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

Resum

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.