Shaping Water Adsorption and Desorption in Multivariate Metal-Organic Frameworks for Optimized...

Ultralow-temperature-driven water-sorption refrigeration provides an energy-saving and eco-friendly solution to realize near-zero-carbon cooling applications. Current water sorbents mainly focused on improving low-pressure water uptakes for boosting cooling efficiency, while often hindered by cooperatively increasing desorption energy to show the opposite effect. Herein, we report a strategy of finely shaping water adsorption and desorption properties simultaneously in multivariate MOFs to maximize cooling efficiency. With broadly regulating the ratio of hydrophobic and hydrophilic linkers within UiO-66, a series of multivariate MOFs [UiO-66-(BDC)_x(PzDC)_1-x] were designed and synthesized, featuring a high tunability on both water uptake at P/P₀ = 0.2 and desorption energy. These high manipulations allow us to realize the optimal UiO-66-(BDC)_0.4(PzDC)_0.6 with the most balance between water adsorption and desorption, as proven by its high water uptake of 0.4 g g^-1 at P/P₀ = 0.2 and low desorption temperature down to 63°C for 90% desorption ratio. This maximizes its coefficient of performance (0.86) and working capacity (0.18 g g^-1) for refrig-2 applications achieved by an ultralow driving temperature of 63°C, outperforming the previously benchmark MIP-200 (0.69 and 0.12 g g^-1) and EMM-8 (0.85 and 0.16 g g^-1). The water-sorption regulatory mechanisms were systematically elucidated by water-loaded crystal structures.