Mixed-Solvothermal Synthesis of MIL-101(Cr) and Its Water Adsorption/Desorption Performance

As one of typical metal organic frameworks (MOFs), MIL-101 (Cr) has potential application in adsorption heat pumps. However, traditional hydrothermal synthetic technology of MIL-101 (Cr) requires high reaction temperature and has a low yield, which hinders its promotion. In this work, a new facile synthetic strategy of MIL-101(Cr) using a mixture of N,N- dimethylformamide (DMF) and water as solvent was developed. The dispersity of the mixed-solvent reaction system was preliminarily analyzed. The effects of DMF/H₂O volume ratio on the crystalloid phase, morphology, and the pore structure of the as-prepared product were systematically discussed through X-ray diffraction, scanning electron microscopy (SEM), and pore size analysis. And its adsorption/desorption performance was measured by static adsorption and thermogravimetry. The results indicated that the new mixed-solvothermal technology could conveniently synthesize MIL-101(Cr) at a low temperature of 140 °C, and the yield was as high as 83.3%. Further, SEM images showed that the MIL-101(Cr) crystals obtained by the present route had an even distribution and small particle size of about 200 nm. In addition, static adsorption revealed the water uptake capacity of MIL-101(Cr) synthesized by the present process was slightly higher than that of the one synthesized by the traditional method. Correspondingly, the desorption peak temperature of the former was slightly higher than that of the latter. It may be attributed to the homogeneity of the mixed-solvent reaction system, resulting in a larger BET specific surface area and smaller crystal particle size.