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Recent innovative adsorption technologies for water purification rely on micrometer-sized activated carbon (AC) for ultrafast adsorption or in situ remediation. In this study, the bottom-up synthesis of tailored activated carbon spheres (aCS) from sucrose as renewable feedstock is demonstrated. The synthesis is based on a hydrothermal carbonization step followed by a targeted thermal activation of the raw material. This preserves its excellent colloid properties, i.e., narrow particle size distribution around 1 µm, ideal spherical shape and excellent aqueous dispersibility. We investigated the ageing of the freshly synthesized, highly de-functionalized AC surface in air and aqueous media under conditions relevant to the practice. A slow but significant ageing due to hydrolysis and oxidation reactions was observed for all carbon samples, leading to an increase of the oxygen contents with storage time. In this study, a tailored aCS product was generated within a single pyrolysis step with 3 vol.-% H2O in N2 in order to obtain the desired pore diameters and surface properties. Adsorption characteristics, including sorption isotherms and kinetics, were investigated with monochlorobenzene (MCB) and perfluorooctanoic acid (PFOA) as adsorbates. The product showed high sorption affinities up to log (KD/[L/kg]) of 7.3 ± 0.1 for MCB and 6.2 ± 0.1 for PFOA, respectively. [ABSTRACT FROM AUTHOR]

• Derivation of thermodynamic parameters from adsorption data neeeds definition of standard states. • Adsorption coefficients have to be transferred into unitless adsorption constants. • Adsorption entropies have to be interpreted with regard to bulk phase processes. Calculation of thermodynamic parameters of adsorption such as Gibbs free energy Δ G ° ads from experimentally determined adsorption data can be helpful for elucidation of sorption mechanisms. This approach includes the transformation of adsorption coefficients K d or K L into dimensionless standard adsorption constants K ads [-]. The present comment reveals recently published misleading approaches and offers thermodynamically sound alternatives. [ABSTRACT FROM AUTHOR]

Eleven well characterized humic substances (HSs) were adsorbed from aqueous solution onto a Na-kaolin clay. The adsorption affinity ([K.sub.L]), maximum adsorption capacity (b), a coefficient of desorption hysteresis (H), and the concentration of irreversibly adsorbed HS (IHS) were derived from adsorption-desorption isotherms. These parameters were correlated with structural features of the HS. The adsorption affinity was shown to correlate directly with the aromaticity of the HS and inversely with their polarity, expressed as the O/C atomic ratio. A dependency between polarity and maximum adsorption capacity was not confirmed. The parameters b, H, and IHS expose close correlation with the molecular weight (MW) and the partial negative charge of HS (Z) at the operating pH value. The following quantitative relationship was obtained: b = 715 - 0.06 x MW - 529 x Z (r = 0.92). it allows a selection of HS with respect to the largest content of organic matter in HS-kaolin clay complexes. Among the HS studied the high molecular weight materials enriched with C- and H-substituted aromatics, such as coal and peat humic acids (HAs), are shown to be the most preferential materials for preparing stable HS-clay complexes.

Dissolved humic substances (DHS) and polyacrylic acid are mixed with pyrene and phenanthrene to help map the sorption of hydrophobic organic compounds in the environment. Aromaticity and polarity factors are recorded through solid-phase microextraction (SPME) and graphed.

Very hydrophobic compound(VHOC) sorption on humic organic matter is important to the environment, containing octanol-water coefficients of 100,000 or greater, and organic chemicals can freely exist dissolved or bound in a state associated with suspended particles, dissolved humic organic matter(DHOM) and other colloidal matter in natural waters. Hydrophobic partitioning which includes a substantial entropic term and nonspecific van der Waals forces, accounts for absorption into polymeric, amorphous humic organic matter.

Researchers from the University of Waterloo, Ontario, used solid-phase microextraction to examine the concentration levels of the adsorption of very hydrophobic organic compounds onto poly(dimethylsiloxane) fiber coatings and dissolved humic organic matter.

The solid phase microextraction (SPME) technique could be an efficient method to determine the sorption behavior of ionogenic and non-ionogenic alkylated organotin compounds onto humic organic matter (HOM). The method allows for more reliable results because the SPME can investigate both dissolved and particulate HOM. Furthermore, SPME takes account of the freely dissolved rather than the total content of the analytes present.