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.