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
The sorption behavior and microscopic sequestration mechanisms of radionuclide 63Ni(II) on mordenite as a function of aging time,ionic strength,initial 63Ni(Ⅱ) concentrations,solid content and coexistent electrolyte ...The sorption behavior and microscopic sequestration mechanisms of radionuclide 63Ni(II) on mordenite as a function of aging time,ionic strength,initial 63Ni(Ⅱ) concentrations,solid content and coexistent electrolyte ions were investigated by the com-bination of batch and EXAFS techniques.Macroscopic experiment results show that the sorption of 63Ni(Ⅱ) is dependent on ionic strength at pH<7,and independent of ionic strength at pH>7.The sorption percentage of 63Ni(Ⅱ) on mordenite increases with increasing solid content,while the sorption capacity decreases as solid content increases.The presence of different elec-trolyte ions can enhance or inhibit the sorption of Ni(II) on mordenite in various degrees.EXAFS analysis results of the sam-ples under three different ionic strengths suggest that the retained 63Ni(Ⅱ) in these samples exists in an octahedral environment with six water ligands.In the initial period of rapid uptake,the sorption of 63Ni(Ⅱ) is dominated by the formation of in-ner-sphere surface complexes.As aging time increases,63Ni(Ⅱ) sequestration behavior tends to be mainly controlled by the formation of Ni phyllosilicate co-precipitates and/or Ni(OH)2(s) precipitates.Results for the second shell fit of the sample pre-pared at an initial 63Ni(Ⅱ) concentration of 100 mg/L indicate the possible formation of Ni polynuclear surface complexes.Both the macroscopic sorption data and the molecular level evidence of 63Ni(Ⅱ) surface speciation at the mordenite/water in-terfaces should be factored into better predictions of the mobility and bioavailability of 63Ni(Ⅱ) in environment mediums.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supported by the National Natural Science Foundation of China (20907055,20971126 & 21077107)the National Basic Research Program of China (2011CB933700)the Knowledge Innovation Program of CAS and Special Foundation for High-level Waste Disposal (2007-840)
文摘The sorption behavior and microscopic sequestration mechanisms of radionuclide 63Ni(II) on mordenite as a function of aging time,ionic strength,initial 63Ni(Ⅱ) concentrations,solid content and coexistent electrolyte ions were investigated by the com-bination of batch and EXAFS techniques.Macroscopic experiment results show that the sorption of 63Ni(Ⅱ) is dependent on ionic strength at pH<7,and independent of ionic strength at pH>7.The sorption percentage of 63Ni(Ⅱ) on mordenite increases with increasing solid content,while the sorption capacity decreases as solid content increases.The presence of different elec-trolyte ions can enhance or inhibit the sorption of Ni(II) on mordenite in various degrees.EXAFS analysis results of the sam-ples under three different ionic strengths suggest that the retained 63Ni(Ⅱ) in these samples exists in an octahedral environment with six water ligands.In the initial period of rapid uptake,the sorption of 63Ni(Ⅱ) is dominated by the formation of in-ner-sphere surface complexes.As aging time increases,63Ni(Ⅱ) sequestration behavior tends to be mainly controlled by the formation of Ni phyllosilicate co-precipitates and/or Ni(OH)2(s) precipitates.Results for the second shell fit of the sample pre-pared at an initial 63Ni(Ⅱ) concentration of 100 mg/L indicate the possible formation of Ni polynuclear surface complexes.Both the macroscopic sorption data and the molecular level evidence of 63Ni(Ⅱ) surface speciation at the mordenite/water in-terfaces should be factored into better predictions of the mobility and bioavailability of 63Ni(Ⅱ) in environment mediums.
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.
