Lee EK  Cho KH  Kim SK  Lim JS  Kim JN

Vol. 24,  No. 1, pp. 55-62, Mar.  2018
10.7464/ksct.2018.24.1.055

MCM-41 MIL-101 Ion exchange Salt impregnation Water adsorption

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The adsorbent used in water-adsorption cooling system utilizing low-temperature heat of below 90 ℃ is required to exhibit high water uptake capacity at a relative humidity (P/P0) between 0.1 and 0.3. Mesoporous silica (MCM-41) and MOF (MIL-101) exhibit quite large water adsorption capacity under saturated water vapor at 35 ℃. However, these adsorbents show small water adsorption capacity (0.027 gwater gads -1, 0.074 gwater gads -1, respectively) in the relative humidity (P/P0) range of 0.1 to 0.3. In this study, the surface properties of mesoporous silica and MOF were modified by simple methods to develop an adsorbent having a higher water uptake than the conventional water adsorbents at a relative humidity (P/P0) of 0.1 ~ 0.3. In the case of mesoporous silica (MCM-41) exhibiting mainly water adsorption at P/P0 = 0.5 ~ 0.7, aluminum species was functionalized on the mesopore walls and then cations existing near the aluminum were exchanged with various cations (e.g., Na+, NH4 +, and (C2H5)4N+). In addition, 20 wt% (to total weight of the composites) of hygroscopic inorganic salt (CaCl2) was impregnated on the MCM-41. In the case of the MIL-101 (MOF), 20 wt% of hygroscopic inorganic salt (CaCl2) was impregnated on the MIL-101. The MCM-41 which was ion-exchanged with various cations has main adsorption branch around 0.5 of P/P0 which was slightly shifted with low-pressure direction in comparison with pristine MCM-41. However, tiny increases were observed on the adsorption in the range of P/P0 between 0.1 and 0.3. After salt impregnation on the MCM-41, the adsorption capacity under P/P0 = 0.1 ~ 0.3 at 35 ℃ was increased from 0.027 gwater gads -1 to 0.152 gwater gads -1. In the case of MIL-101, the amount of water adsorption at 35 ℃ under P/P0 = 0.1 ~ 0.3 was increased from 0.074 gwater gads -1 to 0.330 gwater gads -1 after the salt impregnation.