Hydrous Ferric Oxide-resin Nanocomposites For Arsenite Removal:Effect Of Host Pore Structure And Surface Chemistry

Hydrous ferric oxide (HFO) loaded hybrid sorbents are considered to be excellent materials for arsenic removal from water. Currently, most of the related references focused on the preparation and characterization of the resultant composite sorbents as well as evaluation of their properties for arsenic sequestration. Little is known concerning pore structure and surface chemistry of the host materials on the structure and properties of the composites. In this study, we fabricated several HFO-resin nanocomposites of varying pore structure and surface chemistry, and evaluated the effects of both concerns on the performances of the resulting composite sorbents in terms of arsenite removal from aqueous solution.In the first section of the dissertation, porous chloromethylated polystyrene (CM-PS) resins were used as the supports for HFO loading. The pore structure of the CMPSs was deliberately adjusted through post-cross-linking reactions. Five HFO-resin nanocomposites of similar HFO loadings (3.9-5.3%) but different host pore structures were fabricated for further study. The host polymer and the corresponding composites were denoted PS-X and PS-X-HFO respectively, with X representing the surface area of the host polymer. TEM images demonstrated that the particle size of HFO aggregates decreased with decreasing pore diameter of the host PS. Arsenite adsorption onto the nanocomposites of narrower host pore size achieved a faster equilibrium. The adsorption capacity of the composite sorbents increased as pore size of PS decreased. Intraparticle diffusion model indicated that arsenite adsorption onto PS-HFO nanocomposites with large HFO particles was dominantly controlled by intraparticle diffusion, whereas the control caused by intraparticle diffusion was gradually weakened as the particle size of HFO decreased. Also, its specific adsorption toward arsenite was enhanced in the presence of high-cocentration phosphate as the average pore size of PS decreased (except PS-947-HFO).In the second section of this study, different amounts of quaternary ammonium groups were grafted with the CM-PS matrix through amination by trimethylamine, and these aminated CMPSs were employed as the host materials for further HFO loadings. Thus, four HFO-resin nanocomposites of similar HFO loadings (3.9-4.6%) were fabricated for As(III) removal. TEM images showed that HFO was better dispersed in the aminated CMPSs and the hydrophilicity of the resultant composites was greatly improved as the anion exchange capacity increased. As compared to the fresh CM-PS based composite, the adsorption of arsenite onto the nanocomposites was greatly increased as the host polymer was aminated. However, negligible differentce was observed for those grated with different amounts amino groups. Also, the hybrid sorbents with higher anion exchange capacity achieved a faster equilibrium. The fitting results of the intraparticle diffusion model suggested that the adsorption of As(III) onto hybrid sorbents were controlled by several steps whereas the sorption onto PS-O-HFO were mainly controlled by intraparticle diffusion.In summary, the pore structure and surface functional group of the host resins have a great influence on the performance of the resultant HFO-resin nanocomposites such as adsorption kinetics, capacity and specific adsorption of arsenite. Generally, the performance of the hybrid sorbents can be improved by decreasing the average pore size and increasing the anion exchange capacity of the resin.