An environmental benign organic-free hydrothermal crystallization process is applied to synthesis of gibbsite platelets, which are well-defined, regularly shaped and monodispersed pseudohexagonal submicron structures with an average width of 0.6-0.8 mu m and a thickness of 40 nm. The structure and morphology of resulting solids depend to a great extent on the pH of media for hydrothermal crystallization. An acidic condition of pH 5.0 is favorable for the growth of submicron gibbsite platelets with high purity, whereas alkaline condition results in boehmite and neutral medium is unfavorable for crystal growth in this study. The properties of materials obtained by hydrothermal crystallization have been investigated by SEM, XRD, Al-27 MAS-NMR, XPS, and solid UV-vis spectroscopy, (c) 2006 Elsevier B.V. All rights reserved.