Development of anion stereoselective, activated carbon molecular sieve electrodes prepared by chemical vapor deposition

The electrochemical properties of nanoporous, activated carbon cloth electrodes in NaCl and NaNO₃ solutions were investigated before and after carbon chemical vapor deposition (CVD) on the high surface area of nanoporous carbon samples. Different CVD reagents, temperatures, and pressures were employed. We achieved a sharp ion sieving effect for CDV-treated carbon samples/electrodes by selecting a given CVD reagent (namely, benzene) and a temperature that was too low to affect chemical decomposition of benzene in the gaseous phase, but sufficiently high to enable its decomposition on the outer surface of the carbon substrate, to form surface carbon deposits. The electroadsorption stereo selectivity achieved by optimized CVD treatment was so sharp that clear discrimination could be obtained even between anions of very similar dimensions, such as Cl^- and NO₃^-. Here, the nitrate behaves as the smaller entity since, being a planar ion, it fits better into the carbon micropores known to have slit-shaped pores. The CVD treatment affects mainly the mouths of the pores and not their interior/volume. This was proven by adsorption experiments. From the gas phase, the stereoselectivity obtained by these CVD treatments was also demonstrated by discrimination between the adsorption of CO₂ and N₂ into the CVD-treated activated carbon.