Defect Engineering of MIL-101(Cr) for an Enhanced Water Adsorption Rate

Water adsorbents are essential in our daily lives and in various industrial fields. The water adsorption rate is one of the most important properties of water adsorbents and should be improved to implement high-throughput devices. In this study, we focused on enlarging the pore size of MIL-101(Cr) by defect engineering for a faster water diffusion. MIL-101(Cr) terephthalate linkers were substituted with formate to create the defects. We investigated how the formate substitution influenced the pore size of MIL-101(Cr) and its water adsorption rate. Thermogravimetric measurements and pore size distribution analysis confirm the defect formation. In the evaluation of the water adsorption rate, we confirm three distinct adsorption processes with different adsorption rates, corresponding to water adsorption on the pore surface, into middle pores, and into large pores, respectively. In particular, defects in MIL-101(Cr) obviously influence the third water adsorption process into large pores, in which the water adsorption rate increases by up to 25%. It is suggested that the defect formation promotes water diffusion through an available pathway and condensed water transfer from other pores by the enlargement of windows between pores. These results can help us develop dehumidification devices with higher throughput.