The Adsorption Research Of Hg²⁺ Over The MOFs By The AFS

With the development of industrialization, water pollution is becoming more and more serious. Mercury is one of the most poisonous chemicals in the environment because of its toxicity and bioaccumulation.Even trace concentration of mercury will also pose a great threat to human. In present, it is an arduous task to develope a more sensitive method for trace Hg2+ determination and its faster removal.In this paper, by optimizing the measurement parameters, the optimal detection conditions of atomic fluorescence spetrometer are obtained. The adsorption experiments of Hg2+ onto the MOFs materials(MOF-74, UIO-66-(OH)2, UIO-66-NH2) were studied, which were characterized by XRD, FT-IR, and TG.The adsorption performances of these MOFs materials for trace mercury were investigated by AFS. The results showed that the adsorption processes of Hg2+ over these MOFs materials are spontaneous; moreover, the adsorption capacity is affected by pH, time,temperature and concentration of Hg2+. Under the optimal conditions, the maximum adsorption capacity of MOF-74, UIO-66-(OH)2 and UIO-66-NH2 for Hg2+ are 63.0 mg/g,90.4 mg/g and 52.5 mg/g, respectively, which indicated that –OH group has stronger affinity with Hg2+ than –NH2. In this study, the adsorption of Hg2+ onto MOF-74, UIO-66-(OH)2 and UIO-66-NH2 were followed the pseudo-second-order kinetic model. The initial adsorption rates are 0.03 mg·g-1·min-1, 0.07 mg·g-1·min-1, 0.04 mg·g-1 ·min-1 respectively,which suggested that chemisorption might have controlled the entire adsorption process of Hg2+. Through comparing experiment dates of Langmuir isotherm and Freundlich isotherm, it can be observed that the Langmuir isotherm plot gives a fairly good fit. So it could be concluded that the adsorption behavior of Hg2+ onto MOF-74 and UIO-66-(OH)2 was homogeneous and monolayer. The adsorption of Hg2+ over UIO-66-NH2 well fits both Langmuir isotherm model and the Freundlich isotherm model. Batch adsorption studies were performed on several trace initial mercury concentration( c0(Hg2+)=20 μg·L-1,40 μg·L-1,50 μg·L-1). The removal efficiencies were at 45℃: 54.48 % for 20 μg·L-1, 69.71 % for 40 μg·L-1, 72.26 % for 50 μg·L-1. Comparing with UIO-66-(OH)2 and UIO-66-NH2 materials, MOF-74 showed a higher removal efficiency for trace concentration of Hg2+.In this work, the results showed that UIO-66-(OH)2 has better adsorption capacity on the high concentration of Hg2+; however in the case of trace concentration, removal efficency of Hg2+ over MOF-74 is much higher. Therefore, adsorption capacity of mercury in solution was different, due to its different functional groups and structures of MOFs adsorbent. The meaning of research in this paper is of certainly great significance on treatment of mercury ions in industrial waste water and drinking water.