Synthesis Of Modified Mesocellular Siliceous Foams Materials And Their Adsorption Properties To Iodide

With the rapid development of the social nuclear industry,radioactive nuclear waste has unavoidable harm to humans and the environment.The radioactive iodine nuclear waste ¹²⁹I has a half-life of 1.57×10⁷years and cannot be removed by natural decay.Therefore,how to effectively prevent the difussion of radioactive iodine waste,emergency treatment and safe storage of radioactive iodine waste has become an issue that needs to be solved in the sustainable use of nuclear resources.Mesostructured cellular silica foam（MCF）is a mesoporous silicon-based material with large specific surface area,regular pore structure,large spherical pore diameter and pore volume.The spherical pore diameter can reach 50 nm and the pore volume can reach 2.4 cm³/g.The larger spherical pores are connected to each other through smaller window holes to form a three-dimensional cubic foam-like channel structure.It has the largest pore size among the currently synthesized mesoporous materials.In this paper,mesoporous foamed silicon materials were synthesized and modified by doping.A series of composite materials were synthesized and their adsorption properties for iodine ions were studied.The physical structures and chemical properties were characterized by SEM、TEM、FT-IR、EDS、XPS、XRD、BET.The main research contents are as follows:（1）Synthesizing MCF-Bi₂O₃material and bismuth-embedded in mesoporous foamed silicon（MCF）for iodine capture and storage.MCF was functionalized with thiol（-SH）groups firstly,followed by bismuth adsorption with Bi-S bonding,which was thermally treated to form Bi₂S₃within MCF.The synthesized MCF-Bi₂S₃material is calcined in air at220℃to form MCF-Bi₂O₃material.Through a series of adsorption experiments,it was found that the optimal p H value for the adsorption of iodine ions is 7;the equilibrium time is 120min;the adsorption process agreed well with the pseudo-second-order kinetics and the Langmuir models,It shows that the adsorption process of iodide ions by MCF-Bi₂O₃material is monomolecular layer adsorption,which is dominated by chemical adsorption,and the maximum adsorption capacity reached 211.76 mg/g.the adsorption process is spontaneous and endothermic.After the material was cycles five times,it still maintains a high adsorption capacity on iodine ions.（2）MCF-Ag₂O-Ag₂CO₃was prepared by the impregnation method.and the structure has not been changed during the preparation process.The material’s adsorption mechanism for iodine ions is mainly based on the oxidation-reduction process of Ag⁺and I^-to generate Ag I,while coordinating the photocatalytic oxidation process of Ag₂CO₃.Through a series of adsorption experiments,it was found that the adsorption of iodine ions by the material is little affected by the change of p H.The maximum adsorption capacity can reach 495.05 mg/g at p H4 for 50 min.The adsorption process agreed well with the pseudo-second-order kinetics and the Langmuir models,indicating that the adsorption process is dominated by chemical reaction,and the adsorption process is a spontaneous,endothermic single-layer adsorption.The repeated experiments show that the material still maintain a high adsorption capacity on iodine ions.（3）MCF-Cu₂O was successfully prepared by the hydrothermal method.In this paper,we propose to dope Cu₂O into the adsorbent to protect Cu₂O from oxidation in the air to improve its applicability.The adsorption mechanism is mainly that iodide ion replaces OH^-on the surface of MCF-Cu₂O material to form MCF-Cu₂O-I complex.Then the Cu₂O releases Cu⁺under the acidic condition to capture I^-to form Cu I.In the acidic environment,it is favorable for the release of Cu⁺,shows great adsorption capacity;and in the alkaline environment,the adsorption capacity has a greatly reduced.The maximum adsorption capacity at p H 4 for 120min;After five cycles experiments,the material still maintain a high adsorption capacity on iodine ions.The pseudo-second-order kinetics and the Langmuir models can describe its adsorption behavior,indicating that the adsorption process of the material is dominated by chemisorption process,and the maximum adsorption capacity reached 130.2 mg/g.