Sorption and desorption of synthetic organic chemicals (SOCs) to macromolecule-loaded porous adsorbents.

摘要

In this research, sorption/desorption and desorption hysteresis of synthetic organic chemicals (SOCs) were investigated using various macromolecule-loaded porous media. Such composite materials were synthetic sorbents that can be well-characterized, offer the potential for controlled properties, and can be designed to serve as model soils and sediments.;All of tested polyelectrolytes, four types of HA, and a PSS mixture (1.8 kDa, 18 kDa and 100 kDa monodisperse PSS standards) as model NOM showed preferential adsorption of lower molecular weight (Mw) components to alumina mesopores due to size exclusion and slow adsorption kinetics of higher M w components. The adsorption of purified Aldrich humic acid (PAHA) to silica pores showed similar trends with size exclusion of higher Mw components but was not favorable due to electrostatic repulsion between PAHA and silica surface under neutral pH conditions. PAHA adsorption to non-porous alumina and macro-porous AAMs was opposite to the case of adsorption to porous alumina, showing preferential adsorption of higher Mw components. It was found that PAHA adsorption to porous inorganic substrates was governed by a ratio between the hydrodynamic size (radius of gyration, Rg) of PAHA and the size of pores (radius of pore, Rp). PAHA was separated into 6 fractions (1, 2, 4, 6, 12, 43 kDa) using SEC techniques.;The Freundlich model and the dual-mode model (i.e., a combination of hole-filling and solid phase dissolution) described well phenanthrene sorption to PS (i.e., microg-phenanthrene/mg-PS, phenanthrene uptake normalized by PS loading,) which is loaded in porous silicas with various pore sizes. The characteristics of phenanthrene sorption to PS representd by the Freundlich isotherm model parameters (n and KF) and the ratio of hole-filling to solid phase dissolution (Q°b/K d) of dual-mode model fitting changed depending on the R g (PS size)/Rp (silica pore size) ratios of PS-loaded porous silicas.;Phenanthrene sorption to PAHA (i.e., microg-phenanthrene/mg-C (PAHA), phenanthrene uptake normalized by PAHA loading) loaded in porous aluminas (PAs) and non-porous aluminas (NPAs) decreased with increasing PAHA adsorption/loading density (PAD) (mg-C/m2-adsorbent). This observation was attributed to low phenanthrene accessibility to the entire PAHA adsorbed on PAs and NPAs under higher PAD conditions. In general, the Freunlich isotherm parameter "n" values for phenanthrene sorption to PAHA loaded in PAs were lower than those for PAHA loaded in NPAs. In both cases of PAHA-loaded PAs and NPAs, phenanthrene sorption isotherms were linear or near-linear.;Phenanthrene uptake by TMK NOM-loaded SWNTs was lower than that by SWNTs without TMK NOM loading. This obervation was opposite to the cases of macromolecule (e.g., PS, PAHA)-loaded (hydrophilic) silicas and aluminas, which showed higher phenanthrene uptake by macromolecule-loaded adsorbents than neat adsorbents. Chemical treatments of SWNTs using the Peroxone advanced oxidation process (AOP) (i.e., simultaneous treatment by ozone (O3) and hydrogen peroxide (H2O2)) also decreased phenanthrene uptake by SWNTs. Gas phase nitrogen (N2) adsorption analysis indicated that TMK NOM loading and Peroxone AOP treatments reduced the BET (Brunauer, Emmett, and Teller) specific surface area and pore volume of SWNTs. For Peroxone AOP-treated SWNTs, amorphous carbon increased as evidenced by increase in Raman D/G (D-band/G-band) ratio. The introduction of heterooxygen moieties by Peroxone AOP treatments, verified by FT-IR (Fourier transform infrared spectroscopy) spectra, was attributed to lower phenanthrene uptake.;The association of NOM with hydrophilic/hydrophobic and porous/non-porous adsorbents (e.g., silica, alumina, SWNTs, and activated carbon) and nano-sized silica particles changed Tg of NOM. Such observation was (i) similar to the case of loaded/confined PS (i.e. synthetic macromolecule) in silica pores, of which Tg was different from that of bulk phase (particulate) PS; (ii) implied that the physical characteristics of NOM can be altered by association with the pores and surfaces of soils and sediments, which can affect sorption and desorption behaviors of SOCs released in the environment. (Abstract shortened by UMI.).