Publication: Síntesis, caracterización y desarrollo de nuevos dispositivos y aplicaciones basados en particulas nanoestructuradas híbridas de sistemas semiconductores de óxidos metálicos
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2021-11
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2021-12-20
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Abstract
En la actualidad existe una creciente necesidad de recuperar y reutilizar el agua, ya que, a causa de diversos factores socioeconómicos, se trata de un recurso cada vez más limitado. En los últimos años, la nanotecnología se ha convertido en uno de los campos de investigación más activos gracias a las excepcionales propiedades que presenta en comparación con las escalas superiores y a sus potenciales aplicaciones tecnológicas, destacando su utilidad en fotocatálisis para el tratamiento de las aguas residuales. Entre los nanomateriales utilizados para este fin, el óxido de zinc a escala nanométrica resulta muy interesante porque se trata de un material ambientalmente sostenible, que presenta una excelente actividad fotocatalítica a un bajo precio. Los estudios recientes buscan desarrollar materiales híbridos basados en sistemas semiconductores de ZnO decorado con metales nobles para mejorar su actividad catalítica y su resistencia a la corrosión. En este contexto, el uso de plata o platino resulta una opción de gran interés ya que dificultan la recombinación de los pares electrón-hueco fotoexcitados y prolongan así la vida útil de los fotocatalizadores.
Por todo lo expuesto anteriormente, en la presente Tesis Doctoral se prepararon sistemas micro/nanoestructurados híbridos de MN/ZnO, por el método solvotérmico (ST) y el método de pirolisis por pulverización ultrasónica (USP). En las diversas síntesis se evaluó la influencia de diferentes condiciones experimentales tales como el tiempo y la temperatura de síntesis, la presencia de dispersante, el tipo de metal noble utilizado, la naturaleza química de las sales precursoras, la relación molar de Ag+/Zn2+, etc.
Los materiales obtenidos se caracterizaron mediante difracción de rayos X (XRD), microscopía electrónica de barrido (SEM), microscopía electrónica de transmisión de alta resolución (HR-TEM), espectroscopia de reflectancia difusa UV-vis (DRS), adsorción-desorción de N2 (BET) y espectroscopia Raman (RS). Posteriormente, se estudió la actividad fotocatalítica de los sistemas sintetizados en la reacción de degradación del azul de metileno en disolución acuosa y bajo la excitación de luz UV. Con ello, se ha buscado relacionar el comportamiento fotocatalítico con las diferentes propiedades finales obtenidas en función de los diversos parámetros estudiados.
Los mejores porcentajes de eliminación de contaminante (>99 %) se han obtenido para muestras de Ag/ZnO sintetizadas por el método solvotérmico, a bajas temperaturas, tiempos intermedios y en presencia de dispersante, comprobándose que la morfología y el área superficial disponible, son parámetros decisivos en las propiedades del material obtenido.
Como resultados más relevantes de la presente investigación destacan que se consigue mejorar la actividad fotocatalítica del ZnO mediante su modificación a través de la incorporación de metal noble sobre su superficie, alargando su tiempo de vida útil. Al mismo tiempo que se han mejorado las propiedades estructurales, morfológicas y químicas, gracias a la buena dispersión y homogeneidad obtenida mediante el uso de surfactantes.
Por todo ello, se puede concluir que todos los sistemas de MN/ZnO sintetizados en este trabajo, con resultados de degradación de contaminantes superiores al 45 %, presentan una excelente viabilidad para aplicaciones medioambientales.
Nowadays, there is a rising demand to recover and reuse water, since it is an essential and limited resource, due to various socioeconomic factors. In recent years, nanotechnology has become one of the most active research areas thanks to its exceptional properties compared to bulk scale and to its potential technological applications, outstanding its use in photocatalysis for wastewater treatment. Among the nanomaterials used for this purpose, nanoscale zinc oxide generates great scientific interest because it is an environmentally sustainable material with excellent photocatalytic activity under low price. Recent studies search developing hybrid materials based on ZnO semiconductor systems decorated with noble metals to improve their catalytic activity and corrosion resistance. In this context, the use of silver or platinum is an appropriate option for avoiding the recombination of the photoexcited electron-hole pairs and thus prolong the lifetime of the photocatalysts. Therefore, in this Doctoral Thesis hybrid micro/nanostructured systems based on MN/ZnO were prepared by solvothermal method (ST) and ultrasonic spray pyrolysis (USP) methods. The influence of different experimental conditions such as synthesis time and temperature, dispersant presence, type of noble metal, chemical nature of precursors, Ag+/Zn2+ molar ratio, among others, were evaluated in different syntheses. Furthermore, the synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), UV-vis diffuse reflectance spectroscopy (DRS), adsorption-desorption of N2 (BET) and Raman spectroscopy (RS). Hereinafter, the photocatalytic activity was studied in the degradation reaction of methylene blue in aqueous solution and under UV light, in order to relate the photocatalytic behaviour of the samples with properties obtained on account of different parameters studied. Likewise, the best percentages of contaminant removal (>99 %) were obtained for Ag/ZnO samples synthesized by the solvothermal method, at low temperature, intermediate times and in the presence of dispersant, proving that the morphology and the available surface area are critical parameters in the properties of the obtained material. Thus, the most relevant results of this research stand out the improvement of the photocatalytic activity of ZnO by its surface modification with the noble metal incorporation, stretching out its useful lifetime. At the same time, the structural, morphological, and chemical properties have been improved, thanks to the great dispersion and homogeneity obtained by surfactants use. In light of the observations above, it could be concluded that all MN/ZnO systems which are synthesized in this work, with pollutant degradation results higher than 45%, present an excellent viability for environmental applications.
Nowadays, there is a rising demand to recover and reuse water, since it is an essential and limited resource, due to various socioeconomic factors. In recent years, nanotechnology has become one of the most active research areas thanks to its exceptional properties compared to bulk scale and to its potential technological applications, outstanding its use in photocatalysis for wastewater treatment. Among the nanomaterials used for this purpose, nanoscale zinc oxide generates great scientific interest because it is an environmentally sustainable material with excellent photocatalytic activity under low price. Recent studies search developing hybrid materials based on ZnO semiconductor systems decorated with noble metals to improve their catalytic activity and corrosion resistance. In this context, the use of silver or platinum is an appropriate option for avoiding the recombination of the photoexcited electron-hole pairs and thus prolong the lifetime of the photocatalysts. Therefore, in this Doctoral Thesis hybrid micro/nanostructured systems based on MN/ZnO were prepared by solvothermal method (ST) and ultrasonic spray pyrolysis (USP) methods. The influence of different experimental conditions such as synthesis time and temperature, dispersant presence, type of noble metal, chemical nature of precursors, Ag+/Zn2+ molar ratio, among others, were evaluated in different syntheses. Furthermore, the synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), UV-vis diffuse reflectance spectroscopy (DRS), adsorption-desorption of N2 (BET) and Raman spectroscopy (RS). Hereinafter, the photocatalytic activity was studied in the degradation reaction of methylene blue in aqueous solution and under UV light, in order to relate the photocatalytic behaviour of the samples with properties obtained on account of different parameters studied. Likewise, the best percentages of contaminant removal (>99 %) were obtained for Ag/ZnO samples synthesized by the solvothermal method, at low temperature, intermediate times and in the presence of dispersant, proving that the morphology and the available surface area are critical parameters in the properties of the obtained material. Thus, the most relevant results of this research stand out the improvement of the photocatalytic activity of ZnO by its surface modification with the noble metal incorporation, stretching out its useful lifetime. At the same time, the structural, morphological, and chemical properties have been improved, thanks to the great dispersion and homogeneity obtained by surfactants use. In light of the observations above, it could be concluded that all MN/ZnO systems which are synthesized in this work, with pollutant degradation results higher than 45%, present an excellent viability for environmental applications.
Description
Mención Internacional en el título de doctor
Esta tesis contiene artículos de investigación en anexo
Esta tesis contiene artículos de investigación en anexo
Keywords
Ag/Zno, Nanotecnología, Fotocatálisis, Aguas residuales, Óxido de Zinc, Método solvotérmico (ST), Método de pirólisis por pulverización ultrasónica (USP)