Desarrollo de materiales foto-funcionales para aplicaciones medioambientales

Debido a la creciente industrialización a nivel mundial, se ha tenido un aumento significativo en la cantidad de residuos generados, la gran mayoría de ellos catalogados como peligrosos por su alta toxicidad para diferentes organismos y ecosistemas. De ésta problemática surge una adicional y es la relacionada con su tratamiento, ya que en muchas ocasiones no se tiene una idea clara de cómo disponerlos, siendo la solución en muchos casos el vertido a cuerpos de agua o su almacenamiento, con el potencial riesgo de sufrir infiltraciones que podrían causar contaminación de cuerpos acuíferos subterráneos, las cuales son comúnmente utilizadas para el consumo humano. El agua es un recurso natural vital para la existencia de los seres vivos. Sin embargo, se está presentando una disminución preocupante de los recursos de agua potable, debido al crecimiento de la población, el uso excesivo de los recursos, el cambio climático, contaminación excesiva con agentes como detergentes, fertilizantes, herbicidas, insecticidas, metales pesados, productos químicos de diferente naturaleza, entre otros. Ante la creciente escasez de recursos hídricos de calidad y el aumento de su demanda, surge la reutilización de las aguas residuales como una solución alternativa al uso de aguas potables o prepotables para ciertas aplicaciones. La fotocatálisis heterogénea, enmarcada como una tecnología avanzada e oxidación, surge como una alternativa de descontaminación y desinfección de aguas residuales que ofrece la posibilidad de tener agua limpia para diferentes actividades humanas, gracias al desarrollo de materiales foto-funcionales innovadores y rentables y a procesos que utilizando además la radiación solar pueden ser prometedores dentro del tratamiento del agua y del aire. En esta Tesis Doctoral se han desarrollado fotocatalizadores alternativos al TiO2, con propiedades mejoradas para aplicaciones fotocatalíticas no solo en el rango UV sino en el rango visible del espectro electromagnético. En primer lugar se exploró la síntesis de ZnO por distintos procedimientos, además de estudiar las modificaciones que la incorporación de “islas metálicas” con metales como la plata o el platino, ejercen sobre las actividades fotocatalíticas del ZnO modificado. También se sintetizaron materiales como el ZnWO4, Nb2O5, Bi2WO6 por diferentes procedimientos como síntesis hidrotermal, asistida por microondas, sol-gel o precipitación química; en todos ellos se ha estudiado la influencia de los parámetros de síntesis sobre las propiedades físico-químicas de los materiales obtenidos, a través de una caracterización exhaustiva de los mismos usando un amplio número de técnicas de análisis con el fin de verificar la influencia que la modificación de las distintas variables de síntesis ocasionan a nivel de cualidades morfológicas, texturales y de composición de los mismos. El enfoque primario de esta Tesis Doctoral, es el desarrollo de nanomateriales con propiedades fotocatalíticas mejoradas para la descontaminación y desinfección de aguas, por lo tanto un aspecto importante a tener en cuenta es la evaluación de las actividades fotocatalíticas de los materiales preparados, en procesos de degradación de contaminantes en agua, utilizando tanto la rodamina B y el naranja de metilo, así como el fenol como moléculas modelo, debido a sus características contaminantes desde el punto de vista medioambiental. Además en el caso de los materiales ZnO y el Ag- ZnO, se han realizado estudios de desinfección en aguas residuales provenientes de un efluente urbano, obteniendo resultados altamente satisfactorios en la desactivación de diferentes microorganismos

Mixed α-Fe2O3/Bi2WO6 oxides for photoassisted hetero-Fenton degradation of Methyl Orange and Phenol

Mixed oxides, α-Fe2O3/Bi2WO6, were prepared using a mechanical mixing procedure by adding to the Bi2WO6 previously obtained by hydrothermal method the corresponding amount of a prepared α-Fe2O3, the latter obtained by thermal decomposition of Fe(NO3)∙9H2O. The physicochemical surface, structural, morphological characteristics and optical properties of the samples, single and mixed, were determined by BET, XRD, FE-SEM, XPS and UV–vis diffuse reflectance spectroscopy. UV–vis diffuse reflectance spectra showed that incorporating a 5%wt. of α-Fe2O3 to the corresponding amount of Bi2WO6 sample broadened the visible light absorption of Bi2WO6 as expected. The photocatalytic activity, of single and mixed catalysts, to degrade a selected dye such as Methyl Orange (MO) as well as the transparent substrate Phenol (Ph) was studied, in aqueous medium (pH ≈ 5.5) under UV and sun-like illumination conditions in the absence and presence of H2O2. In the present study the use of a α-Fe2O3-Bi2WO6/H2O2 system demonstrate much higher photocatalytic efficiency to degrade both MO and Ph than pristine Bi2WO6or α-Fe2O3, single or mixed. Using the system α-Fe2O3-Bi2WO6/H2O2, around 85% of MO was degraded in 60 min under sun-like illumination whereas 100% was degraded in 60 min under UV-illumination. However, just around 30% of Ph was degraded in 120 min in the α-Fe2O3-Bi2WO6/H2O2 system under sun-like illumination whereas around a 95% was degraded in 90 min under UV-illumination. Under UV-illumination, the generation of hydroxyl radicals is favorable; whereas under sun-like illumination, only the small fraction of the UV can produces the radical dotOH. Under illumination, the H2O2 could react with photoinduced electrons from the photocatalysts leading to the production of hydroxyl radicals (radical dotOH).Ministerio de Economía y Competitividad CTQ2015-64664- C2-2-

5to. Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad. Memoria académica

El V Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad, CITIS 2019, realizado del 6 al 8 de febrero de 2019 y organizado por la Universidad Politécnica Salesiana, ofreció a la comunidad académica nacional e internacional una plataforma de comunicación unificada, dirigida a cubrir los problemas teóricos y prácticos de mayor impacto en la sociedad moderna desde la ingeniería. En esta edición, dedicada a los 25 años de vida de la UPS, los ejes temáticos estuvieron relacionados con la aplicación de la ciencia, el desarrollo tecnológico y la innovación en cinco pilares fundamentales de nuestra sociedad: la industria, la movilidad, la sostenibilidad ambiental, la información y las telecomunicaciones. El comité científico estuvo conformado formado por 48 investigadores procedentes de diez países: España, Reino Unido, Italia, Bélgica, México, Venezuela, Colombia, Brasil, Estados Unidos y Ecuador. Fueron recibidas un centenar de contribuciones, de las cuales 39 fueron aprobadas en forma de ponencias y 15 en formato poster. Estas contribuciones fueron presentadas de forma oral ante toda la comunidad académica que se dio cita en el Congreso, quienes desde el aula magna, el auditorio y la sala de usos múltiples de la Universidad Politécnica Salesiana, cumplieron respetuosamente la responsabilidad de representar a toda la sociedad en la revisión, aceptación y validación del conocimiento nuevo que fue presentado en cada exposición por los investigadores. Paralelo a las sesiones técnicas, el Congreso contó con espacios de presentación de posters científicos y cinco workshops en temáticas de vanguardia que cautivaron la atención de nuestros docentes y estudiantes. También en el marco del evento se impartieron un total de ocho conferencias magistrales en temas tan actuales como la gestión del conocimiento en la universidad-ecosistema, los retos y oportunidades de la industria 4.0, los avances de la investigación básica y aplicada en mecatrónica para el estudio de robots de nueva generación, la optimización en ingeniería con técnicas multi-objetivo, el desarrollo de las redes avanzadas en Latinoamérica y los mundos, la contaminación del aire debido al tránsito vehicular, el radón y los riesgos que representa este gas radiactivo para la salud humana, entre otros

Effect of synthesis pH on the physicochemical properties of a synthesized Bi2WO6 and the type of substrate chosen, in assessing its photo-catalytic activities

Crystalline orthorhombic Bi2WO6 powders were synthesized by a hydrothermal method from aqueous solutions of Bi(NO3)3 5H2O and Na2WO4 2H2O over a range of three selected pH values (2.0, 5.0 and 7.0), using NaOH as precipitating agent. The as-prepared catalysts were char- acterized by XRD, BET, FE-SEM, TEM, XPS and UV-vis spectroscopy. The effect of pH-synthesis on crystallinity, morphologies, surface area and optical absorption properties, were investigated. Although the pH has a marked influence on morphology, the nature of the precipitating agent (NaOH or TEA) also influences the morphology and surface structure composition, as it is observed in the present work. Three different probe molecules were used to evaluate the photo- catalytic properties under two illumination conditions (UV and Visible): Methyl Orange and Rho- damine B were chosen as dye substrates and Phenol as a transparent substrate. The photo-catalytic activities are strongly dependent not only on the pH used in the synthesis but also on the nature of the chosen substrate in assessing the photo-catalytic activities. Results were compared with those obtained when using TiO2(P25, Evonik) in the same experimental conditions. The photo- catalytic activity of one of the synthesised samples has been evaluated by exposing a mixture of Rhodamine B and Phenol in water, to different illumination conditions. Our results provide new evidences about the issue of whether dyes are suitable substrates to assess the activity of a photo-catalyst

Silver-modified ZnO highly UV-photoactive

ZnO nanoparticles were successfully synthesized by a controlled precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without template addition and ulterior calcination at 400 °C for 2 h. The Ag-ZnO catalysts (ranging from 0.5 to 10 Ag wt.-%) were obtained by photochemical deposition method at the surface of the prepared ZnO sample, using AgNO3 as precursor. The as-prepared catalysts (with and without silver) were characterized by XRD, BET, FE-SEM, TEM, and XPS and diffuse reflectance spectroscopy (DRS). The effect of Ag-phodeposition on the photocatalytic properties of ZnO nanoparticles was investigated. Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination and visible illumination: Methyl Orange and Rhodamine B were chosen as hazardous dyes and Phenol as a transparent substrate. For each of the chosen substrates, it was observed that the UV-photocatalytic properties of ZnO improved with the amount of Ag deposited, up to an optimum percentage around 1–5 wt.-% Ag, being even better than the commercial Evonik-TiO2(P25) in the same conditions. Above this amount, the UV-photocatalytic properties of the Ag-ZnO samples remain unchanged, indicating a maximum for Ag-deposition. While ZnO and Ag-ZnO catalysts can photodegrade Rhodamine B, Methyl Orange and Phenol totally within 60 min under UV-illumination, the process is slightly faster for the case of Ag–ZnO nanoparticles. Under Vis-illumination, the silver-metalized samples did not present photocatalytic activity in the degradation of Methyl Orange. However, a very low photoactivity was present for phenol degradation (10% conversion) and a moderate conversion of ca. 70% for Rhodamine B degradation, after 120 min of Visible-illumination. High conversion values and a total organic carbon (TOC) removal of 86–97% were obtained over the Ag-ZnO photocatalysts after 120 min of UV-illumination, suggesting that these Ag-modified ZnO nanoparticles may have good applications in wastewater treatment, due to its reuse properties.This work was supported by research fund from Project Ref. CTQ2015-64664-C2-2-P (MINECO/FEDER UE). Research services of CITIUS University of Seville are also acknowledged. We thank the University of Tolima for economic support in the studies commission of César Augusto Jaramillo Páez.Peer reviewe

Mixed α-Fe2O3/Bi2WO6 oxides for photoassisted hetero-Fenton degradation of Methyl Orange and Phenol

Mixed oxides, α-Fe2O3/Bi2WO6, were prepared using a mechanical mixing procedure by adding to the Bi2WO6 previously obtained by hydrothermal method the corresponding amount of a prepared α-Fe2O3, the latter obtained by thermal decomposition of Fe(NO3)∙9H2O. The physicochemical surface, structural, morphological characteristics and optical properties of the samples, single and mixed, were determined by BET, XRD, FE-SEM, XPS and UV–vis diffuse reflectance spectroscopy. UV–vis diffuse reflectance spectra showed that incorporating a 5%wt. of α-Fe2O3 to the corresponding amount of Bi2WO6 sample broadened the visible light absorption of Bi2WO6 as expected. The photocatalytic activity, of single and mixed catalysts, to degrade a selected dye such as Methyl Orange (MO) as well as the transparent substrate Phenol (Ph) was studied, in aqueous medium (pH ≈ 5.5) under UV and sun-like illumination conditions in the absence and presence of H2O2. In the present study the use of a α-Fe2O3-Bi2WO6/H2O2 system demonstrate much higher photocatalytic efficiency to degrade both MO and Ph than pristine Bi2WO6or α-Fe2O3, single or mixed. Using the system α-Fe2O3-Bi2WO6/H2O2, around 85% of MO was degraded in 60 min under sun-like illumination whereas 100% was degraded in 60 min under UV-illumination. However, just around 30% of Ph was degraded in 120 min in the α-Fe2O3-Bi2WO6/H2O2 system under sun-like illumination whereas around a 95% was degraded in 90 min under UV-illumination. Under UV-illumination, the generation of hydroxyl radicals is favorable; whereas under sun-like illumination, only the small fraction of the UV can produces the radical dotOH. Under illumination, the H2O2 could react with photoinduced electrons from the photocatalysts leading to the production of hydroxyl radicals (radical dotOH).Peer reviewe

ZnO and Pt-ZnO photocatalysts: characterization and photocatalytic activity assessing by means of three substrates

ZnO nanoparticles have been previously synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without the addition of a template. The as-prepared ZnO material was anealed at 400 °C in air for 2 h. The Pt-ZnO catalysts (0.5 or 1.0 Pt wt.%) were obtained by photochemical deposition method on the surface of the prepared ZnO sample, using hexachloroplatinic acid (H2PtCl6). It has been shown that Zn2+ is lost from the photocatalyst to the medium and a replacement of the cationic vacancies of Zn2+ by Pt4+ cations occurs during the platinization process of the ZnO samples, regardless of whether the platinum metal photodeposition process. The as-prepared catalysts were characterized by XRD, BET, FE-SEM, TEM, XPS and diffuse reflectance spectroscopy (DRS). Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination: Methyl Orange and Rhodamine B were chosen as dye substrates and Phenol as a transparent substrate. High conversion values (ca. 100%) and a total organic carbon (TOC) removal of 90–96%, were obtained over these photocatalysts after 160 min of UV illumination. In general, it was observed that the presence of Pt on ZnO affects the lattice parameters and the crystallite size. Although ZnO can completely degrade RhB, MO and Phenol totally in ca. 60 min, the process is more efficient for Pt–ZnO photocatalysts.This work was supported by research fund from Project Ref. CTQ2015-64664-C2-2-P (MINECO/FEDER, UE). XPS and others research services of CITIUS University of Seville are also acknowledged. We thank the University of Tolima for economic support in the studies commission of Cesar Augusto Jaramillo Páez

High UV-photocatalytic activity of ZnO and Ag/ZnO synthesized by a facile method

ZnO nanoparticles have been successfully synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved NaCO at pH ca. 7.0 without template addition. We have investigated the effect of annealing temperature in the final surface and structural properties. Photocatalytic studies were performed using two selected substrates, Methyl Orange and Phenol, both as single model substrates and in mixtures of them. It has been stated that calcination treatments lead to a significant improvement in the photocatalytic properties of the studied samples, even better than TiO(P25). As expected, the addition of Ag during the photocatalytic degradation of MO increases the reaction rate of the degradation of MO, giving a resultant Ag/ZnO photocatalyst which, after recovery, can be reused at least 18 times for the MO degradation tests, being even more photoactive than ZnO.This work was supported by research fund from Project Ref. CTQ2015-64664-C2-2-P(MINECO/FEDER, EU). XPS and others research services of SITIUS University of Seville are also acknowledged

A comparative assessment of the UV-photocatalytic activities of ZnO synthesized by different routes

ZnO was synthesized by a precipitation procedure, free of template agent, by mixing aqueous solutions of Zn(OAc) and dissolved NaCO at pH ca. 7. This material was calcined at different temperatures (200-600 °C for 2 h). In two other alternative procedures, after the precipitation, the suspension was taken to hydrothermal treatments or to microwave treatments, subjecting them to calcination treatments at the same temperatures as the previous material. All materials were characterized using various techniques. The photocatalytic activity was assessed in the degradation of methyl orange and phenol using UV-illumination and evaluating the corresponding percentages of conversion and mineralization. A minimal difference between the relative intensities of the exposed faces (I/I) related to XRD for the synthesized samples seems to be an important factor in obtaining good photocatalytic properties. This minimum, was achieved with a calcination treatment at 400 °C for 2 h. With this calcination treatment, no significant variations were observed in the photocatalytic activities of ZnO obtained by the three procedures, although in all cases the zinc oxides obtained exhibited, for each substrate, higher UV-photocatalytic activities than those obtained with TiO (P25) used as a reference catalyst. In all cases, the samples showed no photocatalytic activity in the visible region of the spectrum.This work was supported by a research fund from Project Ref. CTQ2015-64664-C2-2-P (MINECO/FEDER UE). We thank the University of Tolima for their economic support in the studies commission of Cesar Augusto Jaramillo Páez

Photo-induced processes on Nb2O5 synthesized by different procedures

The properties of Nb2O5 strongly depend on its synthesis procedure as well as the conditions of ulterior thermal treatment. We report the synthesis of Nb2O5 powders prepared by sol-gel precipitation method using niobium(V) ethoxide as precursor. Two chemical routes were chosen: the presence of tryethyl amine (TEA) as precipitant/template agent, or the oxidant peroxide method. In addition, microwave-assisted activation was also used. The as-prepared samples by the above procedures were amorphous. Structural changes upon heating from room temperature up to 800 °C were investigated by X-ray powder diffraction technique combined with thermogravimetric analysis. The sequential thermal treatment up to 800 °C promotes the crystallization of hexagonal phase to orthorhombic phase whereas the ulterior cooling to room temperature lead to a mixture of both phases. Samples calcined at selected temperatures of either 600 °C or 800 °C for 2 h, were characterized by XRD, SEM, N2-adsorption and diffuse reflectance spectroscopy (DRS). The synthetic approach routes as well as the combined microwave activation followed by ulterior thermal treatment lead to changes not only on particle size but also on the textural properties of the synthesized catalysts. The catalysts synthesized have been evaluated using Rhodamine B (RhB) as a substrate, under both UV and visible lighting conditions. None of the catalysts synthesized showed activity in the visible. Under UV-illumination conditions, some of the catalysts exhibited a relatively low photoactivity in the degradation of RhB, which is associated with a photo-sensitizing effect. However, the addition of Ag+ ions considerably increased the activity of all the catalysts in the degradation of RhB under UV-illumination conditions. A mechanism is proposed to explain the photo-induced processes obtained, leaving the door open to the possible implications of the observed results in relation to the interaction of RhB dye with noble metal nanoparticles such as silver.This work was supported by research fund from Project Ref. CTQ2015-64664-C2-2-P (MINECO/FEDER UE). We thank the University of Tolima for economic support in the studies commission of César Augusto Jaramillo Páez.Peer reviewe