Green Aqueous Synthesis of Defect‐Engineered MOF‐801 via Competitive Coordination for Water Adsorption Regulation

ABSTRACT Metal–organic frameworks (MOFs) are among the most promising sorbents for water adsorption‐based applications. Defect engineering offers an effective route to regulate water adsorption behavior by tailoring the pore size and microenvironment of MOFs. However, precise control of defect structures under environmentally benign synthesis conditions remains an unsolved challenge. Here, we demonstrate a competitive coordination strategy that enables controlled tuning of defect concentrations in MOF‐801 for water adsorption regulation. By employing formic acid as a monodentate competitive ligand under green aqueous conditions, we synthesized a series of defect‐engineered MOF‐801 variants with systematically tuned pore structures and hydrophilic sites. Comprehensive structural characterization confirmed that formic acid effectively competed with fumaric acid, generating well‐controlled missing‐linker defects that modulated pore volume and local chemical environments. Notably, the optimally defect‐engineered sample (MOF‐801@20‐eq) exhibited an exceptional water uptake of 74.5 wt% at 95% relative humidity, representing a 104% increase compared to conventionally synthesized MOF‐801 using N,N ‐dimethylformamide (DMF). This study highlights competitive coordination under aqueous conditions as a powerful and sustainable strategy for defect regulation and offers new insights into the rational design of high‐performance sorbents for water adsorption applications.