Defect engineering in metal–organic frameworks (MOFs) for applied interfaces: from structural imperfections to catalysis, separation, environmental, energy, and biomedical functions

Metal–organic frameworks (MOFs) were long valued for their crystalline regularity, and structural defects, including missing-linker vacancies, missing-node sites, substitutional disorder, surface terminations, and correlated vacancy domains, were initially dismissed as synthetic imperfections to be minimized. Over the past decade, this view has inverted: defects are now recognized as a reproducible, structurally significant feature of MOFs that can be deliberately introduced and controlled. This review discusses the fundamental principles of defect engineering, examining how modulated synthesis, kinetic control, and post-synthetic treatment are used to install specific defect populations, and how multi-technique characterization, including solid-state NMR, pair distribution function analysis (PDF), X-ray absorption spectroscopy (XAS), electron microscopy, and operando measurements, has made it possible to resolve defect type, density, and spatial distribution rather than merely confirm their presence. We then examine how this design-level control translates into the development of applied interfaces and functional materials across both established and emerging domains: defect engineering is now well established for engineering functional interfaces in catalysis and gas adsorption/separation, and is rapidly extending into less mature areas including electrochemical energy storage, environmental remediation, and biomedical delivery, where defect-function relationships remain less quantitatively resolved. We conclude by identifying the reproducibility, quantification, and scalability barriers that currently separate empirical defect discovery from predictive, data-driven of defect-engineered functional materials and applied interfaces.