Abstract:

Fluorine is one of the essential trace elements in human life activities, but excessive intake of fluorine will cause fluorosis such as dental fluorosis and skeletal deformation. In this paper, the Al₂O₃/AC composite material was obtained through simple sonication of activated carbon (AC) and Al₂O₃ nanoparticle. Field emission scanning electron microscopy proved that Al₂O₃ was successfully loaded on the AC surface with a uniform distribution at the doping amount of Al₂O₃ of 5%. The results of N₂ adsorption-desorption test showed that the specific surface area of the Al₂O₃/AC composite increased. Cyclic voltammetry, constant current charge discharge and electrochemical impedance measurements demonstrated the improvement of ionic conductivity and specific capacitance of the composite after Al₂O₃ doping. Effect of Al₂O₃ doping amount was investigated and the 5% Al₂O₃/AC electrode achieved the optimal capacity of 92 F·g^-1 in 7 mmol·L^-1 NaF solution, better than that on AC electrode (62 F·g^-1). When being applied as the anode in capacitive deionization device, the Al₂O₃/AC electrode exhibited a defluorination capacity of 234 μmol·g^-1, much higher than that on AC electrode (115 μmol·g^-1). In addition, the 3-cell CDI stack delivered a 80% removal of F^- in the simulated groundwater containing F^-, Cl^- and SO₄^2-, while only 25% of Cl^- and 56% of SO₄^2- were removed. It demonstrated the excellent selective defluorination performance. The adsorption amount of F^- retained 81% after 10 adsorption/desorption cycles. The electrode material is simple to prepare and has good defluorination selectivity. It is expected to be used in the purification and defluorination of groundwater in high-fluorine areas in the CDI process.

Key words: activated carbon, Al₂O₃, capacitive deionization, selective defluorination, groundwater

摘要：

氟是人类生命活动必需的微量元素之一，但人体摄入过多的氟元素会引发氟斑牙、骨骼变形等氟中毒现象。本文以活性炭 （AC） 为载体，在多孔Al₂O₃纳米分散液中采用简单超声处理，得到Al₂O₃/AC复合材料。场发射扫描电镜证明Al₂O₃成功负载在AC表面，5% Al₂O₃在AC表面分布均匀。N₂吸-脱附测试结果表明Al₂O₃/AC复合材料的比表面积比AC有明显增加。循环伏安、恒流充放电及电化学阻抗测试结果表明Al₂O₃的掺杂可以改善AC的离子导电性，提高比电容；5% Al₂O₃/AC导电性最佳，比电容最高，在7 mmol·L^-1 NaF溶液中为92 F·g^-1，是AC比电容 （62 F·g^-1） 的1.5倍。以Al₂O₃/AC为正极的电容去离子 （CDI） 脱氟测试，结果表明5% Al₂O₃/AC电极脱氟量最大，达234 μmol·g^-1，远高于纯AC的脱氟量 （115 μmol·g^-1）。此外，5% Al₂O₃/AC电极对F^-的选择性吸附性能良好，在含F^-、Cl^-和SO₄^2-的模拟高氟地下水中采用5% Al₂O₃/AC电极对应的三组CDI池串联，可脱除80%的F^-、25%的Cl^-和56%的SO₄^2-，同时经过十次F^-吸脱附循环后，氟去除率仍可保持81%，证明5% Al₂O₃/AC电极对F^-具有良好的选择吸附性和循环稳定性。该电极材料制备简单，脱氟选择性好，在CDI过程中有望用于高氟地区地下水的净化脱氟。

关键词: 活性炭, Al₂O₃, 电容去离子, 选择性脱氟, 地下水