Modifying functionalized-carbon-nanotube capacity to enhance water-vapor adsorption capacity from nitrogen gas

The primary objective of this paper is to enhance the water-vapor-adsorption capacity of multiwall-carbon-nanotube (MWCNT) from nitrogen gas by grafting sulfonic acid groups and doping palladium nanoparticles into the adsorbent. MWCNT has been selected to be modified because of having homogeneous adsorption energy compared to silica gel. As a result, it is capable of creating isotherm having sharp rising zone which is an important feature for gas dehydration application. For this purpose, MWCNT functionalized by hydroxyl groups (MWCNT-OH) was utilized to produce MWCNT functionalized by sulfonic acid groups (MWCNT-OSO3H), MWCNT-OH doped by palladium nanoparticles (MWCNT-OH-Pd) and MWCNT-OSO3H doped by palladium nanoparticles (MWCNT-OSO3H-Pd). Thermal and mass stability, Fourier-transformation infrared and atomic absorption analyses supported the fact that the functional groups and palladium nanoparticles were placed successfully throughout the carbon nanotubes. Then, the water-vapor adsorption isotherms of MWCNT-OH, MWCNT-OSO3H, MWCNT-OH-Pd and MWCNT-OSO3H-Pd were obtained at two temperatures of 15 and 24 oC. The water-vapor adsorption experiments revealed that by substituting sulfonic acid groups for the hydroxyl ones the adsorption of water vapor was enhanced only for higher gas humidity. However, by intercalating palladium nanoparticles into MWCNT-OSO3H the capacity for water-vapor adsorption was improved for lower gas humidity as well. The obtained isotherms followed the isotherms type of V which is prevailing in water-vapor adsorption systems.