Characterization of Sorption Mechanisms of VOCs with Organobentonites Using a LSER Approach

To fully utilize the sorption traits of organobentonites to control volatile organic compounds (VOCs) pollution, the sorption mechanisms of VOCs with organobentonites need to be understood adequately. The sorption of VOCs as vapors to a typical organobentonite, modified with cetyltrimethylammonium bromide (CTMAB-bentonite), was characterized using a linear solvation energy relationship (LSER) of the type log K_c = c + rR₂ + sπ₂^H + a∑α₂^H + b∑β₂^H + /log L¹⁶. The fitted LSER equation, log K_c = 0.434 + 0.968R₂ - 0.0886π ₂^H + 2.170∑α₂^H + 1.611∑β₂^H + 0.417 log L¹⁶, was obtained by a multiple regression of the partition coefficients of 22 probe solutes against the solvation parameters of the solutes. The coefficients of the LSER equation show that CTMAB-bentonite is a sorbent with nonsignificant dipolarity/polarizability, interacts with solutes partly through π-/n-electron pairs, behaves both as hydrogen-bond donor and hydrogen-bond acceptor, and can interact with solutes by cavity/dispersion interactions. The related terms in LSER suggest that the potential factors governing the sorption of VOCs onto CTMAB-bentonite are dispersion interactions, hydrogen-bond acidity interactions, hydrogen-bond basicity interactions, and π-/n-electron interactions. The dispersion interaction is recognized to be the predominant parameter for most solutes, whereas the contributions of the other parameters depend on specific solutes. The derived LSER equation successfully predicted the VOC partition coefficients and the selectivity of CTMAB-bentonite for the VOCs. The relationship between LSER and adsorption/partition model was compared. The classification of sorption mechanisms by LSER goes on the molecular interaction types between sorbate and sorbent, and classification by adsorption/partition model goes on the property difference among various components of sorbent. The LSER approach coupled with inverse gas chromatography (IGC) is a comparatively simple and reliable tool to rapidly characterize the sorption mechanism of VOCs with solid sorbents such as CTMAB-bentonite, and may potentially be applied to the design of an organoclay sorbent for control of VOCs.