Fourier transform infrared spectroscopy study of acid birnessites before and after Pb2+ adsorption
Abstract:To provide fundamental knowledge for studying the relative content of vacant sites and exploring the mechanism of interaction between Pb2+ and birnessite, Fourier transform infrared spectroscopy (FTIR) of birnessites with different Mn average oxidation states (AOS) before and after Pb2+ 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 MnO6 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)-OH in the interlayers. Mn(III) in MnO6 layers partially migrated to interlayers during Pb2+ 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 Pb2+ and/or Mn2+ 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.
Document Type: Research Article
Publication date: 2012-06-01