Dynamic Adsorption and Desorption of Toluene on Carbon Nanotubes Grafted Activated Carbon Fibers

Abstract

Activated carbon fibers (ACFs) are widely used adsorbents due to their small fiber diameter, uniform pore size distribution and rapid adsorption/desorption rate. In addition, carbon nanotubes (CNTs) have received much attention recently because of their excellent mechanical and electrical properties and being candidates for adsorption. Thus, it should be highly interested as grafting CNTs onto ACFs to form a hybrid adsorbent. Therefore, the objective of this paper is to investigate the physicochemical properties of ACFs grafted with nitrogen-doped CNTs (CNs) and determine the adsorption and desorption performance of toluene vapor on this hybrid adsorbent. The chemical vapor deposition method was used for growth of CNs directly onto ACFs. The resulting materials were characterized by several techniques. Next, the adsorption breakthrough behaviors of toluene on the samples were measured in a continuous flow-type fixed-bed system. And then the temperature programmed desorption system was utilized to observe the desorption characteristics of toluene from the samples. Results show that the CNs have been grafted homogeneously onto the ACFs. The attachment of CNs on ACFs was believed to block part of the active surface area, causing the decrease in specific surface area and pore volume, but lead to the increase in microporosity. The adsorption of toluene on ACFs or the hybrid adsorbent was physical adsorption. At higher adsorption temperatures, the hybrid adsorbent could maintain high enough capacities of toluene and even exceed the performance of ACFs. Moreover, toluene could be desorbed completely from ACFs and the hybrid adsorbent up to 400 oC with the highest desorption efficiency at about 180 oC.