Metal Organic Framework MIL-101(Cr): Spectroscopic Investigations to Reveal Iodine Capture Mechanism

Abstract

Molecular scale information is the key to understand adsorption mechanism and consequently, to aid in the design of improved adsorbent materials. This paper reports on the use of two-dimensional correlation Fourier transformation Infrared 2D-COS-FTIR, Raman spectroscopies and X-ray diffraction to provide information about the structure of MIL-101(Cr), and the mechanism of iodine adsorption from cyclohexane solution. X-ray diffraction analysis and structure simulation revealed the presence of three preferable adsorption sites; close to Cr–O clusters and on top of benzene rings. FTIR spectroscopy further confirmed the presence of three different type of interactions (Cr–H2O, H2O–I2 and Cr–I2), which were located at 2930, 2850 and 1117 cm−1 respectively. The nature of iodine was identified as $${\text{I}}_{3}^{ - }$$ and $${\text{I}}_{5}^{ - }$$ from the characteristic peaks at around 106 cm−1, 135 cm−1 and 164 cm−1 in Raman spectra. The results reflected the power of combined 2D-COS-FTIR with Raman spectroscopy and X-ray diffraction in determining the structure of such complex systems.