Understanding the Influence of Pore Heterogeneity on Water Adsorption in Realistic Molecular Models of Activated Carbons

Grand canonical Monte Carlo simulations are performed to study the adsorption of water at 300 K in realistic molecular models of three activated carbon samples, namely, CS400, CS1000, and CS1000a. CS400 and CS1000 models contain micropores only (up to ∼7 A). The CS1000a model contains wide micropores (up to ∼13 A). The water adsorption phenomena in CS400 and CS1000 models follow a continuous curve (as is seen in experiments for microporous carbons), whereas sudden pore filling occurs for the CS1000a model, once a threshold chemical potential is reached. Adsorption of water in micropores is found to occur via formation of small clusters in the different regions of CS400 and CS1000. A large cluster is formed for the CS1000a model owing to wide micropores and pore connectivity. Results for the isosteric heat of adsorption, radial distribution function (O–O and O–H), hydrogen bond statistics, and cluster size distribution of water molecules are presented. The snapshots of water clusters in hybrid reverse Monte Carlo models show that the pores in porous carbons have a complex shape and are interconnected in a complex way. Our results show that realistic models of porous carbons, as used in this work, are required to understand the adsorption phenomena of water in porous carbon samples.