On the general water harvesting capability of metal-organic frameworks under well-defined climatic conditions

The ability of some highly porous materials to adsorb and desorb water vapor under atmospheric conditions without the use of external power sources could become a promising methodology for the capture and release of water in arid or desert regions of the world. Here, the use of some readily available metal-organic frameworks as water harvesting materials has been tested and compared with other porous materials. Water adsorption experiments were conducted at 25 °C and at a relative humidity (RH) of 40%, while the desorption process took place at 45 °C with a RH of 10%. These experimental conditions are in good accordance with the climatic conditions being present in the Sahara desert during the summer season. In all experiments, UiO-66 derived MOFs showed the best water harvesting efficiency, releasing up to 89% of the adsorbed water at 45 °C and 99% at 60 °C. Though, the adsorption capacity of UiO-66 is noticeably lower than that of more hydrophilic materials such as the MOF compound HKUST-1 and the zeolite A3. The latter, however, are only able to release water when they are heated up to at least 60 °C. Finally, the stability of the investigated MOFs after adsorption-desorption cycles have been confirmed through XRD and FT-IR analyses.