Activated alumina (AA) with metastable crystal phase and porous structure has shown great potential for fluoride ion removal. Conventional AA is obtained by direct calcination, which limits its fluoride adsorption ability due to the low surface area and limited active sites. In this work, a highly porous AA was synthesized by a sol–gel method, followed with supercritical drying (including ethanol supercritical drying and carbon dioxide supercritical drying) and calcination. The fluoride ion adsorption properties of AA were studied at different concentrations of fluoride in solution. The Langmuir model, Freundlich model, pseudo-first-order model and pseudo-second-order model were used to describe the adsorption process. The results show that the resulting AAs possess a high porosity and a high specific surface area (up to 660 m²/g). The fluoride adsorption capacity of AA increases with the increase of specific surface area and porosity (up to 119.2 mg/g), which is much higher than that of AA prepared by the traditional method (direct calcination). Moreover, all the fitted correlation coefficients of the four models exceed 90%, indicating both chemical and physical adsorption in AA.

具有亚稳态晶相和多孔结构的活性氧化铝（AA）在去除氟离子方面显示出巨大的潜力。传统的AA是通过直接煅烧获得的，由于表面积小和活性位点有限，限制了其对氟化物的吸附能力。在这项工作中，通过溶胶-凝胶法合成了一种高度多孔的 AA，然后进行超临界干燥（包括乙醇超临界干燥和二氧化碳超临界干燥）和煅烧。在溶液中不同浓度的氟化物下研究了AA的氟离子吸附性能。Langmuir模型、Freundlich模型、拟一级模型和拟二级模型用于描述吸附过程。结果表明，生成的 AA 具有高孔隙率和高比表面积（高达 660 m² /克）。AA的氟化物吸附能力随着比表面积和孔隙率的增加而增加（高达119.2 mg/g），远高于传统方法（直接煅烧）制备的AA。此外，四个模型的所有拟合相关系数均超过 90%，表明 AA 中的化学和物理吸附。