Solar-driven desalination by using porous evaporators has been deemed to be a sustainable pathway to obtain freshwater. Despite the emerging anti-scaling evaporators, the durable evaporation in hypersaline water remains a formidable challenge because of the unpreventable salt accumulation in the porous structures. To enhance the descaling capacity of evaporators, a self-descaling Janus evaporator (SJE) featuring a “moving interface” is developed for durable and efficient desalination of hypersaline water. This evaporator consists of an Fe3O4-embedded poly(N-isopropylacrylamide) (PNIPAM) nanofibrous layer and a hydrophilic polyacrylonitrile (PAN) nanofibrous layer constrcuted by sequential electrospinning. Integrating the photothermal conversion of Fe3O4 and the thermal responsiveness of PNIPAM, the SJE exhibits a reversible solar-induced wettability transition from asymmetric wettability (under sunlight) to hydrophilic wettability (at night). Under sunlight, the top surface and the evaporation interface (i.e. air–water interface) are separated to prevent salt accumulation on the evaporator, benefiting efficient solar steam generation. At night, the air–water interface moves to the upper surface, showing the self-descaling ability. With this design, the SJE exhibits a high-efficiency water evaporation rate of 1.76 kg m−2 h−1 under one sun and demonstrates long-term stability (over 5 days) when treating 20 wt% NaCl solution. Overall, this work provides an exciting material solution with photothermal responsive design for the practical application of Janus evaporators in brine desalination.
A solar evaporator with simple fabrication process, exceptional photothermal conversion efficiency and dependable continuous water evaporation holds significant potential for seawater desalination and wastewater treatment. Despite the substantial research dedicated to developing high-efficiency solar evaporators, there remains a need for additional exploration to tackle concerns such as salt crystallization, low evaporation efficiency, poor durability and stability. Here, an efficient water transport PVA hydrogel (water transport layer) and polydopamine/carbon black modified 3D raised-fabric (photothermal layer) are innovatively designed as solar evaporators. The synergistic effect between the periodic raised structure and polydopamine/carbon black results in outstanding photothermal conversion capabilities of PDA/CB@RF. Meanwhile, the porous structure of PVA hydrogel and its vertically aligned channels facilitate ion exchange and ensure a consistent water supply to the photothermal layer. This phenomenon serves to prevent the accumulation of salt in the photothermal layer, thereby markedly enhance the water evaporation capability of the PDA/CB@RF evaporator. The results demonstrate that the PDA/CB@RF evaporator system exhibits excellent photothermal conversion performance with its surface temperature rapidly ascending to 73.3 ℃ under 1 sun light intensity, and effectively boost the water evaporation rate (1.73 kg m -2 h −1 , 1 sun). Furthermore, the PDA/CB@RF evaporator exhibits excellent conversion efficiency (91.9 %) and self-desalting capability. Overall, this solar evaporator system with a 3D raised fabric design integrates light and thermal energy, consistent water evaporation and self-desalting functionalities, which makes it hold the potential to solve the pressing challenge of water shortage.
Mu Wenxiao,Liang Weidong,Wang Yanqing,Sun Hanxue,Zhu Zhaoqi,Li Jiyan
Improving solar energy conversion efficiency and salt resistance is particularly important for the practical application of green and sustainable solar steam generation technology. In this work, an interfacial evaporation polypyrrole-coated film was fabricated by the mixed-dimensional clay consisting of 1D palygorskite (Pal), 2D montmorillonite (Mt) and mica, etc., that was intercalated using polyaniline (PANI) and then introduced polyvinyl pyrrolidone (PVP) as pore-forming agent and polyvinylidene fluoride (PVDF) as a base film. The prepared film could efficiently convert light energy to heat under solar irradiation with excellent properties of self-desalination and photothermal conversion efficiency as well as superhydrophilicity and low thermal conductivity. The photothermal conversion efficiency achieved up to 93.6% under the simulated sunlight of 1 kW m −2 . The evaporation rate in 15% NaCl brine differed very little from that in pure water, and 0.2 g of NaCl placed on the film would be eliminated in short time at room temperature, which demonstrated that the film had salt resistance and self-cleaning capability. In addition, the resulting film had low thermal conductivity (0.09994 W m −1 K −1 ) and good mechanical properties (tensile strength of 1.1 MPa) and exhibited superhydrophilicity (water contact angle ~ 0°) which could transport water molecules rapidly.
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