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Le Shi1 Yusuf Shi1 Peng Wang1

1, King Abdullah University of Science and Technology, Jeddah, , Saudi Arabia

Efficient utilization of solar energy to generate clean water from seawater or contaminated water has attracted more and more attention to deal with water scarcity. Some of the previous works focused on the water evaporation using synthetic ( 3.5% NaCl) seawater. It is reported that salt crystal accumulation on material surface is easily to be removed in DI water. However, in a practical solar-driven water evaporation, contents in water are more complicated than NaCl. As a result, fouling of the material is one of the biggest concerns, which would reduce the evaporation efficiency and shorten the material’s service lifetime.Therefore, fouling control strategies should be employed including water pretreatment and periodical cleaning.

However, most of the photothermal materials developed previously are too fragile to stand a strong shear force for washing, which is due to the porous structure or physical properties of the materials. Generally, porous structure is designed in order to enhance light absorption by reducing light reflection, as well as to accelerate the steam transport. Therefore, porous photothermal materials with high mechanical strength are needed for washing to control the corrosion and fouling.

Recently, porous SiC ceramics have been increasingly studied due to its excellent mechanical strength and chemical stability, controlled permeability and excellent corrosion resistance at high temperature. Moreover, fortunately, coming with the preparation process of SiC ceramic is the by-product: free carbon. An excess quantity of carbon is distributed uniformly in SiC ceramic, which makes SiC into SiC-C composite. Carbon-based material is one of the most popular photothermal materials, which is providing the possibility for SiC-C composite to be a candidate as photothermal material.

Herein, we rationally designed a tandem-structured SiC-C composite monolith as the photothermal material. Free carbon plays as the light absorber and light to thermal convertor and SiC plays as a strong structure support and heat conductor. The tandem structure is designed in order to reduce the light reflection, and at the same time keep the support with good mechanical property. It is demonstrated that the tandem-structured SiC-C composite monolith can meet the requirements expected for an efficient photothermal material, such as hydrophilic surfaces, high light absorption in the full solar spectrum range and, especially, the high mechanical strength for physical cleaning. More importantly, it is the first time to notice and investigate the difference of the fouling behavior between the synthetic seawater and the natural seawater (Red Sea) on the surface of photothermal material. Furthermore, wastewater collected from WWTP in KAUST is also investigated to see the fouling behavior. All of these results indicated the importance of mechanical properties to design a photothermal material for durable fouling control in solar-driven water evaporation applications.

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