Kinetics of Cluster-Mediated Filling of Water Molecules into Carbon Micropores

Understanding the kinetics of water adsorption/desorption on activated carbon is significant for chemical applications in which competitive adsorption of water occurs. In this study, we investigated the water adsorption process by determining the adsorption rate constant using the novel pressure feedback method (PFM), which measures the rate of adsorption directly with high precision (∼10 nmol s^–1) by controlling the introducing and outgassing flow rates. The PFM was used to investigate water vapor adsorption kinetics on activated carbon fibers (ACFs) of different pore sizes and to obtain a correlation of rate constant with pore size. The systems show good agreement with the stretched exponential model. The adsorption rate constants were found to be lower for ACFs with a larger pore width (average pore width; w = 1.03 nm) as compared with those for smaller pore systems (w = 0.57, 0.72 nm).