Expanding Cluster, Enhancing Adsorption: Investigating the Role of Electrostatic Configurations on Water Vapor Adsorption

Understanding and tuning water vapor adsorption at nanoscale can inform technologies such as atmospheric water harvesting, dehumidification, water-energy nexus design, etc. Porous materials have shown great promise as water adsorbents with studies revealing how different adsorbent properties such as functional groups, pore size, surface charge, etc. can influence adsorption. Present research work engages with this question: can electrostatic configuration influence water vapor adsorption? In this work, continuous fractional component grand-canonical Monte Carlo (CFC-GCMC) is applied to perform water adsorption simulations in idealized cylindrical nanopores for five different charge configurations with varying pore size (1, 1.1 and 1.2 nm) and charge magnitude (~ +/– 0.39-1.17). The alternating along (AA) configuration (positive charges in the inner ring and negative in the outer ring while alternating in z-direction) demonstrates higher water uptake at saturation and water adsorption starts at a much lower pressure than other configurations. Analysis of water clustering pattern in AA reveals radial as well axial expansion of water clusters which facilitates accommodation of extra water molecules. Increasing charge magnitude shifts the type-V isotherm inflexion point leftwards along the pressure axis, thereby increasing the hydrophilic nature of the AA configuration. Probing different energetic interactions and electrostatic potentials of the configurations suggest unique relaxation of the water clusters in the AA patterned cylinders. Investigating the effect of charge magnitude and pore size provides more evidence to their hydrophilic nature. Finally, analyzing the hydrogen bonding and adsorbed phase characteristic at saturation hints at strong ordering induced by the pore confinements and the electrostatic configurations compared to bulk liquid water. The simulations show that tailored charge arrangements can enhance adsorption by facilitating uptake at lower pressure as well as achieve higher water capacity at saturation.