Accumulated Gibbs free energy as a quantitative measure of desorption hysteresis associated with the formation of metastable states. (January 2019)

• Record Type: Journal Article
• Authors: Borisover, Mikhail
• Is Part Of: Chemosphere. Volume 215(2019)
• Page Start: 490
• Page End: 499
• Publication Date: 2019-01
• Subjects: Sorption -- Hysteresis -- "Frozen" state -- Free energy -- Natural organic matter -- Clay; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2018.10.051
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: The persistence of metastable states was proposed in the literature as one explanation for sorption-desorption hysteresis (SDH) of organic compounds on soils and sediments. When such metastable states freely exchange sorbate molecules with the surroundings and there is no spontaneous exit of a whole system from that state, it is possible to determine the extra Gibbs free energy (Δ G ext ) accumulated in a system due to the persistence of metastable states. A novel contribution of this paper is the characterization of SDH, in which the sorption isotherm (SI) and desorption isotherm (DI) do not close a loop, in terms of free energy needed to create "frozen", metastable states. To that end, liquid phase sorption of non-ionized sorbates is considered and by integrating over the sorption-desorption sequence, Δ G ext and an integral hysteresis index (IHI) were obtained. Experimental data collected from the literature on aqueous sorption and desorption of polyaromatic hydrocarbons, triazines and ureas were examined on soils, sediments, organic matter-rich sorbents, montmorillonites and fullerene. Positive Δ G ext values were obtained to quantify the thermodynamic potential for spontaneous exit from a metastable state that is not implemented due to the kinetic barriers. Relating the Δ G ext values to sorbate molecular structure and sorbent properties may allow the prediction of SDH for various chemicals on sorbents in which the sorbate-induced perturbation of a sorbent matrix is believed to be a cause for the formation of persistent metastable states and the appearance of a non-closed sorption-desorption sequence. Graphical abstract: Highlights: Sorption-desorption sequence is integrated to produce excessive free energy Δ G ext . Positive Δ G ext values characterize the formation of "frozen" states in a sorbent. An integral hysteresis index (IHI) is proposed based on the calculated Δ G ext . Δ G ext provides a basis for LFER analysis of sorption-desorption hysteresis. Variable Δ G ext and IHI are examined in soil, organic matter, clay and carbon systems.