Defect location dictates water adsorption enthalpy in CAU-10-H MOFs: A first-principles perspective

Water scarcity is one of the most pressing global risks. The situation is becoming increasingly precarious in underdeveloped regions, driving the search for materials that can efficiently harvest atmospheric moisture under arid conditions. Metal-organic frameworks (MOFs), with their tunable porosity and surface chemistry, have emerged as promising sorbents for sorption-based atmospheric water harvesting (SAWH). Among these, CAU-10-H stands out for its exceptional cyclic stability. By employing first-principles calculations and Grand Canonical Monte Carlo simulations, we elucidate how the position and spatial arrangement of missing-linker defects modulate water adsorption enthalpy in CAU-10-H. Defect location dictates the strength and topology of water-framework interactions, with adsorption enthalpies varying roughly from −25 to −40 kJ mol⁻¹ depending on defect geometry. Density-profile analyses reveal that missing linkers create localized, high-affinity binding pockets within the framework, whose accessibility and multiplicity increase with the separation of defects. Conversely, adjacent defects partially screen open metal sites, reducing adsorption strength. These results demonstrate that water uptake thermodynamics in CAU-10-H is governed not only by defect concentration but also by the spatial correlation of defects. The findings establish a structure-enthalpy relationship that provides a quantitative basis for defect engineering in MOFs, paving the way for next-generation water-harvesting technologies.