Controllable Synthesis Of Silica-based Mesoporous Materials And Their Adsorption Properties For Nuclides

A large amount of radioactive waste water produced in the process of the development and utilization of nuclear energy and nuclear technology,which is a serious threat to human health and environment.It has become one of the bottlenecks of the sustainable development of nuclear energy,which needs to be treated safely and effectively.Up to now,the adsorption method is considered to be an effective and promising radioactive wastewater treatment method,the key of which is the adsorbent material.Therefore,the design and development of efficient adsorbent materials and the study of their nuclides adsorption behavior are hot and difficult issues in the field of radioactive wastewater treatment.Mesoporous materials have been widely used in the field of adsorption due to their large specific surface area and pore size,easy functionalization and doping,and good irradiation stability.Controlled synthesis of mesoporous materials,such as morphology,channel length and composition,can not only broaden its application field,but also improve its application performance.In order to solve the problems of low efficiency,irreversible adsorption,poor selectivity and high cost of traditional adsorbents,silica-based mesoporous materials with good adsorption performance have been synthesized by a simple method,and their adsorption performance toward the main nuclides?uranium,strontium and cesium?contained in radioactive wastewater was studied.These results can provide theoretical and experimental basis for the treatment of radioactive wastewater.This paper is focused on the following three goals:first,design and development of a new type of silica-based mesoporous adsorbent materials with efficient adsorption capacity for specific radionuclides;secondly,exploring a new method for controllable synthesis of new silica-based mesoporous materials;finally,investigating the nuclides adsorption behaviors of silica-based mesoporous materials.The main works are as follows:1.Mesoporous SBA-15 materials with different morphologies?fiber,rod and platelet?were synthesized by simple method and their adsorption capacities of uranium was studied.The obtained mesoporous SBA-15 samples were characterized and analyzed by XRD,SEM,TEM and BET.The results demonstrated that the obtained materials exhibited regular morphology,high ordered mesoporous structure and large specific surface area.The effects of initial solution pH,time,temperature,initial U?VI?concentration and morphology on the adsorption properties were studied.The results showed that the morphology of mesoporous SBA-15 has a great influence on the adsorption behavior of uranium.SBA-15with plate-like morphology shows a fast adsorption rate?10 min to reach equilibrium?and a large adsorption capacity?up to 401 mg/g?for U?VI?because of its short channel.It was found that the adsorption processes of U?VI?on mesoporous SBA-15 were well described by Langmuir model and pseudo-second-order kinetic model.The thermodynamic analysis showed that the adsorption of U?VI?by mesoporous SBA-15 is a spontaneous and exothermic process dominated by physical adsorption.In the range of experimental temperature,increasing the temperature is not benefit to the adsorption of U?VI?by mesoporous SBA-15.Furthermore,the disorder of the interface of solid-liquid was reduced in the process of adsorption of U?VI?.2.Mesoporous SBA-15 materials with controllable size were synthesized by using different types of acid?HCl,H₂SO₄ and H₃PO₄?as medium and cheap quartz powder as silicon source,and their adsorption properties of U?VI?were studied.The effects of the type of acid on the microstructure and morphology of mesoporous SBA-15 were studied.The results showed that the type of acid affected the structure and morphology of the obtained mesoporous SBA-15,and the length and width of rod-like mesoporous SBA-15 particles increased with the increase of the number of H in acid molecular.The effects of initial solution pH,time,temperature,initial U?VI?concentration and SBA-15 channel length on the adsorption properties were studied.The results indicated that the maximum U?VI?adsorption capacities of mesoporous SBA-15 prepared by HCl,H₂SO₄ and H₃PO₄ was 210 mg/g,223 mg/g and 235 mg/g,respectively.The adsorption processes of U?VI?by mesoporous SBA-15 were well described by Langmuir model and pseudo-second-order kinetics model.The adsorption of U?VI?on mesoporous SBA-15 was a spontaneous and exothermic process dominated by physical process.In the process of adsorption of U?VI?,the disorder of the interface of solid-liquid decreased.3.Ammonium 12-Molybdophosphate(AMP,?NH₄?₃[P(MO₁₂O₄₀)])was loaded on mesoporous SBA-15materials with different morphologies?platelet,rod and fiber?.Mesoporous AMP/SBA-15 composites with different morphologies were fabricated and their Cs⁺adsorption capacities were studied.The effects of AMP loading amount,SBA-15 morphology,adsorption time,pH value,temperature,initial Cs⁺concentration and coexisting interfering cations on Cs⁺adsorption were investigated.The results showed that the morphologies of mesoporous SBA-15 have a certain influence on the adsorption capacity of Cs⁺,and the adsorption capacity and rate of Cs⁺increased with decreasing the length of the channel.The interfering cations in solution including Na⁺,K⁺,Ca²⁺and Mg²⁺have little influence on the Cs⁺adsorption process,and AMP/SBA-15 has good adsorption selectivity for Cs⁺.The process of Cs⁺adsorption on AMP/SBA-15'conformed to Langmuir model and pseudo-second-order kinetic model,which is a spontaneous and endothermic ion exchange process,and the disorder of the interface of solid-liquid increased during the Cs⁺adsorption process.4.Mesoporous AMP/SBA-15 composites were prepared for the first time by one-step method using phosphomolybdic acid?PMA?as acid medium,and its Cs⁺adsorption capacities were studied.The effect of PMA content on the morphology and microstructure of mesoporous AMP/SBA-15 was investigated.It was found that the amount of PMA has a great influence on the morphology and microstructure of mesoporous AMP/SBA-15.With the increase of PMA,the ordered degree of mesostructure of AMP/SBA-15 decreased.The leaching rate of AMP in the AMP/SBA-15 composites obtained from one-step method was low,indicating their good stability.Furthermore,the incorporating rate of AMP in samples obtained by one-step method was much higher than that of two-step method.The adsorption of Cs⁺by AMP/SBA-15 conformed Langmuir model and pseudo-second-order kinetic model,which was a spontaneous and endothermic process dominated by ion exchange.The disorder of the interface of solid-liquid increased during the process of Cs⁺adsorption.These results demonstrated that the AMP/SBA-15 adsorbents prepared by one-step method have good reusability.5.A new type of short channel mesoporous MnO₂/SBA-15 inorganic ion exchanger materials were synthesized by immersing SBA-15 in the mixture solutions of KMnO₄ and MnCl₂,and their Sr²⁺adsorption capacities were studied.The effects of solution pH,adsorption time,Sr²⁺concentration,temperature and MnO₂ content on the Sr²⁺adsorption were investigated.It was found that the adsorption capacity of Sr²⁺by mesoporous MnO₂/SBA-15 increased with the increase of pH value,MnO₂ content and temperature,and the Sr²⁺adsorption capacity of SBA-15 was greatly improved by doping MnO₂.Different equilibrium isotherms,kinetic and thermodynamic models were used to study the experimental data of Sr²⁺adsorption.These results showed that Langmuir model can well describe the experimental data of Sr²⁺adsorption.According to Langmuir model,the maximum Sr²⁺adsorption capacity was found to be 75.1mg/g at 283 K.The kinetic analysis exhibited that the Sr²⁺adsorption conformed to the pseudo-second-order kinetic model.In addition,the thermodynamic parameters?G,?H and?S of the adsorption process showed that the Sr²⁺adsorption on MnO₂/SBA-15 was a spontaneous and endothermic process combining physical and chemical processes,and the disorder of the interface of solid-liquid increased during the Sr²⁺adsorption process.