Cesium and cobalt adsorption on synthetic nano manganese oxide: A two dimensional infra-red correlation spectroscopic investigation

• Two-dimensional Infrared spectroscopy is used to analyze Cs+ and Co2+ adsorption.
• An intensity increase in the 3100 cm−1 band indicates an ion-exchange reaction.
• New O–O and M–O bands at 1100, 1160 and 510 cm−1 indicate Inner-sphere complexation.
• Splitting of the 565 cm−1 band indicates the coupled vibrations of M–O and Mn–O.
• Splitting of the 875 cm−1 band indicates two different O–O bond lengths species.

Molecular scale information is of prime importance to understand ions coordination to mineral surfaces and consequently to aid in the design of improved ion exchange materials. This paper reports on the use of two-dimensional correlation infra-red spectroscopy (2D-COS-IR) to investigate the time dependent adsorptions of cesium and cobalt ions onto nano manganese oxide (NMO). The metal ions uptake was driven mainly by inner-sphere complex formation as demonstrated by the production of new absorption bands at 1160, 1100, 585 and 525 cm−1, which were assigned to the O–O bond vibration and the coupled vibrations of M–O and Mn–O bonds. The progressive development of the 3100 cm−1 band, which is attributed to the stretching vibration of the lattice–OH group, indicates an M+/H+ ion-exchange reaction. The new bands at 700 and 755 cm−1 in the case of cobalt ion adsorption and at 800 and 810 cm−1 in the case of cesium ion adsorption, and the splitting of other bands at 1135 and 875 cm−1 indicate the presence of different O–O bond lengths. This suggests different coordination of the two metal ions with oxygen. The infrared spectroscopy combined with 2D-COS provides a powerful tool to investigate the mechanism of interaction between heavy metals and manganese oxide.

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