Functionalization Of Novel Materials And Efficient Extraction Of Radionuclide Uranium From Water

Uranium is the key element for the development of the nuclear industry.The efficient enrichment and extraction of uranium from water has important practical and strategic significance in environmental remediation and the improvement of uranium resource utilization.Exploring and developing advanced materials and methods to extract uranium from waters has become a research hotspot in recent years.Adsorption has attracted much attentions among many uranium extraction techniques due to its simple process,low cost and satisfying efficiency.The preparation of adsorbent is the core technology of adsorption technique.The structural optimization and functional modification of adsorbent is necessary for improving its adsorption performance for uranium.In this work,three kinds of novel phosphorylated composites were designed and prepared by introducing phosphate groups or ligands that bind to uranium with specificity and high affinity.The extraction performance and mechanism of these materials for uranium in aqueous solution were carefully investigated.Besides,considering that uranium is a variable valence element,the extraction can be achieved by regulating its valence state to generate insoluble uranium compounds.Therefore,a novel Sn-based semiconductor composite with unique hollow cubic structure was designed and used as a catalyst.Combined the piezo catalytic reduction-oxidation method and achieved the high efficient extraction of uranium for the first time.The performance and mechanism of piezo catalytic uranium extraction were deeply explored.The research topics and the corresponding results are described as follows:1.A fully phosphorylated 3D porous graphene oxide foam（phos-GOF）was prepared by a facile hydrothermal method.phos-GOF can efficiently enrich and extract U（Ⅵ）from aqueous solution.The adsorption equilibrium can be reached within 5 minutes.The solution pH greatly affects the adsorption performance of phos-GOF towards U（Ⅵ）.The Langmuir model fitted the adsorption isotherm well with a maximum adsorption capacity of～483 mg/g.In addition,the phos-GOF still maintained a high adsorption efficiency after 5 consecutively adsorption-desorption cycles.The phosphate group introduced by phytic acid loading on phos-GOF is the main binding site for U（Ⅵ）,which captured uranium through the formation of stable complex between U（Ⅵ）and phosphate sites.2.The calcination-intercalation method was adopted to prepare a series of phytic acid-modified layered oxide composites（Zn-Al-Ti LMO@PAs）by varying the pH values of intercalation reaction system.The Zn-Al-Ti LMO@PAs showed good adsorption performance.The experimental results indicated that the introduced PA component contributed the most to the adsorption performance of composites by compared with raw material.Among them,Zn-Al-Ti LMO@PA5 exhibited the optimal U（Ⅵ）adsorption performance,which is very fast,efficient and highly selective.The saturated adsorption capacity is estiamted to be～1500 mg/g.The adsorption process conformed to the pseudo-second-order rate equation and Langmuir adsorption model.The superior adsorption performance of Zn-Al-Ti LMO@PA5 stemed from its abundant adsorption sites and strong surface complexation effect.3.In order to further improve the environmental friendliness of adsorbent,chitosan（CS）and cellulose（CMC）,which are abundant and non-toxic,were selected as precursors.A green and safe phosphorylated composite of CSP-CMCP was prepared by cross-linking reaction between phosphorylated CS and CMC.CSP-CMCP has excellent stability within a wide pH range,and exhibited good enrichment performance and excellent adsorption selectivity for U（Ⅵ）.It has a maximum U（Ⅵ）adsorption capacity of～977 mg/g and showed extremely high affinity for selectively U（Ⅵ）capture from simulated wastewater with the coexistence of multiple competing metal ions.The complexation between the phosphate site and uranium was considered to be the main interaction mechanism.In addition,a small fraction of U（Ⅵ）can be reduced to U（Ⅳ）for immobilization.4.The uranyl ion was successfully extracted from aqueous solution by a novel piezo catalytic reduction-oxidation process and immobilized on the surface of Zn₂SnO₄/SnO₂（ZSO/SO）in the form of（UO₂）O₂·2H₂O（s）.Through systematic study and analysis of the piezo catalytic experimental,it is confirmed that the piezo catalytic process is controlled by three steps of adsorption,reduction and oxidation.U（Ⅵ）is first adsorbed on the surface of ZSO/SO,and then reduced by piezo generated free electrons to form UO₂（s）.These electrons can also react with dissolved oxygen in water to produce active H₂O₂,which can re-oxidize UO₂（s）into（UO₂）O₂·2H₂O（s）.The uranium piezo catalytic extraction rate could reach～90%under the ultrasonic waves（40 kHz,120 W）within 5 h and only decreased by～3%after four cycles.The research results in this work provide abundant experimental basis and theoretical support for the development of novel uranium extraction technologies and materials,pollution control of uranium-containing wastewaters,and the extraction of strategic resource uranium from waters.