Efficient water adsorption of UiO-66 at low pressure using confined growth and ligand exchange strategies

Abstract

Atmospheric water adsorption at low humidity is considered to be a major challenge in solving global water problems. As a routine water adsorbent, the University of Oslo-66 (UiO-66) powder has been restricted by its limited low-pressure water absorption capacity, the need for powder molding, and insufficient adsorption rates. To overcome these problems, this work prepares E-UiO-66@PAA spherical composites by crystallizing UiO-66 on the surface of macroporous polyacrylate, i.e. PAA porous spheres, through in situ confined growth and ligand exchange strategies. The average size of the crystals has been reduced by 4 times vtihe nanoscale roughness of the polymer substrate surface and the interfacial enrichment of the precursor solution to lower the energy barriers of heterogeneous nucleation. In addition, the coordination of the hybrid ligand with Zr4+ creates a unique cavity structure and gives rise to novel micropores as a result of ligand defects, which can be fitted into the lattice as binding sites for water. In the water vapor adsorption test at 298 ​K, E-UiO-66@PAA was able to operate at 4.9 times the capacity at low pressure (0.1 ​< ​P/P0 ​< ​0.2) and advanced the adsorption saturation time by 30.7% of the pristine UiO-66. Especially, the relative pressure of the sudden change in water vapor uptake was reduced from 0.3 to 0.1, which could greatly save the energy required for vapor regeneration and reduce its operating cost. This study provides an effective method to improve the adsorption capacity, mass transfer rate, and workability of composites by designing a nanoporous structure and confined growth nuclei as adsorption sites.