Metal–Organic Frameworks for Water Harvesting and Concurrent Carbon Capture: A Review for Hygroscopic Materials

Abstract

As water scarcity becomes a pending global issue, hygroscopic materials prove a significant solution. Thus, there is a good cause following the structure–performance relationship to review the recent development of hygroscopic materials and provide inspirational insight into creative materials. Herein, traditional hygroscopic materials, crystalline frameworks, polymers, and composite materials are reviewed. The similarity in working conditions of water harvesting and carbon capture makes simultaneously addressing water shortages and reduction of greenhouse effects possible. Concurrent water harvesting and carbon capture is likely to become a future challenge. Therefore, an emphasis is laid on metal–organic frameworks (MOFs) for their excellent performance in water and CO2 adsorption, and representative role of micro‐ and mesoporous materials. Herein, the water adsorption mechanisms of MOFs are summarized, followed by a review of MOF's water stability, with a highlight on the emerging machine learning (ML) technique to predict MOF water stability and water uptake. Recent advances in the mechanistic elaboration of moisture's effects on CO2 adsorption are reviewed. This review summarizes recent advances in water–harvesting porous materials with special attention on MOFs and expects to direct researchers’ attention into the topic of concurrent water harvesting and carbon capture as a future challenge.

Ca-MOF-Derived Porous Sorbents for High-Yield Solar-Driven Atmosphere Water Harvesting

“…The chemically adsorbed crystal water (CaCl 2 ·2H 2 O) begins to release above 200 °C and can only be completely desorbed when the temperature is greater than 260 °C. Therefore, the high regeneration temperature of CaCl 2 causes the adsorbed water to be not completely released under practical AWH process . In this work, due to the great photothermal property of PCC-42, it can rapidly heat up to ∼80 °C under one sun illumination (1 kW/m 2 ), and 83% of the adsorbed water was released within 1.5 h (39 and 47% for Ca-MOF and CaCl 2 ·2H 2 O, respectively), proving that the successful fabrication of such porous sorbents decorated with CaCl 2 in situ could achieve more efficient solar-powered water release (Figure f).…”

“…Therefore, the high regeneration temperature of CaCl 2 causes the adsorbed water to be not completely released under practical AWH process. 23 In this work, due to the great photothermal property of PCC-42, it can rapidly heat up to ∼80 °C under one sun illumination (1 kW/m 2 ), and 83% of the adsorbed water was released within 1.5 h (39 and 47% for Ca-MOF and CaCl 2 • 2H 2 O, respectively), proving that the successful fabrication of such porous sorbents decorated with CaCl 2 in situ could achieve more efficient solar-powered water release (Figure 4f). The fast kinetics and great water release abilities of our other MOF-derived sorbents (PCC-41, PCC-51, and PCC-52) also support the above results (see Figure S20).…”

“…Economically friendly deliquescent salts such as lithium chloride (LiCl) and calcium chloride (CaCl 2 ) display strong interactions with water molecules and high equilibrium water uptake in the range 10–100% relative humidity (RH). ,, However, the dissolution of deliquescent salts in the adsorbed water complicates recycling efforts and contributes to environmental pollution. Recently, this issue has been addressed by impregnating porous matrixes with a salt solution under mild ambient conditions. , However, the sorption kinetics and cycle stability of these composites require improvement . In contrast, MOF materials are considered the most promising next-generation water sorbents due to their large specific surface area and abundant adsorption sites. ,, Nevertheless, some MOFs sorbents used for SAWH with poor light absorption ability cannot reach high temperatures under sunlight, resulting in low desorption efficiency and insufficient daily water production …”

“…21,22 However, the sorption kinetics and cycle stability of these composites require improvement. 23 In contrast, MOF materials are considered the most promising next-generation water sorbents due to their large specific surface area and abundant adsorption sites. 8,24,25 Nevertheless, some MOFs sorbents used for SAWH with poor light absorption ability cannot reach high temperatures under sunlight, resulting in low desorption efficiency and insufficient daily water production.…”

A Metal Inorganic Framework Designed as a Propellant Burn Rate Modifier

“…These redshifts in pa-AIH and AIH are due to the intermolecular H-bonds with HIO 3 /IO 3 . Studies explain [28,29] that the 3550-3200 cm À1 peak is indicative of higher surface area associated with increased porosity relative to the weaker O-H stretching for pa-AIH and AIH. Greater surface area for a-AIH is consistent with SEM images in Figure 3.…”