Three-Dimensional Wood-Inspired Bilayer Membrane Device Containing Microchannels for Highly Efficient Solar Steam Generation

Solar interfacial evaporation devices for desalination and water treatment: Perspective and future

Water is an essential commodity for society, and alternate resources such as seawater and wastewater are vital for the future. There are various desalination technologies that can provide sufficient and sustainable water sources. Renewable energy-based desalination technologies like solar-based interfacial evaporation are very efficient and sustainable desalination methods. Solar-based interfacial evaporation has been a focus due to its efficient and easy-to-use methods. Still, research is needed for fouling resistance, scalable and low-cost materials, and devices for solar interfacial evaporation. Recent research focuses on the materials for evaporation devices, but various other aspects of device design and fabrication methods are also necessary to improve device performance. In this article, all the evaporator device configurations and strategies for efficient evaporator devices are compiled and summarized. The evaporator devices have been classified into eight main categories: monolayer, bilayer, tree-like design, low-temperature designs, 3D-Origami-based designs, latent heat recovery design, design with storage/batch process, and contactless design. It was found that a good absorber, well-engineered air-water interface, and bottom-layer insulation are necessary for the best systems. The current research focuses on the vapor production output of the devices but not on the water production from devices. So, the focus on device-based water production and the associated cost of the water produced is essential. This article articulates the strategies and various scalable and efficient devices for evaporation-based solar-driven desalination. This article will be helpful for the researchers in improving devices output and coming up with a sustainable desalination and water treatment.

An efficient interfacial solar evaporator featuring a hierarchical porous structure entirely derived from waste cotton

Interfacial solar evaporators are widely used to purify water. However, photothermal materials commonly constituting most interfacial solar evaporators remain expensive; additionally, the inherent structure of the evaporators limits their performance. Furthermore, the large amount of waste cotton produced by the textile industry is an environmental threat. To address these issues, we propose an interfacial solar evaporator, H-CA-CS, with a hierarchical porous structure. This evaporator is made entirely of waste cotton and uses carbon microspheres (CMS) and cellulose aerogel (CA) as photothermal and substrate materials, respectively. Additionally, its photothermal layer (CS layer) has large pores and a high porosity, which promote light absorption and timely vapor escape. In contrast, the water transport layer (CA layer) has small pores, providing a robust capillary effect for water transport. Combined with the outstanding light absorption properties of CMS, H-CA-CS exhibited superior overall performance. We found that H-CA-CS has an excellent evaporation rate (1.68 kg m-2 h-1) and an efficiency of 90.6 % under one solar illumination (1 kW m-2), which are superior to those of many waste-based solar evaporators. Moreover, H-CA-CS maintained a mean evaporation rate of 1.61 kg m-2 h-1, ensuring sustainable evaporation performance under long-term scenarios. Additionally, H-CA-CS can be used to purify seawater and various types of wastewater with removal efficiencies exceeding 99 %. In conclusion, this study proposes a method for efficiently using waste cotton to purify water and provides novel ideas for the high-value use of other waste fibers to further mitigate ongoing environmental degradation.

Designing a solar interfacial evaporator based on tree structures for great coordination of water transport and salt rejection

Solar interfacial evaporation has been receiving increasing attention but it is still a huge challenge to achieve excellent coordination between efficient water transport and salt rejection. Here, unlike the common wood-inspired evaporators with equal-diameter directional pores, we have constructed an integrated structure with highly connected gradient pores that mimic the xylem vessels and phloem sieve tubes found in trees. The bio-inspired structure can reduce the resistance of water transport and salt rejection in the same channel. The average transport speed of the 6.5 cm high (2 cm in diameter) porous structure reached 1.504 g s^-1, and water was transported 16 cm after 100 seconds. Using multilayer graphene oxide as the photothermal conversion material, the evaporators with different heights can work for more than 9 hours under the condition of 1 sun illumination and 23 wt% brine without any salt crystallization, and the evaporation rates range from 3.28 to 4.51 kg m^-2 h^-1, with the highest energy utilization efficiency of about 80%. When used in heavy metal treatment, the rejection was greater than 99.99%. This research provides a simple but innovative design idea for evaporators and is expected to further expand the application of solar interfacial evaporation.

Tailorable Lignocellulose-Based Aerogel to Achieve the Balance between Evaporation Enthalpy and Water Transport Rate for Efficient Solar Evaporation

Solar-driven interfacial evaporation technology has become an effective approach to alleviate freshwater shortage. To improve its evaporation efficiency, the pore-size dependence of the water transport rate and evaporation enthalpy in the evaporator should be further investigated. Based on the transportation of water and nutrients in natural wood, we facilely designed a lignocellulose aerogel-based evaporator using carboxymethyl nanocellulose (CMNC) cross-linking, bidirectional freezing, acetylation, and MXene-coating. The pore size of the aerogel was adjusted by controlling its CMNC content. When the channel diameter of the aerogel-based evaporator increased from 21.6 to 91.9 μm, the water transport rate of the proposed evaporator increased from 31.94 to 75.84 g min^-1, while its enthalpy increased from 1146.53 to 1791.60 kJ kg^-1. At a pore size of 73.4 μm, the evaporation enthalpy and water transport rate of the aerogel-based evaporator achieved a balance, leading to the best solar evaporation rate (2.86 kg m^-2 h^-1). The evaporator exhibited excellent photothermal conversion efficiency (93.36%) and salt resistance (no salt deposition after three cycles of 8 h). This study could guide the development of efficient solar-driven evaporators for seawater desalination.

Polylactic acid scaffold with directional porous structure for large-segment bone repair

Biodegradable porous scaffolds with different structure, porosity, and strength play a critical role in the repair and regeneration of defects in bone tissue engineering by changing the proliferation condition for cell. In this study, polylactic acid (PLA) scaffold with directional porous structure is designed and fabricated using the method of ice template and phase inversion for speeding up bone repair by promoting the growth and proliferation of bone cells. The morphology, mechanical properties, hydrophilicity, and wicking properties of PLA scaffolds were characterized by scanning electron microscope, universal testing machine, contact angle tester and wicking rate test, respectively. In vitro biocompatibility has been investigated through measuring cell adhesion, proliferation, and viability on PLA scaffold with directional porous structure. Prepared PLA scaffold was implanted into animals to observe the repair mechanism of large-sized bone defects. This study proposes a novel bioporous scaffold design to induce osteocyte growth at the rat calvaria with a directional pore structure, and the scaffold edges were integrated with the calvaria at week 12, effectively promoting the repair and regeneration of defective bone tissue.

A bioinspired solar evaporator with a horizontal channel-like framework for efficient and stable high-salinity brine desalination

In recent years, solar steam generation has been one of the most promising and sustainable techniques for water desalination. However, the heat loss to bulk water dramatically decreases the evaporation rate. Besides, salt deposition on the evaporation surface during brine treatment limits the long-term operation of evaporators. Herein, solar evaporators with a horizontal channel-like framework are reported and high efficiency and outstanding salt resistance are achieved. Firstly, eggplants with a hollow fiber alignment structure were carbonized as CEP evaporators. The CEP-H evaporator with a horizontal fiber growth direction shows a high evaporation efficiency of 90.6% and excellent salt resistance when treating high-salinity brine (20 wt%). The low thermal conductivity perpendicular to the fiber growth direction impedes the conductive heat transfer into bulk water, and fast water transport along the fiber growth direction is beneficial for salt resistance. In addition, a proof-of-concept evaporator polypyrrole-coated polypropylene hollow fiber membrane with a horizontal channel-like framework (PPy/PP-H) has also been developed. This hollow fiber membrane shows a high evaporation rate of 1.64 kg m^-2 h^-1 due to multiangle evaporation and also demonstrates excellent salt-resisting performance for high-salinity brine treatment (20 wt%). The study demonstrates the effect of the horizontal channel-like framework for high evaporation performance and salt resistance, providing new insights into the solar evaporator design for seawater desalination and wastewater treatment.

Magnetically Driven Tunable 3D Structured Fe3 O4 Vertical Array for High-Performance Solar Steam Generation

Structural design of the solar-absorbing layer has been considered as one of the most direct and effective approaches for improving the solar steam generation performance by maximizing the absorption of sunlight, but great challenges in manipulation simplification and structure controllability still remain. Herein, a polyester (PET) fabric covered with a vertically aligned 3D tower-like ferrosoferric oxide (Fe₃ O₄ ) array via a convenient magnetically driven spray-coating method is reported, and both the spatial density and height of the Fe₃ O₄ array are tunable upon spraying time. It shows an extremely high solar absorbance (98.6%) in the entire solar spectrum, which is superior to the corresponding 2D Fe₃ O₄ structure (91.1%). Combining the obtained 3D Fe₃ O₄ /PET with a yolk-shell hydrophobic/superhydrophilic modified melamine-formaldehyde (mMF) sponge, the carefully designed and fabricated 3D Fe₃ O₄ /PET-mMF evaporator can realize a high water evaporation rate of 1.59 kg m^-2 h^-1 under 1 kW m^-2 solar illumination, outperforming most related solar steam generation systems. With the advantages of cost-effectiveness, high evaporation rate, reliable endurance, and structural controllability, this 3D structural design provides an avenue to build up high-performance solar energy-driven water steam generation systems.

Constructing a Solar Evaporator with Salt-Collecting Paper by Stacking Hydrophilic Sponges for Freshwater Production and Salt Collection

Solar water evaporation is universally considered as an effective method to alleviate the freshwater shortage worldwide. A series of three-dimensional, salt-resistant evaporators have been brought out to improve the evaporation performance. However, little attention was paid to the collection of salt from seawater and high salinity brine. In this work, a carbon black polyvinyl alcohol (PVA) sponge was prepared to harvest light using a physical adsorption method to load carbon black on the PVA sponge. The experimental results showed that optimal light absorption (97.8%) and evaporation rate (1.60 kg m^-2 h^-1) were achieved when the carbon black PVA sponge was produced at a carbon black concentration of 1 g L^-1. Moreover, we stacked PVA sponges beneath the carbon black PVA sponge to construct a non-photothermal evaporation area. It was seen that the evaporator with an eight-layer PVA sponge had an excellent evaporation rate as high as 2.35 kg m^-2 h^-1. In addition, the salt-collecting paper, all-black printed by a laser printer, was inserted between the stacked PVA sponges for salt collection, and the eight-layer PVA sponge evaporator with the salt-collecting paper at the fourth floor was tested in a 2 h desalination experiment. The outcome indicated that a square meter of this evaporator can produce about 7.03 L of freshwater and 206 g of salt per day from 10 wt % NaCl solution. As a result, the solar evaporator developed in this work is capable of collecting salt and maintaining a high evaporation rate, which is of great competence in the fields of freshwater production and salt collection.

Interfacial Solar Evaporation by a 3D Graphene Oxide Stalk for Highly Concentrated Brine Treatment

In this work, we demonstrate a 3-dimensional graphene oxide (3D GO) stalk that operates near the capillary wicking limit to achieve an evaporation flux of 34.7 kg m^-2 h^-1 under 1 sun conditions (1 kW/m²). This flux represents nearly a 100 times enhancement over a conventional solar evaporation pond. Interfacial solar evaporation traditionally uses 2D evaporators to vaporize water using sunlight, but their low evaporative water flux limits their practical applicability for desalination. Some recent studies using 3D evaporators demonstrate potential for more efficient water transfer, but the flux improvement has been marginal because of a low evaporation area index (EAI), which is defined as the ratio of the total evaporative surface area to the projected ground area. By using a 3D GO stalk with an ultrahigh EAI of 70, we achieved nearly a 20-fold enhancement over a 2D GO evaporator. The 3D GO stalk also exhibited additional advantages including omnidirectional sunlight utilization, a high evaporation flux under dark conditions from more efficient utilization of ambient heating, a dramatic increase of the evaporation rate by introducing wind, and scaling resistance in evaporating brines with a salt content of up to 17.5 wt %. This performance makes the 3D GO stalk well suited for the development of a low-cost, reduced footprint technology for zero liquid discharge in brine management applications.

Bioinspired Cellulose Foam with Excellent Water Wicking and Flux Properties Prepared Using Ice Template

The application and functionalization of cellulose has been attracting increased attention in academic and industrial studies because of its wide range of sources, short renewable cycle, and low environmental impact. In order to enhance the application field of cellulose and decrease the environmental pollution for organic solvent associated with its preparation, cellulose foam with a vertically hierarchically porous structure similar to wood was designed and fabricated successfully from a cellulose aqueous solution using an ice templated in this study. The cellulose foam prepared using a 3 wt % concentration possessed a uniform vertical hierarchically porous structure, which could provide a pathway for the flow of water or air based on the capillary effect. The highest water wicking rate and flux were 7.8184 mm·s^-1 and 29.49 mL·min^-1·g^-1, respectively, for the porous foam prepared using a 3 wt % concentration. The mechanical testing experiment showed that the porous structure did not reduce the amount of stress that the sample could endure before being damaged. The compression strength increased with increasing cellulose concentration in solution. Therefore, the hierarchical structure formed in the prepared cellulose foam effectively improved the water flux behavior and provided a structural basis for future applications of cellulose scaffolds.

Versatile Janus Composite Nonwoven Solar Absorbers with Salt Resistance for Efficient Wastewater Purification and Desalination

Solar steam generation is an efficient way of harvesting solar energy for water purification. Developing a versatile solar absorber with salt resistance and the capability to purify an oil-in-water emulsion is a grand challenge. Herein, a polypropylene (PP) nonwoven fabric-based photothermal absorber is fabricated by the combination of carbon nanotubes (CNTs), polypyrrole (PPy), and a fluorinated hydrophobic coating in a layer-by-layer approach. The specially designed architecture displays a hierarchical microstructure and Janus wetting properties, facilitating solar absorption and heat generation on the evaporation surface, and can effectively prevent salt crystallization. The water layer formed on the superhydrophilic/underwater superoleophobic bottom surface could repel oil droplets and form a channel to advect concentrated salt back into bulk water, which enabled high purity separation of an oil-in-water emulsion and continuous desalinization of seawater without the reduction of the evaporation rate. As a result, the solar absorber can achieve a remarkable evaporation rate of 1.61 kg m^-2 h^-1 and an energy efficiency of 91.2% under 1 sun irradiation and shows extraordinary performance in the purification of contaminated wastewater (over 99.8% purity). The strategy proposed provides a pathway for developing versatile high-performance solar absorbers for the sustainable treatment of saline water, wastewater, and oil-containing water.

Highly Anisotropic Corncob as an Efficient Solar Steam-Generation Device with Heat Localization and Rapid Water Transportation

Solar steam generation is receiving considerable interest because of its potential application in wastewater treatment and desalination. Many devices with various photothermal materials and structures have been demonstrated to be solar steam evaporators by improving their light absorption, heat loss, water transportation, and vapor escape. However, developing a biomass-based evaporator with heat localization and rapid water transportation is highly desired yet still challenging. Here, corncobs, a kind of agricultural waste with vascular bundle and "vesiculose" structures, are used to fabricate solar steam-generation devices. After high-temperature treatment, the carbonized corncobs maintain the highly anisotropic porous framework and favorable hydrophilicity and thereby have excellent thermal management and water transportation. With efficient solar absorption, heat localization, and rapid water transportation, the lightweight carbonized corncobs can float on water and generate water vapor with a high steam generation efficiency of 86.7% under 1 sun.