Silica-Based Materials for Water Treatment Applications: Adsorption and Supported Noble Metal-based Catalysis

Abstract

Various contaminants have been widely detected in aquatic systems due to both natural and anthropogenic activities, such as conventional and emerging organic pollutants (e.g., nitroarenes, per- and poly-fluoroalkyl substances (PFAS)), and toxic oxyanions (e.g., chlorate, selenate). The presence of these contaminants may pose negative effects on both human health and water systems. Therefore, it is of great desire to develop novel materials and technologies to treat these waterborne pollutants.Catalytic treatment using noble metal (e.g., Pd)-based catalysts has emerged as a promising method for reduction of waterborne contaminants. Silica-based supports may enhance the reactivity and sustainability of Pd-based catalysts by improving the dispersion of noble metal nanoparticles, the local enrichment of contaminants, and the stability of the catalysts. Another effective way to remove waterborne pollutants is adsorption. Periodic mesoporous organosilicas (PMOs) have been considered an ideal adsorbent due to their high surface area, controlled pore size and structure, and tunable and homogeneously distributed functional groups within the mesoporous skeleton. One objective of this research is to prepare monometallic and bimetallic noble metal (e.g., Pd, Rh)-based catalysts on silica-based support to enhance the activity and sustainability of synthesized catalysts in the reduction of waterborne pollutants (e.g., nitroarene, chlorate) and to elucidate the role of modified silica-based support in the performance enhancement mechanism. Another objective is to develop a class of silica-based adsorbents (e.g., PMO) that can effectively remove various anionic contaminants in water (e.g., selenate, PFAS) and exhibit improved performance in comparison with conventional materials even under complex water matrices. This dissertation entails (1) the review of the Pd-based nanostructured catalysts for water treatment application in the last 10 years, (2) the synthesis and characterization of the magnetic structured Pd-based catalysts with silica-based support (Fe3O4@mSiO2-Pd) and its performance for nitroarene reduction, (3) the development and characterization of a novel bimetallic catalyst (WOx-Rh/mSiO2) on amino-functionalized mesoporous silica support and its catalytic reduction of chlorate in aqueous solution, (4) the development and investigation of amine-bridged PMOs with different and tunable amine contents for adsorptive removal of selenate, and (5) the development of bifunctional PMO adsorbents for improved removal of various PFAS.