Flexible and Washable CNT-Embedded PAN Nonwoven Fabrics for Solar-Enabled Evaporation and Desalination of Seawater

Self-Assembled Hydrophobic/Hydrophilic Porphyrin-Ti3C2Tx MXene Janus Membrane for Dual-Functional Enabled Photothermal Desalination

Photothermal desalination is a promising approach for seawater purification by harvesting solar energy. Titanium carbide (Ti₃C₂T_x MXene) membranes have been regarded as potential materials for photothermal desalination by virtue of their excellent light-to-heat conversion. However, achieving a well-balanced synergy between high evaporation rate and good salt resistance remains a significant challenge due to their limited solar absorption and inferior stability. Herein, we report a self-assembled flexible porphyrin-Ti₃C₂T_x MXene Janus membrane (Janus PMX membrane) for dual-functional enabled photothermal desalination. The self-assembly of porphyrin on MXene not only effectively creates a favorable hydrophobic surface but also simultaneously enables efficient solar utilization. The significant interactions and charge redistribution between MXene and porphyrin lead to a stable hydrophobic/hydrophilic Janus structure with synergistically enhanced photothermal conversion. As a result, the Janus PMX membrane demonstrates highly efficient water pumping, heat localization, vapor generation, and salt resistance during photothermal desalination. This work presents an effective and facile strategy toward advancing a well-performing MXene membrane for efficient seawater desalination.

Facile preparation of polydimethylsiloxane/carbon nanotubes modified melamine solar evaporators for efficient steam generation and desalination

Solar driven interfacial evaporation has received extensive attention as a very promising desalination technique to solve the fresh water shortage crisis. However, salt-fouling and poor stability during long-term solar desalination seriously hinder applications of solar evaporators. In addition, most of the reported evaporators rely on expensive materials and complex preparation processes. Here, we report facile preparation of polydimethylsiloxane/carbon nanotubes (PDMS/CNTs) modified melamine solar evaporators for efficient steam generation and desalination. The elastic solar evaporators feature (i) macroporous network with rough skeleton owing to phase separation of PDMS, high solar absorbance (99%) and excellent photothermal performance, low thermal conductivity (0.032 W m^-1 K^-1), and (iii) unique wettability (hydrophobic upper surface and hydrophilic lower part). Consequently, the evaporators have an evaporation rate of 1.44 kg m^-2 h^-1 and a solar-to-vapor conversion efficiency of 84% for solar evaporation of deionized water under 1 sun illumination. Interestingly, the evaporators show similar solar evaporation performance for saline water compared to deionized water. Moreover, the evaporators show excellent salt-resistance and stability during long-term continuous solar desalination owing to rapid water replenishment in the evaporators. The evaporators may find practical applications in solar desalination because of the merits of the evaporators and the simple preparation method.

Plasma-Made Graphene Nanostructures with Molecularly Dispersed F and Na Sites for Solar Desalination of Oil-Contaminated Seawater with Complete In-Water and In-Air Oil Rejection

Solar desalination that exploits interfacial evaporation represents a promising solution to global water scarcity. Real-world feedstocks (e.g., natural seawater and contaminated water) include oil contamination issues, raising a compelling need for desalination systems that offer anti-oil-fouling capability; however, it is still challenging to prepare oil-repellent and meanwhile water-attracting surfaces. This work demonstrates a concept of molecularly dispersing functional F and Na sites on plasma-made vertically oriented graphene nanosheets to achieve an in-air and in-water oleophobic, hydrophilic surface. The graphene architecture presents high in-air (138°) and in-water (145°) oil contact angles, with simultaneously high water affinity (0°). Such surface wettability is enabled by oleophobic, hydrophobic -CF_x, and hydrophilic -COONa groups of the molecules that disperse on graphene surfaces; low-dispersion (0.439 mJ m^-2) and high-polarity (95.199 mJ m^-2) components of the solid surface tension; and increased surface roughness produced by graphene edges. The graphene nanostructures pump water upward by capillary action but repel oil from the surface, leading to complete in-water and in-air oil rejection and universal anti-oil-fouling capability for solar desalination. Consequently, stable solar-vapor energy efficiency of more than 85% is achieved regardless of whether the feedstock is pure or oil-contaminated water (e.g., a mixture of oil floating on water, an oil-in-water emulsion), resulting in the efficient production of clean water over several days. This outstanding performance is attributed to the universal (both in-water and in-air) oleophobic wettability, together with high light absorptance contributed by nanotraps, fast interfacial heat transfer enhanced by finlike nanostructures, and accelerated evaporation enabled by sharp graphene edges.

High Efficiency Solar Membranes Structurally Designed with 3D Core-2D Shell SiO2@Amino-Carbon Hybrid Advanced Composite for Facile Steam Generation

Steam generation through efficient utilization of solar energy is a promising technology in addressing the challenge of global freshwater shortage and water pollution. One of the biggest hurdles for traditional photothermal membranes to function continuously in a high temperature, high salt, and corrosive environment has been attributed to their rapid decline of mechanical properties. In this work, a highly efficient solar-driven interfacial water evaporation system has been developed via a polydopamine/carbon/silicon (PCS) composite membrane supported by a floating insulation foam substrate. A 3.1 fold increase in the water vaporization rate was recorded compared with the pure water system. The 2D-carbon nanolayer on the surface was successfully prepared by carbonizing low-cost linear polyethylene with a glass fiber (GF) membrane as the substrate, and then the carbon membrane was modified with dopamine to control water transport on the carbon coating and within the glass fiber. The PCS membrane has a high efficiency for solar steam generation owing to high optical absorption and has excellent solar thermal conversion capability. The evaporation rate and solar thermal conversion efficiency of the PCS membrane under simulated sunlight irradiation with 1 sun (1 kW·m^-2) are 1.39 kg·m^-2·h^-1 and 80.4% respectively, which are significantly higher compared to GF membrane, carbon/silicon (CS) membrane, and pure water without a photothermal membrane. The water evaporation system retained high efficiency after 20 cycles under simulated sunlight irradiation of 1 sun. This study provides critical insight on the design and fabrication of a highly efficient and durable evaporation system.

Cellular Structured CNTs@SiO2 Nanofibrous Aerogels with Vertically Aligned Vessels for Salt-Resistant Solar Desalination

The emerging solar desalination technology is considered as one of the most promising strategies to ensure water security. However, with the proceeding of solar desalination, salt crystallization on the surface of solar evaporators caused by increasing salinity of seawater will result in a decrease in the evaporation rate. Thus, it is still challenging to fabricate solar evaporators with superior salt resistance. In this work, elastic ceramic-based nanofibrous aerogels with a cellular architecture are fabricated by the combination of electrospinning and fiber freeze-shaping technologies, which are composed of vertically aligned vessels and porous vessel walls. Under the action of convection and diffusion promoted by this unique cellular architecture, the aerogels exhibit a superior salt-resistance without any salt crystals on the surface of aerogels even in 20% brine and under 6-sun irradiation. Moreover, by virtue of the synergistic effect of the promising structure and light absorbance of carbon nanotubes, aerogels possess a high light absorbance of up to 98% and excellent evaporation performance achieving 1.50 kg m^-2 h^-1 under 1-sun irradiation. This work may provide a fascinating avenue for the desalination of seawater in a salt-resistance and efficient manner.

Electrically Conductive Carbon Aerogels with High Salt-Resistance for Efficient Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation (SIE) is a promising approach for obtaining clean water but suffers from serious salt-fouling and poor long-term performance in seawater. Here, we report a high-performance salt-resistant SIE system from the perspective of nature sustainability. An electrically conductive and magnetic carbon aerogel is prepared by carbonization of Fe₃O₄-modified cellulose that originated from waste paper, and then its external surface is activated using O₂-plasma, forming the Janus superhydrophilic/superhydrophobic structure. The superhydrophilic external surface of the aerogel with macroporous skeleton assures ultrafast and adequate water supply and salt diffusion, while the superhydrophobic interior is the thermal insulator hindering water/salt infiltration. Benefiting from high solar absorption (∼97%), low thermal conductivity, unique Janus structure, and photothermal/electrothermal effects, the aerogel shows high evaporation rate (2.1 kg m^-2 h^-1, 1 sun) for simulated seawater. The aerogel features the following remarkable long-term salt-antifouling performance: (i) >20 d continuous evaporation in simulated seawater without degradation, even in 10 wt % NaCl solution, and (ii) >50 h continuous evaporation without seawater replenishment. Moreover, heavy metal ions, soluble organics, and oil can be completely removed from complex wastewater by the aerogel. This study offers an alternative approach in achieving clean water via SIE of seawater and complex wastewater.

Latest development in salt removal from solar-driven interfacial saline water evaporators: Advanced strategies and challenges

Solar-driven interfacial water evaporation, which gets rid of the limitation of saline waters, enables to supply potable water in the worldwide, especially in remote areas where only solar energy and water are available. This technique has also exhibited great potential applications in fields such as seawater desalination, steam sterilization, and fuel production. However, the evaporation efficiency decreases during continuous operation in saline water due to the blockage of the solar absorber resulting from crystalline salt deposition. Therefore, it is still a great challenge to design a stable and efficient solar-driven interfacial saline water evaporator. Herein, a variety of structural designs and engineering strategies for salt removal of evaporators in the latest years were reviewed. We classified these strategies as remaining unsaturated evaporation of saline water, preventing salt ions from contacting the solar absorber, dissolving and/or migrating back of crystalline salts, and keeping salt crystallization away from evaporation area. Finally, the current challenges and future research opportunities were discussed. The purpose of this review was: (1) to provide ideas to solve the problem of the reduced efficiency causing by salt deposition during saline water evaporation and (2) to promote the application of solar-driven interfacial saline water evaporation technology by providing the latest achievements in structural designs for salt removal.

Structure Architecting for Salt-Rejecting Solar Interfacial Desalination to Achieve High-Performance Evaporation With In Situ Energy Generation

The past few years have witnessed a rapid development of solar-driven interfacial evaporation, a promising technology for low-cost water desalination. As of today, solar-to-steam conversion efficiencies close to 100% or even beyond the limit are becoming increasingly achievable in virtue of unique photothermal materials and structures. Herein, the cutting-edge approaches are summarized, and their mechanisms for photothermal structure architecting are uncovered in order to achieve ultrahigh conversion efficiency. Design principles to enhance evaporation performance and currently available salt-rejection strategies for long-term desalination are systematically investigated. The guidelines to utilize every component in solar desalination systems for simultaneous in situ energy generation are also revealed. Finally, opportunities and challenges for future works in this field are also discussed and concluded.

Solar-Driven Freshwater Generation from Seawater and Atmospheric Moisture Enabled by a Hydrophilic Photothermal Foam

The accelerated increase in freshwater demand, particularly among populations displaced in remote locations where conventional water sources and the infrastructure required to produce potable water may be completely absent, highlights the urgent need in creating additional freshwater supply from untapped alternative sources via energy-efficient solutions. Herein, we present a hydrophilic and self-floating photothermal foam that can generate potable water from seawater and atmospheric moisture via solar-driven evaporation at its interface. Specifically, the foam shows an excellent solar-evaporation rate of 1.89 kg m-2 h-1 with a solar-to-vapor conversion efficiency of 92.7% under 1-Sun illumination. The collected water is shown to be suitable for potable use because when synthetic seawater samples (3.5 wt %) are used, the foam is able to cause at least 99.99% of salinity reduction. The foam can also be repeatedly used in multiple hydration-dehydration cycles, consisting of moisture absorption or water collection, followed by solar-driven evaporation; in each cycle, 1 g of the foam can harvest 250-1770 mg of water. To the best of our knowledge, this is the first report of a material that integrates all the desirable properties for solar evaporation, water collection, and atmospheric-water harvesting. The lightweight and versatility of the foam suggest that the developed foams can be a potent solution for water efficiency, especially for off-grid situations.