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Highly Efficient Clean Water Production from Contaminated Air with a Wide Humidity Range

DOI:10.1002/adma.201905875
Authors:
Houze Yao at Tsinghua University
Houze Yao
Panpan Zhang at Tsinghua University
Panpan Zhang
Huang Yaxin at The University of Hong Kong
Huang Yaxin
Huhu Cheng at Tsinghua University
Huhu Cheng
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Abstract and Figures

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.
The concept of the MPWH system. The microporous PGF harvests moisture from contaminated air and desorbs the vapor to generate clean water free of impurities under the sun. Inset is the schematic of the interaction between water molecules and PGF. The water molecules are mainly captured through the formation of hydrogen bonding with PAAS coated on graphene sheets.
The concept of the MPWH system. The microporous PGF harvests moisture from contaminated air and desorbs the vapor to generate clean water free of impurities under the sun. Inset is the schematic of the interaction between water molecules and PGF. The water molecules are mainly captured through the formation of hydrogen bonding with PAAS coated on graphene sheets.
… 
Preparation and characterization of PGF. a) The mixture of GO and PAAS solutions. b) The GO/PAAS foam. c) PGF after reduction under the vapor of hydrazine hydrate (N2H4·H2O). d) Photograph of a PGF with a diameter of 20 cm. e,f) Scanning electron microscopy (SEM) images of PGF under different magnifications, demonstrating the cellular architecture. g) The Na elemental mapping images on graphene nanosheets by energy‐dispersive X‐ray spectroscopy. h) Raman spectra of rGO and PGF. i) Fourier transform infrared (FTIR) spectra of rGO, PAAS, and PGF. j) Thermogravimetric analysis of rGO, PAAS, and PGF in the air.
Preparation and characterization of PGF. a) The mixture of GO and PAAS solutions. b) The GO/PAAS foam. c) PGF after reduction under the vapor of hydrazine hydrate (N2H4·H2O). d) Photograph of a PGF with a diameter of 20 cm. e,f) Scanning electron microscopy (SEM) images of PGF under different magnifications, demonstrating the cellular architecture. g) The Na elemental mapping images on graphene nanosheets by energy‐dispersive X‐ray spectroscopy. h) Raman spectra of rGO and PGF. i) Fourier transform infrared (FTIR) spectra of rGO, PAAS, and PGF. j) Thermogravimetric analysis of rGO, PAAS, and PGF in the air.
… 
The natural moisture sorption property of PGF. a) Water uptake of rGO, PAAS, and PGF for 28 h (25 °C, RH = 100%). b) Water uptake of PGFs with different weight radios of PAAS/GO for 24 h (25 °C, RH = 100%). c) Water uptake of PGF under the RH of 60%, 95%, and 100% versus time, respectively. d) Moisture‐sorption isotherm of PGF under different temperatures.
The natural moisture sorption property of PGF. a) Water uptake of rGO, PAAS, and PGF for 28 h (25 °C, RH = 100%). b) Water uptake of PGFs with different weight radios of PAAS/GO for 24 h (25 °C, RH = 100%). c) Water uptake of PGF under the RH of 60%, 95%, and 100% versus time, respectively. d) Moisture‐sorption isotherm of PGF under different temperatures.
… 
Clean water harvesting performance based on PGF. a) Absorption spectra of PAAS and PGF in the full solar spectrum range (250–2500 nm). b) Water desorption of PGF (D = 10 cm, water uptake of 5.2 g g⁻¹) in the open air under the solar irradiation of 0.5 and 1 sun. c) The temperature of the surface part of PGF (D = 10 cm, water uptake of 5.2 g g⁻¹) during water desorption under 1 sun. d) Schematic of clean water production of PGF under smog‐simulation experiment with PM 2.5 over 200 µg m⁻³. e) Photograph of a smog‐filled box for the water sorption test of PGF. f) The measured concentrations of five primary ions of water samples from smoggy air and PGF. g) The maximum water uptake retention of PGF after alternate adsorption–desorption cycles at high PM 2.5 concentrations. h) The conductivity of condensed water in a cyclic collection test. The red area is the conductivity of general drinking water. i) The ideal amount of water can be harvested per day by PGF via an alternative adsorption–desorption process. The x‐axis represents a different sorption time in a cycle.
Clean water harvesting performance based on PGF. a) Absorption spectra of PAAS and PGF in the full solar spectrum range (250–2500 nm). b) Water desorption of PGF (D = 10 cm, water uptake of 5.2 g g⁻¹) in the open air under the solar irradiation of 0.5 and 1 sun. c) The temperature of the surface part of PGF (D = 10 cm, water uptake of 5.2 g g⁻¹) during water desorption under 1 sun. d) Schematic of clean water production of PGF under smog‐simulation experiment with PM 2.5 over 200 µg m⁻³. e) Photograph of a smog‐filled box for the water sorption test of PGF. f) The measured concentrations of five primary ions of water samples from smoggy air and PGF. g) The maximum water uptake retention of PGF after alternate adsorption–desorption cycles at high PM 2.5 concentrations. h) The conductivity of condensed water in a cyclic collection test. The red area is the conductivity of general drinking water. i) The ideal amount of water can be harvested per day by PGF via an alternative adsorption–desorption process. The x‐axis represents a different sorption time in a cycle.
… 
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.
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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CommuniCation
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
E-mail: huhucheng@mail.tsinghua.edu.cn; lqu@mail.tsinghua.edu.cn
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 https://doi.org/10.1002/adma.201905875.
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 g−1 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 g−1 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 g−1 at a low RH of 15%, and a
superhigh uptake of 5.20 g g−1 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 m−2), 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 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.
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). ...
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... 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. ...
View
... [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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Article
  • Oct 2018
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.
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