# Highly efficient three-dimensional solar evaporator for zero liquid discharge desalination of high-salinity brine

Meichun Ding, Demin Zhao, Panpan Feng, Baolei Wang, Zhenying Duan, Rui

Wei, Yuxi Zhao, Chen-yang Liu, Chenwei Li

► To cite this version:

Meichun Ding, Demin Zhao, Panpan Feng, Baolei Wang, Zhenying Duan, et al. Highly efficient three-dimensional solar evaporator for zero liquid discharge desalination of high-salinity brine. Carbon Energy, 2024, 6, 10.1002/cey2.548. hal-05024885

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# Highly efficient three-dimensional solar evaporator for zero liquid discharge desalination of high-salinity brine

Meichun Ding<fnref n="1" />,<fnref n="2" /> | Demin Zhao<fnref n="1" />,<fnref n="2" /> | Panpan Feng<fnref n="1" />,<fnref n="2" /> | Baolei Wang<fnref n="1" />,<fnref n="2" /> |
Zhenying Duan<fnref n="1" />,<fnref n="2" /> | Rui Wei<fnref n="1" />,<fnref n="2" /> | Yuxi Zhao<fnref n="2" />,<fnref n="3" /> | Chen-Yang Liu<fnref n="4" /> |
Chenwei Li<fnref n="1" />,<fnref n="2" /> ID

**Correspondence**

Chenwei Li, School of Chemistry and Pharmaceutical Engineering, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan 250117, China.

Email: lichenwei@iccas.ac.cn

**Funding information**

National Natural Science Foundation of China, Grant/Award Number: 51802168; Taishan Scholar Foundation of Shandong Province, Grant/Award Number: tsqn202306267; Natural Science Foundation of Shandong Province, Grant/Award Number: ZR2023ME172

**Abstract**

Solar-driven interfacial evaporation is a promising technology for freshwater production from seawater, but salt accumulation on the evaporator surface hinders its performance and sustainability. In this study, we report a simple and green strategy to fabricate a three-dimensional porous graphene spiral roll (3GSR) that enables highly efficient solar evaporation, salt collection, and water production from near-saturated brine with zero liquid discharge (ZLD). The 3GSR design facilitates energy recovery, radial brine transport, and directional salt crystallization, thereby resulting in an ultrahigh evaporation rate of 9.05 kg m⁻<fnref n="2" /> h⁻<fnref n="1" /> in 25 wt% brine under 1-sun illumination for 48 h continuously. Remarkably, the directional salt crystallization on its outer surface not only enlarges the evaporation area but also achieves an ultrahigh salt collection rate of 2.92 kg m⁻<fnref n="2" /> h⁻<fnref n="1" />, thus enabling ZLD desalination. Additionally, 3GSR exhibits a record-high water production rate of 3.14 kg m⁻<fnref n="2" /> h⁻<fnref n="1" /> in an outdoor test. This innovative solution offers a highly efficient and continuous solar desalination method for water production and ZLD brine treatment, which has great implications for addressing global water scarcity and environmental issues arising from brine disposal.

**KEYWORDS**

graphene aerogels, graphene composites, solar desalination, solar-driven interfacial evaporation

# 1 | INTRODUCTION

Freshwater scarcity has become one of the most serious global problems owing to the growth of the global population and the development of modern agriculture

and industry.<fnref n="1" /> Although nearly 75% of the Earth's surface is covered with water, about 97% of it is seawater.<fnref n="2" /> In recent years, desalination technologies such as reverse osmosis (RO) and membrane distillation have improved and become a viable approach to address the shortage of

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2024 The Authors. *Carbon Energy* published by Wenzhou University and John Wiley & Sons Australia, Ltd.

<footnote n="1">¹School of Chemistry and Pharmaceutical Engineering, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan, China</footnote>

<footnote n="2">²Medical Science and Technology Innovation Center, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan, China</footnote>

<footnote n="3">³Institut de Chimie Radicalaire, Aix Marseille University, Marseille, France</footnote>

<footnote n="4">⁴CAS Key Laboratory of Engineering Plastics, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, the Chinese Academy of Sciences, Beijing, China</footnote>
freshwater.³ However, most of the waste brines from desalination plants are directly discharged into adjacent lakes or seas, which severely affects the ecological environment.⁴ As a result of the increasing public environmental protection consciousness, the concept of zero liquid discharge (ZLD), which is the complete separation of water and solute, has attracted more and more attention.⁴,⁵ Nevertheless, conventional desalination technologies are challenged by high-salinity (>7 wt%) brine that is difficult to desalinate continuously. In addition to a dramatic increase in filtration pressure and energy consumption, high-salinity brine also has a negative impact on the service life of conventional equipment.⁶ There is an urgent need to explore a new desalination technology to treat high-salinity brine and achieve complete separation of water and salt with minimal energy and environmental costs.

In the last decade, solar-driven interfacial evaporation (SIE) has been widely regarded as a promising freshwater production technology because of the inexhaustible supply of solar energy and seawater and improved evaporation efficiency through heat localization.⁷⁻⁹ Unlike conventional desalination technologies, SIE could minimize the carbon footprint of high-salinity brine treatment. The rapid evaporation of water causes salt to gradually deposit on the surface of the evaporator, leading to the complete separation of water and salt, which is expected to achieve ZLD.¹⁰ However, the deposition of salt on the evaporator not only significantly impairs sunlight absorption but also hinders the brine supply, leading to a considerable reduction in the rate of evaporation.¹¹ Currently, there are two main strategies to address the issue of decreased evaporation performance caused by salt deposition: “salt-free” and “salt-out.” The “salt-free” strategy aims to avoid salt deposition on the surface of the evaporator by using various methods designed rationally, such as Janus hierarchical design,¹²⁻¹⁴ ionic rejection,¹⁵,¹⁶ self-rotating evaporator,¹⁷,¹⁸ aligned millimeter-sized channels,¹⁹⁻²¹ enhanced salt transport,²²,²³ and so on. However, the “salt-free” strategy fails to achieve ZLD in brine treatment because the salt solute remains in the bulk brine after solar desalination.

The “salt-out” strategy employs various rational designs, such as umbrella-,²⁴⁻²⁸ three-dimensional (3D) cup-,²⁹⁻³¹ and T-shaped evaporators,³²,³³ to facilitate directional crystallization that isolates the salt from the evaporation interface and ensures stable evaporation performance. However, a major challenge for most directional crystallization evaporators is the one-dimensional brine transport that leads to insufficient vertical absorption, which reduces the overall evaporation rate.³⁴,³⁵ Furthermore, the strong binding force between the salt crystals and the evaporator surface prevents most of the salt from falling off by gravity. Salt crystals can only

fall off under certain conditions, such as high water content at the evaporation interface²⁴ or slow evaporation.³⁴ If not removed promptly, the salts will gradually accumulate on the evaporation surface, leading to a decrease in the evaporation rate. This problem worsens with higher salinity brine. In addition, many efficient solar evaporators require complex or dangerous preparation processes involving high-pressure, high-temperature, or low-vacuum treatments, which limit their large-scale applications in solar desalination. Therefore, it is a significant challenge to construct a directional crystallization evaporator using a simple preparation process that can achieve long-term, highly efficient, and stable evaporation and salt collection for ZLD brine treatment, especially when dealing with high-salinity brine.

Herein, we report a simple and environmentally friendly method to fabricate a 3D porous graphene spiral roll (3GSR) that can achieve highly efficient solar evaporation and salt collection from near-saturated brine (Figure 1A). This method addresses the challenge of ZLD desalination, which is crucial for water security and environmental protection. The method only requires air-drying and solar reduction, avoiding time-consuming or dangerous experimental processes, such as freeze-drying, chemical reduction, thermal treatment, and so on. 3GSR has a unique spiral roll structure that enables energy recovery, 3D brine transport, radial brine transport, and directional salt crystallization (Figure 1B). It demonstrates an extraordinarily high average evaporation rate of 9.05 kg m⁻² h⁻¹, an ultrahigh salt collection rate of 2.92 kg m⁻² h⁻¹, and ZLD desalination even in near-saturated (25 wt%) brine under continuous 48-h illumination at 1 kW m⁻², which is the best performance reported so far. Furthermore, a detachable outer layer for 3GSR enables easy salt collection, and the 3GSR can efficiently treat high concentrations of brine for up to 96 h. Moreover, the freshwater collection device based on the 3GSR exhibits a record-high water production rate of 3.14 kg m⁻² h⁻¹ in an outdoor test, showing great potential for practical application. This simple yet effective strategy is expected to advance the development and application of high-performance and low-cost solar evaporators for solar desalination and ZLD brine treatment.

## 2 | RESULTS AND DISCUSSIONS

### 2.1 | Fabrication and characterization of 3GSR

3GSR was fabricated by a three-step process: spray coating, air-drying, and solar reduction (Figure 2A). To minimize the sample consumption and the cost, the
<figure><img src="image_2.png" /><figcaption>FIGURE 1 (A) A schematic of 3GSR for solar evaporator. (B) A schematic illustration of 3GSR for efficient solar evaporation and salt collection by directional salt crystallization.</figcaption></figure>

photothermal material was sprayed selectively on the inner and outer surfaces of 3GSR (Figure S1). In the first spraying step, a stable suspension (7 mg mL⁻¹) containing graphene oxide (GO) shown in Figure S2 and cellulose nanocrystals (CNCs) shown in Figure S3) (the mass ratio of CNCs and GO was 1:4) was coated on a porous melamine film (denoted as pMF) of increasing width from 3 to 6 cm (the dimensions of pMF and 3GSR are shown in Figure S1) by a simple spray method. The commercial low-cost pMF was selected as the skeleton of 3GSR because of its scalable synthesis, excellent processability, low density (8.3 mg cm⁻³), low thermal conductivity (0.03 W m⁻¹ K⁻¹), and abundant porous structure (Figure 2B and Figure S4A). In the following drying, GO/CNCs/pMF composite was directly air-dried by heating to avoid unnecessary freeze-drying,³⁶ supercritical drying,³⁷ and solvent replacement.³⁸ The scanning electron microscopy (SEM) images show that the GO sheets self-assembled on the pMF skeleton because of the interaction of negatively charged GO with the pMF skeleton limbs, forming the 3D network structure (Figure 2C and Figure S4B). These results indicate that the pMF skeleton effectively prevented the GO sheets from restacking through the capillary force of water during the air-drying process (Figure S5).

In the reduction process, the GO/CNC film was rapidly photoreduced by focused sunlight irradiation.

According to Movie S1, the rapid color change from yellow-brown to black occurred as soon as the sunlight was focused on the GO/CNCs film, indicating that the GO was solar-reduced to form reduced GO (rGO). Figure 2D and Figure S4C show that the rGO/CNC film (denoted as GF) still retained a 3D network structure with wrinkles on the surfaces of rGO sheets. At higher magnifications, CNCs were observed both on the surface of the rGO cell walls and in network structures (Figure S6). GF of 6 cm² could be photoreduced line by line within 45 s under natural sunlight conditions (Movie S2). Moreover, the convex lens array can be used for more efficient solar reduction, making the strategy very promising for large-scale 3GSR production (Figure S7). The UV light in solar radiation plays a critical role in the photoreduction of GO.³⁹,⁴⁰ The X-ray diffraction (XRD) peak of rGO shifted from 10.8° to 22.5°, indicating the removal of oxygen-containing functional groups (such as C-COOH, C-OH, C-O-C, and C=O) from the GO sheets during the solar reduction process (Figure 2E). As shown in Figure 2F, GO and rGO were also characterized using X-ray photoelectron spectroscopy (XPS). The C/O mole ratio of rGO increased from 2.1 in GO to 5.4, which shows that most oxygen-containing functional groups were eliminated during the solar reduction process. Raman spectra for GO and rGO showed two main broad D and
<figure><img src="image_3.png" /><figcaption>FIGURE 2 Fabrication and characterization. (A) The process of fabricating 3GSR. The pMF was continuously transformed into 3GSR through three steps: spray coating, air-drying, and solar reduction. SEM images of (B) pMF, (C) GO/CNCs film, and (D) GF. (E) XRD patterns of GO and rGO. (F) XPS survey spectra for C 1s and O 1s of GO and rGO. (G) Raman spectra of GO and rGO.</figcaption></figure>

G bands at 1345 and 1584 cm⁻¹, respectively (Figure 2G). After solar reduction, the increase of the peak intensity ratio of D and G bands for rGO from 0.99 to 1.07 implied the restoration of sp² hybridized conjugation regions on rGO sheets.

## 2.2 | Photothermal conversion, water transport, thermal insulation, and mechanical properties

The primary requirement for solar desalination is high-efficiency light absorption.⁴¹,⁴² To evaluate the light

absorption characteristics, we measured the sunlight absorption properties of GF in the wavelength range of 300–2500 nm. GF shows excellent solar absorption of about 93% weighted by the standard solar spectrum (AM 1.5 G) (Figure S8). This resulted from the intrinsic optical absorption of rGO and light multiscattering in the 3D network structure. Moreover, the photothermal conversion performance of GF was subsequently investigated. The surface temperature of GF (~84°C) is significantly higher than that of pMF due to the photothermal effects generated from the 3D rGO network (Figure S9). The efficient hydrophilic properties of CNCs and pMF enabled GF to exhibit an efficient water transport
performance, ensuring an adequate supply of brine during solar desalination (Figure S10). The ideal solar evaporator should possess excellent thermal insulation properties that effectively confine a significant amount of heat on the evaporation surface while minimizing heat conduction losses to the underlying bulk brine.⁴³ GF met this criterion, as the rGO network structure could effectively block heat transfer, leading to a low thermal conductivity of 0.05 W m⁻¹ K⁻¹, which is only slightly higher than that of pMF (0.03 W m⁻¹ K⁻¹) (Figure S11A). As solar desalination is carried out under aqueous conditions, evaluating the thermal conductivity of a wet sample is more representative of actual test conditions. The wet GF showed a low thermal conductivity (0.45 W m⁻¹ K⁻¹), which was lower than those of water (0.60 W m⁻¹ K⁻¹) and most reported solar evaporators¹⁴,²³,⁴⁴⁻⁵⁰ (Figure S11B and Table S1).

Excellent mechanical performance is crucial for a solar evaporator to achieve long-term, efficient, and stable solar desalination.⁵¹,⁵² We investigated the mechanical performance of GF in different modes, including compression, bending, and tension. Cyclic compression tests were conducted for five stacked pieces of GF with a strain of 70% (Figure S12A). The stacked GF with a density of 10 mg cm⁻³ showed compressive stress of 163 kPa at a maximum strain of 70% and fully recovered to its original height after the force was released. As shown in Figure S12B, GF exhibited excellent bending toughness after 1000 cycles and retained 100% of its bending modulus and 75% of its bending strength. During the tensile test, GF demonstrated a fracture strength of 100 kPa and a breaking elongation of 18% (Figure S12C). Furthermore, in practical desalination applications, solar evaporators are required to maintain a stable structure and evaporation performance under various environmental conditions. To evaluate the stability and durability, a piece of GF was continuously subjected to a series of harsh tests, including high temperature (~95°C, 1 h), ultrasonic agitation (200 W, 1 h), acidic condition (pH ~1, 24 h), alkaline condition (pH ~14, 24 h), 20 cycles of bending in air, and 20 cycles of bending in water (Figure S13). GF maintained its appearance and porous structure after these tests, indicating its excellent durability and structural stability (Figure S14). The elasticity, flexibility, and durability of GF paved the way for long-term solar desalination of 3GSR.

## 2.3 | Solar water evaporation performance of 3GSR

GF exhibited potential for efficient solar evaporation due to its high solar absorbance (Figure S8), fast water transport

(Figure S10), low thermal conductivity (Figure S11), outstanding mechanical properties (Figure S12), and excellent durability (Figure S13). However, the two-dimensional (2D) shape of GF caused energy losses due to diffuse reflection and thermal radiation, which limited its evaporation performance (Figure 3A). In contrast, the unique 3D spiral roll structure of 3GSR enabled its inner surface to reabsorb diffuse reflection and thermal radiation.³⁰,³¹,⁵³ To evaluate the energy recovery effect of 3GSR, we measured the light reflectance properties of GF and 3GSR in the wet state using UV-visible-near-infrared (UV-vis-NIR) spectroscopy. As shown in Figure 3B, 3GSR has a significantly lower light reflectance than GF. Moreover, based on the energy loss calculation (see Section 2.13, Supporting Information S1, for detailed energy loss analysis), the total extrinsic energy losses of 3GSR and GF were 7.3% and 21.6% of solar flux (1 kW m⁻²), respectively. In addition, the outer surface of 3GSR can harvest additional energy from the surrounding environment (Figure 3A and Figure S15). Therefore, 3GSR showed a significantly higher evaporation rate of 4.93 kg m⁻² h⁻¹ than GF (1.71 kg m⁻² h⁻¹) under 1-sun illumination (Figure 3C). The results above demonstrate that 3GSR exhibits excellent solar evaporation performance, which lays the foundation for highly efficient solar desalination.

## 2.4 | High-rate solar desalination of 3GSR with ZLD treatment

Conventional desalination technologies, such as RO, are difficult to continuously treat high-salinity brine. The service life of RO membranes is significantly shortened during the continuous desalination of high-salinity (>7 wt%) brine, due to the significant increase in filtration pressure of the equipment. Herein, near-saturated artificial brine (25 wt% NaCl) was used for the solar desalination tests. To evaluate the solar desalination performance of GF and 3GSR, continuous 28- and 48-h desalination tests were performed in 25 wt% brine under 1-sun illumination, respectively. As shown in Figure 3D and Figure S16, GF showed an initial evaporation rate of 1.50 kg m⁻² h⁻¹ under 1-sun illumination, which gradually decreased to 0.71 kg m⁻² h⁻¹ with the deposition of salt on its surface during the continuous solar desalination for 28 h. In contrast, the 3GSR exhibited an increase in evaporation rate with the deposition of salt (Figure 3D). As shown in Figure 3E,F, salt selectively crystallized on the outer surface of 3GSR rather than the inside, forming a coral-shaped crystal layer. A sufficient evaporation area on the inner surface of 3GSR was enabled by the directional salt crystallization for highly efficient and long-lasting water evaporation. Furthermore, the coral-shaped crystal
<figure><img src="image_4.png" /><figcaption>FIGURE 3 (A) Schematic showing energy loss of GF and energy recovery of 3GSR. (B) UV-vis-NIR reflectance spectra of GF and 3GSR in the wet state. (C) The mass change of water versus time with GF, with 3GSR, and without an evaporator under 1-sun illumination. (D) The evaporation rates of GF and 3GSR in 25 wt% brine under 1-sun illumination for continuous 28 and 48 h, respectively. (E) Photographs of 3GSR during the continuous desalination test under 1-sun illumination. (F) A top view of 3GSR after a continuous 48-h desalination test. (G) A comparison of the evaporation rates and continuous evaporation times of 3GSR and other reported solar desalination systems under 1-sun illumination at the maximum salinity of brine. (H) Photograph showing complete separation of water and salt after a continuous 48-h desalination test. (I) Salt collection performance of 3GSR compared with recent literature reports.</figcaption></figure>

layer consisted of loosely packed balls of rough NaCl crystals with abundant void space for efficient transport of brine and release of vapor.<sup>10,29</sup> The evaporation rate of 3GSR increased gradually with the salt deposition. Therefore, the average evaporation rate reached as high as 9.05 kg m<sup>-2</sup> h<sup>-1</sup> during continuous 48 h desalination. To our knowledge, the comprehensive solar desalination performance achieved by 3GSR, including its average evaporation rate, continuous evaporation time, and salinity, surpasses that of other reported solar desalination systems<sup>13,16,18,19,23,27,29,31,48,54–69</sup> (Figure 3G and Table S2).

What is even more impressive is that 3GSR achieved ZLD from 25 wt% brine during continuous 48 h desalination. As shown in Figure 3E,H, the water evaporated rapidly from the brine, and the salt gradually accumulated on the outer surface of 3GSR until the

water and salt were completely separated. Figure S17 shows that the deposited salts can be easily removed and collected. After removing the salt from the outer surface, the inner surface of 3GSR was almost salt-free (Figure S18), providing a clean evaporative surface that enabled highly efficient and stable solar evaporation over extended periods. To evaluate the salt collection performance of 3GSR, we calculated the salt collection rate by dividing the mass of collected salt by the product of the evaporation time and the projected area. The resulting salt collection rate of 2.92 kg m<sup>-2</sup> h<sup>-1</sup> exceeds that of other reported solar desalination systems<sup>24–27,30–32,35,70–75</sup> (Figure 3I and Figure S19 and Table S3). This demonstrates the superior performance of 3GSR in efficiently collecting salt during the desalination process.
## 2.5 Directional salt crystallization mechanism and high-rate evaporation mechanism of 3GSR

To reveal the critical role of the 3D spiral roll structure in directional salt crystallization, the evaporation processes of 3GSR were simulated using COMSOL Multiphysics. The simulations included salinity distributions and brine flow during evaporation under 1-sun illumination. Figure 4A shows the steady-state simulation of salinity distributions of 3GSR when the input brine has a salinity of 25 wt%. The salinity of the outer surface of 3GSR exceeded the saturation concentration, while the salinity of the inner surface almost remained at the initial brine concentration, indicating that the salt selectively crystallized only on the outer surface of 3GSR. This result is consistent with what was obtained in the continuous solar desalination test shown in Figure 3F,H and Figure S18. Therefore, the 3D spiral roll structure enabled stable solar desalination through directional salt crystallization in near-saturated brine. The spiral roll structure induced an inhomogeneous transport of brine along the radial direction, resulting in directional salt crystallization. Figure 4B illustrates that the brine at the center moves spontaneously toward the outer surface due to the inhomogeneous flow caused by the shrinkage of the cross-section, leading to an increase in radial capillary force. As a result, the directional salt crystallization on the outer surface is achieved through the radial brine transport (Figure 4C).

An umbrella-shaped evaporator is a conventional design that can enable directional crystallization. Herein, we compare the conventional umbrella-shaped evaporators with 3GSR. There are four key factors for the excellent solar desalination performance of 3GSR (Figure 4E). The first is the superior evaporation performance. The unique 3D spiral roll structure of 3GSR enabled it not only to reabsorb diffuse reflection and thermal radiation from its inner surface but also to harvest additional energy from the ambient environment through its outer surface.30,31,53 As a result, 3GSR exhibited a better evaporation performance than umbrella-shaped evaporators with a 2D shape, which lost energy due to diffuse reflection and thermal radiation (Figure S20). The second is the 3D brine transport. Umbrella-shaped evaporators had 1D channels that lacked sufficient vertical brine transport, resulting in a relatively low evaporation rate (Figure S21).34,35 In contrast, 3GSR had enhanced brine transport thanks to its 3D channels composed of GF with excellent hydrophilic properties (Figure S10). The third is the large crystallization area. In umbrella-shaped evaporators, 1D channels in the center

spontaneously transported brine from the center to the edge, resulting in edge-preferential crystallization (Figure S22). However, the thin evaporation disc limited the area available for edge-preferential crystallization. In contrast, 3GSR had the entire outer surface for salt crystallization, which provided a much larger crystallization area and enabled efficient salt collection. The fourth is the increasing evaporation area. In umbrella-shaped evaporators, salt rings comprising NaCl crystals with void spaces for brine transport and vapor release emerged at the edge of the evaporation disc (Figure S23). These salt rings effectively increased the evaporation area. However, as more salts were deposited, they may have deformed the evaporation disc and slightly reduced the evaporation area. Moreover, some of the deposited salts may have fallen off under gravity and lost their function of solar evaporation. Therefore, the stable evaporation rates of umbrella-shaped evaporators during the continuous desalination tests may have resulted from the almost unchanged evaporation area. As shown in Figure S24, the salt deposited on 3GSR gradually turned red after replacing the brine with a dyed one during continuous solar desalination, indicating that there were sufficient void spaces within the loosely packed salt crystals for brine transport. As the water evaporated, the salt layer expanded in diameter, increasing the evaporation area (Figure 4D). The side surface temperature of the salt layer on 3GSR was lower than the ambient temperature due to the evaporative cooling of the salt layer during solar evaporation (Figure 4F). The growing salt layer on the outer surface of 3GSR collected more energy from the environment for evaporation. Moreover, even the salts that partially fell off from 3GSR tended to accumulate around it and continued to transport and evaporate brine like the salts on the outer surface of 3GSR (Figure 4G). Therefore, the high-rate evaporation of 3GSR resulted from the gradual increase in the effective evaporation area due to directional salt crystallization.76

The unique spiral roll structure is the key factor for achieving the breakthrough performance of 3GSR. To investigate the effect of spiral roll size on solar desalination, 3GSRs with different heights of 1, 3, and 5 cm were prepared (Figure S25). After 48 h of continuous desalination, a large amount of salt appeared on the inner surface of 3GSR (1 cm) due to insufficient radial brine transport (Figure S25D). When the height increased to 3 and 5 cm, sufficient brine transport caused the salts to deposit on the outer surface of 3GSR while keeping the inner surface clean (Figure S25E,F). According to the Marangoni effect, the temperature difference between the center and edge of
<figure><img src="image_5.png" /><figcaption>FIGURE 4 Numerical simulation of (A) salt concentration and (B) fluid velocity in 3GSR under 1-sun illumination and in 25 wt% brine. (C) Schematic illustration of the directional crystallization of 3GSR. (D) Top view photographs of 3GSR during a continuous 48-h desalination test under 1-sun illumination. (E) Schematic illustration of the four factors of high-rate evaporation of 3GSR: ① superior evaporation performance, ② 3D brine transport, ③ large crystallization area, and ④ increasing evaporation area. (F) Photograph of the salt layer on the outer surface of 3GSR and the corresponding infrared radiation thermal image. (G) Photograph of salt dropped around 3GSR and its infrared radiation thermal image.</figcaption></figure>

the upper surface of 3GSR (1 cm) was smaller than that of 3GSR (3 and 5 cm), resulting in insufficient radial brine transport (Figure S26).⁷⁷,⁷⁸ Therefore, 3GSR (3 and 5 cm) showed higher average evaporation rates and salt collection rates than 3GSR (1 cm) (Figure S27 and Table S4). As shown in Figures S28 and S29, the average outer surface temperature of 3GSR (5 cm) was significantly higher than that of 3GSR (3 cm), indicating lower evaporation performance of 3GSR (5 cm). This could be attributed to some salts that fell far away

from the high places of 3GSR (5 cm). These salts could not absorb brine from 3GSR and gradually heated up as water evaporated. Therefore, due to its larger effective evaporation area, the evaporation rate and salt collection rate of 3GSR (3 cm) were higher than those of 3GSR (5 cm) (Figure S27 and Table S4). In conclusion, among all sizes tested, 3GSR (3 cm) showed the best solar desalination performance. We used it as the research object throughout this study unless otherwise stated.
## 2.6 | Long-term stability and complete separation of water and salt

Reusability is an important factor to consider in solar evaporators. To enable cyclic desalination tests, it is essential to collect salt quickly after each cycle of solar desalination test. The deposited salts can fall off automatically from most directional crystallization evaporators only under certain conditions. These conditions include high water content at the evaporation interface,²⁴ excessive weight of the salt crystals,²⁵ or low-rate evaporation under dark conditions.³⁴ Therefore, designing an ideal solar desalination system that can combine highly efficient and stable evaporation with convenient salt collection is a big challenge. To solve the problem of salt collection, we attached a detachable GF to 3GSR for quick salt collection (Figure S30). In practical application, the long-term durability of the solar desalination system is an essential factor.⁷⁹ As shown in Figure 5A, 3GSR was continuously illuminated (1 kW m⁻²) for 96 h to treat 25 wt% brine. In the first 48 h, 3GSR exhibited a high average evaporation rate (8.84 kg m⁻² h⁻¹) and achieved solar ZLD desalination. After removing and collecting the salt layer (salt collection rate: 2.84 kg m⁻² h⁻¹) by directly replacing the outer GF without any treatment, 3GSR was able to start the next continuous 48 h test in less than 1 min (Movie S3). Furthermore, 3GSR showed a similar self-accelerated evaporation performance and salt collection rate in the second cycle test, demonstrating its excellent reusability and long-term durability (Figure 5A and Table S5). The inner surface of 3GSR remained very clean after continuous desalination for 96 h (Figure S31). In addition, 3GSR was washed with water and air-dried before being characterized. The SEM image reveals that the porous network of 3GSR was unchanged after continuous desalination for 96 h, indicating good structural stability (Figure S32). Moreover, 3GSR achieved an impressive cost-effectiveness of 328.61 g h⁻¹ $s⁻¹$, which surpassed those of the previously reported solar desalination devices¹⁰,⁸⁰⁻⁸⁵ (Figure S33 and Table S6).

## 2.7 | Feasibility under natural sunlight conditions

Considering that condensate is the goal of solar desalination devices, we assembled a homemade freshwater collection device on the playground at Shandong First Medical University to study the freshwater productivity of 3GSR in the real environment (March 14, 2023, Jinan, China). As shown in Figure 5B, three pieces of 3GSR (diameter 2 cm and height 3 cm) were enclosed by a transparent glass cover in an inner chamber containing 25 wt% brine. According to Figure 5C, the average daytime

light intensity was measured at 714.9 W m⁻². At 1:00 p.m., both the natural light intensity (903 W m⁻²) and the ambient temperature (23.5°C) reached their maximum values. During the process of solar desalination, water vapor condensed continuously on the inner walls of the glass cover, forming freshwater that flowed into the bottom container for collection (Figure 5B and Figure S34). During the test period of 9 h, a total of 26.62 g freshwater was collected with corresponding productivity of 28.26 kg m⁻², which was sufficient to provide the daily potable water for four households.²³ The calculated average water production rate was 3.14 kg m⁻² h⁻¹, which is a record level for the reported single-stage solar desalination systems¹⁸,²³,²⁵,⁵⁹,⁶⁴,⁶⁷,⁷⁵,⁸⁶⁻⁹⁵ (Figure 5D and Table S7). The concentration of Na⁺ in the water condensed from 25 wt% brine after solar desalination was significantly lower than the drinking water standard defined by the World Health Organization (Figure 5E). Moreover, we used real seawater from Qingdao, China for the solar desalination test. The concentrations of primary ions in the condensed water decreased sharply (Figure 5F). Therefore, the above results indicate that 3GSR has great potential in large-scale solar desalination and freshwater production applications.

## 3 | CONCLUSIONS

We have developed a simple and green strategy to fabricate 3GSR with a spiral roll structure that can achieve high-rate solar evaporation, salt collection, ZLD treatment, and water production from near-saturated brine. The unique design enables energy recovery, radial brine transport, and directional salt crystallization, resulting in an ultrahigh evaporation rate of 9.05 kg m⁻² h⁻¹ and a salt collection rate of 2.92 kg m⁻² h⁻¹ in 25 wt% brine under 1-sun illumination for 48 h, which are the best-reported performances for the solar desalination devices so far. More importantly, 3GSR can also achieve ZLD treatment from 25 wt% brine. Moreover, 3GSR exhibits a record-high water production rate of 3.14 kg m⁻² h⁻¹ in an outdoor test. Our work demonstrates the great potential of 3GSR for continuous solar desalination for water production and ZLD brine treatment.

## 4 | EXPERIMENTAL SECTION

### 4.1 | Materials

Graphite powder was obtained from Qingdao Huagao Co., Ltd. (China). KMnO₄, concentrated H₂SO₄ (98%), concentrated HCl (36%-38%), and H₂SO₄ (30%) were all
purchased from Beijing Chemical Factory. The pMF was
provided by Beiyou Company. A dialysis bag was
purchased from Beijing Jingke Hongda Biotechnology
Co., Ltd. Seawater was taken from the Yellow Sea,
Jiaozhou Bay (Qingdao, China).

4.2 | Preparation and purification of GO

The GO was prepared by a modified Hummer's
method.⁹⁶ The detailed preparation method is as follows.
First, natural graphite powder (2 g) was added to

<figure><img src="image_6.png" /><figcaption>FIG URE 5 (See caption on next page).</figcaption></figure>
concentrated $H_2SO_4$ (50 mL) and stirred at room temperature for 24 h. Then, the mixture was stirred in an ice bath for 30 min. $KMnO_4$ (6 g) was slowly added to the mixture with continuous mechanical stirring, and the mixture was stirred in an ice bath for another 30 min. Next, the mixture was transferred to a 35°C water bath and stirred for 30 min. Ultrapure water (200 mL) was slowly added to the mixture, and then the mixture was mechanically stirred for 24 h. After dilution, 5 mL of 30% $H_2O_2$ solution was added dropwise to the mixture. Subsequently, the mixture was centrifuged three times at 5000 rpm/min (30 min) in HCl solution (150 mL), and the resultant wet solid was redispersed in ultrapure water (150 mL), and then centrifuged and rinsed three times with ultrapure water. Finally, the wet GO was dialyzed using ultrapure water for 1 week and sheared at high speed, and stored for future use.

## 4.3 | Preparation of CNCs

The aqueous suspension of CNCs was prepared by modified $H_2SO_4$ hydrolysis with cotton linter pulp (CLP) as the main raw material. First, 5 g of ground CLP was soaked in a 4 wt% aqueous NaOH solution (200 mL) for 24 h at room temperature, which is called alkalization pretreatment. The obtained slurry was filtered, washed with distilled water until the pH was neutral, and then dried in a vacuum oven at 60°C for 24 h. Second, $CuSO_4$ (CLP/CuSO$_4$ = 100:1) was added to 64 wt% $H_2SO_4$ solution (45 mL) to accelerate the acid hydrolysis reaction and improve the yield of CNCs. The CLP was dispersed into an acid solution at room temperature (CLP/acid = 1 g/16 mL) and vigorously stirred at 50°C for 50 min, after which the acid hydrolysis was stopped by diluting the mixture with cold water. The obtained suspension was collected via centrifugation and washed until the pH ≈ 2. Finally, a milky-white suspension was obtained. Due to the negatively charged sulfate ester groups on the surfaces,

the obtained milky-white CNC suspension appeared as a stable water dispersion.⁹⁷

## 4.4 | Preparation of 3GSR

A suspension of CNCs with a concentration of $7.00 mg mL^{-1}$ was added to a GO solution with a concentration of $7 mg mL^{-1}$ under vigorous stirring. The volume ratio of GO to CNCs was determined at 4:1.⁹⁵ A piece of pMF with dimensions of 31 cm (length) × 3–6 cm (width) × 0.2 cm (thickness) was washed with deionized water and ethanol several times and then dried in an oven at 60°C. The 3GSR was continuously processed in three steps, which are spray coating, air drying, and solar reduction. The GO/CNC mixed suspension was coated on a pMF by a simple spray method. After that, the composite was air-dried at 60°C for 1 h. To minimize the sample consumption and the cost, the photothermal material was sprayed selectively on the inner and outer surfaces of 3GSR (Figure S1). Then the GO/CNC film was rapidly photoreduced by focused sunlight irradiation. The rapid color change from yellow-brown to black occurred as soon as the sunlight was focused on the GO/CNC film, indicating that the GO was solar-reduced to rGO. The resulting 3GSR had dimensions of 3 cm (inner height) × 6 cm (outer height) × 2 cm (diameter).

## 4.5 | Preparation of 3GSR (1 and 5 cm)

The 3GSR (1 and 5 cm) were prepared by the aforementioned method (Preparation of 3GSR) based on the pMF with dimensions of 31 cm (length) × 3–4 cm (width) × 0.2 cm (thickness) and 31 cm (length) × 3–8 cm (width) × 0.2 cm (thickness). The dimensions of the resulting 3GSR (1 cm) were 1 cm (inner height), 4 cm (outer height), and 2 cm (diameter). The dimensions of the resulting 3GSR (5 cm) were 5 cm (inner height), 8 cm (outer height), and 2 cm (diameter).

FIGURE 5 (A) The evaporation rates of 3GSR in 25 wt% brine under 1-sun illumination for 96 h. The photographs at the top and bottom show two cycles of continuous 48-h desalination tests for 3GSR, respectively. After collecting the salt layer at the end of the first cycle test, 3GSR was able to start a second cycle of continuous 48-h test. (B) Photographs of the homemade freshwater collection device based on 3GSR (left) before and (right) after outdoor solar desalination. (C) Environmental conditions (temperature and solar irradiation intensity) during the outdoor experiment. (D) Freshwater production performance of the outdoor solar desalination device based on 3GSR in 25 wt% brine compared with recent literature reports. The solid symbols indicate the outdoor water collection tests under natural sunlight conditions, while the hollow symbols indicate the indoor water collection tests under 1-sun illumination. (E) Measured concentration of $Na^+$ in 25 wt% brine before and after solar desalination. (F) Measured concentrations of four primary ions in a real seawater sample (from Qingdao, China) before and after solar desalination.
## ACKNOWLEDGMENTS

This work was supported by the Taishan Young Scholar Program (tsqn202306267), the National Natural Science Foundation of China (51802168), and the Natural Science Foundation of Shandong Province (ZR2023ME172).

## CONFLICT OF INTEREST STATEMENT

The authors declare that there are no conflicts of interests.

## ORCID

Chenwei Li http://orcid.org/0000-0003-0343-3699

## REFERENCES

1. Vörösmarty CJ, Green P, Salisbury J, Lammers RB. Global water resources: vulnerability from climate change and population growth. *Science*. 2000;289(5477):284-288.

2. Haddeland I, Heinke J, Biemans H, et al. Global water resources affected by human interventions and climate change. *Proc Natl Acad Sci USA*. 2014;111(9):3251-3256.

3. Elimelech M, Phillip WA. The future of seawater desalination: energy, technology, and the environment. *Science*. 2011; 333(6043):712-717.

4. Tong T, Elimelech M. The global rise of zero liquid discharge for wastewater management: drivers, technologies, and future directions. *Environ Sci Technol*. 2016;50(13):6846-6855.

5. Muhammad Yaqub Y, Lee W. Zero-liquid discharge (ZLD) technology for resource recovery from wastewater: a review. *Sci Total Environ*. 2019;681:551-563.

6. Jassby D, Cath TY, Buisson H. The role of nanotechnology in industrial water treatment. *Nat Nanotechnol*. 2018;13(8):670-672.

7. Yu J, Wang C, Liu S, et al. Solid waste-derived solar desalination devices: enhanced efficiency in water vapor generation and diffusion. *Chem Eng J*. 2024;485:149870.

8. Li Y, Shi Y, Wang H, et al. Recent advances in carbon-based materials for solar-driven interfacial photothermal conversion water evaporation: assemblies, structures, applications, and prospective. *Carbon Energy*. 2023;5(11):e331.

9. Ding M, Zhao D, Wei R, et al. Multifunctional elastomeric composites based on 3D graphene porous materials. *Exploration*. In press. doi:10.1002/EXP.20230057

10. Finnerty C, Zhang L, Sedlak DL, Nelson KL, Mi B. Synthetic graphene oxide leaf for solar desalination with zero liquid discharge. *Environ Sci Technol*. 2017;51(20):11701-11709.

11. Kuang Y, Chen C, He S, et al. A high-performance self-regenerating solar evaporator for continuous water desalination. *Adv Mater*. 2019;31(23):1900498.

12. Xu W, Hu X, Zhuang S, et al. Flexible and salt resistant Janus absorbers by electrospinning for stable and efficient solar desalination. *Adv Energy Mater*. 2018;8(14):1702884.

13. Chen X, He S, Falinski MM, et al. Sustainable off-grid desalination of hypersaline waters using Janus wood evaporators. *Energy Environ Sci*. 2021;14(10):5347-5357.

14. Dong X, Si Y, Chen C, Ding B, Deng H. Reed leaves inspired silica nanofibrous aerogels with parallel-arranged vessels for salt-resistant solar desalination. *ACS Nano*. 2021;15(7):12256-12266.

15. Zeng J, Wang Q, Shi Y, Liu P, Chen R. Osmotic pumping and salt rejection by polyelectrolyte hydrogel for continuous solar desalination. *Adv Energy Mater*. 2019;9(38):1900552.

16. Zhao W, Gong H, Song Y, et al. Hierarchically designed salt-resistant solar evaporator based on Donnan effect for stable and high-performance brine treatment. *Adv Funct Mater*. 2021;31(23):2100025.

17. Xu N, Zhang H, Lin Z, et al. A scalable fish-school inspired self-assembled particle system for solar-powered water-solute separation. *Natl Sci Rev*. 2021;8(10):nwab065.

18. Wu X, Wang Y, Wu P, et al. Dual-zone photothermal evaporator for antisalt accumulation and highly efficient solar steam generation. *Adv Funct Mater*. 2021;31(34):2102618.

19. He S, Chen C, Kuang Y, et al. Nature-inspired salt resistant bimodal porous solar evaporator for efficient and stable water desalination. *Energy Environ Sci*. 2019;12(5):1558-1567.

20. Wang F, Wei D, Li Y, et al. Chitosan/reduced graphene oxide-modified spacer fabric as a salt-resistant solar absorber for efficient solar steam generation. *J Mater Chem A*. 2019;7(31): 18311-18317.

21. Chen L, He S, Huang W, et al. 3D-printed tripodal porous wood-mimetic cellulosic composite evaporator for salt-free water desalination. *Compos Part B*. 2023;263:110830.

22. Zhang L, Li X, Zhong Y, et al. Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer. *Nat Commun*. 2022;13(1):849.

23. Liu X, Chen F, Li Y, et al. 3D hydrogel evaporator with vertical radiant vessels breaking the trade-off between thermal localization and salt resistance for solar desalination of high-salinity. *Adv Mater*. 2022;34(36):2203137.

24. Xia Y, Hou Q, Jubaer H, et al. Spatially isolating salt crystallisation from water evaporation for continuous solar steam generation and salt harvesting. *Energy Environ Sci*. 2019;12(6):1840-1847.

25. Shao Y, Tang J, Li N, et al. Designing a bioinspired synthetic tree by unidirectional freezing for simultaneous solar steam generation and salt collection. *EcoMat*. 2020;2(1):e12018.

26. Gu R, Yu Z, Sun Y, Xie P, Li Y, Cheng S. Enhancing stability of interfacial solar evaporator in high-salinity solutions by managing salt precipitation with Janus-based directional salt transfer structure. *Desalination*. 2022;524:115470.

27. Yu Z, Li S, Chen Y, et al. Intensifying the co-production of vapor and salts by a one-way brine-flowing structure driven by solar irradiation or waste heat. *Desalination*. 2022;539:115942.

28. Lei Z, Sun X, Zhu S, et al. Nature inspired MXene-decorated 3D honeycomb-fabric architectures toward efficient water desalination and salt harvesting. *Nano-Micro Lett*. 2022;14(1):10.

29. Zhang C, Shi Y, Shi L, et al. Designing a next generation solar crystallizer for real seawater brine treatment with zero liquid discharge. *Nat Commun*. 2021;12(1):998.

30. Shi Y, Zhang C, Li R, et al. Solar evaporator with controlled salt precipitation for zero liquid discharge desalination. *Environ Sci Technol*. 2018;52(20):11822-11830.

31. Ding M, Lu H, Sun Y, et al. Superelastic 3D assembled clay/graphene aerogels for continuous solar desalination and oil/organic solvent absorption. *Adv Sci*. 2022;9(36):2205202.

32. Liu H, Jin R, Duan S, et al. Anisotropic evaporator with a T-shape design for high-performance solar-driven zero-liquid discharge. *Small*. 2021;17(24):2100969.

33. Zhao H, Li X, Du X. T-shape solar evaporator constructed with natural wood and Ti₂O₃ nanoparticles for water evaporation and desalination. *Mater Today Sustain*. 2023;24:100538.
34. Li L, He N, Jiang B, et al. Highly salt-resistant 3D hydrogel evaporator for continuous solar desalination via localized crystallization. *Adv Funct Mater.* 2021;31(43):2104380.

35. Kong Y, Gao Y, Shang Y, et al. Synergistic adjustment of water channels and light absorption pathways to co-generate salt collection and clean water production. *Sci Total Environ.* 2021;797:148912.

36. Li C, Jiang D, Liang H, et al. Superelastic and arbitrary-shaped graphene aerogels with sacrificial skeleton of melamine foam for varied applications. *Adv Funct Mater.* 2018;28(8):1704674.

37. Wang S, Niu Y, Wang C, et al. Modified hollow glass microspheres/reduced graphene oxide composite aerogels with low thermal conductivity for highly efficient solar steam generation. *ACS Appl Mater Interfaces.* 2021;13(36): 42803-42812.

38. Li C, Qiu L, Zhang B, Li D, Liu CY. Robust vacuum-/air-dried graphene aerogels and fast recoverable shape-memory hybrid foams. *Adv Mater.* 2016;28(7):1510-1516.

39. Han DD, Zhang YL, Jiang HB, et al. Moisture-responsive graphene paper prepared by self-controlled photoreduction. *Adv Mater.* 2015;27(2):332-338.

40. Luo C, Zhou L, Chiou K, Huang J. Multifunctional graphene hair dye. *Chem.* 2018;4(4):784-794.

41. Niu R, Ren J, Koh JJ, et al. Bio-inspired sandwich-structured all-day-round solar evaporator for synergistic clean water and electricity generation. *Adv Energy Mater.* 2023;13(45):2302451.

42. He P, Lan H, Bai H, et al. Rational construction of “all-in-one” metal-organic framework for integrated solar steam generation and advanced oxidation process. *Appl Catal B.* 2023;337:123001.

43. He J, Zhang Z, Xiao C, et al. High-performance salt-rejecting and cost-effective superhydrophilic porous monolithic polymer foam for solar steam generation. *ACS Appl Mater Interfaces.* 2020;12(14):16308-16318.

44. Chen C, Liu H, Wang H, Zhao Y, Li M. A scalable broadband plasmonic cuprous telluride nanowire-based hybrid photothermal membrane for efficient solar vapor generation. *Nano Energy.* 2021;84:105868.

45. Liu X, Tian Y, Wu Y, et al. Fully biomass-based hybrid hydrogel for efficient solar desalination with salt self-cleaning property. *ACS Appl Mater Interfaces.* 2021;13(36):42832-42842.

46. Dong X, Cao L, Si Y, Ding B, Deng H. Cellular structured CNTs@SiO₂ nanofibrous aerogels with vertically aligned vessels for salt-resistant solar desalination. *Adv Mater.* 2020; 32(34):1908269.

47. Liu X, Mishra DD, Li Y, et al. Biomass-derived carbonaceous materials with multichannel waterways for solar-driven clean water and thermoelectric power generation. *ACS Sustainable Chem Eng.* 2021;9(12):4571-4582.

48. Kashyap V, Al-Bayati A, Sajadi SM, Irajizad P, Wang SH, Ghasemi H. A flexible anti-clogging graphite film for scalable solar desalination by heat localization. *J Mater Chem A.* 2017;5(29):15227-15234.

49. Peng Q, Qin Y, Zhao X, et al. Superlight, mechanically flexible, thermally superinsulating, and antifrosting anisotropic nanocomposite foam based on hierarchical graphene oxide assembly. *ACS Appl Mater Interfaces.* 2017;9(50):44010-44017.

50. Wang Z, Han M, He F, Peng S, Darling SB, Li Y. Versatile coating with multifunctional performance for solar steam generation. *Nano Energy.* 2020;74:104886.

51. Mu P, Zhang Z, Bai W, et al. Superwetting monolithic hollow-carbon-nanotubes aerogels with hierarchically nanoporous structure for efficient solar steam generation. *Adv Energy Mater.* 2019;9(1):1802158.

52. Mu P, Bai W, Fan Y, et al. Conductive hollow kapok fiber-PPy monolithic aerogels with excellent mechanical robustness for efficient solar steam generation. *J Mater Chem A.* 2019;7(16): 9673-9679.

53. Shi Y, Li R, Jin Y, et al. A 3D photothermal structure toward improved energy efficiency in solar steam generation. *Joule.* 2018;2(6):1171-1186.

54. Chen J, Yin JL, Li B, et al. Janus evaporators with self-recovering hydrophobicity for salt-rejecting interfacial solar desalination. *ACS Nano.* 2020;14(12):17419-17427.

55. Cao N, Lu S, Yao R, et al. A self-regenerating air-laid paper wrapped ASA 3D cone-shaped Janus evaporator for efficient and stable solar desalination. *Chem Eng J.* 2020;397:125522.

56. Xu N, Li J, Wang Y, et al. A water lily-inspired hierarchical design for stable and efficient solar evaporation of high-salinity brine. *Sci Adv.* 2019;5(7):eaaw7013.

57. Hu Y, Ma H, Wu M, et al. A reconfigurable and magnetically responsive assembly for dynamic solar steam generation. *Nat Commun.* 2022;13(1):4335.

58. Liu Z, Wu B, Zhu B, Chen Z, Zhu M, Liu X. Continuously producing watersteam and concentrated brine from seawater by hanging photothermal fabrics under sunlight. *Adv Funct Mater.* 2019;29(43):1905485.

59. Wang Z, Wu X, He F, Peng S, Li Y. Confinement capillarity of thin coating for boosting solar-driven water evaporation. *Adv Funct Mater.* 2021;31(22):2011114.

60. Gu R, Yu Z, Sun Y, Su Y, Wu W, Cheng S. Janus 3D solar crystallizer enabling an eco-friendly zero liquid discharge of high-salinity concentrated seawater with antiscalant. *Desalination.* 2022;537:115862.

61. Mu X, Zhou J, Wang P, et al. A robust starch-polyacrylamide hydrogel with scavenging energy harvesting capacity for efficient solar thermoelectricity-freshwater cogeneration. *Energy Environ Sci.* 2022;15(8):3388-3399.

62. Chen S, Sun Z, Xiang W, et al. Plasmonic wooden flower for highly efficient solar vapor generation. *Nano Energy.* 2020; 76:104998.

63. Menon AK, Haechler I, Kaur S, Lubner S, Prasher RS. Enhanced solar evaporation using a photo-thermal umbrella for wastewater management. *Nat Sustain.* 2020;3(2):144-151.

64. Wang Z, Gao J, Zhou J, et al. Engineering metal-phenolic networks for solar desalination with directional salt crystallization. *Adv Mater.* 2023;35(1):2209015.

65. Zhu L, Sun L, Zhang H, et al. A solution to break the salt barrier for high-rate sustainable solar desalination. *Energy Environ Sci.* 2021;14(4):2451-2459.

66. Liu X, Tian Y, Chen F, et al. An easy-to-fabricate 2.5D evaporator for efficient solar desalination. *Adv Funct Mater.* 2021;31(27):2100911.

67. Zou M, Zhang Y, Cai Z, et al. 3D printing a biomimetic bridge-arch solar evaporator for eliminating salt accumulation with desalination and agricultural applications. *Adv Mater.* 2021; 33(34):2102443.

68. Zhu F, Wang L, Demir B, et al. Accelerating solar desalination in brine through ion activated hierarchically
porous polyion complex hydrogels. *Mater Horizons*. 2020;7(12):3187-3195.

69. Yang Z, Chen L, Yang K, et al. An integrated solar evaporator with multilevel hierarchy and multifunctional properties for efficient and salt fouling-resistant desalination. *J Mater Chem A*. 2022;10(45):24373-24380.

70. Yang L, Sun T, Tang J, et al. Photovoltaic-multistage desalination of hypersaline waters for simultaneous electricity, water and salt harvesting via automatic rinsing. *Nano Energy*. 2021;87:106163.

71. Bian Y, Ye Z, Zhao G, et al. Enhanced contactless salt-collecting solar desalination. *ACS Appl Mater Interfaces*. 2022; 14(29):34151-34158.

72. Li Y, Cheng S, Yu Z, Gu R, He X. Stable, zero liquid discharge, and highly efficient solar-driven multistage distillation device based on tree-inspired radial water transfer. *J Clean Prod*. 2022;375:134025.

73. Zhang T, Zhao J, Liang L, Guo C. Constructing a solar evaporator with salt-collecting paper by stacking hydrophilic sponges for freshwater production and salt collection. *ACS Appl Mater Interfaces*. 2022;14(1):668-676.

74. Ma X, Wan X, Fang Z, et al. Orientational seawater transportation through Cu(TCNQ) nanorod arrays for efficient solar desalination and salt production. *Desalination*. 2022;522:115399.

75. Peng H, Wang D, Fu S. Artificial transpiration with asymmetric photothermal textile for continuous solar-driven evaporation, spatial salt harvesting and electrokinetic power generation. *Chem Eng J*. 2021;426:131818.

76. Dong X, Li H, Gao L, et al. Janus fibrous mats based suspended type evaporator for salt resistant solar desalination and salt recovery. *Small*. 2022;18(13):2107156.

77. Wu L, Dong Z, Cai Z, et al. Highly efficient three-dimensional solar evaporator for high salinity desalination by localized crystallization. *Nat Commun*. 2020;11(1):521.

78. Luo S, Li Z, Cui X, Ge Y. An anti-salt accumulation 2.5 D arch solar-driven evaporator based on Marangoni effect for seawater desalination. *Chem Eng J*. 2023;454:140286.

79. Luo W, Liu M, Jiao R, et al. Efficient antibiotic wastewater treatment via interfacial water evaporation based soot-coated conjugated microporous polymer hollow microspheres. *Chem Eng J*. 2023;475:146226.

80. Bae K, Kang G, Cho SK, Park W, Kim K, Padilla WJ. Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation. *Nat Commun*. 2015;6(1):10103.

81. Li X, Xu W, Tang M, et al. Graphene oxide-based efficient and scalable solar desalination under one sun with a confined 2D water path. *Proc Natl Acad Sci USA*. 2016;113(49): 13953-13958.

82. Li X, Li J, Lu J, et al. Enhancement of interfacial solar vapor generation by environmental energy. *Joule*. 2018;2(7): 1331-1338.

83. Hu R, Zhang J, Kuang Y, et al. A Janus evaporator with low tortuosity for long-term solar desalination. *J Mater Chem A*. 2019;7(25):15333-15340.

84. Liu J, Yao J, Yuan Y, et al. Surface-carbonized bamboos with multilevel functional biostructures deliver high photothermal water evaporation performance. *Adv Sustainable Syst*. 2020; 4(9):2000126.

85. Lv B, Gao C, Xu Y, et al. A self-floating, salt-resistant 3D Janus radish-based evaporator for highly efficient solar desalination. *Desalination*. 2021;510:115093.

86. Yao H, Zhang P, Yang C, et al. Janus-interface engineering boosting solar steam towards high-efficiency water collection. *Energy Environ Sci*. 2021;14(10):5330-5338.

87. Li C, Jiang D, Huo B, et al. Scalable and robust bilayer polymer foams for highly efficient and stable solar desalination. *Nano Energy*. 2019;60:841-849.

88. Wang F, Xu N, Zhao W, et al. A high-performing single-stage invert-structured solar water purifier through enhanced absorption and condensation. *Joule*. 2021;5(6):1602-1612.

89. Zhou W, Zhou C, Deng C, et al. High-performance freshwater harvesting system by coupling solar desalination and fog collection with hierarchical porous microneedle arrays. *Adv Funct Mater*. 2022;32(28):2113264.

90. Ma W, Lu T, Cao W, Xiong R, Huang C. Bioinspired nanofibrous aerogel with vertically aligned channels for efficient water purification and salt-rejecting solar desalination. *Adv Funct Mater*. 2023;33(23):2214157.

91. Wu P, Wu X, Wang Y, Xu H, Owens G. Towards sustainable saline agriculture: interfacial solar evaporation for simultaneous seawater desalination and saline soil remediation. *Water Res*. 2022;212:118099.

92. Mao Z, Chen Y, Li G, et al. Highly interconnected sponge with optimized water absorption and thermal conductivity for efficient solar desalination. *Sep Purif Technol*. 2023; 314:123502.

93. Zhu Y, Tian G, Liu Y, et al. Low-cost, unsinkable, and highly efficient solar evaporators based on coating MWCNTs on nonwovens with unidirectional water-transfer. *Adv Sci*. 2021;8(19):2101727.

94. Yang Y, Feng H, Que W, et al. A diode-like scalable asymmetric solar evaporator with ultra-high salt resistance. *Adv Funct Mater*. 2022;33(6):2210972.

95. Li H, Jia D, Ding M, et al. Robust 3D graphene/cellulose nanocrystals hybrid lamella network for stable and highly efficient solar desalination. *Solar RRL*. 2021;5(8):2100317.

96. Huo B, Jiang D, Cao X, et al. N-doped graphene/carbon hybrid aerogels for efficient solar steam generation. *Carbon*. 2019;142:13-19.

97. Zhang X, Liu P, Duan Y, Jiang M, Zhang J. Graphene/cellulose nanocrystals hybrid aerogel with tunable mechanical strength and hydrophilicity fabricated by ambient pressure drying technique. *RSC Adv*. 2017;7(27):16467-16473.

## SUPPORTING INFORMATION

Additional supporting information can be found online in the Supporting Information section at the end of this article.

**How to cite this article:** Ding M, Zhao D, Feng P, et al. Highly efficient three-dimensional solar evaporator for zero liquid discharge desalination of high-salinity brine. *Carbon Energy*. 2024;6:e548. doi:10.1002/cey2.548