Deuterium adsorption in carbon single walled carbon nanotubes doped by lithium and potassium: Adsorption isotherms and in situ neutron diffraction

In situ neutron diffraction studies of D2 sorption have been performed on two kinds of SWNTs: carbon deposit (from an electric-arc origin) containing close-end SWNTs and purified SWNTs (HiPCO) partly opened by mild oxidation. The D2 adsorption was studied in KC10 and KC7 carbon deposits; and in KC8 and LiC18 HiPCO SWNTs. We have brought out that the effect of doping is to enhance the physisorption and energy of adsorption (deduced from the Clausius-Clapeyron law applied to the isotherms network) if empty micropores sites are preserved after reaction with alkali metals. The diffraction patterns are the signature that deuterium molecules are physisorbed at low pressure 1/exclusively in the interstitial microporous voids between the tubes in SWNTs from electric-arc origin; or 2/ both in this former sites and in inner sites (central canals) in HiPCO SWNTs. Moreover, the capillary condensation of deuterium at low temperature was observed in the mesopores network at T<23 K.