A flexible and salt-rejecting electrospun film-based solar evaporator for economic, stable and efficient solar desalination and wastewater treatment

The emerging solar interfacial evaporation (SIE) technology is an effective measure to address freshwater resources. An efficient and stable solar interfacial evaporator cannot be achieved without the synergy of three key factors: water transport, solar thermal conversion, and thermal management. The performance of a solar interfacial evaporator can be improved through the rational selection of materials and the structural design of these three key factors. Due to superior nanostructures, electrospun nanofibrous materials often exhibit some unique properties that facilitate the construction of solar interface evaporators with good performance. So far, electrospinning has been used to prepare structures such as solar absorbers, water transportation, and thermal insulation in various solar interfacial evaporators. This review presents the fundamental research and technological development in the application of electrospinning techniques to solar interfacial evaporators on structures, morphology, and properties. Then, the latest advances in the use of electrospinning technology in solar interfacial evaporators are summarized and the current issues facing the application of electrospinning technology to solar interfacial evaporators are presented. These systematic discussions can provide ideas and approaches for the rational design of electrospun nanofiber materials for solar interfacial evaporators in the future.

Thermal insulation design for efficient and scalable solar water interfacial evaporation and purification

Interfacial solar evaporation has attracted substantial research interest as an eco-friendly means of desalination. A great deal of work has been devoted to exploring broad-spectrum solar absorbers, porous floating systems, and appropriate thermal insulations. During desalination, salt accumulation may block the evaporation channel and severely decline the evaporation rate. Herein, we designed a salt-resistant solar evaporator (PANI-SPPSU@PU) based on a polyurethane sponge (PU) with the polyaniline (PANI) photothermal layer and a negatively charged sulfonated polyphenylsulfone (SPPSU) interlayer. The negatively charged interlayer appends an energy barrier, which reduces the amount of the salt ions diffusing into the interlayer and regulates the local salt concentration. By this negatively charged structure, the solar evaporator enables stable evaporation from a wide range of salinity (even saturation concentration), and achieves a high evaporation rate above 1.91 kg/m2 h in 10 wt% NaCl (at the state of the art). A promising salt-resistant mechanism via the synergy of the diffusion effect and the Donnan effect is also proposed in this work. Therefore, it provides a promising pathway for practical solar-powered high-salinity seawater desalination.

Directionally tailoring micro-nano hierarchical tower structured Mn0.6Ni1.4Co2Oy toward solar interfacial evaporation

Interfacial solar evaporation based on Janus films: An effective strategy to improve salt tolerance and antifouling performance

Solar interfacial evaporation based oil/water separation from emulsion using a wood-melamine/calcium alginate composite structure

Production of fresh water based on a renewable energy source is one of the most important global challenges for mankind due to ever-accelerating climate changes. Solar thermal evaporation shows promise for overcoming the water scarcity problem by utilizing solar energy, the most abundant and clean energy source. To enhance the performance of solar evaporators, interfacial solar evaporators have been introduced, which harness solar energy onto the water surface. To enable energy conversion and water evaporation at the interfaces of a solar evaporator, multi-scale heat and water transport have been investigated. Furthermore, various light-absorbing materials and system configurations have been studied to achieve the theoretical maximum performance. The fundamental physics of the interfacial solar evaporator, including thermal and water transport, and a broad range of interfacial solar evaporator devices in terms of the fabrication techniques and its structures are reviewed.

Design of MoS2/MMT bi-layered aerogels integrated with phase change materials for sustained and efficient solar desalination

A 3D Corncob-based interfacial solar evaporator enhanced by environment energy with salt-rejecting and anti-corrosion for seawater distillation

Solar interfacial evaporation technology has the advantages of environmentally conscious and sustainable benefits. Recent research on light absorption, water transportation, and thermal management has improved the evaporation performance of solar interfacial evaporators. However, many studies on photothermal materials and structures only aim to improve performance, neglecting explanations for heat and mass transfer coupling or providing evidence for performance enhancement. Numerical simulation can simulate the diffusion paths and heat and water transfer processes to understand the thermal and mass transfer mechanism, thereby better achieving the design of efficient solar interfacial evaporators. Therefore, this review summarizes the latest exciting findings and tremendous advances in numerical simulation for solar interfacial evaporation. First, it presents a macroscopic summary of the application of simulation in temperature distribution, salt concentration distribution, and vapor flux distribution during evaporation. Second, the utilization of simulation in the microscopic is summed up, specifically focusing on the movement of water molecules and the mechanisms of light responses during evaporation. Finally, all simulation methods have the goal of validating the physical processes in solar interfacial evaporation. It is hoped that the use of numerical simulation can provide theoretical guidance and technical support for the application of solar-driven interfacial evaporation technology.

Hyperstable and compressible plant fibers/chitosan aerogel as portable solar evaporator

Solar interfacial evaporation (SIE) has emerged as a highly promising approach for sustainable freshwater harvesting. However, maintaining a stable evaporation rate and achieving a high freshwater yield in high-salinity brines remain a significant challenge. In this study, we present the development of silicone sponge-based evaporators with a "free-salt" structure, designed to enhance the efficiency of SIE and freshwater collection. These evaporators, designated as PSS@Fe3O4/CNTs, were fabricated by grafting durable silicone onto a silicone sponge framework, followed by the incorporation of Fe3O4 nanoparticles and carbon nanotubes. The unique combination of exceptional photothermal properties and a controlled yolk-shell structure with low thermal conductivity enabled the PSS@Fe3O4/CNT evaporators to sustain a stable evaporation rate of 1.87 kg m-2 h-1 in real seawater over 200 h of continuous operation under 1 sun illumination. Importantly, no salt accumulation was observed on the evaporator surfaces, even when exposed to highly concentrated brines. In a closed system equipped with a condenser, these evaporators achieved freshwater production rates of 14.5 and 11.8 kg m-2 over 10 h from 10 and 20 wt % NaCl solutions, respectively, under 1 sun illumination. These values correspond to normalized production rates of 1.45 and 1.18 kg m-2 h-1, showcasing the consistent and efficient performance of the evaporators across varying salinity levels. Beyond salt rejection, the PSS@Fe3O4/CNT evaporators also demonstrated the ability to effectively remove various heavy metal ions (e.g., Cu2+ and Zn2+) and organic pollutants from contaminated water. This work provides valuable insights into innovative evaporator designs for efficient freshwater production from seawater and wastewater.

Hydrogel-based solar interfacial evaporators, featuring various channels such as random, unidirectional, and radial array, are considered effective for seawater desalination owing to their porous structure, lower evaporation enthalpy, and controllable water transport capacity. However, each individual array structure has its own strengths and limitations, influencing water transportation, thermal management, and salt rejection. By combining the benefits of each array configuration into a single evaporator, the evaporation performance can be maximized. Herein, the study develops a unique nanofibrous hydrogel-based solar evaporator featuring a combined radical/vertical array structure. This integrated structure with external radial and internal vertical channels endows this evaporator with excellent water transport capability and reduced heat loss, resulting in superior evaporation performance and high salty resistance. The addition of nanofibers into hydrogels not only enhances the hydrogel's stability but also facilitates water transport. Under 1 sun illumination, this evaporator can achieve an impressive evaporation rate of 4.62 kg m-2 h-1 with an energy efficiency of 149.57%. After 12 h of evaporation in a 20 wt.% NaCl solution, it still maintains an average evaporation rate of 3.98 kg m-2 h-1 with minimal salt accumulation, thereby exhibiting its exceptional salt resistance and durability.

Excellent acid resistance and MXene enhanced photothermal conversion of bilayered porous solar evaporator fabricated by palygorskite and pectin

Solar interfacial evaporation (SIE) by leveraging photothermal conversion could be a clean and sustainable solution to the scarcity of fresh water, decontamination of wastewater, and steam sterilization. However, the process of salt crystallization on photothermal materials used in SIE, especially from saltwater evaporation, has not been completely understood. We report the temporal and spatial evolution of salt crystals on the photothermal layer during SIE. By using a typical oil lamp evaporator, we found that salt crystallization always initiates from the edge of the evaporation surface of the photothermal layer due to the local fast flux of the vapor to the surroundings. Interestingly, the salt crystals exhibit either compact or loose morphology, depending on the location and evaporation duration. By employing a suite of complementary analytical techniques of Raman and infrared spectroscopy and temperature mapping, we followed the evolution and spatial distribution of salt crystals, interfacial water, and surface temperature during evaporation. Our results suggested that the compact crystal structure may emerge from the recrystallization of salt in an initially porous structure, driven by continuous water evaporation from the porous and loose crystals. The holistic view provided in this study may lay the foundation for effective strategies for mitigation of the negative impact of salt crystallization in solar evaporation.