Prediction of phase transitions by investigating CO2 adsorption on 1% lithium doped MIL-101 (Cr) MOF with anomalous type isosteric heat of adsorption

Abstract

The amount of adsorbate uptakes and heats of adsorption (Qst) for CO2 + 1% Li doped MIL-101 (Cr) metal organic framework (MOF) system are measured at wide ranges of pressures and temperatures. Some data are reported for the regions below the triple point (200 K–216.5 K). The multilayer CO2 adsorption uptakes in a series of discontinuous jump are found in the sub-triple region. Various types and shapes of Qst are observed and the unexpected differences in Qst at sub-triple, sub-critical and super critical regions are explained. At sub-triple zone, two sharp spikes of Qst against uptakes are found for identifying the transitions of adsorbate layer from the gaseous phase to the solid phase. The gas – liquid transition is also observed from the uptake dependence Qst data at 220 K and 240 K. A monotonic decrease in Qst is found at higher temperatures.