Peng WANG, et al.
Hydrophilic disc uses solar power to
separate salt from water
by Nick Lavars
Current approaches to water desalination are tremendously
expensive and energy-intensive, so the search is very much on for
new technologies that can get the job done more efficiently.
Scientists in Melbourne have put forward one rather promising
solution, developing a new kind of system that heats up and
purifies water using only the power of the Sun.
The device was developed by scientists at Australia's Monash
University, who say that water treatment accounts for around three
percent of the world's energy supply. Like other researchers
around the globe, they have turned to sunlight to try and lighten
the load, this time directing it toward what is known as a solar
In simple terms, these devices concentrate sunlight onto a body of
water, heating it up and causing it to evaporate. The resulting
steam can then be used to drive turbines that produce electricity
in concentrated solar power plants, perhaps sterilize medical
equipment cheaply for the developing world, or simply to separate
salt from water.
But one problem with the lattermost application is that the salt
tends to gather on the surface of the material, which makes it
difficult to produce pure water. The Monash University researchers
worked around this problem with an intricately designed solar
steam generator that prevents the salt from spoiling the broth.
It consists of a disc crafted from super-hydrophilic filter paper,
a material that attracts water, which is coated with a layer of
carbon nanotubes that convert sunlight into heat. Water is fed
into the center of the disc via a simple cotton thread, where the
heat turns it into steam that builds up on the disc while pushing
the salt to the edge.
In this way, the device removes almost 100 percent of salt from
the water, a level that leader of the team Professor Xiwang Zhang
assures us is "high enough for practical applications." The salts
that accumulate at the edges, meanwhile, can also be harvested for
Zhang and his team tested out the device using salty water from a
bay in South Australia, and found that it absorbed 94 percent of
the light across the solar spectrum. It worked whether wet or dry,
with light exposure heating up the device from 25 to 50° C (77 to
122° F) when dry and from 17.5 to 30° C (63.5 to 86° F) when wet,
within just one minute.
"This device can produce six to eight liters (1.6 to 2.1 gal) of
clean water per square meter (of surface area) per day," Zhang
tells New Atlas. "We are working to further improve the water
Zhang and his colleagues hope that with further work, the device
could be put to use providing clean water to remote communities
that are currently without access. But its value mightn't end
there. The technology could be used in other areas where more
efficient water purification methods might come in handy, such as
mining and wastewater treatment.
We hope this research can be the starting point for further
research in energy-passive ways of providing clean and safe water
to millions of people, illuminating environmental impact of waste
and recovering resource from waste," says Zhang.
Supplementary Video 6
Solar panel generates fresh water and
A new system for removing salt from seawater using the waste heat
from solar panels has been created by Peng Wang and colleagues at
King Abdullah University of Science and Technology in Saudi
Arabia. The team installed a multistage membrane distillation
(MSMD) device directly underneath the solar panels so that the
system occupies the same footprint as the solar panels.
Energy and water are two crucial resources that are often
connected. Creating freshwater from seawater consumes about 15% of
electricity generated in Arab countries, for example, and finding
carbon-free sources of energy for desalination is a huge challenge
facing countries in the driest regions of the world.
Wang’s team have answered this challenge by creating a
desalination system that uses waste heat produced by solar power
plants. While solar cells can convert about 20% of sunlight into
electricity, the remaining 80% simply heats up the solar panels.
The team’s MSMD device comprises three stacked layers of water
distillation channels that run parallel to solar panels. Each
layer is separated by porous hydrophobic membranes and heat
Evaporation and condensation
Within each layer, seawater in the uppermost channel is evaporated
by waste heat from the solar panel, and then condenses to
freshwater inside a second channel on the other side of the
membrane. This desalinated water then flows into a storage
container, while the remaining seawater, along with the rest of
the waste heat, pass down to the layer below, where the process
Salt-free drinkable water comes at a cost
Wang and colleagues show that the MSMD device can be installed
directly underneath existing solar panels; requiring no
specialized mounting equipment, and no extra requirements for land
use. While previous attempts at this technique came at the cost of
overall solar panel performance, the researchers observed
virtually no decrease in power generation efficiency in their
system. At the same time, the MSMD device was able to desalinate
up to 1.64 l of fresh water per square metre per hour. According
to team member Wenbin Wang, this is more than double the water
output of traditional solar stills, which use a one-stage design.
The team points that new technology could encourage energy and
water companies to work together in dry regions. Furthermore, they
point out that creating fresh water offers a way of mitigating the
inherent low efficiency of solar panels and could make their
deployment more attractive.
As a next step, the team wants to study how the system could be
used in an agricultural setting – with the water used for
Spatially isolating salt crystallisation
from water evaporation for continuous solar steam generation
and salt harvesting
Yun Xia, et al.
As a low-cost green technology, solar steam generation using
nanostructured photothermal materials has been drawing increasing
attention in various applications, e.g. seawater desalination, and
zero liquid discharge of industrial wastewater. However, the
crystallisation of salts on the surface of photothermal materials
during steam generation leads to a gradual decline in the water
evaporation rate. Herein, this challenge was overcome by a novel
design involving controlled water transport, edge-preferential
crystallisation and gravity-assisted salt harvesting. The
crystallisation sites of the salt were spatially isolated from the
water evaporation surface, achieving continuous steam generation
and salt harvesting in over 600 hours of non-stop operation. The
study provides new insights into the design of solar steam
generators and advances their applications in sustainable seawater
desalination and wastewater management.
24 July 2019
Water solutions without a grain of salt
Monash University researchers have developed technology that
can deliver clean water to thousands of communities worldwide.
This solar steam generation system produces clean water
from salty (ocean) water with almost 100 per cent salt removal.
It provides a solution to water shortages in regional areas
where grid electricity isn’t available.
An estimated 844 million people don’t have access to clean water,
while every minute a newborn dies from infection caused by lack of
safe water and an unclean environment.
Seawater desalination and wastewater recycling are two ways to
ease the problem of water shortage, but conventional approaches
are energy-intensive and based on the combustion of fossil fuels.
In fact, water treatment uses about 3 per cent of world’s energy
Researchers at Monash University have developed energy-passive
technology that’s able to deliver clean, potable water to
thousands of communities, simply by using photothermal materials
and the power of the sun.
Led by Professor Xiwang Zhang from Monash University’s Department
of Chemical Engineering, researchers have developed a robust solar
steam generation system that achieves efficient and continuous
clean water production from salty water with almost 100 per cent
salt removal. Through precisely controlling salt crystallisation
only at the edge of the evaporation disc, this novel design also
can harvest the salts.
The feasibility and durability of the design have been validated
using seawater from Lacepede Bay in South Australia. This
technology is a promising solution to water shortages in regional
areas where grid electricity isn’t available.
The findings were published in the international journal Energy
& Environmental Science.
“Water security is the biggest challenge the world faces in the
21st century, especially as population grows and the effects of
climate change take shape. Developing and under-resourced
communities feel the effects of these factors the most,” Professor
“Utilising solar energy for water treatment has been widely
considered as one of the sustainable solutions towards addressing
the scarcity of clean water in some communities, without
sacrificing our environment or resources.
“Despite the significant progress achieved in material
development, the evaporation process has been impeded by the
concentration of salt on the surface, which affects the quality of
Researchers created a disc using super-hydrophilic filter paper
with a layer of carbon nanotubes for light absorption. A cotton
thread, with a 1mm diameter, acted as the water transport channel,
pumping saline water to the evaporation disc.
The saline water is carried up by the cotton thread from the bulk
solution to the centre of the evaporation disc. The filter paper
traps the pure water and pushes the remaining salt to the edges of
The light absorbance was measured to 94 per cent across the entire
solar spectrum. The disc also exhibited a rapid temperature
increase when exposed to light in both dry and wet states, rising
from 25C to 50C and 17.5C to 30C respectively within one minute.
This technology has also great potential in other fields, such as
industry wastewater zero liquid discharge, sludge dewatering,
mining tailings management and resource recovery. Future studies
will look to extend the technology to these applications with
“Our study results advance one step further towards the practical
application of solar steam generation technology, demonstrating
great potential in seawater desalination, resource recovery from
wastewater, and zero liquid discharge,” Professor Zhang said.
“We hope this research can be the starting point for further
research in energy-passive ways of providing clean and safe water
to millions of people, illuminating environmental impact of waste
and recovering resource from waste.”
Professor Zhang is the Director of the ARC Research Hub for
Energy-efficient Separation (EESep), which aims to develop
advanced separation materials, innovative products and smart
processes to reduce the energy consumption of separation processes
that underpin Australian industry.
He has just received a $50,000 grant from Perpetual for a separate
project looking at securing better water for rural Australia and
the South-east Asian region.
Nature Communications volume 10, Article number: 3012
Simultaneous production of fresh water and
electricity via multistage solar photovoltaic membrane
Wenbin Wang, et al.
The energy shortage and clean water scarcity are two key
challenges for global sustainable development. Near half of the
total global water withdrawals is consumed by power generation
plants while water desalination consumes lots of electricity.
Here, we demonstrate a photovoltaics-membrane distillation (PV-MD)
device that can stably produce clean water (>1.64 kg·m−2·h−1)
from seawater while simultaneously having uncompromised
electricity generation performance (>11%) under one Sun
irradiation. Its high clean water production rate is realized by
constructing multi stage membrane distillation (MSMD) device at
the backside of the solar cell to recycle the latent heat of water
vapor condensation in each distillation stage. This composite
device can significantly reduce capital investment costs by
sharing the same land and the same mounting system and thus
represents a potential possibility to transform an electricity
power plant from otherwise a water consumer to a fresh water
In this work, we report a strategy for simultaneous production of
fresh water and electricity by an integrated solar PV
panel-membrane distillation (PV-MD) device in which a PV panel is
employed as both photovoltaic component for electricity generation
and photothermal component for clean water production. In a
typical solar cell, 80–90% of the absorbed solar energy is
undesirably converted to heat, and thereafter passively and
wastefully dumped into the ambient air32. In this work, a MSMD
device is integrated on the backside of a commercial solar cell to
directly utilize its waste heat as a heat source to drive water
distillation. Under one Sun illumination, the water production
rate of the PV-MD is 1.79 kg m−2 h−1 for a 3-stage device, which
is three times higher than that of the conventional solar stills.
At the same time, the PV panel generates electricity with energy
efficiency higher than 11%, which is the same as that recorded on
the same PV panel without the back MD device and which is at least
9 times higher than those achieved in the previously published
works. The undoubted benefit of the integration of PV and water
distillation is the highly efficient co-generation of clean water
and electricity in one device at the same time on the same land,
which directly reduces land area requirement and the cost of the
mounting system as compared to two physically separate systems (PV
and solar distillation). Moreover, working directly with
commercial solar cells makes the PV-MD device close to practical
applications. This strategy provides a potential possibility to
transform an electricity generation plant from otherwise a water
consumer to a fresh water producer.
Structure of the MSMD device...
Each stage of the MSMD device was composed of four separate
layers: a top thermal conduction layer, a hydrophilic porous layer
of water evaporation layer, a hydrophobic porous layer of MD
membrane for vapor permeation, and a water vapor condensation
layer. Aluminum nitride (AlN) plate was used as the thermal
conduction layer because of its extremely high thermal
conductivity (>160 W m−1 K−1) and its anti-corrosion property
in salty water34. The hydrophobic porous layer was made of an
electrospun porous polystyrene (PS) membrane. The water
evaporation layer and condensation layer were of the same
material, a commercial hydrophilic quartz glass fibrous (QGF)
membrane with non-woven fabric structure.
In each stage of the MSMD device (Supplementary Fig. 2), the heat
is conducted through the thermal conduction layer to the
underlying hydrophilic porous layer. The source water inside the
hydrophilic porous layer is thus heated up to produce water vapor.
The water vapor passes through the hydrophobic porous membrane
layer and ultimately condenses on the condensation layer to
produce liquid clean water. The driving force for the water
evaporation and vapor condensation is the vapor pressure
difference caused by the temperature gradient between the
evaporation and condensation layers. In each stage, the latent
heat of water vapor, which is released during the condensation
process, is utilized as the heat source to drive water evaporation
in the next stage. The multistage design ensures the heat can be
repeatedly reused to drive multiple water evaporation–condensation
cycles. In a traditional solar still, the heat generated from the
sunlight via photothermal effect only drives one water
evaporation–condensation cycle, which sets up an upper theoretical
ceiling of the clean water production rate, ~1.60 kg m2 h−1, under
one-Sun condition in such a system. The multistage design makes
possible to break the theoretical limit as demonstrated very
recently by two groups27,28.
In this work, two source water flow modes, namely, dead-end mode
and cross-flow mode, are designed for the MSMD device (Fig. 1). In
the dead-end mode, the source water is passively wicked into the
evaporation layer by hydrophilic quartz glass fibrous membrane
strips via capillary effect. In this case, the concentration of
salts and other non-volatile matters in the evaporation layer
keeps increasing till reaching saturation in the end. A washing
operation is indispensable to remove the salts accumulated inside
the device for this mode, as reported in the previous works28.
However, the passive water flow reduces the complexity of the
device and gives a high water production rate in the early stage
for this operation mode. In the cross-flow mode, the source water
flows into the device driven by gravity or by a mechanical pump,
and, it flows out of the device before reaching saturation. In
this case, the outgoing water flow will take away a small amount
of sensible heat, leading to a slight drop in clean water
productivity in the early stage. However, it solves the salt
accumulation problem and avoids the need for frequent cleaning and
salt removal operation, which makes the device suitable for
In some experiments, a commercial spectrally selective absorber
(SSA) (ETA@Al, Alanod Solar) was used to replace the PV panel for
clean water production performance evaluation. This material can
decrease the radiation heat loss during operation because it
possesses a much smaller emissivity than PV panels, and that is
why it was adopted in both of the previous works on solar membrane
distillation28. We use the SSA-MD device to confirm that the
multistage MD device we fabricated in this work is comparable with
the state-of-the-art solar membrane distillation devices...
Synthesis of the polystyrene membrane
The hydrophobic polystyrene membrane was fabricated by
electrospinning method. Polystyrene was firstly dissolved in DMF
by mild stirring for 6 h to obtain 25 wt% homogeneous solution.
The solution was placed in three 5-mL syringes equipped with metal
needle of 0.52 mm inner diameter and then ejected with a feeding
rate of 5.0 mL h−1. The voltage was set at 30 KV and the distance
between the collector and the needle was 10 cm...
The QGF, PS membrane and AlN were assembled as shown in
Supplementary Fig. 1a. To avoid blocking the wick of the dead-end
device by PU foam, the wick was firstly wrapped by plastic film.
The PU foam precursor was obtained by mixing the part A and part B
of the PU system as 1:1 weight ratio and then was painted on the
side of the device. The device was kept at 50 °C for 12 h to
complete the foaming. The assembly of cross-flow MSMD was similar
to that of the dead-end MSMD, except that the wick was replaced
with the silicon tube with the diameter of 1 mm.
Simultaneous production of clean water and electricity
The device was put on the top of a square heat sink with a length
of 5 cm which was immersed in bulk water. Water was transported
from bulk water to the device by capillary effect and
transpiration effect via a small QGF membrane belt which was
connected to the distillation layer. In a practical scenario, the
flow rate of the source water in the cross-flow PV-MD can be
controlled by a flow control valve or flow meter. In our
experiments, an ISMATEC tubing pump was used to control the flow
rate of the source water more precisely. Solar irradiation was
provided by a solar simulator (Newport 94043A) with a standard AM
1.5 G spectrum optical filter. A 100 mL cup was used to collect
clean water and the amount of water collected was monitored and
recorded real-time. To reduce the evaporation of the collected
clean water in the cup, a funnel was put on the top of the cup.
The square photothermal material or square solar cell with the
length of 3.9 mm was put on the top of the device. Photovoltaic
responses (J–V curves) of the solar cell were measured by a
Keithley 2400 series source meter. For the cycling test, after
each cycle, 3 pieces of Kimwipes tissue (11 × 21 cm) were
connected to the inlets of the dead-end devices and stayed there
for 3 h to extract the concentrated water remaining in the QGF
membranes. For each new cycle, salt water was wicked into the QGF
membrane and extracted by the tissue again. This procedure was
repeated at least for 3 times to ensure that the QGFs were
METHOD AND DEVICE FOR ENHANCED WATER PRODUCTION IN
[ PDF ]
Inventor: WANG PENG [SA] SHI YIFENG [SA]
Applicant: UNIV KING ABDULLAH SCI & TECH [SA]
A solar-powered system including a chamber (202) that is bordered
by an evaporation layer (206) and a condensation layer (208); and
a photothermal layer (210) located over the evaporation layer
(206) so that sun rays incident on the photothermal layer (210)
are transformed into heat and the heat is supplied to the
evaporation layer (206) for evaporating water. The sun rays
incident on the photothermal layer (210) do not pass through the
condensation layer (208) prior to arriving at the photothermal
METHOD AND DEVICE FOR WATER EVAPORATION
[ PDF ]
A solar-powered system (200) includes a support portion (201A);
and an evaporation portion (201B) having a pumping layer (212) and
a photothermal layer (214). The support portion (201A) pumps a
fluid (222) to the evaporation portion (201B), the pumping layer
(212) evaporates the fluid (222) based on solar power; and the
photothermal layer (214) is insulated from the pumping layer
HYDROPHOBIC PHOTOTHERMAL MEMBRANES, DEVICES
INCLUDING THE HYDROPHOBIC PHOTOTHERMAL MEMBRANES, AND METHODS
FOR SOLAR DESALINATION
[ PDF ]
Embodiments of the present disclosure provide structures or
membranes including photothermal nanomaterials, devices including
the structure, methods of use, methods of desalination, and the
GRAFTED MEMBRANES AND SUBSTRATES HAVING SURFACES
WITH SWITCHABLE SUPEROLEOPHILICITY AND SUPEROLEOPHOBICITY AND
[ PDF ]
Disclosed herein are surface-modified membranes and other
surface-modified substrates exhibiting switchable oleophobicity
and oleophilicity in aqueous media. These membranes and substrates
may be used for variety of applications, including controllable
oil/water separation processes, oil spill cleanup, and oil/water
purification. Also provided are the making and processing of such
surface-modified membranes and other surface-modified substrates.
COMPOSITIONS AND METHODS FOR MICROPATTERNING
[ PDF ]
Described herein are patterned superhydrophobic surfaces,
substrates, devices, and systems including the patterned
superhydrophobic surfaces, and methods of making and uses thereof.
METHOD FOR PREPARING MICROSTRUCTURE ARRAYS ON THE
SURFACE OF THIN FILM MATERIAL
[ PDF ]
Methods are provided for growing a thin film of a nanoscale
material. Thin films of nanoscale materials are also provided. The
films can be grown with microscale patterning. The method can
include vacuum filtration of a solution containing the
nanostructured material through a porous substrate. The porous
substrate can have a pore size that is comparable to the size of
the nanoscale material. By patterning the pores on the surface of
the substrate, a film can be grown having the pattern on a surface
of the thin film, including on the top surface opposite the
substrate. The nanoscale material can be graphene, graphene oxide,
reduced graphene oxide, molybdenum disulfide, hexagonal boron
nitride, tungsten diselenide, molybdenum trioxide, or clays such
as montmorillonite or lapnotie. The porous substrate can be a
porous organic or inorganic membrane, a silicon stencil membrane,
or similar membrane having pore sizes on the order of microns.
MODERATE TEMPERATURE SYNTHESIS OF MESOPOROUS CARBON
Methods and composition for preparation of mesoporous carbon
material are provided. For example, in certain aspects methods for
carbonization and activation at selected temperature ranges are
described. Furthermore, the invention provides products prepared
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