Experimental study on salt–metal organic framework composites for water absorption

Abstract

In this article, MIL-101(Cr) powder material was successfully prepared by hydrothermal synthesis and combined with different mass fractions of CaCl2 by immersion method to obtain MIL-101(Cr)/CaCl2 composite materials. The physical properties of the adsorbent were determined by X-ray powder diffraction, N2 adsorption/desorption isotherm, TGA and FTIR. The water vapor adsorption performance of MOFs was tested by a gravimetric instrument to analyze the underlying mechanism. Results indicated that the specific surface area, total pore volume, and pore size distribution of micropores and mesopores of MIL-101(Cr)/CaCl2 composites decreased with increasing CaCl2 content. When P/P0 = 0.9, the water vapor equilibrium adsorption capacities of MIL-101(Cr), MIL-101(Cr)/CaCl2-10%, MIL-101(Cr)/CaCl2-20%, and MIL-101(Cr)/CaCl2-30% were 1.05, 0.88, 1.13, and 1.35 g/g, respectively. MIL-101(Cr)/CaCl2-30% agglomerated after water absorption, so MIL-101(Cr)/CaCl2-20% was selected as the final experimental material. The water vapor adsorption heat of MIL-101(Cr)/CaCl2-20% was 42–58 kJ/mol, which is close to the evaporation enthalpy of water (44 kJ/mol at 25 °C). The analysis of the adsorption kinetics showed the relatively uniform adsorption rate of MIL-101(Cr)/CaCl2-20%. Overall, MIL-101(Cr)/CaCl2-20% exhibited superior water vapor adsorption performance and have great potential for application to adsorption heat pumps.