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 Å). The CS1000a
model contains wide micropores (up to ∼13 Å). 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.