由单层薄水铝石制备的活性氧化铝处理水中氟离子

Defluoridation of Water Using Active Alumina Derived from Single-Layer Boehmite

合成高效低成本的氟离子吸附剂仍是具有挑战的研究课题。本文采用无有机物的方法制备了单层结构的薄水铝石,并以此薄水铝石得到大比表面积的活性氧化铝。活性氧化铝的大比表面积保证了很高的吸附效率,合成过程无有机表面活性剂或模板剂的使用,控制了成本。采用X射线衍射(XRD)及扫面电镜(SEM)等方法对样品进行了表征,发现制备的氧化铝前体为单层结构的薄水铝石,其比表面积为789.4 m^(2)∙g^(−1),焙烧后得到活性氧化铝的比表面积为678.4 m^(2)∙g^(−1),孔体积为3.20 cm^(3)∙g^(−1)。并系统研究了吸附剂用量、吸附时间等因素对活性氧化铝吸附水中氟离子的影响。研究结果表明,本文制备活性氧化铝对水中氟离子的吸附量可达67.6 mg∙g^(−1)。仅分别需0.6、1.0或2.6 g∙L^(−1)活性氧化铝就可将10、20或50 mg∙L^(−1)的氟离子溶液处理至中国饮用水标准(1.0 mg∙L^(−1))以下。并且此活性氧化铝在pH=4–9的范围内均可用于水中氟离子的处理,对吸附有较大影响的共存离子为SO_(4)^(2−)及PO_(4)^(3−),进一步研究表明,活性氧化铝对氟离子的吸附遵循准二级模型和朗格缪尔等温模型。

The preparation of high-efficiency and low-cost adsorbents for the defluoridation of drinking water remains a huge challenge.In this study,single-layer and multi-layer boehmite were first synthesized via an organicfree method,and active alumina used for fluoride removal from water was obtained from the boehmite.The advantage of a single layer is that more aluminum is exposed to the surface,which can provide more adsorption sites for fluoride.The active alumina adsorbent derived from single-layer boehmite exhibits a high specific surface area and excellent adsorption capacity.The high surface area ensures a high adsorption capacity,and the organic-free synthesis method lowers the preparation cost.The asprepared adsorbent was characterized by X-ray powder diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),Fourier-transform infrared spectroscopy(FTIR)and nitrogen adsorption-desorption analysis.The single-layer structure of boehmite was determined from the simulated XRD diffraction pattern of single-layer boehmite.The disappearance of the(020)diffraction peak of boehmite illustrates that the dimensions in the b direction are extremely small,and according to the XRD simulation results,the single-layer structure of boehmite could be determined.Single-layer boehmite with a surface area of 789.4 m^(2)∙g^(−1) was formed first.The active alumina obtained from the boehmite had a surface area of 678.4 m^(2)∙g^(−1),and the pore volume was 3.20 cm^(3)∙g^(−1).The fluoride adsorption of the active alumina was systematically studied as a function of the adsorbent dosage,contact time,concentration,co-existing anions,and pH.The fluoride adsorption capacity of the active alumina obtained from the single-layer boehmite reached up to 67.6 mg∙g^(−1),which is higher than those of most alumina adsorbents reported in the literature.The adsorption capacities of the active alumina are related to the specific surface area and the number of hydroxyl groups on the surface.Dosages of 0.6,1.0,and 2.6 g∙L^(−1) of active alumina were able to lower the 10,20,and 50 mg∙L^(−1) fluoride solutions,respectively,below the maximum permissible limit of fluoride in drinking water in China(1.0 mg∙L^(−1)),suggesting that the active alumina synthesized in this work is a promising adsorbent for defluoridation of drinking water.In addition,the fluoride adsorption is applicable in a wide pH range from 4 to 9 and is mainly interfered by SO_(4)^(2−) and PO_(4)^(3−).Further investigation suggested that the fluoride adsorption of the active alumina follows the pseudo second-order model and Langmuir isotherm model.