磁性铝基MOF的表征和对水体中氟化物吸附性能研究

我国多地的地表水受到成土母质或背景值的影响，氟离子浓度均超过1.0 mg/L，即高于GB 3838-2002《地表水环境质量标准》Ⅲ类标准限值.为了实现地表水的快速降氟和吸附材料的便捷回收，通过水热法制备了磁性Al-MOF@Fe₃O₄吸附材料，使用扫描电极（SEM）、X射线衍射仪（XRD）、X射线光电子能谱仪（XPS）和孔隙度分析仪（BET）对材料的形貌和化学组成进行了表征.结果表明:①Al-MOF@Fe₃O₄具有不规则的晶体形状和直径更小的介孔结构，能够提供更高的比表面积吸附氟离子.②吸附试验结果表明，Al-MOF/Fe₃O₄的吸附量达到了75.2 mg/g，吸附过程更加符合拟二阶动力学模型，证明了化学吸附是该除氟过程的主要机理.③增加吸附剂投加和降低氟离子初始浓度，有助于提高除氟效率，但却难以得到较高的吸附量，同时碱性条件不利于氟离子的吸附，阴离子对除氟性能的影响程度表现为CO₃2- > HCO₃- > SO₄2- > PO₄3- > Cl-.④对吸附机理的研究表明，氟离子是通过取代Al-OH实现稳定和快速地脱离水体，使用NaOH溶液淋洗可以实现吸附剂的高效再生.⑤5次循环吸附试验后，复合材料依然保留了71.4 mg/g的吸附能力和良好的磁性.在实际地表水中进行除氟试验，该吸附剂可以将氟化物浓度从1.17 mg/L降至0.2 mg/L以下.研究显示，Al-MOF@Fe₃O₄纳米材料可以作为地表水除氟材料，实现对低浓度氟离子的高效去除. 

Characterization and Adsorption Properties of Magnetic Al-MOF Composite for Fluoride

Surface water in many regions of China is affected by the soil or water background value, and the concentration of fluoride exceeds 1.0 mg/L, which is higher than the Class Ⅲ water specified in the Environmental Quality Standard for Surface Water (GB 3838-2002). In order to reduce fluoride in surface water and recover adsorption materials, magnetic Al-MOF@Fe₃O₄ was prepared by hydrothermal method. The morphology and composition of the adsorbents were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and porosity analyzer (BET). The results showed that Al-MOF@Fe₃O₄ had irregular shape, rough surface and smaller mesoporous structure, which can provide a large specific surface area to absorb fluoride. The adsorption experiment indicated that the adsorption capacity of Al-MOF@Fe₃O₄ was 75.2 mg/g, which was in accordance with the pseudo second-order kinetic model, indicating that chemical adsorption was the main mechanism of the defluorination process. In addition, higher adsorbent dosage and lower initial concentration enhanced the efficiency of defluorination, but decreased the adsorption capacity. Alkaline conditions were not conducive to the adsorption of fluoride. The effects of co-existing anions on defluorination performance was in the order of CO₃2- > HCO₃- > SO₄2- > PO₄3- > Cl-. The study showed that fluoride could be separated from the water rapidly by replacing the surface hydroxyl groups of the adsorbent, and the adsorbent could be efficiently regenerated with NaOH solution. After five cycles of adsorption experiments, the composite still retained 71.4 mg/g adsorption capacity and good magnetic properties. Finally, defluorination experiments using real surface water showed that the adsorbent effectively reduced fluoride concentration from 1.17 mg/L to less than 0.2 mg/L. In conclusion, Al-MOF@Fe₃O₄ nanocomposite can be used as adsorbent to effectively remove fluoride in surface water.