Elemental carbonaceous materials such as char and soot are widespread in the environment. Known as environmental black carbon, these materials have high surface area and surface activity, and therefore are believed to play an important role in the sorption and transport of anthropogenic organic chemicals in soil and sediment. We found that simulated “aging” of wood charcoal particles in a soil-water suspension leads to declines in its surface area (SA) estimated by N2 adsorption at 77 K with BET analysis and its affinity for dissolved benzene. In an attempt to determine the underlying cause, we studied the effects of natural lipids, modeled by triglycerides of a commercial vegetable oil, on surface and adsorptive properties of the char. Lipid-loaded chars were prepared by equilibrating a dilute char suspension in water (25 mg in 65 mL) with vegetable oil added in a small volume of acetone carrier solvent and then filtering. With increasing lipid loading (up to 40% of char weight), N2 adsorption was strongly suppressed (up to 100-fold reduction in N2-BET-SA), while CO2 adsorption at 273K and benzene adsorption at 293K were hardly affected. We propose that externally adsorbed lipid molecules occupy pore throats with assess to interior pore networks. At 77 K, lipid chains are too inflexible to allow passage of adsorbate (N2), in contrast to the higher temperatures. It is concluded that benzene adsorption predominates at interior pore sites and does not correlate with N2 - BET- SA when the char accrues pore-blocking substances from the surroundings.
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