Activated carbon fiber composites for gas phase ammonia adsorption

Low–cost activated carbon fiber composites (ACFCs) were explored as the basis for a system to remove NH3 from the gas phase. ACFCs were synthesized by chemically activating a phenolic precursor on a glass fiber substrate using ZnCl2 as catalyst. Additionally, ACFCs were oxidized with concentrated nitric acid at both room temperature and 83 °C to increase the density of surface oxygen groups. Commercially available phenolic-based physically activated carbon fibers were also oxidized under the same condition as a benchmark. Both physical properties and surface chemical properties of these materials were characterized using SEM, BET, elemental analysis, FTIR, XPS, and Boehm titration. Dynamic flowthrough NH3 adsorption was measured at 500 ppm, at both 0% and 50% relative humidity. Results suggest ACFCs exhibit high surface area, rich oxygen functional groups, with post-treatment further improving surface oxygen content. ACFCs displayed fast sorption kinetics and high NH3 adsorption capacity up to 50 mg/g. Acidic oxygen groups at the surface are correlated with ammonia adsorption. A new anhydride-based reaction mechanism was identified and is proposed, collectively with carboxylic acid functional groups, as being primarily responsible for retaining NH3.