Screening of carbonaceous nanoporous materials for capture of nerve agents

Abstract

A strategy for combined experimental and computational screening of candidate carbonaceous materials for capturing highly volatile nerve agents at ambient temperature using physisorption. Based on theoretical calculations of Henry constants and zero-coverage adsorption enthalpies for sarin and DMMP (its common stimulant) adsorbed in model slit-shaped carbon pores at 298 K, we found the following. Slit-shaped carbon pores with pore width 0.5 nm are optimal for agent adsorption due to strong confinement of adsorbed molecules. Agent adsorption enthalpy at zero coverage computed for optimal pore width is very high and reaches 83 kJ mol-1. Widening of pore width above 1 nm results in a significant decrease of the Henry constant and zero-coverage adsorption enthalpy (44 kJ mol-1). Polydispersity of studied candidate carbonaceous materials strongly affects adsorption capacity for DMMP under the operating conditions. The optimal carbonaceous adsorbent, pitch-based P7 activated carbon fiber, adsorbed 100 µg g-1 DMMP at 0.03 µg m-3. Commercial Norit activated carbon adsorbed only 20 µg g-1 DMMP at 0.03 µg m-3. Surprisingly, a small shift of the pore size distribution towards wider micropores has a great impact on agent adsorption. Because the adsorption enthalpies computed at zero coverage weakly dependent on pore size, the heat released during agent adsorption is similar for all studied candidate adsorbents (i.e. 55–60 kJ mol-1).