Adsorption of halocarbons in nanoporous materials: current status and future challenges

摘要

An increased awareness of environmental issues relating to ozone-depleting chlorofluorocarbons (CFCs) [1] and to the removal of chlorinated solvent residues from contaminated ground water and soils [2] is driving the need to develop new separation and catalytic conversion processes for halocarbons. Zeolites and related nanoporous materials have been recently recognized as interesting alternatives to other media such as activated carbons for the sequestration and conversion of halocarbons, such as methyl chloride [3], trichloroethylene [4], and various hydrofluorocarbons [5], using ZSM-5 or faujasite-type zeolites. Obviously, aluminosilicates and related molecular sieves offer a range of potential advantages: they offer the possibility of fine-tuning separation processes by utilizing polarity differences between various halocarbons and of tailoring separation processes by harnessing chemically specific host-guest interactions. Unlike the situation with hydrocarbons in zeolites, relatively few experimental and simulation data concerning the behavior of halocarbons in zeolites and analogous nanoporous materials have been reported so far. They include calorimetric [6] and isotherms measurements [7,4], FTIR/Raman [8] and NMR [9] spectroscopies studies, diffraction work [10], and generalized forcefield simulations [11] on a variety of sorbate/sorbent systems. However, there remains a great deal to be done in this emerging field.