| Food safety issues caused by heavy metal contamination have become one of the most vital issues all over the world.As（Ⅲ）that enters the food chain through agricultural production and food processing can induce a variety of human diseases.In order to effectively control the introduction of As（Ⅲ）during food processing as well as ensure food safety,it is particularly significant to exploit efficient and convenient removal technologies toward As（Ⅲ）.In this paper,a new type of FeMn-MOF-74s with the ability of simultaneous adsorption and oxidization toward As（Ⅲ）was successfully prepared using an outer and inner structural engineering strategy while the mechanism and performance of the adsorption and oxidation process were explored.The main contents carried out in this paper are as follows:（1）The amorphous FeMn-MOF-74s adsorbents were developed by a temperature-controlled crystallization method as well as an outer and inner structural engineering strategy.The stability of amorphous FeMn-MOF-74s during the adsorption process toward As（Ⅲ）in water was investigated.TEM and SEM results showed that the reaction temperature and feed ratio of metal elements have a great influence on the morphology of FeMn-MOF-74s as well as the reaction time mainly controls the particle sizes of the adsorbents.The HRTEM and XRD results showed that the crystal structure formation of FeMn-MOF-74s primarily through a thermodynamically controlled process in which the material gradually changed from an amorphous structure to a crystalline structure with increasing synthesis temperature.From BET and XPS results,it can be seen that this structural transformation has no significant effect on the specific surface area of FeMn-MOF-74s,but has a greater effect on Fe/Mn distribution.Besides,the SEM and XRD characterization of FeMn-MOF-74s after adsorption showed that the amorphous structure has a better structural stability.（2）The adsorption and oxidation performance toward As（Ⅲ）of the synthesized FeMn-MOF-74s adsorbent was investigated.The adsorption performance under different synthesis conditions was tested and the results showed that the optimal synthesis conditions included a synthesis temperature of 120°C,a Fe/Mn feed ratio of 3/10 and a reaction time of 24 hours.The adsorption properties of optimized materials under different p H conditions were explored and the results showed that the synthesized FeMn-MOF-74s had the best adsorption performance toward As（Ⅲ）at p H 7.Detailed kinetic and isotherm studies further proved that the optimized FeMn-MOF-74s adsorbent for As（Ⅲ）is a combination of multilayer adsorption and chemisorption,showing a high adsorption capacity of 161.6 mg/g.After 4 consecutive repeated uses,the adsorption performance of the optimized FeMn-MOF-74s adsorbent remained above 90%.In the presence of coexisting anions,the adsorption performance did not significantly decrease.The oxidation performance of As（Ⅲ）by FeMn-MOF-74s is mainly verified by XPS.The results showed that different surface distributions of Fe/Mn elements cause significant differences in oxidizing ability.A high proportion of manganese elements would lead to better oxidation performance.By analyzing the results of FTIR and XPS,the adsorption and oxidation mechanism of As（Ⅲ）on FeMn-MOF-74s mainly includes:As（Ⅲ）is mainly adsorbed on the surface of FeMn-MOF-74s through hydroxyl substitution and bonding with H bonds.Via the redox reactions with low-coordinated Mn4+and Mn3+nodes in the adsorbents,the effective oxidation of As（Ⅲ）to As（V）can be definitively achieved at the solid-liquid interfaces.The amorphous structure of optimized FeMn-MOF-74s adsorbents provides many low-coordination adsorption sites and uniformly distributed active sites,which contributes to the removal capacity toward As（Ⅲ）.The exploitation of FeMn-MOF-74s can not only effectively remove As（Ⅲ）from water,but also reduce its toxicity by oxidizing As（Ⅲ）,which provides new ideas for ensuring water resources security and food safety. |
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