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[Display omitted] • Near defect-free and defect-rich UiO-66-type MOFs were successfully prepared. • Affecting mechanism of defects on CO 2 capture performance was elucidated. • Importance of thermal treatment for CO 2 capture performance was illustrated. • Necessity of identifying local fine structure for CO 2 capture evaluation was noted. Carbon capture and storage (CCS) technology is currently an essential response to the global warming problem caused by excessive CO 2 emissions. Efficient and reproducible adsorbents for flue gas treatment play an important role in CCS technology, and metal–organic frameworks (MOFs) are considered to be ideal candidates by virtue of their designable CO 2 sorption sites. However, carbon capture performance evaluation and reproducibility of MOFs still hinder their application promotion in industrial production. In this work, an extended UiO-66-type MOF based on 1,4-naphthalenedicarboxylate, was successfully synthesized in both a near defect-free form (UiO-66N) and a defect-rich form (DUiO-66N), for exploring the influence of crystalline defects and thermal treatments on carbon capture performance. Although powder X-ray diffraction showed that UiO-66N and DUiO-66N possessed the same crystalline phase, transmission electron microscopy, thermalgravimetric analyse and gas/dye sorption confirmed the presence of crystalline defects and the variation of porosity in DUiO-66N. CO 2 sorption isotherms and flue gas breakthrough experiments revealed the defect-induced improved carbon capture performance, which was also supported by density functional theory. Meanwhile, the metastability of defects required low thermal treatment temperatures for activation and regeneration thus maintaining the superior carbon capture performance. These findings suggested that in reproducing and evaluating the carbon capture performance of MOFs, it cannot rely only on the global crystalline phase judgment, but needs to identify the local fine structure as well as optimize activation and regeneration conditions. [ABSTRACT FROM AUTHOR]