LAUSR

Abstract The ethylene glycol monoethyl ether (EGME) adsorption method is an essential and available technique for measuring the total specific surface area (TSSA) of natural rock samples that usually contain an abundant amount of clay-organic matter (clay-OM) complexes. Occurrence sites and types of OM are believed to influence the EGME adsorption behaviors of clay-OM complexes. However, the influence of OM properties on the EGME adsorption mechanism remains unclear until now. In this study, interlayer montmorillonite (Mt)-OM complexes were prepared using the intercalation of OM with various contents and different length of alkyl chains, such as tetramethylammonium bromide (TMAB) and dodecyl trimethyl ammonium bromide (DTAB), based on the cation exchange. EGME adsorption experiments were performed on Mt, OM, and Mt-OM complexes. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structural properties of the samples before and after EGME adsorption. The EGME adsorption capacities and the corresponding TSSA decreased after OM intercalation into the interlayer space of Mt. The OM content and the amounts of alkyl chains significantly affected the EGME adsorption behaviors of Mt-OM complexes. For short alkyl chain OM (TMAB), TSSA values of the Mt-OM complexes decreased with the increase of the interlayer OM content. However, for long alkyl chain OM (DTAB), the TSSA values showed a different variation tendency where the smallest TSSA did not appear in the Mt-OM complex with the highest DTAB content. The initial interlayer distance of Mt-OM complexes and the arrangement of interlayer OM are the primarily factors for EGME adsorption behaviors of the Mt-OM complexes. The large initial interlayer distance favored for incremental expansion of Mt. after EGME adsorption, which promoted EGME molecules entering into the interlayer space. The influence of the arrangement of interlayer OM are primarily involved in some newly formed micropores preventing EGME molecules from entering and more adsorption sites were occupied by OM with a higher ordered mode for the conformation of the alkyl chain and a higher packing density for the arrangement.