Adsorption Behavior of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Activated Carbon by Grand Canonical Monte Carlo: Effect of Pore Size and Distribution

Abstract

Activated carbon with abundant nanoporous structures can effectively adsorb 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) molecules. However, an atomistic understanding of its underlying adsorption mechanism is still urgently needed because TCDD, given its strong toxicity, requires strict testing conditions in experiments. In this work, a series of grand canonical Monte Carlo (GCMC) simulations were performed to evaluate the effects of the slit width and pore size distribution (PSD) of activated carbons on TCDD adsorption. The microstructural analyses of TCDD within nanoslits demonstrate that when the slit width exceeds 0.8 nm, the orientation of TCDD molecules inclines about 30° along the axis’s normal direction, causing the adsorption amount to increase rapidly. When the slit width exceeds 2.0 nm, its disordered orientation causes the adsorption amount to reach a maximum value. Based on this understanding, we determined the effective specific pore volume (or effective specific surface area) for TCDD adsorption. In combination with the full width at half-maximum (FWHM) of the PSD, we propose the experimentally measurable structural parameter V_H>0.8/FWHM (or S_H>0.8/FWHM) and use it as an indicator to reflect the TCDD adsorption performance of different activated carbons. A high structural parameter of activated carbon can indicate a high TCDD adsorption amount.