The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure...The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure(EXAFS) techniques.Macroscopic measurements show that the adsorption is ionic strength dependent at pH < 6.0,but ionic strength independent at pH > 6.0.The presence of humic acid(HA) /fulvic acid(FA) increases Eu(Ⅲ) adsorption on TNTs at low pH,but reduces Eu(Ⅲ) adsorption at high pH.The results of EXAFS analysis indicate that Eu(Ⅲ) adsorption on TNTs is dominated by outer-sphere surface complexation at pH < 6.0,whereas by inner-sphere surface complexation at pH > 6.0.At pH < 6.0,Eu(Ⅲ) consists of ～ 9 O atoms at REu?O ≈ 2.40 in the first coordination sphere,and a decrease in NEu-O with increasing pH indicates the introduction of more asymmetry in the first sphere of adsorbed Eu(Ⅲ).At long contact time or high pH values,the Eu(Ⅲ) consists of ～2 Eu at REu-Eu ≈ 3.60 and ～ 1 Ti at REu-Ti ≈ 4.40 ,indicating the formation of inner-sphere surface complexation,surface precipitation or surface polymers.Surface adsorbed HA/FA on TNTs modifies the species of adsorbed Eu(Ⅲ) as well as the local atomic structures of adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids.Adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids forms both ligand-bridging ternary surface complexes(Eu-HA/FA-TNTs) as well as surface complexes in which Eu(Ⅲ) remains directly bound to TNT surface hydroxyl groups(i.e.,binary Eu-TNTs or Eu-bridging ternary surface complexes(HA/FA-Eu-TNTs)).The findings in this work are important to describe Eu(Ⅲ) interaction with nanomaterials at molecular level and will help to improve the understanding of Eu(Ⅲ) physicochemical behavior in the natural environment.展开更多
In this paper,the macroscopic interaction method and high resolution EXAFS technique with a bent crystal analyzer were combined to study Eu(Ⅲ)interaction mechanism and microstructure withγ-MnOOH as a function of pH....In this paper,the macroscopic interaction method and high resolution EXAFS technique with a bent crystal analyzer were combined to study Eu(Ⅲ)interaction mechanism and microstructure withγ-MnOOH as a function of pH.The results indicated that Eu(Ⅲ)interaction withγ-MnOOH was apparently dependent on pH but independent of ionic strength,suggesting the formation of inner-sphere surface complexation for Eu(Ⅲ)ontoγ-MnOOH.Results of EXAFS analysis indicated that Eu was surrounded by^9.0 O atoms in first coordination shell at REu–O≈2.40,and second shell of Mn atoms at REu–Mn≈3.60 was observed for the three adsorption samples.These findings suggested formation of a bidentate surface complex with Eu(Ⅲ)bonding by edge sharing to MnO6-octahedron on γ-MnOOH surface.Both the macroscopic interaction data and the molecular level evidence of Eu(Ⅲ)microstructure at the γ-MnOOH-water interface should be factored into better understanding the fate and mobility of Eu(Ⅲ)and related radionuclides in the natural soil and water environment.展开更多
基金supported by the National Natural Science Foundation of China(20907055,20971126 & 21077107)the National Basic Research Program of China(2007CB936602 & 2011CB933700)
文摘The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure(EXAFS) techniques.Macroscopic measurements show that the adsorption is ionic strength dependent at pH < 6.0,but ionic strength independent at pH > 6.0.The presence of humic acid(HA) /fulvic acid(FA) increases Eu(Ⅲ) adsorption on TNTs at low pH,but reduces Eu(Ⅲ) adsorption at high pH.The results of EXAFS analysis indicate that Eu(Ⅲ) adsorption on TNTs is dominated by outer-sphere surface complexation at pH < 6.0,whereas by inner-sphere surface complexation at pH > 6.0.At pH < 6.0,Eu(Ⅲ) consists of ～ 9 O atoms at REu?O ≈ 2.40 in the first coordination sphere,and a decrease in NEu-O with increasing pH indicates the introduction of more asymmetry in the first sphere of adsorbed Eu(Ⅲ).At long contact time or high pH values,the Eu(Ⅲ) consists of ～2 Eu at REu-Eu ≈ 3.60 and ～ 1 Ti at REu-Ti ≈ 4.40 ,indicating the formation of inner-sphere surface complexation,surface precipitation or surface polymers.Surface adsorbed HA/FA on TNTs modifies the species of adsorbed Eu(Ⅲ) as well as the local atomic structures of adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids.Adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids forms both ligand-bridging ternary surface complexes(Eu-HA/FA-TNTs) as well as surface complexes in which Eu(Ⅲ) remains directly bound to TNT surface hydroxyl groups(i.e.,binary Eu-TNTs or Eu-bridging ternary surface complexes(HA/FA-Eu-TNTs)).The findings in this work are important to describe Eu(Ⅲ) interaction with nanomaterials at molecular level and will help to improve the understanding of Eu(Ⅲ) physicochemical behavior in the natural environment.
基金Financial supports from the National Natural Science Foundation of China(1117524421207092)+1 种基金the project of Chinese Academy of Sciences(KJCX2-YW-N43)973 projects(2011CB933700)are acknowledged
文摘In this paper,the macroscopic interaction method and high resolution EXAFS technique with a bent crystal analyzer were combined to study Eu(Ⅲ)interaction mechanism and microstructure withγ-MnOOH as a function of pH.The results indicated that Eu(Ⅲ)interaction withγ-MnOOH was apparently dependent on pH but independent of ionic strength,suggesting the formation of inner-sphere surface complexation for Eu(Ⅲ)ontoγ-MnOOH.Results of EXAFS analysis indicated that Eu was surrounded by^9.0 O atoms in first coordination shell at REu–O≈2.40,and second shell of Mn atoms at REu–Mn≈3.60 was observed for the three adsorption samples.These findings suggested formation of a bidentate surface complex with Eu(Ⅲ)bonding by edge sharing to MnO6-octahedron on γ-MnOOH surface.Both the macroscopic interaction data and the molecular level evidence of Eu(Ⅲ)microstructure at the γ-MnOOH-water interface should be factored into better understanding the fate and mobility of Eu(Ⅲ)and related radionuclides in the natural soil and water environment.
