2H-NMR study of molecular reorientation of D2O confined into the slit-shaped micropores of activated carbon fiber

Abstract

AbstractHerein, the reorientation of heavy water (D2O) molecules adsorbed in the slit-type micropores of activated carbon fibers is investigated using the 2H-nuclear magnetic resonance technique. The rotational correlation times (τc) of D2O are evaluated from the 2H spin–lattice relaxation time (T1). The obtained τc values are significantly influenced by both the pore-filling ratio (ϕ) and temperature, thus suggesting that the adsorption of D2O into activated carbon fibers (ACF) effectively influences the reorientation of the D2O molecules within the ACF. The reorientational motion of D2O is examined by the extended jump model. According to this model, the nanoconfinement effect, which results from the reduction in free volume around D2O, is attributed to the transition-state excluded volume effect, whereas the effect of hydrogen bonding between the D2O and surface functional groups is attributed to the transition-state hydrogen bonding effects. Furthermore, the dependence of τc on ϕ is explained by the chemical exchange between the pore surface adsorption sites and the central space of the pore. Thus, the dynamic behavior of adsorbed D2O molecules reveals the mechanism of D2O adsorption into the ACF micropores.