Key Takeaways & Executive Findings
- •• • The CC-3 evaporator achieves a solar evaporation rate of 3.55 kg·m−2·h−1 under 1 sun (1 kW·m−2) with an energy efficiency of 97.53%, outperforming many conventional photothermal materials and enabling high-yield freshwater production. • • Under forced convection at 2.5 m·s−1, the evaporation rate escalates to 10.41 kg·m−2·h−1, demonstrating a 193% enhancement over stagnant conditions, which is critical for real-world outdoor operation where wind is prevalent. • • The evaporator exhibits excellent salt tolerance: in 3.5% saline, it maintains an evaporation rate of 3.46 kg·m−2·h−1 over 5 days without performance degradation, and under 2.5 m·s−1 wind, the rate reaches 9.56 kg·m−2·h−1, ensuring long-term stability in desalination applications. • • The material cost is 48.77 ¥·m−2, yielding a cost-effectiveness of 72.79 g·h−1·¥−1, which is economically competitive for scalable deployment in freshwater-scarce regions.
Abstract
To obtain freshwater from saline water and seawater, a double-layer evaporator consisting of carbon spheres and corn stalks was fabricated (abbreviated as CC). Corn stalks served as the evaporator substrate, and a mixed hydrogel of carbon spheres and polyvinyl alcohol functioned as the photothermal conversion layer. The solar-driven interfacial evaporation and desalination performance of the CC evaporator was investigated. The glucose-derived carbon spheres exhibited a uniform morphology and achieved 95% light absorption across 200–2500 nm. Under 1 sun (1 kW·m−2) irradiation, the CC with 3 cm height (CC-3) reached an exceptional evaporation rate of 3.55 kg·m−2·h−1 with a remarkable energy efficiency of 97.53%. When different wind speeds (1.5, 2, and 2.5 m·s−1) were applied, the evaporation rates further increased to 7.17, 8.92, and 10.41 kg·m−2·h−1, respectively. The evaporation rate of CC-3 for 3.5% saline was 3.46 kg·m−2·h−1. A 5-day long-time experiment exhibited stable desalination and excellent salt tolerance. Under a wind speed of 2.5 m·s−1, the evaporation rate reached 9.56 kg·m−2·h−1. In an outdoor natural light within a closed system and 2.5 m·s−1 of wind speed, the maximum evaporation rate and cumulative evaporation amount for seawater were 9.59 kg·m−2·h−1 and 66.0 kg·m−2, with no salt crystallization observed on the CC surface. These results demonstrate the potential practical application of the CC evaporator in seawater desalination.
1. Introduction
Freshwater scarcity is a pressing global challenge, with conventional desalination technologies such as reverse osmosis and thermal distillation heavily reliant on electricity and fossil fuels, resulting in significant carbon footprints. Solar-driven interfacial evaporation has emerged as a sustainable alternative, offering high evaporation rates, environmental friendliness, and economic efficiency. However, the performance of such systems is often limited by heat losses and inefficient water transport. The key to advancing this technology lies in the rational design of photothermal materials and evaporator structures that maximize light absorption, thermal localization, and water supply while minimizing salt accumulation.
This study addresses these bottlenecks by fabricating a double-layer evaporator (CC) using alkali-treated corn stalks as the substrate and a carbon sphere-polyvinyl alcohol hydrogel as the top photothermal layer. Corn stalks provide rapid water transport and low thermal conductivity, while carbon spheres offer broad-spectrum light absorption. The integration achieves a remarkable evaporation rate of 3.55 kg·m−2·h−1 under one sun, with an energy efficiency of 97.53%. Furthermore, the system demonstrates exceptional salt tolerance and cost-effectiveness, making it a viable candidate for practical seawater desalination. This work not only enhances evaporation performance but also provides a sustainable, low-cost solution to freshwater production.
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SU Mengshi, MA Yujuan, LI Jing, YAN Liangguo (2026). Solar Interfacial Evaporation and Desalination Performance of Carbon Spheres-Corn Stalk Double-Layer Evaporator. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025083003
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Frequently Asked Questions
What is the long-term operational stability of the CC evaporator under continuous saline water exposure, and what failure mechanisms might arise?
The CC-3 evaporator maintained a stable evaporation rate of 3.46 kg·m−2·h−1 for 3.5% saline over 5 days, with no salt crystallization on the surface. However, the authors note that the hydrophilic porous structure of corn stalk and PVA may be susceptible to microbial degradation over extended periods, potentially reducing performance. Additionally, the glucose-derived carbon spheres are not amenable to mass production, and the evaporator's stability under complex natural conditions requires further evaluation.
How does the cost-effectiveness of the CC evaporator compare to existing solar desalination technologies, and what are the main cost contributors?
The CC evaporator has a material cost of 48.77 ¥·m−2, with a cost-effectiveness of 72.79 g·h−1·¥−1. The major cost contributors are sodium hydroxide (24 ¥·m−2), PVA (4.88 ¥·m−2), and glutaraldehyde (6.4 ¥·m−2). This is competitive with other solar evaporators, but the use of glucose-derived carbon spheres and corn stalk may limit scalability. Replacing these with commercial carbon spheres and synthetic polymers could reduce costs and improve durability.
What is the impact of wind speed on the evaporation rate, and how does it affect the energy efficiency?
Wind speed significantly enhances evaporation by facilitating the diffusion of vapor molecules from the evaporator surface. Under 1 sun, the evaporation rate increased from 3.55 kg·m−2·h−1 (no wind) to 7.17, 8.92, and 10.41 kg·m−2·h−1 at wind speeds of 1.5, 2, and 2.5 m·s−1, respectively. This corresponds to a 193% enhancement at 2.5 m·s−1, demonstrating the importance of environmental conditions in practical applications.
How does the CC evaporator perform with real seawater compared to synthetic saline solutions?
In outdoor experiments with real seawater under 2.5 m·s−1 wind, the CC evaporator achieved a maximum evaporation rate of 9.59 kg·m−2·h−1 and a cumulative evaporation of 66.0 kg·m−2 over the test period, with no salt crystallization on the surface. This performance is consistent with laboratory tests using 3.5% saline, indicating robust desalination capability in real-world conditions.
What are the main limitations of the current CC evaporator design, and what improvements are suggested?
The main limitations include the complex and non-scalable synthesis of glucose-derived carbon spheres, potential microbial degradation of the corn stalk/PVA structure, and the need for further evaluation of long-term stability under natural conditions. Suggested improvements include using commercial carbon spheres, replacing corn stalk with synthetic polymers to enhance biofouling resistance, and optimizing the evaporator structure to improve performance.
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