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 degrees C and at a relative humidity (RH) of 40%, while the desorption process took place at 45 degrees 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 degrees C and 99% at 60 degrees 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 degrees C. Finally, the stability of the investigated MOFs after adsorption-desorption cycles have been confirmed through XRD and FT-IR analyses. (C) 2016 Elsevier Inc. All rights reserved.