Controllable hydrothermal synthesis of 2D and 3D dendritic aluminum phosphate crystals

In this work, a controllable hydrothermal synthesis of two-dimensional (2D) and three-dimensional (3D) dendritic aluminum phosphate crystals was implemented from a recipe containing alumina, phosphate, nitric acid and triethylamine (TEA) with or without the addition of cetyltrimethylammonium bromide (CTAB). The 2D dendrite has a three-fold symmetrical structure with angles of 60° between the trunk and branches and the branch and leaves, while the 3D dendrite is assembled by trunks growing from the same central point and reaching in different directions with branches growing perpendicular to them. Interestingly, CTAB functioning as a crystal morphology modifier can change the dendritic structure from 2D into 3D. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and thermogravimetric analysis. Their morphologies and phase compositions are dependent on the concentration of the hydrogels and the crystallization temperature. Through a series of time-dependent morphological evolution studies, the growth process of the dendritic aluminum phosphates has been systematically investigated and the corresponding growth mechanism is proposed.