Evaluation of Hydrophobic, Hydrophilic and Water Adsorption Properties of Microporous Metal-Organic Framework Materials by Unified Isotherm Analysis

Hydrophobic and hydrophilic phenomena displayed by microporous materials are crucial to a wide range of biological and energy storage technologies and are foundational to addressing the water-energy nexus. However, advancement of fundamental understanding is impeded by the failure of classical analyses to identify mechanisms of water interaction, connect fundamental isotherm types, and provide benchmarks for assessment that are not only defined on a continuous scale but are also capable of prediction of hydrophobic conditions. This substantial deficiency is mitigated by a novel definition of hydrophobicity that is proposed herein. It is coherently coupled with unified isotherm analysis which connects a wide array of rigorous isotherm types with transitioning behavior and distinct forms of hydrophobicity. Application to microporous Metal-Organic Framework (MOF) materials that display challenging stepwise Type V isotherm, reveals the utility of Ising-Model-Modified-Kelvin-Analysis (IMMKA). Nanocapillarity and nanowetting components embedded in the analysis are characterized by simple, rigorous, analytic forms that allow verification of widely accepted protocols and “rules of thumb” for prediction of micropore filling pressures and mechanisms of filling. The novel deliverables of this study broadly offer means to successfully capture interactions that underpin hydrophobic behavior and discriminate foundational features of water in extreme confinement.