Bioinspired Soot-Deposited Janus Fabrics for Sustainable Solar Steam Generation with Salt-Rejection.
ABSTRACT: 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-2 h-1 and an efficiency of 86.3% under 1 sun (1 kW m-2) 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 m2, this flexible Janus absorber is a promising tool for portable solar vapor generator.
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: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:Ambient sunlight-driven CO<sub>2</sub> methanation cannot be realized due to the temperature being less than 80?°C upon irradiation with dispersed solar energy. In this work, a selective light absorber was used to construct a photothermal system to generate a high temperature (up to 288?°C) under weak solar irradiation (1?kW?m<sup>-2</sup>), and this temperature is three times higher than that in traditional photothermal catalysis systems. Moreover, ultrathin amorphous Y<sub>2</sub>O<sub>3</sub> nanosheets with confined single nickel atoms (SA Ni/Y<sub>2</sub>O<sub>3</sub>) were synthesized, and they exhibited superior CO<sub>2</sub> methanation activity. As a result, 80% CO<sub>2</sub> conversion efficiency and a CH<sub>4</sub> production rate of 7.5?L?m<sup>-2</sup> h<sup>-1</sup> were achieved through SA Ni/Y<sub>2</sub>O<sub>3</sub> under solar irradiation (from 0.52 to 0.7?kW?m<sup>-2</sup>) when assisted by a selective light absorber, demonstrating that this system can serve as a platform for directly harnessing dispersed solar energy to convert CO<sub>2</sub> to valuable chemicals.
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: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: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: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:Efficient broadband absorption of solar radiation is desired for sea water desalination, icephobicity and other renewable energy applications. We propose an idea of superimposing two high-loss resonances to broaden bandwidths of a few-layer absorber, which is made of dielectric/ metal/dielectric/ metal layers. Both the simulation and experiment show that the structure has an averaged absorption efficiency higher than 97% at wavelengths ranging from 350 to 1200 nm. The bandwidth of the absorption larger than 90% is up to 1000 nm (410-1410 nm), which is greater than that (??750 nm) of previous MIM planar absorbers. Especially, the average absorption from 350 to 1000 nm is kept above 90% at an incidence angle as high as 65°, meanwhile still maintained above 80% even at an incident angle of 75°. The performance of angular insensitivity is much better than that of previous few-layer solar absorbers. The flexible 1D nonoble metasurface absorbers are fabricated in a single evaporation step. Under the illumination of a halogen lamp of P?=?1.2 kW/m<sup>2</sup>, the flexible metasurface increases its surface temperature by 25.1 K from room temperature. Further experiments demonstrate that the heat localization rapidly melts the accumulated ice. Our illumination intensity (P?=?1.2 kW/m<sup>2</sup>) is only half of that (P?=?2.4 kW/m<sup>2</sup>) in previous solar anti-ice studies based on gold/TiO<sub>2</sub> particle metasurfaces, indicating that our metasurface is more advantageous topractical applications. Our results illustrate an effective pathway toward the broadband metasurface absorbers with the attractive properties of mechanical flexibility, low cost of the no-noble metals, and large-area fabrications, which have promising prospects in the applications of solar heat utilization.
Project description:Electrically driven steam generation is a critical process for many heating-related applications such as sterilization and food processing. Current systems, which rely on heating up the bulk water to generate steam, face the dilemma in achieving a large evaporation flux and fast thermal response. Herein, we report a self-floating electrically driven interfacial evaporator for fast high-efficiency steam generation independent of the amount of loaded bulk water in the system. Through localized heating of the wicked water at the air-water interface, the evaporator has achieved an electrical-to-steam energy conversion efficiency of ?90% at a heating power density of 10 kW/m2 and a fast thermal response of 20 s. The interfacial evaporation design not only achieves a high evaporation efficiency within a broad range of heating power densities by using different wicking materials, but also enables attaining a high evaporation temperature under low heating power densities by tuning the ratio of the vapor outlet area and the evaporation surface area. By integrating an interfacial evaporator within a sanitizer, the resultant system has demonstrated a faster steam temperature rise and superior steam sterilization performance than the commercial bulk heating-based approach.
Project description:Efficient and cost-effective solar steam generation requires self-floating evaporators which can convert light into heat, prevent unnecessary heat loss and greatly accelerate evaporation without solar concentrators. Currently, the most efficient evaporators (efficiency of ?80% under 1 sun) are invariably built from inorganic materials, which are difficult to mold into monolithic sheets. Here, we present a new polymer which can be easily solution processed into a self-floating monolithic foam. The single-component foam can be used as an evaporator with an efficiency at 1 sun comparable to that of the best graphene-based evaporators. Even at 0.5 sun, the efficiency can reach 80%. Moreover, the foam is mechanically strong, thermally stable to 300 °C and chemically resistant to organic solvents.