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The huge amount of moisture in the air is an unexplored and overlooked water resource in nature, which can be useful to solve the worldwide water shortage. However, direct water condensation from natural or even hazy air is always inefficient and inevitably contaminated by numerous impurities of dust, toxic gas, and microorganisms. In this regard, a drinkable and clean water harvester from complex contaminated air with a wide humidity range based on porous sodium polyacrylate/graphene framework (PGF), which can actively sorb moisture from common or even smoggy environments, efficiently grabs impurities, and then releases clean water with a high rejection rate of impurities under solar irradiation, is proposed. This PGF shows a superhigh equilibrium uptake of 5.20 g of water per gram of PGF at a relative humidity (RH) of 100% and 0.14 g g-1 at a low RH of 15%. The rejection rate of impurities is up to 97% for the collected clean water. Moreover, a water harvesting system is established to produce over 25 L clean water per kilogram of PGF one day, enough to meet several people's drinking water demand. This work provides a new strategy for effective production of clean water from the atmosphere of practical significance.
Outdoor water harvesting experiment based on the lab‐made MPWH device. a) Exploded‐view drawing of the device used for water sorption. b) Photograph of the device showing water collection. c) Real‐time changes in temperature, humidity, and water uptake in outdoor water sorption experiments. The green curve, blue curve, and background color map represent ambient temperature, the weight of water uptake, and RH, respectively. Outdoor water sorbing experiment from 7:00 p.m. to 6:00 a.m. on October 16, 2018, in Beijing. d) Photograph of the outdoor water sorbing experiment in the natural environment. e) Real‐time changes in temperature, humidity, and solar flux in outdoor water desorption experiments. The red curve, green curve, blue curve, gold curve, and orange curve are the temperatures of PGF, ambient temperature, internal RH, directly measured irradiation, and global horizontal irradiance (GHI), respectively. Outdoor water desorbing experiment from 10:00 a.m. to 12:00 a.m. on October 16, 2018, in Beijing. f) Photograph of the collected clean water on copper. g) Outdoor water harvesting in 24 h under RH > 90%. A long cycle of 15 h sorption per 1 h desorption and 16 cycles of 25 min sorption per 5 min desorption were used. The red column represents the water uptake of PGF after sorption, and the blue column represents the residual water uptake of PGF after desorption. The difference between the red column and the blue column is the theoretical amount of water released in this cycle. The experiment began on October 14 and ended on October 15, 2019, in Beijing.
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1905875 (1 of 8) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Highly Efficient Clean Water Production from Contaminated
Air with a Wide Humidity Range
Houze Yao, Panpan Zhang, Yaxin Huang, Huhu Cheng,* Chun Li, and Liangti Qu*
H. Yao, P. Zhang, Y. Huang, Dr. H. Cheng, Prof. L. Qu
Key Laboratory for Advanced Materials Processing Technology
Ministry of Education of China
State Key Laboratory of Tribology
Department of Mechanical Engineering
Tsinghua University
Beijing 100084, P. R. China
Prof. C. Li, Prof. L. Qu
Department of Chemistry
Tsinghua University
Beijing 100084, P. R. China
Prof. L. Qu
School of Chemistry and Chemical Engineering
Beijing Institute of Technology
Beijing 100081, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under
DOI: 10.1002/adma.201905875
contaminated inevitably by the impurities,
such as microorganisms, fine particulate
matters (PM), and toxic gases like sulfur
oxides (SOx).[11,12] Recently, miscellaneous
hygroscopic materials have been explored
for moisture capture. For instance, metal–
organic frameworks (MOFs) like MOF-801
could harvest 0.25 g g1 water at a rela-
tive humidity (RH) of 20%, and poly(N-
isopropyl acrylamide)/sodium alginate
(PNIPAAm/Alg) polymer hydrogel dem-
onstrated 0.6 g g1 water uptake at the RH
of 80%, respectively.[13–16] However, MOF-
801 only worked in a narrow RH range
(<20% RH) with low water uptake, and
the quality of the oozed water from PNI-
PAAm/Alg hydrogel was uncertain for the
risk of impurities. As a result, it is still a
big challenge for harvesting high-quality
clean water free of impurities from the air
within a full range of humidity.
Herein, we demonstrate a highly effi-
cient clean water production system from
a contaminated environment with a wide range of humidity
based on a rationally designed sodium polyacrylate (PAAS)/gra-
phene framework (PGF). This porous framework with plentiful
oxygen functional groups facilitates the sorption of water vapor
in humid air and simultaneously grabs the impurities under
van der Waals force (Figure 1). Moreover, a high solar-thermal
conversion capability of PGF makes water easily desorbed under
sun irradiation.[2,17,18] As a result, such a PGF presents the equi-
librium water uptake of 0.14 g g1 at a low RH of 15%, and a
superhigh uptake of 5.20 g g1 at an RH of 100%, exhibiting
the excellent water uptake ability in a wide range of humidity.
Under solar irradiation of 1 sun (1 kW m2), the sorbed water
can be quickly desorbed into vapor within a few minutes to
generate clean water free of impurities. Thus, the PGF meets
the requirements of efficient moisture capture, impurities
filtration, and clean water production from natural air. For prac-
tical application, a lab-made prototype of moisture purification
and water harvest (MPWH) system is built to collect over 25 L
clean water per kilogram of PGF daily from the atmospheric
environment. This PGF offers an efficient platform to capture
moisture in ordinary and contaminated air for the production
of high-quality clean water.
The porous PGF is easily prepared through a convenient
freeze-drying method (see details in Materials and Methods,
Supporting Information). Typically, PAAS is well dispersed in
a graphene oxide (GO) dispersion after ultrasonic treatment
(Figure 2a). After the freeze-drying (Figure 2b) and reduction
The huge amount of moisture in the air is an unexplored and overlooked
water resource in nature, which can be useful to solve the worldwide water
shortage. However, direct water condensation from natural or even hazy air
is always inefficient and inevitably contaminated by numerous impurities of
dust, toxic gas, and microorganisms. In this regard, a drinkable and clean
water harvester from complex contaminated air with a wide humidity range
based on porous sodium polyacrylate/graphene framework (PGF), which can
actively sorb moisture from common or even smoggy environments, effi-
ciently grabs impurities, and then releases clean water with a high rejection
rate of impurities under solar irradiation, is proposed. This PGF shows a
superhigh equilibrium uptake of 5.20 g of water per gram of PGF at a rela-
tive humidity (RH) of 100% and 0.14 g g1 at a low RH of 15%. The rejection
rate of impurities is up to 97% for the collected clean water. Moreover, a
water harvesting system is established to produce over 25 L clean water per
kilogram of PGF one day, enough to meet several people’s drinking water
demand. This work provides a new strategy for effective production of clean
water from the atmosphere of practical significance.
Water shortage has been a growing challenge owing to
the booming population and aggravated water pollution, making
it an urgent issue to be solved.[1–3] In nature, vapor transportation
plays an essential role in water circulation, and 13 sextillion
(1021) liters of water exist in the form of the gaseous state
within the atmosphere.[4,5] Therefore, efficient water harvesting
from the air could be a sustainable and low-cost way toward
the solution of the water crisis.[6–10] However, due to global air
pollution, direct water condensation from moisture tends to be
Adv. Mater. 2020, 32, 1905875
... Furthermore, the availability of a variety of monomers, combined with rich polymer synthesis protocols, is pushing the boundaries of hydrogel-based AWH sorbents. The water vapour sorption capacity of a pristine hydrogel sorbent is usually low (<1.5 g g −1 at a relative humidity of 60% 41,90-95 ), with some exceptions 40,96 , whereas the hybrid hydrogels with embedded hygroscopic salts could sorb >3 g g −1 (refs. 30,46,97-100). ...
... As the core of hygroscopic solid adsorption-based AWH, various solid adsorbents have been designed and constructed, 2,8,70,71 mainly including porous adsorbents, 71-74 polymeric gels, [75][76][77][78][79] and non-deliquescent salts 80,81 ( Figure 4A). Among them, porous adsorbents, such as silica gels, 82,83 zeolites, 84,85 MOFs (metal-organic frameworks), 86,87 and their derivates, 88,89 featuring sufficient surface area and pore volume for the capture and storage of water molecules from the atmosphere, stand out for hygroscopic solid adsorption-based AWH. ...
... [9,10] Qu et al. reported the efficient MEGs consisting of various polymers with electrolyte groups. [11][12][13][14][15][16][17][18][19][20] The spontaneously moist-electric polymer membrane generator was able to deliver a V oc of 0.6 V when poly(4-styrene sulfonic acid) and poly(vinyl alcohol) were used as the polymer membrane. [21] Moreover, a heterogeneous moisture-enabled electric generator (HMEG) assembled with a bilayer of polyelectrolyte membranes produced a high voltage of approximately 0.95 V, proving that polymers with proton conduction can be effectively applied in the conversion of moisture energy in MEGs. ...
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Harvesting water from the air using adsorbents and obtaining fresh water by solar-driven desorption is considered as one of the most effective ways to solve the freshwater crisis in arid and desert regions. Based on a simple and low-cost photothermal hygroscopic hydrogel, a new strategy is proposed to boost solar energy efficiency by coupling solar-driven atmospheric water harvesting technology with thermoelectric power generation technology in this paper. Photothermal hygroscopic hydrogel ink PAM-CaCl2 is prepared by in situ polymerization using Acrylamide as monomer, Ammonium persulfate as thermal initiator and CaCl2 as hygroscopic component. During the day, the photothermal hygroscopic hydrogel absorbs solar energy and evaporates its own internal water to obtain fresh water. Simultaneously, the residual waste heat is utilized to power the thermoelectric panel, which produces electricity based on Seebeck effect. At night, the hydrogel harvests water molecules in the air to achieve regeneration. This hybrid system can achieve a water production rate of 0.33 kg m−2 h−1 and an additional electrical energy gain of 124 mW m−2 at 1 kW m−2 solar intensity. Theoretical model of the hybrid system is developed to understand the heat flow and thermoelectric generation process. The results provide new insights into energy and freshwater replenishment options in arid or desert areas with abundant solar energy.
Adsorbent-assisted air water harvesting (AWH) may help alleviate the current global freshwater scarcity crisis. However, the weak sorption capacity of various adsorbents and the high energy required to release water are two long-standing problems. Herein, we propose a class of green and clean adsorbent, TpPa-1@LiCl composite, whose sorption capacity is greatly improved to 0.37 and 0.80 g g−1 under 30% and 90% relative humidity (RH), respectively, and which has excellent stability, showing only a slight decrease (0.79%) after 10 sorption–desorption cycles (1400 min). This TpPa-1@LiCl composite can reach equilibrium within 2 h and undergo complete desorption in 30 min under air mass 1.5 G irradiation. A corresponding solar-driven AWH device can complete up to 4 sorption–desorption cycles per day, with each cycle capable of collecting 0.34 g g−1 water without additional energy input, which implies TpPa-1@LiCl composite has the potential for achieving sorption-assisted AWH with high efficiency and rapid cycling.
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Water scarcity is one of the greatest challenges facing human society. Because of the abundant amount of water present in the atmosphere, there are significant efforts to harvest water from air. Particularly, solar‐driven atmospheric water generators based on sequential adsorption–desorption processes are attracting much attention. However, incomplete daytime desorption is the limiting factor for final water production, as the rate of water desorption typically decreases very quickly with decreased water content in the sorbents. Hereby combining tailored interfacial solar absorbers with an ionic‐liquid‐based sorbent, an atmospheric water generator with a simultaneous adsorption–desorption process is generated. With enhanced desorption capability and stabilized water content in the sorbent, this interfacial solar‐driven atmospheric water generator enables a high rate of water production (≈0.5 L m−2 h−1) and 2.8 L m−2 d−1 for the outdoor environment. It is expected that this interfacial solar‐driven atmospheric water generator, based on the liquid sorbent with a simultaneous adsorption–desorption process opens up a promising pathway to effectively harvest water from air. A novel interfacial solar‐driven atmospheric water generator can simultaneously adsorb water and desorb water based on a liquid sorbent, 1‐ethyl‐3‐methyl‐imidazolium acetate. With enhanced desorption capability and continuous water supplement in the sorbent, this atmospheric water generator can achieve a high rate of water production (≈0.5 L m−2 h−1) and 2.8 L m−2 d−1 for the outdoor environment.
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Water scarcity is a ubiquitous problem with its magnitude expected to rise in the near future, and efforts to seek alternative water sources are on the rise. Harvesting water from air has intrigued enormous research interest among many groups with Scientific American listing this technology as the second most impactful technology that can bring about a massive change in people's lives. Though desalination offers a huge prospect in mitigating water crisis, its practicality is limited by exorbitant energy requirement. Alternatively, the air above sea water is moisture rich, with the quantity of vapor increasing at the rate of 0.41 kg m⁻². Herein, a method to sustainably harvest water from this moisture rich zone is demonstrated by employing a nanoporous superhygroscopic hydrogel, which is capable of absorbing water from highly humid atmospheres by obver 420% (highest) of its own weight. The desorption process from the hydrogel, occurring at 55 °C (lowest), is triggered by natural sunlight (A.M 1.5) thereby ensuing an external energy‐less water harvesting approach. The hydrogel exhibits excellent stability even after 1000 absorption/desorption cycles. Through multiple absorption/desorption cycles, it is possible to harvest over 10 L water per kg of hydrogel daily.
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Harvesting water from air is a promising strategy for fresh water production, particularly desirable for areas that lack direct access to clean water. While high concentration liquid sorbent is well‐known for high sorption, it has not been widely used for atmospheric water collection, primarily limited by the difficulty in desorption. In this paper we show that interfacial solar heating based on a salt‐resistant GO‐based aerogel can enable high concentration liquid sorbent (CaCl2 50 wt% solution) based atmospheric water generator. Fresh water of 2.89 kg m‐2 day‐1 can be produced at ~70% relative humidity, with only solar energy input and energy efficiency of desorption as high as 66.9%. This low‐cost and effective approach provides an attractive pathway to extract water from air, to relieve the thirst of arid, land‐locked, and other fresh water scarce areas.
Atmospheric water harvesting (AWH) is the capture and collection of water that is present in the air either as vapor or small water droplets. AWH has been recognized as a method for decentralized water production, especially in areas where liquid water is physically scarce, or the infrastructure required to bring water from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and utilizing sorbent materials to collect vapor from the air. In this paper, we first distinguish between the geographic/climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temperature and relative humidity (RH). Because utilizing sorbents has the potential to be more widely applicable to areas which are also facing water scarcity, we focus our discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equilibrium vapor uptake in the material (kg of water uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equilibrium property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances associated with heat and mass transport in the bulk material dramatically change the system performance. We focus our discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of water per m2 device per day or L of water per kg adsorbent per day. The former metric is especially important for systems driven by low-grade heat sources because the low power density of these sources makes this technology land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss our previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized water supplies.
As a ubiquitous solar-thermal energy conversion process, solar-driven evaporation has attracted tremendous research attention owing to its high conversion efficiency of solar energy and transformative industrial potential. In recent years, solar-driven interfacial evaporation by localization of solar-thermal energy conversion to the air/liquid interface has been proposed as a promising alternative to conventional bulk heating-based evaporation, potentially reducing thermal losses and improving energy conversion efficiency. In this Review, we discuss the development of the key components for achieving high-performance evaporation, including solar absorbers, evaporation structures, thermal insulators and thermal concentrators, and discuss how they improve the performance of the solar-driven interfacial evaporation system. We describe the possibilities for applying this efficient solar-driven interfacial evaporation process for energy conversion applications. The exciting opportunities and challenges in both fundamental research and practical implementation of the solar-driven interfacial evaporation process are also discussed.
The social development, economic growth and booming population have caused aggravated water pollution, making clean water shortage an urgent issue to be solved. In recent decades, researchers have aroused upsurge studies of direct solar steam generation (DSSG) system for the production of clean water, in which solar thermal conversion materials (STCM) can strongly transform absorbed solar light into thermal energy, tremendously speeding the evaporation of water under sunlight irradiation. DSSG system has been considered an efficient, sustainable, low-cost and environment-friendly way to solve water shortage crisis of practical importance. In this review, we will provide a comprehensive summary of the recent development of DSSG system for clean water production. The introduction about categories of DSSG, principle of solar thermal conversion on STCM and efficiency calculation in DSSG system will first demonstrate the fast water evaporation mechanism. Then strategies for high performance water evaporation in DSSG are detailed including sunlight absorption regulation on STCM for efficient light utilization, system optimization of DSSC for minimizing the heat loss, water transport adjustment for adequate water supply and so on. Benefiting from the basic understanding and effective strategies of DSSG system, the quality of produced clean water, pollutants disposal in remaining water body and various designs of solar stills for high clean water productivity are further presented. Finally, we outline the current challenges and crucial issues of recent DSSG system, aiming to provide guidances and pointers to speed the development of DSSG in clean water production for practical applications.