An Environment-Adaptive and Climate-Responsive MOF Water Harvester with Proven Production of Clean, Drinkable Water
Harvesting water vapor from desert, arid environments by metal-organic framework (MOF) based devices to deliver clean, drinkable liquid water is critically dependent on environment and climate conditions. However, reported devices have yet been developed to adapt in real-time to such conditions during their operation, which severely limits water production efficiency and unnecessarily increases power consumption. Herein, we report and detail a new mode of water harvesting operation, termed 'adaptive water harvesting', from which a MOF-based device was proven capable of adapting the adsorption and desorption phases of its water harvesting cycle to climate fluctuations throughout a given day, week, month, and year such that its water production efficiency is continuously optimized. In performance evaluation experiments in a desert, arid climate (17-32% RH), the adaptive water harvesting device achieved a 169% increase in water production (3.5 LH2O kgMOF -1 d -1 ) when compared to the best-performing, reported active device (0.7 -1.3 LH2O kgMOF -1 d -1 at 10 -32% RH), a lower power consumption (1.67 -5.25 kWh LH2O -1 ), and saved time by requiring nearly 1.5 cycles less than a counterpart active device. Furthermore, the produced water was demonstrated, for the first time, to meet the national drinking standards of a potential technology-adopting country facing considerable water scarcity challenges (Jordan).
INTRODUCTION<!>RESULTS & DISCUSSION<!>CONCLUSION<!>EXPERIMENTAL SECTION
<p>Six billion people will face water insecurity by 2050 as a direct consequence of climate change, improper safeguarding of water resources, expansion of irrigated agricultural practices, and a growing human population. [1][2][3] This water crisis has given rise to the heightened pursuit of new alternative means of water delivery, including desalination, wastewater treatment and reuse, and water harvesting in different forms. [4][5][6] Though these have all proven successful to various degrees in delivering water under different environmental and climate conditions, one emerging technology -adsorbent-based atmospheric water harvesting -stands out for its proven potential in capturing, collecting, and condensing water vapor in climate conditions where its concentration is low (i.e., desert, arid regions). [7][8][9] In adsorbent-based atmospheric water harvesting, metal-organic frameworks (MOFs), a class of extended, porous crystalline materials, reign supreme given their ideal water uptake behavior and capacity at relevant relative humidities (RH), favorable kinetics and thermodynamics of physisorption, and hydrolytic stability. [10][11][12][13][14] When employing MOFs for atmospheric water harvesting, two modes of operation have been reported for devices that exploit their use. 15 The first is a passive mode, in which water is generated by exposing a MOF bed to atmospheric air during the night when RH is at its maximum. [16][17][18] During the day, when the RH is minimal, heat generated by sunlight is used to desorb the water from the MOF where it is then condensed on the surrounding walls of the passive device. The passive mode is effectively one 24 h adsorption-desorption cycle and its performance is dependent on the uptake capacity of the employed MOF at a given RH. When using MOF-801 (37 wt% water uptake capacity at 30% RH), an ideal passive device functioning at 100% efficiency would yield 588 mLH2O kgMOF-801 -1 d -1 at 30% RH. [16][17][18][19] Reported water generation values range from 100 -300 mLH2O kgMOF-801 -1 d -1 , which means that the passive device is operating at an efficiency of <51% of its capacity. To achieve water generation that is suitable for meeting a person's daily needs (³3.5 L), considerably more material must be used (e.g., 12 -35 kgMOF-801). This has consequences with respect to device enclosure geometry and the size of the glass concentrators required for the desorption stage of the cycle. For example, to generate 3.5 L of water at the higher 68% RH, the surface area of the physical enclosure of a single-or dual-stage passive device would need to be 10.3 or 4.54 m 2 , respectively, which is simply too large and not practical. [16][17][18]20 The second mode of operation is an active one, whereby water is generated continuously from air via multiple adsorptiondesorption cycles occurring in a given day. 21 In the active mode, the adsorption phase starts with forcing air through the material bed using a fan for a set period of time. Desorption by an additional heat source occurs at any time to release the captured water and a vapor compression-refrigeration system is used to condense the water vapor. The active mode is dependent upon the dynamic water capacity of the employed MOF, which, in turn, impacts the cycling rate and quantity of water generated on a daily basis. 21 Reported active devices can generate up to 1.3 LH2O kgMOF -1 d -1 at 32% RH and 27 °C -a quantity that is 4-fold larger than that that can be achieved by a passive device under the same conditions. 21 Although this is a significant improvement over the passive mode of operation, water generation remains insufficient per kgMOF used for meeting daily consumption needs.</p><p>Herein, we report the design engineering of a new water harvesting device using MOF-801 that extends the modes of operation beyond passive and active to 'adaptive water harvesting' (Figure 1). This new mode of operation builds upon the previous active one whereby the device carries out multiple water harvesting cycles (WHC; at times referred to as simply 'cycle') per day, but with the critical difference being that the adaptive mode optimizes the timing and efficiency of each WHC based on real-time external climate conditions. In performance evaluation experiments in a desert, arid climate (17-32% RH), the new adaptive device had a greater than 169% increase in water production (3.5 LH2O kgMOF-801 -1 d -1 ) when compared to the best-performing, reported active device (0.7 -1.3 LH2O kgMOF -1 d -1 at 10 -32% RH), a lower power consumption (1.67 -5.25 kWh LH2O -1 ), and saves time by requiring nearly 1.5 cycles less per d than a counterpart active device. 21 Furthermore, we demonstrate the adaptive device's ability to continuously and consistently produce water with no loss in performance after more than 1 yr of operation. Finally, for the first time for MOFbased water harvesters, regardless of their mode of operation, a full panel water analysis was performed to assess and then certify, that the produced water met the national drinking standards of a potential water harvesting technology-adopting country (Jordan).</p><!><p>Design strategy behind the water harvesting device. To extend the scope of MOF-based water harvesting, we constructed a new, three-compartment, modular device that builds upon the active mode of operation. As will be demonstrated, the design plays a significant role in improving the water harvesting process performance. The first compartment, termed the Air Intake Compartment, contains an air filter that prevents solid particulate matter with size >10 nm from entering the device and a fan to push the external air through the device (Figure 1A). An electric heater was placed next to the fan such that during the desorption phase of a given cycle, heated air can provide the necessary energy to release the adsorbed water from the MOF pores and carry that desorbed water vapor at a higher capacity to the condenser. Indeed, air has a maximum water content of 130 g m -3 at 60 °C and 17.3 g m -3 at 20 °C, therefore, heating the air leads to a more than 7-fold increase in the ability of the air to transport the desorbed water vapor. 22 The first RH and temperature sensor was placed in front of the electric heater to measure the air before it passes through the MOF material (See Supporting Information, Section S1).</p><p>The second compartment, termed the Sorption Compartment, was connected directly to the Air Intake Compartment in series and contained 8 trays (with room to add more) placed in parallel to the airflow (Figure 1). Each tray was lined with aluminum (2 mm thickness) to increase heat transport and facilitate desorption of water. Aluminum has a much higher thermal conductivity (KAl = 205 W m -1 K -1 versus Kacrylic = 0.2 W m -1 K -1 ) and, when applying Fourier's Law, will have a 1000-fold higher heat conduction in reaching the same temperature difference as compared to acrylic. 23 For this device, MOF-801 was chosen for use given its high water uptake of 22.5 and 37 wt% at 10 and 30% RH, respectively, and its suitable a inflection point (P/P0 = 0.07) that highlights the material's ability to adsorb water in arid environments. 19 Furthermore, water adsorption by MOF-801 is fully reversible with no hysteresis observed upon desorption and its mild water adsorption enthalpy of 60 kJ mol -1 means that it does not incur a large energy penalty upon regeneration (SI, Section S2). 19 The Sorption Compartment was constructed to hold from 100 g to 10 kg of MOF-801 for performance measurements and has two sensors placed at the top and bottom.</p><p>The third compartment, termed the Condensation Compartment, was connected directly to the Sorption Compartment and contained a condenser that serves as the evaporator of a larger vapor compression-refrigeration cycle. This condenser is fit within a funnel that is used to collect the condensed liquid water and transport it to the mineralization and filtration unit below (Figure 1). The Condensation Compartment contains one sensor that is placed before the condenser to take RH and temperature measurements of the air after it has been exposed to the MOF-801 bed (Figure 1B).</p><p>Performance evaluation of the active water harvesting device. After constructing the device, we then sought to test its performance in generating water at low RH via an active mode of operation. A water harvesting cycle (WHC) was defined as follows: 40 min adsorption phase (an adsorption phase is defined as simply pulling air by the fan from the external environment through all three compartments) followed by a 20 min desorption phase (a desorption phase is defined similarly to the adsorption phase but with the electric heater turned on) that was repeated twice at which point the regeneration phase was carried out before re-starting the next WHC (regeneration is defined as 15 min of airflow without heat, 10 min with no cooling of the condenser to collect the water droplets, and 5 min with no fan to equilibrate the device before starting the next WHC). It is noted that the timings for each phase were concluded based on preliminary measurements that provided visual indications of water production as a function of time (SI, Section S3). Based on this active WHC definition, our water harvesting device was examined over a range of climate conditions (10 -70% RH and 15 -35 °C) and was proven capable of producing 1.2 -2.6 L of water daily with an energy consumption of 3 -7 kWh L -1 (SI, Section S3).</p><p>The importance of using MOFs for functional, efficient atmospheric water harvesting is their ability to effectively concentrate water vapor in air resulting in an increased dew point. [11][12][13] It is important to point out here that previous literature have focused exclusively on RH as the basis for water production without considering the effect of temperature. [7][8][9][16][17][18]20 In fact, for atmospheric water harvesting processes, both RH and temperature must be considered through the dew point value. Indeed, dew point reflects actual water quantity in the air at any given moment and, therefore, all further discussions will rely on the dew point as the basis for water production. This concept is readily visualized when plotting the desorption data from the sensor in the Condensation Compartment for the trial runs of our MOF-801-based device on a psychrometric chart. As shown in Figure 2, when the device is operating with external climate conditions of 30% RH and 22 °C, the dew point corresponds to 3.6 °C. After the adsorption phase is completed, to initiate water desorption from the pores of MOF-801, heating was applied for 10 min leading to an increase in the dew point to 8.3 °C. Furthermore, an additional 10 min of heating led to an even higher dew point of 11.2 °C. This seemingly small rise in dew point has a large impact on condenser power consumption when compared with direct cooling of air without using MOF-801 (i.e., 55% reduction) (SI, Section S3). Any extra heating beyond this point is superfluous and can be considered as an energy loss as such heating does not lead to a further increase in the dew point and thus signals the end of the desorption phase (20 min total heating). This begs the question: if the external climate conditions differ from those measured here, what impact does that have on the prescribed time for carrying out the adsorption and desorption phases of a given WHC? Indeed, it is easy to imagine that these sorption phases of the device are not adaptive nor are optimized to a wide range of climate conditions. Adaptive water harvesting. Based on the limitations of the active mode, we then sought to develop a new, third mode of operation, termed 'adaptive water harvesting'. The fundamental concept of this adaptive mode is to measure the external environment RH and temperature and combine them together through the dew point value. The water harvesting device was then programed to read this measured dew point in real-time and instruct its adsorption and desorption phase operations to react according to that value. In principle, this will yield the highest water quantity because the cycling rate is adaptable and maximized for productivity per time of d.</p><p>Adaptive adsorption phase of a water harvesting cycle. The first step in developing the adaptive device was to understand the time needed for MOF-801 (400 g) to reach full saturation at any given climate condition. To do this, a full desorption process was conducted for MOF-801 by forcing hot air at 80 °C through the Sorption Compartment for 2 h. After this period, MOF-801 was exposed to air at three different RH (15, 18, and 26%) and the dew point response at the Condenser Compartment was recorded. As shown in Figure 3A, the dew point decreases to a steady-state value as a function of time. Given that the difference between the starting and the steadystate dew points reflects the quantity of adsorbed water by MOF-801, the required timing of the adsorption phase can be elucidated. For example, at 26% RH and 14 °C, the air has an absolute humidity (i.e., actual water quantity in the air) of 11.4 gH2O m -3 . If the adsorption time is extended to 51 min, a steadystate dew point of 3.4 °C is reached with an absolute humidity of 5.29 gH2O m -3 , which correlates to 300 gH2O adsorbed within MOF-801 over that time (Figure 3A). Reducing the adsorption time to 21 min, which is the start of the steady-state dew point (at 21 min the dew point = 5.1 °C), then by the same reasoning, 280 gH2O is adsorbed within MOF-801. Though this is 7% less quantity of water adsorbed, the timing difference is significant. Furthermore, the starts of the steady-state dew points for measurements at 18 and 15% RH were also identified with respect to time (17.5 and 15 min) and quantity of adsorbed water (220 and 180 gH2O), respectively. As the profile of the water sorption isotherm for MOF-801 (Figure 3A inset) indicates that total uptake saturation occurs at ca. 40% RH, the measured RHs in this experiment provide satisfactory representation of the material's adsorption performance. From this data, an algorithm was developed to ensure that the adsorption phase of the WHC operates using the minimal required adsorption time needed to reach the start of the steady-state dew point at any climate condition (SI, Section S4).</p><p>Adaptive desorption phase of a water harvesting cycle. Monitoring the timing of the desorption phase is relatively straightforward. The device was prepared for this measurement by carrying out one adsorption phase to ensure that MOF-801 (400 g) was fully saturated with water. Upon beginning the  desorption phase and monitoring the sensor placed at the Condensation Compartment, MOF-801 released water vapor from its pores by observing the dew point of the air increasing to a maximum. Reaching this maximum ultimately signaled the end of the desorption phase, at which time a gradual decrease was observed until this internal dew point value was equivalent to the external dew point (Figure 3B). The desorption phase was tested at different climate conditions (14, 30, 34, and 45% RH), from which all measurements exhibited the same behavior, but with differing rates of change in dew point. In general, a higher RH results in higher water uptake and this requires a longer desorption time. According to the water sorption isotherm of MOF-801, ca. 79% of the total uptake capacity is reached by 20% RH. This means that at RH >20%, the timing of the desorption phase is relatively the same, but significantly different at RH <20% (Figure 3B). From these measurements, a second algorithm was developed to correlate heating time to the external climate conditions (i.e., RH) and the power (W) of the electric heater employed (SI, Section S4).</p><p>Performance evaluation of the adaptive water harvesting device. Using RH and temperature data from sensors positioned throughout the enclosure, the device applies the two adaptive adsorption and desorption phase algorithms to control the timings of these phases as a function of external climate conditions (RH and temperature). To evaluate the performance of this adaptive mode of operation against the previous active mode, we loaded two devices with 400 g of MOF-801 and programmed the operation of each device according to Figures S22 and S28 in the SI. The performance for both devices in terms of change in RH as a function of time is presented in Figure 4 for a 14 h total time period spanning a portion of the day into the night. Over this period, the lowest and highest external RHs were measured to be 17 and 32%, respectively. Interestingly, the first cycle (17% RH and 25 °C) of the adaptive device was found to be 45 min faster than the active device demonstrating its ability to enhance the cycling rate. However, as the RH increased throughout the day and into the night, the difference in cycling rates became indistinguishable (<1 min for cycle 5 at 32% RH and 25 °C) (Figure 4).</p><p>From this comparison, the adaptive device was proven to produce 36% more water (3.52 LH2O kgMOF-801 -1 d -1 ) than our active device (2.6 LH2O kgMOF-801 -1 d -1 ) under the same climate conditions. This performance is represented in Figure 4 as the difference between the highest and lowest RH for each phase of the WHC. For example, in cycle 3, the RH difference during the adsorption phase of the adaptive device was 39% compared with 28% calculated for the active device. This is a 36% increase in water adsorption by MOF-801 during this WHC. Similarly, in cycle 3, the RH difference during the desorption phase of the adaptive and active devices were 37 and 26%, respectively, which represents a 45% increase in desorbed water by the adaptive device. Resulting from the increased WHC rates, the adaptive device realized a 44% reduction in the consumed power per WHC under low RH conditions (10-20%) in comparison to the active device (SI, Section S5). When operating at high RH conditions (>20%), a 26% reduction in consumed power per WHC was achieved by the adaptive device with respect to the active device. Overall, the adaptive device consumed 1.67 -5.25 kWh LH2O -1 based on the climate conditions of that specific day (17 -32% RH) and saved considerable time by requiring 1.5 cycles less than the active device (Table 1).</p><p>Dependency of MOF quantity on water production. It is well-known that water production is directly dependent on MOF quantity in water harvesters operating in passive mode. However, direct dependence for active mode of operation is unclear and is yet to be proven because of limitations of compartment size and the power consumption requirements from increasing that size. To assess this dependency in the adaptive mode of operation, a control experiment was pursued whereby the water production output was correlated to MOF-801 quantity loaded into the device. Specifically, the device was gradually loaded with MOF-801 starting from 0 g (empty device) to 100, 200, and 400 g and operated under controlled climate conditions of 20, 30, and 40% RH. Water production for the device loaded (or not) with each amount was measured 3 times for 24 h for each controlled climate condition with the average output presented in SI, Figure S29. At 50% RH and 400 gMOF-801, the device produced 870 mLH2O compared with 420 and 190 mLH2O when using 200 and 100 gMOF-801, respectively. When the device was empty (0 g of MOF-801), no water was produced. A similar trend is observed for the other measured conditions. Therefore, the dependence of MOF quantity on water production is clearly observed. Based on this experiment, our device requires ca 1.6 kgMOF to produce enough water to meet personal consumption needs, which is significantly less than what is needed for reported MOF-based active water harvesting devices (³2.9 kgMOF required) and the 12 -35 kgMOF needed for passive devices to achieve the same production amount. When taken together with compartment size considerations, our device's physical design is clearly superior.</p><p>Long-term performance. Long-term (i.e., >1 yr) water stability and sorption capability are pre-conditions for using MOFs in water harvesting applications. 24 Although the physicochemical properties of MOFs play a critical role in determining their lifetime, the device engineering must be considered as a potential influencer (positive or negative) of the MOF's properties and resulting lifetime for use. For example, the device can optimize heat transfer and air flow, which will lessen the strain on the MOF material. Furthermore, the adaptive mode of operation ensures that cycling rates result in maximum performance output while not overextending material stability. To demonstrate our adaptive device's long-term performance, we performed a 24 h stress test under extreme climate conditions (22% RH and 25 °C) after the device had been run for 1000 cycles, which is equivalent to ca. 1 yr of operation. As shown in Figure 5A, the adaptive device produced an appreciable amount of water (40 mL cycle -1 ) even after it had been used for more than 1 yr. To confirm the stability of MOF-801, we measured the powder Xray diffraction pattern after this test, which confirmed that the crystallinity was retained, and the diffraction pattern matched that of the simulated one from the single crystal structure (SI, Section S6).</p><p>Practical production of water from desert climates. In general, atmospheric water harvesting in desert, arid regions is difficult, if not practically impossible for other conventional water harvesting technology, due to the low relative humidity. 15,25 This is because conventional water harvesting techniques (i.e., direct cooling of air, condensation, fogging) require an enormous amount of energy to be effective under these climate conditions. 6,26 The attraction of MOF-based water harvesting is the fact that these materials can selectively capture water vapor at low RH, concentrate and release it to increase the dew point for condensation purposes. 15 Therefore, in order to demonstrate the utility of our adaptive device, we conducted an experiment whereby the device (400 gMOF-801) was exposed to natural, desert air (17% RH and 25 °C) for 24 h. Again, this experiment utilized the device after it had been operated for more than 1000 cycles (i.e., >1 yr of operation).</p><p>From this experiment, we observed that during the low RH of the desert day, the adaptive device produced 52 mL cycle -1 , which is significant given the extreme desert climate conditions. The production amount is doubled per cycle during the higher RH conditions of the desert night (105 mL cycle -1 ). To push this experiment further, we continuously operated the device in a desert, arid environment for 1 continuous week that was extended to >1 continuous month. As depicted in Figure 5B-D, the adaptive device effectively responded to the daily changes in climate conditions and continuously produced appreciable amounts of liquid water under extreme desert conditions.</p><p>Full water quality analysis. Before the condensed water can be used for personal consumption, the water was gravity-filtered and mineralized through a column containing alternating layers (2 -3 mm) of activated carbon, sand, and limestone. A full water analysis panel was then carried out for the collected water to assess whether it met the national drinking standards of Jordan. The first analysis followed the Standard Methods for the Examination of Water and Wastewater (SM 3120-B, 4110-B, 3111-B, and 31112-B), in which metal identification and concentration was determined by inductively-coupled optical emission spectroscopy. Specifically, the water was analyzed for: Al (<0.1 ppm), Na (5.7 ppm), Pb (<0.01 ppm), Cd (<0.003 ppm), Cu (<0.05 ppm), Mn (<0.05 ppm), As (<0.01 ppm), Zn (3.58 ppm), Fe (<0.1 ppm), Sb (<0.002 ppm), Mo (<0.01 ppm), Zr (<0.1 ppm), B (<0.1 ppm), Se (<0.04 ppm), Ba (<0.1 ppm), Cr (<0.02 ppm), Hg (<0.001 ppm), Ag (<0.1 ppm), and Ni (<0.05 ppm). As indicated, all were less than the specification limits of the national drinking standards. The volatile organic compound content was then determined following the same standard methods. For this, the concentrations of benzene (<10 ppm), total xylene (<20 ppm), trichloroethene (<20 ppm), tetrachloroethene (<20 ppm), ethylbenzene (<20 ppm), and toluene (<20 ppm) were determined to be less than the specification limits. Finally, microbiological analysis (SM 9213 E, 9230 B, 10200, 9215 AB) was carried out, in which the content of pseudomonas aeruginosa (<1 colony forming unit 100 mL -1 ; CFU), fecal streptococci (<1.1 most probable number; 100 mL -1 ; MPN), fecal enterococcus (<1.1 MPN 100 mL -1 ), algae type and count (not seen); and heterotrophic plate count (8.3 × 10 2 CFU mL -1 ) were determined to meet the national standards. Detailed results and certification of the collected water for meeting Jordanian standards of drinking water are provided in the SI, Section S7.</p><!><p>Variations in climate conditions significantly affect the water harvesting process in terms of water production efficiency and power consumption. By developing a new mode of water harvesting operation, termed 'adaptive water harvesting', we demonstrate how a MOF-based device could be environmentally-responsive and climate-adaptive. This led to considerable advancements in performance, most notably, a 169% increase in water productivity and a 44% reduction in power consumption compared to state-of-the-art reported devices. Moving forward, it is clear that maximizing heat and mass transfer via optimized air flow dynamics will lead to further exploitation of the sorption properties of MOFs for practical water harvesting. Furthermore, monitoring the performance of adaptive water harvesting devices over periods of time longer than 1 yr will provide insight into such devices' ability to respond to multiple seasonal climate changes. All in all, coupling the results from these future investigations to an adaptive mode of operation will yield a water harvesting device that can bring water security and independence to anyone, anywhere at any time.</p><!><p>Water harvesting device construction. The water harvesting device is comprised of three rectangular prismatic compartments held together by cell cast acrylic sheets (Moden Glas) as walls. One acrylic sheet is used as the base of the device (1 × 0.6 m, 5 mm thickness), which extends across all three compartments. The base has regularly cut slots (40 × 5 mm) to fit the walls of each compartment in place. The first compartment ('Air Intake Compartment') is constructed from 4 cell cast acrylic sheets as walls (280 × 280 × 200 mm, 5 mm thickness). The internal front wall has rubber lining and is connected to the top and side walls by pre-designed facets that are screw-sealed to allow easy access to the compartment. This wall has a 230 × 250 mm window cut by a CO2 laser cutter (Trotec Speedy 400), which is fitted with an air-panel filter (M Filter No. K418). The remaining top and side walls are sealed together via chloroform.</p><p>Inside the Air Intake Compartment is an electric aluminumfinned copper coil heater (500 W) and a one-phase alternating current fan (Orix No. MRS18-DC-F6) placed consecutively next to the air-panel filter. The second compartment ('Sorption Compartment') is directly connected to the Air Intake Compartment and is constructed from 5 cell cast acrylic sheets as follows: (i) shared wall with Air Intake Compartment: 290 × 370 mm with 8, 270 × 8.5 mm slots laser cut to direct air flow; (ii) back wall: 290 × 478 mm; (iii) top wall: 300 × 400 mm; (iv) front wall: 290 × 478 mm; and (v) shared wall with the third compartment ('Condensation Compartment'): 290 × 370 mm with 8, 270 × 8.5 mm slots laser cut to direct air flow. The front wall has rubber lining and is connected to the top and side walls by pre-designed facets that are screw-sealed to allow easy access to the compartment. The remaining top and side walls are sealed together via chloroform. The Sorption Compartment is comprised of 8 cell cast acrylic trays (470 × 360 mm) each having an aluminum lining (2 mm thickness) to facilitate heat transfer. The trays are held in parallel to the airflow by acrylic shelving that are attached beneath rows of airflow slots fastened to the two shared walls. The Condensation Compartment is constructed from 3 cell cast acrylic sheets (280 × 280 × 200 mm, 5 mm thickness) and has a 3-lined aluminum-finned condenser (250 × 250 mm) housed inside. This condenser is fit within a stainless-steel funnel (250 × 100 mm) that is used to collect condensed liquid water and transport it to the mineralization and filtration unit below. This condenser is the evaporator of a larger compression-refrigeration cycle and is, therefore, connected via copper tubing (1/4 in) to a refrigeration compressor (1/3 hp, Model No. GFF86AA; Siberia Co.), 2-lined aluminum-finned condenser with attached cooling fan (250 × 250 mm; 5 W), and an expansion tube. This compressor was operated using R-134a as the working fluid (Schild Refrigerant). To monitor temperature and relative humidity throughout the device, 4 holes (20 mm diameter) were laser cut into the following walls: (i) top wall of the Air Intake Compartment in a position of 70 mm after the heater; (ii) front wall of the Sorption Compartment in centered positions on the top and bottom of this wall; (iii) top wall of the Condensation Compartment in a position of 70 mm before the condenser. These holes were prepared in order to fix sensor probes (Logitech, RCW800 Wi-Fi). One additional sensor probe was used to monitor external environmental conditions. The collected water from the Condensation Unit is immediately fed into a glass column (30 × 150 mm; l × d) that is packed with alternating layers of limestone, sand, and activated carbon. The water is subsequentially gravity-filtered and mineralized and collected in a 5 L anti-microbial carboy. Detailed schematics are provided in Section S1.</p><p>The synthesis and characterization of MOF-801. MOF synthesis and characterization details are presented in Section S2.</p><p>Active water harvesting device operation. The active water harvesting mode of operation is based on a simple adsorption-desorption cycle. In a typical run, the fan and the condenser, drawing 54.5 and 184 W of power, respectively, are activated for 40 min. This provides exposure of the MOF material to external airflow to facilitate adsorption of water vapor. The condenser was set at an arbitrary temperature well-below the ambient environment's dew point. After 40 min, the heater is activated for 20 min to initiate desorption. Since the fan and the condenser remain active, this stage draws 239 W of power. The heated air reached 45 °C on average when reaching the Sorption Compartment containing the MOF material. Water droplets</p>