The absorption band observed at 631 cm−1 was ascribed to the stretching vibration of the Tisingle bondO bond [32]. The regions 3100–4000 cm−1 and 900–1800 cm−1 are hydroxyl stretching region and characteristics vibration of Alsingle bondO stretching, respectively [33] and [34]. Thus, 3290–3430 cm−1 peaks were associated with the stretching vibrations of the Al atoms bridged by an O atom and the Osingle bondH bonds, whereas 1040–1110 cm−1 were attributed to poorly crystallized modification of aluminum hydroxide (AlOOH) and Alsingle bondO stretching vibration of alumna [33], [35] and [36] as also confirmed by XPS measurements (Fig. SI 4). Relatively low wave-number position of the hydroxyl stretching vibrations of 3292 cm−1 and 3430 cm−1 for SSL in DI and SPW, respectively, indicated significant hydrogen bonding between the neighboring hydroxyls, whereas broad bands (Fig. 5a) suggested a high level of heterogeneity and the presence of largely distributed hydroxyls [37]. Furthermore, there was no Osingle bondH stretching region observed in MT 500SA nanoparticles (Fig. 5b).