Hydrogarnets are promising candidates for environmental applications such as the purification of industrial exhaust gas and waste water. However, traditional synthesis routes require highly concentrated NaOH solutions as the mineralizer for precipitating the hydrogarnets. Here, we have developed a waterbased precipitation method for Sr-hydrogarnet synthesis, which involves planetary ball milling at room temperature. Nanocrystalline Sr3Al2(OH)(12) powder was obtained by milling Sr(OH)(2)center dot 8H(2)O and gamma-Al2O3 in water for 1 h without any mineralizer. The formation mechanism of Sr3Al2(OH)(12) can be explained by a dissolution-precipitation process. Additionally, milder process conditions were used to suppress contamination from the milling vessel. Further, we analyzed the thermal decomposition behavior of Sr3Al2(OH)(12) in both air and water vapor atmospheres. The presence of water vapor in the atmosphere affects the product phases. Our work indicates that the usage environment of hydrogarnets needs to be considered to maintain their physicochemical properties to ensure their effective application as purifiers. (C) 2018 Elsevier B.V. All rights reserved.