A high-efficiency salt-rejecting solar evaporator with optimized porous structure for continuous solar desalination

Pyramid-shaped solar evaporator with high-efficient interfacial evaporation and salt harvesting capability

Bio-inspired solar evaporators for stable and efficient desalination of high-salinity brine with zero liquid discharge.

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Interfacial solar evaporation offers a green and sustainable solution to solve clean water shortages via solar‐driven desalination. However, salt crystallization and accumulation on solar evaporators have become the primary hindrances to the long‐term practical application of interfacial solar evaporation technology. To tackle this challenge, a photothermal evaporator with a novel parallel two‐water paths strategy is developed in this study. Unlike the conventional one‐way water path, which generally leads to salt accumulation at the water supply end on the evaporation surfaces, thereby limiting the lifespan of the evaporator and compromising solar evaporation performance, here, with the second parallel water supply path, the ion diffusion and distribution within the solar evaporator is reconfigured and optimized. No salt accumulation occurs on either the evaporation surfaces or the water paths, eliminating the impact of salt crystallization on evaporation performance and enabling convenient salt collection. A high and stable evaporation rate of 3.09–3.26 kg m−2 h−1 is recorded over 84 h continuous evaporation of NaCl solution (3.5 wt.%) without salt accumulation on the evaporator, making it an ideal strategy for zero liquid discharge solar evaporation.

Interfacial solar evaporation has emerged as a promising strategy for freshwater production, where 3D evaporators offer distinct advantages in heat management and salt rejection. Freeze–thaw cycling is a widely adopted fabrication method for 3D hydrogel evaporators, yet the impact of preparation conditions (e.g., freezing temperature) on their evaporation performance remains poorly understood, hindering rational optimization of fabrication protocols. Herein, we report the fabrication of chitosan-based hydrogel evaporators via freeze–thaw cycles at different freezing temperatures (−20 °C, −40 °C, and −80 °C), leveraging its low cost and environmental friendliness. Characterizations of crosslinking density and microstructure reveal a direct correlation between freezing temperature and network porosity, which significantly influences evaporation rate, photothermal conversion efficiency, and anti-salt performance. It is noteworthy that the chitosan hydrogel prepared at −80 °C demonstrates an excellent evaporation rate in high-salinity environments and exhibits superior salt resistance during continuous evaporation testing. Long-term cyclic experiments indicate that there was an average evaporation rate of 3.76 kg m−2 h−1 over 10 cycles, with only a 2.5% decrease observed in the 10th cycle. This work not only elucidates the structure–property relationship of freeze–thaw fabricated hydrogels but also provides a strategic guideline for tailoring evaporator architectures to different salinity conditions, bridging the gap between material design and practical seawater desalination.

Recent advances in thermally localized solar evaporation hold significant promise for vapor generation, seawater desalination, wastewater treatment, and medical sterilization. However, salt accumulation is one of the key bottlenecks for reliable adoption. Here, we demonstrate highly efficient (>80% solar-to-vapor conversion efficiency) and salt rejecting (20 weight % salinity) solar evaporation by engineering the fluidic flow in a wick-free confined water layer. With mechanistic modeling and experimental characterization of salt transport, we show that natural convection can be triggered in the confined water. More notably, there exists a regime enabling simultaneous thermal localization and salt rejection, i.e., natural convection significantly accelerates salt rejection while inducing negligible additional heat loss. Furthermore, we show the broad applicability by integrating this confined water layer with a recently developed contactless solar evaporator and report an improved efficiency. This work elucidates the fundamentals of salt transport and offers a low-cost strategy for high-performance solar evaporation.

A biomass hybrid hydrogel with hierarchical porous structure for efficient solar steam generation

A lotus leaf like vertical hierarchical solar vapor generator for stable and efficient evaporation of high-salinity brine

Rational and sustainable utilization of resources is critical for the continuous development of this society. Solar energy, as one of the renewables, shows great potential in replacing part of the traditional energy supplies since it is clean, abundant, and easily convertible to thermal, electrical, and biological energies. Using solar energy as the green driving force, interfacial solar evaporation is a promising way for clean water production to alleviate global water shortage, taking advantage of its high evaporation efficiency (more than 80%) and strong adaptability toward various water sources and fields. In recent years, various kinds of materials with diverse designs have been synthesized and applied in interfacial solar evaporation for clean water production. Herein, recent progress in interfacial solar evaporators for clean water production is systematically reviewed, based on the photothermal conversion mechanisms of solar absorbers, including carbonous, semiconductor‐based, and plasmatic ones. Furthermore, key design factors and strategies in interfacial solar evaporators are reviewed and discussed from material and structural design point of view, such as water transport, thermal management, latent heat for water vaporization, and salt accumulation. Finally, some perspectives related to resolving existing problems in the field are given.

Zero liquid discharge (ZLD) is a technique for treating high-salinity brine to obtain freshwater and/or salt using a solar interface evaporator. However, salt accumulation on the surface of the evaporator is a big challenge to maintaining stable water evaporation. In this study, a simple and easy-to-manufacture evaporator, also called a crystallizer, was designed and fabricated by 3D printing. The photothermal layer printed with polylactic acid/carbon composites had acceptable light absorption (93%) within the wavelength zone of 250 nm–2500 nm. The micron-sized voids formed during 3D printing provided abundant water transportation channels inside the crystallizer. After surface hydrophilic modification, the crystallizer had an ultra-hydrophilic channel structure and gravity-assisted salt recovery function. The results revealed that the angles between the photothermal layers affected the efficacy of solar evaporation and the yield of solid salt. The crystallizer with the angle of 90° between two photothermal layers could collect more solid salt than the three other designs with angles of 30°, 60°, and 120°, respectively. The crystallizer has high evaporation and salt crystallization efficiency in a high-salinity brine environment, which is expected to have application potentials in the zero liquid discharge of wastewater and valuable salt recovery.

A loofah-based all-day-round solar evaporator with phenolic lignin as the light-absorbing material for a highly efficient photothermal conversion

A bio-based 3D evaporator nanocomposite for highly efficient solar desalination

Interfacial solar-driven evaporation of saline water is a promising technique that enables worldwide upscaling of freshwater with a minimum of carbon footprint. For this purpose, wood is demonstrating a desirable substrate due to its high porosity and low thermal conductivity. Despite much effort has been dedicated to improving the performance of wood evaporators, their scalability and reliability still restrict applications. Here we present a large-scale and highly-efficient wood-based evaporator with corrugated sheet structures using a facile mechanical processing strategy that utilizes the excellent processability of wood. The corrugated structure of the longitudinal wood block, transports water in the longitudinal direction and thereby increases the evaporation area. With the inclusion of a Chinese ink layer and hydrophobic treatment, the prepared wood-based evaporators exhibit a high evaporation rate (1.77 kg m−2 h−1 for spruce wood, 1.42 kg m−2 h−1 for beech wood) and efficiency (111.53% for spruce wood, 88.73% for beech wood) at 1 sun irradiation and continuous water desalination, which is superior to both reported longitudinal and most transverse wood-based evaporators. This work demonstrates a universal and economy strategy for preparing large-sized wood-based solar evaporators with processability, stable performance and high efficiency.

Modular solar interfacial evaporation and crystallization– Functional partitioning

Biomass-based high-efficiency solar-driven interface evaporator based on natural pomelo peel with multi-curvature gradient structure