Metal organic frameworks for atmospheric water harvesting in desert environments: A comparative study

Air-water harvesting (AWH) technology is an effective way to solve the human water shortage. In arid and desert areas, the excellent flexibility and adaptability of adsorption-based atmospheric water harvesting (ABAWH) can overcome restrictions of conventional water sources, accomplishing decentralized water supply. Metal-organic frameworks (MOFs), a class of emerging materials, are promising in improving efficiency of atmospheric water harvesting under low humidity conditions. The adsorption and desorption capacities of the adsorbent (MOF-801, silica gel, 13X molecular sieve and calcium chloride) were determined gravimetrically under a simulated desert environment (20 degree celsius-relative humidity (RH) 20%; 20 degree celsius-RH 30%; 20 degree celsius-RH 40%; 30 degree celsius-RH 30%; 40 degree celsius-RH 30%). The main conclusions are as follows. (1) The water content in the air is directly proportional to the efficiency of atmospheric water harvesting, which is mainly determined by temperature and relative humidity. Under low humidity experimental conditions, the adsorption (desorption) amount for the MOF-801 is determined to be on average 190% (109%) and 132% (146%) of that of silica gel and the 13X molecular sieve, respectively. (2) We also illustrate the first-order kinetics of adsorption using MOF-801 by linear driving force model, with R-2 values of 0.9935. (3) The "matrix sets of differences" result shows an increasing weight of impact on performance as: number of particles per gram of adsorbent (N) > particle radius (R) > relative humidity (H) > temperature (T) > material type (M). Only R shows a negative correlation, and the remaining factors show a positive correlation.