Sustainable Solar Evaporation from Solute Surface via Energy Downconversion
ABSTRACT: Abstract Solar?powered interfacial evaporation, a cost?effective and ecofriendly way to obtain freshwater from contaminated water, provides a promising path to ease the global water crisis. However, solute accumulation has severely impacted efficient light?to?heat?to?vapor generation in conventional solar evaporators. Here, it is demonstrated that an interfacial solar thermal photo?vapor generator is an efficient light?to?heat photo?vapor generator that can evaporate water stably in the presence of solute accumulation. An energy downconversion strategy which shifts sunlight energy from visible?near infrared to mid infrared?far infrared bands turns water from transparent to its own absorber, thus changing the fixed evaporation surface (black absorber) in a traditional solar evaporator to a dynamic front (solute surface). Light reflected from the solute can be recycled to drive evaporation. The prototype evaporator can evaporate at a high speed of 1.94 kg m?2 h?1 during a persistent solute accumulation process for 32 h. Such an ability to produce purified water while recycle valuable heavy metals from waste water containing heavy metal ions can inspire more advanced solar?driven water treatment devices. An interfacial solar thermal photo?vapor generator which shifts sunlight energy from visible?near infrared to mid infrared?far infrared bands can enable sustainable and efficient water evaporation from a solute surface as water serves as its own absorber at the dynamic evaporation front (solute layer) and the reflected light can be recycled.
Project description:Inspired by lotus leaves, self-floating Janus cotton fabric is successfully fabricated for solar steam generation with salt-rejecting property. The layer-selective soot-deposited fabrics not only act as a solar absorber but also provide the required superhydrophobicity for floating on the water. With a polyester protector, the prepared Janus evaporator exhibits a sustainable evaporation rate of 1.375 kW m<sup>-2</sup> h<sup>-1</sup> and an efficiency of 86.3% under 1 sun (1 kW m<sup>-2</sup>) and also performs well under low intensity and inclined radiation. Furthermore, no special apparatus and/or tedious processes are needed for preparing this device. With a cost of less than $1 per m<sup>2</sup>, this flexible Janus absorber is a promising tool for portable solar vapor generator.
Project description:Abstract The solar?assisted desalination generator (SADG) shows great potential for solving water scarcity problems. However, salt precipitation and accumulation is still a challenge for SADG, which slows down solar steam generation performance of evaporator during operation. Here, a facile integrative evaporator featuring stable and high evaporation performance breaks this bottleneck. By using a rational design in which amorphous carbon particles are evenly composited within the porous chitosan aerogel, the evaporator not only integrates excellent light absorption, heat management, and water transportation abilities but also endows a large vapor escape space. Upon desalination, salt concentration ingredients between carbon particles and chitosan membranes can be quickly balanced by water transport in interconnected chitosan chains, and thus salt precipiation on the evaporator surface would be avoided. Compared to other salt?rejection evaporators, the integrative evaporator can operate in 3.5 wt% brine for 60 days without salt precipiation and exhibits a stable evaporation rate (1.70 kg m?2 h?1), indicating its potential for practical applications in seawater desalination and the harvest of clean drinking water. An integrative aerogel is fabricated by a facile freeze?drying method. During solar?assisted desalination, the interconnected chitosan networks of the aerogel balances the salt concentration gradient between particles and chitosan skeleton depending on the effect of solar?driven water transportation. The generator has stable solar?assisted desalination performance with an evaporation rate of 1.70 kg m?2 h?1 under one?sun illumination for 60 days in 3.5 wt% brine.
Project description:Solar-driven vapor generation is a promising method to mitigate freshwater shortage and water contamination. However, most of the current highly efficient solar evaporators suffer from low robustness, tedious preparation procedures, and high cost. In this study, an easy-to-manufacture, low-cost, and high-reliability solar-driven evaporator is designed using a black cotton towel with a hollow conical shape. The reactive dye molecules diffuse into the cotton and form strong covalent bonds with the fiber after dyeing, which firmly fixes light-absorbing materials on the substrate. The looped pile structure of towels and hierarchical structure of yarns enable the evaporator enlarged surface area. The hollow conical shape of the cotton towel can effectively suppress the heat loss to the environment without compromising light absorption. The 3D vapor generator exhibits an evaporation rate of 1.40 and 1.27 kg m<sup>-2</sup> h<sup>-1</sup> for pure water and saline water, respectively. Meanwhile, this towel-based solar-driven evaporator exhibits a promising antifouling property as well as superior reusability and provides a reliable pathway in dealing with realistic waters, such as seawater and dyeing sewage. Therefore, the low-cost, solar-driven water evaporation system offers a complementary approach for high-efficiency vapor generation and water purification in practical application.
Project description:Abstract Highly efficient vapor generation with considerable stability under natural solar irradiance is a promising technology for seawater desalination and wastewater purification. Here a broadband solar absorber of reduced graphene oxide hydrogel membrane (rGOHM), synthesized via an environmentally friendly one?step hydrothermal reduction process, is demonstrated, which shows a high rate of solar vapor production and superior stability. The porous rGOHM containing more than 99.5% water within its small volume floats on the surface of water, exhibiting efficient solar absorption of ?98% across 300–2500 nm, as well as sufficient water?pumping pathways. The evaporation rate can be tuned by changing the water volume. By controlling the water volume, the self?floating rGOHM can enable efficient interfacial solar vapor generation at a high rate of ?2.33 kg m?2 h?1 under 1 sun, which is comparable to the rate generated by the evaporator with an extra insulator. In addition, the evaporation rate of rGOHM is only slightly affected at a high saltwater concentration (at least 15 wt%), and the rGOHM shows mechanical and physical stability. The superior evaporation performance combined with efficient eradication of wastewater contaminants, cost?effectiveness, and straightforward fabrication process, makes this rGOHMs ideal for advanced high?concentration seawater desalination and wastewater treatment technologies. A self?floating reduced graphene oxide hydrogel membrane (rGOHM) is demonstrated for stable, high?performing solar vapor evaporation under 1 sun. The rGOHM shows an interfacial solar vapor generation rate of 2.33 kg m?2 h?1, which is comparable to the rate generated by an evaporator with an extra insulator and is only slightly degraded in highly concentrated brine up to 15 wt%.
Project description:Solar-driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high-cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three-dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light-facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light-to-vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO<sub>2</sub> photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu<sub>2</sub> O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy-to-perform construction on-site, providing a promising opportunity for efficient and decentralized water and clean fuel production.
Project description:Biomass wastes are abundant and common in our daily life, and they are cost-effective, promising, and renewable. Herein, collected willow catkins were used to prepare a hydrophilic biochar composite membrane, which was placed in a tree-like evaporation configuration to simulate a natural transpiration process. The strong light absorption (?96%) of the biochar layer could harvest light and convert it into thermal energy, which then is used to heat the surrounding water pumped by a porous water channel via capillary action. A hydrophilic light-absorber layer remarkably increased the attachment sites of water molecules, thereby maximizing the use of thermal energy. At the same time, hierarchically porous structure and large specific surface area (?1380 m2 g-1) supplied more available channels for rapid water vapor diffusion. The as-prepared composite membrane with a low-cost advantage realized a high evaporation rate (1.65 kg m-2 h-1) only under 1 sun illumination (1 kW m-2), which was improved by roughly 27% in comparison with the unmodified hydrophobic composite membrane. The tree-like evaporation configuration with excellent heat localization resulted in the evaporator achieving a high solar-to-vapor conversion efficiency of ?90.5%. Besides, the composite membrane could remove 99.9% sodium ions from actual seawater and 99.5% heavy metal ions from simulated wastewater, and the long-term stable evaporation performance proved its potential in actual solar desalination. This work not only fabricated an efficient evaporator but also provided a strategy for reusing various natural wastes for water purification.
Project description:Solar steam generation is critical for many important solar-thermal applications, but is challenging to achieve under low solar flux due to the large evaporation enthalpy of water. Here, we demonstrate a three-dimensional porous solar-driven interfacial evaporator that can generate 100 °C steam under 1 sun illumination with a record high solar-to-steam conversion efficiency of 48%. The high steam generation efficiency is achieved by localizing solar-thermal heating at the evaporation surface and controlling the water supply onto the porous evaporator through tuning its surface wettability, which prevents overheating of the evaporator and thus minimizes conductive, convective, and radiative heat losses from the evaporator. The design of steam outlet located at the sidewall of the evaporator rather than from the solar absorber surface not only facilitates the collection of generated steam, but also avoids potential blockage of solar radiation by the condensing steam. The high-efficiency solar-driven evaporator has been used to generate hot steam for outdoor removal of paraffin on the wall of oil pipelines, offering a promising solution to mitigate the wax deposition issue in petroleum extraction processes.
Project description:Solar vapor generation technology is promising in seawater desalination, sewage purification, and other fields. However, wide application of this technology is still largely confined due to its high cost and difficulties for scalable production. In this study, an ever-floating solar evaporator is fabricated by coating multiwall carbon nanotubes on a bicomponent nonwoven composed of polypropylene/polyethylene core-sheath fibers. This all-fiber structure is highly porous and ultralight, with large specific area (for efficient water evaporation), interconnected channels (for easy vapor escape), and low thermal conductivity (to avoid heat loss). The unique unidirectional water-transfer behavior of the nonwoven enables it to spontaneously pump an adjustable amount of water for interfacial solar heating and a delicate balance between water supply and loss may accelerate the evaporation speed of water. These distinct benefits endow the solar evaporator with excellent evaporation rates of 1.44 kg m<sup>-2</sup> h<sup>-1</sup> under the simulated irradiation of 1 sun and 12.81 kg m<sup>-2</sup> d<sup>-1</sup> under natural sunlight. Moreover, the evaporator can be fabricated by using low-cost materials and industrialized methods (overall cost ≈2.4 USD m<sup>-2</sup> ), making one believe its practical significance for commercial solar steam evaporation.
Project description:Interfacial water evaporation technology by using solar energy provides one of the promising pathways for freshwater shortage management. However, current research mainly focuses on the improvement of evaporation efficiency by macro or microregulations, ignoring the steam temperature, which is a manifestation of the quality of water. Herein not only is a high-rate solar evaporation achieved but also steam temperature is enhanced by a simple three-tier (wet absorber-air gap-dry absorber) device. In a routine interfacial evaporation test, the evaporator achieves a stable evaporation rate up to 2.15 kg m<sup>-2</sup> h<sup>-1</sup> under one sun, demonstrating a competitive evaporation rate compared with other reports. With the three-tier device, the steam temperature can increase 33.7%, 41.13%, and 47% without dry absorber under one sun, two sun, and three sun illumination, respectively. At the same time, the steam temperature can be as high as 95.5 °C under three sun intensities. This work provides the possibility of using a simple three-tier device for high-temperature steam generation without extra energy input, which contributes to an idea for future research on the production high-quality water.
Project description:Interfacial solar steam generation is a highly efficient and sustainable technology for clean water production and wastewater treatment. Although great progress has been achieved in improving evaporation rate and energy efficiency, it's still challenging to fully eliminate the energy loss to the surrounding environment during solar steam generation. To achieve this, a novel heatsink-like evaporator (HSE) is developed herein. During solar evaporation, the temperature on the top solar evaporation surface can be regulated by the fin structures of the HSE. For the evaporators with 5 to 7 heatsink fins, the temperature of the solar evaporation surface is decreased to be lower than the ambient temperature, which fully eliminates the radiation, convection, and conduction heat losses, leading to the absolute cold evaporation over the entire evaporator under 1.0 sun irradiation. As a result, massive energy (4.26 W), which is over 170% of the received light energy, is harvested from the environment due to the temperature deficit, significantly enhancing the energy efficiency of solar steam generation. An extremely high evaporation rate of 4.10 kg m<sup>-2</sup> h<sup>-1</sup> is realized with a 6-fin photothermal HSE, corresponding to an energy conversion efficiency far beyond the theoretical limit, assuming 100% light-to-vapor energy conversion.