Water Capture Mechanisms at Zeolitic Imidazolate Framework Interfaces

Abstract

Water capture mechanisms of zeolitic imidazolate framework ZIF-90 are revealed by differentiating the water clustering at interior interfaces of ZIF-90 and the center pore filling step, using vibrational sum-frequency generation spectroscopy (VSFG) at a one-micron spatial resolution. Spectral lineshapes of VSFG and IR spectra suggest that OD modes of heavy water in both water clustering and center pore filling steps experience similar environments, which is unexpected as weaker hydrogen bond interactions are involved in initial water clustering at interior surfaces. VSFG intensity shows similar dependence on the relative humidity as the adsorption isotherm, suggesting that water clustering and pore filling occur simultaneously. MD simulations based on MB-pol corroborate the experimental observations, indicating that water clustering and center pore filling happen nearly simultaneously within each pore, with water filling the other pores sequentially. The integration of nonlinear optics with computational simulations provides critical mechanistic insights into the pore filling mechanism that could be applied to the rational design of future MOFs.

Prospects for Simultaneously Capturing Carbon Dioxide and Harvesting Water from Air

“…Like zeolites, some MOFs contain coordinatively unsaturated metal sites that can electrostatically interact with the dipole moment of H 2 O. Depending upon the pore diameter, water can participate in reversible cluster formation [75][76][77][78] or capillary condensation. [79][80][81] In many cases, strong hydrogen bonding interactions between adsorbed H 2 O molecules enable cooperative water adsorption, characterized by a step-shaped adsorption isotherm.…”

Water Induced Structural Transformations in Flexible Two-Dimensional Layered Conductive Metal–Organic Frameworks

“…As the water content increases, the computed Δ H ads values of Cu 3 (HHTP) 2 and Co 3 (HHTP) 2 both reach an almost plateau value though Co 3 (HHTP) 2 still shows higher enthalpy of adsorption per water molecule than its Cu counterpart. For comparison, recently the Δ H ads per water molecules for the zeolitic imidazolate framework-90, which is generally classified as a hydrophilic material, is calculated to be ∼−11 kcal/mol . Overall, adsorption of water leads to formation of water coordinated complexes and partial hydrolysis of the layers in the Co 3 (HHTP) 2 2D MOF with most Co centers accepting two or more water molecules.…”

Revealing the Molecular Physics of Lattice Self-Assembly by Vibrational Hyperspectral Imaging

“…For example, many materials can be classified as LSAs, such as amyloid proteins, DNA self-assembly crystals, and nucleosomes . Many LSAs, along with other materials such as metal–organic frameworks, have chirality and are heterogeneous. Thereby, the method demonstrated here could provide spatially resolved structural and dynamic knowledge with molecular specificity, without any labels.…”