“…As shown in Fig. 4, the spectrum of the amorphous solid prior to the hydrothermal treatment displayed one main resonance signal at d ¼ 3:6 ppm, and two satellite signal peaks at d ¼ 31:2 and 60.3 ppm, which were indicative of six-, five-and four-coordinate aluminum species, respectively [29][30][31]. In the gibbsite submicron platelets, only the six-coordinated Al species were observed, indicating that the four-and five-coordinated Al species were restructured to six-coordinated species during the hydrothermal crystallization at pH 5.0.…”