Atomic Layer Deposition-Assisted Surface-Selective Isotopic Labeling for the 17O Solid-State NMR Studies of Metal Oxide Surfaces

¹⁷O solid-state NMR spectroscopy is widely used to investigate metal oxide surfaces and is increasingly recognized for the unique insights into surface structures. Given the low natural abundance of the ¹⁷O nucleus (0.037%), ¹⁷O surface-selective isotopic labeling is commonly employed in relevant studies. Conventional thermal treatment (CTT)-labeling methods rely on rapid ¹⁷O/¹⁶O exchange may yield insufficient labeling on less reactive surfaces. Our approach uses atomic layer deposition (ALD) epitaxial growth to directly deposit ¹⁷O onto metal oxide surfaces regardless of surface reactivity. This method minimizes the formation of excessive surface hydroxyl groups, reducing overlapping NMR signals and enabling better ¹⁷O NMR identification of hydroxyl groups, as observed in Al₂O₃. Moreover, heteronuclear ²⁷Al{¹⁷O} J-HMQC NMR analysis reveals that the CTT method creates more correlations between penta-coordinated Al sites and hydroxyl groups in Al₂O₃ compared to ALD, indicating that the labeling techniques vary in their effectiveness at different surface sites.