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.

Li H ，Yan Z ，Li Y ，Hong W ... -  《-》

Aligned Millineedle Arrays for Solar Power Seawater Desalination with Site-Specific Salt Formation.

As a sustainable and clean water production technology, solar thermal water evaporation has been extensively studied in the past few years. One challenge is that upon operation, salt would form on surface of the solar absorbers leading to inefficient water supply and light absorption and thus much reduced water vaporization rate. To address this problem, a simple solar evaporator based on an array of aligned millineedles for efficient solar water evaporation and controlled site-specific salt formation is demonstrated. The maximum solar evaporation rate achieved is 2.94 kg m-2 h-1 under one Sun irradiation in brine of high salinity (25 wt% NaCl), achieving energy conversion efficiency of 94.5% simultaneously. More importantly, the spontaneously site-specific salt formation on the tips of millineedles endows this solar evaporator with salt harvesting capacity. Rationally separating the clean water and salt from brine by condensation and gravity assistance, this tip-preferential crystallization solar evaporator is not affected by the salt clogging compared with conventional 2D solar evaporators. This study provides new insights on the design of solar evaporators and advances their applications in sustainable seawater desalination and wastewater management.

Huang Z ，Wei J ，Wan Y ，Li P ，Yu J ，Dong J ，Wang S ，Li S ，Lee CS ... -  《-》

Reviewing wood-based solar-driven interfacial evaporators for desalination.

Solar‒driven interfacial water evaporation is a convenient and efficient strategy for harvesting solar energy and desalinating seawater. However, the design and fabrication of solar evaporators still challenge reliable evaporation and practical applications. Wood-based solar-driven interfacial water evaporation emerge as a promising and environmentally friendly approach for water desalinating as it provides renewable and porous structures. In recent years, surface modifications and innovative structural designs to prepare high performance wood-based evaporators is widely explored. In this review, we firstly describe the superiority of wood for the fabrication of wood-based solar evaporators, including the pore structure, chemical structure and thermal insulation. Secondly, we summarize the recent developments in wood-based evaporators from surface carbonization, decoration with photothermal materials, bulk modification and structural design, and discuss from the aspects of water transportation capacity, thermal conductivity and photothermal efficiency. Finally, based on these previous results and analysis, we highlight the remaining challenges and potential future directions, including the selection of high-efficient photothermal materials, heat and mass transfer mechanism in wood-based evaporators including large-scale production at a low cost.

Dong Y ，Tan Y ，Wang K ，Cai Y ，Li J ，Sonne C ，Li C ... -  《-》

Honeycomb-structured fabric with enhanced photothermal management and site-specific salt crystallization enables sustainable solar steam generation.

The emerging of solar-driven interfacial evaporation provides new opportunities to alleviate the shortage of fresh water resource. Nevertheless, in practical solar desalination, salt precipitation will lead to the decrease of evaporation rate due to reduced light absorption and blocked evaporation channels of evaporator. It still remains a challenge to eliminate salt accumulation and simultaneously maintain high-efficient evaporation. In this work, a solar evaporator was prepared based on reduced graphene oxide and chitosan coated honeycomb-structured fabric (rCHF). The rCHF showed a high light absorbance of 97.2% due to enhanced light trapping of the honeycomb structure and ultra-low thermal conductivity of 0.044 W m-1 K-1. Furthermore, the temperature gradient generated inside the honeycomb unit can induce the Marangoni effect, which led to the site-specific salt crystallization on rCHF in seawater evaporation. As a result, the rCHF realized an excellent solar evaporation rate of 2.02 kg m-2h-1 under one sun irradiation (1 kW m-2). The site-specific salt crystallization on the surface of rCHF ensured stable evaporation even in 20% brine, and the isolated salt can be removed by natural dissolution owing to the excellent hydrophilicity of rCHF. This work provides a new perspective for the design of solar evaporator for practical solar seawater desalination.

Gao C ，Zhu J ，Li J ，Zhou B ，Liu X ，Chen Y ，Zhang Z ，Guo J ... -  《-》

3D carbonized grooved straw with efficient evaporation and salt resistance for solar steam generation.

Solar steam generation (SSG) is considered an effective solution to the global shortage of freshwater resources. To solve the practical application challenges of SSG in remote outdoor environments where electricity is scarce, it is of great importance to developing new solar evaporators. In this study, a three-dimensional (3D) biochar solar evaporator based on carbonized grooved straw was prepared from agricultural waste corn straw, which had high solar energy conversion efficiency and excellent salt resistance. The existence of grooves increases the surface area to absorb more sunlight and makes the light multilevel reflection improve the evaporation rate. The excellent light absorption, super hydrophilic, and heat shielding properties of 3D carbonized grooved straw resulted in a good evaporation rate (1.57 kg⋅m-2·h-1) and energy efficiency (85.9%) under 1 sun irradiation. The 3D grooved biochar solar distiller also demonstrated efficient formation evaporation performance and excellent salt resistance in practical applications in seawater desalination and surface water purification. The 3D grooved biochar solar distiller prepared from agricultural waste has the advantages of being economical and environmentally friendly, with good application prospects.

Hou X ，Sun H ，Dong F ，Wang H ，Bian Z ... -  《-》