Bridging experimental and DFT approaches to probe chlorinated aromatics and toluene adsorption in FAU-NaX zeolite

Organochlorine compounds (OClCs), a major class of persistent organic pollutants (POPs), pose environmental and health risks due to their toxicity, stability, and bioaccumulation. Commonly used in industrial processes and generated during waste incineration, they persist in both gas and liquid effluents. Their efficient removal therefore remains an important environmental challenge. FAU-NaX zeolite is a promising adsorbent for OClC capture, as its 12-membered-ring windows (≈7.4 Å aperture) and large supercages provide suitable sites for chlorinated aromatic molecules. We investigate the adsorption and thermodynamic behavior of toluene (TOL), chlorobenzene (CB), and three dichlorobenzene isomers in FAU-NaX, with the aim of clarifying how chlorine substitution, isomerism, and molecular polarity control adsorption in the zeolite supercage. Liquid-phase adsorption isotherms measured in isooctane at 298 K showed saturation capacities of approximately 3–4 molecules per FAU supercage. Liquid-phase microcalorimetry, combined with a solvent-displacement thermodynamic cycle, yielded gas-phase-corrected adsorption enthalpies of 87–103 kJ.mol -1 at zero coverage, while DFT adsorption energies ranged from 97 to 133 kJ.mol -1 depending on the molecule and adsorption geometry. Desorption temperature distributions were determined by thermogravimetric analysis coupled with mass spectrometry (TG–MS), providing an independent probe of adsorption strength and site heterogeneity. A consistent relationship was observed between gas-phase-corrected adsorption enthalpies, DFT interaction energies, and TG–MS desorption temperatures. By combining infinite-dilution adsorption measurements, gas-phase enthalpy derived from liquid-phase calorimetry, TG-MS desorption analysis, and DFT modelling of single-molecule interactions in the FAU supercage, this work establishes a structure–property relationship linking dipole moment, adsorption strength, and molecular–cation interactions in FAU-NaX zeolites.