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《Geochimica》 2011-01
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FTIR study on the variance of substructure of birnessite before and after Pb~(2+) adsorption

ZHAO Wei1,2,LIU Fan1,FENG Xiong-han1,TAN Wen-feng1,2,QIU Guo-hong1 and CHEN Xiu-hua1 1.Key Laboratory of Subtropical Agriculture Resource & Environment,Ministry of Agriculture of China,Huazhong Agricultural University,Wuhan 430070,China;2.State Key Laboratory of Soil Erosion and Dryland Farming in the Loess Plateau,Institute of Soil and Water Conservation,Chinese Academy of Sciences,Yangling,712100,China  
The structural features of birnessites with different Mn average oxidation state(AOS) before and after Pb2+ adsorption were characterized by Fourier Transform Infrared(FTIR),and the absorption band centers of FTIR were determined by second derivatives of these spectra.The band at 899-920 cm-1 was assigned to the bending vibration of -OH located at vacant Mn octahedral sites.The lower AOS in birnessite,the more Mn4+ coordinated to -OH located at vacant Mn octahedral sites displaced by Mn3+,which led to the position of -OH bending vibration shifting to a relative low wave number.The bands at 1059-1070,1115-1124 and 1165-1171 cm-1 were assigned to the vibration of Mn3+-OH located in the layer,and the intensity of these bands increased with the decrease of AOS in birnessite.The bands at 990 and 1023-1027 cm-1 were assigned to the vibration of Mn3+-OH located in the interlayer.A partial of Mn3+ in the layer migrated to the interlayer during the Pb2+ adsorption inducing the intensity of the band at 990 cm-1 to increase and its position shifting to a relative high wave number.The band at 564-567cm-1 was assigned to the vibration of Mn-O located at vacant Mn octahedral sites,and would split due to the effect of coupling on vibration when Pb2+ or Mn3+ was adsorbed above or below vacant sites.The space between the bands at 610-626 and 638-659 cm-1 reflected the symmetry of Mn3+ distribution in the birnessite,and increased after Pb2+ was adsorbed on the birnessite.
【Fund】: 国家自然科学基金(40771102 40671088)
【CateGory Index】: P575.4
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