| Excessive boron in water has great harm to animals,plants,and humans,which should be removed before emission.While,the high abundance boron-10 isotope is of great significance for nuclear power and military industry as its ability to stabilize neutrons.However,the removal and isotopic separation has always been subjects of widespread concern.In this paper,the performance of boron removal and isotope separation was explored through the prepared magnetic magnetite nanoparticles(MMN),and the mechanism was studied by combining experimental characterization and quantum chemistry calculation.In this paper,the optimized co-precipitation method was used to synthesize magnetic nanoparticles with nice properties,which were used to carry out boron adsorption and boron isotope separation studies,including the adsorption kinetics,isotherms,thermal kinetics analysis and cyclic desorption.In addition,the research experimentally characterizes the changes of atoms,functional groups and chemical bonds before and after the adsorption of boric acid on magnetic nanoparticles at different pH.Quantitative analysis of the experimental results was employed to explore the separation mechanism of boron isotope,which could explain the changes in the boron capacity on MMN and the isotope separation factor with pH.Then,the quantum chemical density functional theory(DFT)calculation is further used to theoretically explore the adsorption and isotope separation of boric acid by magnetic nanoparticles at different pH.An equivalent HMMN model is established to calculate the energy change(ΔE)before and after HMMN combined with boric acid in different ways.The frequency calculation method was used to calculate the Gibbs free energy change(ΔG)of the isotope exchange reaction,and the mechanism of the adsorption and isotope separation of boric acid by magnetic nanoparticles at different pH was further obtained.The experimental results and theoretical investigations in this article show that the method used to synthesize magnetic nanoparticles in this paper is economical and the product has strong para magnetism.The adsorption capacity for boron reaches the maximum value of 4.57 mmol/g and the boron isotope separation factor can reach 1.332,which is currently reported as an adsorbent with a large amount of boron adsorption and isotope separation factor.The adsorption of boron on MMN is a spontaneous endothermic process in which entropy becomes a driving force.The adsorption process formed the Fe-O-B coordination bond through dihydroxy complexation.When pH<=pHzpc and pH>pHzpc,the magnetic particles were adsorbing[B(OH)4]-and H3BO3 selectively.DFT calculations show that the complex formed by the complexation of dihydroxyl has higher chemical stability,and the hydroxyl on Fe(Ⅲ)is the main adsorption site of boric acid.The selectivity of magnetic nanoparticles to boric acid structure at different pH is mainly due to the low energy required for the adsorption path.Boron-10 tends to exist in the form of four-coordinated boric acid.Therefore,the MMN has a higher isotopic separation factor of the material when pH<=pHZpc.The magnetic nanoparticles had great potential for boron adsorption and boron isotope separation and this study would pave a new way for future theoretical research and practical applications in this field. |
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