Preparation Of Fe-Mn Composite MOFs And Research On Its Removal Effect On Arsenic In Water

Arsenic contamination is an important environmental problem in China and even around the world,especially in remote rural areas of China,where some residents still directly use untreated groundwater or surface water as drinking water sources,which seriously endangers the health of the nation.The use of Metal-Organic Frameworks（MOFs）to remove arsenic from water by adsorption is one of the current research trends.In this study,two kinds of Fe-Mn composite MOFs named MnO₂@Fe-BTC and KMnO₄@Fe-BTC,were prepared by mild and environmentally friendly reaction conditions,and their efficiency and mechanism of arsenic removal from water were investigated.The main conclusions obtained are as follows:MnO₂@Fe-BTC with a large specific surface area（352.16 m²/g）was prepared by the HF-free solvothermal method;the optimal Fe-Mn ratio of this material for the arsenic adsorption process was 2:1,the dosage was 100 mg/L,and the speed of the thermostatic oscillator was 150 rpm,and the removal rates of As（Ⅲ）and As（Ⅴ）with an initial concentration of 2 mg/L was 92.67%and 91.84%.The maximum adsorption capacity was 75.31 mg/g and 59.65 mg/g,respectively;the adsorption process was significantly inhibited by alkaline conditions and the presence of PO₄^3-;after five cycles,the removal rate of the material was only about 20%for both kinds of arsenic.Its regeneration performance was poor.The KMnO₄@Fe-BTC material was prepared by mechanical synthesis at room temperature.The material has an amorphous structure with a folded surface and uneven pore distribution,a specific surface area of 263.7490 m²/g and a pore volume of 0.2598 cm³/g.The removal rate of As（Ⅲ）and As（Ⅴ）at an initial concentration of 2 mg/L was 95.18%and 96.43%with an optimum molar ratio of 2:1 and a dosage of 100 mg/L.The maximum adsorption capacity of As（Ⅲ）and As（Ⅴ）was 73.70 mg/g and 84.62 mg/g,respectively.As（Ⅴ）is removed by adsorption through the generation of complexes by electrostatic interaction and internal ligand exchange,while for As（Ⅲ）,it is oxidized to As（Ⅴ）by the Mn component in the material first,and then adsorbed by electrostatic interaction and ligand interaction,finally achieving efficient removal of As（Ⅲ）and As（Ⅴ）.Compared with MnO₂@Fe-BTC,KMnO₄@Fe-BTC has the advantages of high removal rate and good regeneration performance.A continuous flow adsorption column was designed for the removal of arsenic.KMnO₄@Fe-BTC was used as the packing material of the adsorption column,and its effect on the penetration of arsenic adsorption under different conditions was investigated.The results showed that when the height of the adsorption column was 20 cm,the initial concentration of arsenic solution was 500μg/L,the flow rate was0.5 m L/min,the adsorbent dosage was 50 mg,and the p H was 7.0±0.1,the adsorption penetration time and saturation time during dynamic adsorption were the longest.In other words,reducing the flow rate,increasing the adsorption column and increasing the adsorbent dosage can effectively prolong the adsorption penetration time and saturation time of arsenic,so that the adsorbent can be utilized for a longer period of time.This study provides theoretical support for the practical application of adsorbents.