting materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, diffuse reflectance spectroscopy (DRS) and photoluminescence measurements (PL). The photocatalytic activity of BiOI samples was evaluated in the photo-oxidation reaction of nitric oxide (NO) in gas phase under visible light irradiation. BiOI sample synthesized after 15 min of microwave exposition shows the highest photocatalytic activity, even greater than that obtained when TiO2 Evonik P-25 is used. This nanostructured material was applied into the formulation of two types of materials (ceramic paint and stucco) for its potential use in the construction industry. Preliminary results show that the application of nanostructured BiOI into stucco formulation has a great potential to develop commercial products to remove NO from air.