Emerging hierarchical porous silica-based nanomaterials as sorbents for the analytical determination of organic hazardous compounds

Actualment, l'exposició humana a compostos orgànics perillosos s'ha convertit en una preocupació molt important. La presència de contaminants orgànics al medi ambient ha provocat l'aparició de noves normatives per tal de restringir o prohibir aquestes substàncies perilloses, i el desenvolupament de noves metodologies analítiques per a la seua determinació ha esdevingut un gran repte per a la química analítica actual. A més a més, a part del desenvolupament de noves tècniques instrumentals, l'anàlisi de matrius complexes requereix d’un pas de preconcentració i neteja, per al qual s’han proposat diversos materials nous com a alternatives als adsorbents clàssics. Entre ells, la sílice mesoporosa ofereix grans característiques per al seu ús com a material adsorbent, gràcies a l’ús de surfactants com a agents directors de la porositat, destacant entre ells els materials UVM-7 desenvolupats a la Universitat de València, que poden ser considerats com una versió nanomètrica dels coneguts materials MCM-41. Així, l'objectiu principal d'aquesta Tesi Doctoral ha estat l'aplicació de materials de sílice mesoporosa jeràrquica tipus UVM-7 a la retenció de contaminants orgànics per tal de desenvolupar mètodes analítics per a la seua determinació. Al primer bloc de d’aquesta tesi, es recullen els procediments de síntesi que s’han emprat per tal d’obtenir els diferents materials de sílice que s’han estudiat al llarg de tota la tesi doctoral, principalment els materials d’estructura UVM-7. Posteriorment, en un segon bloc, es van aplicar materials purs UVM-7 per a l'extracció d'aflatoxines de mostres d'aliments. Després de caracteritzar adequadament l’estructura del material, en comparació amb altres materials de sílice, la seua estructura porosa va permetre el desenvolupament de dos mètodes analítics per a l’extracció i determinació d’aflatoxines en mostres d’aliments com el té o la llet. Al tercer bloc de la tesi, es va estudiar la modificació del material UVM-7 mitjançant l'addició de metalls com el titani, el ferro i l'or per tal de conferir-li al material una major selectivitat per a la determinació de famílies de contaminants ambientals més concretes. Així, amb els materials UVM-7 contenint titani, es va desenvolupar un mètode per al mostreig en aire de pesticides organofosforats, així com un mètode per a la seua extracció i determinació en mostres d’aigües. A més a més, la impregnació del material amb nanopartícules d’or va donar lloc també al desenvolupament d’un mètode per a la determinació de pesticides organoclorats en mostres d’aigua. En segon lloc, aquestos materials funcionalitzats amb metalls es van aplicar també a la retenció i extracció de contaminants emergents de mostres d’aigües mediambientals, permetent el desenvolupament de dos mètodes analítics basats en l’SPE per a la determinació de retardants de flama organofosforats (mitjançant materials modificats amb titani) i de compostos perfluoroalquilats gràcies a la modificació del material amb ferro, i també a la modulació de la grandària dels mesoporus utilitzant surfactants de cadena més curta. Finalment, a l’últim bloc de la tesi, el material UVM-7 es va modificar mitjançant l’ancoratge de β-ciclodextrina a la seua superfície. Amb aquest material es va desenvolupar un mètode per a l'extracció de disruptors endocrins de mostres d'orina per a la seua determinació en estudis de biomonitoratge. Tots els materials sintetitzats es van caracteritzar adequadament mitjançant diverses tècniques, i el desenvolupament dels mètodes analítics es va dur a terme incloent l'optimització dels principals paràmetres analítics, la descripció de les característiques analítiques del mètode en comparació amb altres mètodes prèviament publicats i la seua viabilitat es va estudiar mitjançant l’aplicació a l’anàlisi de mostres reals en comparació amb un mètode de referència. Com a conclusió general de la Tesi Doctoral, els materials UVM-7 han mostrat un gran potencial com a fases adsorbents per a la retenció de materials orgànics perillosos, permetent la seua aplicació en diversos mètodes per a la determinació d’aquestos contaminants, amb bons paràmetres analítics i resultats satisfactoris.Currently, human exposure to hazardous organic compounds has become a very important concern. The presence of organic pollutants in the environment has led to the emergence of new regulations to restrict or ban these hazardous substances, and the development of new analytical methodologies for their determination has become an important challenge for current analytical chemistry. In addition to the development of new instrumental techniques, the analysis of complex matrices requires a step of preconcentration and clean-up, for which several new materials have been proposed as alternatives to classical adsorbents. Among them, mesoporous silica offers great features for its use as an adsorbent material, owing to the surfactant-assisted formation of the porous structure. Among them, it can be highlighted the UVM-7 materials developed at the University of Valencia, which can be considered a nanometric version of the well-known MCM-41 materials. Thus, the main objective of this Doctoral Thesis was the application of UVM-7 type hierarchical mesoporous silica materials to the retention of organic pollutants in order to develop analytical methods for their determination. The first section of this thesis summarizes the synthesis procedures that have been used to obtain the different silica materials that have been studied throughout the doctoral thesis, mainly UVM-7 materials. Subsequently, in a second section, pure UVM-7 materials were applied for the extraction of aflatoxins from food samples. After the proper characterization of the structure of the material, in comparison to other silica materials, its porous structure allowed the development of two analytical methods for the extraction and determination of aflatoxins in food samples such as tea or milk. In the third section of the thesis, the modification of the UVM-7 material was studied by adding metals such as titanium, iron, and gold in order to give the material a greater selectivity for the determination of specific families of environmental pollutants. Thus, with titanium-containing UVM-7 materials, a method for the air sampling of organophosphorus pesticides was developed, as well as a method for their extraction and determination in water samples. In addition, the impregnation of the material with gold nanoparticles also led to the development of a method for the determination of organochlorine pesticides in water samples. Moreover, these metal-functionalized materials were also applied to the retention and extraction of emerging contaminants from environmental water samples, allowing the development of two SPE-based analytical methods for the determination of organophosphorus flame retardants (using materials modified with titanium) and perfluoroalkyl compounds thanks to the modification of the material with iron, and also to the modulation of the mesopore size using short-chain surfactants. Finally, in the last section of the thesis, the UVM-7 material was modified by anchoring β-cyclodextrin to its surface. With this material, a method for the extraction of endocrine-disrupting chemicals from urine samples was developed for their determination in biomonitoring studies. All the synthesized materials were properly characterized by various techniques, and the development of the analytical methods was carried out including the optimization of the main analytical parameters, the description of the analytical figures of merit of the method in comparison to other previously published methods and its feasibility was studied by applying it to the analysis of real samples in comparison to a reference method. As a general conclusion of the Doctoral Thesis, UVM-7 materials have shown great potential as adsorbent materials for the retention of hazardous organic compounds, allowing their application in several methods for the determination of these contaminants, with good analytical parameters and satisfactory results

Acción por el clima: El tratamiento del ODS 13 en la enseñanza de Física y Química en Educación Secundaria

El propósito de este trabajo es presentar algunos resultados de una amplia investigación en torno a la atención prestada a la problemática del cambio climático en la asignatura de Física y Química en Educación Secundaria, enmarcada dentro de los Objetivos de Desarrollo Sostenible (ODS) de la Agenda 2030 de Naciones Unidas, en particular, en el ODS 13 Acción por el Clima. Para ello se ha abordado el estudio de la presencia y relevancia del ODS 13 en el currículum y en los libros de texto de Física y Química de ESO y Bachillerato, así como, de las concepciones de docentes y estudiantes sobre esta problemática y de la formación inicial del profesorado. Además de analizar la situación actual, se han diseñado propuestas fundamentadas de intervención didáctica para el tratamiento del ODS 13 en Educación Secundaria que permitan implicar al alumnado en la adopción de medidas para avanzar en la construcción de un presente y un futuro sostenible

Bimodal porous silica nanomaterials as sorbents for an efficient and inexpensive determination of aflatoxin M1 in milk and dairy products

An extraction procedure was developed for the determination of aflatoxin M1 in milk and dairy products. A sorbent based on UVM-7 mesoporous silica was used as solid phase for the sample clean-up, and the analyte determination was carried out by HPLC coupled to a fluorescence detector. The material architecture was characterized by transmission electronic microscopy, X-ray diffraction, 29Si NMR and nitrogen adsorption-desorption. After the optimization of extraction parameters, the influence of the matrix has been evaluated, obtaining recoveries in the range 78-105% for whole and skimmed milk and yogurt matrix. The reusability of the material was also proved. The sensitivity of the method was also evaluated, and a LOQ (0.015 μg kg−1) below the European legislation limit was obtained. The procedure was successfully applied for the determination of aflatoxin M1 in real samples. The results were compared with those obtained with a reference method, being the results statistically comparabl

Cyclodextrins as a Key Piece in Nanostructured Materials: Quantitation and Remediation of Pollutants

Separation and pre-concentration of trace pollutants from their matrix by reversible formation of inclusion complexes has turned into a widely studied field, especially for the benefits provided to different areas. Cyclodextrins are non-toxic oligosaccharides that are well known for their host–guest chemistry, low prices, and negligible environmental impact. Therefore, they have been widely used as chiral selectors and delivery systems in the pharmaceutical and food industry over time. However, their use for extraction purposes is hampered by their high solubility in water. This difficulty is being overcome with a variety of investigations in materials science. The setting-up of novel solid sorbents with improved properties thanks to the presence of cyclodextrins at their structure is still an open research area. Some properties they can offer, such as an increased selectivity or a good distribution along the surface of a solid support, which provides better accessibility for guest molecules, are characteristics of great interest. This systematic review reports the most significant uses of cyclodextrins for the adsorption of pollutants in different-origin samples based on the works reported in the literature in the last years. The study has been carried out indistinctly for quantitation and remediation purposes

Study of silica-structured materials as sorbents for organophosphorus pesticides determination in environmental water samples

A novel sorbent based on a UVM-7 mesoporous silica doped with Ti has been synthesized and used for solid-phase extraction of several organophosphorus pesticides in environmental water samples followed by gas chromatography coupled to a nitrogen-phosphorus selective detector. Thus, mesoporous silica materials doped with Ti and Fe as well as immobilized cyclodextrin silica-based supports were prepared and morphologically characterized by several techniques such as transmission electronic microscopy, nitrogen adsorption-desorption and X-ray diffraction. These sorbents were comparatively evaluated, and Ti25-UVM-7 material was selected as the best solid phase. After optimization of extraction parameters such as amount of solid-phase, type and volume of eluent, pH and ionic strength and breakthrough volume, recoveries between 81% and 104.5% were achieved, with RSD values below 7.8% and 12% for intra-day and inter-day repeatability respectively. Moreover, limits of quantification in the range 0.5-4.4 μg L−1 were achieved for all target compounds using mass spectrometry detector. In addition, the developed method was applied for analysis of real water samples and it was validated with commercial C18 cartridges. Matrix effect was demonstrated in complex environmental matrices and the good reusability of synthesized material was also proved

Assessment of migrating endocrine-disrupting chemicals in bottled acidic juice using type UVM-7 mesoporous silica modified with cyclodextrin

An innovative material based in type UVM-7 mesoporous silica containing analyte-accessible cyclodextrin units is described and assessed as a selectivity-enhancing sorbent for extracting endocrine-disrupting chemicals from bottled apple juice to subsequently quantify them. The synthesis procedure has been carried out using both β- and γ-cyclodextrin for their later comparison. Then, a complete analytical method for the isolation and determination of the above analytes has been validated. Following the optimized procedure, recoveries between 94% and 100% have been achieved and good repeatability is obtained with deviations under 6.8% for intra-day and inter-day experiments. The detection limits of the method have been established in the ng L-1 level, which demonstrates the ability to quantify the trace concentrations established by sanitary restrictions. A low matrix effect is found when working with real samples. To end, a comparison with an alternative extraction method using C18 extraction cartridges has been carried out and the results obtained with both procedures are comparabl

Extraction of aflatoxins by using mesoporous silica (type UVM-7), and their quantitation by HPLC-MS

A solid-phase extraction procedure has been developed by using a sorbent derived from UVM-7 mesoporous silica. The sorbent was applied to the extraction of aflatoxins B1, B2, G1 and G2 from tea samples followed by HPLC with mass spectrometric detection. The sorbent was characterized by transmission electron microscopy, nuclear magnetic resonance, X-ray diffraction and nitrogen adsorption-desorption. UVM-7 is found to be the best solid phase. The amount of solid-phase, type and volume of eluent, pH value and ionic strength and breakthrough volume were optimized. Following the recommended procedure, recoveries between 96.0 and 98.2% were achieved, with RSD values of 88%. The results were compared with those obtained by immunoaffinity columns as a reference method. Only low concentrations of aflatoxin G2 were found in some samples, and results obtained with both methods are shown to be statistically sound and comparabl