Effect of Calcination Temperature on Structural Properties and Photocatalytic Activity of Ceria Nanoparticles Synthesized Employing Chitosan as Template

Ceria nanoparticles were synthesized employing chitosan as template and thermal treatment at different temperatures (350, 650, and 960°C). The effect of calcination temperature on structural properties and photocatalytic activity of ceria nanopowder was also tested. Degradation of an azo dye, Congo Red (CR) as a model aqueous pollutant, was investigated by means of photocatalysis of ceria nanoparticles under visible light irradiation. The influence of catalyst amount, initial CR concentrations, and degradation reaction kinetics were studied. The results were compared with commercial CeO2 at the same degradation conditions

Modulation of the Bifunctional CrVI to CrIII Photoreduction and Adsorption Capacity in ZrIV and TiIV Benchmark Metal-Organic Frameworks

The presence of hexavalent chromium water pollution is a growing global concern. Among the currently applied technologies to remove CrVI, its adsorption and photocatalytic reduction to CrIII less mobile and toxic forms are the most appealing because of their simplicity, reusability, and low energy consumption. However, little attention has been paid to bifunctional catalysts, that is, materials that can reduce CrVI to CrIII and retain both hexavalent and trivalent chromium species at the same time. In this work, the dual CrVI adsorption–reduction capacity of two iconic photoactive water-stable zirconium and titanium-based metal–organic frameworks (MOFs) has been investigated: UiO-66-NH2 and MIL-125. The bifunctionality of photoactive MOFs depends on different parameters, such as the particle size in MIL-125 or organic linker functionalization/defective positions in UiO-66 type sorbents. For instance, the presence of organic linker defects in UiO-66 has shown to be detrimental for the chromium photoreduction but beneficial for the retention of the CrIII phototransformed species. Both compounds are able to retain from 90 to 98% of the initial chromium present at acidic solutions as well as immobilize the reduced CrIII species, demonstrating the suitability of the materials for CrVI environmental remediation. In addition, it has been demonstrated that adsorption can be carried out also in a continuous flux mode through a diluted photoactive MOF/sand chromatographic column. The obtained results open the perspective to assess the bifunctional sorption and photoreduction ability of a plethora of MOF materials that have been applied for chromium capture and photoreduction purposes. In parallel, this work opens the perspective to develop specific chemical encoding strategies within MOFs to transfer this bifunctionality to other related water remediation applications.The authors thank the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through projects MAT2016-76739-R (AEI/FEDER, EU) and MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK (LION, ACTIMAT), HAZITEK (SIMAN) and PIBA (PIBA-2018-06) programs, respectively. The European Commission Research & Innovation H2020-MSCA-RISE-2017 (Ref.: 778412) INDESMOF project

Síntesis controlada de semiconductores metal-óxido nanoestructurados y su efecto en el tratamiento de aguas contaminadas por fotocatálisis heterogénea

Tesis para optar al grado de Doctora en Ciencias de la Ingeniería, Mención Ciencia de la IngenieríaEn este trabajo de investigación se desarrolló una comprensión exhaustiva acerca del diseño y síntesis por vía hidrotermal de semiconductores nanoestructurados metal-óxido de TiO2 y SnO2 con morfologías y unidad dimensional controladas, abarcando nanoestructuras cero- (0D), uni- (1D), bi- (2D) y tri-dimensionales (3D). Se estudió la correlación entre el efecto de la variación en la dimensionalidad estructural sobre el comportamiento catalítico de estos materiales para foto-oxidar contaminantes de diferente naturaleza química (orgánicos e inorgánicos), evaluada a partir de sus capacidades para fotogenerar especies reactivas de oxígeno (ROS). Los ROS generados fueron cuantificados a través de la producción de radicales hidroxilo (•OH) y oxígeno singlete (1O2), mientras que la actividad fotocatalítica fue evaluada bajo condiciones de operación optimizadas para cada set de semiconductores metal-óxido. El naranja de metilo (NM) y la Rodamina B (RhB) fueron empleados como contaminantes orgánicos modelos, mientras que el arsénico (As), en su forma más tóxica de arsenito (H3AsO30) fue estudiado como contaminante inorgánico. Los resultados indicaron que estas reacciones de oxidación proceden preferencialmente a través de reacciones directas con los radicales •OH, más que con el O2-• y el 1O2. El amplio barrido realizado en el estudio de evolución morfológica y dimensional de los diferentes materiales de TiO2 y SnO2, proporcionó las bases para establecer una buena correlación lineal entre la velocidad de foto-oxidación de cada contaminante y la concentración de ROS generada, según la varia la dimensionalidad del material, demostrando que cuanto más alta es la generación de ROS, mayor es la actividad de oxidación del fotocatalizador. El incremento en el área superficial al disminuir el tamaño de partícula también se correlacionó positivamente con el aumento en la tasa de generación •OH y por ende con un aumento en la fotoactividad, como resultado de una mayor superficie total disponible para llevar a cabo las reacciones redox. La dimensionalidad y la morfología nanométrica del material afectan su estructura electrónica dirigiendo el camino de difusión de los pares electrón-hueco para evitar su recombinación, y modificando las posiciones de sus bandas de valencia y de conducción que definen la capacidad energética del material para producir un tipo específico de ROS. Adicionalmente, se ha sugerido que la presencia de defectos estructurales del tipo vacancias de oxígeno (VO) actúa como sitios activos que favorecen una mayor generación de ROS

The influence of the morphology of 1D TiO 2 nanostructures on photogeneration of reactive oxygen species and enhanced photocatalytic activity

The influence of morphology in one-dimensional (1D) TiO 2 nanostructures—specifically nanotubes (TNT), nanofibers (TNF), nanorods (TNR), and nanowires (TNW)—on the photogeneration of reactive oxygen species (ROS) and the resulting effect on photocatalytic activity were investigated. 1D TiO 2 nanostructures were obtained by hydrothermal route, by employing changes in the crystalline phase of TiO 2 precursor and reaction temperature as the morphology-controlling factors. Morphological, structural, textural, and optical properties were studied using scanning and transmission electron microscopy, X-ray diffraction, BET surface area analysis, diffuse reflectance and photoluminescence spectroscopy. The photochemical behaviour of these 1D TiO 2 nanostructures was evaluated through ROS quantification including 1 O 2 and [rad]OH, and it was found that TNF exhibits the highest amount of generated ROS, the following tendency was observed: TNF > TNT > TNR > TNW. In addition,

Porous, lightweight, metal organic materials: environment sustainability

Metal organic frameworks (MOFs) are crystalline inorganic-organichybrid materials that are assembled and sustained by coordination bonds between metal ions or metal-oxo clusters and negatively charged organic linkers bearing a complexing function (e.g., carboxylate, phosphonate, azolate .). The emerging research interest in MOFs results from the simultaneous occurrence of five key characteristics that are (i) the crystallinity, (ii) the tunable porosity, (iii) high surface area (MOF materials have so far the highest surface area of all porous materials), (iv) the existence of strong metal-ligand interactions, and (v) the structural diversity that allows to precisely design materials for a particular application.Fil: Valdeverde, Ainara. No especifíca;Fil: Sainz, Paula G.. No especifíca;Fil: Orive, Joseba. Universidad de Chile; ChileFil: Larrera, Edurne. Loire Valley Institute for Advanced Studies; FranciaFil: Reizabal Para, Ander. No especifíca;Fil: Tovar Jimenez, Gabriel Ibrahin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Copello, Guillermo Javier. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Química Analítica y Fisicoquímica. Cátedra de Química Analítica Instrumental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Lazaro Martinez, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Rodriguez, Barbara. Universidad de Chile; ChileFil: Gonzalez Navarrete, Barbara. Universidad de Chile; ChileFil: Quintero, Yurieth Marcela. Universidad de Chile; ChileFil: Rosales, Maibelin. Universidad de Chile; ChileFil: Garcia, Andreina. Universidad de Chile; ChileFil: Arriortua, María I.. Universidad de Chile; ChileFil: Fernández de Luis, Roberto. No especifíca

Chromium speciation in Zirconium-based metal–organic frameworks for environmental remediation

Acute Cr(VI)water pollution due to anthropogenic activities is an increasing worldwide concern. The high toxicity and mobility of Cr(VI)makes it necessary to develop dual adsorbent/ion-reductive materials that are able to capture Cr(VI)and transform it efficiently into the less hazardous Cr-III. An accurate description of chromium speciation at the adsorbent/ion-reductive matrix is key to assessing whether Cr(VI)is completely reduced to Cr-III, or if its incomplete transformation has led to the stabilization of highly reactive, transient Cr(V)species within the material. With this goal in mind, a dual ultraviolet-visible and electron paramagnetic spectroscopy approach has been applied to determine the chromium speciation within zirconium-based metal-organic frameworks (MOFs). Our findings point out that the generation of defects at Zr-MOFs boosts Cr(VI)adsorption, whilst the presence of reductive groups on the organic linkers play a key role in stabilizing it as isolated and/or clustered Cr(III)ions.Spanish Ministry of Economy and Competitiveness (MINECO) (AEI/FEDER, UE) (FEDER) MAT2016-76739-R MAT2016-76039-C4-3-R Basque Government Industry and Education Departments PIBA-2018-06 European Commission Research & Innovation H2020-MSCA-RISE-2017 INDESMOF project 77841

Designing Metal-Chelator-like Traps by Encoding Amino Acids in Zirconium-Based Metal-Organic Frameworks

Metal chelators and porous sorbents are two of the forefront technologies applied for the recovery and separation of hazardous and/or valuable metal ions from aqueous solutions (i.e., polluted water sources, metal-rich mining wastewaters, acid leachates, and so forth). The transfer of the metal coordination functions of metal chelators to chemically stable host materials had only limited success so far. Here, we report the installation of natural acids (i.e., malic acid, mercaptosuccinic acid, succinic acid, fumaric acid, and citric acid) and amino acids (i.e., histidine, cysteine, and asparagine) within a porous zirconium-based trimesate metal-organic framework (MOF), namely, MOF-808. Applying this strategy, we were able to produce a pore environment spatially decorated with multiple functional groups usually found in commercial chelator molecules. The chemical stability of the amino acid molecules installed by the solvent-assisted ligand exchange has been studied to delimitate the applicability window of these materials. The adsorption affinity of MOF-808@(amino)acids in static and column-bed configurations can be fine-tuned as a function of the amino acid residues installed in the framework. MOF-808(amino)acid columns can be applied efficiently both for water remediation of heavy metals and for the separation of metal ions with different acidities. For instance, the initial trends for the dispersion of rare-earth elements have been identified. Electron paramagnetic resonance and inelastic neutron scattering spectroscopy reveal that MOF-808@(amino)acids stabilize metal centers as isolated and clustered species in a coordination fashion that involves both the amine and thiol functionals and that affects the vibrational freedom of some of the chemical groups of the amino acid molecules. The metal-ion stabilization within amino acid-decorated MOFs opens the avenue for application for pseudo biocatalysis purposes in the near future.Fil: Valverde, Ainara. Universidad del País Vasco; EspañaFil: Tovar, Gabriel I.. Universidad de Buenos Aires; ArgentinaFil: Rio López, Natalia A.. No especifíca;Fil: Torres, Dimas Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Rosales, Maibelin. Advanced Mining Technology Center; ChileFil: Wuttke, Stefan. No especifíca;Fil: Fidalgo Marijuan, Arkaitz. No especifíca;Fil: Porro, José María. No especifíca;Fil: Jiménez Ruiz, Mónica. Institut Laue Langevin; FranciaFil: García Sakai, Victoria. No especifíca;Fil: García, Andreina. No especifíca;Fil: Laza, José Manuel. Universidad del País Vasco; EspañaFil: Vilas Vilela, José Luis. Universidad del País Vasco; EspañaFil: Lezama, Luis. Universidad del País Vasco; EspañaFil: Arriortua, María I.. Universidad del País Vasco; EspañaFil: Copello, Guillermo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Fernández De Luis, Roberto. No especifíca