FUNCTIONALIZED SILICA MATERIALS AND MIXED-MATRIX MEMBRANES FOR ENVIRONMENTAL APPLICATIONS

Functionalized silica materials are synthesized for various environmental applications. The overall objective is functionalization with sulfur-containing moieties for mercury sorption and as a platform for nanoparticle synthesis. The first objective is quantifying this functionalization for various silica platforms. The second objective is development of effective mercury sorbents, for both aqueous mercury and elemental mercury vapor. Third, those sorbents are incorporated into mixed matrix membranes (MMM) for aqueous mercury sorption. Fourth, functionalized silica materials are developed as platforms for the synthesis of reactive metal nanoparticles (NP) for the degradation of trichloroethylene. Thiol-functionalized silica is used as a sorbent for aqueous mercury, and a novel functionalized material (thiol-functionalized silica shell surrounding a carbon core) has been developed for this application. Total capacity and kinetics of aqueous mercury sorption were determined. The silica-coated carbon was functionalized with thiol and sulfonate moieties for regeneration under mild conditions. Finally, the sorbent particles were incorporated into polysulfone to form a mixed matrix membrane (MMM) for toxic metal capture under convective-flow conditions. High loadings (up to 50% particles, base particles of ~80 nm) were achieved in the MMM. The particles are well-dispersed which can lower mass transfer resistance to the sorption sites. The MMM also imparts several practical advantages such as ease of sorbent handling. Silica functionalized with tetrasulfide silane is used for mercury vapor sorption. Sorption kinetics and dynamic capacity depend upon pore structures of the functionalized material. The particles are thermally stable and exhibit a glass transition in the tetrasulfide silane coating, with high total sorption capacity achieved by addition of copper sulfate. Temperature effects on mercury sorption indicate a chemisorptive mechanism. Silica particles functionalized with sulfonate moieties were used as a platform for the synthesis of dispersed iron nanoparticles. These NP are applied for degradation of trichloroethylene (TCE), a persistent, toxic, and widespread pollutant. The particles were stabilized against agglomeration. Natural product reducing agents, such as ascorbic acid, adsorb to the particle surface and can protect against oxidation. These particles were demonstrated for the reductive as well as oxidative degradation of TCE