Synergistically Enabling Fast-Cycling and High-Yield Atmospheric Water Harvesting with Plasma-Treated Magnetic Flower-Like Porous Carbons.

Sorption-based atmospheric water harvesting (AWH) offers a promising solution to the water scarcity in arid regions. However, majority of the existing AWH sorbents are suffering from rather poor water productivity due to their slow water adsorption-desorption cycling capability especially when they are applied in high packing thickness. Herein, an oxygen plasma-treated magnetic flower-like porous carbon (P-MFPC) with large open surfaces, abundant surface oxygen-containing moieties, and excellent localized magnetic induction heating (LMIH) capacity is developed. These merits, together with the use of air-blowing-assisted water adsorption and LMIH-driven water desorption strategy, synergistically allow P-MFPC with 2 cm of packing thickness to complete a AWH cycling in 20 min and deliver a record 4.5 LH2O kg-1 day-1 of water productivity at 30% relative humidity. Synergistically enabling such an ultrafast AWH cycling at high sorbent packing thickness provides a promising way for the scalable high-yield AWH with compact AWH systems.

Magnetic Stuffed Bun-Structured Metal-Organic Framework Monoliths with Noncompromised Accessible Pores and Highly Efficient Recycling Capability.

Development of industrially favorable metal-organic framework (MOF) monoliths is of paramount importance for their real-world applications. However, MOF monoliths prepared with the existing MOF shaping methods usually have seriously compromised accessible pores and suffer from inefficient and energy-intensive recycling, thereby greatly limiting their practical applications. We herein present a magnetic stuffed bun-structured MOF (mSBM) bead consisting of highly porous poly(vinyl alcohol) wraps stuffed with a binder-free powder mixture of UiO-66 and Fe3O4 nanoparticles. Such a unique structure and composition of the mSBM not only make its MOF component have a well-reserved crystal structure, surface area, and porosity and the corresponding accessible pores but also impart it with excellent localized magnetic induction heating (LMIH) capability that enables the sufficient heating and highly efficient recycling of the mSBM. These merits of mSBMs are further exemplified by assessing their atmospheric water adsorption and LMIH-driven water desorption performance. The mSBMs exhibit well-reserved atmospheric water adsorption capacities, up to 100% LMIH-driven water desorption, excellent reusability, and durability toward the practical applications. Our current work, therefore, demonstrates a new MOF shaping strategy to produce MOF monoliths with well-defined shapes, noncompromised accessible pores, and highly efficient recycling capabilities, paving a bright avenue to accelerate the practical applications of MOF monoliths.

Sandwich-Structured Carbon Paper/Metal-Organic Framework Monoliths for Flexible Solar-Powered Atmospheric Water Harvesting On Demand.

Solar-powered atmospheric water harvesting (AWH) with metal-organic frameworks (MOFs) has been recognized as an attractive way to alleviate water shortage stress in rural arid areas given the naturally abundant solar energy. However, the existing solar-powered AWH technologies only allow a singular water production mode: either solar heating-driven AWH which usually results in rather poor water productivity due to the limited availability of sufficient sunlight or conductive heating-driven all-day AWH with significantly improved water productivity but requiring additional electricity provided with a photovoltaic module. This greatly limits the flexibility in managing AWH based on climate conditions, water productivity, and energy cost. Herein, a sandwich-structured MOF monolith (denoted as CACS) with dual heating capacity, localized solar heating (LSH) and electrical heating (LEH), is presented. Compared with LSH, the use of LEH leads to more rapid and uniform heating of CACS monoliths, thereby driving a significantly enhanced water desorption efficiency with faster kinetics. Using the CACS monolith as an AWH sorbent, a new type of atmospheric water harvester is developed and able to produce water in multiple working modes: LSH-, LEH-, and LSH-/LEH-driven AWH, thereby enabling flexible AWH on demand: direct use of sunlight for LSH-driven AWH during the sunlight-sufficient day and/or LEH-driven all-day AWH powered by a photovoltaic module particularly during the sunlight-absent/-insufficient time (night or cloudy day). When working at the LSH-/LEH-driven AWH mode, the resulting prototype delivers 1.4 LH2O kgMOF-1 day-1 of water productivity with 2.3 kW·h L-1H2O of energy consumption, corresponding to 5.4 times higher water productivity than the LSH-driven AWH working mode alone and 17.9% of energy saving at the cost of 22.2% of water productivity reduction compared with the LEH-driven AWH working mode alone. The current work, therefore, demonstrates a novel solar-powered AWH strategy that enables all-day water production with flexible choices on AWH working modes in terms of climate conditions, desired water productivity, and energy cost.

Embedding metal foam into metal-organic framework monoliths for triggering a highly efficient release of adsorbed atmospheric water by localized eddy current heating.

Using metal-organic frameworks (MOFs) to harvest water from the atmosphere represents an attractive way to alleviate the global water shortage stress. However, the intrinsic thermal insulating nature of MOFs makes it rather challenging to scale-up water production by utilizing industrially favorable bulky MOF monoliths due to the insufficient water desorption triggered by the existing water desorption methods. To overcome this challenge, metal foam (MF) embedded MOF monoliths (MF@MOFs) are presented. In MF@MOFs, MF not only serves as the backbone of MOF monoliths to support them with excellent mechanical robustness, but also enables the rapid generation of enormous localized eddy current heating (LECH) upon their exposure to an alternating magnetic field. Compared with the traditional heating methods, the use of LECH can effectively overcome the thermal insulating nature of MOF monoliths and realize their rapid and uniform heating, thereby triggering a complete water desorption from MF@MOFs with significantly improved desorption kinetics. The viability of the LECH-triggered water release method for practical atmospheric water harvesting is also validated through a newly designed LECH-based atmospheric water harvester. Note that this is the first exploration that uses LECH to overcome the intrinsic insulating nature of MOF monoliths.

Enabling Continuous and Improved Solar-Driven Atmospheric Water Harvesting with Ti3C2-Incorporated Metal-Organic Framework Monoliths.

Solar-powered atmospheric water harvest (SAWH) with metal-organic frameworks (MOFs) represents one of the most sustainable, energy-efficient, and low-cost ways to alleviate water shortage stress in arid regions. However, the daily water productivity of previously developed SAWH devices remains low as they are merely allowed to be operated in batch mode and complete one water harvest cycle every day. This inevitably makes it rather challenging to deploy MOF-based SAWH for water production at scales. To overcome this challenge, MXene Ti3C2-incorporated UiO-66-NH2 (TUN) cylindrical monoliths (13 mm diameter, 4 mm thickness) with vertically aligned porous networks have been prepared and exhibited greatly enhanced solar heating capacity and atmospheric water adsorption/desorption kinetics. Using TUN monoliths as atmospheric water adsorbents, a novel SAWH device containing a flippable adsorbent stage with dual TUN monolith layers attached on both sides has been fabricated. Such a novel design enables the prototype to produce water in a continuous mode under sunlight irradiation, delivering 57.8 mLH2O kgMOF-1 h-1 of water productivity in a simulated indoor arid environment (20% relative humidity, 298 K). This is the first exploration in continuous water production with MOF-based SAWH, demonstrating a promising way to achieve scalable and low-cost SAWH in arid areas.

Metal Microfibers Delivered Eddy Current Heating for Efficient Synthesis and Regeneration of Metal-Organic Framework Monoliths.

On the basis of stainless-steel fiber (SSF)-delivered localized Eddy current heating (LECH) in response to an alternating magnetic field, a novel LECH-driven framework synthesis (LIFS) strategy has been developed for highly efficient metal-organic framework (MOF) synthesis, resulting in the production of a set of SSF/MOF composites consisting of MOF-coated SSF (SSF@MOF) fibers and free MOF crystals. Detailed studies on the LIFS reaction kinetics indicate that the use of LIFS can greatly promote MOF production in comparison to the conventional solvothermal reactions. To facilitate the practical applications, the resulting powder SSF/UiO-66-NH2 composites, as a typical example, are further processed into well-shaped SSF/UiO-66-NH2 monoliths (SUS) with varied MOF loadings. In SUSs, the embedded SSFs exhibit well-controlled LECH capacities depending on the applied magnetic field strength. Driven by LECH, SUS monoliths can be uniformly heated and fully regenerated, demonstrating a LECH-triggered framework regeneration (LIFR) process for highly efficient regenerating MOF monoliths. As LECH is delivered by the low-cost commercial SSFs and remotely triggered by an external magnetic field, our currently developed LIFS and LIFR processes provide a novel, low-cost, and energy-efficient way to highly efficiently synthesize and regenerate MOF materials.

Localized Electrical Induction Heating for Highly Efficient Synthesis and Regeneration of Metal-Organic Frameworks.

Based on carbon fibers (CFs) delivered localized electrical induction heat, a novel electrical induction framework synthesis (EIFS) strategy has been developed to in-situ grow versatile metal-organic frameworks (MOFs) on CFs, resulting in the production of a set of MOF-coated CF (MOF@CF) fibers. Detailed studies on the production of UiO-66-NH2@CFs indicate that the use of EIFS leads to dramatically accelerated MOF growth at dozen times higher reaction rate than that of the conventional solvothermal reaction. By periodically switching anodes during EIFS reactions, uniform MOF@CF fibers with well-controlled MOF loadings have been achieved depending on the reaction conditions. Mediated by the embedded CFs in the resulting MOF@CFs, MOF@CFs exhibit well-regulated electrical induction heating capacities depending on MOF loadings and the applied voltages. Driven by such localized heat, up to 100% of the adsorbed CO2 in UiO-66-NH2@CF can be rapidly released, demonstrating an electrical induction framework regeneration (EIFR) process for highly efficient regeneration of MOFs. As CFs enable to rapidly deliver localized electrical induction with over 90% of electrothermal conversion efficiency and at rather low operation voltage, currently developed EIFS and EIFR process provide a highly efficient, low-energy, low operation cost, and safe way to highly efficient synthesis and regeneration of MOF materials.