Dielectric spectroscopy studies of aqueous ionic solutions ACl/H, 0 (A = Li, Rb, Cs) were carried out at frequencies between 45 MHz and 20 GHz, using recently developed coaxial measurement techniques. The behavior of the static dielectric constant es0 and the dielectric relaxation time Q-, of the solutions were studied as functions of ion size and concentration. For moderate concentrations both es0 and r, decrease linearly with solution conductivity. While the behavior of gso can be understood in terms of either static or Hubbard-Onsager kinetic polarization models, the experimental results for 7. are at present not understood quantitatively in terms of these models. However we point out the good correlation of the 7. data with empirical viscosity results, which suggests an alternative explanation based upon the solution viscosity, modified by ion size effects, which play an important role in the dielectric response. We also discuss the various length scales relevant to dielectric and conductivity processes in the solutions.Dielectric spectroscopy can be a powerful probe of microscopic processes in a liquid, particularly when carried out over a broad range of frequency. The frequency dependence of the dielectric function e(w) of a liquid (pure, solution or mixture), reflects the dynamic response of the constituents of the liquid, whether ionic or dipolar.'-3 An ionic solution may be considered to consist of 3 constituents: the charged anions and cations, "hydration" solvent molecules near the vicinity of the ions, and "free" solvent molecules. At high concentration, an additional component may exist in the form of ion pairs due to incomplete dissociation.4'5 The distinction between the hydration and free solvent molecules is largely a matter of the time scales involved, and the strength of the ion-solvent interaction. Furthermore, the dynamical processes are affected by the ion size and charge. These aspects are some of the issues addressed in this work.While ionic conductivity and viscosity has been the subject of intense research,6 the dynamic aspects of the dielectric properties of ionic solutions have received less attention. Certain phenomena, such as the (static) dielectric decrement, are well known.' Reliable experimental data on the dynamic aspects, such as the relaxation time TV, have not been easily available, partly because of the higher frequencies required ( -10 GHz) particularly for aqueous solutions. In this paper we present detailed studies and analysis of the dielectric spectra of AC1 (A = Li, Rb, Cs) in H,O. The complex dielectric functions E(O) = E)(w)k" (w) were measured between 45 MHz and 20 GHz at 25 C, using recently developed techniques8*9 which enables the measurement of continuous spectra in this frequency range. E' and (T = E"WE" (E, = 8.85 X 10 -'* F/m) vs frequency for RbCl/H,O for various concentrations are shown in Figs.

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Sorption is a common treatment for removing pollutants from natural environments. Layered double hydroxides (LDHs), which consist of brucite-like positive layers and sodium dodecyl sulfate intercalated with LDH (SDS-LDH), are considered to be potential organic pollutant sorbents. The objectives of this study were (1) to evaluate the impact of removing 2-chlorophenol (2-CP) using Mg 3 -Al-(NO 3 ) LDH and SDS-LDH and (2) to investigate the removal efficiencies of these two compounds. All fitted sorption data reveal that the second-order model and the Langmuir model best describe the sorption kinetics and isotherms, respectively. By visual MinteqA2 (2000) calculation, the dissociation pK a of 2-CP is 8.56. The experimental results indicate that a high concentration of 2-CP is sorbed by the hydrophilic-hydrophilic physical interaction of LDH when the pH is >8.56; however, the hydrophobic-hydrophobic partition interaction of SDS-LDH is more vital when the pH is <8.56. LDH and SDS-LDH can be removed not only in the ionic form, but also in the molecular form of 2-CP. The efficiencies of LDH and SDS-LDH, in regard to enhancing 2-CP sorption, are strongly dependent on the pH, 2-CP speciation, ionic strength, and metal dissolution. These results are of practical interest, with respect to the selection of sorbents, to optimize aquatic environment remediation technologies.

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Interactions of toxic Cr(VI) with renewable biomaterials are considered an important pathway for Cr(VI) removal in ecosystems. Biomaterials are susceptible to dissolution, and their dissolved derivatives may provide an alternative to surface-involved pathway for scavenging of Cr(VI). In this study, dissolved organic carbon (DOC) derived from Neurospora crassa biomass was investigated. The proportion of Cr(VI) reduction by DOC to that on biomass was determined to evaluate the importance of DOC to Cr(VI) reduction. A rapid increase in DOC concentration from 145.6 to 193.7 mg L(-1) was observed when N. crassa-biomass was immersed in 0.01 M KCl solution at pH of 1-5, and polysaccharides, peptides, and glycoproteins with carboxyl, amide, and -NH functional groups, are the major compositions of DOC. On reaction of 96.2 microM Cr(VI) with N. crassa-biomass or DOC, it was estimated that DOC contributed approximately 53.8-59.5% of the total Cr(VI) reduction on biomass in the dark. Illumination enhanced Cr(VI) reduction via photo-oxidation of biomass/DOC under aeration conditions, which formed superoxide for Cr(VI) reduction. At pH 1, photoinduced Cr(VI) reduction by DOC proceeded more rapidly than reduction on the biomass surface. However, at pH >3, with a decrease in Cr(VI) reduction by DOC, photon-excited biomass may become an important electron source for Cr(VI) photoreduction.

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