Hierarchical Photothermal Fabrics with Low Evaporation Enthalpy as Heliotropic Evaporators for Efficient, Continuous, Salt-Free Desalination

Abstract

Solar-driven seawater evaporation is usually achieved on floating evaporators, but the performances are substantially limited by high evaporation enthalpy, solid salt crystallization, and reduced evaporation due to inclined sunlight. To solve these problems, we fabricated hierarchical polyacrylonitrile@copper sulfide (PAN@CuS) fabrics and proposed a prototype of heliotropic evaporator. Hierarchical PAN@CuS fabrics show significantly decreased water-evaporation enthalpy (1956.32 kJ kg −1 , 40 °C), compared with that of pure water (2406.17 kJ kg −1 , 40 °C), because of the disorganization of the hydrogen bonds at the CuS interfaces. Based on this fabric, a heliotropic evaporation model was developed, where seawater slowly flows from high to low in the fabric. Under solar irradiation (1.0 kW m −2 ), this model exhibits a high-rate evaporation (∼2.27 kg m −2 h −1 ) and saturated brine production without solid salt crystallization. In particular, under inclined sunlight (angle range: from −90°to +90°), the heliotropic model retains an almost unchanged solar evaporation rate, whereas the floating model shows severe evaporation reduction (83.9%). Therefore, our study provides a strategy for reducing the evaporation enthalpy, maximally utilizing solar energy and continuous salt-free desalination.

Electricity‐Boosted Solar‐to‐Vapor Conversion upon Fiber‐Supported CDs@CuS for Rapidly Vaporizing Seawater

“…As for larger flaky crystals shown in Figure 1a, the interplanar distance between the lattice fringes is 0.31 nm and corresponded to the (102) plane of the hexagonal CuS. [ 36 ] The observed CDs display two kinds of lattice fringes with an interlayer spacing of 0.33 and 0.21 nm, matching with 002 and 001 facets of graphitic carbon, respectively. As depicted in Figure 1b, CDs could serve as heterogeneous nucleating agents of CuS nanocrystals, promoting their growth.…”

A Review on Photothermal Conversion of Solar Energy with Nanomaterials and Nanostructures: From Fundamentals to Applications

“…treat different water sources (seawater, wastewater, and unpurified water) with highly efficient, environmentally friendly, and cost-effective to obtain fresh water, salts, and high energy water vapor for electric power generation. [26,45,81,82,92,97,101,102] For this type of application, the main challenges lay in finding suitable absorbers or absorber systems with high light absorption and fast heat transfer and water transport abilities to achieve high photothermal conversion efficiency, and a lot of theoretical and experimental studies have been concentrated on such issues.…”

Towards highly salt-rejecting solar interfacial evaporation: Photothermal materials selection, structural designs, and energy management

“…As we know, the evaporation of liquid water is mainly limited by the stable hydrogen bonds between the water molecules, and the required energy for phase transition of water from liquid to vapor to break the hydrogen bonds [9,111]. Yu's group has revealed that the water state in the polymer network can be manipulated to affect the evaporation enthalpy [112,113].…”

“…A strong enough wicking effect could transport a large amount of bulk water to achieve the purpose of salt rejection. Another scheme to achieve the salt-rejection by washing effect with bulk water is to set the pressure difference in different areas of the evaporator to make the bulk water flow through the whole evaporator, and the excessive supplement of bulk water eliminates the crystallization of salt fundamentally [19,111]. As shown in Fig.…”