Research On Adsorption Performance Of Radionuclide U(?) On Core-shell Layered Double Hydroxides

With ever-lasting spotlight about global warming and the depletion of natural resources,nuclear power,a clean energy without greenhouse gas emission,has been regarded as a crucial source in energy system.The predominant nuclear fuel resources is uranium,and has inevitably released into environment,which has caused great threat to the safety of humans and other species.Therefore,taking the aspects of energy security and environmental protection into consideration,it is of importance to remove and reduce the potential toxicity of U(VI).By virtue of their special physicochemical performances,including good dispersity,excellent anion exchange ability,ideal specific surface and favourable biocompatibility,layered double hydroxides,a kind of advanced adsorbent,has become a research hotspot at home and abroad.Core-shell material,a new functional material,endowed the dual synergistic effect,and thus promising application in environmental pollutant treatment.In this paper,we synthesized core-shell Si O2@LDH,Fe3O4@LDH and Fe3O4@PDA@LDH nanocomposite which was used as U(VI)scavenger to evaluate their environmental implications and interaction mechanism in various ambient conditions.The specific methods and conclusions were as follows:(1)The monodispersed Si O2@LDH nanocomposite was prepared by co-precipitation method,and characterized by X-ray diffraction(XRD),field emission scanning electron microscopy(FE-SEM),Fourier transformed infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS)in detail.Batch adsorption experiment results indicated that the adsorption of U(VI)was strongly dependent on p H,and weakly dependent on ionic strength,demonstrating that the interaction of U(VI)was mainly dominated by inner-sphere surface complexation.The kinetics adsorption of U(VI)followed the pseudo-second-order model well with the 98% removal efficiency.The adsorption isotherms of U(VI)on Si O2@LDH was perfectly fitted by the Langmuir model,and the maximum adsorption capacities of Si O2@LDH were calculated to be 303.1 mg/g at p H=5.0.Moreover,the thermodynamic parameters revealed that the adsorption of U(VI)was spontaneous and endothermic process.The interaction mechanism between U(VI)and Si O2@LDH was attributed to the electrostatic interaction and surface complexation.(2)The magnetic layered double hydroxide nanoparticles(Fe3O4@LDH)were synthesized via a mild hydrothermal method,and used it as efficient environmental scavenger for the U(VI)enrichment.under various conditions.The results displayed that the interaction of U(VI)with Fe3O4 and Fe3O4@LDH were significantly dependent on p H and independent of ionic strength.Kinetic study revealed the U(VI)adsorption on Fe3O4 and Fe3O4@LDH were well simulated by pseudo-second-order model.The U(VI)adsorption on Fe3O4 and Fe3O4@LDH were perfectly fitted by Langmuir model,and the maximum adsorption capacity of Fe3O4@LDH(Qmax = 142 mg/g)was much higher than that of Fe3O4(Qmax = 34 mg/g)at p H=5.The thermodynamic parameters calculated from temperature-dependent isotherms showed that the adsorption was spontaneous and exothermal processes.Leaching test demonstrated that the Fe3O4@LDH hollow microspheres exhibited excellent regeneration performance,and the interaction mechanism was ascribed to the electrostatic interaction and surface complexation.(3)The hierarchical LDH onto polydopamine-encapsulated hollow Fe3O4 microspheres(MPL)were synthesized via a polymerization deposition process of dopamine and mild hydrothermal method,and thoroughly investigated with techniques such as TEM,SEM,XRD,XPS and so on.Compared with Fe3O4,MP and other MPx Lx materials,MP2L2 endowed highest adsorption capacity.The experimental results showed that the adsorption was significantly affected by p H value rather than ionic strength.The adsorption kinetics can be perfectly depicted by the pseudo-second-order model with high uptake percentage of 94.8%.More importantly,the maximum adsorption performance can be tuned by changing the thickness of polydopamine shell and the content of LDH,in the order of MP2L2(344 mg/g)> MP2L3(291 mg/g)> MP3L2(245 mg/g)> MP2L1(211 mg/g)> MP1L2(141 mg/g)> MP2(71 mg/g)> Fe3O4(34 mg/g)at 298.15 K and p H 5.0.The desorption experiments of MP2L2 were conducted by adopting 0.1 M Na2CO3 solution as desorbing agent.It was worthwhile to note that the adsorption efficiency of U(VI)on MP2L2 was still over ~85% after five cycles.The interaction of U(VI)with MP2L2 was mainly dominated by surface complexation owing to the multiple functional groups including imine,catechol,amine,and hydroxyl groups.In this paper,a novel bifunctional MP2L2 nanoparticles were synthesized with Si O2 as well as Fe3O4 as core and layered double hydroxide as shell,and used their as outstanding adsorbents to capture highly toxic uranium,aiming to provide new insights into practical U(VI)-contaminated media treatment via an MP2L2 hollow microspheres.