| The radioactive pollutant produced in the rapid development of nuclear energy is one of the most concerned issues,During the nuclear accident and spent fuel reprocessing,large amounts of nuclear sewage containing radionuclides and radioactive organic pollutant could be released.Radioactive sewage with strong migration ability is easy to be ingested by human and other biology,causing huge threat.On the other hand,radionuclides like uranium and plutonium in radio sewage are necessary to recover for cyclic utilization.As a result,removal of radioactive substance from radioactive sewage is beneficial for not only environment and human production but also recycle of resource.In order to remove radioactive substance,lots of method like chemical precipitation,membrane separation,electrochemistry,extraction,photochemistry,and adsorption,have been developed.Adsorption is regarded as the ideal method for treatment of radioactive sewage owing to is easy operation,low cost,and high efficiency.Treating radioactive sewage by adsorption requires that adsorbents possess both high adsorption capacity and fast adsorption rate.The adsorption performance of modifying chemical structure and adsorbent depends on functional groups and porous groups.By combining the synthetic strategy of optimizing physical structure,functionalizing adsorbent with suitable groups or optimizing the porous structure of the adsorbent,it is possible to obtain adsorbent with excellent adsorption properties for radioactive substances.Hierarchically porous possess pores with different size simultaneously,which endows adsorbent with both high adsorption capacity and fast adsorption rate.As a result,for obtain adsorbent with excellent adsorption performance for radioactive substance,adsorbent with hierarchically porous structure was further functionalized and the porous structure was optimized in this work.The main research contents and conclusions are as follows:1.For improving the adsorption property of commercial Reillex 425 resin for radioactive Tc(Ⅶ),a series of dicationic pyridinium(DCP)derivative groups was used to modify Reillex 425 resin.DCP groups greatly increased the adsorption capacities for Re(Ⅶ),analog of T(Ⅶ)c,under neutral condition.Moreover,the adsorption kinetic of initial and modified Reillex 425 resins was investigated.The results showed that-Py+C2H4N+Me3 with the shortest alkyl spacers could enhance intraparticle diffusion,thus the adsorption rate was efficiently accelerated.The adsorption performance of Tc(Ⅶ)on modified resin also verified this conclusion,so resin modified with-Py+ C2H4N+Me3 could meet the need for rapid decontamination.The analysis of adsorption isotherm for modified resins showed that with the increase of alkyl spacers,the utilization rate of quaternary ammonium pyridine in DCP groups increased.For-Py+C5H10N+Me3 with longest alkyl spacers,both adsorption sites could adsorb Re(Ⅶ)simultaneously,of which maximum adsorption amounts was reached 588.2 mg g-1.So resin modified with-Py+C5H10N+Me3 is suitable for treatment of sewage with high concentration of Tc(Ⅶ).As a result,modifying Reillex 425 resin with different DCP groups could efficiently enhance its adsorption property for Tc(Ⅶ),and Tc(Ⅶ)removal requirements in different scenarios could be met.2.In order to develop adsorbent with both fast adsorption rate and high adsorption capacity,diamide-pyridine-modified hierarchically porous boron nitride(HPBN-DAPy)was prepared.Initial BN hardly adsorb U(Ⅵ)owing to the lacking of functional groups,in comparison,diamide-pyridine groups endowed HPBN-DAPy with excellent adsorption ability for U(Ⅵ).Thanks to the hierarchically porous structure with both pore of 20 and 3 nm,HPBN-DAPy exhibited ultrafast adsorption for U(Ⅵ)and temporary adsorption equilibrium was reached with 0.5 min.Subsequently,U(Ⅵ)differed into small mesopores and large mesopores connected by small mesopores gradually,adsorption amount increased and reach adsorption equilibrium finally.The adsorption mechanism was investigated by analysis of adsorption isotherm.,U(Ⅵ)was chemically adsorbed in monolayer when U(Ⅵ)initial concentration was low while U(Ⅵ)was physically adsorbed in the form of polynuclear complexes as a high U(Ⅵ)initial concentration.Furthermore,HPBN-DAPy performed outstanding adsorption selectivity,salty tolerance,and reusability,which should be promising in removal of U(Ⅵ)from contaminated water.3.In order to further improve the adsorption property for U(Ⅵ)of boron nitride based adsorbent and simplify the synthesis procedure,diamide bipyridine(DABP)modified hierarchically porous carbon doped boron nitride(BCN-DABP)was prepared.BCN-DABP exhibited excellent adsorption performance for U(Ⅵ)in both weakly and strongly acidic condition.Under weakly acidic condition,DABP adsorbed UO22+through chelation,and each DABP group could adsorb two UO22+at high U(Ⅵ)concentration,the maximum adsorption amount reached 818.7 mg g-1.Under strongly acidic condition,protonated DABP adsorbed UO2(NO3)3-through electrostatic attraction,and each DABP group could adsorb two UO2(NO3)3-as well,the maximum adsorption amount reached 1296.7 mg g-1.In this condition,electrostatic attraction efficiently accelerated the boundary diffusion,thus BCN-DABP exhibited ultrafast adsorption rate for U(Ⅵ)and equilibrium was reached within 0.5 min.In addition,outstanding radiation resistance and adsorption selectivity also endowed BCN-DABP with great potential for removal of U(Ⅵ)from high level liquid waste and environmental contaminated water.4.For obtaining adsorbent with great adsorption performance for radioactive organic pollutant,reduced graphene oxide-Eu(rGO-Eu)aerogel was prepared through irradiation method.The pre-assembly induced by Eu3+ broadened the pH range and decreased absorbed dose required for gel formation.The analysis of mechanism for gel formation indicated that Eu3+ effected on not only the reduction procedure of graphene oxide(GO)but also the porous structure of aerogel.When pH=2,Eu3+inhibited the reduction of GO and equipped rGO-Eu aerogel with hierarchically porous structure,which caused high adsorption amounts and ultrafast adsorption rate for organic solvents on rGO-Eu aerogel.Meanwhile,the unique luminescence of rGO-Eu also allowed the in situ detection for certain organic solvents during adsorption.When pH=6,Eu3+promoted the reduction of GO and caused lots of macropores,the strong hydrophobicity and large specific surface area caused by which endowed rGO-Eu with high adsorption amounts for water-soluble organic pollutant.The rGO-Eu prepared by radiation reduction might be suitable as a broad-spectrum adsorbent for radioactive organic pollutants. |
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