Structural Modeling of Nanoporous Carbon: A Review of Approaches to Simulating an Aperiodic and Non-Equilibrium Solid

Abstract

Nanoporous materials as a class are the subjects of intense research at present because they offer the potential for substantially new technologies in areas as diverse as electronics and medicine. Carbons derived by pyrolysis of polymeric precursors are an interesting case in point of a nanotechnological application which is already practiced.’ The separation of air has been done for over a century by brute force, and energetically intensive, method of cryogenic distillation. Zeolites (Li-X) offer an alternative means to producing oxygen via an adsorptive procedure. Nitrogen is preferentially attracted to and held the lithium cations. Nanoporous carbons (NPC) produce enriched nitrogen by a process which is quite different. Experiments show that oxygen is adsorbed substantially faster than nitrogen at pressures from 101 to 10,100 Kpa or more at room temperature.²More recently, membranes consisting of fibrous or supported forms of nanoporous carbon have been shown to display a similar preference to the transport of oxygen over nitrogen.³While much recent work has been done, the fundamental aspects of why oxygen is more rapidly transported than nitrogen remains elusive. As to whether this difference in rate is caused by a lower enthalpy barrier or an increased entropy of transition for oxygen at the narrowest constrictions of the pore structure,⁴ there is still considerable disagreement.