Detailed Sorption Isotherms of Polar and Apolar Compounds in a High-Organic Soil

Abstract

Sorption isotherms of 13 apolar liquids and solids and polar solids-six in unprecedented detail-are used to evaluate a polymer-based model for natural organic matter. While all isotherms are nonlinear, the "running" Freundlich exponent n varies markedly with concentration. The isotherms show linear-scale inflection consistent with the presence of flexible (deformable) porosity as predicted by the glassy polymer-based Extended Dual-Mode Model (EDMM). The EDMM assumes dissolution and hole-filling domains in the organic solid, with provision for sorbate-caused plasticization of the solid and "melting" of the holes. Features of the EDMM are illustrated for chlorinated benzenes in poly(vinyl chloride). The solutes fall into categories of "hard" (aliphatics and 2,4-dichlorophenol) and "soft" (chlorinated benzenes, 2-chloronitrobenzene) according to their ability to plasticize organic matter. Comparison of domain coefficients at infinite dilution reveals that organic solutes have a modestly greater affinity for holes than dissolution sites (by 0.1-0.6 log unit), as expected by the polymer model. Sorption of CHCl3 shows time-dependent hysteresis diminished at high concentrations by the plasticizing effect. Sorption of CHCl3 also shows a type of hysteresis for glassy solids known as the "conditioning effect" in which high loading of sorbate increases hole population upon its removal and thus leads to enhanced uptake and nonlinearity when a second sorption is performed. A Polanyi-based, fixed-pore filling model applied to the adsorption component of the isotherms gave widely variant volumetric pore capacity, contrary to its own stipulations, and could not explain the hysteresis.

The water vapor sorption behavior of natural fibers

“…As the isotherm temperature is increased, the size of the hysteresis loop is predicted to decrease until the glass transition temperature of the material is reached, at which point it becomes zero. The glass transition temperature of lignin in the presence of moisture is in the region of 60 to 90 C 61 and linear projections of the decrease in hysteresis loops reached zero in this temperature range for Sitka spruce.…”

Sorption of Atrazine in Tropical Soil by Biochar Prepared from Cassava Waste

“…The BC comprised carbonized and noncarbonized fractions, which demonstrated that BC was heterogeneous (Chen et al 2008;Cao et al 2009). The sorption for AT by BC had two principal types of sorption domains; one was a soft carbon domain analogous to rubbery polymers and characterized by a PEER-REVIEWED ARTICLE bioresources.com partition mechanism exhibiting a linear sorption behavior, and the other was a hard carbon domain analogous to glassy polymers and characterized by a pore-filling mechanism; its sorption behavior was nonlinear (Xia and Pignatello 2001). Sorption isotherms of AT in BC-added soil were linear/nonlinear (Fig.…”

Adsorption Characteristics of Norfloxacin by Biochar Prepared by Cassava Dreg: Kinetics, Isotherms, and Thermodynamic Analysis

“…Therefore, the adsorption of NOR on biochars have two principal types of sorption domains. One is a soft carbon domain similar to rubbery polymers, which is characterized by a partition mechanism to exhibit a linear; the other is a hard carbon domain analogous to glassy polymers, characterized by a pore-filling mechanism, which sorption isotherm is nonlinear (Xia and Pignatello 2001). Hence, for BC450 and BC550, partition was a dominant mechanism, while for BC350, BC650, and BC750, the major mechanism was a pore-filling.…”