Supramolecular Functional Materials And The Study On Uranium Adsorption

Resources and environment are two eternal themes of contemporary social development.Faced with the increasing energy demand,nuclear energy has been a green energy with great potential in the future.A small amount of nuclear fuel can produce a huge amount of electric energy needed by people in nuclear power plants,and its power generation process is low-carbon,environmentally friendly and almost zero emission.Nuclear energy is one of the most ideal energy on the way of human development in the future.To ensure the long-term sufficient supply of nuclear fuel,it is imperative for uranium recovery from seawater.Although hydrogel-based sorbents can be very ideal as uranium sorbents due to their superior hydrophilicity and designability,in order to improve the performance of polyamidoxime-based（PAO）and other amidoxime-based functionalized polymerization due to the hydrophilicity of the sorbent,additional hydrophilic gel with three-dimensional（3D）networks are usually introduced,and these additional networks account for the high mass percentage of the sorbent so that it is difficult to achieve the ultra-high uranium adsorption efficiency of the sorbent material.For this unavoidable key technical problem in the research of uranium extraction from seawater,a new type of supramolecular hydrogel adsorbent with high adsorption capacity were designed in this study.On this basis,the introduction of antibacterial active nano-oxides can endow the adsorption materials with additional functions to resist the influence of complex microorganisms in the real marine environment,thereby improving their adsorption performance of uranium in natural unfiltered seawater;more importantly,this kind of hydrogel-based raw material is cheap,and the operation process is simple,which is convenient for later industrial production.Although uranium species are a limited strategic alternative resource for nuclear energy,their presence poses a huge threat to ecology and human health and safety due to their long-time radionuclides and toxicity,rapid uranium nuclides removal and recovery from the environment are a priority,hydrogen-bonded organic frameworks（HOFs）have emerged as the most promising candidates for ultrafast uranium recovery from uranium-containing wastewater due to selective recognition and abundant exposed active sites.Therefore,it is of great significance to develop high-efficiency adsorption and excellent selective materials for the uranium nuclides removal and recovery from nuclear wastewater,and the main research contents are as follows:（1）A mild and simple method for successfully preparing a new ionic crosslinked Zn²⁺-PAO supramolecular hydrogel is explored,which exhibited ultra-high and ultra-fast uranium adsorption properties.Compared with existing oxime-based adsorbents,the hydrogel has a high PAO content（≈96 wt%dry gel）and good hydrophilicity,enabling it to achieve ultra-high uranium adsorption performance（The saturated adsorption capacity is 1188±18.9 mg/g in 32 ppm uranium-spiked aqueous solution）.More importantly,after 4 weeks of immersion in natural seawater,the uranium adsorption of the Zn²⁺-PAO hydrogel membrane reached9.23±0.52 mg/g,and the average adsorption rate was 0.330±0.019 mg/g/day,which made it be a candidate material for large-scale ultra-high and ultra-fast uranium extraction from seawater.（2）On the basis of the research on supramolecular hydrogels in the previous research,in view of the problem that much bacteria and microorganism in seawater which can damage the hydrogel-bsaed adsorption materials for a long time,we further introduce a kind of antibacterial active nanomaterial.The introduction of vanadium pentoxide（V₂O₅）nanowires with strong antibacterial activity and super hydrophilicity can directly entangle and crossing-link with PAO to form nanocomposite supramolecular hydrogels,which endow the hydrogels with excellent antibacterial properties and uranium extraction performance,the saturated uranium adsorption amount can reach 986.31 mg/g after being adsorbed in 32 ppm uranium-spiked aqueous solution for 144 hours.After 6 weeks of adsorption in natural seawater containing much bacteria and microorganism,the uranium adsorption performance of V₂O₅NW-PAO supramolecular hydrogel can reach 7.69 mg/g,and the equilibrium absorption capacity is 16.38%higher than that of the blank control group.This low-cost,environment-friendly antibacterial supramolecular nanocomposite hydrogels are expected to achieve large-scale uranium recovery from seawater in the future.（3）We employed crystalline MA-TA HOFs nanowires with precise molecular structure as adsorbents for fast and selective uranium adsorption from low-concentration uranium-containing aqueous solutions and simulated radioactive effluents.Ultrafast and ultra-high adsorption capacity of 601.40 mg/g has been achieved in 10 min in acid aqueous solution under 8 ppm uranium-cotaning aqueous solution.And the above excellent adsorption performance can be better explained from the molecular structure of MA-TA HOFs.In addition to the excellent adsorption performance,the low-concentration uranium adsorption in this work can drive the microstructure of the adsorbent material from one-dimensional（1D）nanowires to two-dimensional（2D）ultrathin nanosheets（3.6 nm）with specific nanostructures.The transformation is more simple,which can provide a simple and controllable method for the construction of 2D materials.This specific nanostructure transformation is unique to uranyl adsorption,and related structural analysis methods have also confirmed the excellent adsorption and adsorption-induced structural transformation process in detail.