Fourier transform infrared spectroscopy study of acid birnessites before and after Pb~(2+) adsorption

摘要

To provide fundamental knowledge for studying the relative content of vacant sites and exploring the mechanism of interaction between Pb~(2+) and birnessite, Fourier transform infrared spectroscopy (FTIR) of birnessites with different Mn average oxidation states (AOS) before and after Pb~(2+) adsorption were investigated. The number of absorption bands of FTIR spectra was determined by using the second derivatives of the original spectra. The band at 899-920 cm~(-1) was assigned to the bending vibration of -OH located at vacancies. The bands at 1059-1070, 1115-1124 and 1165 - 1171 cm~(-1) could be attributed to the vibrations of Mn(III)-OH in MnO_6 layers, and the intensities of these bands increased with decreasing Mn AOS, The bands at 990 and 1023 - 1027 cm~(-1) were ascribed to the vibrations of Mn(III)-0H in the interlayers. Mn(III) in MnO_6 layers partially migrated to interlayers during Pb~(2+) adsorption, which led to an increased intensity of the band at 990 cm~(-1). The band at 564-567cm~(-1) was assigned to the vibration of Mn-O located at vacancies. This band could split by coupling of vibrations due to Pb~(2+) and/or Mn~(2+) adsorbed at vacant sites. The large distance between the band at 610-626 cm~(-1) and that at 638-659 cm~(-1) might reflect small Mn(III) ions located in Mn(III)-rich rows.